If not caught by anglers or eaten by fish, they may live to be two years old. To grow they must cast off their shell and form another. They get larger before the new shell becomes firm. Shrimp grow rapidly when the water is 68 degrees F and above. If bay water temperatures fall below 60 degrees F, shrimp growth is much slower and at temperatures below 40 degrees F mortalities may occur.
Lines run from the shrimp boat to each door.
As the shrimp boat tows the trawl over the sea bottom, the trawl is held open by the kite-like spreading action of the doors. Shrimp and bottom fish scooped into the open trawl pile up in the cod-end. When the net is boated, a line that holds the cod-end closed is released and the catch falls to the deck. The heads are thrown away. Evidence from tag returns show that they remain in the same area and generally move less than 3 miles from where they were tagged.