A Model Expressing the Relationship between Catch and Soak Time for Trap Fisheries

Abstract

In trap fisheries, catch per trap haul changes with soak time. Catch rates should therefore be standardized for differences in soak time when used to measure abundance. Several models have been used to describe catch per trap haul while adjusting for soak time. Some of these models are limited with respect to time spent fishing or have difficulties in parameter estimation. In this paper, we describe a model without limitations on soak time. The model is C_t = ab + a(t – b)e^–ct ; C_t is the catch per trap haul at soak time t; a, b, and c are parameters to be estimated. When sufficient data are used, the term ab denotes asymptotic catch after an infinite soak time, and a and c depend on local animal density, entry rate, and escape probability. These parameters can be readily estimated by many popular computer programs. This model is equivalent, or superior, to other models and is the only suitable model for long soak times with nonzero catch.