Excluder devices

These can consist of a grid of metal bars or mesh placed usually within the neck of a trawl that has an opening for escape at either the top or bottom. Examples include “skylights” which consist of a mesh opening located at the top of the codend. ”Skylights” can be combined with guiding funnels that create visual and tactile stimuli to direct finfish towards the “skylight” escape sections. A different but similar type of design is the fisheye (including Gulf and yarrow fisheyes and bigeyes) which are openings typically forming a rigid frame constructed of aluminum or steel rods and placed along the top center portion of the codend (i.e. Catchpole and Revill 2007). Typically, large animals that strike the bar exit through the opening, while the smaller target species pass through the bars and are captured in the net or codend. Examples of excluder devices in trawls are the Nordmore grid, the Turtle Excluder Device (TED), and the Sea Lion Excluder Device (SLED). A sea turtle excluder chain mat is used in the Northwest Atlantic scallop dredge fishery. A new modification to pound nets may reduce sea turtle bycatch by replacing the upper two-thirds of the leader netting with vertical ropes spaced wide enough apart to let sea turtles swim through without becoming entangled (DeAlteris et al., 2005).

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Study Type: 

Field study in the wild

Location: 

Lake Opinicon, Canada

Target catch: 

Bluegill and other bony fish

Effect on bycatch species: 

The exclusion device with bars across the net significantly reduced turtle catch rates. All turtles were able to escape through the escape chimney.

Effect on target catch: 

Fish catch rates were not impacted by either excluder device. The majority (88%) of fish were retained when the escape chimney was used.

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Study Type: 

Field study in the wild

Location: 

Massachusetts Bay

Target catch: 

Silver hake

Effect on bycatch species: 

Over 88% of spiny dogfish were excluded by the grate regardless of color or gear configuration.

Effect on target catch: 

Within typical commercial quantities

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Study Type: 

Field study in the wild

Location: 

Gulf of Maine

Target catch: 

Pink shrimp (Pandalus borealis)

Effect on bycatch species: 

Reduced the bycatch of silver hake, red hake, American plaice and witch flounder compared to the Nordmore Grid and allowed larger fish to escape

Effect on target catch: 

The catch and size of pink shrimp was not significantly different between the Nordmore Grid and Rope Grid

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Study Type: 

Field study in the wild

Location: 

New South Wales Australia

Target catch: 

Prawns

Effect on bycatch species: 

The Nordmore-grid codend caught 50% fewer yellowfin bream than the radial escape section net and 55% fewer than the control net. Both trial codends significantly reduced the predicted mean weight (36% Nordmore-grid and 74.3% radial escape section) and n

Effect on target catch: 

The codend with a radial escape section and the simplified Nordmore-grid retained fewer school prawns by weight 11.5% and 4.6% resepectively, compared to the control net.

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Study Type: 

Field study in the wild

Location: 

Gulf of California

Target catch: 

Shrimp

Effect on bycatch species: 

The industrial version of the prototype reduced bycatch-to-shrimp ratios from 20-50% and the artisanal version also reduced the bycatch-to-shrimp ratios.

Effect on target catch: 

The industrial prototype increased target catch efficiency

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Study Type: 

Field study in the wild

Location: 

Mid Atlantic Bight

Target catch: 

Longfin squid

Effect on bycatch species: 

The square-mesh escape panel significantly reduced the average catches of scup and black sea bass. The panel also reduced catches of sublegal-size scup and black sea bass.

Effect on target catch: 

Longfin squid catch was reduced by 88% and 84% in numbers and weight respectively.

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Reduction technique: 

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Study Type: 

Field study in the wild

Location: 

Northern Australia

Target catch: 

Prawns

Effect on bycatch species: 

Upward facing TED's reduced sea turtle bycatch by 99%

Effect on target catch: 

Reduced the proportion of soft and damaged prawns by 35.8% and reduced catches of tiger prawns by 6.3%

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