Interactions of age-dependent mortality and selectivity functions in age-based stock assessment models

He, Xi and Ralston, Stephen and MacCall, Alec D. (2011) Interactions of age-dependent mortality and selectivity functions in age-based stock assessment models. Fishery Bulletin, 109(2), pp. 198-216.

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Abstract

The natural mortality rate (M) of fish varies with size and age, although it is often assumed to be constant in stock assessments. Misspecification of M may bias important assessment quantities. We simulated fishery data, using an age-based population model, and then conducted stock assessments on the simulated data. Results were compared to known values. Misspecification of M had a negligible effect on the estimation of relative stock depletion; however, misspecification of M had a large effect on the estimation of parameters describing the stock recruitment relationship, age-specific selectivity, and catchability. If high M occurs in juvenile and old fish, but is misspecified in the assessment model, virgin biomass and catchability are often poorly estimated. In addition, stock recruitment relationships are often very difficult to estimate, and steepness values are commonly estimated at the upper bound (1.0) and overfishing limits tend to be biased low. Natural mortality can be estimated in assessment models if M is constant across ages or if selectivity is asymptotic. However if M is higher in old fish and selectivity is dome-shaped, M and the selectivity cannot both be adequately estimated because of strong interactions between M and selectivity.

Item Type: Article
Title: Interactions of age-dependent mortality and selectivity functions in age-based stock assessment models
Personal Creator/Author:
CreatorsEmail
He, Xi
Ralston, Stephen
MacCall, Alec D.
Refereed: Yes
Journal or Publication Title: Fishery Bulletin
Volume: 109
Number: 2
Page Range: pp. 198-216
Date: 2011
ISSN: 0090-0656
Issuing Agency: United States National Marine Fisheries Service
Subjects: Biology
Ecology
Fisheries
Item ID: 8717
Depositing User: Patti M. Marraro
Date Deposited: 07 Jun 2012 14:54
Last Modified: 07 Jun 2012 14:54
URI: http://aquaticcommons.org/id/eprint/8717

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