Turtle Excluder Devices (TEDs) act as an escape hatch for turtles, while allowing shrimp and other small fish to pass into the net. Although trawling is one of the most destructive, non-selective ways to fish, providing animals with an escape route dramatically reduces the number of sea turtles that drown in the end of the net. When installed correctly, TEDs can reduce sea turtle mortality by 97 percent. In the Gulf of Mexico and southeast Atlantic, requiring TEDs in shallow water skimmer shrimp trawls, which do not currently use them, could save more than 2,500 turtles each year.
Lesser known versions of this escape hatch include Bycatch Reduction Devices (BRDs) and Seal Excluder Devices (SEDs) that allow larger animals to go free while retaining the targeted species. In the Gulf of Mexico, BRDs allow larger finfish to swim out of the net as shrimp are captured in the back of the net. In the Gulf of California, BRDs reduced total bycatch by 40 percent. Off Tasmania, experimental SEDs reduced the capture of seals in trawl nets that target winter-blue grenadiers, after observed seal deaths were witnessed in the fishery.
Greenstick gear is emerging as an alternative to longlining that allows up to ten hooks to be fished simultaneously while being more closely monitored. Fishermen bring in individual lines within minutes - rather than hours - of a bite, greatly reducing bycatch mortality and improving the quality of captured fish. Developed by the Japanese, it is commonly used to target yellowfin tuna, but also bigeye, skipjack and blackfin tunas. In this method, tall poles are fixed to the back of a boat towing a series of lines with hooks at the surface of the water.
Streamers can be attached to longlines as a visual and physical deterrent to seabirds while lines are being set in the water. The streamers prevent birds from approaching the baited hooks, thus reducing bycatch and bait loss. During an experimental study, streamers deployed in pairs reduced seabird bycatch by 88 to 100 percent. Setting lines underwater using a funnel to guide baited hooks below the surface and away from hungry birds is an additional way to reduce longline bycatch. Similarly, line shooters are designed to set longlines with extra slack, allowing them to sink below the diving range of most seabirds more quickly than traditionally set lines.
The fishing industry has had great success in improving the selectivity of its catch by specifying the shape, size, strength and material of their hooks and bait. Circle hooks and “weak” hooks are an alternative to traditional, non-selective hooks and have been shown to reduce mortality of sea turtles, sharks and swordfish. In the Hawaii longline fishery switching hook and bait type resulted in fewer landings of endangered sea turtles.
Did you Know? Through new and innovative research, scientists have been able to deter sharks by including certain types of magnetic earth metals and elements in nets and hooks. The repellants rely on sharks’ highly developed sensory system and act electrochemically to produce low-level voltage that overwhelms and repels the sharks.
Many fish and other marine wildlife prefer to swim in certain areas over others, and can therefore be targeted by fishermen based on their underwater “niche.” By changing the depth, configuration, time of day, or location of fishing lines, fishermen can improve fishing efficiency and minimize bycatch.
For example, research has shown that sea turtles and many billfish are usually encountered in the top 100 meters of the water column while some species of tuna spend most of their daylight hours at depths greater than 100 meters. Tuna longline fishermen can avoid catching sea turtles and billfish and focus on catching more tuna if they set their hooks at depths greater than 100 meters. In addition gear regulations, such as extending the length of certain lines to allow entangled turtles to swim to the surface, and limited soak time can significantly reduce bycatch and bycatch mortality.