The effect of maternal age of spawning on estimation of Fmsy for Alaska ocean perch

The effect of maternal age of spawning on estimation of Fmsy for Alaska ocean perch

P. Spencer, D. Hanselman, and M. Dorn

The effect of maternal age of spawning on estimation of Fmsy for Alaska ocean perchThis is part of Biology, Assessment, and Management of North Pacific Rockfishes
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Description

Recent laboratory research suggests that rockfish larval survival rates increase with the age of the spawner, thus potentially necessitating more conservative harvest policies that explicitly consider the age structure of the spawning stock biomass. In this study, we use simple deterministic population dynamic equations to examine the effect of reduced survival of larvae from younger females on commonly used fishing rate reference points such as Fmsy and Fxx%, the fishing rates corresponding to the maximum sustained yield and conservation of xx% of the reproductive potential per recruit relative to an unfished population, respectively. Reduced survival of larvae from younger females results in reduced reproductive potential per recruit for a given level of fishing mortality and also increased estimated resiliency, which results from the estimated recruitments being associated with a reduced measure of reproductive potential. For Bering Sea/Aleutian Islands and Gulf of Alaska Pacific ocean perch, these two effects nearly counteract each other, producing Fmsy estimates that were relatively insensitive but decreased slightly as maternal effects were considered. Estimates of Fxx% rates that correspond to Fmsy proxies are more conservative (i.e., correspond to reduced fishing intensity) when uncertainty in the degree to which maternal age affects reproductive potential is considered, as compared to analyses using spawning stock biomass as reproductive potential. These results indicate that estimated stock resiliency is not necessarily independent of the life-history parameters describing production of reproductive potential.

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