Fishing tactics and fish abundance, and their influence on catch rates

Sampson, David B.
January 1991
ICES Journal of Marine Science / Journal du Conseil;1991, Vol. 48 Issue 3, p291
Academic Journal
Choosing a location for fishing is the major short-run decision made by the skipper of a fishing vessel. Because the spatial density of fish is not uniform everywhere, where a skipper decides to fish largely determines the size and value of his catch. For that to be a rational decision, the skipper must consider not only the catches he is likely to make at different locations but also the costs incurred in fishing at those locations. As a consequence the catch rates and the catch per unit effort observed in a fishery depend not just on fish stock abundance but also on economic factors such as wage rates and fish and fuel prices. This paper develops some simple theoretical models for examining a fisherman's selection of fishing location. The spatial distribution of the fish stock is reduced to a single dimension, distance from port, and it is assumed that fish density increases linearly with distance from port and that the relative densities remain constant regardless of the absolute level offish stock abundance. If a skipper operates his vessel further from port, he gains access to greater densities offish and higher instantaneous catch rates but uses more fuel and time for travel. A skipper can maximize his share of the fishing profits by operating his vessel at a particular distance from port. The skipper operates within constraints which determine the form of the revenue and cost functions. Two models are considered. In the first, the duration of a fishing trip is constrained by the size of the fish hold or by some other limit to the amount of fish that can be landed; each fishing trip continues until the hold is filled. In this case catch and revenue per trip are constant but the fishing costs vary non-linearly with distance from port. Here the catch per unit effort (c.p.u.e., catch per trip divided by time spent fishing per trip) is a non-linear function of the total biomass of the fish stock but the c.p.u.e. is independent of the price offish. In the second model, there is a time constraint; to fill the hold would take too much time. In this case each trip is of a fixed duration and catch and revenue per trip are quadratic functions of distance from port and operating costs vary linearly. Here c.p.u.e. is a linear function offish stock biomass and a non-linear function offish price.


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