Investigation of Scientific Information on the
Impacts of California Sea Lions and Pacific Harbor Seals on Salmonids and on the Coastal Ecosystems of Washington, Oregon, and CaliforniaNational Marine Fisheries Service
Northwest Fisheries Science Center
2725 Montlake Blvd. E.
Seattle WA 98112-2097
National Marine Fisheries Service
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
|Appendix A.||Information on Steller Sea Lions|
|Appendix B.||Definitions of Stock Status Classifications|
|Appendix C.||Definitions of Terms Used to Describe Salmonids|
|Appendix D.||Status of Wild Salmonid Populations by Region, Timing of the Outmigration of Smolts in the Estuaries, and Species and Numbers of Pinnipeds Present During Adult Salmonid Return Migration.|
|Appendix E.||Status of Wild Salmonid Populations by Species and Region Based on Classification System of Each State.|
|Appendix F.||Summary of Food Habit Studies of California Sea Lions in Washington, Oregon, and California Since 1970|
|Appendix G.||Summary of Food Habit Studies of Pacific Harbor Seals in Washington, Oregon, and California Since 1970|
|Appendix H.||Common Names and Genus/Species of Pinniped Prey Items Reported in Washington, Oregon, and California|
This NMFS report was prepared by a Working Group and other contributors listed below.
|Robin Brown||Oregon Department of Fish and Wildlife|
|Robert DeLong||National Marine Fisheries Service|
|Steve Grabowski||National Marine Fisheries Service|
|Doyle Hanan||California Department of Fish and Game|
|Steve Jeffries||Washington Department of Fish and Wildlife|
|Linda Jones (chair)||National Marine Fisheries Service|
|James Lecky||National Marine Fisheries Service|
|Mark Lowry||National Marine Fisheries Service|
|Joe Scordino||National Marine Fisheries Service|
|Working Group alternates and report contributors|
|Marilyn Beeson||California Department of Fish and Game|
|Al Didier||Pacific States Marine Fisheries Commission|
|Tom Eagle||National Marine Fisheries Service|
|Sarah Fangman||National Marine Fisheries Service|
|Patrick Gearin||National Marine Fisheries Service|
|Matt Griswold||National Marine Fisheries Service|
|Harriet Huber||National Marine Fisheries Service|
|Irma Lagomarsino||National Marine Fisheries Service|
|Chuck Tracy||Washington Department of Fish and Wildlife|
In the 1994 Amendments to the Marine Mammal Protection Act (MMPA), Congress directed that a scientific investigation be conducted to "determine whether California sea lions and Pacific harbor seals a) are having a significant negative impact on the recovery of Salmonid fishery stocks which havebeen listed as endangered species or threatened species under the Endangered Species Act of 1973 (16 U.S.C. 1531 et seq.), or which the Secretary finds are approaching such endangered species or threatened species status; or b) are having broader impacts on the coastal ecosystems of Washington, Oregon, and California." This report provides the results of the scientific investigation requested by Congress.
Investigation into the existing scientific information addressing these issues was undertaken by a Working Group established by the National Marine Fisheries Service (NMFS). NMFS determined it did not have the resources nor was there sufficient time to conduct thorough field investigations on the issues identified by Congress within a 1-year time frame, so the investigation focused on a Working Group review of information from past field studies. The Working Group compiled and reviewed all available information on the status and trends of California sea lions (Zalophus californianus), Pacific harbor seals (Phoca vitulina), and the seven species of Salmonids found in Washington, Oregon. and California. Members of the Working Group also conducted several additional studies to augment existing information.
The status of many Salmonid populations has become precarious in recent years. Six populations of Pacific Salmonids have been listed under the Endangered Species Act (ESA) and 12 populations are proposed for listing as of February 1997. Serious declines in these and many other populations of Salmonids are the result of a complex array of factors over time, including changes in Salmonid riverine habitat, changes in oceanic conditions, overharvest, development of hydroelectric power systems in major riverine migratory routes, and detrimental impacts of hatchery programs. Predation by California sea lions and Pacific harbor seals may now constitute an additional factor in Salmonid population decline and can affect recovery of depressed Salmonid populations in somesituations.
