The Relative Importance of Somatic Growth and Recruitment in Population Production

Fisheries researchers have long documented variability in recruitment as a significant driver of production in marine stocks. Recently, there is an increasing awareness that somatic growth variation also can drive productivity, yet few studies have compared the relative and combined effects of variability in these demographic processes on production across stocks. In this study, we use a simulation approach to contrast these relative effects across several life history types. Realistic growth and recruitment variability time series are generated across a number of scenarios (i.e. low and high coefficient of variation [CV] for each process) and input into a standard age-structured fisheries population model parameterized using fisheries stock assessment estimates. We quantify and compare variability in the output surplus production across life history and fishing rate. We find that life history governs the relative effect of recruitment and growth variability on production. For example, life histories experiencing periodic strong recruitment events and determinate growth (i.e. rockfish) are more responsive to recruitment variability, while stocks with a low recruitment CV and relatively indeterminate growth (i.e. flatfish) show a stronger response to growth variability. Our results highlight the importance of both somatic growth and recruitment in inducing variability in population production.