Sea turtles and the Deepwater Horizon oil spill

October 5, 2010, 9:45 am
Source: NOAA
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Credit: NOAA

Overview

Sea turtle stranding responders, working under the guidance of the Wildlife Branch Unit of the Unified Command, which includes several NOAA experts, are responding to dead and live sea turtle strandings and offshore teams are searching for and rescuing oiled sea turtles from the area affected by the Deepwater Horizon oil spill .

caption Kemp's ridley hatchling. Credit: NPS.

All the live oiled turtles are cleaned of oil and are being treated and cared for at one of four primarily de-oiling centers across the northern Gulf of Mexico or at secondary rehabilitation facilities once they are stabilized.

NOAA experts are examining turtles that have stranded in the area affected by the oil spill to determine, if possible, whether their deaths can be linked to oil, or another cause. All of the turtles are being sampled externally for oil and tissue samples are being taken during necropsy when the condition of the carcass is sufficiently fresh. The majority of the turtles recovered as strandings have not had external oil.

In contrast, the vast majority of turtles captured offshore during directed surveys are externally oiled. Aerial surveys have documented sea turtles swimming in oiled areas and in unoiled areas. We do believe that this spill will significantly affect sea turtles in the Gulf of Mexico.

General Effects of Oil on Sea Turtles

Sea turtles may be exposed to chemicals in oil or to chemicals in products such as dispersants used in two ways: internally (eating or swallowing oil, consuming prey containing oil based chemicals, or inhaling of volatile oil related compounds) and externally (swimming in oil or dispersants).

Several aspects of sea turtle behavior put them at risk. Young turtles use highly productive areas where ocean currents meet, known as surface converage zones. Here, the marine algae Sargassum grows and thrives at the surface, providing feeding and sheltering habitat. Oil has also collected in these zones, leading many of these small, young turtles to come into direct contact with oil. Oil covering their bodies can interfere with breathing, coat the eyes and skin, and can cause them to become stuck in the oil. Oil ingested directly or when eating oiled prey items may interfere with digestion or cause internal organ damage.

caption Credit: NOAA

Sea turtles are air breathers and all must come to the surface frequently to breathe. In an oil spill, they may be exposed to volatile chemicals at the surface during inhalation.

Additionally, sea turtles may experience oiling impacts on nesting beaches when they come ashore to lay their eggs, and their eggs may be exposed during incubation potentially resulting in increased egg mortality and/or possibly developmental defects in hatchlings.

Hatchlings emerging from their nests may encounter oil on the beach and in the water as they begin their lives at sea.

External Effects: Oil and other chemicals on skin and body may result in skin and eye irritation, burns to mucous membranes of eyes and mouth, and increased susceptibility to infection.

Internal Effects: Inhalation of volatile organics from oil or dispersants may result in respiratory irritation, tissue injury, and pneumonia. Ingestion of oil or dispersants may result in gastrointestinal inflammation, ulcers, bleeding, diarrhea, and maldigestion. Absorption of inhaled and ingested chemicals may damage organs such as the liver or kidney, result in anemia and immune suppression, or lead to reproductive failure or death.

Sea Turtle Strandings

There are thousands of sea turtle strandings every year along the Gulf of Mexico and U.S. east coast. NOAA is working to understand why sea turtles are stranding in the area of interest. In previous years, this same area has experienced increased strandings during this time of year. The stranding numbers we are seeing currently in Louisiana, Mississippi and Alabama are much higher than normal, however. This may be due in part to increased detection and reporting, but this does not fully account for the increase.

The primary human cause for sea turtle deaths in the Gulf of Mexico is bycatch in fishing gear. Bycatch in shrimp trawls is recognized as a leading source of sea turtle mortality if Turtle Excluder Devices (TEDs) are not properly used or not required.

The other primary types of fishing gear that incidentally catch and can kill sea turtles include longline gear and gillnets. Vessel strikes also cause mortality of sea turtles, especially where turtle abundance and vessel activity are high, such as areas near ports, marinas, and navigation channels.

