Turtle Excluder Devices Research Articles

Turtles, TEDs, tuna, dolphins, and diffusion of innovations: key drivers of adoption of bycatch reduction devices

AbstractFisheries extension programmes frequently fail to secure mandatory or voluntary adoption of bycatch reduction devices and techniques. Approaches for improving the outcomes of extension programmes are often based on ad hoc assessments and do not consider human behaviour or change theories. This paper offers an in-depth analysis of extension activities that led to various adoption outcomes in two prominent bycatch case studies in the United States: turtle excluder devices in shrimp trawl fisheries and dolphin bycatch in the tuna purse seine fishery. Using a grounded theory approach to text analysis of interviews and documents, I examine five periods of voluntary or mandatory adoption efforts. I explain the outcomes through the lens of diffusion of innovation theory. The most effective extension programme involved informative and persuasive efforts, enforced regulations, and commercially practical bycatch reduction devices. Voluntary adoption occurred under exceptional circumstances of public and political pressure and a device that offered substantial benefits to the adopter. The two periods of successful adoption applied the most core principles of diffusion theory. This paper concludes with recommendations for how change agents can apply diffusion theory to future fisheries extension programmes to improve the adoption of bycatch reduction devices.

Present status of conservation and management of sea turtle in Cox’s Bazar district, Bangladesh

The study was conducted to know the present status of conservation and management of sea turtle in Cox’s Bazar district, Bangladesh. Two species of sea turtles have been making nest in Bangladesh. A total of 251 turtle individuals were found. The highest nesting frequency of Olive ridley (108) and Green turtles (10) were observed in February. About 21,942 hatchlings were produced and released by the hatcheries for conservational step. A total of one hundred people were selected randomly for taking interview to assess their knowledge and attitude towards sea turtle conservation and management. Most of the respondents were fishermen (55%), student and housewife were 20% and 8%, 5% were found involving in business and rest 12% were involved in others activities. About 45% of the respondents thought that turtles were beneficial while other 40% of the respondents thought turtles were harmful. The rest of the respondents (15%) answered that they were not sure whether sea turtle was beneficial or harmful. Most of the fishermen did not know about Turtle Excluder Devices (TEDs) or its uses. It was found that the nesting of sea turtles was reducing and there was lack of knowledge among the people of the study area about the importance of sea turtle conservation and management.

The role of fisher engagement in the acceptance of turtle excluder devices in Georgia's shrimping industry

AbstractThe “Georgia Jumper” turtle excluder device (TED) is a rare example of a well-accepted conservation tool required by regulation. Mediated by the UGA Marine Extension and Georgia Sea Grant, Georgia's shrimping industry was integral to the design, revision, and implementation of excluder devices, since the earliest “jellyball shooter” proposed to NMFS in 1980. This paper highlights fisher involvement in the creation of the popular “Georgia Jumper” TED. Both the Diffusion of Innovation and the Traditional Ecological Knowledge literatures stress the importance of meaningful engagement of user communities in the development of new management approaches, and make specific recommendations for improving uptake of new methods. Consistent with literature expectations, fisher and industry participation in the development, testing, and implementation of TEDs has been key to the general acceptance of TEDs in Georgia. This paper illustrates the importance of fisher participation in conservation efforts such as these.

Net benefit: using a turtle excluder device in the Adriatic Sea

Net benefit: using a turtle excluder device in the Adriatic Sea

Voluntary fishing logbooks are essential for unveiling unsustainable bycatch levels and appropriate mitigating measures: The case of sea turtles in the Gulf of Manfredonia, Adriatic Sea

