Estimating growth from sex ratio-at-length data in species with sexual size dimorphism

Abstract

Individual growth is one of the main processes which drive the population dynamic and stock productivity. Many fish have differential individual growth by sex. Growth is affected by sexual development, which is frequently reached at different sizes in males and females. Differences in growth per sex after maturity produce different patterns in sex proportions-at-length in the population. If these patterns are the consequence of changes in life history parameters, sex ratio-at-length data can be expected to contain significant information on the population life history. In this paper I first explore how post-maturity changes in life history may shape these patterns in sex ratio-at-length; secondly I explore how these data may be used to estimate growth parameters and finally I discuss how this information may be useful for stock assessment purposes. I use European hake data and life history parameters to model expected sex ratios. The results suggest that reproductive energy allocation leads to a lower growth rate in male hakes than in females. Moreover the sex ratio-at-length may provide useful information for estimating growth parameters in dimorphic species if additional information from other sources is available. Finally, these data can easily be factored into stock assessment models to help provide a better estimation of growth parameters and mortality rates. This valuable, accurate and cheap biological information (sex ratio-at-length) may play an important role in population dynamic models and stock assessment for species with sexual size dimorphism.