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Resource Ecology & Fisheries Management (REFM) Division

Status of Stocks & Multispecies Assessment Program

Ecosystem Studies of Sub-Arctic Seas (ESSAS) Meeting

Scientists from REFM participated in the Ecosystem Studies of Sub-Arctic Seas (ESSAS) Climate Variability and Sub-Arctic Marine Ecosystems Symposium held 16-20 May 2005 in Victoria, British Columbia. The symposium was timely because recent changes in species abundance or distribution have been observed within several Sub-Arctic marine ecosystems. These changes appear to correlate with fluctuations in the physical environment, and there is growing concern about anthropogenically induced climate change. Also, several new national programs in Sub-Arctic seas have recently been initiated, for example, Bering Ecosystem Study (BEST), Effects of North Atlantic Climate Variability on the Barents Sea Ecosystem (ECOBE) and the Oyashio-pollock project in Japan. The symposium offered the opportunity to influence the implementation plans of ESSAS and BEST through 1-day workshops.

Presentations by REFM staff included:

  1. Kerim Aydin (Resource Ecology and Ecosystem Modeling Program Leader) gave an introductory talk on climate and the Bering Sea ecosystem.
  2. Sarah Gaichas (Status of Stocks and Multispecies Assessments Program) and Kerim Aydin gave a presentation comparing ecosystem structure and biological regimes between the eastern Bering Sea and Gulf of Alaska continental shelf systems. The authors examined the transfer of energy and biomass through similarly structured model food webs of each ecosystem and the reaction of each system to standardized frequencies of simulated "climate" variation.

    They found that some of the distinctive patterns of variation in biomass can emerge from identical "climate" frequencies propagating through food webs with different structural properties. The authors attempted to characterize the distinctive structural properties of each food web that resulted in different apparent "climate" effects. It is possible that identifying structural properties of fished ecosystems may hold as much promise for fisheries management as attempting to predict climate effects within each system individually.
  3. Anne Hollowed (Status of Stocks and Multispecies Assessments Program Leader) and Vera Agostini (UW) gave a presentation on environmental disturbance and resource partitioning as a source of population regulation of Northeast Pacific groundfish. The presentation reviewed the influence of environmental variability on the spatial distribution of habitat creating dynamic patterns of resource availability and species interaction. Their study provides evidence for ecological disturbance and its role in modifying pelagic habitats. Processes were reviewed using case studies.

    The presentation addressed factors influencing survival of Gulf of Alaska walleye pollock. The analysis revealed that successful recruitment is linked to a complex sequence of events leading to intermittent recruitment events. Predator controls appear to be regulated by spatial temporal overlap of predators, abundance of alternative prey, and the abundance of juvenile pollock. An alternative functional form for modeling spawners and recruitment was introduced that addresses temporal sequences of environmental disturbance. Statistical analysis based on this relationship explained approximately 60% of the variance in recruitment.
  4. Jennifer Boldt, (REEM Program), Pat Livingston, (REFM Division Director), and Anne Hollowed presented a poster on the past and present indicators of climate and fishing effects on the Bering Sea ecosystem. Both climate and fishing are agents of change that can affect the production and distribution of marine organisms in the North Pacific. It is well known that a major climate shift occurred in the North Pacific around 1976-77, a minor climate shift was observed in 1989, and another climate shift occurred in 1998-99. These climate shifts are reflected in ocean conditions, such as sea surface temperature, ice cover, and wind-driven transport.

    The relative importance of each of these climate shifts to physical conditions in the Bering Sea varies, as does their impact on the production and distribution of marine organisms. Fisheries can impact fish and ecosystems directly by selectivity, magnitude, timing, location, and methods of fish removals.

    There are other effects of fishing such as vessel disturbance, nutrient cycling, introduction of exotic species, pollution, unobserved mortality, and habitat alteration. Both ocean conditions and fishing activity may affect the marine communities of the Bering Sea. The Ecosystem Considerations section of the SAFE report of the NPFMC provides a current and historical perspective on status and trends of ecosystem components and ecosystem-level attributes using an indicator approach.