Abstract Studying the impact of bycatch on marine megafauna, including sea turtles, is challenging for a variety of technical and biological reasons. The Mediterranean Sea has among the highest levels of turtle bycatch globally, notably of the loggerhead sea turtle (Caretta caretta), and bottom trawling represents a particularly relevant threat. Bottom trawlers from a recently discovered neritic foraging area, the Gulf of Manfredonia, reported 1,152 loggerhead turtles incidentally caught in the period 2015–2020. Capture locations were available for 497 turtles. These data were complemented by the distribution of fishing effort obtained by the vessel monitoring system. High bycatch rates were observed, leading to more than an estimated 5,600 annual captures and to the death of a minimum of 560 large individuals with high reproductive value. These findings are extremely concerning for the affected population and require immediate action. A strong seasonality of turtle bycatch was observed, with most captures occurring in November–March when fishing effort occurs in shallow waters where turtles concentrate all year round. Therefore, a seasonal approach (e.g. adopting measures only in the high‐turtle bycatch season) can be pursued as long as the spatial distribution of fishing effort varies among seasons. However, such a spatio‐temporal pattern should be monitored; then, in the case of change, although more difficult to implement, an area‐based conservation approach should be pursued. Several recommendations are provided, including the urgent implementation of turtle excluder devices, at least on a seasonal basis. This case shows that identifying the best conservation approaches requires information on the actual spatio‐temporal pattern of turtle occurrence and bycatch. Such information can only be derived from spatial distribution of bycatch and fishing effort obtained through a voluntary collaboration of fishers.

Gillnet illumination as an effective measure to reduce sea turtle bycatch

The growing demand for fish around the world is an immediate threat to marine megafauna that are unintentionally captured in commercial and artisanal fishery operations. Bycatch mitigation strategies, such as turtle excluder devices, circle hooks, and net illumination, have successfully reduced this risk in some fisheries. We explored the effectiveness of gillnet illumination to reduce sea turtle captures in 2 artisanal fisheries (Mankoadze and Winneba, Ghana) under normal fishing conditions. We first quantified sea turtle bycatch in Ghana's artisanal gillnet fishery from 15 boats for 12 months. We then quantified catch of targeted species and sea turtle bycatch from 20 boats for 15 months (7427 net sets). For 10 of these boats, we placed a Centro Economy green light (1 LED) at each 10-m interval on the net. We also quantified target catch and sea turtle bycatch from 30 boats for 8 months (2250 net sets). In 15 of these boats, a Centro Deluxe green light (3 LEDs) was installed at 15-m intervals. Boats with economy lights and those with deluxe lights both exhibited an 81% decrease in sea turtle captures (W = 1, p < 0.001, n = 20; W = 215, p < 0.001, n = 30, respectively) compared with control boats without lights. Illuminated nets resulted in fewer turtle catches for leatherback (Dermochelys coriacea), olive ridley (Lepidochelys olivacea), and green sea turtles (Chelonia mydas) (p < 0.05 for all species). Target catch (mass) (W = 53, p = 0.853 n = 20; W = 76, p = 0.449, n = 23) and value (W = 50, p = 1, n = 20; W = 69, p = 0.728, = 23) were not different across treatments. Our study affirms net illumination can reduce capture rates of 3 species of sea turtles, including the imperiled leatherback. Gear modification methods can successfully reduce bycatch if they are affordable and have broad applications for multiple species in different fisheries.

On-board study of gas embolism in marine turtles caught in bottom trawl fisheries in the Atlantic Ocean

Decompression sickness (DCS) was first diagnosed in marine turtles in 2014. After capture in net fisheries, animals typically start showing clinical evidence of DCS hours after being hauled on-board, often dying if untreated. These turtles are normally immediately released without any understanding of subsequent clinical problems or outcome. The objectives of this study were to describe early occurrence and severity of gaseous embolism (GE) and DCS in marine turtles after incidental capture in trawl gear, and to provide estimates of on-board and post-release mortality. Twenty-eight marine turtles were examined on-board fishing vessels. All 20 turtles assessed by ultrasound and/or post-mortem examination developed GE, independent of season, depth and duration of trawl and ascent speed. Gas emboli were obvious by ultrasound within 15 minutes after surfacing and worsened over the course of 2 hours. Blood data were consistent with extreme lactic acidosis, reduced glomerular filtration, and stress. Twelve of 28 (43%) animals died on-board, and 3 of 15 (20%) active turtles released with satellite tags died within 6 days. This is the first empirically-based estimate of on-board and post-release mortality of bycaught marine turtles that has until now been unaccounted for in trawl fisheries not equipped with turtle excluder devices.

