Juan Manuel Rodriquez-Baron
Assessment of Bycatch and Physiological Rates of Post Release East Pacific Leatherback
Turtles at Foraging Grounds off the Coasts of Central and South America
1. Background of the research question
The East Pacific (EP) leatherback turtle (Dermochelys coriacea) ranges from Mexico to Chile, with major nesting beaches in Mexico and Costa Rica (Santidrián Tomillo et al. 2007; Sarti Martínez et al. 2007) and primary foraging grounds in waters offshore of Central and South America (Shillinger et al. 2008, 2011; Bailey et al. 2012). The EP leatherback turtle is listed by the IUCN as Critically Endangered, and dramatic declines in the number of nesting females at the major index nesting beaches have been documented (http://www.iucnredlist.org/details/46967807/0). It is estimated that there are currently fewer than 1000 adult female EP leatherback turtles. Unintended capture of adult and sub-adult EP leatherback turtles by fisheries operating within this species’ foraging habitats are of particular concern, given the strong influence that these life stages have on population dynamics (Alfaro-Shigueto et al. 2007, 2011; Wallace et al. 2008). Results from port-based surveys administered along the coast of South America indicate that between 1000 and 2000 EP leatherback turtles are caught in regional small-scale fisheries annually, and approximately 30% - 50% of the captured turtles die (NFWF and IUCN/SSC Marine Turtle Specialist Group). NOAA has listed the Pacific leatherback turtle as one of eight “Species in the Spotlight”, and designated bycatch mitigation as one of the top conservation priorities for recovery of this species.
In March 2012, an Expert Working Group was assembled to develop a Regional Action Plan to halt and reverse the decline of the EP leatherback turtle. The Regional Action Plan emphasizes the critical importance of identifying areas of high bycatch risk, and specifically recommends the expansion of port-based marine turtle bycatch assessments to include Panama and Colombia. Moreover, The Regional Action Plan acknowledges that mortality due to fisheries bycatch presents a formidable challenge to EP leatherback turtle recovery efforts, and asserts that a better understanding of post-interaction mortality rates is crucial for a sound assessment of the true impact of fisheries bycatch on this species.
2.1. Inform on which fleets are interacting with leatherbacks and which seasons and areas have particular importance for those interactions; also, to conduct workshops with fishers to share survey results, promote best practices for handling and releasing captured turtles, and foster cooperative relationships to facilitate future studies.
2.2. Refine estimates of leatherback turtle mortality due to fisheries interactions, and document leatherback turtle movements in East Pacific foraging areas to assess potential hotspots for fisheries interactions.
2.3. Cooperate with region-wide initiatives (LaudOPO, NFWF) and NOAA to characterize bycatch of leatherback turtles in the fisheries of Central and South America and inform management decisions regarding goals for threat reduction.
3.1. Phase one (in progress) We conducted standardized bycatch assessment surveys at three ports in Colombia (Buenaventura, Tumaco, and Bahía Solano) and seven ports in Panama (Vacamonte, Pedregal, Remedios, Muelle Fiscal, Coquira, Juan Diaz and Mutis). Selection of ports for survey administration was based on government data regarding the main fishing fleets operating within Colombian and Panamanian waters. Moreover, information on which fleets are interacting with leatherbacks and initial collection of coordinates of interactions (via GPS units distributed to fishermen willing to participate). These data will allow us to assess which fleets to work with in order to collect more detailed information on interactions. By doing national workshops in June of 2017, we propose to provide the training and tools to promote fishing practices that will increase chances of post-release survival of leatherback turtles caught in coastal and pelagic fisheries in both countries.
3.2. Phase two We will deploy satellite transmitters on and conduct health assessments with leatherback turtles captured in the Colombian and Panamanian long-line/gillnet fisheries. We will work cooperatively with government scientists from the Colombian and Panamanian National Fisheries Service (AUNAP and ARAP) and fishermen working in areas of high bycatch risk, as indicated by port-based bycatch surveys. Health assessments and transmitter attachments will be conducted, according to published protocols (Harris et al. 2011; Casey et al. 2014), with leatherback turtles captured during the course of routine fishing operations. Blood samples will be analyzed for specific variables on-board the vessel with a point-of-care analyzer, and a sub-sample of blood will be frozen for later analysis. PAT tags will be programmed to release from the carapacial attachment site under conditions indicative of mortality (i.e. depth >1200m or constant depth for 24 hours) or after a monitoring period of 6 months. We will use a modelling approach appropriate for collected data to compare physiological characteristics of survivors, mortalities, and healthy turtles captured at sea for scientific research. Post-release movements will be monitored and spatial and temporal trends in habitat utilization will be investigated.
4. Expected outcomes, how the results will be disseminated
We will use survey data and government statistics on the size and effort of fishing fleets to estimate the number of leatherback turtle interactions that occur annually in small-scale and industrial fisheries. Comparisons of leatherback turtle bycatch between fisheries will permit us to identify the primary threats and opportunities for bycatch reduction in this region. Integration of physiological data with post-release behavior data will enhance our ability to evaluate mortality due to fisheries interactions. Satellite tracking of released leatherback turtles will also contribute to the Regional Action Plan goal of identifying patterns of habitat utilization and the potential for spatial and temporal overlap of leatherback turtles and fisheries operations in the East Pacific.
All our results will be presented in the final report for Boyd Lyon Sea Turtle Fund, published in peer-reviewed scientific journals, and presented at the International Sea Turtle Symposium. Furthermore, they will be highlighted on websites hosted through UNCW (https://williarda.com/) and JUSTSEA Foundation (http://justsea.org/).