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Assessing the Accuracy of Published Natural Mortality Estimators Using Rates Determined from Five Unexploited Freshwater Fish Populations
- Maceina, Michael J., Sammons, Steven M.
- North American Journal of Fisheries Management 2016 v.36 no.2 pp. 433-446
- Ameiurus, Lepomis gibbosus, Micropterus dolomieu, Micropterus salmoides, Perca flavescens, data collection, equations, fisheries, freshwater, freshwater fish, marine fish, mortality, otoliths, population dynamics, prediction, uncertainty, water temperature, Hudson River, New York
- Natural mortality is a vital demographic variable that is necessary for describing population dynamics and conducting fishery assessments. The instantaneous natural mortality rate (M) can be estimated through a variety of empirical methods, but they typically require extensive data collection (e.g., aging, tagging, and estimates of exploitation). Alternatively, M has been estimated using theoretically and empirically derived equations, some of which require minimal data, making their use attractive for application to information-limited fisheries. Most such equations were derived from marine stock assessments and have not been validated for freshwater fishes. We used age-frequency analyses to estimate M for unexploited populations of Largemouth Bass Micropterus salmoides , Smallmouth Bass M. dolomieu , Brown Bullheads Ameiurus nebulosus , Yellow Perch Perca flavescens , and Pumpkinseeds Lepomis gibbosus in the upper Hudson River, New York. We then compared our field-based estimates to M values predicted from nine published estimators. Using catch-curve regressions and the Robson and Chapman (1961) method, we estimated M for these populations with a sample of over 12,000 fish—nearly 2,000 of which were aged with otoliths. Variables used in the nine published estimators included maximum age, length, and weight; coefficients of the von Bertalanffy (VB) equation; the sample size used for aging; and average annual water temperature. The published estimators predicted M values that were fairly similar to our empirically derived values, although some estimators performed better than others. The mean of M values from the estimators was within ±0.12 units of the average derived from our age-frequency analyses. For the five estimators that utilized the VB growth relation, the M values were sensitive to changes in VB coefficients. For Largemouth Bass and Brown Bullheads, the unmodified VB growth functions did not conform to our observed length-at-age data, so we present modified VB equations for those species; coefficients derived from the modified equations appeared to provide more accurate predictions of M . Although the published estimators of M were primarily developed for marine fishes, they provided fairly accurate initial estimates of M (when bounded by uncertainty) for the five freshwater species we examined. Received July 10, 2015; accepted November 30, 2015 Published online April 5, 2016