Smolowitz, R. J., Patel, S. H., Haas, H. L., & Miller, S. A. (2015). Using a remotely operated vehicle (ROV) to observe loggerhead sea turtle (Caretta caretta) behavior on foraging grounds off the mid-Atlantic United States. Journal of Experimental Marine Biology and Ecology, 471, pp. 84-91. DOI: 10.1016/j.jembe.2015.05.016 (Open Access).
There are seven species of sea turtle in the world, all of which are either threatened or endangered. The loggerhead sea turtle is found in most of the world’s oceans, excluding polar regions. It is also one of four species of sea turtle that is commonly found in the Atlantic Ocean.
The loggerhead sea turtle is listed as endangered and its recovery is threatened by a variety of factors, including commercial fishing and human development along nesting beaches. Like all other turtles, loggerheads must breathe air. This is what makes them so susceptible to deadly encounters with fishing gear. Sea turtles suffer mortality as bycatch in a number of commercial fishing methods, including longlines, gillnets, trawling, and scallop dredging (check out this oceanbites article about longline fishing impacts on animals like sea turtles!).
Advances in biotelemetry (tracking animal movements), including GPS satellite tracking, have led to great discoveries of broad scale marine animal movement behaviors. However, the findings from tracking studies have informed scientists about where sea turtles are going, but not exactly what they are doing. Gaining insights into specific information like what sea turtles are eating and how they interact with other animals may teach scientists about specific behaviors of sea turtles, which may help in developing methods for mitigating deadly turtle interactions with fishing gear.
To figure out exactly what sea turtles are doing beneath the surface we must directly observe them. One way of doing this has been by snorkel and scuba observations. However, sea turtles make repeated deep dives (which humans cannot do) and can easily outswim humans. Additionally, there is a potential risk of danger each time an observer enters the water. A new article published with open access in the Journal of Experimental Marine Biology and Ecology introduces a method of observing turtles that may bridge the gap between the large amout of data obtained from tracking techniques with a lot of uncertainty and visual surveys which provide a small amount of data with great detail – and the bridge is a robot!
The researchers in this study present the first published findings from a new technique for studying sea turtles. The researchers used remotely operated vehicles (ROVs) equipped with a high powered video camera to follow and observe sea turtles for as long as they could. This technique does not require researchers to first capture and handle the animal, which reduces the likelihood of a change in behavior following handling by humans.
Airplanes and observers equipped with binoculars on the top deck of the boat scan for loggerheads at the surface of the water along a foraging area in the Atlantic Ocean between New Jersey and Virginia. Once an observer spots a turtle, they direct the ship’s captain slowly towards the animal. Then, the ROV is deployed and an operator onboard the vessel slowly approaches, attempting to keep the turtle in the frame of the camera at all times while avoiding startling the animal by getting too close (Figure 1). The ROV also contains a sonar device which assists in finding the turtle again if it escaped the view of the camera temporarily.
Ten ROV trips were made during the summer months from 2008-2014 (Figure 2) recording over 2,500 minutes (about 40 hours) of turtle footage. Turtles were observed diving to the bottom 23 times, with 12 of these occasions consisting of continuous footage of the turtle throughout the dive downward. Five of those cases the observers were successfully able to track the turtle through the entire dive, from the surface to the bottom and back again. Loggerheads dove up to 200 ft (61m) down, and remained submerged for 15.6 – 37.8 minutes!
Loggerheads fed on hermit crabs, rock crabs, and sea scallops (Figure 3b) on the bottom four times. They were also seen feeding on comb jellies, lion’s mane jellies (Figure 3c), and salps (another gelatinous sea creature) in the middle of the water column four times.
The researchers observed a number of interesting interactions between two or more loggerheads, and between loggerheads and other animals. Social interactions between 2-4 loggerheads were observed 19 times. The turtles rub their carapaces – the backs of their shells – on each other (Figure 3f), and bite the algae growing on the shell of another turtle (Figure 3e). The researchers state that it was unclear if the biting of the algae was motivated by feeding or cleaning.
Turtles were also seen interacting with several species of fish. Small species of fish like triggerfish, pilotfish, and barrelfish would get very close to the turtle, especially if the turtle had a large amount of algae growing on its shell (Figure 3d). It was unclear if the fish were motivated by feeding or hiding along the turtle as refuge. One turtle came across a large shark while being followed by the ROV. The turtle displayed an immediate reaction of turning sharply away from the shark while simultaneously turning on its side, putting the back of its shell towards the shark (Figure 4. Sea turtles are a favorite food source for many large sharks; however, this shark did not make any clear attempt to attack.
This study represents an investigation into a new technique for studying sea turtle behavior. ROVs have several advantages over traditional methods like scuba surveys, such as the ability to conduct repeated deep water dives, a greater likelihood of keeping up with the turtle at all times during the dive, and most importantly, keeping researchers out of danger by preventing the need for humans to enter the water.
Better understanding what sea turtles like the endangered loggerhead are doing beneath the surface, what they are feeding on, and how long they are spending at the bottom may all help in developing and improving methods for excluding turtles from commercial fishing gear (Figure 5). Additionally, high quality images and video of animals like sea turtles is increasingly being utilized to identify individuals based on unique marking patterns (check out this oceanbites article about identifying individual sea turtles from images). Combining telemetry tracking data with video surveillance from ROVs and the ability to uniquely identify individual turtles could lead to a very detailed and complete picture of sea turtle behavior in the wild – an incredibly valuable commodity for such an iconic endangered species.
Derrick is pursuing a Ph.D. in the Organismic and Evolutionary Biology Program at the University of Massachusetts Amherst. He is interested in anadromous fish migrations, how aquatic organisms interact with their physical environment, and the impact of human development on natural systems.