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Application of a Surplus Production Model to a Swordfish‐Like Simulated Stock with Time‐Changing Gear Selectivity
Author(s) -
Prager Michael H.,
Goodyear C. Phillip,
Scott Gerald P.
Publication year - 1996
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1996)125<0729:aoaspm>2.3.co;2
Subject(s) - swordfish , fishing , stock (firearms) , maximum sustainable yield , fishery , population , environmental science , statistics , mathematics , geography , fisheries management , biology , demography , fish <actinopterygii> , tuna , archaeology , sociology
Should a surplus production model be applied to a stock that exhibits pronounced age structure? Should it be applied to a stock that has experienced changing fishing mortality rates on fish of different sizes over time (i.e., changing selectivity)? These questions are of general interest to those engaged in stock assessment and of particular interest in the assessment of North Atlantic swordfish Xiphias gladius . In an attempt to answer them, we simulated an age‐structured population, with fishery, similar to that of swordfish in the North Atlantic. The 30‐year simulation included biological characteristics from the literature on swordfish and simulated fishing with increasing mortality of young fish over time; simulated catches approximated the actual catches of swordfish from 1962 through 1991. We fit a lumped‐biomass, dynamic surplus production model to summary non‐age‐structured data from the simulated fishery. The resulting parameter estimates were compared to management benchmarks, including maximum sustainable yield (MSY), computed by age‐structured methods from the growth and recruitment characteristics of the underlying simulation. The changing selectivity resulted in a small (<10%) decrease in MSY from the beginning of the series to its end; estimates from the production model were close to these underlying MSY values. Nine additional population trajectories were simulated with the same biological characteristics but other fishing histories; in most cases, the production model provided qualitatively correct estimates of stock status. Two new reliability statistics appear to be of value in judging the quality of production model fits. We conclude that for stocks similar to swordfish, the presence of strong age structure and moderate changes in selectivity should not proscribe the application of simple production models.