Disentangling the effects of size-selective mortality, density, and temperature on length-at-age

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Abstract
The relative importance of size-selective mortality, density-dependent growth, and temperature on growth of a commercial fish population was investigated using an integrated statistical analysis. Two indices of size-selective mortality were determined using otolith backcalculations. One index measured the direct effect on population mean growth increments in the year of the growth increment. The second index measured the cumulative effect on the growth potential of a cohort. Indices of population density, occupied temperature, and bottom temperature were developed from annual synoptic research vessel surveys of the population. We simultaneously tested effects of these factors using a modified von Bertalanffy growth model. The strongest effect was variation in size-selective mortality, followed by a negative effect of population density and a weak positive effect of occupied temperature. Effects of bottom temperature conditions were not significant. Failure to simultaneously consider alternative mechanisms, especially size-selective mortality, can lead to incorrect conclusions about the role of environmental factors in determining growth of fishes.

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