Coping with a Challenging Stock Assessment Situation: The Kamishak Bay Sac-Roe Herring Fishery
E.O. Otis, W.R. Bechtol, and W.A. Bucher
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Aerial biomass estimates and commercial-catch and total-run age compositions were the principal components of an integrative age-structured model used to forecast spawning biomass of Pacific herring Clupea pallasi returning to Kamishak Bay, Alaska. Poor weather in Kamishak Bay created gaps in aerial survey coverage, and when surveys could be flown, the ability of surveyors to observe herring schools was often limited by poor water clarity. Resultant aerial biomass estimates were influenced by survey effort and conditions. Although we used standardized procedures to quantify the surface area of observed herring schools and convert them to biomass estimates, these standards could not compensate for poor survey conditions or extended gaps in survey coverage. Aerial survey difficulties highlighted the importance of maximizing the quality and influence of other data sources in the integrative model. Total-run age-composition data, derived from fishery-independent samples, were instrumental in tracking cohorts and evaluating the strength of recruiting year classes. Historical and current data indicate that age structure was not static throughout the Kamishak Bay run. In most years the age structure of herring returning to the spawning grounds shifted from older to younger fish around early May. This created the potential for a temporal sampling bias that was mitigated by collecting age data from both early- and late-spawning components of the run and weighting the data according to the relative biomasses associated with these temporally distinct spawning aggregations. Uncertainty about current abundance is increasing and warrants a conservative harvest strategy.
- Item number: AK-SG-98-01ac
- Year: 1998
- DOI: https://doi.org/10.4027/fsam.1998.29