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FOCI | |
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Fisheries-Oceanography Coordinated Investigations |
The
National Marine Fisheries Service advises the North Pacific Fishery Management
Council on the status of walleye pollock stocks in the Gulf of Alaska and
Bering Sea. The advisory process includes developing a stock projection
based on an initial stock assessment. Stock projection predicts future
abundances as a function of different harvest and recruitment scenarios.
Stock assessment requires information independent of the fishery to calibrate
estimates of absolute abundance. Before FOCI, fishery-independent information
was limited to data from hydroacoustic and bottom trawl surveys. FOCI's
spawning mass estimates derived from an annual egg production model provide
a valuable third source of information.
FOCI has established the life history pattern of walleye pollock in the Gulf of Alaska between the time of the spawning migration and the development of the first young of the year. Using results from egg and larval surveys together with estimates of the spawning adult population from hydroacoustic observations and indices of juvenile abundance, the critical stage when year-class strength is established can be determined. A necessary condition for average or relatively strong recruitment is a large abundance of larvae. However, there are years when large numbers of larvae do not result in above-average recruitment, implying that processes during the juvenile stage, and after, can also be critical. FOCI scientists have developed a conceptual model of conditions necessary in the Gulf of Alaska for enhanced survival of walleye pollock that leads to successful recruitment to the fishery. This model is based on continuous research begun in 1984 on life stages and distribution of walleye pollock, their behavior, and the physical and biological processes that influence them. The major components of the model are climate, the preconditioning of the environment prior to spawning, the ability of the physical environment to retain the planktonic life stages on the continental shelf, and the abundance and distribution of prey and predators on the shelf. Year-class strength is generally established within 90 days of hatching.
To incorporate research data into qualitative recruitment estimates
for walleye pollock in the Gulf of Alaska, FOCI uses sophisticated correlative
modeling methods to analyze hydroacoustic survey results of spawning aggregations,
ichthyoplankton surveys of eggs and larvae, estimates of spawning biomass
and recruitment from the annual stock assessment, measurements of ocean
temperature, winds, rainfall, sea-level pressure gradient, and other biological
and physical factors. This approach was applied to a recruitment time series
for adult walleye pollock (1962-89) and egg and larval series (1981-89). 
Results
suggest that recruitment is related to the amount of precipitation, an
index of sea level pressure, and wind mixing. FOCI scientists have developed,
and continue to refine, an empirical model based the conceptual model,
and have made forecasts
of pollock recruitment annually since 1992. Survey results
from the past several years have been used to score
FOCI's initial recruitment estimates.
Although many questions remain, FOCI research is generating valuable
information on current spawning biomass and recent year-class strength
necessary for management models to project stock abundance of walleye pollock
in future years.
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FOCI Project Office NOAA/PMEL and NOAA/AFSC |
| 7600 Sand Point Way NE Seattle, Washington 98115 Comments and information |
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