The joint policy of the U.S. Fish and Wildlife Service (USFWS) and the National Marine Fisheries Service (NMFS) provides guidelines for defining distinct population segments below the taxonomic level of species (USFWS-NMFS 1996). The first of two elements to be considered is the discreteness of a population segment with respect to the rest of the populations within the species. Discreteness may result from physical factors that isolate the population segment and may be reflected as life-history differences in physiology, ecology, or behavior between the DPS and other populations. Genetic or morphological differences between the population segment being considered and other populations may also be used to evaluate discreteness. The policy also states that international boundaries within the geographical range of the species may be used to delimit a distinct population segment in the United States. This criterion is applicable if differences in the control of exploitation of the species, the management of the species' habitat, the conservation status of the species, or regulatory mechanisms differ between countries that would influence the conservation status of the population segment in the United States. In past assessments of evolutionarily significant units (ESUs) in Pacific salmon, however, NMFS has placed the emphasis on biological information in defining DPSs and has considered political boundaries only at the implementation of ESA listings.
A second element in defining distinct population segments is that the segment must be biologically or ecologically significant. Significance is evaluated in terms of the importance of the population segment to the overall welfare of the species and may be considered in the light of, but not limited to, the following factors. The population segment may be considered significant if it persists in an unusual or unique ecological setting for the species. A population segment may also be considered significant, if its loss would result in a significant gap in the geographical range of the species. Such a gap may disrupt the normal connectivity between populations. A segment also meets the significance guideline, if it represents the only surviving natural occurrence of the species that may be more abundant elsewhere as an introduced population outside its historical range. Another guideline is that the population segment differs markedly in its genetic characteristics from other populations of the species. Genetic differences may be detected by molecular genetic methods or may be reflected in unique adaptations to habitats not found in other parts of the species' geographical range. Other classes of information may also bear on the biological or ecological importance of a discrete population segment.
We considered several kinds of information in this status review to attempt to delineate DPSs of copper rockfish, quillback rockfish and brown rockfish in greater Puget Sound. The first kind of information considered was geographical variability in life-history characteristics and morphology. Such traits usually have an underlying genetic basis, but are often strongly influenced by environmental factors from one locality to another. The second kind of information consisted of tag and recapture studies, which give insight into the physical movement of individuals between areas. The third kind of information consisted of genetic markers of traits that are inherited in a predictable way and remain unchanged throughout the life of an individual. Differences among populations in the frequencies of markers at these traits may reflect isolation between the populations. Finally, we considered characteristics of greater Puget Sound that might suggest that it is an unusual or distinctive habitat for quillback, copper and brown rockfish. The analyses of these kinds of information are discussed briefly in the following sections.
Isolation between populations may be reflected in several life-history variables, including differences in behavior (e.g., spawning timing, migration) and demography (e.g., growth rate, fecundity, age structure), among others. Although some of these traits may have a broad genetic basis and may reflect local adaptations of evolutionary importance, they are usually strongly influenced by environmental factors over the lifetime of an individual or over a few generations. Differences can arise among populations in response to environmental variability among areas and they can sometimes be used to infer the degree of independence among populations. However, differences in phenotypic and life-history traits among populations do not provide definitive information on reproductive isolation between populations, because the genetic basis of many phenotypic and life-history traits is weak or unknown. Likewise, elemental profiles present in otoliths, and other structures, reflect local environmental conditions or diets and although they may indicate that different areas or environments are occupied, they also provide little definitive information on the degree of reproductive isolation between populations.
Variation in reproductive behavior within a species of marine fish is an important factor to consider because it may provide the isolating mechanism required for differentiation. The presence of geographically-discrete and temporally-persistent spawning aggregations in a species indicates that reproductive isolation may be occurring. However, it is necessary to evaluate the degree of reproductive isolation by addressing the questions of migration rate, gene flow, and recolonization rate. These later considerations are dependent on the degree of homing ability and natal-site fidelity of adults.
