The Importance of Incorporating Protogynous Sex Change Into Stock Assessments

Although it is generally recognized that management strategies should consider life-history variation, little is known about how various reproductive strategies affect stock dynamics. Protogynous (female-to-male) sex change is a relatively common life history pattern in fishes for which standard assessment methods do not exist. We developed a stock-assessment model for a commercially and recreationally exploited sex-changing species [California sheephead, Semicossyphus pulcher (Ayres, 1854)] to determine how ignoring or including sex change affects the assessment of the stock. First, we demonstrated that ignoring sex change leads to an overestimate of spawning biomass and very different conclusions regarding the effect of exploitation on the spawning potential ratio (SPR). Furthermore, we found that the stock assessment is highly uncertain (current SPR estimates range from 0.08 to 0.6) because we do not know how male depletion affects reproduction or what determines individual and population variation in the size of sex change. Our results demonstrate that, although incorporating sex change into stock-assessment models is important, assessment of protogynous stocks also requires knowledge of the effect of male depletion on spawning potential and the factors that determine sex change.