Stress hormones soar in whales trapped by fishing lines
In one more sign that North Atlantic right whales are struggling, a new study finds sky-high levels of stress in animals that have been caught in fishing nets.
Researchers determined the stress hormone levels of more than 100 North Atlantic right whales over a 15-year period by examining their feces. Sometimes guided by sniffing dogs, researchers followed the animals, collecting waste samples that they then analyzed in their lab at the New England Aquarium.
Results from the feces of 113 seemingly healthy whales helped establish a baseline of stress hormone levels, which had never before been known for the species. “We have a good idea of what normal is now,” said Rosalind Rolland, who developed the research technique and is the lead author of the study published in the journal Endangered Species Research.
She then compared these baselines to hormone levels in the feces of six whales that had become entangled in fishing lines, and one that had been stranded for several days, finding that those animals were off-the-charts anxious.
One whale, a young female named Bayla, showed stress levels eight times higher after she was found entangled in synthetic fishing ropes in January 2011. Several biologists trained in disentanglement could not get all the gear off her, so they sedated the emaciated animal and gave her antibiotics. Two weeks later, an aerial survey team found her corpse floating at sea, possibly after being attacked by sharks, which typically leave healthy animals alone. A necropsy conducted a few days later found rope embedded in the back of Bayla’s throat, which possibly prevented her from eating.
“This highlights the extreme physical suffering these animals are going through when they’re entangled in fishing lines,” said Rolland, a senior scientist in the Ocean Health and Marine Stress Lab at the Anderson Cabot Center for Ocean Life at the New England Aquarium.
Because hormone levels take several hours to rise after a stressful event, Rolland said that tests on five animals that died quickly when hit by ships showed stress levels similar to those in healthy animals.
This has been a disastrous year for the North Atlantic right whale, whose population now hovers below 450. Sixteen or 17 animals have died since the beginning of the summer, and only five have been born, according to Charles “Stormy” Mayo, director of the Right Whale Ecology Program at the Center for Coastal Studies in Provincetown, Mass., who was not involved in the new study.
“It used to be if we heard about one or two whales dying in a year, it was an appalling tragedy,” Mayo said.
Although once considered a species conservation success story, the population of North Atlantic right whales has been falling since about 2010, he said.
Although the reasons for the deaths are varied, and some remain mysterious, it seems the animals are exploring new areas in search of food, putting them in direct conflict with ships and heavy fishing lines, Rolland said.
The Gulf of Maine, which has long been central to their habitat, is one of the fastest-warming bodies of water on earth, she said.
North Atlantic right whales, which can weigh as much as the space shuttle, exclusively eat nearly microscopic creatures called zooplankton. About 80 percent of the animals carry scars from past entanglements or ship strikes.
Analyzing hormones in feces — in addition to newer efforts to study the vapor exhaled from the animals’ blowholes — provides scientists an objective way to test what is stressing the whales and whether efforts to improve their habitats are working.