Studies of parasite incidence can provide important information about the degree of intermingling of marine fish stocks, particularly when a parasite is present in one area and totally absent in an adjoining area. However, parasite studies have some inherent interpretation problems: 1) in most cases parasite incidences exhibit clinal trends with latitude, and the degree to which parasite occurrence is due to environmental differences, acting on the parasite, or to a lack of host stock intermingling, is unknown, 2) the lack of a parasite in an area may be due to a regional absence of an alternate host organism, independent of host distribution, and 3) parasites may not be permanent natural tags in that parasites may be lost during the lifetime of the host.
Two problems inherent in the use of morphometric and meristic characteristics to separate marine fish populations are: 1) the characteristics are often under strong environmental influence and are not inherited in a simple Mendelian fashion, and 2) the characteristics are continuously variable and exhibit clinal trends and a high variance about the mean. A further drawback of using morphometric and meristic characteristics to detect population structure in fish is that few of these characteristics have been examined from a genetic standpoint. As shown by studies on several species, environmental parameters such as temperature, salinity, pH, and oxygen concentration can modify the expression of genes responsible for meristic characters (Ihssen et al. 1981).
The analysis of applied or acquired tags can indicate the degree of migration between localities. These tags consist of physical tags that are attached to a fish and later recovered. These tags provide evidence of movement of individuals from one place to another, but not necessarily of population connectivity through gene flow. Since these kinds of population markers largely lack a genetic basis and are not inherited, they must be applied each generation or must arise naturally anew each generation.
The application and recovery of physical tags on adult marine fish on spawning grounds can answer the question of whether fish return to the same locality to spawn in subsequent years, but these studies lack the direct evidence of parent-offspring linkage. In other words, these studies do not provide direct evidence that fish return to their natal area for spawning; however, they may provide evidence of straying and thus, the potential for gene flow between spawning aggregations.
The BRT considered molecular genetic evidence that might be used to define reproductively-isolated populations or groups of populations of copper, quillback and brown rockfish in greater Puget Sound, as well as throughout their respective ranges. Molecular genetic markers appear to be largely unaffected by natural selection, so that geographical differences in gene frequencies can be interpreted in terms of genetic flow and genetic drift. The analysis of the geographical distributions of these markers may reveal historical dispersals, equilibrium levels of migration (gene flow), and past isolation. Evidence for genetic population structure is based on the analysis of protein variants (allozymes), microsatellite loci (variable numbers of short tandem DNA repeats), and mitochondrial DNA (mtDNA).
Evidence of substantial genetic divergence between populations, as shown through analysis of these neutral molecular markers, is an important aspect of distinctiveness because even a small amount of interbreeding between populations will reduce the genetic differentiation between them. Although these molecular genetic methods "provide valuable insight into the process of genetic differentiation among populations" they offer "little direct information regarding the extent of adaptive genetic differences" (Waples 1995).
One widely-used method of population analysis is sequence or RFLP (restriction fragment length polymorphism) analysis of mtDNA, which codes for several genes that are not found in the cell nucleus. Mitochondrial DNA differs from nuclear DNA (nDNA) in two important ways. One way is that recombination is lacking in mtDNA, so that gene combinations (haplotypes) are passed unaltered from one generation to the next, except for new mutations. A second way is that mtDNA is inherited from only the maternal parent in most fishes, so that gene phylogenies correspond to female lineages. A greater amount of random genetic drift among populations is expected for mtDNA genes, because the effective population size for mtDNA is about one-fourth of that for nuclear genes. These characteristics permit phylogeographical analyses of mtDNA haplotypes, which can potentially indicate dispersal pathways for females and the extent of gene flow between populations (Avise et al. 1987).
Microsatellite DNA markers can potentially detect stock structure on finer spatial and temporal scales than can other DNA or protein markers, because of higher levels of polymorphism found in microsatellite DNA (reflecting a high mutation rate). When populations are at least partially isolated, genetic markers at loci with high mutation rates may accumulate more rapidly in some areas than in others.
