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- Title
Including predation mortality in stock assessments: a case study for Gulf of Alaska walleye pollock.
- Authors
Hollowed, Anne Babcock; Ianelli, James N.; Livingston, Patricia A.
- Abstract
A separable catch-age stock assessment model that accommodates predation mortality is applied to the Gulf of Alaska walleye pollock (Theragra chalcogramma) assessment. Three predators are incorporated in the model: arrowtooth flounder (Atheresthes stomias), Pacific halibut (Hippoglossus stenolepis), and Steller sea lion (Eumetopias jubatus). The effect of these predators is examined by defining the predation mortality as a type of fishery. The model is used to quantify changes in the relative fit to the survey, fishery, and predator data when the assumption of constant natural mortality is relaxed. Specifically, we examine the effect of assumptions regarding the functional feeding response, residual naturaly mortality, and uncertainty in predator biomass on stock assessment. Total natural mortality rates (including predation) tended to be higher than estimated from life history characteristics of the stock. Models that did not account for uncertainty in natural mortality underestimated uncertainty in current stock biomass by as much as 20%. Our results indicate that independent estimates of survey selectivity, additional food habits data, and estimates of the feeding responses of predators to different prey densities are all needed to improve our ability to develop stock assessment models that address ecosystem concerns.
- Subjects
GULF of Alaska (Alaska); FISH age; PREDATION; FISH population measurement; FISHERY management; WALLEYE pollock fisheries; PACIFIC halibut; STELLER'S sea lion
- Publication
ICES Journal of Marine Science / Journal du Conseil, 2000, Vol 57, Issue 2, p279
- ISSN
1054-3139
- Publication type
Case Study
- DOI
10.1006/jmsc.1999.0637