|A stochastic model for purse seining in a two-species fishery|
Pella, J. (1969). A stochastic model for purse seining in a two-species fishery. J. Theor. Biol. 22(2): 209-226
In: Journal of Theoretical Biology. Elsevier: London,New York,. ISSN 0022-5193, more
Purse seine fishing in a two-species fishery is viewed as a semi-Markov process. Activities of a vessel during a fishing day are assigned to five states: searching, successfully setting on either species, and unsuccessfully setting on either species. Searching for fish schools is assumed to be a Poisson process. Transition probabilities are defined in terms of species densities in the fishing area, the chance that a sighted school is captured, and the chance of relocating an escaped school. Waiting time in the search state is determined by school density in the fishing area and search rate of the vessel. Waiting times in the remaining states depend on numerous factors such as vessel characteristics and weather. With results from renewal theory, expectations of the number of successful sets on each species during a time interval of arbitrary length are approximated. Numerical comparison with exact results from a simpler fishing model indicates the approximation from renewal theory for the expectations to be excellent. Several examples are given to demonstrate the model's utility. It can be used to develop abundance measures for the two species which account for temporal changes in efficiency of the vessels, dead time after a school is encountered while the vessel is not searching, and the fact that two species are being exploited simultaneously.