Clean Gear: Innovation Saves Marine Wildlife
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 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 5,700 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 pass through while retaining the targeted fish. In the Gulf of Mexico, BRDs allow larger billfish to swim out of the net as passively floating shrimp are captured in the back of the net. In the Gulf of California, BRDs quadrupled the efficiency of shrimp catch, used less fuel and cut bycatch by as much as half. Off Tasmania, experimental SEDs reduced the capture of Australian sea lions and fur seals in trawl nets that target winter-blue grenadiers, after almost 1,000 animals were captured previously each year.
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 in Hawaii, New England, the Carolinas, and the Gulf of Mexico. 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, only two birds were captured out of a total of 185,000 hooks, representing more than a 99% reduction compared to average rates observed throughout the early 2000s. 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.
Hooks and Bait
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. Additionally, researchers have found that using fish bait exponentially improves catch efficiency compared to using squid, which attracts a variety of other marine wildlife. In the Hawaii longline fishery, 30 percent fewer sharks and sea turtles were hooked in the first year after instituting a change in bait and hook type, with no statistically significant difference in the number of swordfish that were caught.
Did you Know? Through new and innovative research, scientists have been able to deter sharks simply 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. These repellants include gels or time-release pills that activate once placed into the bait, lasting up to four hours.
Fishing Lines – Configuration, Weight, and Depth
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, a study of an Australian tuna fishery found that fishermen caught yellowfin tuna and billfish in shallow waters during daylight, but caught deeper-dwelling swordfish and bigeye tuna at night. In California, researchers have tested ways to avoid sea turtles and marine mammals by adjusting line length to target deeper-swimming swordfish. 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.