Feeding ecology of South African Argyrosomus japonicus (Pisces: Sciaenidae), with emphasis on the Eastern Cape surf zone

Abstract

The feeding ecology of dusky kob A. japonicus was determined from the stomach contents of line-caught specimens from several estuarine, surf zone and nearshore localities in KwaZulu-Natal and the Eastern and Western Cape. The accuracy of dietary descriptions for dusky kob depends on sample size, sampling frequency and sampling period. A. japonicus in the marine environment fed on a wide variety of organisms, including benthic, epibenthic and pelagic crustaceans, cephalopods and teleosts. Teleosts were by far the most important taxon, but at the species level the principal items varied with environment. There was a general increase in the importance of squid and teleosts, and a concomitant decrease in the importance of crustacea with growth. Feeding frequency and intensity were generally higher in the surf zone than in nearby estuaries, which demonstrates the importance of the former as a foraging area. Dusky kob from surf zones with mixed reef/sand substrata fed more regularly, ate larger meals and consumed a wider variety of organisms (38 v. 28) than did those from predominantly sandy substrata. It is concluded that A. japonicus is a top predator that influences the pelagic and demersal food chains of estuaries, the surf zone and the nearshore environment, and that its currently depleted condition has almost certainly had an impact on the foodwebs of all three of those habitats.