Right Whale Die-Offs: Toxic Algal Blooms May Be Culprit, New Study Shows

The Valdes Peninsula is a very important calving ground for southern right whales on the coast of Argentina. In recent years, however, right whales – the the majority of them were young calves – have been dying off at an alarming rate. Until now, scientists were unsure what could be causing such a spike in mortality, but a recent analysis suggests toxic algal blooms may be to blame.

For their study, researchers from the National Oceanic and Atmospheric Association (NOAA) took a closer look at recent whale deaths near the Valdes Peninsula. In doing so, they found that an increase in deaths occurred around the same time toxic algae (Pseudo-nitzschia) bloomed, according to the group's news release.

Some species of Pseudo-nitzschia produce a potent neurotoxin called domoic acid that affects the brain, causing right whales to become lethargic, disoriented and even seizures, which may ultimately result in death. Researchers found domoic acid present in some tissues of dead whales and in some whale feces. While their study does not provide definitive proof, it point researchers in the right direction.  

"The numbers hinge at the same point and have the same pattern," Cara Wilson, lead author of the study and an oceanographer at NOAA Fisheries' Southwest Fisheries Science Center, said in the release. "What's unusual about this is how long these bloom events continued to reoccur. You don't usually have deaths every year but the calves died in high numbers every year from 2007 to 2013."

The whales could have either directly consumed the toxic algae when filtering ocean water for food or when consuming contaminated prey. While some adults may be able to filter out the water-soluble toxin through their urine or feces, developing calves are increasingly vulnerable. This is beacause fetuses may absorb the toxins during early development and then might be born in a compromised condition, researchers explained. (Scroll to read more...)

"For us, the more opportunities we have to try to examine that relationship, to link up these mortality events to potentially toxic blooms, the better we can assess the possible effects," Gregory Doucette, coauthor of the study and an oceanographer at NOAA's Ocean Service who studies the effects of harmful algal blooms on marine mammals, explained in the release. "The toxins may be causing non-lethal effects that are not fatal by themselves but affect the animals' survival."

Since algal blooms are expected to increase as a result of climate change, studies such as this one could help researchers better understand how marine species will be affected. The findings were recently published in the journal Marine Mammal Science.

Southern right whales (Eubalaena australis) are large baleen whales that can grow to be between 45 and 55 feet in length. Right whales are mostly black, but can have some white spots or raised patches of rough skin. They have a stocky body, no dorsal fin, a large head and a broad tail. Right whales prefer to eat zooplankton such as copepods or krill, which are small crustaceans. The large whales can be seen in marine waters in the southern hemisphere and their distribution depends on whether the animals are feeding, calving, nursing, or breeding. However, for much of the year their location is closely related to the distribution of their prey. In the winter, the whales are known to travel to waters near South Africa, Argentina, Australian and sub-Antarctic New Zealand. It is believed that the whales were given their name because whalers believed they were the "right" whales to hunt, according to the NOAA, in part because they swim slowly and make easy targets. They also float well when killed, which made it easier for whalers to pull on board a ship. 

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