Research Document - 2009/072
Herring multi-stock analysis: Integration of tagging data and evaluation of alternative dynamics
By V. Haist and J. Schweigert
The work presented in this document extends the multi-stock functionality of the HCAM model through inclusion of a tag-recapture module, and investigates alternative hypotheses about the natural mortality process and its impact on stock dynamics. The primary objective of the work is to investigate alternative stock dynamics assumptions in support of a future herring MSE project.
The assumption that natural mortality is related (inversely) to stock abundance fits the herring data as well as modelling natural mortality as a random walk process, though with considerably fewer parameters estimated. General patterns in the natural mortality trends are similar between the two parameterizations. In terms of developing operating models for a future MSE project, the density-dependent natural mortality assumption is more satisfactory because natural mortality rates are driven by internal stock dynamics rather than by external and unknown factors. Some difficulty was encountered in finding formulations for the stock-recruitment and density-dependent natural mortality that did not generate implausible estimates of B0, but a Ricker stock-recruitment relationship produced reasonable results when other restricting assumptions were included in the model formulation.
The estimates of spawning site fidelity obtained from the integrated HCAM analysis are quite high, at the stock assessment region level. Spawning region fidelity estimates were 89% for QCI, 98% for PRD, 96% for CC, 98% for SoG, and for WCVI. Dispersal rate estimates were highest between regions that are geographically close.
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