The signs were evident. Oscar DiCaprio, a male elephant seal pup named after the famous actor and environmentalist, was rescued last April at Oceano Dunes State Park in San Luis Obispo County, CA, by volunteers at the Marine Mammal Center. He was found on the shore weighing less than 80 pounds. Elephant seal pups should weigh 250 pounds.
A month earlier, Heyerdahl, a newly born harbor seal pup named after the Norwegian adventurer, was found alone on a beach with no mother in sight. He, too, was brought to the center for special care.
Oscar DiCaprio and Heyerdahl were nursed back to health and recently released back into the ocean. While under the care of Shawn Johnson, director of veterinary science at the MMC, DiCaprio and Heyerdahl exhibited clues that their habitat was warming.
Johnson along with many volunteers at the MCC started seeing an increase of seals and sea lions washing up on the shores in 2013, but they weren’t sure what caused the major increase in strandings. “At the time, we were seeing an unusually large number of undernourished young animals on the shore,” Johnson said.
The sea lion and seal pups were often separated from their mothers, which is quite unusual.
“The mothers were probably searching for sardines and anchovies, a mainstay of their diet,” Johnson said. “These small fish moved farther north for cooler temperatures. That combined with overfishing made their source of food scarce.”
Johnson and his team worked closely with biologists at the National Marine Mammal Laboratory to better understand what was happening. The lab has been monitoring sea lions for the past 40 years.
“We found a dramatic shift within the last three years,” Johnson said. “Pups are born extremely underweight, about half of what they should be. And mothers aren’t producing enough milk to feed their pups; as a result, between 80 and 90% of all pups have died.”
Last year the MCC rescued 1,800 seals and sea lions, breaking nearly every record in their 40-year history. “We’ve pretty much been in crisis mode for the last three years,” Johnson said. “We now know it’s because of increased ocean temperatures and the lack of food. This raises alarming questions about the health of our ocean.”
The cause is linked to a climatological phenomenon called "the blob," an unusually large and persistent area of warm water that originates in the Gulf of Alaska and at times extends all the way down the Pacific coast to Mexico. In addition to the blob, the monster El Niño recently warmed the Pacific Ocean by several degrees Celsius. The warm water from the blob helped fuel El Niño, creating a vicious cycle.
“When the top predators in the ocean have a hard time surviving that means the whole system is disrupted,” Johnson said. “Initially, there was a lot of skepticism regarding climate change. The seals and sea lions are showing us a different picture—that climate change exists.”
While Johnson and his colleagues help seals and sea lions survive the challenges imposed on their habitats by manmade environmental changes, Daniel P. Costa, distinguished professor of ecology and evolutionary biology at the University of California, Santa Cruz, and his team at the Costa Lab, are putting sensors on these sea mammals in order to get a better understanding of how exactly their environment is changing.
Costa initially started out studying elephant seals, but now he sees them as collaborators. “Elephant seals help us understand the planet and the environment,” he said.
The trackers that he and his team place on the fur of elephant seals are light enough so they’re not a distraction, but advanced enough to allow scientists to collect data via satellite. In addition to learning about the animals' habitat, the data documents ocean temperatures, salinity, ocean circulation patterns, the health and size of U.S. salmon populations, and other undersea conditions. The sensors stick to the elephant seal’s fur and fall off when they molt.
Currently, Costa and his team are collaborating with 20 Southern elephant seals. The seals are excellent divers—they can stay underwater for up to two hours and dive to depths of a mile. The data they gather at these hard-to-reach depths show certain ice shelves melting due to warm water coming from below, not above.
A study published in June in Geophysical Research Letters showed just how these seal-acquired observations are helping scientists understand just how giant ice shelves are melting.
As The Washington Post reported, "the study certainly validates—via seals—the idea that warm water can get up onto the continental shelf and near the marine glaciers of the Bellingshausen Sea."
“Elephant seals are helping us understand the climate and how ice dynamics are changing,” he said. “But why should we care? Another ice shelf called the Pine Island Glacier, one of largest ice streams in Antarctica, will change the sea level of the planet by three feet once it collapses. So things in the Southern Ocean do have an effect on us because much of the weather in the planet is driven by what’s happening in the Southern Ocean.”
Both the Bellingshausen Sea and the Pine Island Glacier are located along the west side of the Antarctic Peninsula.
The data helps explain climate change and it brings Costa and his team closer to the elephant seals. “We have a relationship with many of these animals because some of the elephants seals we tagged a number of years ago, we are still tracking,” Costa said.
He’s watched a few elephant seals grow from pups to adults. “It’s a different kind of connection,” he said. “They’re not like dogs or even cats. They’re wild animals so we keep our distance.”
Costa shares his data with other scientists around the world. They started out studying and caring for these creatures and now they value them for the information they’re providing.
And they get a thrill each time they see a sea mammal with one of their tags.