By Jennifer Boldt, Sarah Gaichas, Kerim Aydin and Anne Hollowed

Fishery Interaction Team Presentations to the North Pacific Fishery Management Council

Liz Conners and Libby Logerwell gave presentations to the Advisory Panel, Science and Statistical Committee and Council during the NPFMC’s June meeting in Girdwood, Alaska. The purpose of the presentations was to provide an update on Fishery Interaction Team (FIT) research on the potential impacts of commercial fishing on Steller sea lion prey fields. Input was also sought with regard to future FIT research. The research activities of FIT currently focus on three commercially fished groundfish species in Alaska: Pacific cod, Atka mackerel, and walleye pollock. Summaries of the presentations follow.

FIT’s Pacific cod local depletion study is conducted by Elizabeth Conners, Peter Munro, Sandi Neidetcher, and Yunbing Shi. They have now completed 3 years of the Pacific cod local depletion experiment at Cape Sarichef. The study was designed to determine if intensive trawl fishing for cod creates a localized depletion in fish abundance that could adversely affect prey availability for Steller sea lions.

The experiment uses a before-after, treatment-control type design to compare the seasonal rate of change in cod abundance within the Cape Sarichef no-trawl zone to the rate of change in the adjacent heavily-trawled area. In each of the 3 years, the nonparametric statistical test has overwhelmingly indicated no difference between sites in the trawled and untrawled areas (P-values of 0.81 to 0.98). Power calculations indicate that the experiments in 2004 and 2005 would have been able to detect a reduction in the average catch of the trawled zone in the range of 20%-30%. Maps of the observed catches and seasonal percentage changes show no consistent spatial pattern.

FIT’s study on the short-term effects of commercial fishing on walleye pollock is led by Chris Wilson and Paul Walline (RACE Division) and Anne Hollowed and Libby Logerwell (REFM Division). The purpose of this research is to determine whether commercial pollock fishing results in localized depletion or disturbance of Steller sea lion prey fields. A pollock fishery interaction experiment has been conducted off Kodiak Island during 4 years: 2000-04. The sampling design utilized control (unfished) and treatment (fished) areas. Barnabus Trough was open to fishing and thus was the treatment site. Chiniak Trough was closed to fishing and thus was the control site.

In 2001 and 2004, substantial (> 1500 metric tons (t)) amounts of adult pollock were removed from the study area during the C season. Results from the 2001 experiment show high temporal variability in adult pollock biomass in the treatment area, but not in response to fishing. In contrast, results from 2004 show a statistically significant decrease in pollock biomass in the treatment area following the start of commercial fishing. No concurrent decrease in adult pollock biomass in the control area was observed.

Results from 2000 and 2002 are not shown because the region was closed to pollock fishing in 2000, and fishery removals were very small (roughly 300 t) in the study area in 2002. Statistical power analyses based on the 2004 data show that differences in biomass of 35% could be detected 80% of the time in the treatment area.

FIT’s study on Atka mackerel biomass and movement relative to trawl exclusion zones in the Aleutian Islands is conducted by Suzanne McDermott, Jim Ianelli, and Logerwell. The objective of this project is to evaluate the efficacy of trawl exclusion zones (TEZs) at maintaining sufficient quantities of Atka mackerel prey for Steller sea lions in the Aleutian Islands. Tag release-recovery methods were used to estimate local abundance and movement rates inside and outside TEZs at several sites in the Aleutian Islands. Movement rates are of interest because fish moving from inside to outside TEZs are vulnerable to commercial fishing.

From 2000 to 2003, Atka mackerel have been tagged, released and recovered at Seguam Pass, Tanaga Pass, and Amchitka Island. Biomass and movement rates were estimated with an integrated model that uses maximum likelihood to estimate all parameters simultaneously. Biomass was highest at Seguam Pass and lowest at the south end of Amchitka Island. In all areas, biomass inside the TEZs was similar to or greater than biomass outside the TEZs. In all areas, movement rates from inside to outside were similar to or less than movement rates from outside to inside, with the exception of Amchitka Island where movement rates may have been greater from inside to outside. In addition, movement rates were greater overall at Amchitka Island than at any of the other study areas.

The results suggest that TEZs in Seguam and Tanaga Passes, where Atka mackerel biomass is relatively high and movement is relatively low, may be effective at preserving local foraging areas for Steller sea lions. In contrast, the TEZ at the south end of Amchitka, where biomass is low compared to other areas and movement is high, may be less effective.

More information about the FIT program including the presentations above are available on the AFSC website at or contact: Libby Logerwell (FIT Lead)

By Libby Logerwel


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