Action

Install exclusion and escape devices on fishing gear

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Six studies evaluated the effects of installing exclusion and escape devices on fishing gear on reptile populations. Two studies each were off the coast of Australia, in the Gulf of Carpentaria (Australia) and in the Adriatic Sea.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (0 STUDIES)

BEHAVIOUR (2 STUDIES)

  • Use (2 studies): Two replicated studies (including one controlled study) in the Adriatic Sea found that one or two loggerhead turtles were able to escape from a trawl net with an exclusion and escape device.

OTHER (5 STUDIES)

  • Unwanted catch (5 studies): Four studies (including two replicated, paired, controlled studies) off the coast of Australia and in the Gulf of Carpentaria (Australia) found that that trawl nets with an exclusion and escape device caught fewer loggerhead turtles or sea turtles and sea snakes compared to unmodified nets. One replicated study in the Adriatic Sea found that no loggerhead turtles were caught by a trawl net with an exclusion and escape device.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A replicated, controlled study in 1991–1992 in oceanic and estuarine waters off the coast of Queensland, Australia (Robins-Troeger et al. 1994) found that when a soft mesh panel with escape hole (‘Morrison soft TED’) was added to a trawl net no loggerhead turtles Caretta caretta were caught accidentally. No loggerhead turtles were caught in the modified net but were occasionally caught in the unmodified net (no data on turtles are provided). Catch rates of target prawns Penaeus spp. and Metapenaeus bennettae varied between no significant reduction and a 29% reduction in modified compared to unmodified nets, depending on location and season (data reported as a cross-site analysis of fishing power, see original paper for details). Trawl nets modified by adding a polypropylene mesh panel with an escape hole in front of the codend were tested in two trials (May 1991 and January 1992) on a 15 m research trawler in an oceanic site with sandy substrate and an estuarine site with a muddy bottom. Unmodified nets were towed first (number of trawls not specified) and then the modified net was used. Between 17 and 23 tows were completed in each trial, each lasting 45–100 minutes.

    Study and other actions tested
  2. A replicated, paired, controlled study (years not provided) in five oceanic-sand and estuarine-silt-bottomed sites in the coast off of southeastern Queensland, Australia (Robins-Troeger et al. 1995) found that adding a device that included a funnel to direct unwanted catch, an upward-facing flexible grid and covered escape panel (“ausTED” design turtle excluder device) onto a trawl net reduced the catch of loggerhead turtles Caretta caretta compared to a standard net. Using the device reduced the catch of loggerhead turtles (0 turtles) compared to nets without the device (7 turtles). In a separate experiment, six juvenile green turtles Chelonia mydas were placed in the path of nets with the device. Only three passed into the net entrance and all were successfully excluded from the main part of the net. Commercially-targeted prawn Penaeus spp. and Metapenaeus spp. catch rates, size and quality were similar in nets with and without the device (see original paper for details). Two commercial 6.8 m long trawl nets (40 mm mesh) were attached to a 15 m trawler. The device was fitted to one of the nets. Between 13 and 27 linear tows were conducted per site (each 60 minutes long, 85 tows used the device in total). Juvenile green turtles placed in the path of the net were videoed to assess how the device assisted their escape.

    Study and other actions tested
  3. A randomized, paired, controlled study in 1995 in seabed areas in the Gulf of Carpentaria, northern Australia (Brewer et al. 1998) found that trawl nets fitted with one of three different grids accompanied by an escape hole (“turtle excluder device”) and a secondary escape zone (“bycatch reduction device”) reduced the catch of sea turtles and sea snakes, compared to unmodified nets. No statistical tests were carried out. Nets fitted with both a turtle excluder device and a bycatch reduction device caught fewer turtles (0.005 turtles/tow, 1 individual) compared to unmodified nets (0.10 turtles/tow, 11 individuals). Overall, nets fitted with both a turtle excluder device and a bycatch reduction device caught fewer sea snakes (0.36 snakes/tow, 45 individuals), than unmodified nets (0.42 snakes/tow, 15 individuals). However, some combinations of a turtle excluder device and a bycatch reduction device caught fewer sea snakes (flexible upward grid with fisheye in front of grid: 0.2 snakes/tow, 3 individuals; square upward grid with square mesh: 0.2 snakes/tow, 8 individuals) compared to unmodified nets or other combinations tested (see original paper for details). The unwanted catch included three species of turtles and three of snakes. The effect of grids and escape zones on the commercially targeted prawn catch varied by design (see original paper for details). Devices tested included a flexible, circular, upward tilted grid with top escape hole (‘AusTED’) and a secondary escape zone in front of the grid; a square, upward tilted grid with a top escape hole (‘Nordmøre’) and secondary escape zone after the grid; and a circular downward tilted grid (‘Super Shooter’) with a secondary escape zone after the grid. Secondary escape zones included different configurations of a ‘fish eye’ or ‘square mesh window’ (see original paper for full details). Vessels towed twin Florida Flyer prawn trawl nets from each side of the vessel in scientific trials of one-month duration (sea turtles: February 1995, October 1995, October 1996; sea snakes: October 1995). Nets fitted with one of the designs of grid and an unmodified net were randomly assigned to either side of the vessel.

