Management of South African dusky kob Argyrosomus japonicus (Sciaenidae) based on per-recruit models

Abstract

The dusky kob Argyrosomus japonicus is an important linefish species that is abundant in South African waters between Cape Agulhas and the Mocambique border. The juveniles (<1 070 mm) occur inshore, where they are targeted by surf-zone and estuarine anglers, and the adults are caught mainly beyond the surf by recreational and commercial linefishermen. Yield-per-recruit (Y/R) and spawner biomass-per-recruit (SB/R) models were applied to the South African dusky kob stock, with accommodation for different inshore (F inshore ) and offshore (F offshore ) fishing mortality. It is shown that, as a result of high juvenile mortality (F inshore = 4–6-fold F SB25 and 6–10-fold F SB40), dusky kob were exploited far beyond optimal (F SB40) and threshold (F SB25) fishing limits, and that SB/R was 1.0 – 4.5% of the pristine value. This is indicative of severe stock depletion and of recruitment overfishing. Based on the bag frequencies of 16 367 angler outings, it is clear that the current recreational bag limit of 10 fi...