Several standard statistical methods have been used to analyze molecular genetic data to detect reproductive isolation between populations. Comparisons of genotypic frequencies in a sample with frequencies expected under random mating (Hardy-Weinberg proportions) may be used to infer the breeding structure of a population or to detect population mixing (Wahlund's effect). Contingency-table comparisons of allozyme or microsatellite allele frequencies among population samples with chi-square or G (log-likelihood ratio) test statistics, or with randomization tests, can be used to detect significant differences between populations, which may be evidence of reproductive isolation.
A complementary way of assessing genetic isolation between populations is to analyze genetic distances based on allele-frequency estimates. Several genetic distance measures (Cavalli-Sforza and Edwards 1967, Nei 1972, 1978) have been used to study the population genetic structure of anadromous salmonids. It is unclear, however, which measure is most appropriate in a particular case or whether there is one measure that is always most appropriate. Discussions of the features of genetic distances appear in Nei (1978), Rogers (1991), and Hillis et al. (1996). Most of this discussion has focused on the merits of the various measures for phylogenetic reconstruction among species or higher taxa.
Sample sizes and heterozygosity may also influence the power of the genetic-distance approach to resolving genetic population structure. When sample sizes used to estimate allelic frequencies are 50 individuals or more, the difference between Nei's genetic distance, D, (Nei 1972) and Nei's unbiased genetic distance (Nei 1978) is small in absolute terms, but still might be a substantial proportion of D, if D is small. When genetic distances between populations are also small, as they often are between populations of marine fishes, low but significant levels of genetic differentiation may not be detected by an unbiased distance measure because sample-size corrections may reduce estimates of genetic distance to zero. These measures range from 0.0 (identity) to infinity (complete dissimilarity). In most cases, the different genetic-distance measures yield highly-correlated results.
The degree of reproductive isolation between populations can be inferred from an analysis of the pattern of genetic distances between populations. Clustering methods, such as the unweighted pair group method with averages (UPGMA, Sneath and Sokal 1973) and the neighbor-joining method (Saitou and Nei 1987), find hierarchical groupings of genetically similar populations. Multivariate methods, such as multidimensional scaling (MDS, Kruskal 1964) or principal components analysis (PCA), find groupings of genetically-similar populations in several dimensions, which are depicted here in two or three dimensions.
Various studies have estimated levels of genetic variability within populations, because the level of within-population variability may reflect evolutionary or historical differences in population size and in migration patterns between populations. Within-population gene diversity was measured by the expected proportion of heterozygous genotypes in a population of randomly-mating individuals averaged over the number of loci examined (H). Estimates of H based on a small number of individuals are usually accurate, as long as a large number of loci (>30) are surveyed for variability (Nei 1978).
Genetic differentiation between populations at various hierarchical levels has been estimated in many studies with a gene-diversity analysis (Nei 1973, Chakraborty 1980), which apportions allele-frequency variability among populations into its geographical or ecological components. For example, the proportion of the total genetic variability in a set of samples that is due to differences among populations may be estimated with FST or the multiallelic equivalent statistics, GST. These variables range from 0.0 (no difference among populations) to 1.0 (fixed allele-frequency differences). The range 0.05-0.15 for FST indicates moderate differentiation, and the range 0.15-0.25 indicates strong genetic differentiation among populations (Wright 1978). These statistics facilitate comparisons among groups of populations that may reveal regional differences in gene flow between populations.
The analysis of habitat characteristics may indicate that a population segment occupies an unusual or distinctive habitat, relative to the biological species as a whole. The persistence of a discrete population segment in an ecological setting unusual or unique for the taxon is one factor identified in the joint DPS policy (USFWS-NMFS 1996) that may provide evidence of the population's significance. However, Waples (1991a) commented that people should use caution when drawing inferences based on physical characteristics of the habitat without supporting biological information linking the habitat differences to adaptations.
