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The Natural History, Biology, and Conservation of Loggerhead Sea Turtles

Sequoia, a loggerhead sea turtle and previous patient of NMLC

The Loggerhead sea turtle (Caretta caretta), is the largest hard-shelled sea turtle in the world (National Geographic). It is found in warm temperate and subtropical waters throughout the Mediterranean Sea and the Atlantic, Pacific, and Indian Oceans (National Oceanic and Atmospheric Administration [NOAA]). Although it’s the most populous sea turtle in the western and eastern Atlantic Ocean, all of its distinct populations around the world are recognized as threatened or endangered under the Endangered Species Act (NOAA). As an opportunistic carnivore, the Loggerhead’s diet is primarily composed of benthic invertebrates, such as crustaceans, molluscs, and whelks (Donaton et al., 2018). Though researchers are still learning about their life cycle, it’s known that Loggerhead turtles return to shallow waters after about five years drifting in currents; it isn’t until they’re between 12 and 30 years old that they reach sexual maturity, with females often returning to the same beach they hatched from to nest (Bowen et al., 1993). Reliant on both their marine ecosystem and terrestrial nesting grounds, they are recognized as one of the ocean’s indicator species for environmental issues (Nicolau et al., 2017). For this reason, their population distributions, diet, and nesting trends have become topics of significant study to help understand how climate change and other anthropogenic factors have impacted these turtles, and potentially other organisms in their ecosystem.

 

Some of the greatest anthropogenic challenges facing Loggerhead sea turtles, in both terrestrial and marine circumstances, include loss of nesting area from rising sea levels, marine debris, fishing bycatch, and boat collisions (Witt et al., 2010; Blasi & Mattei, 2017). Some impacts are difficult to quantify on a global scale since distinct populations may be affected differently. However, research using distinct populations can provide insight into what threatens each population and how they compare to other regions. One study discovered that more than 35% of rescued or deceased Loggerhead sea turtles found in the Aeolian Archipelago had complications due to ingested marine debris (Blasi & Mattei). A smaller but significant portion of the sample showed signs of boat collision or entanglement (Blasi & Mattei). Further, it’s been found that Loggerhead turtles in the Adriatic Sea show higher levels of certain organic pollutants and industrial products, such as polychlorinated biphenyls, than those who live in the Eastern Atlantic Ocean (Bucchia, 2015). Research that focuses on these distinct populations helps scientists understand specific regional threats so policy and regulation changes can make a greater impact, and potentially be implemented for other populations.

Although sea turtles are often grouped together when considering potential anthropogenic threats like climate change, scientists are especially interested in studying how specific species adapt, or fail to adapt, to new challenges posed by their environment. Recent research has suggested that many Loggerhead sea turtles in the western Atlantic Ocean overwinter along the Gulf Stream, at both high and low latitudes (Hawkes et al., 2007). Here, the Gulf Stream provides proximity to summer feeding grounds for northern turtles and safety without migrating far for southern turtles (Hawkes et al.). However, climate change may impact the Gulf Stream’s location, influencing its critical use for this distinct population (Hawkes et al.). These studies have potentially long-term impacts, both in monitoring and planning for the conservation of distinct populations.

Long-term studies are also valuable to learn about changes and adaptations in Loggerhead populations. The distinct population off the coast of New York has shifted its diet from eating larger crab prey to smaller crab prey in the last 20 years, potentially suggesting climate change-induced shifts in the Gulf Stream ecosystem (Donaton et al.). Similarly, multiple studies have shown Loggerhead populations nesting earlier than previous years, with more poleward populations having greater sensitivity to annual temperature fluctuations (Mazaris et al., 2013; Weishampel et al., 2008).

The exact outcomes of these changes are not completely understood. For example, a shift to smaller prey may suggest a change in the ecosystem structure, but it isn’t known how much more the Loggerhead population’s diet can change without causing harm. Additionally, earlier nesting time may decrease foraging time for Loggerheads, but it also might allow them to have more clutches and hatchlings each season (Weishampel et al.). These nuances must be examined when considering how to address each species’ conservation needs; they allow scientists to advocate for habitat protection, minimizing anthropogenic threats, and making more informed decisions for the appropriate level of protection (NOAA). Steps toward managing Loggerhead sea turtle conservation start from this type of research, but take form in a multitude of ways.

