Whale Earwax Helps Reconstruct Stress Levels Spanning More Than a
November 12, 2018
In a follow-up to
their groundbreaking study, Baylor researchers were able to reconstruct
baleen whales’ lifetime stress response to whaling and other manmade and
environmental factors spanning nearly 150 years.
Using a technique they pioneered six years ago, Stephen J. Trumble,
Ph.D., associate professor of biology, and Sascha Usenko, Ph.D.,
associate professor of environmental science, both in Baylor
University’s College of Arts & Sciences, analyzed earplug laminae, a
growth layer representing six months found in whale earwax, as part of
their recent study published in Nature Communications this month.
Using earplugs taken from fin, humpback and blue whales originating in
the Pacific and Atlantic Oceans from 1870 to 2016, Trumble and Usenko
were able to determine the whales’ cortisol levels, a stress-response
hormone, to industrial whaling, World War II wartime activities and
“This is the first-ever study to quantify temporal stress patterns in
baleen whales,” Trumble said. “While the generated stress profile spans
nearly 150 years, we show that these whales experienced survivor stress,
meaning the exposure to the indirect effects of whaling, including ship
noise, ship proximity and constant harassment, results in elevated
stress hormones in whales spanning vast distances.”
J. Trumble, Ph.D., associate professor of biology in Baylor University's
College of Arts & Sciences
Whaling had a
significant impact on whales’ cortisol levels. During the 1960s when
whaling was at its peak with 150,000 whales harvested, cortisol peaked
to a maximum and was the highest average in whales in the 20th century,
according to the study’s findings.
Second in a three-part exclusive online look at content from the Natural
History Museum's Whales: Beneath the surface exhibition featuring Dr.
Stephen J. Trumble and Dr. Sascha Usenko.
During World War II when whaling declined, whales still showed an
increase in cortisol levels. Trumble and Usenko suggest the impact of
the theater of war.
Usenko, Ph.D., associate professor of environmental science in Baylor
University's College of Arts & Sciences
associated with activities specific to WWII may supplant the stressors
associated with industrial whaling for baleen whales,” Usenko said. “We
surmised that wartime activities such as under water detonation, naval
battles including ships, planes and submarines, as well as increased
vessel numbers, contributed to increase cortisol concentrations during
this period of reduced whaling.”
When whaling moratoriums were introduced in the mid-1970s, whaling
decreased as well as cortisol levels—reaching their lowest
the 1970s through the 2010s whaling counts were reportedly zero in the
Northern Hemisphere, but mean cortisol levels steadily increased, with
recent peaks reaching near the maximum levels observed before whaling
moratoriums,” Usenko said.
The impact of stress on whales could have larger implications for baleen
whales, which are “considered sentinels of their environment and
indicators of anthropogenic or manmade stressors,” Usenko said.
“This study shows that anthropogenic stressors results in a
physiological response in large whales. These chronic stressors may
impact life history events such as reproductive parameters,” Trumble
said. “Lastly, human-based stressors such as warming sea surface
temperatures may also result in elevated stress in these whales.”
The research pair has expanded the number of museums they partner with
and currently have more than 100 additional earplugs to process.
Earplugs were provided through a collaboration between the investigators
and the Smithsonian Museum of Natural History and the Museum of Natural