Genetic population sub-structuring of kingklip (Genypterus capensis – Ophidiidiae), a commercially exploited demersal fish off South Africa

Abstract

Kingklip, Genypterus capensis, is one of the most valuable fishery resources in South Africa, mainly caught as by-catch in the trawl and longline fisheries for hakes. Intense exploitation has contributed to substantial population declines in the past, but current exploitation levels are considered to be sustainable. Management is presently based on a Replacement Yield model, with total catches regulated through a Precautionary Upper Catch Limit. However, there is no consensus regarding population structure, which may have a direct impact on the management of the resource. Assessment of historical and current genetic sub-structuring of kingklip (N=418) off South Africa was conducted using a fragment of mtDNA Control Region and ten microsatellite loci, for three consecutive years. Kingklip exhibited high historical genetic diversity levels (h=0.901; π=0.009), but lower contemporary measures (HE=0.802; HO=0.777, AR=18.601) and low effective population sizes, which may be linked to past exploitation levels. Significant genetic divergence was detected for both mtDNA and microsatellites (ϕST=0.070 and FST=0.004; p<0.001), although the differentiation pattern was not consistent through time. Results suggest the presence of population sub-structuring, with at least two genetic units detected: western coast and southern coast of South Africa. The observed low levels of genetic differentiation point to significant gene flow between populations. The absence of temporal stability may result from reproductive sweepstakes, with differential reproductive success between cohorts. These findings suggest that management of South African kingklip should consider two independent stocks, and catches should remain at levels that will ensure the long-term viability of the resource.