Would enhanced fecundity per unit mass for large hake likely have consequences for hake recruitment and for approaches to hake management

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University of Cape Town

The hypothesis that increases in spawning frequency for and more viable eggs from larger hake lead to their making a disproportionately large contribution to recruitment is critically examined. The high steepness (h) estimated for stock-recruitment relationships for other than short-lived fish species worldwide, together with high h estimates from assessments for the South African hake populations, are at variance with this hypothesis, and suggest that the effect postulated is more than compensated by other densitydependent effects operative over the egg-to-recruit stage. This conclusion is supported by the relative insensitivity of OMP robustness test performance statistics to variations in underlying resource dynamics to incorporate this effect. Furthermore, even if larger hake off South Africa had been effectively protected from trawling in refugia, their numbers would have fallen as a result of the effects of fishing on younger animals; however no substantial decrease in recruitment is evident in assessments. While these counter-arguments do not exclude the possibility that recruitment is notably influenced by such effects (perhaps under more complex stock structure hypotheses), models fitted to data which demonstrate such behaviour would need to be developed before the hypothesis might be accorded any priority for attention in further research planning.