<
https://www.biographic.com/are-there-plenty-of-fish-in-the-sea-ask-an-elephant-seal/>
"The deep sea contains many things: shipwrecks laden with gold, submersibles
stuffed with sightseeing billionaires, and an absolutely unfathomable number of
fish. If you could somehow put all the world’s fish in a giant pile—all the
tuna; all the herring; all the mackerel, sardines, and anglerfish—around 90
percent, by weight, would have come from the ocean’s twilight zone.
Faced with crushing water pressure, a near-total lack of light, and vast areas
to search, scientists have long struggled to keep tabs on the trove of fish
hiding out in the deep. But for a recent study, scientists led by Roxanne
Beltran, an expert on marine mammals at the University of California, Santa
Cruz (UC Santa Cruz), strapped sensors to one of the deep sea’s most formidable
predators: the northern elephant seal (
Mirounga angustirostris). Tracking
these hunters, the scientists show, offers a new way of monitoring the
fluctuations of fish populations across swaths of otherwise obscured ocean.
Northern elephant seals have big blubbery bodies that can weigh as much as a
car and reach nearly four meters (13 feet) long. But don’t let their physiques
fool you, says Beltran. These animals annually migrate 10,000 kilometers (6,000
miles) round trip between North America’s west coast and open-ocean feeding
grounds in the heart of the North Pacific. “They’re routinely diving down 1,000
meters (3,280 feet) below the ocean’s surface while holding their breath,” says
Beltran. “And the females do all of that while pregnant with next year’s pups.”
Northern elephant seals spend around seven months of the year hunting nearly
nonstop. During this time, each seal makes tens of thousands of dives in search
of fish and squid.
For decades, scientists from UC Santa Cruz have been monitoring the weights,
survival rates, and reproductive success of northern elephant seals living near
California’s Año Nuevo State Park. They’ve also been attaching satellite tags
to the seals to track their foraging trips. Collecting this data took three
generations of scientists and hordes of undergraduate researchers, all willing
to endure long days of hoisting elephant seals onto tarps so they could weigh
the animals using a gigantic tripod, and otherwise struggling to keep their
equipment free of seal poop.
But the real magic came when Beltran and her colleagues cross-referenced this
hard-won data against records of historical ocean conditions.
“Elephant seal foraging success, survival, and reproduction all fluctuate
substantially with ocean conditions,” says Beltran. Looking at how elephant
seals fare in different conditions, Beltran and her colleagues realized they
could use the measurements of foraging success and pup growth to gauge how much
these seals must be eating and, from there, estimate the otherwise invisible
swings in fish populations.
Their findings suggest that populations of fish and squid in the deep sea
within the northern elephant seals’ foraging range go through cycles of
abundance and scarcity every three to five years. And they found that seals
thrive about two years after a bout of particularly favorable oceanographic
conditions. That’s “when the seals have a ton of food to eat,” Beltran says.
By identifying the relationship between seals, deep-sea fish, and ocean
conditions, Beltran and her team now say they can predict the size of the
deep-sea fish stock up to two years out—a potential boon for fisheries
scientists and conservationists."
Via
Reasons to be Cheerful:
https://reasonstobecheerful.world/wildfire-recovery-seed-library-la/
Cheers,
*** Xanni ***
--
mailto:xanni@xanadu.net Andrew Pam
http://xanadu.com.au/ Chief Scientist, Xanadu
https://glasswings.com.au/ Partner, Glass Wings
https://sericyb.com.au/ Manager, Serious Cybernetics
