Future of the IUCN Endangered white steenbras Lithognathus lithognathus (Sparidae) – a tale of two estuaries

Abstract

This review draws on a long history of ichthyological and fisheries research to examine the changing stock status of the estuary- dependent white steenbras Lithognathus lithognathus in the South African Swartkops and Knysna estuaries. The available evidence  points to a major decline in the L. lithognathus population of the Swartkops Estuary, from an already exploited status in the late 1800s and  early 1900s to a collapsed status by the late 1900s, and the loss of adults which were recorded as prevalent in the estuary in 1915. In  recent decades, the spotted grunter Pomadasys commersonnii appears to have occupied the niche previously used by L. lithognathus in  the Swartkops Estuary, although climate change may also be playing a role in this trend. The Knysna Estuary had a healthy juvenile L.  lithognathus population in the 1970s and 1980s, but increasing anthropogenic pressures on the system, including exploitation by  recreational anglers and small-scale fishers, are cause for concern, particularly as fishery regulations for this species are not being  adhered to in this and other systems. No-take marine protected areas (MPAs) appear to have been successful in providing some  opportunity for stock recovery by adult populations of L. lithognathus in certain coastal regions within the distributional range. In  conjunction with adequate enforcement of current fishery regulations, the proclamation of estuarine protected areas (EPAs) for juveniles  in important estuarine nursery areas is required to enable the stock to recover and for the status of this fishery resource to be upgraded  from collapsed to sustainable in the future. By providing protection for L. lithognathus in selected no-take EPAs, these same areas could  also benefit other overexploited marine fish species, such as the dusky kob Argyrosomus japonicus and leervis Lichia amia.