Factors affecting elasmobranch escape from turtle excluder devices (TEDs) in a tropical penaeid-trawl fishery

The use of turtle excluder devices (TEDs) has resulted in fewer elasmobranchs (i.e. sharks and rays) caught in tropical penaeid-trawl fisheries. However, very few studies in the primary literature have quantified the effects of various TED design aspects affecting the escape of elasmobranchs. Data collected by observers on board commercial trawlers operating in Australia’s northern prawn fishery (NPF) during 2001 were re-examined to quantify the effect of TEDs on catches of various elasmobranchs. During this sampling, a total of 6204 elasmobranchs were caught from 1440 net trawls. The 34 species identified, from 15 families and four taxonomic orders, were dominated by small carcharhinids (n = 2160, median total length = 75 cm) and dasyatids (n = 2030, median disc width = 24 cm). The TEDs assessed significantly reduced the numbers of large elasmobranchs caught: increasing fish size was found to result in higher escape for all taxonomic orders. Further, top-shooter TEDs increased the escape of Carcharhiniformes, while bottom-shooter TEDs facilitated greater escape of Myliobatiformes. Grid orientation had no effect on the escape of Orectolobiformes or Rhinopristiformes. Decreasing bar space was found to increase the escape of only one species, the Australian blacktip shark (Carcharhinus tilstoni). The TEDs facilitated the escape of several species of conservation interest including the globally endangered scalloped hammerhead (Sphyrna lewini) and zebra shark (Stegostoma fasciatum). However, the rostrum of the narrow sawfish (Anoxypristis cuspidata) inhibited the escape of this globally important species. Fishery-specific research is required to determine the appropriate TED bar spaces that reduce catches of elasmobranchs while minimising the loss of commercially important species.

Reducing Sea Turtle Bycatch in the Mediterranean Mixed Demersal Fisheries

The sea turtle (Caretta caretta) is the most common sea turtle in the Mediterranean, where incidental catches due to fishing activities are considered the main threat to its conservation. Over 50,000 capture events and likely over 10,000 deaths are estimated to occur in the Italian waters alone. However, current knowledge on the interaction of sea turtles with fishing gears and the implementation of mitigation measures are still poor to hinder the decline of turtle populations in the Mediterranean. In this basin, where fisheries are multispecies, multi-gears and multinational, making demersal fishing activities profitable while preserving sea turtles is a challenge. This study aimed to develop Bycatch Reducer Devices (BRDs) and alternative fishing gears to mitigate the impact of demersal fishing gears on sea turtles: a) hard and flexible Turtle Excluder Devices (TEDs) were tested in bottom trawling to immediately exclude turtles from the net; b) visual deterrents (ultraviolet LEDs) were used to illuminate set nets and to alter turtle visual cues, avoiding entanglement during depredation activity. The results showed the different devices did not affect the commercial catch, while bycatch reduction was instead evident. Thus, the study highlights that introducing mitigation measures to reduce sea turtle bycatch in the Mediterranean, where the bycatch of vulnerable species seems as a global issue, can be possible at least in certain areas and periods. Considering fishermen reticence to change the gear traditionally used, determining the optimal gear configuration to minimise commercial loss while reducing bycatch, is the main issue while introducing new technologies. Therefore, a global effort should be done to introduce BRDs in different areas and fisheries of the Mediterranean.

Challenges in adopting turtle excluder devices (TEDs) in Brazilian penaeid-trawl fisheries

The incidental capture and mortality of endangered, threatened and protected (ETP) marine species remains a global problem. Among the most problematic fishing methods is penaeid trawling, which is responsible for one quarter of the world's discarded bycatch and remains a key threatening process to ETP species (turtles and some elasmobranchs). So-called ‘turtle excluder devices’ (TEDs) legislated among USA penaeid trawlers and subsequently fleets in other countries during the 1990s alleviated some concerns over impacts to ETP species, but adoption has not been global. One country characterised by resistance to TEDs is Brazil—despite federal legislation mandating usage for almost 25 years. The reasons for this deficit, reiterated here via interviews with 64 southern penaeid-trawler captains, are threefold. First, are perceived issues with mandated designs and minimal third-party expertise, leading to a sustained misconception that TEDs simply do not work in Brazilian penaeid trawls. Second, is the perpetuated belief of minimum negative impacts to ETP species; exacerbated by few quantitative data. Third, is jurisdictional failure to promote the concept that slight economic loss associated with not catching ETP species (elasmobranchs) is necessary for broader ecological sustainability. We propose TED use among Brazilian penaeid-trawl fisheries might be promoted via a co-management strategy facilitated by sustained education and technical expertise from research providers encouraging fishers to develop fishery-specific solutions. If industries can be encouraged to accept the concept of TEDs, they might then be expected to refine and develop ownership of the most appropriate configurations.

