An innovative fishing gear to enhance the release of non-target species in coastal shark-control programs: The SMART (shark management alert in real-time) drumline

In response to a spate of shark attacks in Reunion Island in the southwest Indian Ocean since 2011, local authorities developed an experimental shark-control program based on those conducted for decades in Australia and South Africa. In order to greatly reduce, if not eliminate, the impact of such a shark fishing program on bycatch and undersized target shark species, the use of conventional “drumlines” was improved by the addition of an innovative “Catch-A-Live”® system, making the drumlines ‘SMART’ (Shark Management Alert in Real Time). This is a real-time strike alert system based on an adapted triggering mechanism, which links the fishing line to a GPS buoy connected to the Iridium satellite. This system alerts fishers on duty via a computer-based communication system within just a few minutes, enabling immediate intervention. Off Reunion Island, up to 20 SMART drumlines (SDLs) were deployed along the west and southwest coast in coastal waters to target bull (Carcharhinus leucas) and tiger sharks (Galeocerdo cuvier) in trials conducted between 2014 and 2017. During 58,770 h of fishing there were 269 catches of more than 14 species, of which 86.9% were retrieved alive. There were marked differences in survival among species. While the most fragile species were the giant trevally (Caranx ignobilis), scalloped hammerhead sharks (Sphyrna lewini) and small carcharhinid species, most of the other bycatch species (stingrays Dasyatis sp., giant guitarfish Rhyncobathus djiddensis, and tawny nurse sharks Nebrius ferrugineus) were generally found alive and in a condition suitable for tag and release. Of the target species, 94.8% of all individuals were found alive. These survival rates are far higher than those of other programs using conventional drumlines in KwaZulu-Natal (South Africa) and Queensland (Australia). There were strong diurnal and lunar catch patterns. This information is invaluable in planning fishing operations to maximise the catch of the target species, while reducing the chances of killing the bycatch. These results highlight the potential for use of SDLs in research programs aimed at tagging large sharks capable of tripping the trigger, especially in situations where catch rates are so low that it is impractical for the fishing vessel to remain at sea for the duration of each fishing operation.