Little is known about this threatened species, but a satellite tag gives researchers never-before-seen insights into what happens when a Guadalupe fur seal is rehabilitated and released off the coast of California.
December 2, 2014
Stranding Coordinator Geno DeRango knew he had a fur seal on his hands as soon as he heard the growl coming from inside the crate he was lifting off of The Marine Mammal Center’s rescue truck.
He had been told the truck was transporting a California sea lion named Sterling Archer, but this growl was most definitely a fur seal. Geno was sure of it—he had recently returned from a research trip in Chile where he worked with South American fur seals and listened to those growls nearly nonstop for weeks.
Once he had weighed the animal and brought her to an empty pen, Geno opened the crate door and a Guadalupe fur seal hopped out. Although called “seals,” Guadalupe fur seals are actually members of the sea lion family. They have external ear flaps and long front and hind flippers, making them difficult to distinguish from juvenile California sea lions based on looks alone.
The volunteers who had identified Sterling Archer as a California sea lion had likely never seen a Guadalupe fur seal before, as these animals are rarely seen near shore. In its nearly 40-year history, The Marine Mammal Center has rescued fewer than 60 Guadalupe fur seals—and only six of these have been adult females like Sterling Archer.
Guadalupe fur seals disappeared from California waters by 1825 due to hunting for the fur trade, and today the only known breeding colony is on Guadalupe Island, 150 miles off the coast of Baja California. These animals are considered a threatened species under the Endangered Species Act; they are protected by law in both in the United States and in Mexico. And Guadalupe Island is now a protected area for seals and sea lions.
Because Guadalupe fur seals are so rarely in our care, Geno and the Center’s veterinary team worked closely with the volunteer animal care crews to ensure they had the proper training before working with Sterling Archer.
Their dense fur makes them difficult to grab and restrain for medical procedures, and adults like Sterling Archer are often stronger than restrainers realize—sometimes resulting in what Geno calls a “bucking bronco” situation. That thick fur also requires a lot of grooming, so volunteers were instructed to monitor for this behavior, which can be an important health indicator.
© The Marine Mammal Center, NOAA Fisheries permits #932-1905/MA-009526
When Sterling Archer first arrived in our care, she was emaciated and malnourished. She was also lethargic, refused to eat and moved erratically—all behaviors similar to those seen in California sea lions affected by domoic acid, a neurotoxin produced by microscopic algae.
Sterling Archer was started on a regimen of fluids delivered subcutaneously, or under the skin, a treatment used to help quickly rehydrate sick animals and flush any toxins. Because she wouldn’t eat on her own, trained volunteers fed her ground-up fish “smoothies” pushed through a tube into her stomach.
Within a week, volunteers began noting Sterling Archer’s grooming behavior, and soon she was eating whole fish on her own. Sterling Archer continued to improve and put on a healthy amount of weight over several weeks. After proving to veterinary staff that she could catch live fish, she was approved for release back to the wild.
An Eye in the Sky
Researchers know very little about what Guadalupe fur seals do out in the wild once they leave their rookeries on Guadalupe Island. This is in part because there are so few of them, but also because these animals are pelagic, meaning they spend most of their time out at sea, far from shore.
So before Sterling Archer left the Center’s care, Research Biologist Lauren Rust and Marine Scientist Tenaya Norris attached a satellite tag smaller than a deck of cards to her fur with special waterproof glue. The tag is fitted with an antenna that can send data to satellite receivers any time the animal surfaces.
When the tag pings multiple satellites, it is able to triangulate an approximate location. Sensors within the tag also monitor pressure to determine depth, which provides researchers information on the number of dives the animal makes as well as length of dive.
© The Marine Mammal Center, NOAA Fisheries permits #932-1905/MA-009526
By putting all of this data together, The Marine Mammal Center’s research team is able to better understand this mysterious animal’s behavior. While monitoring Sterling Archer’s individual journey, they may also gain potential baseline data about the overall range and feeding habits of Guadalupe fur seals in the Pacific Ocean that can help inform policymakers reviewing the animal’s threatened status.
Sterling Archer’s Journey
Sterling Archer was released at Rodeo Beach, just north of San Francisco, during National Geographic’s annual BioBlitz event to inventory species in our national parks. Renowned marine biologist and National Geographic Explorer-in-Residence Sylvia Earle opened the door of Sterling Archer’s crate and wished her well. From there, Sterling Archer headed out into the Pacific. In 1998, researchers satellite-tagged an adult female Guadalupe fur seal that had been rescued and rehabilitated at the Center. That animal, Emiliano, swam back to Guadalupe Island, Mexico, within two weeks of her release.
The Center’s research on Emiliano’s journey is one of few scientific publications documenting Guadalupe fur seal behavior at sea, so the scientists monitoring Sterling Archer’s movements thought she might head south too.
Instead, she headed west.
For the first few weeks of her journey, Sterling Archer traveled long distances each day (indicated by the dots on the map—one for each day her tag sent location data). But then she began to slow down, spending more time in particular areas (noted on the map as clusters of daily locations).
Had Sterling Archer lost her way? Quite the contrary, as it turns out.
At first, the researchers monitoring her progress worried that she was confused or lost. Long-term exposure to domoic acid, the neurotoxin that may have caused Sterling Archer’s health problems, can result in memory loss and neurological damage.
But as the Center’s research team continued to watch her movements and began to analyze the full set of data they received, they saw a pattern.
By overlaying oceanographic data on the map of Sterling Archer’s journey, the Center’s researchers were able to determine that she had potentially found a region called the North Pacific Transition Zone. In this area of the ocean, which shifts seasonally and annually, cold, nutrient-rich polar water to the north meets warmer, nutrient-poor water to the south. The North Pacific Transition Zone is known to be a highly productive area—essentially an all-you-can-eat seafood buffet for large marine animals like elephant seals, tuna and leatherback sea turtles. But Sterling Archer’s movement into this area is the first time this behavior has been documented in Guadalupe fur seals.
Contributing to Greater Scientific Understanding
Sterling Archer’s satellite tag stopped transmitting after approximately three months, likely when the satellite tag’s battery ran out. But what we learned during her short journey will continue to live on.
After conducting a detailed analysis of all of the data from Sterling Archer’s satellite tag, the Center’s research team will publish their findings in a scientific journal, giving other researchers access to this valuable discovery and greatly enhancing the scientific community’s overall understanding of Guadalupe fur seal behavior.
The more we know about what Guadalupe fur seals do once they leave Guadalupe Island, the better we can protect this threatened species and ensure its continued survival.
You Can Make a Difference
The satellite tag used to track Sterling Archer’s journey gave researchers invaluable knowledge, but the technology isn’t cheap. The tag itself can cost several thousand dollars, but researchers must also pay for the expensive satellite time used each time the antenna sends information. Help ensure that The Marine Mammal Center continues to have access to the scientific technology needed to learn from the hundreds of animals we rescue every year. Your support goes a long way to help marine mammals like Sterling Archer pave the way for their species.
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