There are five sea turtle species in the Gulf of Mexico: Kemp’s ridley, leatherback, hawksbill, and green sea turtles are listed as endangered under the Endangered Species Act; loggerhead sea turtles are listed as threatened but are currently proposed for endangered listing in the western North Atlantic, which includes the Gulf of Mexico.

Rehabilitating Oiled Sea Turtles

The Wildlife Branch, Marine Mammal and Sea Turtle Unit of the Unified Command has implemented region-wide protocols for caring for turtles in distress and established four rehabilitation/de-oiling centers: one in Louisiana, one in Mississippi, and two in Florida. Additional facilities are on standby if needed.

NOAA is working closely with the U.S. Fish and Wildlife Service, through the Unified Command, on addressing issues of concern on sea turtle nesting beaches in the Gulf of Mexico as well. Wildlife teams on the water have been instructed to bring any turtles in distress back to shore for transport to the rehabilitation facilities.

Kemp's ridley turtles

caption As adults, Kemp's ridley sea turtles have shells about two feet across and reach about 100 pounds in weight. Credit: NPS

Kemp’s ridleys are one of five sea turtle species found in the Gulf of Mexico, and have been listed as endangered under the Endangered Species Act since 1973. Juvenile and adult Kemp’s ridleys are found in U.S and Mexican waters in the Gulf of Mexico, and along the Atlantic coast as far north as Massachusetts.

Young turtles use Sargassum habitat in offshore waters, but transition to spent most of their lives in shallow waters, where they feed mostly on crabs. They nest primarily along the northeast coast of Mexico, with some nesting in southern Texas. After migrating to nesting areas, they are known to return to foraging areas. Kemp’s ridleys do not get as big as other sea turtles, but reach maturity earlier (approximately 12 years). While there is no way to directly age sea turtles, we estimate based on size that the turtles released today are 1-3 years old. We do not know how long Kemp’s ridleys live.

Rehabilitated Kemp’s Ridley Sea Turtles Released

On August 18, 23 Kemp’s ridley turtles were released, 22 of which were found offshore, moderately to heavily oiled. The other turtle was found on shore, and though not oiled, was debilitated and underwent rehabilitation.

The goal with any wild animal taken into captivity for care and treatment is to release it to its natural habitat as soon as possible. The turtles have been treated and cared for, and are healthy and ready for release.

The 22 oiled turtles rescued from offshore waters were found between 40 and 60 nautical miles offshore of Destin, Florida (11 turtles) and Venice, Louisiana (11 turtles). The turtle that stranded on shore was found in the Florida panhandle.

All were rescued by teams working under the direction of the Wildlife Branch within Unified Command. These teams consist of dedicated sea turtle biologists from NOAA, U.S. Fish and Wildlife Service, Florida Fish and Wildlife Conservation Commission, Georgia Department of Natural Resources, U.S. Geological Survey, Riverhead Foundation, and In-Water Research Group. They have been supported by an expert group of captains and crews working within the Vessel of Opportunity program.

caption Kemp's Ridley turtles are returned to the Gulf for release off Cedar Key, Florida, following rehabilitation from oil exposure resulting from the Deepwater Horizon/BP spill. Credit: NOAA

All previously oiled turtles released were cleaned of oil, treated, and cared for at The Audubon Aquarium in New Orleans and Gulf World in Panama City, Florida. After initial care and stabilization, they were moved to secondary rehabilitation facilities – Sea World Florida, Mote Marine Laboratory, and the Florida Aquarium. Other facilities assisting in this effort include the Institute for Marine Mammal Studies, Gulfarium, Clearwater Aquarium, and Disney’s Living Seas.

These turtles were released offshore of Cedar Key, Florida, back into the Gulf of Mexico. These turtles are at the size at which they transition from an oceanic to a nearshore life stage, and the Cedar Key area is home to many of this size and age.

