WALLEYE POLLOCK

General Biology

Geographical distribution

Walleye pollock are found in the waters of the Northeastern Pacific Ocean from the Sea of Japan, north to the Sea of Okhotsk, east in the Bering Sea and Gulf of Alaska, and south in the Northwestern Pacific Ocean along the Canadian and U.S. west coast to Carmel, California (Fig. 41) (Phillips 1942, 1943; Hart 1973; Bailey et al. 1999).Currents, eddies, and meso-scale physical structures along a coast influence the distribution of early life-history stages.The distributions of later life-history stages of walleye pollock appear to be influenced by temperature, light, and prey abundance, variables that may change in an area from year to year (Bailey 1989; Swartzman et al. 1994; Olla et al. 1996; Sogard and Olla, 1996a, b; Brodeur et al. 1997).

Adult walleye pollock are generally a semi-demersal species that inhabit the continental shelf and slope (Saunders et al. 1989).Moreover, various life history stages are capable of inhabiting nearshore areas, large estuaries (such as Puget Sound), coastal embayments, and open ocean basins, such as the Aleutian Basin of the Bering Sea (Bailey et al. 1999).The primary densities of numerous populations are in the North Pacific Ocean, including the northern Gulf of Alaska, Bering Sea, and the Sea of Okhotsk, suggesting that walleye pollock populations in Puget Sound are relatively isolated and distant (Fig. 42, Table 27) (Bailey et al. 1999, Bakkala et al. 1986).Adults occur as deep as 366 m (Hart 1973), but the vast majority occur between 100 and 300 m.Spawning takes place at depths of from 50 to 300 m (Garrison and Miller 1982, Bailey et al. 1999).Eggs are pelagic and are found throughout the water column (Bailey et al. 1999, Kanamaru et al. 1979).Larvae and small juveniles are pelagic, and are generally found in the upper water column to depths of 60 m (Garrison and Miller 1982, Bailey et al. 1999).Postlarvae and small juveniles occupy a wider depth range, generally with diel movements which involve rising to the surface at night to feed and sinking down in schools during the day (Garrison and Miller 1982, Merati and Brodeur 1996).Juvenile pollock have been found in a variety of habitat types, including eelgrass (over sand and mud), gravel and cobble (Miller et al. 1976); however, because of their pelagic mode, they are not thought to consistently associate with many types of substrates (Matthews 1987).

Information about the bathymetric distribution of Puget Sound walleye pollock was reported by Quinnell and Schmitt (1991).In a resource survey conducted in Puget Sound in 1987, they collected walleye pollock from four depth strata: 10-40 m, 41-80 m, 81-120 m, and > 120 m.The largest numbers of walleye pollock were collected at 41-80 m (43%) and > 120 m (41%).A gradual increase in mean length was observed between these two depth ranges, with walleye pollock from 41-80 m having a mean of 11 cm, those from 81-120 m have a mean of 13 cm, and those from > 120 m having a mean of 17 cm.This progression suggests that the tendency for juvenile walleye pollock to move into deeper waters with age, as has been reported in coastal walleye pollock populations, also occurs in Puget Sound.

Migration

Larvae tend to aggregate in patches under the influence of currents, geographical formations, and availability of prey.Juveniles form schools, and move in to deeper water with growth.Adults and juveniles continue to practice the above-mentioned diel vertical migrations (Bailey et al. 1999).

Reproduction and development

Walleye pollock are oviparous and have external fertilization (NOAA 1990).During spawning, walleye pollock apparently pair and spawn after a complex courtship (Sakurai 1982, Baird and Olla 1991).Females spawn several batches of eggs over a short period of time (multiple-batch spawning) (Sakurai 1982, Hinckley 1987).Eggs are usually spawned in deep water and remain at 100-400 m at most spawning localities (Kendall et al. 1994), but can also be spawned in shallower waters in coastal bays.Walleye pollock eggs are pelagic, colorless, spherical and transparent.Incubation times for artificially fertilized eggs held at temperatures ranging from 6-10^oC ranged from 10 to14 days, and the hatching success ranged from 0.3-80%.However, at 2^oC, the incubation time was 24 to 27 days and hatching success was 83-94% (Table 28) (Garrison and Miller 1982).Fertilized eggs from walleye pollock captured near British Columbia were 1.35-1.45 mm in diameter (Hart 1973); however, walleye pollock from the Bering Sea possessed larger eggs (1.48-1.66 mm) (Serobaba 1968).Larvae are about 3.5_4.5 mm in length at hatching, with a yolk sac that is absorbed in about 11-21 days at 6-7^oC, depending upon the availability of prey.Larvae metamorphose at about 25 mm (Dunn and Matarese 1987).

Early-stage larvae grow about 0.10-0.20 mm per day (Nishimura and Yamada 1984, Kendall et al. 1987, Bailey et al. 1996), and metamorphose into juveniles at a length of about 18 mm (Bailey 1989, Grover 1990, Merati and Brodeur 1996).In the first year, juveniles grow about 1 mm per day, reaching 80-100 mm in length in six months and 120-140 mm by the end of the first year.In western Gulf of Alaska waters, males have been reported to be sexually mature at age-3 and at a length of 29-32 cm; similarly, 3-year-old females (30-35 cm) were sexually mature (Garrison and Miller 1982).The growth rates of juvenile and adult walleye pollock in the Georgia Basin appears to be retarded compared to walleye pollock from coastal waters.In a study reported by Saunders et al. (1989), they found that male walleye pollock from coastal waters off of British Columbia reached a maximum length of approximately 50 cm by age-7, whereas male walleye pollock from the Strait of Georgia reached a maximum length of 40 cm by age-5.Female walleye pollock from these areas showed a similar trend, but their maximum length was a few cm longer.

Trophic interactions

Early-stage walleye pollock larvae feed chiefly on copepod nauplii (Nakatani 1988, Canino et al. 1991) and juveniles mostly prey on euphausiids, copepods, decapod larvae, and larvaceans (Grover 1990, Merati and Brodeur 1996, Brodeur 1998, Bailey et al. 1999).Adults are carnivorous, and feed primarily on euphausiids, small fishes, copepods, and amphipods (Bailey et al. 1999).Walleye pollock tend to be opportunistic feeders preying on whatever food organisms are available.For example, Bering Sea juvenile and adult walleye pollock generally feed on fish in the winter; euphausiids in the spring; and a wide variety of prey in the summer and fall, including copepods, euphausiids, and fish (Dwyer et al. 1986).In some areas, cannibalism can be an important source of food for the adult population (Dwyer et al. 1987; Livingston 1989, 1993).Up to 80% of the average stomach contents of adult walleye pollock in autumn and winter can consist of age-0 juvenile walleye pollock.

Predators of walleye pollock eggs and larvae include a variety of invertebrates, such as euphausiids and amphipods, and small fishes (Bailey et al. 1999).Juvenile walleye pollock are preyed upon by a number of seabirds (e.g., kittiwakes [Rissa spp.] and common murre [Uria aalge]) and marine mammals, including harbor seals (Phoca vitulina) (Bailey et al. 1999, Hunt et al. 1996, Lowry et al. 1996).Studies conducted in the Gulf of Alaska showed that walleye pollock, including adults, was the most important prey for harbor seals (Lowry et al. 1996).

Size and age distributions

Quinnell and Schmitt (1991) presented information about the length distributions of walleye pollock from Puget Sound.The mean length of walleye pollock collected in North Puget Sound was approximately 14 cm, suggesting they were largely young-of-the-year (Table 29).The mean length of walleye pollock from the Main Basin was 20 cm.Although the catch-per-unit effort for walleye pollock was quite low (0.32) in Hood Canal, fish from this region were among the largest, with a mean length of 28 cm.Of particular interest were walleye pollock collected in South Puget Sound, where the CPUE was also low (1.22), and mean length was 16 cm.This small size suggests the presence of a spawning population in or near South Puget Sound.The authors also presented length/frequency data (Fig. 43) which supported the above observations; the length distribution was bimodal, with most of walleye pollock being 9 to 14 cm, and a small number being 25 to 28 cm.

Similar regional differences in the distribution of age classes of walleye pollock have been reported in the Bering Sea (Dawson 1989).Three regions were investigated:the Eastern Bering along the shelf, an area just north of the Aleutian Islands, and the Aleutian Basin (also known as the "donut hole" located near the center of the Bering Sea).Walleye pollock from the Eastern Bering Sea were youngest (mean age 4.5 years), intermediate ages were found near the Aleutians (mean age 6.7 years), and older ages were observed in the Basin (mean age 8.9 years).In fact, very few 0- to 4-year-old walleye pollock were collected in the Basin.The author hypothesized that the Basin is a major spawning ground, and that eggs and larvae are transported by currents to the East Bering Sea shelf, which serves as a nursery area, a distance of 300 to 400 miles.

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Phenetic and Genetic Information Relating to the Species Question

Phenetic and genetic information examined for evidence of DPS delineations of walleye pollock included presence of geographically-discrete and temporally-persistent spawning aggregations, stock structure, tagging studies, and variation in seasonal migrations, parasite incidence, growth rate and body size, length and age at maturity, length frequency, fecundity, meristics and morphometrics, and genetic population structure.

Life History Information

Pre-historical and historical persistence in Puget Sound

Tunnicliffe et al. (in press) examined fish remains in a complete Holocene sediment core sequence from Saanich Inlet, Vancouver Island, British Columbia.Walleye pollock first appear in the sediment record of Saanich Inlet around 6,000 BP (Tunnicliffe et al. in press).Fish abundance and species diversity peaked in Saanich Inlet between 7,500 and 6,000 BP, and the last 1,000 years have seen some of the lowest abundances of fishes in Saanich Inlet's marine history (Tunnicliffe et al. in press).The close proximity of Saanich Inlet to Puget Sound would suggest that walleye pollock were also likely established in Puget Sound by approximately 6,000 BP.