Conservation practices continue to evolve as more information is collected about these turtles around the world. These efforts have introduced crucial regulations in the fishing industry to reduce bycatch with turtle exclusion devices, or TEDs (National Wildlife Federation [NWF]). Nests in the United States are often protected and monitored to maximize their success, and populations continue to be tracked (NOAA). International cooperation is critical in protecting global populations like Loggerhead sea turtles, and treaties and agreements help highlight these issues (NWF). However, modifications continue to be made as more research is conducted. With potential shifts in the Gulf Stream, an important source of food and protection, further fishing and vessel regulations may be necessary to protect Loggerhead turtles and their prey (Hawkes et al.). Although scientists have gained a better understanding of how Loggerhead sea turtles are impacted by anthropogenic influence and climate change, the species’ needs and ability to adapt must continue to be monitored.

Though Loggerheads are the most populous sea turtle in certain regions of the world, without proper regulation, their populations will suffer greatly. As keystone species, they play critical roles in their benthic communities, which further help nutrient movement throughout the ocean (Donaton et al.). To help support these ecosystems, research involving Loggerhead populations, diet, nesting tendencies are critical. Learning about their responses to climate change, such as shifts in diet or nesting, can further inform people what progress has been made, and what has yet to be done.

 

Research review paper written by fall intern, Bradlie M. Bradlie is a graduate from Boston College with a degree in Biology.

 

References

Blasi, M. F., & Mattei, D. (2017). Seasonal Encounter rate, life stages, and main threats to the loggerhead sea turtle. Aquatic Conservation: Marine and Freshwater Ecosystems, 27(3).

Bowen, B., Avise, J. C., Richardson, J. I., Meylan, A. B., Margaritoulis, D., &

Hopkins-Murphey, S. R. (1993). Population Structure of Loggerhead Turtles (Caretta caretta) in the Northwestern Atlantic Ocean and Mediterranean Sea. Conservation Biology, 7(4), 834-844.

Bucchia, M., Camacho, M., Santos, M. R. D., Boada, L. D., Roncada, P., Mateo, R., Ortiz-Santaliestra, M. E., Rodríguez-Estival, J., Zumbado, M., Orós, J., Henríquez-Hernández, L. A., García-Álvarez, N., & Luzardo, O. P. (2015). Plasma levels of pollutants are much higher in loggerhead turtle populations from the Adriatic Sea than in those from open waters (Eastern Atlantic Ocean). Science of The Total Environment, 523, 161-169.

Donaton, J., Durham, K., Cerrato, R., Schewerzmann, J., & Thorne, L. H. (2018). Long-term changes in loggerhead sea turtle diet indicate shifts in the benthic community associated with warming temperatures. Estuarine, Coastal and Shelf Science, 218(5), 139-147.

Hawkes, L. A., Broderick, A. C., Coyne, M. S., Godfrey, M. H., & Godley, B. J. (2007). Only some like it hot — quantifying the environmental niche of the loggerhead sea turtle. Diversity and Distributions, 13(4).

Mazaris, A. D., Kallimanis, A. S., Pantis, J. D., & Hays, G. C. (2013). Phenological response of sea turtles to environmental variation across a species’ northern range. Proceedings B, 280(1751), 2012-2397.

National Geographic. Loggerhead sea turtle. Retrieved from https://www.nationalgeographic.com/animals/reptiles/l/loggerhead-sea-turtle/

National Oceanic and Atmospheric Administration Fisheries. (n.d.). Loggerhead Turtle.Retrieved from  https://www.fisheries.noaa.gov/species/loggerhead-turtle

National Wildlife Federation. (n.d.) Loggerhead Sea Turtle. Retrieved from https://www.nwf.org/Educational-Resources/Wildlife-Guide/Reptiles/Sea-Turtles/Loggerhead-Sea-Turtle

Nicolau, L., Monteiro, S. S., Pereira, A. T., Maralo, A., Ferreira, M., Torres, J., Vingada, J., & Eira, C. (2017). Trace elements in loggerhead turtles (Caretta caretta) stranded in mainland Portugal: Bioaccumulation and tissue distribution. Chemosphere, 179, 120-126.

Weishampel, J. F., Bagley, D. A., & Ehrhart, L. M. (2008). Earlier nesting by loggerhead sea turtles following sea surface warming. Global Change Biology, 10(8).

Witt, M. J., Hawkes, L. A., Godfrey, M. H., Godley, B. J.,& A. C. Broderick. (2010). Predicting the impacts of climate change on a globally distributed species: the case of the loggerhead turtle. Journal of Experimental Biology, 213, 901-911.

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