Conversely, the continuous distribution of a population segment within a region possessing similar habitat and ecological characteristics makes it less likely that unique adaptations have arisen in local populations. Without associated compelling phenetic or genetic evidence for a finer population structure, marine fish continuously distributed throughout similar habitat and lacking physical or behavioral barriers to migration, are not likely to be composed of multiple DPSs.
The term "stock" has been used rather loosely in fisheries management and no single definition has been accepted by all fisheries biologists. Stock may be used to refer to groups of fish being harvested in a particular area, whether these fish are genetically related or not. However, in most cases, identification of a group of fish as a stock implies that these fish are in some way different or distinct from those in another stock, and generally implies some genetic relatedness among its members (Ihssen et al. 1981). Evidence of stock structure may be shown through differences in demographic population statistics (age composition, growth rate, fecundity, etc.), morphology (morphometrics and meristics), or genetics (differentiation at allozyme or DNA loci).
Ricker (1972) defined a salmon stock as "the fish spawning in a particular lake or stream (or portion of it) at a particular season, which fish to a substantial degree do not interbreed with any group spawning in a different place, or in the same place at a different season." Larkin (1972) defined a stock as "a population of organisms, which, sharing a common environment and participating in a common gene pool, is sufficiently discrete to warrant consideration as a self-perpetuating system which can be managed." Booke (1981) provided a general definition of a stock as "a species group, or population, of fish that maintains and sustains itself over time in a definable area." Ihssen et al. (1981) defined a stock as "an intraspecific group of randomly-mating individuals with temporal or spatial integrity." In none of these definitions is it implied that a fish stock is ecologically or biologically significant in relation to the biological species as a whole.
By contrast, not only must a marine fish DPS be "markedly separated from other populations of the same taxon," it must also exhibit ecological or biological significance in comparison to other population segments of the biological species. Thus, following the guidance supplied by the joint policy statement (USFWS-NMFS 1996), a distinct population segment of marine fish may be viewed as a group of related stocks (or in some cases, if the evidence warrants, a single stock) that form(s) a discrete population and are(is) significant to the biological species as a whole. As stated previously, considerations that can be used to determine a discrete population's significance to the taxon as a whole include: 1) persistence of the population segment in an ecological setting unusual or unique for the taxon, 2) evidence that loss of the population segment would result in a significant gap in the range of the taxon, 3) evidence that the population segment represents the only surviving natural occurrence of a taxon that may be more abundant elsewhere as an introduced population outside its historic range, and 4) evidence that the population segment differs markedly from other populations of the species in its genetic characteristics.
Greater Puget Sound and the Georgia Basin are of recent post-glacial geological origin. The geological history and present-day physical characteristics may affect the colonization and movement of individuals and hence the genetic structure of populations. Glacial recession, isostatic rebound, and sea-level rise allowed marine species to enter the greater Puget Sound only in the past 12,000 years. A non-random group of founders could have produced populations with limited genetic diversity. Furthermore, different areas of the Basin could have been colonized by different routes, at different times and from different parent stocks via the Strait of Juan de Fuca and Strait of Georgia, resulting in founder effects.
Regardless of whether the founding stocks were homogeneous or heterogeneous, typical oceanic-larval dispersal would quickly return populations to equilibrium in the absence of barriers to dispersal. The long and sinuous water bodies, shallow sills, and unidirectional flows due to freshwater inputs, could limit movements into and out of different basins. This might maintain separation and allow isolated populations to undergo local mutation and genetic drift. Small population sizes may also favor hybridization between closely-related species. It has been proposed (Seeb 1998) that hybridization is important in Puget Sound proper populations of rockfishes. However, these microsatellite studies do not agree with conclusions based on mtDNA.
Behavioral barriers can affect isolation both at the planktonic larval stage and the adult stage. Rockfish larvae are live-born and the larvae may maintain position in a basin by active swimming, depth regulation, or timing of parturition. In addition, seasonal timing of reproduction and mating behavior may isolate adults from different basins even if they successfully disperse into an adjacent basin. If portions of the Georgia Basin were colonized by founders from different areas of the outer coast they could differ in color pattern, mating behavior, or timing of reproduction. Factors such as lower salinity may also promote local adaptation and select against foreign larvae. Fresh-water inputs differ within regions of the Georgia Basin and between the Basin and the outer coast.