Walleye pollock were identified in prehistoric fish skeletal remains from the Duwamish No. 1 archeological site (45-KI-23), located 3.8 km upstream from Elliott Bay on the Duwamish River, utilized by aboriginal humans between A.D. 15 and A.D. 1654 (Butler 1987).Gadiforms were present throughout the occupational history of this site, and were third and fourth in rank order of taxonomic abundance in two separate studies of fish bones performed at this site (following Salmonidae, Pleuronectiformes, and in one case Squalidae) (Butler 1987).Conversely, archaeological investigations of the West Point site on the north side of Discovery Park in Seattle (utilized by hunter-fisher-gatherers between 4,250 and 200 BP) found few remains of gadiforms, although some Pacific cod bones were identified at this site (Wigen 1995).Wigen (1995) postulated that differences in the frequency of gadiform remains found between the Duwamish and West Point sites may be related to the possible use of fish traps at West Point versus hook and line methods at the Duwamish site, or perhaps to differences in the season of human occupation between the two sites.Walleye pollock remains were also reported from the early component of the Bear Cove archaeological site on northeastern Vancouver Island that was occupied 6,500 to 5,000 years ago (Carlson 1979, Hebda and Frederick 1990).In historic times, Jordan and Starks (1895) reported that walleye pollock were "occasionally taken" in Puget Sound.

Spawning location and spawn timing

Bailey et al. (1997, 1999) illustrated major spawning locations throughout the range of walleye pollock. Figure 41 is a modified version of these spawning location maps.Table A-6 summarizes available data on spawn timing in various locations for walleye pollock.Bailey et al. (1999) stated that:

Most pollock populations spawn at predictable times, in the late winter and early spring, in the same locations year after year, usually in sea valleys, canyons, or indentations in the outer margin of the continental shelf.They are also known to spawn in fjords or deep-water bays (such as Puget Sound) and in some deep-water locations over the Aleutian Basin.

Puget Sound-Puget Sound is near the southern limit of the range of walleye pollock spawning populations (Pedersen and DiDonato 1982).Miller and Borton (1980) summarized distribution records of walleye pollock in Puget Sound as found in published records, museum collections, and various boat logs.Centers of collection of walleye pollock in Puget Sound were heavily influenced by fishing effort and ease of access, and centered around East Sound on Orcas Island, off Discovery Bay, Port Susan, Possession Sound, Saratoga Passage, Penn Cove, Holmes Harbor, the central Sound from Shilshole Bay to Port Madison, Port Orchard, Elliott Bay, Alki Point, Carr Inlet, and the mouth of Case Inlet (Miller and Borton 1980).From 1976-1980, walleye pollock was the first or second most important groundfish species taken by recreational anglers in Puget Sound (walleye pollock surpassed Pacific cod in this category in 3 of these 5 years) (Pedersen and DiDonato 1982).Although walleye pollock were once widespread and abundant in Puget Sound (Miller and Borton 1980, Matthews 1987), very little is known concerning reproductive characteristics of the species in Puget Sound (Garrison and Miller 1982).Historically, commercial and recreational fisheries for walleye pollock in Puget Sound were centered near the Canadian border in southern Strait of Georgia and at West Point, Elliott Bay, Colvos Passage, Point Defiance, and Point Fosdick (see Figs. 33, 44) (Pedersen and DiDonato 1982).

Walleye pollock reportedly form spawning aggregations on localized grounds in Puget Sound during March and April at depths of 110-145 m (Figs. 45, 46, Table A-6) (Pedersen and DiDonato 1982).Spawning walleye pollock occurred in the Washington portion of the southern Strait of Georgia in the late 1970s and early 1980s and a short-lived walleye pollock roe fishery harvested this portion of the transboundary Strait of Georgia stock (WDFW North Sound walleye pollock stock) for several years (Palsson et al. 1997).The occurrence of walleye pollock eggs near Point Roberts in the late 1970s and early 1980s and the possibility of major spawning activity in the vicinity led the Washington Department of Ecology to designate the open waters off this region as an Area of Major Biological Significance (Matthews 1987).Davis (1986) noted that the large spawning aggregation of walleye pollock in this region had decreased markedly in size by the mid 1980s (Davis 1986).This spawning aggregation on the U.S. side of the border appears to be the south-east extension of the spawning grounds of walleye pollock identified by Canadian researchers as lying between Active Pass/Mayne Island and Point Roberts (Thompson 1981, Shaw and McFarlane 1986).Pedersen and DiDonato (1982) identified a walleye pollock trawl fishery that operated from December to April (with a peak in March-April at an average depth of 128 m) along the international border, southwest of Point Roberts in an area termed "West Side" (Fig. 33).Timing and depth of this fishery suggest that it was likely targeting spawning walleye pollock.

Based on occurrence of larval walleye pollock in ichthyoplankton samples taken in 1978 and 1979 in Port Townsend Bay and Kilisut Harbor, Walters (1984) suggested that walleye pollock were spawning in the vicinity of Port Townsend from February through April (Table A-6) (Matthews 1987).In the Strait of Georgia where walleye pollock spawn in the open Strait, juveniles move quickly into nearshore nursery areas (Beamish et al. 1978a) and a similar situation may pertain to walleye pollock that spawn near Port Townsend (Walters 1984).Sogard and Olla (1993) also found juvenile walleye pollock in Port Townsend Bay in May and June, associated with seagrass habitat.

Walleye pollock were known to spawn in the vicinity of Tacoma in March and April (WDFHMD 1992), although it is uncertain if they still do so.A large recreational walleye pollock fishery occurred during the mid-1970s to 1988, (Palsson et al. 1997), in an area extending from Fox Island-Port Gibson, through the Tacoma Narrows, to Point Defiance in the vicinity of Tacoma (Fig. 44) (Pedersen and DiDonato 1982).This fishery collapsed in 1988 (Palsson et al. 1997) and was likely targeting the walleye pollock pre-spawning or spawning population.

British Columbia-Saunders et al. (1989) identified four general areas where concentrated spawning of walleye pollock occurs off the Pacific Coast of Canada during March and April:1) the Strait of Georgia, 2) off the west coast of Vancouver Island, 3) Queen Charlotte Sound, and 4) Dixon Entrance/northern Hecate Strait (Figs. 45, 46, Table A-6).Saunders et al. (1989) noted that the simultaneously occurrence of spawning in these four distinctly separate areas suggests that, as larvae, walleye pollock form discrete stocks.Spawning distributions were derived from a series of coastwide surveys for adults in spawning condition (Cass et al. 1978, Taylor and Kieser 1980, Thompson and Beamish 1979, Thompson et al. 1981, Thompson 1981, Thompson and McFarlane 1982) or from egg and larval distribution (Mason et al. 1981a, b, c, d; Shaw and McFarlane 1986).

In the Strait of Georgia, a major spawning aggregation of walleye pollock occurs south of Texada Island and south and west of Halibut Bank (Figs. 15, 45) (Thompson 1981, Shaw and McFarlane 1986).Other spawning concentrations have been reported off the Fraser River, and between Active Pass/Mayne Island and Point Roberts (Thompson 1981, Shaw and McFarlane 1986).Some walleye pollock may also spawn at the entrance to Jervis Inlet on the mainland coast and in Swanson Channel in the Gulf Islands (Figs. 15, 45)(Thompson 1981, Saunders et al. 1989).Based on the distribution and abundance of eggs detected in ichthyoplankton surveys, conducted in 1981, Mason et al. (1984) reported four similar areas of high walleye pollock spawning activity in the Strait of Georgia; a large region in Porlier Pass from mid-Galiano Island westward to Gabriola Island and three smaller areas, the mid-Strait south of Halibut Bank, south of Bowen Island to the northwest of Vancouver, B.C., and east of Mayne Island off Active Pass in the southern Strait.Based on egg distribution detected in ichthyoplankton surveys, Mason et al. (1984) reported that walleye pollock spawn in the Strait of Georgia from the first week in February to mid-May with a peak in late March.Walleye pollock are associated with Pacific hake during spawning in the south central Strait of Georgia in two midwater layers, a shallow layer from 50-110 m and a deeper layer between 110 and 320 m (Thompson and McFarlane 1982, Shaw and McFarlane 1986, Shaw et al. 1989c).The Pacific hake:walleye pollock ratio in the 1980s in these layers ranged from 6:1 to 8:1 (Shaw et al. 1989c).

Although walleye pollock eggs and larvae have been found of the southwest coast of Vancouver Island (Saunders et al. 1989), information regarding walleye pollock spawning locations in this region was not found (Fig. 45).Thompson (1981) reported that walleye pollock were beginning to spawn off the west coast of Vancouver Island in March, but the full extent of the spawning season was unknown.

A recent trawl fishery that began to develop in 1992 in Queen Charlotte Strait (northern extension of Strait of Georgia) in MSA 12 (Figs. 45, 47) (Saunders and Andrews 1998) may have targeted spawning fish, as the walleye pollock in the area were only available during the first quarter of the year.It is assumed that the MSA 12 stock is not part of the Strait of Georgia walleye pollock stock but is related to walleye pollock in Queen Charlotte Sound.

