By Melissa Marcon
Sea turtles are globally distributed and can be found in tropical and subtropical seas in all oceans. Five of the seven species that exist on the planet use the Brazilian coast for feeding and reproduction.
The five sea turtle species that can be found in the Brazilian coast. A) Loggerhead turtle; B) Green turtle; C) Leatherback turtle; D) Hawksbill turtle; and
Sea turtle populations are decreasing either directly or indirectly because of human destruction of the environment in nesting beaches (like lights, car traffic and others), nest predation, interaction with fisheries and pollution. The interaction with fisheries is one of the greatest causes of mortality and injury in young and adult sea turtles all over the world.
In my master’s degree thesis I evaluated the interactions of leatherback and loggerhead turtles with the longline pelagic fisheries of the Southeast/South regions of Brazil. My main goal with this study was to quantify the distribution patterns of these species' incidental catches and correlate them with environmental (oceanographic), biological and operational variables, hoping to contribute in the formulation of conservation and management of fisheries strategies that would benefit the maintenance of the fishing ecosystem.
Estimates of incidental capture of these turtles by pelagic longlines are concerning when compared to the mortality rates in fisheries and to the low recovery potential of these populations in the Atlantic Ocean. To understand more about this fisheries technique, access the links at the end of the post.
Pelagic longline fishing (Source: NOAA)
Monitoring accidental catches combined with abiotic and operational data, which is often obtained by onboard observers in the commercial fleet, must be valued as a rich source of information. These data allow a better understanding of the behavior of sea turtle populations and of the importance of environmental variations in population dynamics.
In my study I identified that loggerhead turtles were more frequently accidentally captured than leatherback turtles, similar to what other researchers had found. The fact that most loggerhead individuals were hooked by the mouth agrees with the fact that the species feeds on fish, therefore feeding from the longline bait. Leatherbacks, on other hand, were more commonly found with the hook externally attached to their body, which can also be related to their feeding habits, as they prey on gelatinous plankton.
I also observed that there were more captures in the fall. It is possible that some oceanographic phenomena happens during this season, increasing the turtles' relative abundance. Therefore, the peak of accidental captures in the fall might be related to their migration to inner coastal regions, possibly for feeding, and, consequently, they are more vulnerable to longline fishing in this season.
The accidental captures of loggerhead turtles analyzed in my dissertation was significantly higher when squid was used as bait in fisheries, showing that there's a preference for this food by the species. It's important to point out that observations made by other authors show a decrease of loggerhead captures when Atlantic mackerel (Scomber scombrus) is used as bait. Circle hooks have also been showed to minimize damages of accidental catches. The opportunistic feeding of the loggerhead in its juvenile stage makes it a very susceptible species for the incidental catch in pelagic longline fishing.
Circle hooks help reduce sea turtle bycatch. Additionally, if the barb
of the hook is flattened, other impacts are minimized while
maintaining fishing function (Source: NOAA)
In general terms, I was able to identify behavioral patterns, like location and preferences for types of bait, kinds of hooks and seasons, when loggerhead and leatherback sea turtles are more frequently captured.
It is important to say that the data I used from the fisheries showed to be very useful, being sometimes the only source of information for the pattern of migratory behavior analysis, location and preferred habitat by sea turtles in various parts of the world. It might be a paradox that the activity that causes the impact itself can help us understand the affected populations in more detail. Data on accidental or accessory capture is becoming more and more complete and allows better identification of potential impacts in these populations.
Thus, based on the results of my thesis, various initiatives and measures can be proposed to contribute to the conservation of the species studied and with the management of the fishing activity.
Life in the ocean is not easy for our beautiful marine giants. Therefore, all efforts to understand and protect them and the environment they live in are extremely valid and gratifying.
References and additional information:
ICMBIO - Centro Nacional de Pesquisa e Conservação da Biodiversidade Marinha do Sudeste e Sul – CEPSUL. Espinhel de superfície e fundo. Available at: http://www.icmbio.gov.br/cepsul/images/stories/artes_de_pesca/industrial/espinhel/espinhel_superficie_fundo.pdf
NOAA. Fishing Gear: Pelagic Longlines. Available at: https://www.fisheries.noaa.gov/national/bycatch/fishing-gear-pelagic-longlines
FAO Fisheries and Aquaculture Department. Guidelines to reduce sea turtle mortality in fishing operations. Rome, FAO. 2009. 128pp. Available at: http://www.fao.org/3/i0725e/i0725e.pdf
About the author:
Melissa Marcon graduated in veterinary medicine from the Faculdade de Jaguariúna (2009). Her love for the ocean and its inhabitants led her to complete a master’s degree in biological oceanography at the Oceanographic Institute of the University of São Paulo. Melissa works in the field of medical and surgical clinic of small animals and wildlife. She has experience in collecting biological material, beach monitoring, necropsy, rescue and rehabilitation of marine fauna, especially sea turtles.
Melissa has published another post here in the blog. Check it out (Portuguese version only) here: "Uma veterinária, a tartarugas marinhas, e a oceanografia"