Using the turtle excluder device (TED) in the pink shrimp trawling fishery off southern Brazil

The use of the turtle excluder device (TED) has been mandatory in Brazil since 1994. In spite of the importance of sea turtle bycatch reduction, TED effectiveness to maintain target species capture had never been evaluated in shrimp fisheries off southern Brazil. For this purpose, a test was carried out in November 2013 with the TED installed with two different configurations, top or bottom opening under the supervision of a technician of the National Oceanic and Atmospheric Administration (NOAA). Absolute catch and fishery yields were simultaneously monitored in 10 fishing hauls of a double-rig trawler by an onboard observer in one net equipped with a TED and the other without a TED. Although a Bayesian hypothesis test demonstrated no significant differences through the simultaneous comparison of absolute capture considering the use and nonuse of the TED, the credibility interval of posterior beta distributions intercepted almost its minimum limit which weakens the hypothesis of equality. In terms of orientation, the model mounted with the top opening showed no differences in absolute catches of the target species in respect to control.

Flexible Turtle Excluder Device (TED): an effective tool for Mediterranean coastal multispecies bottom trawl fisheries

The effect of a flexible Turtle Excluder Device (TED) on the catching efficiency and performance of a commercial bottom trawl was tested in a gear comparison study for a Mediterranean coastal multispecies bottom trawl fishery. The device affected neither bottom trawl technical performances (horizontal and vertical net opening and door spread) nor did it increase the required towing force, hence fuel consumption remained constant. Comparison of commercial catches for the major species demonstrated that using the TED did not affect catching efficiency, while it reduced the amount of debris. The device did not influence the size of commercial species, leaving the selective performance of the trawl unmodified. Underwater video camera recordings documented that fish caught in the net swam through the grid and easily reached the cod-end, missing the TED escape opening. Easy storage and improved catch retention compared with previous devices tested in this area make the present flexible TED a practical and valuable solution to reduce turtle bycatch in coastal Mediterranean demersal multispecies fisheries.

An Analysis of Innovation Decision Process among the Mechanized Fishing Boat Operators

The study was conducted among the large mechanised wooden trawl boat operators involved in marine fishing in three selected major fishing harbours of the country viz ., Visakhapatnam in Andhra Pradesh, Thoothukudi in Tamil Nadu and Veraval in Gujarat. The socio-economic and psychological characteristics of fishermen were assessed. The overall innovation decision efficiency index (IDEI) score was 55.25%. The findings on centre-wise and technology-wise IDEI scores are also discussed. The respondents from the three fishing centres differed significantly (p<0.05) in their innovation decision behaviour pertaining to adoption of the technologies viz ., FRP sheathing for fishing vessels, marine anticorrosive painting, marine antifouling painting, turtle excluder device (TED), square mesh codend and use of adequate ice onboard. The regression coefficients of four variables viz., investment on fishing craft and gears, innovativeness, training undergone and extent of linkage with research and extension systems significantly and positively influenced the innovation decision process (p<0.05). The R2 value was found to be 0.838, indicating that the 17 characteristics taken together accounted to 83.80% of variations in the innovation decision efficiency level. The constraints in the innovation adoption decision process pertaining to the identified technologies were also documented.

EVALUACIÓN EXPERIMENTAL DE DISPOSITIVOS EXCLUIDORES DE FAUNA ACOMPAÑANTE EN REDES DE ARRASTRE PARA CAMARÓN DE AGUAS SOMERAS EN EL PACÍFICO COLOMBIANO

