How Are Tuna Caught?

By PSU EcoMerge Capstone - 2:28 AM


The two most common methods to catch tuna commercially are “purse seining,” and “long lines.”

Purse Seining
A purse seine is a large cylindrical net that wraps around a school of fish much like a drawstring coin purse, except that the draw string opening is at the bottom, toward the ocean floor, rather than at the top. Unfortunately by-catch is high with this method. (Bycatch is unwanted fish and animals caught accidentally in fishing gear and discarded overboard, dead or dying. This bycatch could be sea turtles, dolphins, and numerous species of fish.) The reason that bycatch is high is that in the ocean different species of fish may school together for protection. Tuna tend to school with dolphins because dolphins keep the tuna’s natural enemy, the shark away. Hence the public outcry for dolphin safe tuna.

Longlining

As an alternative to the purse seine method longlining is the next most economically feasible method for catching tuna. It is one long main line stretched up to 50 miles with secondary hook lines branching off of it. Each hook is set with bait and left to attract fish until the boat returns to collect the catch. Still bycatch is high because the baited hooks also attract a variety of pelagic (pelagic refers to the open sea, away from coast and sea floor) sea life, such as sea turtles, shark, swordfish, and sea birds like the albatross which dive for the bait. Pelagic longline gear is not allowed to directly target Bluefin tuna but boats are allowed to retain a limited amount of Bluefin tuna caught incidentally while targeting other species (such as swordfish, yellowfin tuna, and bigeye tuna).

Good Old Fishing Pole and Line
By far the most sustainable method for catching Tuna is the old fashioned way, with a fishing pole and line. By throwing live sardines and anchovies overboard you can attract a school of tuna. The tuna swarm and you can catch them one by one with little to no risk of catching untargeted species. If on the off chance you did catch something on your line unintentionally you would know it and could unset the hook and release the fish or animal with minimal harm. Unfortunately in the case of the Bluefin, stocks have been so decimated and the mercury levels are such, that one must ask themselves if it is worth it, despite the large profit and high demand.



References:
http://www.montereybayaquarium.org/

http://www.nmfs.noaa.gov/fishwatch/species/atl_bluefin_tuna.htm


Posted by Lisa Adza

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