Marine species with extended pelagic larval and juvenile stages are considered to be high-dispersal species. It is generally expected that such species will show little genetic structure over wide geographic distances (Palumbi 1994,1996; Waples 1987, 1998). Populations colonizing an area in the past few thousand years will generally have had little time to accumulate genetic mutations and the differences between populations will be expressed as differences in allele frequency due primarily to the effects of random genetic drift. Factors that can alter the expectation of panmixia during the pelagic phase are extrinsic mechanisms, such as currents and eddies, that retain larvae or act as invisible barriers to dispersal and behavioral factors, such as larval swimming behaviors that actively promote retention. Factors that act to promote structure during the adult portion of the life history would include site fidelity, homing behavior, local adaptation, unequal-reproductive success, and assortative mating.
Copper rockfish (Sebastes caurinus), was originally described from a Sitka, Alaska type specimen. Subsequently a southern form, the whitebelly rockfish (Sebastes vexillaris), was described as a separate species. Most authors now subsume the white bellied form into the S. caurinus species. Chen (1986) examined the basis for the vexillaris-caurinus distinction. The type specimen from Sitka has been lost, but in a comparison of greater Puget Sound copper rockfish with southern copper rockfish from Monterey and Southern California, statistically significant morphometric and meristic differences were observed between the three locations. Chen (1986) felt that the differences were not of a magnitude to warrant species separation. Although greater Puget Sound populations were different from Monterey it is not possible to determine if populations were different from other populations in the Georgia Basin or on the outer coast.
Seeb (1998) examined population differences in copper rockfish from southern California, northern California, Washington coast, San Juan Island (North Puget Sound), Puget Sound proper, and Alaska. Seeb (1998) examined differences in protein electrophoretic patterns and restriction length polymorphisms (RFLPs) in mitochondrial DNA (Fig. 15). Species identification was unambiguous outside of Puget Sound proper but within Puget Sound proper numerous individuals could not confidently be assigned to copper, quillback or brown rockfishes. These specimens were compared as "unknowns" to look for evidence of hybridization. Over the entire sample range (California to Alaska), there was significant population structure as measured by FST. However, no marked discontinuity in allele frequencies was observed within Washington sampling sites. Significance remained even when the Puget Sound proper population was excluded. In summary, there appeared to be isolation by distance but no special degree of divergence in Puget Sound proper.
Peter Wimberger and colleagues have recently examined population structure in copper rockfishes with particular attention to the Georgia Basin (P. Wimberger4). The results are not to be cited outside the context of the BRT process without permission of the authors. Their study used seven microsatellite loci to examine population subdivision in seven populations of copper rockfish from southern California to the Queen Charlotte Islands, British Columbia. The greatest sampling effort focused on populations from around the greater Puget Sound region. In addition to the California and British Columbia populations, Wimberger and colleagues looked at populations from Puget Sound proper, (Central Puget Sound), Admiralty Inlet, Hood Canal, the San Juan Islands (North Puget Sound), and Canadian Gulf Islands in the Georgia Strait, British Columbia. The comparisons most relevant to the proposed listing of the Puget Sound populations are comparisons between the Central Puget Sound proper (CPS) and Admiralty Inlet (AI) populations with the populations outside the Sound. The most striking differences are between populations in both CPS and AI with populations outside Puget Sound proper. The population nearest to the Puget Sound proper populations is the San Juan Island (SJI) population in North Puget Sound which is about 35-75 km distant from the Puget Sound proper samples. The FST values paint a picture of the Puget Sound proper populations being more differentiated from populations outside the Sound as the number of basins between the populations increases. For instance, the CPS/AI FST=.011, while the CPS/SJI FST=.027 and the AI/SJI FST=.018. The SJI population appears equally differentiated from the Canadian Gulf Islands in the Strait of Georgia (CGI) and the northern Vancouver Island population (ave. FST=~.0275) suggesting that the SJI population also comprises a relatively distinct population. In general, all populations are similarly different from the two oceanic populations (FST range from .037 - .055, with the exception of SJI and northern Vancouver Island FST= .026). With the exception of the Canadian Gulf Island population, all the inland marine populations were more similar to the northern Vancouver Island (NVI) population than to the southern California (SC) population.
