BY ANNELIESE MOLL
For the UAS Whalesong
Within any fishery, there is bycatch. Bycatch are fish or other marine species that are caught unintentionally. It can consist of the target species, but the wrong sex or size. However, some species that are often bycatch are dolphins, marine turtles, and seabirds.
Modern fishing equipment is extremely, and often unfortunately, durable. Currently, there are thousands of miles of fishing lines and nets within the ocean. Bycatch that is pulled aboard with the target species is often left on deck while the target species are sorted, before being tossed back into the water dead or very close to dying. However, there are people all over the world who are working on ways to reduce the amount of bycatch obtained by fisheries.
Now, the green sea turtle (Chelonia mydas) is a fascinating organism. They are one of the largest sea turtle species and are known to migrate between their nesting and feeding sites sometimes swimming distances over 1600 miles. Similarly to our Pacific salmon, adults often return to the beach they hatched from. However, their feeding habits are a largely a mystery.
In the past, these turtles were collected and used in the production of handbags. In some countries they were used as a food resource, and, in some counties, that practice still continues.
Unfortunately, they are currently listed as an endangered species. However, in many countries, particularly developing ones, this does not necessarily mean much. These turtles are also often caught in the nets used by several fisheries, like gillnets and bottom trawls.
In an effort to reduce the rate at which green sea turtles are dying due to being bycatch, a team of scientists have been investigating cost effective methods and alternatives. One new method of reducing sea turtle bycatch is through the use of small green LED lights that are attached to fishing nets. Recently, a team of researchers from the Centre for Ecology and Conservation at the University’s Penryn Campus have discovered that by attaching green LED lights to gillnets used within small-scale fisheries had the ability to reduce the number of green sea turtle deaths by 63.9%. They also found that the addition of the lights did not impact the number of target species obtained.
The team conducted the study in Sechura Bay, which is in the northern part of Peru. For the study they used 114 pairs of nets, which were about 500 meters long. The lights were placed along the nets 10 meters apart along the floatline. The cost of each light was around $2. The control nets, as expected, were placed in the water without lights. During the study the target species were guitarfish. After the nets were pulled up, they found that the control nets had caught 125 turtles while the LED adorned nets caught only 62.
Unfortunately, even with the amount of work that is going into reducing bycatch, it is still a major problem that impacts a wide range of organisms within the oceans. Lost or discarded fishing equipment also presents a problem because it is very easy for birds, turtles, fish, along with marine mammals to become entangled.
If you would like more information about bycatch and what is being done, the World Wildlife Fund has some great resources and information available.