Kemp’s Ridley NRDA Assessment
Excerpt from Natural Resource Damage Assessment Status Update for Deepwater Horizon Oil Spill
6. Sea Turtles
There are five sea turtle species living in the Gulf of Mexico listed as threatened or endangered under the Endangered Species Act: Kemp’s ridley (Lepidochelys kempii), green (Chelonia mydas), leatherback (Dermochelys coriacea), loggerhead (Caretta caretta) and hawksbill (Eretmochelys imbricata). The western Gulf of Mexico is the primary place in the world where the Kemp’s ridley sea turtle nests.
Sea turtles can be exposed to chemicals in oil or dispersants in several ways:
- Internal exposure by consuming oil or contaminated prey or inhaling volatile oil and dispersant-related compounds,
- External exposure to sea turtles or eggs from oiled nesting beaches,
- External exposure by swimming in oil or dispersants and having oil or dispersants directly on the skin and body, and
- Maternal transfer of contaminants to embryos and eggs.
In addition to chemical exposure, response activities, such as collecting and burning oil at sea, skimmer operations, boom deployment, berm construction, increased light at night on or near nesting beaches, equipment use and storage as a result of beach cleanup operations and boat traffic could directly injure sea turtles, block access to turtle nesting beaches and/or cause behavioral changes.
The goals of the sea turtle assessment plans are:
- To document the pathway, exposure and injury using field measurements and observations and
- To quantify the level of injury using field sampling, population observations, laboratory analysis and existing toxicity literature.
Information on Kemp’s ridley nesting success and habitat utilization collected by National Park Service Padre Island National Seashore, home to a successful nesting colony of Kemp’s ridley, will provide baseline for sea turtles. Sea turtle nesting surveys have been routinely conducted on ~368 km of Florida Panhandle beaches (Escambia County through Franklin County) since 1989 and on 75 km of Alabama beaches (Mobile and Baldwin counties) since 2003. These surveys are conducted with consistent levels of effort that allow year to year comparisons.
Trustees are assessing exposure to all sea turtles but specifically those observed to be most affected: loggerhead and Kemp’s ridley sea turtles. The trustees have divided the northern Gulf of Mexico assessment area into three geographic ecological zones:
(1) nesting beaches,
(2) coastal waters (neritic zone) where juveniles and adults live and feed, and
(3) open ocean waters where post-hatchlings, juveniles and adults live and feed, especially in and around floating Sargassum.
Given the potential routes of exposure and threats described above, the trustees are conducting a series of studies designed to better understand and quantify the presence and distribution of these sea turtles in the northern Gulf of Mexico and the level of contaminant exposure they may have experienced.
For the neritic turtles, aerial surveys and satellite telemetry have been and are being conducted to document abundance and spatial distributions. Samples from dead, stranded animals are collected in an attempt to determine potential exposure to oil-related contaminants. Figure 17 shows locations where trustees have located stranded sea turtles.
For oceanic turtles, an important component of the sea turtle assessment is the assessment of Sargassum habitat. Sargassum is highly productive marine seaweed that floats at the surface of the ocean and provides the framework for a large, floating oceanic ecosystem. This habitat or mini-ecosystem provides an environment for a distinctive and specialized group of marine animals and plants, many of which are not found elsewhere. The habitat is important to juvenile fish and turtles, which seek food and shelter in Sargassum. It, like the surface oil, tends to aggregate in oceanic convergence zones created by the wind and currents.
Throughout the summer and into the early fall 2010, large swaths of Sargassum were observed as being oiled. As a result, the Sargassum habitat acted as a focal point for the exposure of oil to many types of sea life, including sea turtles, which are susceptible to dermal contact, inhalation and ingestion of oil. Oiled Sargassum can sink — resulting in a loss of habitat —which also contributes to the injury.
As presented in Section III.4, Sargassum is a vital open water habitat for sea turtles, particularly juveniles. During the oil spill, sea turtle rescue efforts documented 574 turtles in this habitat, 464 of them visibly oiled. Also, the floating mat provides shelter and attracts a diverse array of marine organisms. The trustees are examining the density and diet of sea turtles in this geographic zone via boat surveys. To this end (impact on prey abundance), they also are looking at fish and invertebrate density, abundance, diversity and contaminant concentration in and around Sargassum habitats that may have been impacted by the oil spill.
To determine the direct impacts of oil to sea turtle health and reproductive output, the trustees have conducted and continue to conduct studies assessing the physical condition of the nesting female loggerhead and Kemp’s ridley sea turtles, as well as inter-nesting movements, blood chemistry, egg and hatchling toxicity, and hatching and emergence success.
Trustees working as part of the spill response translocated 274 nests from northern Gulf of Mexico beaches to the Atlantic coast of Florida during summer 2010. A total of 14,796 hatchlings were released into the Atlantic to avoid potential exposure to Deepwater Horizon oil. Trustees also have collected more than 500 turtle eggs for chemical and toxicological analysis. To document changes in the abundance, distribution and movement of female sea turtles, the trustees have collected satellite tag data on 28 sea turtles, which could indicate potential impacts resulting from the oil spill. Additionally, trustees are collecting and analyzing beach sand for chemical, toxicological and physiologically relevant levels of oil and constituents along nesting beaches in the Gulf of Mexico.
Figure 17. This map illustrates the locations in which trustee researchers have located stranded sea turtles in the Gulf of Mexico from the start of the spill through late 2011.
Turtle nests were relocated as part of the oil spill response.
Aerial surveys were conducted seasonally from April 2011 through April 2012 to cover broad-scale synoptic surveys of the continental shelf and shelf break from Brownsville, Texas, to Dry Tortugas, Florida. The purpose was to collect information on distribution, abundance, species identification and exposure of sea turtles.
Sea turtle prey sampling began in September 2011 to assess potential exposure through contaminated prey in the estuarine/coastal environment. The prey samples, including those taken in 2010 and 2011, will undergo chemical analysis for oil and dispersant-related compounds.
During the response, hematology and blood chemistry data were collected for 350 live sea turtles. The trustees plan to do a full analysis and interpretation of the results to assess the health impacts and mortality risk for these animals.
Several sea turtle studies concluded in 2011. These include Sargassum studies related to sea turtle abundance and prey availability, necropsy analysis of sea turtles and netting surveys west of the Mississippi River Delta.
For Kemp’s ridley and loggerhead sea turtles, the trustees are continuing a multi-year field study to assess potential exposure and effects on nesting females, their nests and eggs. The study will include tagging females for post- and inter-nesting distribution information and chemical and toxicological analysis of embryo mortalities and hatchling tissue. The trustees will also assess the role the response actions may have had on nesting and hatchling success (e.g., beach cleaning and nest translocations).
Relevant Work Plans
Relevant work plans can be found by visiting http://www.gulfspillrestoration.noaa.gov/oil-spill/gulf-spill-data.
View NRDA Status Assessment Update April 2012 at http://www.gulfspillrestoration.noaa.gov/.