Seals thriving in face of change

09/13/2012

For the last 31 years, Point Reyes National Seashore’s southern tip has provided a safe haven for a burgeoning northern elephant seal population. Early this year, observers with the National Park Service counted over 1,600 of the large pinnipeds, including roughly 800 pups.

Despite those healthy numbers, seashore scientists remain concerned that the possibility of El Niño storms in the near future could kill a significant number of pups, as they have in the past. Meanwhile, they anticipate the release of a new federal sea-level study that they say will help them prepare for the seals’ future. United States Geological Survey (USGS) scientists are still gathering data for the report, which they plan to release by the end of the year.

“This study is intended for coastal managers,” USGS coastal geologist Patrick Barnard, based in Santa Cruz, said. “It will clearly identify areas that are 
vulnerable.”

Dr. Sarah Allen is one of those managers. Now directing the ocean stewardship program for the park service’s Pacific West regional office, Dr. Allen began studying elephant seals when they established a colony at Point Reyes in 1981.

“This really is a success story,” Dr. Allen said. “With simple protection and interpretation by the park, this species has recovered.”
Indigenous coast peoples long hunted seals for their meat and fur. Early 19th century European and American commercial whalers contributed to a booming industrial economy with necessary blubber oil for fuel and machine lubrication. But whalers began to overhunt their game, and by 1846 they turned their attention to the blubber-rich northern elephant seal.

Hauled out on the beach and vulnerable, the seals provided former whalers with a much more efficient income and fewer hazards. Sealers rapidly hunted their new game to the brink of extinction, leaving as few as 100 animals by 1871.

The Mexican government first banned seal hunting in 1922, and the United States banned it shortly thereafter. Congress passed the Marine Mammal Protection Act in 1972, which prohibits the hunting of all marine mammals. Today, Dr. Allen estimates the elephant seal population at roughly 150,000 and increasing 6 percent every year.

Few elephant seals presently occupy the seashore’s beaches. The animals return twice a year to Point Reyes and 11 other sites on the California and Baja California coasts. Most of the adult males, which can weigh up to 6,000 pounds, are currently feeding in waters south of the Aleutian Islands, while the females are feeding in the northeastern Pacific and near Hawaii.

Juvenile seals start hauling out on sheltered beaches this month, most likely acclimating to the breeding cycle, and their numbers will peak in October. In November, male seals arrive from their feeding grounds, and pregnant females will swim in a few weeks later. Most give birth in January and the breeding cycle begins almost immediately after, when older, larger and more aggressive males crowd out most juveniles and establish harems of several females.

They again return in late spring and summer to molt. Elephants seals endure what scientists call a “radical molt,” in which they lose their entire coat of insulating fur at once. Females molt in April and May, and males from May to July, remaining on the beach until they grow new coats.

The seals migrate 12,000 to 14,000 miles a year and dive to depths between 1,000 to 2,000 feet. They feed on squid, octopus, rockfish, hake and other deepwater creatures.

Despite the restoration of the species, elephant seals face a new set of challenges. Pollution poses a significant threat, and biologists routinely discover seals injured by fishing nets, plastic garbage and boat hulls and propellers. Dr. Allen remains concerned about the possibility of an upcoming El Niño year, when late-winter storms could wash young pups out to sea.

Combined with storms, rising sea levels also threaten the seals. Dr. Barnard said a rising sea level would erode the elephant seals’ beach habitat, and a concurrent increased ocean temperature could effect their migration and reproductive cycles.

He and his collaborators designed the study to be used by a variety of scientific professionals. It integrates data collected by USGS, PRBO Conservation Science and the National Oceanic and Atmospheric Administration. It simulates a range of possible sea-level changes, from none up to a two-meter rise by the year 2100, as well as possible weather systems, from normal winter conditions to the arrival of a hundred-year storm. It assesses two years’ worth of collected data and will project future flooding levels and coastal change effects.

The partners in the study, which Dr. Barnard expects to release by December, have developed the physical impact model over the last four years.

In the meantime, the international Census of Marine Life’s Tagging of Pacific Predators project maintains near realtime tracking information on tagged seals and 22 other species, accessible on the Internet at topp.org.