Within Hecate Strait and Queen Charlotte Sound, spawning walleye pollock have been reported from Dana and Selwyn Inlets on the east coast of Moresby Island (Queen Charlotte Islands), and in Finlayson Channel, Squally Channel, and Caamano Sound on the mainland coast (Fig. 46, Table A-6) (Thompson et al. 1981, Thompson 1981, Shaw and McFarlane 1986).Eggs of walleye pollock have been found throughout Dixon Entrance and northern Hecate Strait, but were reportedly absent from central Hecate Strait, the northwest coast of Vancouver Island, and the west coast of the Queen Charlotte Islands and western Dixon Entrance (Saunders et al. 1989).Spawning walleye pollock are reportedly found where bottom depths exceed 90 m and are distributed between 50-130 m during the spawning period (Taylor and Kieser 1981, Shaw and McFarlane 1986).No walleye pollock in spawning condition have been reported from northern Hecate Strait, where depths do not exceed 90 m (Shaw and McFarlane 1986).

On the north side of Dixon Entrance spawning walleye pollock have been found off Cape Chacon (southern tip of Prince of Wales Island) at depths of 212-226 m, in Portland Inlet (on the mainland coast north of Prince Rupert), north of Dundas Island (on the east side of Dixon Entrance), in Cordova Bay (west of Prince of Wales Island) (Fig. 46), and throughout inside channels of Southeast Alaska south of Ketchikan (Thompson 1981).

Alaska-Although walleye pollock are continually distributed throughout Southeast Alaska to the northern Gulf of Alaska, with the exception of Shelikof Strait, little information was found on spawning locations for walleye pollock in this region.At Auke Bay in Southeast Alaska, back-calculation from the weekly distribution of 7-day-old walleye pollock larvae obtained in ichthyoplankton samples indicated that extensive walleye pollock spawning occurs from late-March to mid-May (Haldorson et al. 1989).Müter and Norcross (1994) reported similar observations of large concentrations of walleye pollock larvae during ichthyoplankton surveys in ichthyoplankton samples in Prince William Sound, indicating spawning was occurring in the vicinity during late-March to early June.Müter and Norcross (1994) thought it likely "that many embayments along the Gulf of Alaska are utilized by this species."Hirschberger and Smith (1983) summarized fisheries surveys in the Gulf of Alaska spanning the years 1975-81 that recorded walleye pollock spawning "at numerous locations in the Shelikof Strait and Kodiak Island region, and along the edge of the outer continental shelf from Chirikof Island to the northeastern Gulf of Alaska."

The most important spawning location for walleye pollock in the Gulf of Alaska is Shelikof Strait, a deep (> 250 m) and narrow channel located between Kodiak Island and the Alaska Peninsula (Dunn and Matarese 1987, Kim 1989, Bailey et al. 1997).Spawning in Shelikof Strait is concentrated near Cape Kekurnoi at depths of 150-250 m in early April, and the area of spawning varies little over the season, which lasts until late May (Kim 1989, Kendall and Picquelle 1990, Kendall and Nakatani 1992, Kendall et al. 1996).No concentrations of spawning walleye pollock similar to the magnitude of that seen in Shelikof Strait have been observed elsewhere in the Gulf of Alaska, although Lloyd and Davis (1989) identified several additional walleye pollock spawning locations in the Gulf of Alaska, including near Middleton Island, east of Kodiak Island, near the Shumagin Islands, and along the Alaska Peninsula.Kendall and Picquelle (1990) saw evidence of some walleye pollock spawning south of Chirikof Island.Brown and Bailey (1992) analyzed hatch date distributions of walleye pollock juveniles in the western Gulf of Alaska, as determined by daily increments deposited on otoliths, and found evidence of several minor spawning populations of walleye pollock located near Unimak Pass and around Kodiak Island.

Bering Sea-Aggregations of spawning walleye pollock have been consistently observed in several areas in the eastern Bering Sea, and spawning has been found to occur in all months of the year (Fig. 41, Table A-6) (Bailey et al. 1997, Dunn and Matarese 1987).Based on the distribution of spawning fish and larvae, Maeda and Hirakawa (1977) concluded that the spawning grounds of walleye pollock in the eastern Bering Sea were separated by the shallow seas around the Pribilof Islands and by a sea valley near the southeastern part of the islands.These authors stated that one area of spawning activity stretched from northwest of Unimak Island to southwest of the Pribilof Islands and a second occurred near the continental slope to the northwest of the Pribilof Islands (Maeda and Hirakawa 1977).Hinckley (1987) concluded that three separate spawning stocks exist in the Bering Sea:1) the Aleutian Basin, 2) the northwest continental slope, and 3) a combination of the southeast and northwest continental shelves and the southeast continental slope.This conclusion was based on spatial and temporal observations of fish in spawning condition, length-at-age differences, differences in the length-fecundity relationship, and histological examination of ovaries (Hinckley 1987).Mulligan et al. (1989) referred to unpublished data from 1982 and 1983 (Bailey, unpubl. data) that agreed with Hinckley's (1987) spatial and temporal distribution of spawning walleye pollock in the eastern Bering Sea.Walleye pollock were observed spawning from January to March in the Aleutian Basin, from April to June on the southeast slope and southeast and northwest shelves, and from July to November on the northwest slope (Mulligan et al. 1989).Dunn and Matarese (1987) also reported that spawning walleye pollock occurred in the Aleutian Basin from January to March in depths of 100-250 m, and on the continental slope and shelf to the southeast of the Pribilof Islands from March to June.In addition, walleye pollock eggs have been observed along the outer continental shelf and slope from the Aleutian Islands to 60°N from February to July (Dunn and Matarese 1987).Dawson (1989, 1994) used age composition, length-at-age, and morphometrics to suggest that there is one stock of walleye pollock on the eastern Bering Sea shelf that spawns mainly on the southeastern continental shelf, a second stock in the Aleutian Basin that spawns in the Bogoslof Island area, and a third stock termed "Aleutian Islands," whose spawning location was not identified.

Fadeyev (1989) came to a different conclusion concerning spawning populations of walleye pollock in the northern Bering Sea, based on ichthyoplankton and acoustic-trawl survey.Fadeyev (1989) concluded that a single unified population occurs in this region, with spawning taking place primarily in the Unimak Island to Pribilof Islands area and that there is no separate walleye pollock stock or local spawning area to the north of the Pribilof Islands.Bulatov (1989) stated that Bering Sea walleye pollock spawn over a 10 month period from January to October and suggested there were two main peaks of spawning; winter spawning over deep water from February to early March and spring spawning over the continental shelf from the end of April to early May.Bulatov (1989) identified the main centers of reproduction in the Bering Sea as Olyutorsky Bay off east Kamchatka and Unimak Island.Bulatov and Sobolevskii (1991) concluded that Bering Sea walleye pollock spawn during February to March in the southeastern part of the Aleutian Basin in the vicinity of Bogoslof Island.

Asia-Bakkala et al. (1986) listed numerous spawning locations of walleye pollock along the Asian coast, including:1) Olyutorsky Bay to Cape Navarin in the western Bering Sea, 2) the east coast of the Kamchatka Peninsula to the northern Kurile Islands, 3) the east coast of Iturup Island in the southern Kurile Islands 4) the west coast of the Kamchatka Peninsula, 5) Terpeniya Bay on the east coast of Sakhalin Island, 6) the west coast of Sakhalin Island, 7) Nemuro Strait (between Hokkaido and the southernmost Kurile Islands), 8) the northern coast of Hokkaido, 9) the west coast of Hokkaido, 10) Funka Bay (Uchiura Bay) off southeast Hokkaido, 11) Cape Erimo on the east coast of Hokkaido, 12) Sado Island to Toyama Bay on the west coast of Honshu Island, and 13) Peter the Great Bay to the Bay of Korea off the Asian mainland (Fig. 41, Table A-6).

Kitano (1972) stated that walleye pollock spawn from mid-March to the end of May on the western coast of Kamchatka and from early April to the end of May on the east coast of Kamchatka.Several researchers (Avdeev and Avdeev 1989 and citations therein) distinguish two to seven walleye pollock populations in the Sea of Okhotsk.On the other hand, the broad area of spawning in the eastern, northern, and northwestern parts of the Sea of Okhotsk, during April and May, and the broad distribution of eggs and larvae led Zver'kova (1987) to question the level of isolation among local spawning populations.A more recent study (Kotenev et al. 1998) of spawning stock structure in the eastern Sea of Okhotsk off western Kamchatka, identified five groups of walleye pollock that were separated by sizes of mature fish and place and time of spawning.Three of these groups spawned in the winter and two in the spring (Kotenev et al. 1998).

Maeda (1972) stated that walleye pollock spawned earlier in southern regions of Japan than in the north; from January to February in the Niigata Region (northwest coast of Honshu, Japan) and from February to April in the vicinity of Hokkaido.Maeda et al. (1988) reported that walleye pollock spawn on the continental shelf off the southwest coast of Hokkaido between Otobe and Ainuma in depths of 120-200 m.Distribution of eggs indicates that spawning occurs in January and February in this region (Maeda et al. 1988).Hamatsu and Yabuki (1995) found that peak spawning of walleye pollock along the Pacific coast of eastern Hokkaido north of Cape Erimo occurred during March.

Walleye pollock in Korean waters of the Sea of Japan are at the southern limit of their distribution in Asia and, unlike Pacific cod, do not extend into the Yellow Sea (Fig. 41) (Gong and Zhang 1986).As in Puget Sound, walleye pollock in Korean waters generally move to shallower waters in the winter to spawn (Gong and Zhang 1986).Walleye pollock spawn in Korean waters at depths of 50-100 m in three general areas:1) off Gyeonbuk and Gangweon (southeast to central east coast of Korea) from November to December, 2) off Hamnan (northeast coast ofKorea) in December, and 3) off Hambuk (extreme northeast coast of Korea) in January and February (Gong and Zhang 1986).

