What was killing the young right whales? New research finds a suspect

http://www.eurekalert.org/pub_releases/2015-10/nfwc-wwk102315.php

Public Release: 26-Oct-2015
What was killing the young right whales? New research finds a suspect
Study links mysterious deaths of right whale calves to harmful algal blooms
NOAA Fisheries West Coast Region

The baby whales suddenly began dying in 2005. And continued for several years running.

Scientists had never seen anything like it around Peninsula Valdes, an important calving ground for southern right whales on the coast of Argentina, or anywhere else for that matter. The average number of right whale deaths per year at Peninsula Valdes jumped more than 10-fold, from fewer than six per year before 2005 to 65 per year from 2005 to 2014.

Even more striking, 90 percent of the deaths from 2005 to 2014 were very young calves fewer than three months old. The mystery killer appeared to be targeting the nearly newborn, sometimes more than 100 calves of the endangered species each year.

Now researchers have closed in on a prime suspect: Blooms of toxic algae, the same kind that sometimes force the closure of clamming and other shellfish harvesting.

In a new paper published in Marine Mammal Science, NOAA Fisheries and NOAA Ocean Service scientists and others from the United States and Argentina found that the number of whale deaths at Peninsula Valdes closely track the concentrations of the toxic algae Pseudo-nitzschia. The higher the density of Pseudo-nitzschia, some species of which can produce a potent neurotoxin called domoic acid, the more young whales that died. When the density of algae dropped, so did the number of deaths.

The correlation is not definitive proof that the algae caused the deaths, but is strongly suggestive.

"The numbers hinge at the same point and have the same pattern," said Cara Wilson, an oceanographer at NOAA Fisheries' Southwest Fisheries Science Center and lead author of the paper. "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 finding has significance beyond Argentina, since it demonstrates that some of the largest creatures in the ocean can be vulnerable to algal blooms that are projected to increase with climate change. One of the largest harmful algal blooms of its kind hit the West Coast of the United States earlier this year following close to a year of unusually warm water temperatures offshore.

Scientists are also studying whether harmful algae could have contributed to a recent spike in the deaths of adult whales in Alaska, which NOAA has declared an Unusual Mortality Event.

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