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Estimating fishing and natural mortality rates, and catchability coefficient, from a series of observations on mean length and fishing effort
Then, AY Hoenig, JM Huynh, QC
Then, AY
Hoenig, JM
Huynh, QC
Abstract
Gedamke and Hoenig (2006) (Transactions of the American Fisheries Society, 135: 476-487) developed a non-equilibrium version of the Beverton and Holt estimator of total mortality rate, Z, based on mean length and thereby increased the usefulness of length-based methods. In this study, we extend their model by replacing period-specific Z parameters with the year-specific parameterization Z(y) = qf(y) + M where q is the catchability coefficient, f(y) is the fishing effort in year y, F (= qf) is the fishing mortality rate, and M is the natural mortality rate. Thus, the problem reduces to estimating just three parameters: q, M and residual variance. We used Monte Carlo simulation to study the model behaviour. Estimates of q and M are highly negatively correlated and may or may not be reliable; however, the estimates of corresponding Z's are more precise than estimates of F and are generally reliable, even when uncertainty about the mean lengths is high. This length-based method appears to work best for stocks with rapid growth rate. Contrast in effort data may not be necessary for reliable estimates of Z's. This approach forms a bridge between data-limited models and more complex models. We apply the method to the Norway lobster Nephrops norvegicus stock in Portugal as an example.
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2018-01-01
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fsx177.pdf
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Biological Sciences Peer-Reviewed Articles, Nonequilibrium Situations; Stock Assessments; Catch
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Virginia Institute of Marine Science
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https://doi.org/10.1093/icesjms/fsx177