bycatch

Gill net

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Gill net (image credit: Michigan Sea Grant).

A gill net is a simple type of fishing gear that is staked to a substrate to create a wall of mesh.  Gill nets are often made of a material, such as monofilament nylon, which is practically invisible to fish attempting to swim by.  As the name implies, fish are often caught by the gills because these nets are designed for the head of a fish to fit through but not its body.

Management strategies to reduce bycatch in gill nets include regulating the mesh size so that the net openings are large enough, for example, for undersized fish to swim through unharmed but for legal-sized fish to be harvested.

For an example of how this fishing gear is used, please visit “Know Your Nets” from Michigan Sea Grant.

BRD

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A shrimp net with a mesh-panel, bycatch reduction device (BRD) and grill-type, turtle excluder device (TED; photo credit: NOAA).

BRD is an acronym for bycatch reduction device.  Bycatch is non-target catch within any fishery.

For certain fisheries, these modifications to the gear (i.e., BRDs) can help lower the amount of bycatch.  For example, a turtle excluder device (TED) is a specific type of BRD designed to help turtles escape trawl nets.  Especially in cases where fisheries have bycatch quotas, the use of BRDs can often allow fisheries to operate longer, and more profitably, because the quotas are not exceeded quickly.

BRDs are generally designed with the cooperation of the fishery – they can be continually modified and improved to help ensure their effectiveness without compromising the productivity of the fishery – which is in the best interests of the industry and conservation, alike.

TED (Turtle Excluder Device)

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TEDs significantly reduce turtle bycatch

TEDs significantly reduce turtle bycatch

Turtle Excluder Devices (TEDs) are a specific type of bycatch reduction device (BRD) that are a modification to a trawl net to keep turtles, which are not targets of the fishery, from being caught in the net.  TEDs are generally composed of a set of bars over the trawl net.  While small target animals, such as shrimp, pass easily between the bars into the trawl net, larger animals, such as turtles or even sharks, can escape through a side opening in the net after they have hit the grid of bars.  TEDs were developed to eliminate turtle mortality from trawl fisheries.  Because turtles and other bycatch, or non-target catch, species often come from threatened or endangered populations, the fisheries had strict regulations on how much bycatch was allowed.   TEDs, by reducing bycatch, allows the shrimp trawls to operate more with more ecological and economic efficiency.

For more information, please visit: http://www.fisheries.noaa.gov/pr/species/turtles/teds.htm

Bycatch

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1280px-Shrimp_bycatch

Shrimp fisheries have historically had very high bycatch

Bycatch is non-target catch within any fishery.  Bycatch can be either different species from the target of the fishery or individuals from the target species, generally juveniles, which are not of a marketable size.  Most bycatch is tossed back because it is illegal to possess or it has no commercial value.  In certain fisheries, however, a certain amount of marketable bycatch can be kept to sell.  Including bycatch reduction devices (BRDs) that have been specifically developed for some fisheries can have significant impacts on the amount of bycatch and/or bycatch survival.  In cases where fisheries have bycatch quotas, the use of BRDs, such as Turtle Excluder Devices (TEDs), can often allow fisheries to operate longer because the quotas are not exceeded quickly.

Because bycatch is difficult to quantify, it makes it very difficult to assess the population status of bycaught species.  Overfishing for these species is sometimes not recognized until the population is severely overfished.  Including bycatch in stock assessment techniques is helping to improve sustainability of these species.