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.

Field Study 561

Study Type: 

wild

Location: 

Baltic

Target catch: 

None reported

Effect on bycatch species: 

Pingers significantly reduced echolocation encounter rates by 50-100% at 500m; sighting reduced up to 375m. Porpoise return time was 6 hrs when pingers were silent after being active for 24 hrs 50 min

Effect on target catch: 

None reported

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Field Study

Study Type: 

wild

Location: 

North Carolina

Target catch: 

Spanish mackerel, menhaden, spot

Effect on bycatch species: 

Catch rates of Atlantic sharpnose sharks were significantly lower in the 4" modified net

Effect on target catch: 

Did not reduce catch rates

Article: 

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Field Study 371

Study Type: 

wild

Location: 

Izmir Bay, Turkey

Target catch: 

Prawns

Effect on bycatch species: 

Trial 1, experimental net caught 44% fewer crabs and mantis shrimp and 49% fewer murex than control net. Trial 2, experimental net 1 caught 66% fewer crabs, 27% fewer mantis shrimp and 32% fewer murex, while experiemnetal net 2 caught 51% fewer crabs,

Effect on target catch: 

Trial 1, experimental net 1 caught 17% fewer prawns than the control net. Trial 2, experimental net 2 caught 2% fewer prawns than the control net.

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Field Study 320

Study Type: 

wild

Location: 

North Carolina

Target catch: 

Spanish mackerel, menhaden, spot

Effect on bycatch species: 

The selectivity of blacknose sharks varied between the modified and unmodified nets

Effect on target catch: 

Did not reduce catch rates

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Field Study 319

Study Type: 

wild

Location: 

North Carolina

Target catch: 

Spanish mackerel, menhaden, spot

Effect on bycatch species: 

Significantly less blacktip sharks were wrapped in the 3" modified net

Effect on target catch: 

Did not reduce catch rates

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Field Study 318

Study Type: 

wild

Location: 

North Carolina

Target catch: 

Spanish mackerel, menhaden, spot

Effect on bycatch species: 

The proportion of hammer-wrapped bonnethead sharks was significantly higher in the 4" unmodified net

Effect on target catch: 

Did not reduce catch rates

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Field Study 317

Study Type: 

wild

Location: 

North Carolina

Target catch: 

Spanish mackerel, menhaden, spot

Effect on bycatch species: 

Catch rates of bonnethead sharks were significantly lower in the 4" modified net

Effect on target catch: 

Did not reduce catch rates

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Field Study 311

Study Type: 

wild

Location: 

North Sea

Target catch: 

Cod

Effect on bycatch species: 

Reduced catch rates from 0.00229 and 0.00295 for nets with dummy pingers and no pingers respectively, to 0.00015 for nets with active pingers

Effect on target catch: 

None reported

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