    Study and other actions tested
  4. A replicated, paired, controlled study in 2001 in areas of seabed in the Gulf of Carpentaria, northern Australia (Brewer et al. 2006) found that nets fitted with a mesh escape window (“bycatch reduction device”) and a grid (“turtle excluder device”) caught fewer sea turtles and sea snakes, compared to unmodified nets. Nets fitted with both an escape window and grid caught 100% fewer sea turtles (with devices: 0 turtles; unmodified nets: 66 turtles) and 5% fewer sea snakes (number not provided), compared to unmodified nets. The use of a “turtle excluder device” and a “bycatch reduction device” had been compulsory since 2000 in the Australian prawn fishery. Commercial vessels towed twin Florida Flyer prawn trawl nets from each side of the vessels in August–November 2001. Modified nets were fitted with one of two designs of escape window (a “Bigeye” design or a square-mesh escape window) and either an upward or downward facing exclusion grid (rigid or semi-rigid frame with ≤120 mm bar spacing and an opening of ≥700 mm). A modified and an unmodified net were randomly assigned to either side of the vessel and towed simultaneously (33 modified nets examined for sea turtles, 214 for sea snakes; 84 unmodified nets for sea turtles, 432 for sea snakes). The combinations of various device designs were not compared. Where possible, sea turtles (4 species) and sea snakes (12 species) caught were identified to species. The “Bigeye” design was later removed from the Australian list of approved escape zone designs.

    Study and other actions tested
  5. A replicated study in 2008 on the sea bottom in the Adriatic Sea (Sala et al. 2011) found that adding a downward-facing grid and bottom escape hole (‘Super Shooter’ model of ‘turtle excluder device’) to standard trawl nets allowed a loggerhead turtle Caretta caretta to escape after being caught. No statistical tests were carried out for unwanted catch. During trials, one turtle entered a trawl net modified with a ‘Super Shooter’ and was successfully excluded. No turtles entered trawl nets modified with two other excluder devices that were tested. The ‘Super Shooter’ retained the most catch (20 kg/tow) and had the lowest discards (9 kg/tow) of commercially-targeted European hake Merluccius merluccius, compared to the two other excluder devices that were tested (retention rate: 13–18 kg/tow; discard rate: 12–21 kg/tow). All turtle excluder devices were downward-facing grids (set to an angle of 45–48 degrees) located immediately in front of the codend and accompanied by a bottom escape hole. Four different excluder devices were tested: a lightweight rigid aluminium grid (which broke down and was excluded from the study); a flexible mixed-cable grid; a semi-rigid grid of steel and rubber; a ‘Super Shooter’ aluminium grid with enlarged space between bars (see original paper for details). Data were collected during 42 tows with an average duration of 48 minutes (11–15 tows/excluder device). Excluder devices were tested on a four-sided net using standard commercial trawl fishing rigging and operation.

    Study and other actions tested
  6. A replicated, controlled study in 2014 on muddy-sandy seabed in the northern Adriatic Sea (Lucchetti et al. 2016) found that using an upward-facing flexible grid with escape hole (‘turtle excluder device’) in a bottom-trawl net allowed loggerhead turtles Caretta caretta to escape after entering the net. No statistical tests were carried out. Nets with a flexible grid and escape hole allowed two loggerhead turtles Caretta caretta to escape¸ while one turtle was caught in an unmodified net. Commercial fish catch was similar between modified and unmodified nets (modified net: 8–26 kg/hr; unmodified net: 10–34 kg/hr). Fifty-five bottom trawl trials were carried out (20–40 m depths) in spring, autumn and winter 2014. A total of 25 trawls used the experimental turtle excluder device and 30 used a traditional net as a control (nets were 58 m long). The turtle excluder device was a circular plastic grid set at an upward angle with a top escape hole (a net panel with three sides sewn onto the trawl net) installed front of the codend. Escapes from modified nets were monitored using an underwater camera.

    Study and other actions tested
Please cite as:

Sainsbury K.A., Morgan W.H., Watson M., Rotem G., Bouskila A., Smith R.K. & Sutherland W.J. (2021) Reptile Conservation: Global Evidence for the Effects of Interventions for reptiles. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

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Reptile Conservation - Published 2021

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