Diagnosing Systematic Errors in Reported Fishery Catch

Diagnosing Systematic Errors in Reported Fishery Catch

S. Gavaris and L. Van Eeckhaute

Diagnosing Systematic Errors in Reported Fishery CatchThis is part of Fishery Stock Assessment Models
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Age structured assessment methods integrate information from the commercial fishery catch and from indices of abundance. Systematic errors in the catch at age, often caused by mis reporting of landings or discarding of small fish, could introduce appreciable bias to the results of stock assessments. Important inconsistencies were revealed when results from a base assessment employing catch at age were compared to results from a model that employs proportion caught at age but estimates total numbers caught each year in addition to the other model parameters, terminal year abundance and index catchability. For eastern Georges Bank haddock, the diagnostic model suggested that the base model had underestimated the year-class abundance for years prior to 1977. It also indicated that the mid-1980s year classes might have been overestimated by the base model. Though not recommended for estimation, the diagnostic model subjects data to different assumptions, making it useful as an investigative tool for evaluating the robustness of results.

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