A study of trawl fishing in South Africa suggests that around 18,000 seabirds may be killed annually in this fishery, highlighting trawl fisheries as a major threat to seabirds, especially several species of albatross already facing a risk of extinction.
Published in the journal Animal Conservation, the study was based on scientists monitoring catches on 14 different vessels, operating in the Benguela Current, off South Africa; one of the main hotspots for seabirds in the Southern Hemisphere. The vessels were trawling for hake, and the majority of bird deaths were a result of collisions with wires - known as warp lines - leading from the stern of the vessels.
"We believe the seabird deaths the scientists recorded might be just the tip of the iceberg", said John Croxall, Chair of BirdLife's Global Seabird Programme. "It suggests that around 18,000 seabirds may be killed annually in this fishery alone," he added.
"Most mortality relates to the dumping of fishing waste behind the boat. This attracts seabirds which can either hit the warp lines or become entangled in the nets," commented Dr Croxall.
The species killed during the study include South African breeding species such as Vulerable Cape Gannet Morus capensis, and species such as Vulnerable White-chinned Petrel Procellaria aequinoctialis, Endangered Black-browed Diomedea melanophris and Near Threatened Shy Albatross Thalassarche cauta - although genetic evidence suggests Near Threatened White-capped Albatross Thalassarche steadi is more frequently observed in the area than the morphologically similar Shy Albatross - which visit the Benguela Current region from nesting islands dotted around the Southern Ocean. "The impact of this one local fishery has very widespread geographical repercussions", warned Dr Croxall. "Potential mortality at this scale for the albatrosses is unsustainable".
Data of this nature are very difficult to obtain, as fatal collisions are relatively rare events. However, collecting this information is an obligation - under the United Nations Fish Stocks Agreement and the Code of Conduct for Responsible Fishing - on the managers and practitioners of a fishery. "One would hope that further data like these will now become available through appropriate collaborations involving fishery managers", noted Dr Croxall.