Just like the rings on a tree detail a history of drought in a forest, a whale’s baleen plate can paint a picture of the whale’s life and death. By analyzing hormones across the length of a bowhead whale’s baleen plate, scientists at the New England Aquarium’s Anderson Cabot Center for Ocean Life found evidence of months of chronic stress from a severe entanglement in fishing gear.
“This was not a subtle change. There was a very clear stress hormone signal on the plate when the whale became entangled,” said Dr. Rosalind Rolland, lead author on the paper and Senior Scientist at the Anderson Cabot Center.
Baleen, it turns out, is a treasure trove of information for scientists. Using estimated baleen growth rates, scientists can determine when a stressful event happens within a span of months.
Rolland obtained a baleen plate from a bowhead whale that was severely entangled in fishing gear when he died in May 2017. A paper outlining the study of whale 17B6 was published online on March 25 in Marine Mammal Science.
By taking samples of glucocorticoid hormones along the length of the plate, the scientists estimated the timeline of the entanglement event between autumn 2016 and early winter 2017. They compared the levels of stress hormones before and after the entanglement occurred. Compared to healthy bowhead baselines, the the entangled whale’s cortisol jumped to six to 10 times higher. The peak cortisol level was 20 times higher than the whale’s baseline. This whale was in poor condition and declining health for months before its death.
In addition to the poor condition of the whale, the growth of algae and marine worms on the rope wrapped around 17B6 suggested the entanglement was of long duration. Although the gear wasn’t marked, rope characteristics were consistent with Bering Sea fixed gear pot fisheries (crab and cod).
The team compared whale 17B6’s baleen hormone levels with those of seven other bowhead whales, and fecal stress hormones in the entangled whale were also highly elevated at the time of death, demonstrating a stress response in a second sample type.
“We were able to compare the levels of hormones both to this whale’s own baseline for a decade before entanglement and seven other bowhead whales,” said Rolland.
Why is all this data important?
“You can get a lot of health history with baleen,” said Rolland. “At times when you can’t get a blood sample or any other way to study physiology, it’s amazing that you can use baleen to get a health record for the previous decade of a whale’s life.”
And the more information you have, the better.
“When your doctor draws blood on you and looks at a diagnostic panel of biomarkers or blood cells, there are established ranges that are normal. There is some individual variation, but for most molecules, there’s a normal range of values,” said Rolland. “It’s the same for whales.”
A Changing World
Because of climate change, human activity in the Arctic and human impacts on Arctic wildlife are on the rise. From resource extraction to vessel traffic and commercial fishing, human activities have greater affects on Arctic ecosystems.
Entanglement in fishing gear is already among the most significant human-caused threats to the world’s large whale species. As fishing and shipping increase in the Arctic, it’s vital to have a system in place to evaluate long-term stress physiology in the species native to those waters. This study shows that baleen hormone analysis has great promise as an approach for monitoring of stress physiology to assess bowhead whale responses to environmental changes and increased human activity occurring in Arctic ecosystems.
“This study shows that levels of baleen stress hormones are biologically meaningful. The hormones we are measuring have a relationship to what’s happening physically inside the whale,” said Rolland. “It’s a big-time validation of this scientific approach.”
Banner Image: Two bowheads swim near sea ice.
Credit: Kate M. Stafford, Univ. of Washington.