Gillnets

Gillnets are single, double, or triple layers of net suspended vertically in the water column. The top of the net is connected to floats (headrope), while the bottom is weighted (footrope). Adjustment of the floats and weights allows gillnets to be positioned at varying depth, depending on the target species. Gillnets are generally deployed in large numbers and trap fish either by entangling the gills or by entangling all or part of the fish body. Variation in net mesh size allows fishermen to control the size of their catch.
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<i>Set nets</i> are stationary gillnets set near the bottom or at a particular depth. A subset of set gillnets, <i> fixed nets </i> are stretched between stakes driven into the bottom in intertidal areas. In contrast, <i>drift nets</i> are unanchored and float with the current. Drift nets are mostly used near the sea surface. <i>Trammel nets</i> are multi-layered gillnets usually set near the ocean bottom. FIsh are ensnared in the middle layer, which has the finest mesh size. <i>Encircling gillnets</i> are set in a circle in shallow water. Fishers create a disturbance in the water that drives fish into the nets. Several gillnet types may be used in conjunction; combined gill-trammel nets are particularly popular.
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For more detailed information, please visit the FAO Fisheries and Aquarculture Department <a href="http://www.fao.org/fishery/geartype/107/en" target="_blank"> gillnets </a> web page.

Acoustic alarms reduce porpoise mortality

Study Type: 

wild

Location: 

United States

Target catch: 

Multiple species

Effect on bycatch species: 

Reduced harbor porpoise bycatch

Effect on target catch: 

Effect varied by species

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Deterring harbour porpoise from gillnets: observed reactions to passive reflectors and pingers

Study Type: 

wild

Location: 

Canada

Target catch: 

n/a

Effect on bycatch species: 

92.4% of porpoise groups avoided pinger equipped floatlines

Effect on target catch: 

n/a

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Reactions of harbor porpoises Phocoena phocoena and herring Clupea harengus to acoustic alarms

Study Type: 

wild

Location: 

Canada

Target catch: 

Herring

Effect on bycatch species: 

Harbor porpoise avoided area

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Field Study 122

Study Type: 

wild

Location: 

Argentina

Target catch: 

Sea trout, croaker, letherjack, Patagonian smooth hound

Effect on bycatch species: 

Reduced dolphin bycatch

Effect on target catch: 

No effect

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Field Study 123

Study Type: 

wild

Location: 

Argentina

Target catch: 

Sea trout, croaker, letherjack, Patagonian smooth hound

Effect on bycatch species: 

Increased interactions between gear and sea lions

Effect on target catch: 

No effect

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