Tropical Olive Ridley Sea Turtle Sighted in Channel Islands National Marine Sanctuary
By Ellie Cherryhomes
Dr. Lindsey Peavey Reeves thought her chapter of studying tropical olive ridley sea turtles in graduate school was over when she began to work as a researcher for Channel Islands National Marine Sanctuary. But in November, local fisherman Steve Escobar spotted one in the Santa Barbara Channel just outside Channel Islands National Marine Sanctuary. He initially thought it was debris, but soon realized it was a turtle with eelgrass running down its shell. After he snapped a photograph, the turtle quickly dove below the surface. When Escobar texted the image to Reeves, she quickly identified it as an olive ridley.
The sanctuary’s remote, isolated position is home to thriving biodiversity, but olive ridleys are not generally spotted here. While it’s exciting to see one, it’s also worrying: “It usually indicates they are wayward, not in good health, and may become cold-stunned and strand,” says Reeves. But in this case, warm water anomalies have been affecting the ecosystem and it may be “because the conditions have been changing pretty dramatically over the last several years.”
Following a Warming Ocean
Solitary, open exploration between Baja California, Mexico, and Chile is a life-defining feat of the olive ridley sea turtle. They thrive in warm water where they can ride the current, rest at the surface, and forage on invertebrates like crabs, shrimp, rock lobsters, and jellies. Like other reptiles, olive ridleys are ectothermic, meaning their body temperature changes with the environment around them. Generally, species distribute where it is best for them thermally and where they can find the most prey.
From 2013 to 2015, the largest marine heatwave on record, known as the Blob, spread warm temperatures across the Northeast Pacific Ocean. Once the Blob diminished, an El Niño Southern Oscillation (ESNO) event occurred. Marine heatwaves and ENSO events both increase the poleward flow of coastal currents and sustain abnormally high temperatures, and the West Coast saw years of warming. “If the turtles find a warming ocean, they potentially find a track to a different habitat,” says NOAA Fisheries ecologist Dr. Elliott Hazen. After the Blob subsided and ENSO returned to neutral, a new heat wave occurred: currently, the Northeast Pacific Marine Heatwave of 2019 stretches from Alaska to California and the highest temperatures shown are more than 5 degrees Fahrenheit above average.
Seeing an olive ridley so far north may indicate that the warming ocean temperatures serve as a bridge for marine animals to travel to new foraging grounds that typically would be unavailable to them, says Hazen. They could be following a signal that leads them farther north in a warm year than their traditional migration.
Marine heat waves affect pelagic waters more than coastal waters, so that might be a mechanism by which the olive ridley could come up here, says NOAA Fisheries scientist Dr. Jeffrey Seminoff. “But I think even the olive ridleys that are here don’t want to be here – they are swept off course.” The olive ridley does not have the thermal tolerance for the usually cooler waters of the Channel Islands. Typically, says Seminoff, “the ones that are here are really lethargic and just float. They are still alive and can live for a couple of years in a really suboptimal habitat.”
Science Adapts to Changing Conditions
It’s unclear why this rare turtle was so far from its typical range, but it’s not the only tropical species that has been found here. Notably, the tropical brown booby, threatened by rising ocean temperatures and limited prey availability, has shifted north and now nests on Santa Barbara and Anacapa Islands. Consistent monitoring by NOAA researchers and opportunistic sightings shared by the public help track these changes of this precious ecosystem and its inhabitants.
“If we are facing these extreme events more frequently, we might be getting into a new normal,” says Hazen. “Either way, we provide the science in a way that is more adaptive and proactive: if it looks like something is changing down the road, what can we do to anticipate that and be as forward-looking as possible?”
With extreme warming events occurring more frequently and for longer periods of time, adaptive management strategies in places like Channel Islands National Marine Sanctuary are crucial. The presence of these animals in the sanctuary provides an opportunity to highlight the plight of species whose distributions are shifting, says Reeves. But adaptive management also helps native species compete towards their continued existence, she says. “Change is happening,” says Reeves. “It’s an opportunity to bring more people into the sanctuary, and to encourage all to care more deeply about this special place and even more species.”
Ellie Cherryhomes is a journalism student at the University of Missouri and a Virtual Student Federal Service intern with NOAA’s Office of National Marine Sanctuaries.