Field Notes
U.S. Fish & Wildlife Service
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FARALLON NWR: Warm Weather, Warm Ocean Disrupt Wildlife on Farallon Islands
California-Nevada Offices , April 22, 2015
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A Brown Booby, one of a dozen sighted on the Farallon National Wildlife Refuge this winter, an unprecedented number for the tropical seabird.
A Brown Booby, one of a dozen sighted on the Farallon National Wildlife Refuge this winter, an unprecedented number for the tropical seabird. - Photo Credit: Jim Tietz
Breeding for elephant seals on the Farallon Islands was disrupted this winter by warmer air and ocean temperatures.
Breeding for elephant seals on the Farallon Islands was disrupted this winter by warmer air and ocean temperatures. - Photo Credit: Sophie Webb

by Doug Cordell and Melissa Pitkin


This winter’s unusually warm air and ocean temperatures are disrupting marine wildlife at the Farallon National Wildlife Refuge, as observed by biologists from Point Blue Conservation Science and refuge managers at the U.S. Fish and Wildlife Service. Over the past four months, seals and sea lions are having difficulty reproducing, local seabirds have had low colony attendance, and two tropical species of seabird have shown up on the island, far from their normal range.

The cause: warm air and ocean temperatures from the high pressure system responsible for California’s mildest, driest and warmest winter on record. This unusual weather has resulted in a lack of ocean upwelling, the process that brings nutrient rich waters from the bottom of the ocean to the surface. When upwelling is disrupted, the ocean food web is thrown out of balance – and the result is less food for marine wildlife, which disrupts their ability to breed successfully.

“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.”

Observations of disrupted breeding activities include:

  • 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: Elephant seals just completed their winter breeding season. 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 winter attendance was unusually low. In fact, the Cassin’s Auklet, a bird observed to have suffered a large die-off from California to British Columbia this past fall and winter from lack of food, has been largely absent from the islands in the last few months, suggesting auklets have to search for food far from the islands. Since auklets feed mainly on krill, their activity and nesting success are good indicators of the availability of this food resource, which is very important for many marine predators, including whales and salmon.

Observations of marine animals occurring out of their range include:

  • Tristram’s Storm-Petrel, 3rd 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 species typically occurs in the central and western Pacific Ocean, where it breeds on the northwest Hawaiian Islands and islands off southern Japan. This was only the 3rd 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 in California, where they are mostly seen in summer and fall. 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 Fall 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 unusually high air temperature, together with the decline of sand at the elephant seal breeding colony—a result of ongoing erosion from increased storm surges, itself a likely impact of climate change. Elephant seals use sand to keep themselves cool while on land; a lack of sand, combined with high air temperatures, produce conditions that make it difficult for the young to survive.

“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.

“These unusual observations highlight the importance of monitoring our coastal wildlife,” says McChesney. “They are significant indicators of ocean health, and help us understand and protect valuable coastal resources.”

The Farallon National Wildlife Refuge is located about 30 miles west of San Francisco. Since 1968 Point Blue has monitored wildlife populations and environmental change on the islands daily, working in close collaboration with the U.S. Fish and Wildlife Service, which manages the Refuge. The Farallones host the largest seabird nesting colony in the contiguous U.S., as well as rookeries of seals and sea lions. Point Blue’s long-term research on the Farallon Islands has helped monitor the Refuge’s valuable natural resources and California’s highly productive marine ecosystem.

- FWS -

Doug Cordell is the Public Affairs Officer for the San Francisco Bay National Wildlife Refuge Complex. Melissa Pitkin is Director of Education and Outreach for Point Blue Conservation Science.

Contact Info: Doug Cordell, 510-774-4080, doug_cordell@fws.gov
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