Reduce Sea Turtle Bycatch Research Articles

Developing visual deterrents to reduce sea turtle bycatch in gill net fisheries

Visual cues play important roles in sea turtle foraging behavior and likely influence their interactions with fishing gear. Altering these cues may be a useful strategy to reduce the inci- dental catch of sea turtles in various fisheries. We examined the potential effectiveness of 3 visual cues — shark shapes placed along the length of the gill net, illumination of nets by LED lights, and nets illuminated with chemical lightsticks — in reducing bycatch of green sea turtles Chelonia mydas in gill nets. We then adapted these potential deterrents into commercial bottom gill net fishery to quantify their effects on target fish catch rates and the catch value. Our results indicate that the pres- ence of shark shapes significantly reduced the mean catch rates of green turtles by 54% but also reduced target catch by 45% and, correspondingly, catch value by 47%. In contrast, nets illuminated by LED lights significantly reduced mean sea turtle catch rates by 40% while having negligible impacts on target catch and catch value. Similarly, nets illuminated by chemical lightsticks also sig- nificantly reduced mean sea turtle catch rates by 60% while having no significant impact on target catch and catch value. These results illustrate the potential for modifying fishing gear with visual deterrents to effectively reduce sea turtle catch rates.

Using telemetry to mitigate the bycatch of long‐lived marine vertebrates

The unintended bycatch of long-lived marine species in fishing gear is an important global conservation issue. One suite of management approaches used to address this problem restricts or modifies fishing practices in areas where the probability of bycatch is believed to be high. Information on the distribution and behavior of the bycaught species is a desirable component of any such scheme, but such observations are often lacking. We describe a spatially explicit approach that combines data on the distribution of fishing effort and observations of the distribution of bycatch species derived from satellite telemetry. In a case study, we used a spatially explicit predator-prey model to investigate real-time interactions between three species of sea turtles (Caretta caretta, Chelonia mydas, and Lepidochelys kempii) and the fall large-mesh gill net fishery that targets southern flounder (Paralichthys lethostigma) in Pamlico Sound, North Carolina between 2002 and 2004. The model calculates a spatial overlap index, thereby allowing us to identify which fishing areas have the greatest risk of encountering bycatch. In this study, our telemetry deployments (n = 50) were designed specifically to address existing fisheries conservation measures in Pamlico Sound intended to reduce sea turtle bycatch. We were able to predict the spatial distribution of bycatch and evaluate management measures. This approach offers a powerful tool to managers faced with the need to reduce bycatch.

Sea turtle bycatch to fish catch ratios for differentiating Hawaii longline-caught seafood products

Sea turtles can be incidentally caught in pelagic longline fishing gear targeting tuna and swordfish. Bycatch to fish catch (B/C) ratios can differentiate seafood based on sea turtle impacts. This study demonstrates the use of B/C ratios indexed to the weight of fish catch: (1) to report on the significant progress in reducing sea turtle bycatch in Hawaii's swordfish longline sector and (2) to compare Hawaii and other Pacific longline fisheries by number of sea turtle interactions per weight of catch. Hawaii's longline tuna fishery sets the benchmark of 1 sea turtle interaction per 190,000 kg of tuna caught.

Quantitative evaluation of the performance of a permit auction system in reducing bycatch of sea turtles in the Hawaii Swordfish longline fishery

Many authors have suggested the use of a cap and trade auction system to help reduce bycatch—the incidental take of species by fishing gear targeting other species—of sea turtles in the Hawaii-based swordfish longline fishery. However, we know of no quantitative evaluations of the method. We present a simple mathematical model to serve as a framework to evaluate bycatch auction systems quantitatively. We conclude that cap and trade auction systems have the potential to reduce sea turtle bycatch by creating a financial incentive, while keeping permit costs down to 2–3% of total revenues. While stringent regulations aimed at conserving endangered sea turtles would still be essential, implementation of an auction for issuing transferable bycatch permits would likely enhance the economic efficiency of the fleet. Sea turtle mortality could be reduced further if a shrinking cap on total turtle mortality was introduced, taking advantage of the incentives for reducing turtle mortality that are introduced by the cap and trade auction system.

