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Recognisable by their round, pale-hued shells and parrot-like profile, Kemp’s ridley turtles are the world’s smallest and most endangered marine turtle species.
They also happen to be one of the most abundant in the bays and estuaries of western Florida, U.S. The species appeared to be headed for extinction in 1986 when I was hired to assist with mark-recapture studies of immature Kemp’s ridleys inhabiting the Cedar Keys. Our recovery of tagged turtles revealed endpoints and duration of movements but offered little information on their activities between capture and recapture. Furthermore, it is difficult to observe the behaviors of an animal that that lives in murky estuarine waters and spends most of its time below the surface. Wildlife tracking technologies since given us a better understanding of this species cryptic habits.
The critically endangered Kemp’s ridley, found all along The Gulf of Mexico, have faced half a century of turmoil. On one day in 1947, an estimated 40,000 turtles were filmed coming ashore to nest on a beach near Rancho Nuevo, Mexico. By the mid-60s, nest numbers had plummeted to around 5,000 for the entire year and 1985 saw a low of just 702 nests.
Conservation efforts aimed at protecting nesting beaches and reducing incidental captures in fisheries have brought the Kemp’s ridley back from the brink of extinction. However, their recovery remains uncertain.
Coastal waters from Texas to Massachusetts provide vital feeding grounds for young Kemp’s ridleys, but there is limited information on how these turtles interact with their environment. One way we’ve been unlocking these critically endangered animals’ secrets is by tracking them from space.
Satellite telemetry has become a popular tool for studying patterns of marine turtle distribution over time. This is a fundamental aspect to conservation and provides the basis for all other aspects of research. Transmitters are attached to the shell, and orbiting satellites receive a unique signal for each turtle during the brief period when they surface to breathe. The satellite data are transmitted back to ground-based stations which estimate locations for each turtle.
This Space Age technology solved a mystery of where Kemp’s ridleys in northwest Florida went in winter. Previous hypotheses had suggested they left when it got cold or, according to local fishers, buried in the mud to brumate (the reptilian version of hibernation). We revealed that Kemp’s ridleys did indeed leave nearshore feeding grounds in November when temperatures fell and travelled south to warmer, deeper waters offshore the west-central coast and coastal waters off southwestern Florida. In late January, all the turtles reversed their course to travel back to the same feeding area. The satellite tracking data showed a strong faithfulness to specific coastal regions and also revealed a seasonal migratory corridor along the coast.
When studying Kemp’s ridleys on their feeding grounds in southwest Florida, we were surprised to find differences in movements between tracking years despite similar water temperatures, indicating other environmental variables were influencing their behavior. A clue came from the satellite data of a Kemp’s ridley that had moved offshore and had spent an unusual amount of time at the surface, perhaps sick or injured, prior to loss of transmissions.
The west coast of Florida experiences episodic blooms of the harmful algae Karenia brevis, referred to as “red tide.” Toxins (brevetoxins) produced by the algae are dangerous to animals. Marine turtles wash ashore during major red tide events with high levels of toxins in their system and those that are still alive exhibit physical signs of exposure (lethargy or paralysis, muscle twitching, and other neurological symptoms). It was later discovered the satellite-tagged Kemp’s ridley had traversed an area with a high concentrations of red tide algae. The behavioral anomalies suggest the turtle may have succumbed to the powerful neurotoxins and lay immobilized at the surface before perishing. This was purely conjecture, highlighting a problem with remote tracking rather than directly observing behavior.
Red tide blooms are unpredictable so it is very difficult, if not impossible, to design a study on the potential effects to free-ranging marine turtles. Nonetheless, Kemp’s ridleys have been inadvertently tracked during red tides and their movements appear to be affected by the blooms. Combining the turtles’ locational data with that of red tide water sampling programs indicated Kemp’s ridleys may exhibit “red tide avoidance”. This behavior has never been documented before and suggests turtles are somehow able to detect the concentration of red tide toxin in water and try to find other areas with lower concentrations. Perhaps it is similar to human beach-goers who experience respiratory irritation during a red tide and respond by leaving the beach. Additional non-telemetric research is needed to unravel how turtles may detect the toxin and their possible response to avoid high concentrations of the bloom.
Kemp’s ridley satellite tracking studies are ongoing in Ten Thousand Islands, a network of water and mangroves in southwest Florida, but this feeding area took a direct hit from Hurricane Irma in 2017.
There were major impacts to the estuarine ecosystem and turtles appear to have moved to other areas. Adding insult to injury, there has been a persistent red tide following “Irmageddon” and a number of Kemp’s ridley carcasses have been recovered in the aftermath of the algal bloom. If and when conditions improve, we will be in a unique position to study how this endangered species adapts to catastrophic changes in their foraging habitat.
Jeff Schmid is Research Manager with the Conservancy of Southwest Florida where he conducts in-water studies of marine turtles. He is especially interested in identifying how Kemp’s ridleys use their coastal foraging areas and incorporating this information in conservation and management strategies. Find out more here
Featured image © Stocktrek images | Getty