Investigating mysterious deaths is all in a day's work for many a whale scientist. The gargantuan animals they study spend much of their lives at depth or offshore, their day-to-day activities out of sight. So when one washes up dead, it can be nearly impossible to trace the clues back to a particular cause. That is the case for a team of scientists struggling to figure out what killed not one, but nine endangered fin whales off the coast of Alaska's Kodiak Island.

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Image: University of Alaska Fairbanks Gulf Apex Predatory-Prey Project/Used with permission.
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Image: MV Kennicott Crew courtesy of NOAA

The first whale washed up in late May, and at the time, the team didn't think much of it. "This particular whale was an adult female," explains University of Alaska Fairbanks marine biologist Briana Witteveen. "The second was a very small female calf, so our first thoughts were that the adult was killed by a ship strike and the calf simply died as a direct result of losing its mother. It wasn't until the third adult whale was reported dead that we began to become concerned that something more was going on." 

Because of the locations of the carcasses, the team has only been able to perform a necropsy on one whale, which was pushed ashore by heavy surf. A bit of careful cutting revealed a healthy blubber layer, indicating the behemoth whale was able to feed properly, and likely wasn't sick.

"We had plans to conduct a second necropsy, but the carcass washed away with the tide the night before," says Witteveen. "The remaining carcasses are either floating or inaccessible. Unfortunately, they're now getting quite old and necropsies on any that make landfall at this point would not be very informative."

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Image: University of Alaska Fairbanks Gulf Apex Predatory-Prey Project

The deaths coincide with sightings of toxic algal blooms (or red tides) in the area, and while initial reports suggested these might not be the cause, they're now beginning to look more and more like the culprit. 

"At this point, it's the most likely answer," says Witteveen. "But we may never be able to say for certain. It does seem odd that if [red tides] were the cause that we would not see fish or other species die-offs, but there have been reports of a large number of common murres [marine birds] dying, as well as a number of walruses on the Alaska Peninsula."

At the heart of the problem, Witteveen explains, is that we don't fully understand how the biotoxins released by algal blooms impact cetaceans such as whales. Their elaborate physiology might make these ocean giants and their kin more sensitive to the neurological effects of biotoxins.

"A very local bloom may have disproportionately impacted a single group of whales, while not impacting fish," she says. 

Fin whales can be spotted off the Kodiak Archipelago year round, but peak sightings occur between May and October, when more whales come North in search of food. So it's likely these nine whales were foraging in a single locale. 

"They can be found feeding in tight aggregations," Witteveen explains. "If the biotoxin was localised, it could affect a group of whales that were feeding together." 

The team is still exploring all possibilities while they await test results from the sinlge necropsy, and hope to at least figure out if this was a single event. "We'll be monitoring water samples at various locations around Kodiak to look for potential biotoxins," says Witteveen. "We'll continue to do so throughout the remainder of the summer, and are encouraging continued reports of unusual observations or die-offs from other scientists, as well as recreational boaters or beach combers." 

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Foraging fin whales can be seen around Kodiak Island year round. Image: University of Alaska Fairbanks Gulf Apex Predatory-Prey Project

Top header image: Georgia Wildlife Resources Division/Flickr