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Assessing the Information Content of Catch-in-Numbers: A Simulation Comparison of Catch and Effort Data Sets

Assessing the Information Content of Catch-in-Numbers: A Simulation Comparison of Catch and Effort Data Sets

Richard McGarvey, André E. Punt, and Janet M. Matthews

Assessing the Information Content of Catch-in-Numbers: A Simulation Comparison of Catch and Effort Data SetsThis is part of Fisheries Assessment and Management in Data-Limited Situations
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Description

The fishing industry provides totals for landed catch-in-weight and fishing effort in skippers’ logbooks. Because this data gathering infrastructure is in place, one potentially inexpensive source of additional information could be the catch reported in numbers of individuals landed. The performance of stock assessment models based on three logbook data sets, (1) catch-in-weight and fishing effort, (2) that of (1) plus catch-in-numbers, and (3) catch-in-weight and catch-in-numbers (no effort), was evaluated by means of simulation. Simulated data sets were generated from an individual-based model of a lobster fishery and used to test the ability of these three data sets to estimate recruitment, biomass, population numbers, and exploitation rate. The agreement of estimates from two different delay-difference models with true simulation values were quantified. With perfect knowledge of growth and natural mortality, and under nineteen simulated variations from perfect knowledge, adding catch-in-numbers to the traditional data set of catch-in-weight and effort substantially improved the precision and accuracy of the yearly population estimates. Adding catch-in numbers allowed the stock assessment to estimate absolute fishable population size, and track yearly changes in fishable stock size, yielding very large improvements in the estimates of both, with the greatest improvement being in estimation of absolute abundance. We recommend that methods which utilize catch-in-numbers be included in the standard stock assessment toolbox for data-poor species.

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