Nav: Home

Stress test: New study finds seals are stressed-out by sharks

December 05, 2017

MIAMI -- While a little added stress may be helpful to flee a dangerous situation, or to meet an approaching deadline, it's no secret that prolonged exposure to the stress hormone cortisol is linked to health problems. So, what effects does stress have on animals in the wild that need to navigate the same waters as the ocean's top predator -- great white sharks?

Predators are known to impact the population abundances of their prey by killing and consuming them. But can predators in the wild also exert control over their prey from the stress associated with living in high-risk waters?

University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science-led research team found just the right situation -- fur seals living among one of the densest populations of great white shark off South Africa's Western Cape -- to test this predation-stress hypothesis in the wild.

In the three-year study, the scientists focused their investigation on six islands in the region where Cape fur seals (Arctocephalus pusillus) colonies have varied seasonal exposure to hunting great white sharks (Carcharodon carcharias). To evaluate the seals' stress levels in relationship to hunting sharks, the team collected hundreds of seal fecal samples and measured them for glucocorticoid metabolite concentrations (fGCM), a cortisol stress hormone.

The team compared stress hormone levels in seal fecal samples with residency patterns of great white sharks at the different seal colonies based on satellite tagging data. The team also compared seal fecal cortisol concentrations with measured shark attack rates on seals at one the sites.

The researchers found that seals exhibited high stress levels when the risk of great white shark attack was high, at locations where and when the seals were under risk of unpredictable and lethal attack from great whites as the seals they left the safety of an island's inner perimeter and passed through a gauntlet of white sharks hunting to reach offshore feeding grounds.

"Our findings showed that seals exhibited high stress in the places and at the times when great whites were hunting and the seals had no way of anticipating or effectively preventing a predation attempt from any shark that decided to attack," said the study's lead author Neil Hammerschlag, a research assistant professor at the UM Rosenstiel School and UM Abess Center for Ecosystem Science and Policy.

"Comparable stress responses were not detected in places and times where sharks were not hunting. Interestingly, stress responses were also not detected at one island where seals could reduce their risk of attack by using kelp beds and reef as underwater refuges, despite the presence of hunting great whites," said study co-author Scott Creel, a Professor at Montana State University.

In one location, called Seal Island in False Bay, the seals' fecal stress levels were highly correlated with weekly shark attack rates. However, seals did not show comparable signs of stress at another location known as Geyser Rock in Gansbaii, which contains kelp beds and reefs that the seals use as natural safe passageways from sharks as the move about the island.

Based on the findings, the authors suggest that predation risk will produce physiological costs in the form of a stress response when risk cannot be adequately predicted or controlled by behavioral responses.

"These results underline the ecological importance of apex predators," said Hammerschlag. "Any resulting loss in health or survival of prey due to predator-induced stress could have cascading effects on the entire ecosystem and food web."
-end-
The study, titled "Physiological stress responses to natural variation in predation risk: evidence from white sharks and seals," was published on December 1 in the journal Ecology, DOI: 10.1002/ecy.2049.

The study's authors include: Michael Meÿer, Simon Mduduzi Seakamela and Steve Kirkman from the Republic of South Africa's Department of Environmental Affairs, Chris Fallows of Apex Shark Expeditions, and Scott Creel from Montana State University. Funding for the study for provided in part by Canon USA and the Herbert W. Hoover Foundation.

VIDEO: https://youtu.be/RgLvDaIuYG4

About the University of Miami's Rosenstiel School

The University of Miami is one of the largest private research institutions in the southeastern United States. The University's mission is to provide quality education, attract and retain outstanding students, support the faculty and their research, and build an endowment for University initiatives. Founded in the 1940's, the Rosenstiel School of Marine & Atmospheric Science has grown into one of the world's premier marine and atmospheric research institutions. Offering dynamic interdisciplinary academics, the Rosenstiel School is dedicated to helping communities to better understand the planet, participating in the establishment of environmental policies, and aiding in the improvement of society and quality of life. For more information, visit: http://www.rsmas.miami.edu. To learn more about the Unviersity of Miami's Shark Research and Conservation Program, visit http://www.SharkTagging.com

University of Miami Rosenstiel School of Marine & Atmospheric Science

Related Stress Articles:

How do our cells respond to stress?
Molecular biologists reverse-engineer a complex cellular structure that is associated with neurodegenerative diseases such as ALS
How stress remodels the brain
Stress restructures the brain by halting the production of crucial ion channel proteins, according to research in mice recently published in JNeurosci.
Why stress doesn't always cause depression
Rats susceptible to anhedonia, a core symptom of depression, possess more serotonin neurons after being exposed to chronic stress, but the effect can be reversed through amygdala activation, according to new research in JNeurosci.
How plants handle stress
Plants get stressed too. Drought or too much salt disrupt their physiology.
Stress in the powerhouse of the cell
University of Freiburg researchers discover a new principle -- how cells protect themselves from mitochondrial defects.
Measuring stress around cells
Tissues and organs in the human body are shaped through forces generated by cells, that push and pull, to ''sculpt'' biological structures.
Cellular stress at the movies
For the first time, biological imaging experts have used a custom fluorescence microscope and a novel antibody tagging tool to watch living cells undergoing stress.
Maternal stress at conception linked to children's stress response at age 11
A new study published in the Journal of Developmental Origins of Health and Disease finds that mothers' stress levels at the moment they conceive their children are linked to the way children respond to life challenges at age 11.
A new way to see stress -- using supercomputers
Supercomputer simulations show that at the atomic level, material stress doesn't behave symmetrically.
Beware of evening stress
Stressful events in the evening release less of the body's stress hormones than those that happen in the morning, suggesting possible vulnerability to stress in the evening.
More Stress News and Stress Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at Radiolab.org/donate.