While I was in San Francisco in the fall of 2015, I headed across the Golden Gate Bridge to take a tour of The Marine Mammal Center, a nonprofit veterinary research hospital in Sausalito, California. I had heard that a blob of unusually warm water off the Pacific coast had taken a toll on marine life and caused an increase in the number strandings.
When I visited on December 16, 2015, the hospital was taking care of 81 northern fur seals, 7 California sea lions, 1 northern elephant seal, and 1 Guadalupe fur seal. That is a lot of northern fur seals—three times more than the center rescued the previous year and more than twice the previous record, which was set in 2006.
While sea lions, elephant seals, and Guadalupe fur seals were scarce when I visited, had I come earlier in the year there would have been plenty of these species as well. By February 2015, the center had rescued record numbers of starving sea lion pups; by April, they were dealing with record numbers of elephant and harbor seals; by June, they had taken in five times the normal number of Guadalupe fur seals.
The photograph above shows one of the northern fur seals resting on a warming mat. “Northern fur seals are smaller, furrier and feistier than the California sea lion pups we rescued earlier this year,” noted Shawn Johnson, the director of veterinary science at The Marine Mammal Center, in a November press release. “But otherwise the scene here is the same—our rescue trucks continue to arrive day after day with more starving pups in need of our care.” By the end of the year, the center had rescued 1,800 animals, breaking nearly every record in the facility’s 40-year history.
What was causing all of the trouble? Most marine scientists think the warm water blob in the northeast Pacific was a key culprit. The warm water was driven by the emergence of an unusually strong and persistent ridge of atmospheric high pressure in the northeastern Pacific Ocean. The feature, which was so unrelenting that meteorologists took to calling it the Ridiculously Resilient Ridge, weakened winds in the area enough that the normal wind-driven churning of the sea eased.
Those winds usually promote upwelling, which brings deep, cool water up toward the surface; instead, the resilient ridge shut down the ocean circulation, leaving a large lens of unusually warm surface water in the northeastern Pacific. Upwelling brings dissolved nutrients to the surface, so the slowdown in upwelling meant many animals had less to eat. In addition, the warm water extended the time that certain type of algae bloom produced toxins that can cause serious health problems for marine mammals.
The maps below show sea surface temperature anomalies in the Pacific in July 2015. Large patches of warm water dominated the Gulf of Alaska and along the California coast. The map is based on data collected by the U.S. Navy’s WindSAT instrument on the Coriolis satellite and the AMSR2 instrument on Japan’s GCOM-W. Note that the maps do not depict absolute temperatures; instead, they show how much above (red) or below (blue) water temperatures were compared to the average from 2003 to 2012.
The good news it that the blob has finally broken up. By January 2016, more seasonable temperatures had returned to the northeast Pacific, thanks to the strong El Niño in the equatorial Pacific. The breakup of the warm blob came as no surprise to weather watchers. In September 2015, Clifford Mass, a University of Washington atmospheric scientist, explained in his blog that El Niño generally brings lower-than-normal sea surface pressures to the eastern Pacific—the opposite of the systems that sustained the blob. By mid-December 2015, around the time that I was visiting the Marine Mammal Center, Mass declared that the blob was dead.
However, remnants of the warm blob still persist. “There are significant temperature anomalies extending down to a depth of about 300 meters. So while the weather patterns the past few months have not been that favorable to warming, it will take a while for all of the accumulated heat to go away,” explained Nicholas Bond, a University of Washington meteorologist and Washington state’s climatologist. That means impacts on marine life and on weather in the Pacific Northwest could linger, though Bond does not think the blob will return in the near term.
The type of type of algae that has caused harmful blooms is Pseudonitzschia, which produces the neurotoxin domoic acid. The Marine Mammal Center is where scientists first discovered (in 1998) that domoic acid could be toxic to marine mammals. The toxin accumulates in shellfish, sardines, and anchovies, common food sources for marine mammals. Exposure to domoic acid affects the brains of mammals; it can cause them to become lethargic, disoriented, and have seizures that sometimes result in death.
High levels of domoic acid likely contributed to the record number of marine mammal strandings. Since the toxin can also affect humans and was found in the meat of commercial fish and crabs (rather than just the guts), authorities also closed major fisheries including Dungeness and rock crab, anchovy, oyster, razor clams, and mussels in 2015.
In many areas, domoic acid remained a concern in mid-February 2016. Though the situation has improved somewhat, California’s commercial dunegrass crab season will remain closed until more of the coast is clear of the toxin, according to the San Francisco Chronicle.
Meanwhile, National Oceanic and Atmospheric (NOAA) scientists recently reported that domoic acid is present in Alaskan marine food webs in high enough concentrations to be detected in marine mammals such as whales, walruses, sea lions, seals, porpoises and sea otters. “Since 1998, algal toxin poisoning has been a common occurrence in California sea lions in Central California. However, this report is the first documentation of algal toxins in northern ranging marine mammals from southeast Alaska to the Arctic Ocean,” a NOAA press release said.
“We do not know whether the toxin concentrations found in marine mammals in Alaska were high enough to cause health impacts to those animals. It’s difficult to confirm the cause of death of stranded animals. But we do know that warming trends are likely to expand blooms, making it more likely that marine mammals could be affected in the future,” NOAA research scientist Kathi Lefebvre said.
For more details about the unusual conditions in the Pacific Ocean, see this story from the University of California.