Glossary of Fishery Terms - T

T

• Tag and release - marking or attaching a tag to a fish so that it can be identified on recapture. Used for the study of fish growth, movement, migration, and stock structure and size.

• Threatened species - Threatened species are species which are vulnerable to extinction in the near future. The IUCN further divides them into three categories: vulnerable, endangered, and critically endangered.

• Tidal current - alternating horizontal movement of water in coastal areas, associated with the rise and fall of the tide as the earth rotates. The rise and fall is caused by gravitational forces exerted by the moon and the sun. Unlike ocean currents, tidal currents change in regular patterns that can be predicted for future dates.

• Tidal flats - are coastal wetlands that form when mud is deposited by tides or rivers. Also called mudflats.

• Transboundary stocks - are fish stocks which range across the EEZs of two or more countries. They can be contrasted with straddling stocks. A stock can be both transboundary and straddling.

• Trap fishing - fishing by means of traps, often designed to catch a particular species, such with lobster pots.

• Trash fish - catch with no commercial value which is discarded, especially when trawling. Also called rough fish. See also coarse fish.

• Trawling - is fishing with a large bag-like net, called a trawl, which is drawn along behind a boat called a trawler. The net can be dragged along the sea bottom in order to target demersal fish, or pulled through clear water in order to target pelagic fish. Trawling along the sea bottom can result in significant bycatch and habitat destruction.

• Trophic level - The position that a species occupies in a food chain. The species it eats are at a lower trophic level, and the species that eats it are at a higher trophic level.

• Trolling - a method of fishing where one or more fishing lines, baited with lures or bait fish, are drawn slowly through the water behind a boat. Trolling is used to catch pelagic fish such as mackerel and tuna species.

• Turbidity current - a current of rapidly moving, sediment-laden water that is heavier than clear water and therefore flows downslope along the bottom of the sea or a lake. The term is most commonly used to describe underwater currents in lakes and oceans, which are usually triggered by earthquakes or slumping.

• Turtle excluder device (TED) - a specialized device that allows a captured sea turtle to escape when caught in a trawl net.