Walleye pollock management stock

The WDFW recognizes two stocks of walleye pollock in Puget Sound, North Sound and South Sound stocks, which are differentiated by spawning location, growth rates, and other biological characteristics (Palsson et al. 1997).Several stocks of walleye pollock are recognized in British Columbia based on parasitological data, utilization of discrete spawning grounds, and differences in age and growth parameters (Shaw and McFarlane 1986).Walleye pollock in Dixon Entrance, northern Hecate Strait, and southern Southeast Alaska are considered a single stock, as are walleye pollock in the Strait of Georgia.Length frequency analysis indicated that there is "little intermingling" of walleye pollock stocks north and south of Queen Charlotte Sound, and that walleye pollock in Dixon Entrance are part of the same stock as found off Southeast Alaska (Thompson 1981, Shaw and McFarlane 1986, Saunders et al. 1989).Strait of Georgia walleye pollock are regarded as one stock, based on their smaller size at any given age, and the fact that they are smaller and younger at maturity than walleye pollock in Dixon Entrance (Shaw and McFarlane 1986, Saunders et al. 1989).Further evidence for stock separation of walleye pollock in the Strait of Georgia, off the west coast of Vancouver Island, and north of Queen Charlotte Strait was shown by a comparison of the prevalence of 13 species of parasites that indicated walleye pollock in these three regions were discrete from one another (Shaw and McFarlane 1986, Saunders et al. 1989).

Two walleye pollock stocks are recognized in the Gulf of Alaska:an Eastern Gulf stock and a Western/Central Gulf stock (Bailey et al. 1999).Walleye pollock in the U.S. portion of the Bering Sea/Aleutian Islands are divided into three stocks for management purposes:1) eastern Bering Sea, 2) Aleutian Islands, and 3) Bogoslof Island-Aleutian Basin (Bailey et al. 1999).The eastern Bering Sea continental shelf has a stock that is thought to be separate from the eastern Bering Sea stock.Walleye pollock from the eastern and western Bering Sea are thought to mix during feeding in the northern Bering Sea.For current management purposes, the mixing of these two "stocks" is also thought to occur in the "donut hole" or Aleutian Basin (Bailey et al. 1999).

Tsuji (1989) summarized knowledge concerning walleye pollock stock structure around Japan and recognized five separate stocks:North Japan Sea, Kitami, Nemuro, Pacific, and South Primorskan.The North Japan Sea stock occurs on the west coasts of Hokkaido and Sakhalin and along the Russian coast in the southern Tatar Strait.The Kitami stock occurs along the east coast of Sakhalin and the northern coast of Hokkaido.The Nemuro stock spawns in the Nemuro Strait between Hokkaido and the southern Kurile Islands and shares feeding grounds with the Kitami stock.The Pacific stock ranges along the Pacific coast of Hokkaido and northern Honshu.The South Primorskan stock occurs principally along the east coast of the Korean Peninsula, but also extends onto the southwest coast of Honshu in the Sea of Japan (Tsuji 1989).

Tagging and distribution

There is very little tagging information for walleye pollock that can be used to estimate the degree of interchange, if any, between spawning populations or for that matter the degree of homing to a spawning location.Records of fish released during feeding seasons are not appropriate for discrimination of stock structure (Tsuji 1989).

Saunders et al. (1989) reported on a tagging study off Gabriola Island in the Strait of Georgia in which 942 walleye pollock were tagged and only two were subsequently recovered.However, the recovery of these two fish, one near Jervis Inlet and the other off Port Renfrew, indicated "that dispersion north and south of the central Strait of Georgia is taking place" (Saunders et al. 1989).

Tagging studies in the Bering Sea have shown individual adult walleye pollock to undertake extensive seasonal feeding and spawning migrations (Dawson 1994, Bailey et al. 1999).Low (1989) cited discussions with Soviet scientists describing walleye pollock tagging studies that showed "populations off Kamchatka, the northern Okhotsk Sea, and Sakhalin Island are intermixing even during spawning."Several tagging experiments summarized by Tsuji (1989) indicate extensive migration of walleye pollock during the feeding seasons in Japanese coastal waters and in the Sea of Okhotsk.However, only two of these studies appear to have included fish tagged on the spawning grounds.Walleye pollock tagged just after the spawning season in April of 1968 in Ishikari Bay off western Hokkaido "were recaptured in the next spawning period at locations in a wide range up to the southern Sakhalin coast" (Tsuji 1989, p. 168), although the majority of recaptures appear to have occurred in Ishikari Bay during the 1969 and 1970 spawning seasons (Tsuji 1989, his Fig. 19).A second tagging experiment summarized by Tsuji (1989) involved walleye pollock tagged during the spawning season in the Nemuro Strait (a known spawning ground), between Hokkaido and the southernmost Kurile Islands.Nine tagged walleye pollock were recaptured during successive spawning seasons in Nemuro Strait, while all recaptures in other areas (Sea of Okhotsk) occurred during the feeding migration and not during spawning (Tsuji 1989).

Gong and Zhang (1986) reported that of over 47,000 walleye pollock tagged off the coast of Korea from 1931-1936, 226 were recaptured off Korea and 13 were recaptured off the west coast of Hokkaido (Tsuji 1989).Further details of this tagging program were provided in Tsuji (1989), and it is apparent that recaptures of Korean tagged walleye pollock off Hokkaido occurred in only one year (1935 fishing season) of the study, during the active feeding period, which was not during the spawning season.Tsuji (1989) suggested that this one-time migration of Korean walleye pollock to Hokkaido may have resulted from straying of an exceptionally large year class.

Seasonal migrations

Juvenile walleye pollock ranging in length from 21-87 mm were found to be associated with shallow seagrass beds in Port Townsend Bay in Puget Sound in May through June 1992 (Sogard and Olla 1993).It was postulated that juvenile walleye pollock were utilizing seagrass beds as cover from predation, although other factors such as prey items may also attract juveniles to seagrass beds.As walleye pollock juveniles increased in size in Port Townsend Bay they evidently migrated to deeper water beyond the range of seagrass.It is unknown whether juvenile walleye pollock utilize seagrass beds as nursery habitat in other regions of the species' range (Sogard and Olla 1993).Miller et al. (1976) also found juvenile walleye pollock in shallow nearshore eelgrass, cobble, and gravel habitats in northern Puget Sound.

Age-frequency data reviewed by Saunders et al. (1989) indicates that young walleye pollock are segregated from adults in the each of the major walleye pollock areas in British Columbia:Dixon Entrance/Hecate Strait, Queen Charlotte Sound, west coast of Vancouver Island, and Strait of Georgia.Younger walleye pollock are frequently encountered in nearshore areas and progressively migrate to more offshore areas with age (Saunders et al. 1989).It appears likely that walleye pollock in Dana and Selwyn Inlets leave these areas at age-3, moving out into Hecate Strait and Queen Charlotte Sound at that time (Saunders et al. 1989).

Bakkala et al. (1986) stated that walleye pollock in Asian waters migrate toward the coast from demersal and pelagic waters to spawn in depths of 70-150 m at temperatures of 2°-5°C. Although, in Funka Bay and Nemuro Strait they spawn in depths of 300 m or more.

Parasite incidence

Arthur (1983, 1984) and Avdeev and Avdeev (1989) utilized regional differences in the frequency of parasite infestation to detect walleye pollock stock structure off the west coast of Canada and in the Sea of Okhotsk, respectively.The principle requirement for indicator parasites is that their infestation "be of sufficient duration to make them potentially useful as biological tags" (Arthur 1983, 1984; Avdeev and Avdeev 1989).Arthur (1983) surveyed 13 species of parasites in walleye pollock from Swanson Channel in the Strait of Georgia, the west coast of Vancouver Island, Queen Charlotte Sound, and Dixon Entrance, and found four species that contributed significantly to stock separation (two trematodes, one cestode flatworm, and a nematode roundworm).Based on these parasitological data, Arthur (1983) stated that "stocks of walleye pollock from the Strait of Georgia and the west coast of Vancouver Island are relatively discrete from each other and from fish from the two northern areas."One species of trematode flatworm (Prosorhynchus sp. metacercaria), was found in 100% of walleye pollock from Dixon Entrance, 60% in Queen Charlotte Sound, 10% off the west coast of Vancouver Island, but was absent from Strait of Georgia walleye pollock.Arthur (1983) stated that this parasites' absence from Strait of Georgia walleye pollock indicates that "little or no immigration of adult fish from other areas to this stock occurs."Unfortunately, with the exception of the Strait of Georgia sample, all of the walleye pollock collected for Arthur's (1983) parasitological study were collected outside of the spawning season and have the potential to represent a mixture of spawning populations.

Avdeev and Avdeev (1989) investigated the regional differences in the occurrence of 9 indicator parasites amongst 6-yr-old walleye pollock from various spawning areas within the Sea of Okhotsk.These parasitological data allowed Avdeev and Avdeev (1989) to distinguish between seven spawning groups in the Sea of Okhotsk (Swan's shoal, southwestern Kamchatka, western Kamchatka, Shelikhov Gulf, Pritauyskiy, and Swan's Height) and a minimum of three separate groups off the east coast of Kamchatka (Komandorsky Islands, east coast of Kamchatka, and Shirshov Ridge).

Growth rate and body size

Determination of exact age in walleye pollock has been problematical and until ageing methods are validated and methods are standardized for ageing of older fish the problem of ageing errors will remain in walleye pollock growth and mortality studies (Chilton and Beamish 1982, Lai and Yeh 1986).Lai and Yeh (1986) compared otolith, scale, dorsal fin ray, and pectoral fin ray as structures to determine age of walleye pollock and found good agreement among these methods for ages less than 5 years, but the use of both otolith surface readings and "break and burn" techniques gave the best precision and percentage agreement among readers for older fish.

