Two Years After Irma: Turtle Populations Prove Resilient

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A hawksbill turtle soars through the sea. (photo by Caroline Rogers)

When Hurricanes Irma and Maria struck in September 2017, hundreds of people who have been involved with sea turtle conservation in the territory worried about the storms’ effects on the three species of endangered sea turtles that live in Virgin Islands waters.

Any species, however, that has roamed the planet for 100 million years has had to develop some pretty successful survival strategies. Though not all the data is in, it appears that sea turtle populations in the Virgin Islands are showing signs of resiliency since ‘Irmaria.’

The first report that a turtle population had recovered was announced by researchers at the University of the Virgin Islands’ Center for Marine Studies. They reported that all 11 juvenile hawksbill turtles they had been tracking in Brewers Bay on St. Thomas prior to Hurricane Irma found safe places to shelter nearby, and all 11 returned to their normal home range within a matter of days.

Since 2018, St. John social media sites have been full of enthusiastic postings from snorkelers who regularly swim with turtles at Maho Bay. One retired National Park Service ranger counted as many as 17 different turtles during an afternoon swim.

Although sea turtles are monitored on St. Thomas and St. John, St. Croix’s Sandy Point on the island’s west end is the hub of turtle tracking activity. Established as a National Wildlife Refuge in 1984, Sandy Point is home to the largest population of leatherback sea turtles within the United States; scientists have been tagging leatherbacks there and tracking their return visits since 1977.

Leatherback sea turtles can grow up to six feet in length and weigh more than one thousand pounds. Fortunately, leatherbacks lay their nests in the summer months; their eggs’ incubation period lasts between 55 and 72 days, so all of their nests had hatched by the time the storms of September 2017 hit.

A leatherback sea turtle (photo from Wikicommons)

Adult leatherback turtles were probably unaffected by the storms as well. “Our turtles weren’t here,” said Claudia Lombard, a wildlife biologist with the U.S. Fish and Wildlife Service. “Leatherbacks are migratory. They were already migrating back to their foraging grounds in the waters off of North America.”

However, nests laid by hawksbill and green sea turtles prior to Irma and Maria did not fare as well. “We lost a lot of our nests at Sandy Point,” said Lombard. “After Maria, some beach areas washed away including any incubating eggs buried in the sand. Other beach areas had several feet of sand deposited on top resulting in the hatchlings becoming trapped under a deep layer of compact sand.”

Green and hawksbill turtles typically lay their nests from late July through October; this puts their nests’ incubation periods in the middle of peak hurricane season.

Sea turtles tend to return to the same location to lay their nests during a season and will usually return several times to lay their nests at regular intervals which range from 10-14 days, depending on the species.

It’s part of a reproductive strategy that is very different from humans’, Lombard says. Whereas a human female will take nine months to bear a child and then raise it for 18 years, a female turtle will lay several nests in a season averaging 100-150 eggs, depending on the species. “She disperses them across the season, and across the beach, so if one nest is lost to a hurricane, hopefully she will have others that survive,” said Lombard. “If you’re a turtle, you don’t want to put all your eggs in one basket.”

Once the eggs are laid, the female turtles’ maternal role ends, and it’s up to the hatchlings to find their way out of the nest, across the beach and into the sea. Predators from land, sea and air take their toll. Scientists estimate that only one out of a thousand turtles survives to reproductive maturity.

Hurricane Maria had a devastating effect on the forest adjacent to the beach at Sandy Point which particularly affected hawksbill turtles. Green turtles and leatherbacks lay their eggs in the open beach areas, but hawksbills crawl all the way into the coastal forest to lay their nests.

“Trees were uprooted and knocked down,” said Lombard. “This created a barrier to the forest and a hazard to nesting turtles. Turtles really don’t have a reverse [gear.] They can’t turn on a dime. Our staff has rescued six turtles that got entrapped in downed trees and couldn’t get back out to the beach.” Since Maria, she’s been on the lookout for tracks that lead into the forest but don’t have an associated outbound track.

On St. John, nearly two dozen volunteers regularly patrol the beaches looking for the tracks of nesting turtles. Adren Anderson, who heads up the Sea Turtle Monitoring Project funded by the Friends of the Virgin Islands National Park, said she didn’t think any of the nests she knew about prior to Hurricane Irma survived the storm.

Sea turtle hatchlings photographed at night using a red light emerge from a nest. (photo provided by STJ Turtle Team)

In 2018, members of the sea turtle monitoring team counted 24 nests on St. John beaches. (All but one of the nests were made by hawksbill turtles.) Based on the number of empty turtle shells after the hatching events, Anderson said that nearly 1,700 hatchlings made it into the sea. So far this year 19 hawksbill nests have been documented. For the third year in a row, one green sea turtle nest has been found on St. John.

Lombard did not have the exact numbers of nests lost to recent storms; however, with each storm that brings heavy seas and storm surge, she said the resulting beach loss causes the destruction of a significant number of nests. When a nest has been found, scientists and volunteers track those nests through the incubation period and protect them from predators, such as dogs and mongooses. They put in hundreds of hours to protect the nests they find, knowing that a major storm could destroy all of their efforts.

“Natural events such as storms we cannot control,” said Lombard. “But there are ways we can protect sea turtles – -by keeping beaches clean, by driving boats safely, by keeping dogs on leashes, and by employing sea turtle-friendly lighting in nesting areas.”

Newly hatched sea turtles make their way to the sea. (photo provided by St. John Turtle Team)

Original Source: https://stjohnsource.com/2019/10/10/two-years-after-irma-turtle-populations-prove-resilient/