In a recently completed study, Buonacoursi et al. (In prep.) examined population structure in copper rockfish along the outer coast and within the Georgia Basin. They used a different set of microsatellite loci. They compared populations from San Miguel Island in southern California (SM), Big Creek in central California (BC), Crescent City in northern California (CC), and Queen Charlotte Island in British Columbia (QC), along the outer West Coast and the Canadian Gulf Islands (GI) in the Strait of Georgia, and Puget Sound proper (PS). Populations were highly structured. FST values combined across loci and at many individual loci showed highly significant differences between sampling sites (Figs.16, 17). Most populations conformed to an isolation by distance model, but differences between Puget Sound proper and the nearest population outside Puget Sound proper (GI) had a much greater genetic distance than predicted by geographic distance alone (Fig. 18). Private alleles were found in the Puget Sound proper population. Assignment testing on the basis of microsatellite genotypes revealed that Puget Sound proper fish were correctly assigned to Puget Sound proper at a frequency approaching 80% (Fig. 19). No evidence of hybridization between copper and brown rockfishes and copper and quillback rockfishes was observed on the basis of assignment frequency (Figs. 20a, 20b).
The rockfish BRT considered five possible configurations that incorporate greater Puget Sound populations of copper rockfish. The first is a coastwide DPS that encompasses Puget Sound proper. The second scenario includes a coastal DPS that includes the Queen Charlotte Islands, a Puget Sound proper DPS, a Gulf Island DPS, a northern Puget Sound DPS (including the San Juan Islands) whose boundaries are uncertain and a Strait of Georgia DPS whose boundaries cannot be defined at present. The third scenario consists of a coastal DPS, and a Georgia Basin DPS. A fourth scenario consists of a coastal and Gulf Islands DPS, and a Puget Sound proper DPS. The last scenario includes a coastal DPS, a Puget Sound proper DPS, and a northern Puget Sound DPS which includes the Canadian Gulf Islands and extends to an uncertain degree northward into the Strait of Georgia and westward toward the coastal DPS. All BRT members agreed that this last scenario (Fig. 1) is the most consistent with available information for copper rockfish, although substantial uncertainties remain especially with regard to the extent of the northern Puget Sound DPS.
Members of the BRT utilized a variety of evidence to support their identification of a Puget Sound proper DPS for copper rockfish. The preponderance of these are genetic in nature and come from work by Seeb (1998), P. Wimberger (see Footnote 4) and Buonacoursi et al. (In prep.). The presence of a private allele in Puget Sound proper, as well as assignment testing based on microsatellite genotypes provided convincing evidence of discreteness in the population. In addition, the life-history traits of copper rockfish such as live-bearing of young, internal fertilization, short-pelagic larval stages, fidelity to habitat and physical isolation due to current and water residence times in Puget Sound proper and North Puget Sound provide processes that could provide isolating mechanisms that are consistent with a relatively high degree of genetic structure in copper rockfish populations. These physical characteristics were utilized as evidence of the significance of the populations in that they provide unusual or unique habitat features not experienced by other copper rockfish populations.
The BRT also agreed that genetic evidence points to a possible separate northern Puget Sound DPS. Uncertainties do exist with regard to this DPS delineation, however. The oceanography of North Puget Sound, Gulf Islands and rest of the Georgia Basin is sufficiently restricted from the outer coast to reasonably allow reproductive isolation, but it is not as restricted or as unique as Puget Sound proper. Also, there are no genetic data for the rest of the Georgia Basin, so the question remains as to how Gulf Islands fish relate to the rest of the Georgia Basin as well as to the coast. Support was given to additional studies aimed at clarifying this information in the near future.
