Two simulation approaches for evaluating catch curve models as an assessment method for river herring
LE3 .A278 2020
Gibson, Jamie F.
Master of Science
Stock assessment methods for river herring (Alewife, Alosa pseudoharengus, and Blueback Herring, A.aestivalis) were tested using two simulation approaches as part of a larger assessment program for river herring in DFO’s Maritimes Region. Catch curve models, which produce estimates of the instantaneous total mortality rate (Z) from age composition data collected in a single year were the type of stock assessment model evaluated in each approach. In the first set of simulations statistical criteria (bias and precision) were used to evaluate eight versions of catch curve models. All models performed poorly, with highly variable and negatively biased estimates of Z, indicating that catch curves are not useful for river herring. In the second set of simulations management strategy evaluation was used to evaluate the performance of a fishery where catch curves were used to inform management of the fishery. The preferred catch curve model was used in conjunction with a suite of harvest control rules, assessment schedules and management schedules to determine whether spawning escapements, landings and exploitation rates could be kept within pre-defined boundaries if catch curves are used for the stock status assessment. Despite the poor performance of catch curve models from a statistical perspective, they led to reduced exploitation rates in fisheries where over-exploitation was occurring and to increased exploitation rates for under-exploited stocks, in addition to increased landings in the fishery. The results of these simulations are dependent on the assumptions of representative sampling, which can be difficult to achieve. The results from the two simulation approaches suggest that the methods used to evaluate stock assessment models can alter the conclusions that are drawn.
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