Install exclusion devices on fishing gear: Sea turtles

Overall effectiveness category Awaiting assessment
Number of studies: 3
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Background information and definitions

Aquatic reptiles may become trapped or entangled in fishing nets (e.g. trawl nets, hoop nets, fyke nets) and traps. Exclusion devices, such as grids, mesh, funnels, rings, or rectangular inserts, can be installed in an attempt to reduce the number of non-target animals that are caught.

Due to the number of studies found, this action has been split by species group. See here for: Tortoises, terrapins, side-necked & softshell turtles; Snakes & lizards or Crocodilians.

For studies that discuss the effect of using devices that allow reptiles to escape from fishing gear, see Install escape devices on fishing gear, and for studies on the effect of using a combination of exclusion and escape devices see Install exclusion and escape devices on fishing gear.

Study locations

Key messages

Three studies evaluated the effects of installing exclusion devices on fishing gear on sea turtle populations. One study was in the Gulf of Mexico (USA), one was in the Mid-Atlantic (USA) and one was off the coast of Western Australia.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Survival (1 study): One replicated, before-and-after study in the Gulf of Mexico found that when exclusion grids with escape holes were used in a shrimp trawl fishery there were fewer lethal strandings of loggerhead turtles compared to when grids were not used.

BEHAVIOUR (1 STUDY)

Use (1 study): One controlled study in the Mid-Atlantic found that when exclusion devices were used on scallop dredges there were fewer interactions with sea turtles than when no devices were used.

OTHER (1 STUDY)

Unwanted catch (1 study): One replicated study off the coast of Western Australia found that exclusion grids with escape hatches prevented sea turtles entering trawl nets.

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

A replicated, before-and-after study in 1980–2000 on beaches in the Gulf of Mexico, Texas, USA (Lewison et al. 2003) found that mandating use of exclusionary grids with escape holes (‘turtle excluder device’) in a shrimp trawl fishery reduced lethal strandings of loggerhead turtles Caretta caretta. Lethal strandings of loggerhead turtles reduced by 7% after turtle excluder device use was mandated in the fishery compared to beforehand (results reported as model outputs). There was not enough data to assess the effect on Kemp’s ridley Lepidochelys kempii turtles. Data from the Sea Turtle Stranding and Salvage Network was used to analyse changes in the size and number of stranded turtles before excluder devices were mandated in the shrimp trawl fishery (1986–1990) and afterwards (1995–1999).
Study and other actions tested
Referenced paper
Lewison R.L., Crowder L.B. & Shaver D.J. (2003) The impact of turtle excluder devices and fisheries closures on loggerhead and Kemp's ridley strandings in the Western Gulf of Mexico. Conservation Biology, 17, 1089-1097.
A controlled study in 2001–2008 of a pelagic area in the Mid-Atlantic, USA (Murray 2011) found that scallop dredges with chain mats had lower interaction rates with sea turtles than dredges without chain mats. Overall, the interaction rate of dredges with chain mats and sea turtles was estimated to be 86% lower than that of dredges without chain mats (data reported as statistical model results). The author reported a small number of entanglements with dredges with or without chain mats (see original paper). Turtles observed were loggerhead turtles Caretta caretta (47), Kemp’s ridley turtles Lepidochelys kempii (1) or unidentified species (16). Commercial vessels harvested sea scallops Placopecten magellanicus using dredges with and without chain mats attached (fishing effort for each not reported). Chain mats (vertical and horizontal chains hung on the dredge bag) became mandatory from September 2006 in part of the fishing area during May–November each year. Observers onboard the fishing vessels recorded turtles interacting with the dredge gear during a total of 125,658 h (approximately 3% of all commercial fishing trips) in 2001–2008.
Study and other actions tested
Referenced paper
Murray K.T. (2011) Interactions between sea turtles and dredge gear in the US sea scallop (Placopecten magellanicus) fishery, 2001-2008. Fisheries Research, 107, 137-146.
A replicated study in 2012 in demersal waters off the coast of Western Australia (Wakefield et al. 2017) found that exclusion grids with escape hatches (‘bycatch reduction device’) prevented sea turtles from entering the codend of trawl nets in a tropical teleost fishery. All 11 sea turtles that entered trawl nets modified with an exclusion grid and escape hatch were expelled (downward-facing grid with square mesh net: 6 turtles; upward-facing grid in diamond mesh: 5 turtles) and 9 of 11 turtles exited in <2.5 minutes. Loss of commercially-targeted teleost species from all trawls was 1.2–1.4% of catch. In June–December 2012, the catch (target and unwanted) from three commercial trawl vessels was monitored using in-net and onboard cameras during daylight. Vessels were fitted with either: upward-facing grid and escape hatch with diamond-mesh net (372 trawl hours on 2 vessels), downward-facing grid and escape hatch with diamond-mesh net (559 trawl hours on 2 vessels), or downward-facing grid and escape hatch with square mesh net (389 trawl hours on 1 vessel; see original paper for all specifications). Use of bycatch reduction grids with escape hatches had been mandatory in this fishery since 2006.
Study and other actions tested
Referenced paper
Wakefield C.B., Santana-Garcon J., Dorman S.R., Blight S., Denham A., Wakeford J., Molony B.W. & Newman S.J. (2017) Performance of bycatch reduction devices varies for chondrichthyan, reptile, and cetacean mitigation in demersal fish trawls: assimilating subsurface interactions and unaccounted mortality. ICES Journal of Marine Science, 74, 343-358.

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.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Reptile Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Install escape devices on fishing gear: Tortoises, terrapins, side-necked & softshell turtles Action Link	Awaiting assessment	3	Synopsis Link
Use non-ringed hooks Action Link	Awaiting assessment	1	Synopsis Link
Install escape devices on fishing gear: Snakes & lizards Action Link	Awaiting assessment	3	Synopsis Link