There is no evidence that oil from the Deepwater Horizon incident ever entered the habitat in Cedar Key. The habitat is healthy, supports a healthy population of Kemp’s ridleys and will provide all the elements required for their survival and growth.

All of the turtles had internal tags placed in a flipper. These Passive Integrated Transponders (PIT tags) are the same kind veterinarians place in dogs and cats. All turtles found stranded or captured during directed sea turtle research programs are scanned for PIT tags, providing a way to identify turtles throughout their life.

Current status of turtles

Since early in the spill, responders have searched for turtles offshore and onshore. Over time, the number of turtles requiring rehabilitative care has declined. Now, unoiled turtles can be found in places where, before mid-July, only oiled turtles were found. Those that are still found with evidence of oiling are only lightly or very lightly oiled. The convergence areas now contain living, unoiled prey, with turtles actively feeding and behaving normally in most cases. Most turtles found offshore now are quickly examined by wildlife teams and released to their habitat.

Additional threats to Kemp’s ridleys and other species of turtles

The primary threat to turtles is incidental capture in commercial and recreational fisheries, primarily by trawls not equipped with Turtle Excluder Devices (TEDs) and gillnets. A significant number are also caught on hook and line gear used on piers. The historically significant threat posed by poaching of eggs and nesting turtles has been greatly reduced by strong efforts by Mexico and the U.S.

Oil Spill Clean-Up and Nesting Turtles

Night operations are a viable method for oil clean-up because they minimize heat stress in light of rising heat indices that occur during the day, promoting worker safety. Since sea turtles may potentially nest at any shoreline location, it is important to recognize potential risks to turtles during clean-up operations.

Nighttime clean-up of oiled beaches and spill-related debris can present risks to turtles, which are sensitive to human disturbance. The operation of heavy machinery and vibrations from its use, the use of bright lighting, and large numbers of people moving on the beach can cause great disturbance. Nesting turtles can get injured by foot and equipment traffic that compress sand, which also makes it difficult for females to dig nests and for hatchlings to dig out. Machinery and boom may interfere physically with a turtle’s ability to get into the water or may prohibit females from beaching to nest. Machinery may inadvertently destroy eggs or erase turtle tracks that help us find, protect, and possibly relocate eggs. Vibrations from heavy machinery may result in hatchlings emerging from their nests during the day, timing that may leave them more vulnerable to predators. Hatchlings can become disoriented by machinery’s bright light, which interferes with their ability to be guided to the surf by moonlight.

caption Kemp's ridley hatchlings. Credit: NPS

Some clean-up crews have discovered nests as a result of observations during oil clean-up. These efforts will keep beaches clear of oil, which should help turtles as they crawl down to the shoreline and enter the surf after nesting.

Conservation agencies working with the Unified Command have established measures to minimize the potential adverse effects of clean-up efforts on turtles. All beaches are considered potential turtle habitats, and personnel are informed that turtles may be present in any operations area.

Generally, certain notifications need to be made prior to any nighttime operation. A turtle advisor (TA) will examine the area prior to work and look for any evidence of sea turtle activity. If turtles are located, the TA will be responsible for staging areas to avoid the site, and the area will be flagged so there will be no human or equipment intrusion. A resource advisor (READ) also will be onsite to monitor and advise the work crew about turtle presence. In areas where turtles nests are positively observed, people should keep noise to a minimum, use conversational voices, and not shout or yell within a nest perimeter. Efforts should be made to avoid nests on beach. The number of crews and active cleaners at any given time will be limited to necessary personnel, and a 200-foot perimeter will be maintained between turtles and any beach clean-up operation. If turtle tracks are spotted, READs and TAs will document this evidence.
 

Glossary

Citation

(2010). Sea turtles and the Deepwater Horizon oil spill. Retrieved from http://www.eoearth.org/view/article/51cbefbc7896bb431f69ed82

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