Palsson et al. (1997, 1998) referred to unpublished data on growth rate differences as an indication that the South Sound walleye pollock are of a different biological stock than those in North Sound.Matthews (1987) stated that walleye pollock in Puget Sound rarely live for more than 10 years, have an average body length of 48 cm and a maximum size of 91.4 cm.By comparison, data in Saunders et al. (1989) indicates that maximum age of walleye pollock is12 years in Dixon Entrance/Hecate Strait, 11 years in Queen Charlotte Sound, 10 years in the Strait of Georgia, and 8 years off the west coast of Vancouver Island.Maximum length in cm of walleye pollock in Dixon Entrance/Hecate Strait, Queen Charlotte Sound, Strait of Georgia, and off the west coast of Vancouver Island were reported to be 71, 74, 66, and 61, respectively (Saunders et al. 1989).Shaw and McFarlane (1986) stated that walleye pollock in the Strait of Georgia reached a maximum age of 8 years.

Thompson (1981), Shaw and McFarlane (1986), and Saunders et al. (1989) provided evidence that walleye pollock in the Strait of Georgia are smaller for a given age than walleye pollock found off the west coast of Vancouver Island or further north in Queen Charlotte Sound and Dixon Entrance.Shaw and McFarlane (1986) and Saunders et al. (1989) stated that walleye pollock growth rates are similar coastwide in British Columbia until age-2, after which growth rate is reduced in the Strait of Georgia.Saunders et al. (1989, their Fig. 9) illustrated some growth rate differences (as mean length-at-age) between areas in the Strait of Georgia; however, the growth rates for east of Mayne Island, U.S. portion of the Strait of Georgia, and central Strait of Georgia were very similar for both sexes.Saunders et al. (1989) also illustrated mean length-at-age data (their Fig. 11) for the now defunct walleye pollock fishery in the U.S. portion of the Strait of Georgia from 1978 to 1985 that indicated this relationship was stable over time.

Nishimura and Yamada (1988) postulated that rapid initial growth and small body size attained in the first year (consistent across year classes) of Sea of Okhotsk walleye pollock compared to walleye pollock in the Sea of Japan and Pacific Ocean side of Japan may indicate a genetic sub-population in the Sea of Okhotsk.

Length and age at maturity

Table A-7 summarizes length at first maturity, at 50% maturity, and at 100% maturity for selected walleye pollock populations.Virtually all male and female walleye pollock in Puget Sound mature at age-1 (between 25 and 38 cm in length) in South Puget Sound (WDFW 2000).Walleye pollock were found to mature later in the U.S. portion of the Strait of Georgia than in South Puget Sound; 37% of males and 43% of females were mature at age-2, and 92.5% of males and 93% of females were mature at age-3 (WDFW 2000).Thompson (1981) and Shaw and McFarlane (1986) provided evidence that walleye pollock in the Strait of Georgia spawn at a smaller size than do walleye pollock found off the west coast of Vancouver Island or further north in Queen Charlotte Sound and Dixon Entrance.Saunders et al. (1989) also reported that walleye pollock in the Strait of Georgia matured at smaller sizes (length at 50% maturity of 26-32 cm for males and 30-35 cm for females) than did walleye pollock from more northern areas in Dixon Entrance and Queen Charlotte Sound (length at 50% maturity of 37-41 cm for males and 39-44 cm for females).Walleye pollock from the west coast of Vancouver Island (length at 50% maturity of 37-40 cm for males and 40 cm for females) were more similar to northern samples than to the Strait of Georgia walleye pollock (Saunders et al. 1989).

Length frequency analysis

Analysis of length frequency data for walleye pollock stocks in British Columbia suggested that little intermingling of walleye pollock occurred north and south of Queen Charlotte Sound and that walleye pollock in Dixon Entrance are part of a larger Southeast Alaska stock (Thompson 1981, Shaw and McFarlane 1986, Saunders et al. 1989).

Otolith elemental composition

Mulligan et al. (1989), Mulligan (1997), and Severin et al. (1995) reported on efforts to discriminate walleye pollock stock structure through the analysis of elemental composition of the early larval increments retained on juvenile and adult otoliths.Juvenile walleye pollock collected from four areas in the Bering Sea could be correctly assigned to their collection site with 65% accuracy based on otolith chemistry (Mulligan et al. 1989).Mulligan et al. (1989) suggested mis-identifications "may be explained by a chemical similarity of adjacent water masses." Severin et al. (1995) were able to correctly assign specimens of walleye pollock, collected from five locations in the Gulf of Alaska and Bering Sea, to their capture locality 60-80% of the time using discriminant analysis of a combination of otolith chemistry and age and length data.Development of the full potential of otolith elemental composition in stock discrimination will require a more complete correlation of otolith chemistry and chemical oceanographic parameters (Severin et al. 1995).

Fecundity and egg size

Caution should be taken when comparing fecundity of walleye pollock between different regions due to the possibility of interannual variability within regions (Hinckley 1987) and the lack of standardization of methodology.However, some comparisons do reflect geographical differences in fecundity (see Table A-8 and Fig. 48). In most studies the length-fecundity relationship for walleye pollock has been found to be curvilinear and can be expressed as:

F = aL^b

Where F is fecundity in number of eggs, L is fork length in cm, and a and b are coefficients that characterize the y-intercept and the slope of the curve, respectively.

Table A-8 presents fecundity-length relationships for selected walleye pollock populations. Fecundity estimates are not available for walleye pollock in Puget Sound (Matthews 1987).Miller et al. (1986) compared published studies of walleye pollock fecundity and found that, for similar size females, reported fecundity from the Bering Sea was almost half that reported for Shelikof Strait, which in turn was about half the reported fecundity of walleye pollock in the Strait of Georgia (see Fig. 48).Hinckley (1987) also noted a general trend of declining fecundity for walleye pollock with increasing latitude.

Female walleye pollock are batch spawners in that groups of eggs ripen and are spawned at intervals of 1-7 d in separate spawning events, over a period of several weeks to a month, as observed in captive fish (Dunn and Matarese 1987, Balykin 1988, Sakurai 1989, Hinckley 1990).In laboratory studies of walleye pollock obtained from Puget Sound, the number of egg batches spawned per female ranged from 2 to 21, over a period of 3 to 26 days (Hinckley 1990).Balykin (1988) determined that female walleye pollock in the western Bering Sea spawn eggs in a total of 4 batches, based on the distribution of ovarian egg sizes.Sakurai (1989) reported that captive walleye pollock females spawned repeatedly over a month period with intervals of 1-7 days between spawning events.Several thousand to about 50 thousand eggs were released at a time (Sakurai 1989).The number of eggs spawned by an individual female has been shown to decrease with successive spawning events (Sakurai 1989, Hinckley 1990).

The average egg size in successive spawning events also decreases in later spawnings of captive female walleye pollock (Sakurai 1989, Hinckley 1990).In Shelikof Strait, egg size of walleye pollock has been shown to vary interannually and to decrease during the spawning season (Hinckley 1990).Sakurai (1989) also stated that egg diameter of spawning walleye pollock populations become smaller over time, presumably due to the decreasing trend in egg size of individual repeat spawners in the population.Hinckley (1990) reviewed geographic variation in egg size of walleye pollock and stated that "there appears to be a positive correlation between egg size and latitude in walleye Pollock" and that this correlation is likely related to latitudinal temperature gradients.

Morphological Differences

Meristic and morphometric variability

Numerous researchers have analyzed morphometric and/or meristic variability in walleye pollock in an attempt to identify population or stock structure (see recent summary in Bailey et al. 1999).The original separation of walleye pollock has been divided into two subspecies, Theragra c. chalcogramma (Pallas) and T. c. fucensis (Jordan and Gilbert) (the later having been described from Puget Sound (Jordan and Gilbert 1883), was based mainly on differences in median fin-ray counts of four specimens from Puget Sound and three from Alaska (Wilimovsky et al. 1967).Schultz and Welander (1935) re-examined walleye pollock fin-ray and vertebral counts for 27 specimens from Puget Sound and 30 from Alaska, and found little difference in fin-ray counts from the two areas suggesting this may not be a valid character for subspecific determination in walleye pollock, although they chose not to synonymize the two subspecies (Wilimovsky et al. 1967).Wilimovsky et al. (1967) examined variability in seven morphometric and eight meristic characters in walleye pollock from northern Washington, southern B.C, Southeast Alaska/northern B.C., Aleutian Islands, Bering Sea, Western Bering Sea, and the Sea of Okhotsk.Neither morphometric nor meristic characters showed significant differences between geographic areas, although some meristic counts showed clinal trends in north-south reduction (Wilimovsky et al. 1967).Based on these studies, Wilimovsky et al. (1967) synonymized T. c. chalcogramma and T. c. fucencis and invalidated these subspecific names.

Serobaba (1977) examined population structure of Bering Sea walleye pollock through the analysis of 27 morphometric characters and identified four "groupings"; eastern Bering Sea, northern Bering Sea, western Bering Sea, and southern Bering Sea.Specimens examined by Serobaba (1977) were collected on the "feeding grounds" in the Bering Sea and do not represent spawning populations, which limits the studies' utility for distinguishing population structure.Dawson (1989) had little success in discriminating young-of-the-year walleye pollock from 5 different regions in the Bering Sea using morphometric characters.However, Dawson (1994) was able to show that shape of walleye pollock varied significantly between areas in the Bering Sea.Walleye pollock from the central Aleutian Basin and Aleutian Islands were well separated from each other and from all other areas in this analysis (Dawson 1994).Samples from the northwest Bering Sea and western Bering Sea were well separated from one another and moderately well separated from all other areas (Dawson 1994).Dawson (1994) stated that walleye pollock samples from the eastern Bering Sea were most similar in shape and could not be successfully discriminated, indicating some interchange occurs between regions on the eastern Bering Sea shelf.

