Biology of Shrimp
Brown shrimp have a similar life cycle but spawn in the late winter. The postlarvae, ten to thirteen millimeters long, move into estuaries in late March and April. By June the shrimp are adults and begin to move offshore. They are an important harvest from June to August.
The Shrimping Industry
Shrimp are harvested by otter trawls, cast nets, and seines. More than 400 licensed shrimp boats do most of the commercial harvesting in Georgia. The fleet is made up of boats, or trawlers, 20 feet to 100 feet in length, with the bulk of the fleet between 55 feet and 75 feet long. They shrimp from the coast all the way to eight miles offshore. The boats pull as many as four otter trawls, which may have head ropes (the lines at the top of the net's mouth) as long as fifty-five feet. Wooden doors act as hydrofoils to open the nets under water; the faster the
Catching animals other than shrimp, called by-catch, is a particular concern. Up to 2.7 pounds of by-catch are caught for every pound of shrimp harvested off the Southeast coast. Sea turtles, which are protected by law, are part of the by-catch. Sea turtles move into shallow nearshore areas, and the female crawls onto the beach to lay her eggs during the summer, at about the same time the shrimp season begins. Turtles swim in front of the trawls until they are exhausted and then are swept into the net. In the past they had no way to escape and drowned if the trawl was pulled for longer than an hour and a half.
Turtle excluder devices (TEDs) were developed by the U.S. National Marine Fisheries Service, the University of Georgia Marine Extension Service, and fishers. TEDs provide a hole in the trawl that allows turtles to escape. Each TED has a grill or large mesh net panel that is sewn into the net. This guides turtles and large fish out through the opening. Shrimp are poor swimmers, so they are swept into the back of the net, called the bag, along with the small fish.
Federal and state agencies, concerned about fish populations, wanted to reduce the fish by-catch by 50 percent, but TEDs reduce it by only 23 percent. This problem led to the introduction of the by-catch reduction device (BRD), a simple frame that keeps small holes open and allows small fish to swim out of the net. The use of BRDs has significantly reduced the amount of by-catch. There is some shrimp loss, at least 8 percent to 10 percent under the best of operating conditions, but it can be much higher.
Mac V. Rawson, University of Georgia
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