The Gulf of Mexico is home to approximately 1,700 sperm whales. Many of them feed just off the continental shelf, particularly around the Mississippi River delta, an area filled with ample food for these huge marine mammals. The whales reside in family groups, and rarely mingle with other sperm whale groups from the open Atlantic Ocean. They live as long as us, but reproduce at most only every five years. The Gulf of Mexico is their full-time home.
Since the Deepwater Horizon oil rig exploded and sank over sixty days ago, scientists have been concerned with the fate of Gulf of Mexico sperm whales. Sperm whales have been sighted in the fouled waters themselves, and no one knows what effect oil droplets will have on whale physiology and behavior. In addition, BP and the U.S. Coast Guard have been using unprecedented levels of chemical dispersants to scatter oil in the water, and no research has been done on the effect of even small amounts of these dispersants on cetaceans.
Given these uncertainties, the National Oceanic and Atmospheric Administration’s discovery this week of a dead sperm whale near the spill zone is a particularly troubling find. On Tuesday, the NOAA ship Pisces cited the decayed corpse of a young, 25 foot long sperm whale adrift nearly 80 miles from the site of the (former) Deepwater Horizon oil rig. Based on the decay of the body and the degree of scavenging by sharks, scientists estimate the whale perished several days ago, but don’t yet know the cause of death. They have taken tissue samples to help determine how the whale may have died, and hopefully analysis of the whale’s genome will determine its sex, and whether or not it was definitely from the endangered Gulf of Mexico population (which, given its location, it probably was). Skin samples taken may determine whether the whale was exposed to large amounts of oil before it died. However, since the whale’s body was adrift for days, scientists will have to infer where it died based on current patterns in the area where the body was found, weather conditions over the past week, and forensic clues of the time of the whale’s death.
All in all, a dead sperm whale is a rare find in the Gulf of Mexico, and this discovery so close to the site of the oil spill may be a harbinger of the spill’s lasting effects on the Gulf’s ecosystem. However, more won’t be known until scientists announce the whale’s cause, time, and location of death. In the meantime, the NOAA vessel Gordon Gunter put to sea on Wednesday to survey Gulf of Mexico cetaceans and catalog some of the oil spill’s effects on their ecology, physiology, and behavior. The ship’s mission also includes orders to observe the Gulf’s endangered sperm whales, all 1,699 of them.
Image of a sperm whale diving near a deep water rig in the Gulf of Mexico provided courtesy of Christoph Richter, the Sperm Whale Seismic Study, the U.S. Office of Naval Research, the Minerals Management Service of the U.S. Department of the Interior, Oregon State University, and Texas A & M University.