With advances in technology such as faster boats fitted with modern gadgets such as fish-finders, radar, and water temperature sensors to enable fishermen to quickly find schools of fish, and the use of helicopters in commercial fisheries to scout for fish, combined with an increase in performance of modern fishing gear, the pressure on the target species has intensified.
Big-game fisherman fish with rod, reel and tackle commonly using trolling methods to lure bluefin tuna onto the moving baited hooks towed behind a big-game fishing launch. Kite fishing is another method used by sport fishermen for catching bluefin tuna.
Trolling is also used in small-scale commercial fishing operations to catch bluefin tuna. Multiple fishing lines are set using outriggers to keep the lines apart and prevent them from getting tangled.
Pelagic long-lining is commonly used by commercial fisheries to catch bluefin tuna. This involves setting a line of hundreds, or even thousands, of baited hooks near the surface of the ocean to catch bluefin tuna. Unfortunately, if mitigating measures are not followed, a high by-catch of non-target species, particularly seabirds can result. Thousands of endangered albatross species are killed each year as a result of getting hooked and drowned after being attracted to the baited hooks during deployment.
Purse seine nets is another method used by commercial fisheries to trap large numbers of bluefin tuna in a single haul, after the net, which is set around the school of tuna by the circling fishing vessel or by an auxiliary vessel known as a skiff, is drawn into the fishing boat trapping the entire school of tuna in the catch. This method of fishing also has a by-catch of non-target species such as sharks, dolphins, turtles, and other non-target fish species. However, depending on the mesh size used in the nets, smaller fish may be able to escape, thus reducing the by-catch of certain non-targeted fish species.
Cage farming of bluefin tuna is a fishery that has been established primarily in Japan to meet the demand for this species commercially and to reduce the pressure on wild stocks by producing bluefin tuna for the sushi and sashimi market in local fish farms. However, cage farming of tuna causes a whole new set of ecological problems, as they are predatory fish and have to be fed. Consequently, prey fish are being fished out of the ocean in huge numbers to support this fishery, upsetting the ecological balance and leaving other marine predators starving. Read this thought provoking article on the overfishing of prey species to find out more about this critical problem.