A Simulation Study of the Effects of Aging Error and Sample Size on Sustained Yield Estimates

A Simulation Study of the Effects of Aging Error and Sample Size on Sustained Yield Estimates

L.G. Coggins Jr. and T.J. Quinn II

A Simulation Study of the Effects of Aging Error and Sample Size on Sustained Yield EstimatesThis is part of Fishery Stock Assessment Models
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A Monte Carlo simulation model of an exploited age-structured fish population was constructed to evaluate the effects of sampling and aging the catch on estimates of population parameters from catch-age analysis and resultant estimates of sustained yield. Aging error, error in the annual catch estimates, and error in the annual survey exploitable abundance estimates were included in the simulation. Three sets of simulation runs were conducted among small (100), medium (300), and large(900) sample sizes to estimate the catch-at-age composition. The simulation included five reader types with differing aging abilities resulting in a total of five catch-at-age compositions evaluated for each program replication. Sustained yield estimates from 1,000 replications of each reader type were compared to true sustained yield. Aging bias and imprecision had dramatic effects on estimated sustained yield: positive aging bias and imprecision generally caused underestimation of sustained yield, while negative aging bias caused overestimation of sustained yield. These results suggest that this component in stock assessment deserves greater attention in planning and practice. In addition increases in sample size resulted in increased precision in sustained yield estimates only if the catch-at-age composition was estimated using a precise and unbiased reader type. While this evaluation was based on the Arctic grayling (Thymallus arcticus) population within the Gulkana River in Alaska, the simulation model can be used for a variety of sport fish populations; a diskette and user manual are available.

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