Seeb (1998) examined 291 specimens from California, Washington and Alaska including five locations within the Georgia Basin (four in Puget Sound proper). Allele frequencies were remarkably different between Puget Sound proper and even the closest location (San Juan Islands, North Puget Sound) outside of Puget Sound proper. Alleles G3PDH-1*88 and slDHP-1*100 were particularly informative (Fig. 15, and shown in Figures 2 and 3 in Seeb 1998). FST among populations was 0.028 p<.005). When the Puget Sound proper populations were dropped from the analysis the FST was 0.005 and was no longer significant.
Wimberger and coworkers (P. Wimberger, see Footnote 4) have recently examined population structure in quillback rockfish (Table 2). They used a series of six microsatellite markers to examine population structure between five locations (39 to 58 individuals per site). They compared two sites in Puget Sound proper with populations in the San Juan Islands, Washington and Sitka and Prince William (PW) Sound in Alaska. One of the Puget Sound proper samples was problematic (a single trawl in Hood Canal consisting of a cohort of juveniles that may have been misidentified) and was excluded from the analyses. The remainder of the study supported the basic conclusions of the allozyme study (Seeb 1998). There were significant differences in FST between Puget Sound proper and San Juan Island (North Puget Sound), which is only a short distance outside the Sound (P. Wimberger, see Footnote 4). Differences got progressively larger with greater geographic distance. The SJI population was more similar to the Sitka population than to the Puget Sound proper population. On the basis of the microsatellite data they considered and rejected the idea that the differences in Puget Sound proper could be accounted for by introgression.
Members of the BRT considered three possible configurations that incorporate greater Puget Sound populations of quillback rockfish. The first scenario includes a coastwide DPS that encompasses greater Puget Sound. A small minority of the BRT supported this scenario. The second DPS configuration includes a coastal and San Juan Islands DPS and a Puget Sound proper DPS. A slightly larger, small minority favored this scenario. The third configuration is a coastal DPS, a Puget Sound proper DPS and a northern Puget Sound DPS which extends into the Strait of Georgia and to the coast to an uncertain degree. A majority (66%) of the BRT approved of this DPS scenario (Fig. 2) for quillback rockfish. The geographic boundaries of the Puget Sound proper DPS, the northern Puget Sound DPS, and the coastal DPS are shown in Figure 2.
A variety of evidence was utilized by the BRT to support their tentative identification of a Puget Sound proper DPS for quillback rockfish. Most were genetic in nature and come from the allele and microsatellite work by Seeb (1998), and Wimberger (see Footnote 4). BRT members also considered that the life-history traits of quillback rockfish such as live-bearing of young, internal fertilization, short-pelagic larval stages, fidelity to habitat and physical isolation due to current and water residence times in Puget Sound proper and North Puget Sound, provide appropriate isolating mechanisms that are consistent with a relatively high degree of genetic structure in quillback rockfish populations. These physical characteristics were utilized as evidence of the significance of the populations in that they provide unusual or unique habitat features not experienced by other quillback rockfish populations.
The boundaries of the northern Puget Sound DPS are not certain. It extends to an uncertain degree northward into the Canadian portion of the Georgia Basin, and its western boundary is provisionally placed at Cape Flattery. The BRT concluded that the Puget Sound proper quillback rockfish are different from the coast, but beyond Puget Sound proper, there is no genetic evidence of structure in the population to support differences between the San Juan Islands (North Puget Sound) and the coast. However, the similarities of quillback and copper rockfish life histories and the oceanographic features of North Puget Sound led the BRT to conclude that the isolating mechanisms for copper rockfish probably apply to quillback rockfish as well. This led to the identification of a northern Puget Sound DPS for quillback rockfish. More genetic information is needed to clarify the existence and extent of this northern Puget Sound DPS.
