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SoutherrightwhaleCredit: Andrea Chirife, Southern right whale health monitoring program

Deaths of Whale Calves Linked to Algal Blooms

A new study by NOAA has found evidence that links the mysterious deaths of right whale calves to harmful algal blooms

The baby whales suddenly began dying in 2005, with the average number of right whale deaths per year at Peninsula Valdes on the coast of Argentina jumping from fewer than six per year before 2005 to 65 per year from 2005 to 2014.

90 per cent 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.

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.’

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.

Scientists know that whales may directly consume the toxic algae as they filter ocean water for food or may be exposed indirectly through their prey, which can also feed on the toxic algal cells. But the blooms can be spotty, with high concentrations in some places but not others. Scientists also have a difficult time obtaining blood or tissue samples from stricken whales for testing. Only a very few Argentinian whales tested for domoic acid carried detectable levels of the toxin.

Given the lack of solid evidence the new study does not definitively prove that the toxic algae caused the spike in deaths of whale calves. But it does offer strong circumstantial evidence, and that puts researchers in a better position to understand the possible impacts of future algal blooms.

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