A more recent study (Temnykh 1994), examined morphometric characters of walleye pollock collected during the spawning season and did not find differences between populations across the entire western Bering Sea.However, walleye pollock from the western Bering Sea, Sea of Okhotsk, and southeastern Kamchatka were found to be morphologically distinct.Temnykh (1994) observed a high level of polymorphism in morphometric characters with "a high degree of overlap of morphological subsets in each sample," and although each area had a morphotype characteristic of its area, in each area examined "pollock are present with the morphotypes of other, frequently rather remote, regions."Temnykh (1994) postulated that this polymorphism may result from "mixing of pollock resulting from the absence in this species of strongly pronounced homing."

A number of studies of geographic variation in morphometric and meristic characters of walleye pollock in Japanese coastal waters, and beyond, have indicated population structure (Ishida 1954, Ogata 1959, Hashimoto and Koyachi 1969, Iwata and Hamai 1972, Iwata 1975a, Koyachi and Hashimoto 1977).Ishida (1954) observed that similar-sized walleye pollock had larger otoliths in the Sea of Japan than in the Sea of Okhotsk.However, otoliths of fish from off the Pacific Ocean coast of Japan and in the Sea of Japan were of equal size (Ishida 1954).Ogata (1959) found significant differences in counts of vertebrae between walleye pollock on the Pacific Ocean side and the Sea of Japan side of Japan.Within the Sea of Japan, Ogata (1959) differentiated three stocks:1) the west coast of Hokkaido, 2) western and northern coasts of Honshu, and 3) the south-east coast of Siberia.Based on differences in vertebral counts, Iwata and Hamai (1972) determined that there were eight "local forms" of walleye pollock in the Sea of Okhotsk and the waters around Japan; 1) northeastern Sea of Okhotsk form, 2) western Sea of Okhotsk form, 3) western Sakhalin form, 4) western Hokkaido form, 5) northern Kurile Island form, 6) Rausu form (southern Kurile Islands), 7) east of Cape Erimo form (Pacific coast of Hokkaido), and 8) west of Cape Erimo form (Pacific coast of Hokkaido).As is common in a number of fish species, Iwata and Hamai (1972) noted that the mean number of vertebrae increased with latitude in walleye pollock.The vertebral study of Iwata and Hamai (1972) was expanded on and also presented in Iwata (1975a).Morphometric analyses of walleye pollock by Iwata (1975a) led to the identification of six "local forms"; northern Sea of Japan, Uchiura (=Funka) Bay, eastern Kamchatka westward to Kushiro, Rausu, western Sea of Okhotsk, and eastern Sea of Okhotsk.

Koyachi and Hashimoto (1977) examined meristic character variation across almost the entire geographic range of walleye pollock and identified 12 "sub-populations":1) western Honshu, 2) northern Honshu, 3) Hokkaido, and 4) Pormorskaya, all in the Sea of Japan; 5) southern Hokkaido and northern Honshu, and 6) southern Kurile Islands, both on the Pacific Coast of Japan; 7) southwestern Sea of Okhotsk, 8) northern Sea of Okhotsk; 9) Kamchatka Peninsula, 10) eastern Bering Sea, 11) Gulf of Alaska, and 12) Pacific coast of Canada.Koyachi and Hashimoto (1977) found vertebral counts to be the most informative, and also noted higher counts in northern waters than in southern waters.Hashimoto and Koyachi (1977) distinguished 7 "sub-populations" of walleye pollock in waters near Japan by means of allometric and morphometric comparisons:1) northwestern Honshu, 2) western Hokkaido, and 3) Pormorskaya in the Sea of Japan; 4) southern Hokkaido and northern Honshu, and 5) southern Kurile Islands, both on the Pacific Ocean side of Japan; 6) southwestern Sea of Okhotsk, and 7) northern Sea of Okhotsk.Other "sub-populations" tentatively identified by Hashimoto and Koyachi (1977) were Kamchatka Peninsula, eastern Bering Sea, Gulf of Alaska, and the Pacific coast of Canada.

Genetic Information

Several molecular genetic techniques have been used to infer population structure in walleye pollock, especially in the Bering Sea and the Gulf of Alaska.The results of these give a general indication of the level of genetic differentiation that might be expected for populations in Puget Sound and adjoining areas.A detailed study of genetic population structure in Puget Sound is lacking, although samples from Puget Sound have been included in studies of geographically large-scale variability.The results of previous studies of walleye pollock and the results of empirical and theoretical studies of high gene flow species of fish indicate that only low levels of genetic differentiation would be expected among populations of walleye pollock where physical barriers to migration are lacking (Waples 1987, Ward et al. 1994).

Bailey et al. (1999) recently reviewed genetic population structure studies for walleye pollock and illustrated a hypothetical model of population structure for walleye pollock in the North Pacific Ocean (Fig. 42).On very broad spatial scales across the North Pacific, protein electrophoretic studies of several species detected population differences that apparently resulted from isolation in the distant past.A similar North Pacific Ocean discontinuity in gene frequency has been observed for the enzyme superoxide dismutase (SOD) in walleye pollock (Iwata 1973, 1975a, b, c; Grant and Utter 1980).In this case, the demarcation between the two oceanic groups appears to be located on the Asian side of the Bering Sea or in the Sea of Okhotsk.These ocean_wide differences indicate that fish generally do not disperse over large distances across the North Pacific.If they did, gene frequency differences across the North Pacific would disappear.The lack of mixing also implies that partially isolated stocks may exist on a smaller geographical scale.The presence of ocean-wide gene frequency differences may provide the basis for identifying stocks and dispersal pathways between stocks in areas of mixing between the two major groups.

Grant and Utter (1980) found some significant genetic differences between walleye pollock samples from the Gulf of Alaska and those from the southeastern Bering Sea; however, only the SOD locus showed significance in tests between these two regions.Bailey et al. (1999) stated that "F_ST among samples within each region was 0.021, and is typical of values for several other species of marine fishes with apparently high equilibrium levels of gene flow between populations."Seeb et al. (in press) reported that although an examination of variation at 29 allozyme loci between walleye pollock from the Bering Sea and Gulf of Alaska revealed no striking differences, SOD allele frequencies did distinguish Gulf of Alaska and eastern Bering Sea samples of spawning fish.Seeb et al. (in press) also reported that as alleles of SOD genes in other species have been shown to be under directional selection.This may also be the case for SOD in walleye pollock.Yanagimoto (in press) summarized Japanese studies of walleye pollock genetic analyses and reported that SOD alleles also show a clinal trend in frequencies in the western Bering Sea through Hokkaido.This has served to discriminate populations from these two major regions.

Mitochondrial DNA (mtDNA) has been used to study walleye pollock, but with little success in detecting population groupings.Mulligan et al. (1992) sampled four localities: 1) Gulf of Alaska, 2) the "donut hole" in the mid-Bering Sea, 3) Bogoslof Island in the southeastern Bering Sea, and 4) Adak Island in the Aleutian Archipelago.Tests of haplotypic frequencies showed significant differences between the Adak Island sample and the three other samples.Nevertheless, the overall level of differentiation between these samples was small (F_ST = 0.019) and was similar to the level detected with allozymes (Grant and Utter 1980).The apparent lack of stock structure in the Bering Sea may lie with the failure to sample populations during spawning, when stock separation is expected to be the largest.

A second study of mtDNA variability in the Bering Sea populations showed another pattern of differentiation among samples.Shields and Gust (1995) sampled walleye pollock from six areas:1) western Bering Sea, 2) northwestern Bering Sea, 3) the "donut hole", 4) Aleutian Islands, 5) southeastern Bering Sea, and 6) Gulf of Alaska.None of these samples differed from each other in pairwise tests.However, the comparison between samples 1-2 combined and samples 5-6 was significant.These results indicate at least some east-west differentiation across the Bering Sea.The samples for this study also appear to have been collected out of the spawning season when stocks may have been mixed.

Yanagimoto (in press) reported on Japanese studies of RFLP analysis of mtDNA (see "Glossary") that found significant differences among walleye pollock samples from three areas in the Bering Sea (west, northeast, and southeast) but no differences between these areas and the "donut hole."The apparent discrepancy between mtDNA RFLP studies of Mulligan et al. (1992) and studies reported in Yanagimoto (in press) may be due to differences in the restriction enzymes used in the two studies (Yanagimoto in press).Seeb et al. (in press) also examined RFLP polymorphism at the mtDNA genes for cytochrome b, cytochrome oxidase, and the ND 5/6 regions, and detected no haplotype differences between spawning populations of walleye pollock from Prince William Sound and Shelikof Strait.

In Atlantic cod, the analysis of microsatellite loci resolved fine scale genetic differences between stocks that were not isolated by any apparent barriers to gene flow (Bentzen et al. 1996).Early studies of microsatellite variability in walleye pollock showed variable results, possibly because of technical difficulties in the DNA analysis itself or because of the sampling of mixed populations outside spawning areas.More recent studies of walleye pollock populations with microsatellites are based on improved technologies and on spawning-area samples (Seeb et al. in press, O'Reilly et al. in press).

