April 6, 2015
Warmer Conditions Disrupt Farallones Wildlife
From dead Cassin’s Auklets to shores littered with bright blue sailor jellyfish, this winter brought unusual conditions for West Coast ocean life. The Farallon National Wildlife Refuge, 30 miles outside of San Francisco, wasn’t exempt.
Biologists with Point Blue Conservation Science and the U.S. Fish and Wildlife Service documented seals and sea lions having difficulty reproducing, local seabirds with low colony attendance and two tropical seabird species appearing on the islands, far from their normal range.
“The reasons for these rare observations have to do with the unusually warm air and ocean temperatures and how they impact the ecosystem,” says Russ Bradley, Farallon Researcher for Point Blue Conservation Science. “In February, average air temperature and average sea surface temperature were the highest recorded in 45 years.”
Warmer air and ocean temperatures resulted in a lack of ocean upwelling, which brings up nutrient-rich waters from the ocean bottom. This throws the ocean food web out of balance – and the result is less food for marine wildlife and less ability to breed successfully.
- California sea lions aborting pups due to poor body condition of the mothers. Since January 9th, 94 aborted sea lion fetuses have been recorded on the islands, well in advance of their June due date. Ninety-four is almost half the total number of sea lions born on the island in 2014.
- High elephant seal pup mortality due to warmer air temperatures. Pup survival was low this year, partly because of unusually warm air temperatures. Many pups died when overheating mothers led them to a cliff edge in attempts to get cool; pups then fell to their deaths.
- Low attendance of breeding seabirds. Farallon nesting seabirds usually visit the islands during winter, but this year’s attendance was unusually low. Cassin’s Auklets, observed to have suffered a large die-off from California to British Columbia from lack of food, have been largely absent from the islands. Since auklets feed mainly on krill, their activity and nesting success are also good indicators of food availability for many marine predators, including whales and salmon.
- Tristram’s Storm-Petrel, third observation ever for all of North America. On March 18, a freshly killed Tristram’s Storm-Petrel was discovered on the islands, most likely the victim of a Burrowing Owl. This tropical seabird typically breeds on the Hawaiian Islands and islands off southern Japan. This was only the third record of the species in North America, the first of which was captured alive (and released) on the Farallon Islands in 2006.
- Overwintering Brown Boobies. These tropical seabirds, commonly found in Mexico and Central America, are typically very rare during winter in California. But unprecedented numbers have been at the islands all winter, with counts up to 12 birds. The previous record count at the Farallones was three birds in 2006.
Climate change is clearly a factor in some, if not all of these unusual occurrences, but it will take ongoing monitoring and time to fully understand the connection. The high elephant seal pup mortality, for example, can be attributed to the decline of sand at the elephant seal breeding colony, which is a result of ongoing erosion from storm surges, an impact of climate change.
“It will take several years to see if these unusual wildlife patterns hold,” says Gerry McChesney, Farallon National Wildlife Refuge Manager for the U.S. Fish and Wildlife Service. “If they do, it can probably be said that climate change is a major driving force.”
Observations such as those on the Farallon Islands help researchers understand the effects of changing weather patterns and predict their effects on other ocean resources—such as fisheries, which are critical to the survival of seabirds and marine mammals and an important food source for humans.
Main Photo: An elephant seal and her pup on a rocky beach on the Farallon Islands this past winter. Elephant seals prefer sandy beaches, but most of the sandy beaches they once inhabited on the Farallones are now washed out by storm events. Photo: Ryan Berger
Learn about Point Blue’s work on the Farallon Islands.