Marine Mammals: GFNMS

Within the Greater Farallones region, marine mammals reign as both apex predators and high-profile species, or “charismatic megafauna.” Many of these animals come to the gulf to haul-out, rest and rear their young. All are attracted to the Farallones because of the high productivity and prey species distributed and retained here via circulatory patterns and intense upwelling.

36 marine mammal species have been observed in the Greater Farallones National Marine Sanctuary. These include:

• 28 cetacean (whale, dolphin, and porpoise) species
• Six pinniped (seal and sea lion) species
• Two otter species

11 marine mammal species dominate the coastal and pelagic zones (see Table 1). An additional 26 species are seen in the sanctuary less frequently (see Table 2).

Cetaceans

The gray whale, Eschrichtius robustus, is the most common large cetacean seen from the shore. These baleen whales migrate annually from their feeding grounds in the Arctic Ocean and Bering Sea to the warm lagoons of Baja California (Mexico), where they give birth to their young.

Gray whales migrate south through the Greater Farallones beginning in November – with peak sightings during January and March. Males, newly impregnated females and juveniles come through from February through April, and females with their newborn calves follow along, from April through June. A few juveniles may appear in the gulf year-round, off the Farallon Islands and in Bodega Bay.

Gray whales are primarily bottom feeders who power-shovel on their side for bottom-dwelling amphipods (crustacean-like organisms), krill and an occasional fish species such as herring.

Humpback whales, Megaptera novaeangliae, are the most acrobatic of the baleen whales seen here. They use the gulf and Cordell Bank to the north as a feeding ground during the summer and fall months – feeding primarily over the continental shelf and slope break.

Lunges and surface thrusts are signs of surface feeding. Humpback prey consists primarily of the euphausiids, Thysanoessa spinifera and Euphausia pacifica, but they will also feed on schooling fishes such as herring, juvenile rockfishes and anchovy. Humpback whale distribution within the gulf is dependent on the distribution of prey species.

Blue whales, Balaenoptera musculus, the largest animals ever to live on earth, migrate to the sanctuary during the late summer and are found here throughout the fall. The blue whale population seeems to be increasing slowly.

At least 2,000 individual blue whales are found off the coast of California and Mexico. Their primary feeding grounds are in the Greater Farallones, Cordell Bank and the Santa Barbara Channel. Their principal prey consists of krill species such as Thysanoessa spinifera and Euphausia pacifica.

Pacific white-sided dolphins, Lagenorhynchus obliquidens, are small odontocetes (toothed whales and dolphins) that are abundant in the gulf from July through October. These small, schooling dolphins occur over continental slopes and deeper waters in large schools ranging from tens to thousands of individuals.

They are often found in mixed groups with Risso’s dolphins, Grampus griseus, or northern right whale dolphins, Lissodelphis borealis; calves are seen during the spring and summer months. They feed on small schooling fishes and squid.

Harbor porpoises, Phocoena phocoena, are shy and often elusive. They are most often seen in nearshore waters, less than 110 meters (360 feet) deep – but often all that one sees are a few (1-25) small, dark triangular dorsal fins – no blow or splash. These porpoises feed primarily on schooling fishes – such as anchovy, mackerel, herring and smelt – as well as on squid and other invertebrates. Calves are present in the sanctuary during the summer months.

Dall’s porpoises, Phocoenoides dalli, spend their time further offshore, along the seaward edge of the continental shelf and along the slope. These fast-moving mammals are often inclined to ride the bow wave in front of a boat. At a distance, one can see their rooster-tail-like splash as they surface to breathe.

Dall’s porpoises may migrate seasonally onshore-offshore, occurring onshore during the summer months. They are primarily nocturnal feeders, seeking prey such as anchovies, squid, crustaceans and deep-water fishes.

Pinnipeds

California sea lions, Zalophus californianus, are seen locally on docks, on near-shore rocks and in large numbers at the Farallon and Año Nuevo Islands, along the Point Reyes Headlands and at Bodega Rock. An occasional pup is born at the South Farallon and Año Nuevo islands during the summer months.

Males, juveniles and some females are abundant in the gulf during their nonbreeding season, August through May, during which between 10 and 40 percent of the total local population will be females.

These mammals are gregarious and can be seen leaving their haul-outs (on-shore resting areas) in large numbers in search of prey. They feed on anchovy, herring, hake, mackerel, crabs and squid. In times of low productivity they have been known to feed on red pelagic crabs, sharks, eels, birds and algae.

Northern fur seals, Callorhinus ursinus, were once abundant, numbering in the tens of thousands, along the California coast; but they were all but exterminated from their California breeding areas during the early 1800s. From 1807 to 1812, for example, an estimated 100,000 hides were collected from the Farallon Islands. By the mid-1800s the fur seal population was eliminated from the Islands.

In 1996, fur seals began to breed on the South Farallon Islands, and the pupping colony is growing every year. In 2006, more than 90 fur seals were born there.

Northern fur seals from the Channel Islands migrate to the gulf in relatively dense numbers, about one fur seal per square kilometer (about two-thirds of a square mile). Visitors to the shorelines of the Greater Farallones do not readily find fur seals on beaches or rocks: these mammals remain at sea during their non-breeding season (September through May), and individuals seldom come ashore.