Seeb et al. (in press) did not find differences at two microsatellite loci between spawning populations of walleye pollock in 1997 from Prince William Sound, Shelikof Strait, and Bogoslof Island.O'Reilly et al. (2000) reported the development of 14 new microsatellite loci that should prove useful in analysis of population structure in walleye pollock.Based on some of these new microsatellite loci, O'Reilly et al. (in press) presented preliminary results of genetic variation at 10 microsatellite loci among six samples:Port Townsend, Washington (juveniles), Prince William Sound (adult spawners), southeast Bering Sea at Unimak Island (March, adult spawners), southeast Bering Sea at Unimak Island (April, adult spawners), northwest Bering Sea (non-spawning adults), and Funka Bay, Japan (adult spawners).O'Reilly et al. (in press) found significant single locus differences in all pair-wise population comparisons, differences at 6-10 loci between both Port Townsend and Prince William Sound and other east Pacific populations, and differences at 8-10 loci for comparisons between Japan and east Pacific samples.O'Reilly et al. (in press) stated that "population pairs surveyed here appear to follow an isolation by distance model" where geographical distance is measured along the continental shelves.The finding most significant to this status review is that "global significance of single locus tests of differentiation were observed between walleye pollock from Port Townsend and Prince William Sound, suggesting genetic structuring within the northeast Pacific" (O'Reilly et al. in press).

Information Relevant to the Walleye Pollock DPS Question

As stated in the previous "Approaches to the Species Question and to Determining Risk" section, four broad types of information were analyzed by the BRT in its determinations of whether walleye pollock in Puget Sound represent a "discrete" and "significant" population and therefore qualifies as a DPS under the ESA:habitat characteristics, phenotypic and life-history traits, mark-recapture studies, and analysis of neutral genetic markers.As such data can only be properly evaluated in relation to similar information for the biological species as a whole, Puget Sound walleye pollock data were compared with data from walleye pollock from throughout the species' range.

As detailed in the previous sections on "Environmental Features..." and "Phenetic and Genetic Information Relating to the Species Question," specific information for Puget Sound walleye pollock was available in the following categories: 1) physical habitat, 2) spawning time and location, 3) migration patterns, 4) year-class strength, 5) growth rate and body size,6)size and age at maturity, 7) length frequency, 8) meristics and morphometrics, and 9) very limited data on genetic population structure relative to a recent microsatellite DNA study.Information on tagging, parasite incidence, fecundity, and local genetic population structure for walleye pollock in Puget Sound was largely unavailable.A similar assemblage of data was available for walleye pollock from the Strait of Georgia, including fecundity and parasite-incidence data; although, year-class strength and length frequency data were lacking.Very little biological data was found for walleye pollock in Southeast Alaska, data on physical habitat, spawning time and location, migration patterns, parasite incidence, growth rate and body size, size and age at maturity, length frequency, and meristics and morphometrics were available from central and northern British Columbia.Limited genetic population structure information was available for walleye pollock off Southeast Alaska.The previous section on "Approaches to the Species Question and to Determining Risk" should be consulted for a general discussion of the relative usefulness of the various categories of data for DPS delineation.Issues of biological data quality for walleye pollock are addressed for each category in the preceding section entitled "Phenetic and Genetic Information Relating to the Species Question."

Discussion and Conclusions on Walleye Pollock DPS Determinations

The BRT considered several possible DPS configurations for populations of walleye pollock in the northeastern Pacific Ocean in its attempt to identify a "discrete" and "significant" segment of the biological species that incorporates Puget Sound fish.After careful consideration of the available information, its usefulness for delineating walleye pollock DPSs, and the accompanying uncertainty, the BRT concluded that aggregations of spawning walleye pollock in the eastern North Pacific Ocean, south of the provisional northern boundary of 140^oW, are part of a single DPS and can be thought of as a "species" under the ESA.Since the area occupied by this unit roughly corresponds to the region identified by Briggs (1974, p. 278) as containing a "well-defined lower boreal fauna," the walleye pollock in this area will hereafter be identified as the Lower boreal Eastern Pacific DPS (Fig. 3).

The BRT's conclusion that the walleye pollock DPS is significantly larger than Puget Sound was supported by the following considerations:1) the walleye pollock reproductive traits of pelagic spawning and pelagic eggs and larvae, 2) the ecological similarity of fjord-type marine habitat in Puget Sound to habitats along the coasts of British Columbia and Southeast Alaska, and 3) comparisons made with walleye pollock from areas outside of Puget Sound where much more data is available concerning the biology and population structure of walleye pollock populations.The BRT did not preclude the possibility that further information on the behavior, ecology, and genetic population structure might provide a basis for delineating smaller DPSs of walleye pollock within the Lower boreal Eastern Pacific DPS.

Although the BRT acknowledged that more studies on genetic population structure were available for analysis in the case of walleye pollock than for the other gadiforms under review, most of these genetic studies were flawed by samples having been collected outside of the spawning season, which may result in collections that represent mixtures of different populations or stocks.Most studies of genetic population structure in walleye pollock have revealed low levels of differentiation where physical barriers to migration are lacking.These genetic studies did not include spawning aggregations of walleye pollock from Puget Sound.However, microsatellite DNA data on walleye pollock showed statistically significant differences between samples from Port Townsend and populations in the southeastern Bering Sea and Gulf of Alaska.Overall, the BRT found the available evidence for genetic differentiation of walleye pollock populations at scales smaller than Asia versus North America to be ambiguous.Numerous spawning populations occur in embayments along southeastern Alaska, British Columbia, and Puget Sound and may be more or less demographically independent of one another.No genetic information on these populations is available.

The BRT examined several scenarios as to where the northern boundary of the Lower boreal Eastern Pacific DPS may occur, including:1) the Georgia Basin, 2) the northern end of Vancouver Island, 3) Southeast Alaska to 140^oW, and 4) the Aleutian Islands.Although none of the BRT members ruled out the possibility that the Georgia Basin could be the northern boundary of the DPS (scenario 1), there was little support for scenarios 2 or 4.The majority opinion of the BRT supported scenario 3.Evidence supporting a walleye pollock DPS that extends from Puget Sound northward to encompass all of Southeast Alaska includes:1) the more or less continuous distribution of spawning sites for walleye pollock throughout the region, 2) that regulatory agencies in the area consider walleye pollock in northern British Columbia and Southeast Alaska to consist of a single stock, 3) recognition of a significant zoogeographic faunal break in Southeast Alaska, 4) the consideration that walleye pollock north through Southeast Alaska are spawning in fjords, whereas further north walleye pollock are spawning in more open water, and 5) the unlikely potential for walleye pollock from Southeast Alaska to mix with walleye pollock from the central and western Gulf of Alaska.The boundary between Gulf of Alaska and Southeast Alaska walleye pollock management units has been set at 140^oW (Dorn et al. 1999b).Densities of walleye pollock vary to either side of 140^oW and there is a substantial reduction in abundance east of 140^oW (Dorn et al. 1999b).With the above considerations in mind, the BRT provisionally placed the northern boundary of the Lower boreal Eastern Pacific DPS at 140^oW (Fig. 3).

Within the Lower boreal Eastern Pacific DPS, walleye pollock spawn in numerous geographically-discrete aggregations, including (but not limited to) Port Townsend, Tacoma Narrows (although it is uncertain whether remnants of this spawning aggregation still exist), the south-central Strait of Georgia, off the west coast of Vancouver Island, and in numerous inlets in Queen Charlotte Sound, Hecate Strait, Dixon Entrance, and the inside waters of Southeast Alaska (Figs. 3, 45, 46).Therefore, the BRT considered whether there is evidence for multiple populations or stocks of walleye pollock within the Lower boreal Eastern Pacific DPS and, perhaps, multiple DPSs within the region.

Evidence that supports a geographically smaller DPS included:1) geographically-discrete and temporally-persistent spawning aggregations of walleye pollock, 2) regional differences in the frequency of occurrence of the trematode flatworm parasite (Prosorhynchus sp.), 3) synchronous trends in commercial catch between Puget Sound and the Strait of Georgia, which differs from the trends in other areas, and 4) regional demographic differences.However, the latter two lines of evidence may be related to climate or environmental factors working on a large scale (see previous section on "Approaches to the Species Question and to Determining Risk" for a general discussion of the relative usefulness of the various categories of data for DPS delineation).In addition, although spawning aggregations of walleye pollock appear to be persistent, evidence for a direct parent/offspring linkage is missing.The BRT considered the above evidence and agreed that there are probably multiple stocks of walleye pollock within the DPS.Some BRT members expressed the opinion that there is enough stock structure and local adaptation among walleye pollock to support a geographically smaller DPS that would include Puget Sound populations.Although the BRT as a whole did not find compelling evidence for multiple DPS of walleye pollock in the Georgia Basin, the precautionary approach would indicate that walleye pollock in Puget Sound should be managed as a stock separate from the Strait of Georgia.The BRT also recognized that the Lower boreal Eastern Pacific DPS may represent fish that are uniquely adapted to survive at the southern end of the species' range.

Although the BRT could not with any certainty identify multiple populations or DPSs of walleye pollock within the Lower boreal Eastern Pacific area, they acknowledged the possibility that more than one DPS for walleye pollock may exist in the range from Puget Sound to Southeast Alaska.However, the BRT was unable to find compelling evidence that this finer DPS structure exists.As an example of the uncertainty inherent in the walleye pollock DPS decision it should be noted that none of the BRT members ruled out the possibility that there could be a DPS for walleye pollock at the level of the Georgia Basin.

Assessment of Extinction Risk

Population Status and Trends

The BRT considered the status and trends of walleye pollock in the Lower boreal Eastern Pacific DPS in their analysis of extinction risk.Although multiple DPSs within this geographic area were not ruled out, the BRT did not evaluate extinction risks for smaller areas, such as Georgia Basin.Known information about the status of stocks in the Lower boreal Eastern Pacific bioregion is described in following sections and considered in determining extinction risk.The status of walleye pollock stocks off the west coast of Washington, Oregon, California, and Alaska beyond the Lower boreal Eastern Pacific bioregion were also not considered in the analyses of extinction risk.

