Mortality estimates and biological reference points for the Natal stumpnose Rhabdosargus sarba (Pisces: Sparidae) in KwaZulu-Natal, South Africa

Abstract

A per-recruit stock assessment was
undertaken for the sparid Rhabdosargus sarba, which is caught in
estuarine and marine shore fisheries in KwaZulu-Natal. Input parameters used
in
the analyses included age and growth parameters and mortality estimates from
catch curves. The mortality estimates from estuarine and coastal catch curves
were very different. Total and fishing mortality from estuaries was much
higher, because adult R. sarba emigrate out of estuaries and fishing
pressure on juveniles in estuaries is substantial. As a consequence two
separate models were run for estuarine and coastal fisheries. The results of
the spawning biomass per-recruit model indicate that R. sarba is at 34%
(in estuaries) to 63% (in coastal fisheries) of its unfished level. Because
estuarine estimates of fishing mortality (F) include emigration, the results
indicate that R. sarba in KwaZulu-Natal is not at present overexploited.
These results were substantiated by analysing available trends in catch per
unit effort (CPUE) for this species.



African Journal of Aquatic Science
2004, 29(1): 67–74