Study

Identification and evaluation of shark bycatch in Georgia’s commercial shrimp trawl fishery with implications for management

  • Published source details Belcher C.N. & Jennings C.A. (2011) Identification and evaluation of shark bycatch in Georgia’s commercial shrimp trawl fishery with implications for management. Fisheries Management and Ecology, 18, 104-112.

Actions

This study is summarised as evidence for the following.

Action Category

Fit a size-sorting escape grid (rigid or flexible) and large, supported escape openings to trawl nets

Action Link
Marine Fish Conservation

Use a different design or configuration of size-sorting escape grid/system in trawl fishing gear (bottom and mid-water)

Action Link
Marine Fish Conservation

Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

Action Link
Marine Fish Conservation
  1. Fit a size-sorting escape grid (rigid or flexible) and large, supported escape openings to trawl nets

    A replicated study in 1995–1998 of seabed sites in the Atlantic Ocean off the coast of Georgia, USA (Belcher & Jennings 2011) found that the amount of unwanted sharks (Selachii) caught by commercial shrimp trawl nets did not differ between those fitted with both a large, supported opening and rigid size-sorting escape grid compared to just a grid. Average shark catch rates in mongoose nets (most commonly used commercially) fitted with ‘Super Shooter’ grids were similar with and without a ‘Fisheye’ escape opening in the codend (with: 15 sharks net/h, without: 17 sharks net/h). In addition, compared to other trawl/grid types without Fisheyes, shark catch rate with the mongoose/Super Shooter/Fisheye combination was not significantly different (mongoose/Georgia Jumper: 2, flat net/Super Shooter: 2, triple wing net/Super Shooter: 23 sharks/net/h). In April 1995–January 1998 (except February and March), data were collected by fishery observers from 30 trawl deployments using mongoose, flat and triple wing nets, carried out by commercial vessels fishing for shrimp. All nets had a size-sorting escape grid (Super Shooter or Georgia Jumper). Nine mongoose net deployments were made with the supported escape opening (Fisheye) and eight without. See original paper for further gear descriptions.

    (Summarised by: Leo Clarke)

  2. Use a different design or configuration of size-sorting escape grid/system in trawl fishing gear (bottom and mid-water)

    A replicated, randomized, controlled study in 1995–1998 at multiple coastal sites in the Atlantic Ocean, USA (Belcher & Jennings 2011) found that the effect of using different designs or configurations of size-sorting escape grid on reducing the amount of unwanted shark (Selachii) catch in shrimp trawl nets varied with the type of trawl net used. Across all grid and trawl net combinations, shark catch rates were lowest in mongoose commercial trawl nets fitted with a Georgia Jumper grid (2 sharks/net/h) and flat nets with a Super Shooter grid (2 sharks/net/h). Intermediate catch rates (similar to both the lowest and highest rates) were found for mongoose nets with a Super Shooter grid, either with (15 sharks/net/h) or without (17 sharks/net/h) an additional catch escape device (a Fish Eye). The highest catch rates were found for a triple-wing net with a Super Shooter grid (23 sharks/net/h). A subset of data (June-July) was taken from monthly shrimp trawl discard data collected during the shrimp trawling season (April-January) from 1995–1998, onboard vessels engaged in the shrimp Penaeidae fishery off Georgia. Catches sampled were randomly selected from one of three commercial shrimp trawl net designs: flat net, mongoose or triple wing trawls. Each used a Super Shooter escape grid, except some mongoose nets that used a Georgia Jumper grid. Both grid types were metal and oval but differed in the angle of the bars. Some mongoose net/Super Shooter combinations also included a ‘Fish Eye’ escape opening in the codend. Full details of trawl and grid designs are provided in the original study.

    (Summarised by: Leo Clarke)

  3. Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

    A replicated, randomized study in 1995–1998 at multiple coastal sites in the Atlantic Ocean, USA (Belcher & Jennings 2011) found that the amount of unwanted shark catch in shrimp trawls fitted with a rigid size-sorting escape grid depended on the type of trawl net and grid used. Commercial mongoose and flat net shrimp trawls fitted with two types of rigid grids with bottom escape openings (Super Shooter or Georgia Jumper respectively) caught fewer unwanted sharks Elasmobranchii (2/h) than triple wing shrimp trawl nets fitted with only Super Shooter grids (23/h). Shark catch rates in mongoose trawl nets fitted with Super Shooter grids were not statistically different to other gear combinations, both with and without an additional supported escape opening (Fish Eye) in the codend (with: 15/h, without: 17/h). In addition, the duration and towing speed of the trawl deployments did not affect shark catch rates (data reported as statistical model results). From April 1995–January 1998 (except February and March each year) shrimp trawl discard data were collected by fishery observers onboard vessels in the penaeid Penaeidae shrimp fishery off Georgia. Vessels randomly selected one of three commercial shrimp trawl net designs to use: flat net, mongoose or triple wing trawls. Each was fitted with a ‘Super Shooter’ escape grid, except some mongoose nets that used a ‘Georgia Jumper’ grid. Both grid types were metal and oval, but differed in the angle of the bars. Some mongoose net/Super Shooter combinations also included a ‘Fish Eye’ escape opening in the codend. Full details of trawl and grid designs are provided in the original study.

    (Summarised by: Leo Clarke)

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