Puget Sound

Trends in fishery statistics for walleye pollock in Puget Sound are the basis for assessing the status of stocks (Palsson et al. 1997).The primary stock indicator for Puget Sound, north of Admiralty Inlet, was the catch rate in the bottom trawl fishery.Trawl catch rates between 1970 and 1994 were low, usually less than 3 kg/hour, except during 1978-1981, when they were about ten times higher, ranging from 21 to 46 kg/hour (Table 30).Similarly, catches were usually less than 50 mt, except during the peak 1978-1981 period when catches usually exceeded 500 mt.During 1992-1994, negligible amounts of walleye pollock were landed by the commercial trawl fishery in northern Puget Sound (Table 30).Palsson et al. (1997) reported that it is unclear whether the stock is depressed, not targeted by the fishery, or was simply unavailable to the fishery during these years.

Walleye pollock in southern Puget Sound are on the extreme southern end of their distribution, yet a sport fishery near Tacoma once made walleye pollock the most common bottomfish harvested in Puget Sound recreational fisheries.Catches in southern Puget Sound exceeded 181 mt per year from 1977 to 1986.After 1986, catches dropped and the fishery collapsed (Palsson et al. 1997).The primary stock indicator for Puget Sound, south of Admiralty Inlet, was the recreational catch rate from the WDFW boat-based recreational survey (Palsson et al. 1997).Catch rates exceeded 1.3 walleye pollock per angler trip in 1978 and 1979, then declined rather steadily to 0.5 fish per trip in 1986 and to negligible levels by 1991, where they remained through 1998 (Table 31).Due to concerns about the status of the population, the daily bag limit for walleye pollock in the recreational fishery in Puget Sound was reduced from 15 fish to five fish in 1992.The walleye pollock daily bag limit was changed from five fish per day to zero in 1997.

Recreational catches in Puget Sound remained very low during the late 1990s.Results from the WDFW boat-based recreational survey showed that 9 walleye pollock were reportedly landed during 90,000 bottomfish angler trips from Puget Sound in 1996, and results of the Marine Recreational Fisheries Statistical Survey indicate no walleye pollock were reportedly caught in recreational fisheries in Puget Sound during 1996 and 1997 (WDFW 1998).More recent data are not yet available.

Bottom trawl surveys were conducted throughout Puget Sound in 1987, 1989, and 1991.Subsequent surveys covered only portions of Puget Sound in 1994, 1995, 1996, and 1997.Estimated biomass and numbers in the population vulnerable to the survey trawl, and average size of walleye pollock within each WDFW management region (see Fig. 14) are shown in Table 32 (W. Palsson^[34]).Estimates for biomass and numbers of fish in 1987 were much higher than in other years and the average sizes of walleye pollock taken were usually smaller.This may not represent a change in fish abundance, but may be due to other factors.The 1987 survey was exploratory, being the first such survey ever conducted in Puget Sound.Also, the survey vessel used in 1987 was much larger than those used in subsequent years and the survey was conducted in the fall, whereas other surveys were presumably conducted in the spring.Otherwise, there was no apparent trend, except that the abundance of walleye pollock in central Puget Sound in 1995 was much larger than in other years.For the three years when all management regions were surveyed, estimated biomass exceeded 975 mt of walleye pollock in Puget Sound and numbers exceeded 7 million fish each year (Table 32).

British Columbia

Discrete walleye pollock stocks are present in Dixon Entrance/Hecate Strait, Queen Charlotte Sound, west coast Vancouver Island, and the Strait of Georgia.Walleye pollock in Dixon Entrance/Hecate Strait are thought to be part of a stock that includes the southern waters of southeast Alaska but the relationship with large Gulf of Alaska stocks is unclear.It is possible that high abundance in the Gulf of Alaska results in movement into northern Canadian waters (Saunders and Andrews 1998).

A stock assessment for walleye pollock in 1997 (Saunders and Andrews 1998) provides the most recent information on the status of stocks in Canadian waters.Catch histories during 1954-1996 are given for each management area in Table 33.During 1970-1991 when catch data were available for Puget Sound and the Strait of Georgia, catch patterns in the Strait of Georgia closely matched those in Puget Sound until the late 1980s when catch patterns began diverging, as shown in Fig. 40B (Schmitt et al. 1994).In the Strait of Georgia (Area 4B), excluding minor Area 12 (see Fig. 47), sustainable yield estimates range from 470 to 1,760 mt.Within Area 12, a detailed assessment has not been done and yields between 1,000 and 2,580 mt are recommended.It is believed that walleye pollock within Area 12 are not part of the Strait of Georgia stock, but rather contribute to the body of walleye pollock residing in Queen Charlotte Sound.In Queen Charlotte Sound, catches dropped from 695 mt in 1995 to 57 mt in 1996.A detailed assessment has not been completed for walleye pollock in Queen Charlotte Sound.

Off the west coast of Vancouver Island (Area 3C and 3D, see Fig. 12), walleye pollock are taken incidentally in the joint venture fishery for Pacific hake and domestic fisheries off the southwest coast of Vancouver Island.Walleye pollock catches in both fisheries increased dramatically in 1996 compared to 1995.The total catch in these fisheries was estimated to be 2,737 mt in 1996, compared to 14 mt in 1995.This increase appeared to be due to the 1994 year-class entering the fishery as two-year-olds.A detailed assessment has not been done for this area.

The walleye pollock fishery in northern Hecate Strait and Dixon Entrance (Areas 5C and 5D, see Fig. 12) occurs mainly in the winter, and landings during the 1990s have been at record highs.However, walleye pollock landings in 1996 were 882 mt, well below the quota of 3,190 mt.The status of this stock is not well known, although Saunders and Andrews (1998) recommend a quota ranging from 330 mt to 1,320 mt until an assessment can be done.

Gulf of Alaska

Walleye pollock in the Gulf of Alaska are managed as a single stock, and the exploitable biomass (age 3+) for 1999 was projected at 738,000 mt (Witherell 1999).The stock is considered to be at medium relative abundance.The 1994 year-class is forecast to be above average, primarily in Shelikof Strait.Preliminary information suggests weak year-classes in 1995 and 1996, and a moderate 1997 year-class.Under these recruitment scenarios, the biomass of spawners is expected to decline through 2003 (Witherell 1999).

A formal stock assessment for the Southeast Alaska portion of the Gulf of Alaska has not been conducted.Historically, there has been very little directed fishing for walleye pollock in Southeast Alaska, and catches in the Southeast and East Yakutat statistical areas averaged 27 mt during 1991-1998 (Table 34).However, commercial trawling is currently banned east of 140^oW, and bottom trawl surveys indicated a substantial reduction in walleye pollock abundance in this region (Dorn et al. 1999b).

Stock structure of walleye pollock in the Southeast Alaska portion of the Gulf of Alaska is poorly understood and may be characterized by numerous fjord populations.In the 1996 and 1999 bottom trawl surveys, higher catch rates in Southeast Alaska occurred mainly from Cape Ommaney to Dixon Entrance, where the shelf is more extensive.Smaller fish (<40 cm) dominated the size composition for the 1993, 1996, and 1999 surveys.It is thought that these juvenile fish are unlikely to influence the population dynamics of walleye pollock in the central and western Gulf of Alaska.Ocean currents are generally northward in this area, suggesting that juvenile settlement is a result of spawning further south (Dorn et al. 1999b).

Dorn et al. (1999b) estimated the biomass of walleye pollock in Southeast Alaska from area-swept estimates of bottom trawl survey data, split to match the area east of 140EW.Walleye pollock biomass estimates from bottom trawl surveys are highly variable, partially as a result of differences in survey coverage among years.The 1996 and 1999 surveys had the most complete coverage of shallow strata in Southeast Alaska and indicated that the stock size of walleye pollock was about 30,000-50,000 mt (Dorn et al. 1999b).

Summary and Conclusions of Walleye Pollock Risk Assessment

The BRT considered extinction risk for walleye pollock in the Lower boreal Eastern Pacific DPS.In most respects, the BRT's deliberations for the walleye pollock DPS considered similar risk factors to those described earlier for Pacific cod.Walleye pollock and Pacific cod have similar life histories, except at the egg stage, and both populations in Puget Sound and off the West Coast are at the southern extreme of the range for these species.Data were insufficient to quantitatively assess the extinction risks for walleye pollock, and the same list of potential factors affecting Pacific cod abundance were considered as potential risk factors for walleye pollock.The contributions of these potential risk factors, either singly or in combination, to the current low abundance of walleye pollock in Puget Sound, are not well known.

A major difference in deliberations for these two species is that a single DPS was identified for walleye pollock whereas three scenarios were considered for Pacific cod.Also unlike Pacific cod, the populations of walleye pollock in waters of British Columbia did not appear to be declining or at low levels, although information on the status of these stocks is very limited.Consequently, walleye pollock stocks with apparent low abundance were mainly those in Puget Sound and not as widespread as for Pacific cod.In addition, walleye pollock spawn pelagic eggs whereas Pacific cod spawn demersal eggs.It is unknown whether this difference in spawning requirements contributes significantly to the different trends observed in stock conditions between the two species.

The BRT concluded that walleye pollock in the Lower boreal Eastern Pacific DPS are not in danger of extinction, nor are they likely to become endangered in the foreseeable future if present trends continue.However, most BRT members could not entirely rule out the possibility that walleye pollock in this DPS, although not presently in danger of extinction, are likely to become so in the foreseeable future.

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