A yield-per-recruit model is developed for use on a protogynous hermaphrodite. It allows for sex change followed by a growth spurt. An approach is outlined which can be used to account qualitatively for the consequences of a stock-recruitment relationship. The model is used to make predictions for the stocks of slinger Chrysoblephus puniceus off South-East Africa. Model predictions of sex ratios compare favourably with field observations. Predictions of yield-per-recruit models that ignore any relationship between spawner stock size and recruitment can be misleading. Three scenarios concerning recruitment to the Natal stock of slinger can be postulated from the present robust nature of the stock to a high level of fishing mortality. Either recruitment is not dependent only on the number of males in the stock, or there is sufficient migration of 0-year-olds from nearby regions into the Natal stock, or recruitment is related to spawner stock size by the Ricker relationship. If lack of males is a limiting factor for recruitment, intensive exploitation of the virtually pristine stocks in the St Lucia Marine Reserve and off southern Moçambique could collapse the Natal stock and even the entire resource.
ASJC Scopus subject areas
- Aquatic Science