The California sea lion population has been increasing at an annual rate of about 5% per year since the mid-1970s. The number of California sea lions off Washington, Oregon, and California was estimated at more than 161,000 sea lions in 1994. California sea lions are present year-round in southern California where they breed and pup. Male sea lions migrate northward into Washington, Oregon, and northern California each year from September to May, coinciding with spawning runs of many depressed Salmonid populations. California sea lions are opportunistic feeders, foraging on schooling fish and other prey that form dense aggregations. Their diet is diverse and varies regionally, seasonally, and annually. The proportion of Salmonids found in the California sea lion food habits samples varied by site, season, and year. California sea lions have had a significant negative impact on the recovery of one Salmonid population-winter steelhead that migrate through the Hiram M. Chittenden Locks (Ballard Locks) in Seattle, Washington.
Pacific harbor seals are present in Washington, Oregon, and California year-round; pupping occurs in all three states. Harbor seal populations in the three states have been increasing at a rate ofabout 5-7% annually since the mid-1970s. The estimated abundance by state from 1993-95 was 34,134 seals in Washington, 9,251 in Oregon, and 32,699 in California. Pacific harbor seals are opportunistic feeders, preying on a wide variety of benthic and epibenthic fish and cephalopods. Their diet also varies regionally, seasonally, and annually. The proportion of Salmonids found in Pacific harbor seal food habits samples varied between studies as well as by site, season, and area.
The Working Group found that the presence of California sea lions and Pacific harbor seals in rivers and estuaries concurrent with migrations of depressed Salmonid populations is a concern because pinniped predation can impact small runs of depressed Salmonids. The Working Group could not determine if either pinniped species is having a significant negative impact on any wild Salmonid population, except winter steelhead that migrate through the Ballard Locks, because of the limitations of the available data. Although the Working Group concluded that substantial additional research is needed to fully address this issue, it found that existing information on the seriously depressed status of many Salmonid stocks issufficient to warrant actions to remove pinnipeds in areas of co-occurrence where pinnipeds prey on depressed Salmonid populations. The Working Group identified the elements of a research program to assess impacts of pinniped predation on depressed Salmonids and identified the geographic areas of greatest concern for impacts on Salmonids in each state.
The Working Group found that California sea lions and Pacific harbor seals are interacting with many commercial and recreational fisheries on the West Coast. It also found numerous instances of conflicts at docks and marinas, primarily with California sea lions, that raise human safety concerns. In all three states, reports of pinnipeds removing Salmonids and other fish from fishing gear and damaging gear have increased. Interactions appear to be most severe, in terms of lost catch and gear damage, in Salmonid gillnet, salmon troll, salmon net-pens, and southern California charterboat fisheries. The Working Group reviewed mitigation measures that have been used to reduce or eliminate pinniped predation on Salmonids or minimize interactions with fisheries and found that most nonlethal deterrence measures have limited or short-term effectiveness. Development of new technologies and techniques is needed to effectively deter pinnipeds from fishery conflicts and from marinas where human safety issues arise.
The Working Group could not determine ecosystem-level impacts because of the complexity of ecosystems and the limited knowledge of how they function. The Working Group reviewed existing biomass consumption estimates for California sea lions and Pacific harbor seals and noted problems with the estimates. New estimates of annual food consumption by harbor seals and sea lions were calculated by the Working Group using a bioenergetics model integrating data on abundance, sex and age structure, and feeding rates. The Working Group estimated a minimum total biomass consumption of about 217,400 metric tons by sea lions and seals in Washington, Oregon, and California and found that it amounted to almost half of what is harvested in commercial fisheries. The Working Group determined it is reasonable to assume that increasing numbers of pinnipeds areconsuming an increasing number of prey composed of a variety of species; however, to what degree the increased presence of pinnipeds and increased biomass consumption affects ecosystems is unknown. Research was identified to determine the coastwide degree of interaction between pinnipeds, fisheries, and other West Coast ecosystem elements.