The effects of the introduction of bycatch reduction devices in the shrimp trawling fleet in shallow waters of the Colombian Pacific, were tested through an experiment fishing involving the industrial fishing sector. Following the commercial fishing conditions, we evaluated the turtle excluder device (TED), the "fish eye" fish excluder device (OP) and the combination of both devices (DET + OP). The variables used to assess the effects of the devices on the different components of the catch [target catch (CO), bycatch (CI) and discard (D)] were the relative abundance and length distribution of individuals. The effects of device type, fishing areas and their interaction were assessed by two-way ANOVA, while the effect of the devices on the length structure of catches was evaluated by comparison of size distributions using the Chi-square test. The overall ratio between the target catch (shrimp) and bycatch was 1:14. Groups of species caught were fish (83 %), crustaceans (13 %), molluscs (1.1 %), cnidarians (1.3 %), reptiles (1 %) and echinoderms (0.6 %), which together included 216 taxa. The variables TCO, CI (commercial fish) and D (discards) all varied significantly between fishing grounds. The devices did not affect shrimp catch in trawl nets, but fish catch did depending on the fishing grounds. The performance of devices showed with respect to the CI that DET excluded 45 %, the OP 36 % and OP+DET 78 %, while the discard was reduced by 22 % with the DET, 39 % with OP and 58 % in the DET + OP. The length distributions of the trawl-net with devices did differ significantly from the control net. The devices tested reduced the impact of trawling on marine biodiversity by allowing the escape of many species. However, the escape of commercial size fish could affect the income of fishermen.

EVALUACIÓN EXPERIMENTAL BIOECONÓMICA DE CAMBIOS EN LA TECNOLOGÍA DE CAPTURA DE CAMARÓN CON REDES DE ARRASTRE EN AGUAS SOMERAS DEL PACÍFICO COLOMBIANO

With active participation of the fishing industry, the biological and economic effects of technological changes in shrimp trawling fishing on the Colombian Pacific coast were evaluated to reduce bycatch and fuel consumption. Two boats were used simultaneously in experimental fishing surveys that compared the performance of a trawl net prototype and the conventional trawl net used by the fleet, quantifying in both cases the effects of the turtle excluder device (DET) and two fishing grounds (central-north and centralsouth). The performance fishing variables used to test the effect of changes in fishing technology on the target catch (CO) and the bycatch [incidental catch (CI) and discard (D)], were the relative fish or shellfish abundance, individual sizes, net revenues and fuel consumption by boat. Effects of fishing grounds, trawl net type, presence of device and the interaction between these factors, were evaluated using a three way ANOVA. The effect of new technologies on lengths of organisms from the catch components (CO, CI and D), was evaluated by comparison of the length frequency distributions using the Chi-square test and by modeling size selectivity of the trawl net prototype. Differences in fuel consumption between types of trawl nets of each boat were evaluated by t- test. Totals of CO, CI and D were 1436, 12163 and 15428 kg, respectively, with a global proportion between target catch and bycatch of 1:19. The bycatch was composed by 217 taxa, of which 32 families, mainly fishes, made up the CI and 52 were part of discard (fish, crustaceans and mollusks). The CO showed greater abundance on the central-north fishing ground than on the central-south one, whereas a contrary tendency showed the CI and D, in response to resources availability provided by oceanographic conditions and habitat. The prototype trawl net reduced in 34.8% the CO, 16.3% the CI and 28.7% the D (45% of bycatch), being significant the reductions of CO and D; whereas the DET reduced significantly the CI and D, without affecting the CO mainly in the conventional trawl net. Lengths frequency distributions of CO, CI and D differed between trawl net types, with a clear tendency to that the prototype trawl net selected greater lengths of shrimps and fishes. The use of the trawl net prototype implied a non significant reduction of the net revenues by haul (23.4%), whereas the use of the DET represented a significant reduction in net revenues of 77 %, mainly in the conventional trawl net. The prototype trawl net with prototype trawl doors reduced the fuel consumption in 36%, whereas the same net with conventional trawl doors reduced 23 %, which represents a saving in variable costs per fishing trip between $ 10`125 000 and $ 6`468 750 (Colombian pesos in 2005). The adoption of new fishing technologies by the industrial shrimp fleet from the Colombian Pacific has scientific evidence that it demonstrates the reduction of byctach without putting at risk the economic benefits derived from a selective fishing

Ray bycatch in a tropical shrimp fishery: Do Bycatch Reduction Devices and Turtle Excluder Devices effectively exclude rays?

