Study indicates where many drifting sea turtles may have died – via Herp Digest

By LAUREN WALCK

11/23 2013 - The Mississippi Sound is a popular hangout for a lot of underwater creatures, but for young Kemp's ridley sea turtles it's the place to be. The warm, shallow waters and plentiful supplies of tasty blue crabs and shrimp make it downright irresistible for a juvenile reptile on the go.

Unfortunately, it's also where the carcasses of many of the world's most-endangered species of turtle have been washing ashore after a too-short life.

Since spring 2010, strandings of Kemp's ridley sea turtle have increased dramatically. And most of the strandings have been on the Mississippi Coast.

A group of researchers at the Institute for Marine Mammal Studies has been trying to figure out why and where the turtles died.

"We were getting almost 50 percent of all the turtles stranded between Alabama and Louisiana," said Moby Solangi, IMMS executive director.

The group created mock turtle carcasses from a lawnmower tire and bits of leather, plastic and fabric, affixed satellite trackers and dropped them off in different areas of the Gulf at different times of the year starting in April 2012.

The telemetry the tire turtles have provided has helped a computer model predict where a turtle is likely to have died. The results point to eastern Louisiana waters, but not very far offshore.

"Although the majority of dead sea turtles were found on Mississippi beaches, backtrack analysis of the strandings indicates that much of the at-sea mortality probably occurred in a region just southwest of (Louisiana's) Cat Island and included inshore Louisiana state waters to the northern part of Chandeleur Sound," the study states.

From the mid-1980s to 2009, an average of 97 sea turtle were stranded, according to the study. In 2010, 664 stranded turtles were found, 85 percent of which were young Kemp's ridleys.

Andy Coleman, a senior

researcher and turtle ecologist at IMMS, said the oil spill may not be the only factor in the phenomenon.

"The mystery surrounding the whole issue is NOAA Fisheries, who do most of the necropsies, have found the majority of the turtles are fairly healthy," Coleman said.

The dead turtles are found with a normal fat supply, but many have the remains of fish in their digestive systems, which is "not a normal prey item," he said.

Coleman said the federal government thinks a large majority of the deaths are "by-catch mortalities," which means they get caught in the nets of fishing or shrimping vessels and drown. A healthy sea turtles can hold its breath for only about 30 minutes at a time.

However, he said the sudden increase in strandings occurred during the off season of the shrimping industry.

"There's not a consensus on what is the real cause," he said. "It could be a number of factors."

Coleman said NOAA is not releasing data related to the oil spill, such as pH levels, because of ongoing litigation. But he said studying the turtles will reveal important data about the post-spill health of the entire Gulf.

"By focusing on the species and looking at the health and the ecology of these animals, it gives us insight into the overall health of the ecosystem," Coleman said. "Because if their habitat and ecosystem is not healthy it will affect them, and at some point eventually get up to us."

An animal is considered stranded when it washes ashore, dead or alive, or floats into shallow waters and becomes stuck there, according to the National Oceanic and Atmospheric Administration's National Marine Fisheries Service, which collaborated on the study.

Coleman said the idea for the study came after IMMS began satellite tracking of rehabilitated sea turtles in 2010. The researchers could tell one of the tagged turtles had died and begun drifting.

Using that data, Woody Nero at NOAA Fisheries created a computer model to predict the drift path for a turtle carcass. The tire turtle study is helping to fine-tune the program.

"It's basically backtracking," Solangi said.

Coleman said the Coast Guard uses a similar program to find people in the ocean. Using the person's last known position, rescuers can calculate a probable search radius.

Tracking rehabilitated turtles led to another important discovery, Solangi said. After the oil spill, he said, many of the turtles were flown to Florida to safer waters but most of them just swam back to the Sound.

"We found out that many of them came back," he said. "All they (IMMS) did was put them through a 2,000 mile journey … so that myth changed."

He said researchers now know the Sound is very important for juvenile Kemp's ridley turtles.

"By tracking them we found out that this is a very important habitat -- even though they nest in Mexico this is where they spend quite a bit of their time," Solangi said.

He said the study is just the tip of the iceberg for IMMS' plans to examine sea turtles.

For example, the IMMS has seen an increase in accidental captures of turtles off fishing piers in the past two summers. The researchers plan to look into why the animals are suddenly attracted to the bait and fish associated with the piers.

Most important, though, Solangi said anyone who accidentally catches a sea turtle, whether on a pier or in the Gulf, is asked to call the IMMS hotline at 1- 888-SOS-DOLPHIN (888-767-3657).