Seeb (1998) reported the only completed data set on population structure of brown rockfish with relevance to greater Puget Sound. As with copper rockfish, she used protein allozyme patterns and RFLP analyses of mtDNA. Of the three species (copper, quillback and brown rockfishes) she had the smallest sample size (27) and the fewest locations (3) for brown rockfish. In a comparison of two Puget Sound proper locations with California samples there was a significant FST of 0.098 for brown rockfish on the basis of allozyme data. The G3PDH-1*88 allele was absent from the California population and reached 27% in the Puget Sound proper populations.
The genetics group at the SWFSC, La Jolla, NMFS has begun a microsatellite study of brown rockfish along the outer coast of California (R. Vetter5), and is receiving existing samples from WDFW (J. West6). No information is presently available on greater Puget Sound stocks.
Two possible configurations were considered by the BRT that incorporate greater Puget Sound populations of brown rockfish. The first is a coastwide DPS that includes greater Puget Sound. None of the BRT considered that this describes the appropriate scale for the DPS. The second scenario includes a coastal DPS, and a Puget Sound proper DPS. All members of the BRT members supported this second DPS delineation (Fig. 3). As with quillback and copper rockfish, the geographic boundaries of the Puget Sound proper DPS are the areas south of Admiralty Inlet and east of Deception Pass. Unlike copper and quillback rockfish, brown rockfish are uncommon in North Puget Sound. The few brown rockfish found outside of Puget Sound proper and inland of Cape Flattery are considered to most likely represent vagrant brown rockfish from the Puget Sound proper DPS.
The BRT identified a variety of evidence to support a Puget Sound proper DPS for brown rockfish. Genetic evidence comes from work by Seeb (1998). Brown rockfish have somewhat different life history and habits than do quillback and copper rockfish, however, key life-history traits that would contribute to isolation of copper and quillback rockfish are true of brown rockfish as well. These traits include live-bearing of young, internal fertilization, and short-pelagic larval stages. Physical isolation due to current and water residence times in Puget Sound proper and North Puget Sound also provide an isolating mechanism that is consistent with the genetic information. The distribution of brown rockfish is also important in that it occurs in Puget Sound proper with a large geographical disjunction between greater Puget Sound and Oregon. This makes it a possible remnant population in ecologically-unique habitats when compared to the California population (the populations that were sampled for genetics research).
BRT members were confident that, based on genetic information, this Puget Sound proper DPS is different from the coastal DPS, although the extent of the coastal DPS is unknown.
In summary, a Puget Sound proper DPS was identified for copper, quillback
and brown rockfish based on genetic information, life-history characteristics
and oceanographic-current patterns. The BRT agreed that the information
that provides a mechanism for genetic isolation was convincing and that
populations in Puget Sound proper are significant due to the uniqueness
of the environment in the Sound. For copper rockfish, there was sufficient
genetic, habitat and life-history information to conclude that copper rockfish
in North Puget Sound probably represented a DPS that had an uncertain western
boundary with the coastal DPS and extended northward to an uncertain degree
to include copper rockfish in the Canadian portion of the Georgia Basin.
For quillback rockfish, there was less genetic evidence to determine the
boundaries of a similarly-defined northern Puget Sound DPS. Brown rockfish
are uncommon in North Puget Sound so fish found in that area are considered
to be vagrants from the Puget Sound proper DPS. Data limitations were a
source of frustration, however, due to studies that provided glimpses of
information, but which were not designed to answer the questions we were
posing. Small sample sizes, localities of sampling and spottiness of sampling
were all difficulties in the available data. Studies to clarify these difficulties
have been proposed and would warrant revisiting these DPS delineations
once they are completed.
4 P. Wimberger, Department of Biology, University of Puget Sound, Tacoma, WA 98416-0088, Pers. commun, August, 2000.
5 R. Vetter, NMFS, SWFSC, La Jolla Laboratory, 8604 La Jolla Shores Drive, La Jolla, CA 92038-0271. Pers. commun., August, 2000.
6 J. West, WDFW, 600 Capitol Way N.,
Olympia, WA 98501. Pers. commun., September, 2000.