Evaluating Methods for Setting Catch Limits for Gag Grouper: Data-Rich versus Data-Limited

Evaluating Methods for Setting Catch Limits for Gag Grouper: Data-Rich versus Data-Limited

Skyler R. Sagarese, John F. Walter III, Meaghan D. Bryan, and Thomas R. Carruthers

Evaluating Methods for Setting Catch Limits for Gag Grouper: Data-Rich versus Data-LimitedThis is part of Assessing and Managing Data-Limited Fish Stocks
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Description

The majority of shallow-water grouper stocks in the Gulf of Mexico are considered data-limited, with the exceptions of gag Mycteroperca microlepis and red Epinephelus morio groupers. Both species are data-rich and assessed using Stock Synthesis integrated assessment models that demand substantial data inputs and analytical time. Given that data limitations hinder the same detailed analysis for other shallow-water grouper species, there is substantial interest in applying data-limited methods (DLMs) to derive annual catch limits. In this paper we apply a suite of DLMs to Gulf of Mexico gag grouper using the “DLMtool” package in R to test whether a similar assessment result can be achieved with less data or with computationally less-intensive methods on aggregated data. Most DLMs provided lower estimates of the overfishing limit compared with Stock Synthesis, treated here as the “true” value, suggesting that in the absence of a data-rich assessment for gag grouper, quotas set by DLMs underestimate the overfishing limit compared to Stock Synthesis. Index-based methods and depletion-based methods such as Depletion-Corrected Average Catch produced results similar to Stock Synthesis. Overall, the broad overfishing limit distributions that resulted from many DLMs suggest a high level of uncertainty. Sensitivity analyses revealed that DLM quota recommendations were often influenced by key data inputs such as natural mortality, catch, current abundance, and depletion estimates where required. These results emphasize important issues including selectivity, episodic mortality, and hermaphroditism, which may confound assessment of shallow-water grouper stocks.

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