Minimum Stock Size Thresholds: How Well Can We Detect Whether Stocks Are below Them?

Minimum Stock Size Thresholds: How Well Can We Detect Whether Stocks Are below Them?

Z. Teresa A’mar and André E. Punt

Minimum Stock Size Thresholds: How Well Can We Detect Whether Stocks Are below Them?This is part of Fisheries Assessment and Management in Data-Limited Situations
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Description

Management of marine fisheries in U.S. waters is based on the Magnuson-Stevens Fishery Conservation and Management Act. Rebuilding plans need to be developed for fish stocks that have been depleted to below a minimum stock size threshold, MSST. Whether a stock is below MSST is based on the results from a stock assessment. Two types of error can arise when a stock is assessed relative to MSST: (a) it can be assessed to be above MSST when it is not, or (b) it can be assessed to be below MSST when it is not. Simulation is used to assess the likelihood of making these two types of errors as a function of the true status of the resource, the stock assessment method applied, and the quality and quantity of the data available for assessment purposes. All three of the methods of stock assessment considered in this study (two age-structured methods and a production model) make the two errors, especially when the true status of the resource is close to MSST. The major factor influencing the likelihood of under- and over-protection errors is the extent of variability in recruitment, the impact of which is larger than that of data quality and quantity, at least within the range for data quality and quantity considered in this paper.

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