Unusual Whale Deaths Could be Linked to Warming Oceans

On August 20, the National Oceanic and Atmospheric Administration (NOAA) released a statement declaring the recent deaths of 30 large whales in the Gulf of Alaska an "unusual mortality event." According to NOAA, an unusual mortality event is an unexpected and significant die-off of a marine mammal population. In this case, the reported die-off included 11 fin whales, 14 humpback whales, one gray whale and four unidentified cetaceans, all of which were found beached on Alaska's coastlines in the region's largest recorded stranding yet.

The exact reasons behind the recent whale deaths, three times the region's historical annual average for whale deaths, remain unknown. NOAA's declaration will prompt the formation of a collaborative investigation into the event's causes which could span months or years. Although the investigation is not yet underway, NOAA has suggested that a record-breaking toxic algal bloom caused by warmer ocean temperatures may be behind the deaths. As NOAA spokesperson Julie Speegle told The Guardian, “Our leading theory at this point is that the harmful algal bloom has contributed to the deaths.”

A large mass of warm water, commonly referred to as “the blob,” has been lingering in the North Pacific since 2013, from the Gulf of Alaska all the way down to California. The blob, which has temperatures three to five degrees Celsius (5.4 to 9 degrees Fahrenheit) above the local averages, is thought to have triggered a series of record-breaking, algal blooms. These algal blooms can contain toxins which accumulate along the good chain. Whales, which can swallow thousands of pounds of prey a day during their summer feeding season, would be particularly vulnerable to the accumulation of such toxins.

Bruce Wright, a scientist focused on toxic algal blooms, said that in the case of the blob, "All the conditions seem to be right for a significant [algal bloom] event. And associated with this major event, you would expect to see die-offs of marine mammals and seabirds and fish, and that's what we're seeing." Humans are also potentially at risk: Wright has sampled clams in Alaska containing toxin levels 80 times the levels considered safe for human consumption.

A study released earlier this year suggests mass animal die-offs are on the rise throughout the world, and as many as a quarter of them are caused by biotoxins in the environment. The study, published in the journal Proceedings of the National Academy of Sciences, found that mass die-offs have increased over time for birds, marine invertebrates and fish. The study found that biotoxicity from events such as algal blooms caused about a fourth of all mass die-off events. While the study said mammals, such as whales, have not experienced a similar increase in mass die-offs (their die-off rates remain steady), marine mammals could still be affected by the increasing number of harmful algal blooms and a changing food web.

 

Author: Gabriela Zayas