In recent years, the status of some salmonid populations has become precarious. As of February 1997, 6 populations of Pacific salmonids have been listed under the Endangered Species Act (ESA), and 12 populations are proposed for listing under the ESA. Serious declines in these and many other populations of salmonids are the result of a complex array of factors over time, including changes in salmonid riverine habitat, changes in oceanic conditions, overharvest, development of hydroelectric power systems in major riverine migratory routes, and detrimental impacts of hatchery programs. Predation by California sea lions (Zalophus californianus) and Pacific harbor seals (Phoca vitulina) may now constitute an additional factor in salmonid population decline and may affect recovery of depressed salmonid populations.
Since passage of the Marine Mammal Protection Act (MMPA) in 1972, populations of California sea lions and Pacific harbor seals (pinnipeds) have increased steadily in Washington, Oregon, and California. These two pinniped populations are healthy and productive, and are not considered to be depressed, threatened, or endangered. Reports of pinniped interactions with salmonid fisheries have increased in recent years, as have reports of scarring of salmonids attributed to pinnipeds. This has raised concern that predation on salmonids by pinnipeds could be increasing and causing significant negative impacts on threatened, endangered, or severely depleted salmonid populations. Increased predation could not only cause further declines in salmonid populations, but could also prevent or slow the recovery of listed salmonid stocks. The proposed National Marine Fisheries Service (NMFS) Recovery Plan for Snake River salmon specifically identifies pinniped predation on salmon as a factor that must be considered for recovery of Snake River chinook salmon that are listed under the ESA (NMFS 1995a).
Because of public concern over salmonid population declines and the role pinnipeds may have, Congress mandated a review of the impacts of increasing pinniped populations on decreasing salmonid populations as well as impacts on the West Coast ecosystems. The 1994 Amendments to the MMPA directed the Secretary of Commerce to conduct a "scientific investigation to determine whether California sea lions and Pacific harbor seals a) are having a significant negative impact on the recovery of salmonid fishery stocks which have been listed as endangered species or threatened species under the Endangered Species Act of 1973 (16 U.S.C. 1531 et seq.), or which the Secretary finds are approaching such endangered species or threatened species status; or b) are having broader impacts on the coastal ecosystems of Washington, Oregon, and California." After completion of the investigation, the NMFS on the behalf of the Secretary is directed to "enter into discussions with the Pacific States Marine Fisheries Commission on behalf of the states of Washington, Oregon, and California, for the purposes of addressing any issues or problems identified as a result of the scientific investigation, and to develop recommendations to address such issues or problems." These recommendations are then to be submitted, along with this report, to the House of Representatives' Committee on Resources and the Senate's Committee on Commerce, Science, and Transportation.
NMFS determined it did not have the resources nor was there sufficient time to conduct thorough field investigations on the issues identified by Congress within a 1-year timeframe, so the investigation therefore focused on a review of information from past field studies. A review of the existing scientific data on pinniped predation as a potential factor in the decline and recovery of salmonid populations as well as broader ecosystem impacts was undertaken by a Working Group established by NMFS. Working Group members were selected based on their knowledge of salmonids, marine mammals, and the interactions between them. The Working Group established the following objectives for this investigation:
During the investigation of available information, the Working Group found significant gaps in the information needed to evaluate the interactions and impacts of pinnipeds on salmonids. Similar information gaps on potential impacts of pinnipeds on Snake River spring/summer and fall chinook salmon (listed as threatened under the ESA) were also identified by NMFS in the recovery plan for Snake River salmon (NMFS 1995a). To address some of these shortcomings, scientists of the Working Group obtained new information on occurrence of California sea lions in California, reevaluated the occurrence of salmonids in the diet of sea lions and harbor seals, and made new estimates of overall biomass consumption by California sea lions and harbor seals.
The Working Group believed it was important to include information beyond that specified by the Congressional mandate. Consequently, this report includes a review of mitigation methods used to reduce pinniped predation on fish populations, and information on Steller sea lions (Appendix A) because this species also is occasionally involved in interactions.