Critical hormones affected in almost half the marine mammals studied
By Bob Berwyn
SUMMIT COUNTY —The scope of the Deepwater Horizon oil disaster was so unprecedented that biologists weren’t sure what they would find when they started investigating dolphin health in Barataria Bay, off the coast of Louisiana.
What they did find was disturbing. Many dolphins are underweight and anemic, have low blood sugar and suffers symptoms of liver and lung disease, NOAA researchers said last week. Nearly half of the 32 dolphins studied also have abnormally low levels of hormones that help with stress response, metabolism and immune function.
“This was truly an unprecedented event – there was little existing data that would indicate what effects might be seen specifically in dolphins (or other cetaceans) exposed to oil for a prolonged period of time,” Dr. Lori Schwacke said via email. “However, there have been experimental studies of health effects in another mammal (mink) exposed to oil over several months, and the health issues that we see in these dolphins are consistent with the adverse effects seen in the mink studies,” she said.
Schwacke said 44 percent of the dolphins sampled in Barataria Bay had abnormally low levels of serum cortisol, a hormone produced by the adrenal glands which is crucial for stress response but also has an important role in other body functions such as metabolism and immune function, Schwacke said.
“In addition, many of the dolphins also had low levels of another adrenal hormone, aldosterone. The low levels of both of these hormones provide evidence for adrenal insufficiency,” she said.
One quarter of the dolphins studied in the bay were classified as underweight and four of the 32 dolphins (12.5 percent) were given a “poor” or “grave” prognosis (indicating that they likely would not survive). Nearly half of the Barataria Bay dolphins were given a “guarded” or worse prognosis. (Prognosis scale = good – fair – guarded – poor – grave).
The NOAA researchers also used a control group of dolphins that weren’t exposed to oil to check their results.
“We … worked with collaborators from the Chicago Zoological Society to conduct similar evaluations of dolphins in Sarasota Bay, Florida, which did not receive oil following the (Deepwater Horizon) oil spill,” Schwacke said. In all, 27 dolphins were evaluated from Sarasota Bay using the same methods during May 2010 and May 2011.
“None of the Sarasota dolphins showed low cortisol levels and none were classified as underweight. Only one of the 27 dolphins was given a “guarded” prognosis, all others were at least fair or good,” she said. A preliminary estimate suggests there are about 1,000 dolphins in Barataria Bay.
“We believe that the dolphins that we evaluated are representative of the Barataria Bay population. We attached satellite-linked tags to 25 of the dolphins and have been able to track their movements for several months following the health evaluations. We’re finding that the dolphins we evaluated are staying inside Barataria Bay or in coastal waters just outside the Bay,” she said.
“We have also been conducting photo-identification surveys in Barataria Bay periodically (every 4 months) since the summer of 2010, also as part of the Natural Resource Damage Assessment. The photo-identification surveys are showing that many of the same dolphins are being resighted over time, indicating that there is a resident population in Barataria Bay. So, the fact that our tagged dolphins appear to be staying in the Barataria Bay area is consistent with our photo-identification study which indicates a resident population,” she said.
The researchers are still trying to determine exactly how the dolphins were exposed to the oil with additional studies.
“It’s possible they could have inhaled vapors at the water’s surface, they could have ingested oil from sediment or water while feeding, they could have absorbed it through their skin, and/or they could have ingested it by eating whole fish, including internal organs and fluids such as bile and liver which harbor chemical contaminants,” Schwacke concluded.
Filed under: biodiversity, BP Gulf oil spill, Environment, Marine biology Tagged: | Barataria Bay, Deepwater horizon oil spill, dolphins, Gulf of Mexico, marine mammals, National Oceanic and Atmospheric Administration