Stranded Marine Mammals Hit All-Time High in 2015

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In the United States, abnormally lower temperatures in the south and abnormally higher temperatures in the north have produced what The Weather Channel projected to be the strongest El Niño storm in 18 years. In Santa Cruz, these patterns have negatively impacted wildlife and led to a surge of stranded marine mammals.

Members of the Marine Mammal Center release California sea lions back into the ocean after rehabilitation. Due to a number of changing environmental conditions, some marine mammals are forced to venture farther from their normal foraging grounds for food. Sea lion pups are prone to becoming stranded. Photo Courtesy of Marine Mammal Society
Members of the Marine Mammal Center release California sea lions back into the ocean after rehabilitation. Due to a number of changing environmental conditions, some marine mammals are forced to venture farther from their normal foraging grounds for food. Sea lion pups are prone to becoming stranded. Photo Courtesy of Marine Mammal Society

El Niño is the oceanic warming of the central to eastern Pacific, which has an average span of two to seven years. The current El Niño conditions have been ongoing since early 2015 and according to a three-month winter outlook by The Weather Channel, it’s projected to continue for another two months.

Some scientists believe the prolonged effects of El Niño combined with the effects of climate change are to blame for the increase in stranded marine mammals. An estimated 3,000 young California sea lions were stranded in California in 2015, according to the Marine Mammal Center (MMC). The MMC is the primary responder for Santa Cruz and Monterey counties for the intake of stranded seals and sea lions.

“What’s happening off the California coast is caused not by any one environmental condition but rather a perfect storm,” said MMC public relations specialist Laura Sherr in an email. “These warmer waters, which some scientists also link to global climate change, seem to be affecting distributions of fish, causing marine mammals like sea lions and fur seals to have a harder time finding food close to their typical habitat range.”

Sherr said this results in marine mammals becoming stranded as they venture away from their usual habitats in search of food.

Martha Arciniega, a Ph.D. candidate at UC Santa Cruz studying ocean sciences, is the vice president of community relations of Sea Slugs, an on-campus organization dedicated to environmental stewardship. She said El Niño events alter the distribution of nutrients in ocean waters, bringing them closer to shore.

“The larger marine mammals, such as humpback whales, follow the food near shore and outcompete the smaller marine mammals such as the sea lions,” Arciniega said. “[This leads to] adult sea lions being outcompeted for food and are pushed further offshore to collect food.”

Although the warmer water temperatures affect the diets of all animals in the ecosystem, Teri Sigler, the marine mammal stranding coordinator at the Long Marine Lab, said she has only seen an increase in the number of stranded seals and sea lions — not cetaceans like dolphins and whales. She said this is partly because it’s in seals’ and sea lions’ biology to leave their young on shore while they forage for food, while cetaceans do not.

“Cetaceans’ young are with them all the time,” Sigler said. “They don’t have a shore component to their life biology, so they’re able to more easily follow the prey, whereas seals and sea lions have specific breeding grounds they go to every year.”

Seal and sea lion pups wait for their mothers to bring food back to them on shore. But since the mothers must now venture farther out to forage, “it’s taking them a much longer transit time to get out to where the food source is, and so the pups essentially become abandoned,” Sigler said.

In 2015 alone, the MMC rescued about 1,800 stranded seals and sea lions — a record-breaking number for the center, as it usually responds to only 600-800 marine mammal rescue cases yearly.

“[And] with an unusually strong El Niño taking shape in the equatorial Pacific, conditions are not likely to change much any time soon,” Laura Sherr said in an email. “The warm waters El Niño is expected to bring will simply reinforce or extend the dramatic effects we’ve seen to date.”

Gary Griggs, director of the Institute of Marine Sciences at UCSC, asserts that the increase in stranded marine mammals isn’t solely due to the prolonged effects of El Niño, but rather several factors.

“We have El Niño coming, but within, we’ve got this climate change which is long-term taking place,” Griggs said. “The oceans are warming, the air is warming, circulation is changing. So it’s not really a simple, straightforward connection.”

For over a year now, a large cauldron of warm water temperatures along the coast of the Pacific Northwest contributed to the development of a harmful algal bloom, which scientists are calling “the blob,” reaching from Alaska to California. The “blob” in the Pacific has already affected food availability and habitats for marine life, Griggs said.

“The sea lions are being affected by both these harmful algal blooms and domoic acid,” Griggs said.

Domoic acid is found in the algae produced by the “blob” and alters marine ecosystems through the accumulation of biotoxins in shellfish, sardines and anchovies which are then consumed by sea otters, sea lions and humans. Consequently, cases of stranded and sick marine mammals have increased as the “blob” spreads.

In response to the high numbers of stranded marine mammals expected in 2016, the MMC plans to increase the recruitment of volunteers and other resources in order to manage the growing number of stranded marine mammals.