Weddell seal count: Fewer seals than previously thought
Results provide benchmark for global environmental change and
conservation

Date:
October 4, 2021
Source:
University of Minnesota
Summary:
A research team has completed a global population estimate of
Weddell seals in Antarctica, showing that there are significantly
fewer seals than previously thought. Documenting the seals'
population trends over time will help scientists better understand
the effects of climate change and commercial fishing.



FULL STORY ==========================================================================
A research team led by the University of Minnesota Twin Cities has
completed a first-ever global population estimate of Weddell seals
in Antarctica, showing that there are significantly fewer seals than
previously thought. Documenting the seals' population trends over time
will help scientists better understand the effects of climate change
and commercial fishing.


==========================================================================
The study is published in Science Advances.

The researchers, along with more than 330,000 international volunteer
citizen scientists, used hundreds of high-resolution satellite images
covering huge areas of Antarctica to complete the count. It is the first
direct population estimate ever conducted for the global distribution
of any wide-ranging wild animal species on Earth.

Their research estimates about 202,000 sub-adult and adult female
Weddell seals in Antarctica. In November, when the satellite images were
taken, male seals are mostly in the water under the ice guarding their territories so they are not captured in the images. Previous estimates
of female seals were at about 800,000.

"That doesn't necessarily mean there has been a big decrease of Weddell
seals recently, but instead this is probably a more accurate count that
we can use as a baseline to determine change over time," said Michelle
LaRue, a University of Minnesota research associate in the Department of
Earth and Environmental Sciences and the lead author of the study. "We've
also developed an efficient process for monitoring them to see if the population has changed from this baseline. Tracking the population of
seals against this benchmark is critical for conservation efforts."
Weddell seals are one of Antarctica's most iconic species. In addition
to being undeniably charismatic, they live the farthest south out of any
mammal in the world and can live up to 30 years in some of the harshest conditions on the planet. They are seasonal occupants of the coastal sea
ice that surrounds Antarctica. By counting seals on satellite imagery, scientists hope to learn more about how climate change and fishing in
Antarctic waters may be affecting the number of seals and the entire
ecosystem over time.



==========================================================================
"The reason Weddell seals are so important is because they're a
key indicator species for the Southern Ocean," said LaRue, who is
also a senior lecturer in the School of Earth and Environment at the
University of Canterbury. "Weddell seals live on fast ice, which is the
ice that's attached to the Antarctic continent -- the same habitat as
Emperor penguins. As the climate continues to change, we might expect
that fast ice to change as well. So if we understand where the seals are
and how many there are, that gives us an idea of how the ecosystem might
be changing." LaRue said Weddell seals are also important because they
prey on Antarctic Toothfish, which are fished commercially and end up
on our plates as Chilean Sea Bass.

"So, not only do they give us an idea about climate change, but they
also give us an idea about how the entire ecosystem might be functioning because Antarctic Toothfish, or Chilean Sea Bass, are a really important
part of the Antarctic ecosystem," LaRue added.

In addition to this first-ever count, the researchers gained new insights
into the habitat of Weddell seals. The seals prefer to be near the
continental shore but also near deep water -- possibly because of the
location of predators and the fish they eat. Perhaps most interestingly,
the seals appear to prefer to be near Emperor penguins, but only if
there aren't too many of them.

"There seems to be a trade off. It's good to be near Emperor penguins
but only if the penguin colony size doesn't get too big and there is
not too much competition for food," LaRue said.



========================================================================== While Weddell seals are extremely important to the Southern Ocean
ecosystem and have been studied since the early 1960s, no one has been
able to do a comprehensive count of the seals due to the harsh Antarctic weather and remote locations in which the seals live. Now researchers
can use high-resolution satellite images to count the seals. However,
the downside of that is there are too many images for scientists to
handle alone. That's why they turned to citizen scientists.

"There is absolutely no other way we could've done an accurate count
of Weddell seals," said Leo Salas, a co-author of the study and senior scientist at Point Blue Conservation Science. "Even though our team
includes seasoned researchers who know how to count seals on the images,
it would have taken many years for our small team to search all the
images. We also haven't been able to use automated tools because the human
eye is still more accurate than any computer algorithm." But, Salas
said, that might change soon. With the help of citizen scientists, the researchers now have the data to train computers to help automate future
counts that will give them more information about this important species.

In addition to knowledge on the ecology of the seals, the feat required a variety of skills. This includes new technologies to process and expose
very large satellite images to the volunteers, project promotion to
recruit volunteers, knowledge of the geophysics of sea ice formation
along the coast of Antarctica, and advanced statistical methods. LaRue assembled team of researchers and engineers to make that possible.

In addition to LaRue and Salas, the research team included Nadav Nur
at Point Blue Conservation Science, David Ainley and Jean Pennycook at
H. T. Harvey and Associates Ecological Consultants, Sharon Stammerjohn
at the University of Colorado-Boulder, Melissa Dozier and Jon Saints
at Maxar Technologeies, Kostas Stamatiou at Blue Sky Resources, Luke
Barrington at Google, and Jay Rotella at Montana State University.

The research was funded primarily by the U.S. National Science Foundation
in collaboration with Maxar Technologies and the Antarctic and Southern
Ocean Coalition.

========================================================================== Story Source: Materials provided by University_of_Minnesota. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Michelle LaRue, Leo Salas, Nadav Nur, David Ainley, Sharon
Stammerjohn,
Jean Pennycook, Melissa Dozier, Jon Saints, Kostas Stamatiou, Luke
Barrington, Jay Rotella. Insights from the first global population
estimate of Weddell seals in Antarctica. Science Advances, 2021;
7 (39) DOI: 10.1126/sciadv.abh3674 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211004153731.htm

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