Not all of the marine species caught in fishing nets, traps, or on lines are kept and used. In fact, an amazing 27 million tonnes of marine life is caught and often discarded overboard each year. This waste equals nearly one third of all the fish caught by humans worldwide. These unwanted fish and other species are called bycatch. The species a fisher intends to catch is called the target species. Bycatch can include juveniles of the target species that are too small (which means they will never grow and reproduce to ensure future populations!), other species of fish, and also birds, turtles, and marine mammals that are accidentally caught.

Bycatch is the result of fishing gear and methods that are not selective. If harvests from the ocean are to be sustainable in the future, the issue of wasted bycatch must be addressed. With awareness, creativity, and new technology, huge reductions in bycatch can be made. It is estimated that using more selective fishing gear around the world could reduce bycatch discards by at least 60%. (UNFAO, WWF, 2001). Changing the type of fishing gear is an obvious solution, but many other factors may have an effect on levels of bycatch. These factors may include the time of day, the height of the tide, migratory species, the density of fish in the area, and even the weather. Let’s take a closer look at some fisheries that have worked to reduce wasted catch.

Eastern Pacific Tuna Fishery

The capture of dolphins in the tropical Pacific tuna fishery is probably the most well known example of commercial bycatch. The number of dolphins killed in this fishery is the highest known of any fishery. There is a unique ecological relationship between tuna, the target species, and dolphins. Scientists don’t really know why, but large yellowfin tuna are often found swimming beneath pods of dolphins. In the past, tuna were caught one at a time using a hook and line. These days, strong synthetic nets and hydraulic pumps allow fishing boats to encircle entire schools of tuna with huge purse seine nets. In doing this, the dolphins are also captured. It has been estimated that over 6 million dolphins have been killed since this fishery began. Contrast this to the fact that in the entire history of commercial whaling about 2 million whales have been killed (Encyclopedia of Marine Mammals, 2002).

It is largely due to public pressure that the bycatch of dolphins has been reduced. In North America, the largest market for canned tuna, you can choose to purchase tuna with a “dolphin-safe” label. To make the tuna “safe”, dolphins are released from the purse seines at sea by lowering the net below the surface so that dolphins may swim out, and yet the tuna remain trapped. This has greatly reduced the number of dolphins killed. However, populations of dolphins in the Eastern Pacific are not coming back and there may be more complicated environmental and social effects on the dolphins from the tuna fishery. Also, some dolphin safe netting methods have turned out to be unsafe for a lot of other marine life, like sharks and sea turtles (WWF, 2001).

Shrimp Trawl Fishery (see article on fishing methods)

For years shrimp trawlers have been criticized for the amount of bycatch they produce, and also for damaging benthic (sea floor) habitats. Overall, the world trade in shrimp is more valuable than any other fishery, so there is a strong incentive to keep this fishery open.

Off the coast of British Columbia the shrimp fishery occurs in areas of hard bottom, around 100m in depth. In the past many small fish and shellfish were also trapped in the nets as they were “trawled” along the bottom. This bycatch became especially important as one of the species of fish being caught as bycatch was eulachon. You see, bycatch doesn’t only affect glamorous marine mammals and sea turtles. Eulachon, “candle fish”, are a small species of fish that are traditionally important to First Nations people in BC. Eulachon are also an endangered species. Grates and large rigid meshes that allow small fish to escape from the nets are now found on all shrimp boats. There are also size grates that allow for the separation of different sizes and ages of shrimp.

On the East Coast of the United States shrimp trawlers were catching sea turtles as bycatch. Most of these turtles would drown after becoming tangled in the nets. Many species of sea turtles are endangered and the populations are struggling to survive. Scientists and fishers developed technology that would reduce the bycatch of turtles. These “turtle excluder devices” (TED) are big metal grids that let the shrimp through into the net, and yet allow the turtles, and other larger animals, to escape. Essentially, they are “Trap doors for turtles”. This was done without decreasing the efficiency of the nets for catching shrimp. Now all shrimp fishers must use these TEDs by law and it is helping rebuild the sea turtle populations.

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