Hierarchical modeling of bycatch rates of sea turtles in the western North Atlantic

Previous studies indicate that the locations of the endangered loggerhead Caretta caretta and critically endangered leatherback Dermochelys coriacea sea turtles are influenced by water temperatures, and that incidental catch rates in the pelagic longline fishery vary by region. We present a Bayesian hierarchical model to examine the effects of environmental variables, including water temperature, on the number of sea turtles captured in the US pelagic longline fishery in the western North Atlantic. The modeling structure is highly flexible, utilizes a Bayesian model selection technique, and is fully implemented in the software program WinBUGS. The number of sea turtles captured is modeled as a zero-inflated Poisson distribution and the model incorporates fixed effects to examine region-specific differences in the parameter estimates. Results indicate that water tem- perature, region, bottom depth, and target species are all significant predictors of the number of log- gerhead sea turtles captured. For leatherback sea turtles, the model with only target species had the most posterior model weight, though a re-parameterization of the model indicates that temperature influences the zero-inflation parameter. The relationship between the number of sea turtles captured and the variables of interest all varied by region. This suggests that management decisions aimed at reducing sea turtle bycatch may be more effective if they are spatially explicit.

Assessment of incidental sea turtle catch in the artisanal gillnet fishery in Trinidad and Tobago, West Indies

A study was conducted on the incidental capture of sea turtles in the artisanal gillnet fishery in Trinidad and Tobago. The objectives were (i) to determine the fishing effort; (ii) to identify gillnet fishing areas and seasonality of turtle capture; (iii) to quantify the numbers, species and fate of captured turtles; (iv) to solicit the opinions of fishermen on turtle capture and; (v) to recommend measures to reduce sea turtle bycatch, if necessary. A survey questionnaire was used to carry out field surveys from March 2001 to February 2002 at 27 fish landing sites around Trinidad. Results indicated that green multifilament net was generally used in artisanal drift gillnet operations that target carite, Scomberomorus brasiliensis , and kingfish, S. cavalla , on all coasts. Gillnet fishing was conducted year-round by 71% of the fishermen interviewed. Of the turtle species captured in this fishery, the leatherback turtle, Dermochelys coriacea , was reported as the most common and problematic. Over 3000 adult turtles were estimated to have been caught in the gillnet fishery in 2000. Incidental capture occurred off the north and east coasts of Trinidad during January to August, when these marine reptiles are approaching nesting beaches. Fishermen reported that approximately 73% of leatherback captures on the north coast and 66% on the east coast were released alive during the study period. Recommended measures to reduce the incidental capture of sea turtles include revising fisheries legislation; providing training and financial support for fishermen to increase the adoption of alternative fishing methods; and educating fishermen on how their fishing practices can affect the survival of a species facing extinction.

Midwater float system for standardizing hook depths on tuna longlines to reduce sea turtle by-catch

Midwater float system for standardizing hook depths on tuna longlines to reduce sea turtle by-catch

Food color and marine turtle feeding behavior: Can blue bait reduce turtle bycatch in commercial fisheries?

We conducted laboratory and field experiments to investigate the behavioral responses of Kemp's ridley Lepidochelys kempii and loggerhead turtles Caretta caretta to whole squid dyed different colors. Our ultimate goal was to identify bait modifications that could reduce the interaction of turtles with longline fishing gear. In captivity, both turtle species clearly preferred untreated squid over squid that had been dyed dark blue. Loggerhead turtles also preferred untreated squid over red- dyed squid, whereas Kemp's ridley showed the opposite response. Field trials of blue-dyed bait were conducted on commercial fishing boats in the Gulf of Papagayo, Costa Rica, where the incidental capture of olive ridley turtles Lepidochelys olivacea is high (long-term average, approximately 7 turtles per 1000 hooks). We found no differences in rates of turtle interactions (8.4 and 8.1 individu- als per 1000 hooks) when using untreated versus blue-dyed baits. Although effective in laboratory settings with captive turtles, dyeing bait does not appear to have potential as an effective mitigation measure to reduce sea turtle bycatch in longline fisheries.