Worldwide, many species of elasmobranchs (Chondrichthyes: Elasmobranchii) are currently threatened by marine fisheries activity and are on the Red List of the International Union for Conservation of Nature (IUCN). Although Bycatch Reduction Devices (BRDs) for teleost fish and Turtle Excluder Devices (TEDs) are now widespread in tropical shrimp trawling, information on their ability to mitigate bycatch of elasmobranchs, particularly rays (Batoidea), is scarce and limited to only a few isolated fisheries. The objective of this study was to evaluate the potential of trawls fitted with a square-mesh panel BRD and super-shooter TED in reducing ray bycatch. In this study, 65 catch-comparison hauls were conducted in the Atlantic seabob shrimp (Xiphopenaeus kroyeri) fishery off Suriname. Trawls with a BRD and TED combination reduced ray catch rate by 36%. A 21% reduction in mean size indicated the preferential exclusion of large rays. Hence, high escape ratios were observed for Dasyatis geijskesi (77%), a large-sized species, while exclusion of the small species Urotrygon microphthalmum was not significant, although their disc width is small enough to pass through the meshes of the BRD. Furthermore, a size-dependent escape for the two most abundant mid-sized ray species Dasyatis guttata and Gymnura micrura was observed. Exclusion-at-size differed for both species, however, likely related to species-specific morphology or behavior in response to the TED. This study shows that the combination of BRD and TED causes an important reduction in ray bycatch in seabob shrimp fisheries off Suriname. The great reduction in catch of large-sized rays is positive, but the mortality of juvenile rays is likely to have negative consequences for their populations. We therefore recommend gear-based and non-gear adaptations to further reduce the bycatch of small-sized rays.

The importance of location and operational fishing factors in estimating and reducing loggerhead turtle (Caretta caretta) interactions in U.S. bottom trawl gear

Mortalities due to interactions between loggerhead (Caretta caretta) turtles and commercial bottom trawl fisheries impede the recovery of loggerhead populations worldwide. In the U.S. Mid-Atlantic, several hundred loggerheads interact with commercial bottom trawl gear each year despite the implementation of temporal and spatial conservation measures. In this analysis a Generalized Additive Model (GAM) is developed using fisheries observer data to estimate the magnitude of loggerhead interactions and mortalities in U.S. Mid-Atlantic bottom trawl gear from 2009 to 2013. Based on the results, the potential conservation benefits of hypothetical spatial closures or turtle excluder device (TED) requirements in times and areas of high estimated interactions is then evaluated. Loggerhead interaction rates were modeled as a function of retained catch, depth, latitude, and sea surface temperature. From 2009–2013, a total of 1156 (CV=0.13, 908–1488) loggerheads were estimated to have interacted with bottom trawl gear in the U.S. Mid-Atlantic, of which 479 resulted in mortality. The total number of estimated interactions was equivalent to 166 adults, of which 68 resulted in mortality. The trawl fishery targeting Atlantic croaker (Micropogonias undulatus) in the southern Mid-Atlantic had the highest turtle interactions among fisheries investigated; this may be due to larger mesh sizes in the mouth of the trawl and high headline height of the gear. The potential conservation benefit of hypothetical spatial closures or TEDs differs depending on the metric used to define “benefit”, and further depends on factors such as the spatial and temporal design of the closure, the magnitude and distribution of effort displacement, the spatial distribution of observed loggerhead life stages, and the assumed survival rate of animals passing through TEDs.

An assessment of bycatch reduction devices in Kuwait's shrimp trawl fishery

Summary Three bycatch reduction devices (BRDs), i.e. the Turtle Excluder Device (TED), Square Mesh Codend (SMC) and Fisheye (FE), were tested to evaluate their feasibility in the Kuwait shrimp-trawl fishery. All three BRDs could be fitted to a shrimp trawl and normal fishing activities could be conducted both on an industrial trawler and an artisanal dhow boat. The comparisons of the catch from a net equipped with a BRD on one side and a standard net (exact same net configuration but without a BRD device) on the other side of a double-rigged shrimp trawler (steel boat) showed different results in the three BRD types. The net fitted with a TED performed well without capturing any turtles or large animals, and did not significantly reduce shrimp catch or fish bycatch (124.4: 117.0 and 852.0: 905.8, both P > 0.05). Although the SMC reduced both shrimp catch and bycatch in general, the Wilcoxon's signed rank test showed a significant difference only among bycatch (1034.2: 1147.3, P < 0.05). Chi-square tests showed that a net fitted with SMC caught significantly larger shrimp (more large and fewer small sizes) than a standard net for all three major shrimp species (33.5: 32.5; 26.9: 25.0; 20.3: 19.3, all P < 0.01). This indicates that the SMC reduced the catch of small size shrimps as well as smaller size fish. A net fitted with a fisheye significantly reduced both the shrimp catch and bycatch (137.4: 174.6; 997.5: 1377.8, both P < 0.01); the shrimp loss was probably due to an inappropriate location of the FE in the trawl.

