Wednesday, June 13, 2012


A shrimping boat photographed in 1970
Bycatch is a term that many people are probably not aware of. It's used to describe all of the things that are not being targeted by fisheries, but are caught anyway. Every form of fishing can produce bycatch, which may or may not be fatal to the unintended catch.

Bycatch caught off the coast of Florida
As you can imagine, bycatch is quite controversial, especially when creatures such as dolphins and turtles are unintentionally killed. Unlike sea life, if an air-breathing creature such as a turtle becomes tangled in a net, it can easily suffocate from being denied access to the surface. Water-breathers are far more likely to survive, but that doesn't mean that their lives will be spared. Crowding in the net could still cause oxygen deprivation. The hauling in of the net can also be quite traumatic, especially if sensitive areas such as the gills are damaged. Then, there is time spent away from the water while the desirable catch is sorted out from the bycatch. The vast majority of bycatch is then thrown back as it was not intended to be caught in the first place. Anytime during this process, the bycatch may be eaten by predators, who often take advantage of fishing operations and whatever they throw overboard.

However, this doesn't mean that fishing operations are necessarily bad. Regulations have greatly reduced overall bycatch and provided protection for a number of endangered or threatened species. Also, food that is caught via fisheries can be a significantly better option than farmed alternatives, depending on the species and methods being used. A good example of this is shrimp. Though some farmed shrimp is not so bad, other shrimp farms seriously damage their environment. The farms are more productive if the shrimp are raised in fresh water, so a large number of farms are set up in mangrove forests and flooded with fresh water. This fresh water contamination will easily kill species in the surrounding area since mangroves are naturally saltwater systems and the species living there are adapted to salt water. Fresh water completely messes with their chemistry, especially their ability to retain essential dissolved minerals. Depending on how and where the shrimp are caught, it's far less damaging to the environment to catch them in the wild.

A turtle escaping a net thanks to a TED
Bycatch is still a concern, though. When looking at net design, a mesh meant to catch a certain species will allow smaller species through, but will catch basically anything that is larger than the target species. This is what causes most bycatch. As I mentioned before, regulations require the use of devices that help reduce or eliminate bycatch numbers. Two very important devices that are used in trawling are Turtle Excluder Devices (TEDs) and Bycatch Reduction Devices (BRDs). Both have numerous different variations, but what they accomplish is always essentially the same. A TED is specifically meant to protect sea turtles by giving them a route to escape through before they become trapped in the net. It will also provide an escape point for any large animal. In the case of the one pictured, the bar size is what determines the size of the animal that is allowed past into the codend, or the part of the net where the catch gathers. BRDs are usually placed past the TED, closer the codend. BRDs are often little more than holes in the net that are meant to allow bycatch an escape route. However, fishers are often not fond of them as it can lead to loss of some of the target species. Another interesting aspect of both TEDs and BRDs is that at least one animal, dolphins, have begun exploiting the holes in the net. There has been footage taken of these intelligent mammals poking their heads into the net holes and catching passing fish.

I feel lucky to have observed first-hand some of the research that is being done to try and reduce bycatch, specifically in shrimping. Through the University of Georgia Marine Extension Service, I was part of a group to take a trip on the R/V Sea Dawg, a shrimp boat turned research vessel. Some of the research that is being done on the vessel is the use of a different sort of TED that could also act as a more effective BRD. Results were looking promising with very large reductions in bycatch, so hopefully the modified TED will help reduce what can sometimes be absurdly copious amounts of unintentionally caught species. This setup would also be favored by fishers as it reduces the modifications that have to be made to their nets.

The fact remains that certain fishing methods produce far more bycatch than others. Poll fishing is usually more species-specific and less traumatic for what unintended animals that are caught. Purse seining, in contrast, can produce terribly excessive amounts of bycatch. For those who want to be environmentally conscious about their seafood choices, many organizations provide information on which methods are most damaging and what species should be avoided altogether.

Sources are the Consortium for Wildlife Bycatch Reduction, National Oceanic and Atmospheric Administration, World Wildlife Fund Smartgear Competition, Monterey Bay Aquarium, and Sea Grant Rhode Island. Images are from Wikipedia or Wikimedia Commons and are copyright free: one, two, three.

No comments:

Post a Comment