A Review of Natural Mortality Estimation for Crab Stocks: Data-Limited for Every Stock?

A Review of Natural Mortality Estimation for Crab Stocks: Data-Limited for Every Stock?

Jie Zheng

A Review of Natural Mortality Estimation for Crab Stocks: Data-Limited for Every Stock?This is part of Fisheries Assessment and Management in Data-Limited Situations
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Description

Among the four factors influencing population dynamics, recruitment, growth, instantaneous natural mortality (M) and harvest, M is the least understood. M estimates are not only confounded with the other three factors, but M is also difficult to observe directly. For hard-to-age stocks like crabs, estimating M is even more challenging without age information. Estimating M is a first step to develop an optimal harvest strategy for a stock. For stocks in data-limited situations, harvest rates are usually set based on M values. In this study, I reviewed M estimation methods and compared estimates of M values for crab stocks worldwide. Advantages and disadvantages of each approach were contrasted. The most significant feature of M estimates for crab stocks is high variation. Estimated M also appears to be higher for crabs than for fish with the same maximum age. Even for a crab stock with very rich data, estimates of M still depend on methods and fluctuate greatly over body size and time. The data-rich stock in this study, Bristol Bay red king crab (Paralithodes camtschaticus), appears still data-limited in terms of estimating M due to changes in M over time and confounding among M and other population model parameters.

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