Effects of bycatch reduction devices in Queensland's (Australia) deepwater eastern king prawn (Melicertus plebejus) trawl fishery

This paper quantifies the effects of a square mesh codend bycatch reduction device (BRD) and turtle excluder device (TED) in the deepwater eastern king prawn (Melicertus plebejus) fishery on the southeast Queensland coast, based upon on a 10-day research charter. The bycatch comprised 224 taxa, mainly gurnards, flatheads, sandpaper fish, hermit and charybdid crabs, mantis shrimps, sand dollars (i.e. sea urchins), dragonets, snipefish, carids and lizardfish. The total mean bycatch rate was comparatively low (1114.0gha−1 from the standard diamond mesh codend), mainly because of the relatively deep waters associated with the fishery. When the TED and square mesh codend BRD were used together the total mean bycatch rate was significantly reduced by 29% (796.0gha−1) compared to the standard codend, with no significant effect on the prawn catch rate or size frequency distribution. Several bycatch species experienced very large reductions in mean catch rate, due to the square mesh codend, including Graham's conger Gnathophis grahamii (98.2% reduction), dumpling squid Euprymna tasmanica (95.9%), shortsnout threadsail Aulopus curtirostris (90.6%) and sandpaper fish Aulotrachichthys sp. (90.0%). Multidimensional scaling indicated that bycatch assemblages were more affected by latitude and depth than codend type. Based on the results, we recommend that the 47.6mm square mesh codend be made mandatory in the deepwater eastern king prawn fishery as a highly effective BRD.

Refinement of bycatch reduction devices to exclude freshwater turtles from commercial fishing nets

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 22:251-261 (2013) - DOI: https://doi.org/10.3354/esr00549 Refinement of bycatch reduction devices to exclude freshwater turtles from commercial fishing nets Nicholas A. Cairns1,2,*, Lauren J. Stoot1,2, Gabriel Blouin-Demers2, Steven J. Cooke1,3 1Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, 1125 Colonel By Dr., Ottawa, Ontario K1S 5B6, Canada 2Herpetology Laboratory, Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario K1N 6N5, Canada 3Institute of Environmental Science, Carleton University, 1125 Colonel By Dr., Ottawa, Ontario K1S 5B6, Canada *Email: nacairns@gmail.com ABSTRACT: The capture of non-target species is a conservation issue in many commercial fisheries. Bycatch reduction devices (BRDs) are commonly used as mitigation tools to improve selectivity of fishing gear and thus reduce bycatch. The aim of this paper was to refine a simple BRD to exclude 4 species of freshwater turtles from commercial fyke nets in a fishery in eastern Ontario, Canada, that targets a variety of fish species. We tested the efficacy of modified exclusion devices (vertically oriented exclusion bars and a constriction rectangle) using an adaptive approach including in situ observations, controlled behavioural experiments and field trials. In situ observations made by camera were used to estimate turtle catchability and to document turtle behaviour during net interactions, which was used to inform BRD design and placement. In controlled behavioural experiments, the passage rates of target fish (i.e. sunfish), bycatch fish (e.g. game fish) and turtles across a modified net throat suggested that a 5 cm constriction rectangle should be suitable for reducing bycatch in this fishery; turtles readily turned sideways to pass through larger openings. Paired field trials indicated that a 5 cm constriction rectangle reduced turtle bycatch for all species. The constriction rectangle also reduced captures of non-target game fish. In controlled behavioural experiments, there was little evidence of a reduction in catches of target sunfish; however, in paired field trials, there was a 23.4% reduction in sunfish catches. We recommend the use of a 5 cm constriction rectangle for fisheries targeting sunfish in areas where freshwater turtles are present. KEY WORDS: Non-target species · Small-scale fishery · Catchability · Turtle excluder device · Selectivity · Sunfish · Time-lapse photography Full text in pdf format PreviousNextCite this article as: Cairns NA, Stoot LJ, Blouin-Demers G, Cooke SJ (2013) Refinement of bycatch reduction devices to exclude freshwater turtles from commercial fishing nets. Endang Species Res 22:251-261. https://doi.org/10.3354/esr00549 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 22, No. 3. Online publication date: December 19, 2013 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2013 Inter-Research.