Tuna fishing received much publicity in the 1990s when a boycott led to changes in fishing practices to avoid catching dolphins which often swim alongside yellowfin tuna. They did this by fitting special hatches in the nets from which dolphins could escape.
To combat the sale of tuna likely to involve dolphin catching you can look out for the 'dolphin safe' logo on tins of tuna at the supermarket. But be wary - this doesn't guarantee sustainable fishing practices are in use.
Skipjack tuna are more likely to be dolphin safe because they do not associate with dolphins. However the dolphin safe label does not guarantee the safety of other marine creatures such as sharks, rays and turtles. Between 60 - 70% of tuna are caught using the purse seine method. Usually they are lured by fish aggregation devices (FADS), floating devices which the tuna congregate under and the net is pulled up around them like a large drawstring bag/purse. In fact 10% of the catch using this method are unwanted bycatch, amounting to 100,000 tonnes annually. Some of the bycatch is made up of sharks, many of which are threatened species. Their fins are cut off to sell to make a Chinese delicacy - shark fin soup. Without the FADS, this method can be specifically targetted to a school of one adult species and avoids much of the bycatch.
Longline fishing is a method used to catch more expensive kinds of tuna. This method involves putting out fishing lines up to 100km long from which there are as many as one thousand shorter lines attached with baited hooks. This still indiscriminately kills untargetted marine life such as turtles (of which 6 out of 7 species are considered threatened) which are tempted by the jelly fish appearance of the bait. Abatrosses and other seabirds can also get caught on the hooks. An estimated 500,000 - 1.4 million sharks are killed every year this way.
The pole and line method and “trolling” (where baited lines are dragged through the water behind a boat) are considered as the most sensible methods of fishing as it targets the adult fish, bycatch is much reduced and unwanted catches can be returned to the sea, alive. This is often the chosen method of smaller fisheries.Read More: Shark and Chips. Are endangered sharks being sold in a fish and chip shop near you?