Great Fish River: promoting sound fishing practices

In a boat in the Great Fish River estuary, in South Africa´s Eastern Cape province, researchers gather around the screen of a laptop computer to watch a series of moving dots indicating the movements of fish beneath the water. Science (SAIAB) and the Norwegian Institute for Nature Research (NINA), are collaborating in a project using acoustic telemetry, or electronic tagging, to monitor the numbers and the behaviour of two species of fish - the spotted grunter and the dusky kob - as they migrate between the open sea and the estuary. The project´s findings will be used to promote more sustainable fishing practices in order to protect the estuary´s valuable resources. After being spawned at sea, spotted grunter fiction or science gone overboard? Neither - the researchers, from the South African Institute for Aquatic Biodiversity (Pomadasys commersonnii) and dusky kob (Argyrosomus japonicus) enter the nutrient-rich waters of estuaries where they spend the first few years of their lives. Here, juveniles of the two species are heavily exploited, both by local subsistence communities for food, and recreational fishers, to the extent that the sustainability of these fisheries hangs in the balance. Better resource management, based on knowledge of the population biology, habitat and migratory behaviour of the species, is essential. The project team aims to describe the movements of the fish, how long they spend at sea and in the estuary, and the timing of their migration between the two habitats. Answers to these questions will promote the sustainable development of the fisheries, and provide local and national authorities with the information they need to ensure an equitable distribution of the estuary´s resources among the different user groups. The telemetry equipment consists of a battery-powered acoustic transmitter (fish tag) that is either attached externally or surgically implanted. Each transmitter emits unique coded signals on a fixed frequency and allows several individual fish to be tracked simultaneously. ...