Their dense fur protects them from heat loss to the water and allows them to spend more time feeding at night on species such as sablefish, rockfishes, anchovies, squid and crabs. Northern fur seals have been known to feed on birds in times of low productivity and low food availability.

Steller sea lions, Eumetopias jubatus, are federally listed as threatened under the Endangered Species Act. Their population has been in decline for the past 25 years.

These sea lions once bred in great numbers at the Channel Islands in the Southern California Bight, but since 1982 their southernmost breeding colonies are within the Monterey Bay and Greater Farallones National Marine Sanctuaries at Año Nuevo Island and the Farallon Islands, respectively.

Steller sea lions are the largest of the otariid species. Males can reach up to 280 centimeters (9.2 feet) and 1,000 kilograms (2,205 pounds), and adult females reach 240 centimeters and 273 kilograms.

Females and juveniles stay within the gulf year-round, while males migrate north and offshore during the non-breeding season from the end of August through May. They feed primarily on rockfishes, sardines, smelt, squid, octopus and salmonids.

Northern elephant seals, Mirounga angustirostris, are one of the deepest diving marine mammals. Adult female elephant seals can dive to depths of 1,200 meters (4,000 feet) and males, to 1,565 meters. While at sea, they remain submerged 80 to 90 percent of the time; they swim, hunt, feed and sleep underwater.

These animals come on land only to breed and molt. Their breeding season begins during December and ends in mid-March. Females and immatures return to the haul-out sites to molt during the spring, and males molt during the summer. Deep-water fishes and invertebrates are their primary food source: squid, octopus, hagfish, ratfish, anchovies, hake and rockfishes.

Harbor seals, Phoca vitulina, are cosmopolitan and are found throughout the northern hemisphere. The gulf provides feeding grounds, haul-out space and pupping areas for one-quarter to one-fifth of California’s harbor seal population. These mammals reside here year-round, but some individuals may disperse north and south of the gulf during the non-breeding season (June through February).

Harbor seals are shy while on land, fleeing into the water when perceived danger approaches. However, they are frequently seen on nearshore rocks and in the surf zone, curiously following beachcombers. They feed in shallow waters on whatever is locally abundant, such as anchovy, herring, hake, smelt, rockfishes, mackerel or squid. They are rarely found in water deeper than 180 meters (590 feet).

Impacts
Human impacts to marine mammal populations worldwide include competition for food with commercial and recreational fisheries, ingestion of marine debris, entanglement in fishing gear and other marine debris, disturbance and injury from ocean noise (including vessel traffic, human-generated middle-frequency sonar from military vessels and seismic surveys for oil and gas deposits), and injury or death from ship strikes. Toxins, oil pollution and other water quality issues also affect the health of these animals. In addition, some species, such as the northern fur seal, are still recovering from past harvesting or bycatch.

In addition to human impacts, changes in climate and oceanographic conditions affect marine mammals. The prevalence of these animals in gulf waters changes from year to year due to fluctuations in marine conditions, including El Niño, Pacific Decadal Oscillations and changes in intensity and timing of upwelling conditions in the spring/summer.

For example, the occurrence of blue whales within the central California region appears to be dependent on the timing and intensity of oceanographic upwelling conditions, which influence krill production within the area. In addition, variability in the distribution of delphinids (“ocean dolphins”) is related to ocean temperature changes.

Monitoring

The following list includes some of the projects underway in the sanctuary. Please click on the Projects tab at the top of this page for more information.

Sanctuary Ecosystem Assessment Surveys (SEA Surveys)
SEA Surveys are designed to investigate the relationship among hydrographic conditions, physical features and the distribution and abundance of marine organisms in the gulf of the Farallones. These surveys include counts of marine turtles, birds and mammals along set transect lines.

Distribution and Abundance of Marine Birds, Mammals and Zooplankton Relative to the Physical Oceanography of the Greater Farallones and Cordell Bank
PRBO Conservation Science scientists, in partnership with University of California-Bodega Marine Laboratory and the Cordell Bank and Greater Farallones National Marine Sanctuaries, have been investigating the spatial and temporal relationships among krill, krill predators and oceanographic processes in the Greater Farallones and the region surrounding Cordell Bank. This project aims to 1) understand the effects of varying oceanographic regimes on predator-prey relationships and food-web dynamics in the central California region and 2) provide a scientific basis for the design and implementation of a marine protected area (MPA).

Research cruises were conducted winter, spring-summer and fall (three to five cruises/year) from 2004-2007. This study has shown large inter-seasonal and inter-annual differences in lower trophic level abundance as well as predator presence in the sanctuaries. Data have allowed scientists to begin to develop a picture of how mobile marine organisms may benefit from a pelagic marine reserve within the highly productive areas of the California Current marine ecosystem.

Beach Watch
The Beach Watch ecosystem monitoring program is a public-private partnership of the Greater Farallones National Marine Sanctuary and the Farallones Marine Sanctuary Association to study and protect the shoreline of the Marine Sanctuary. Since 1993, citizen scientists have regularly monitored Sanctuary beaches documenting wildlife, oil spills, and seasonal changes. Trained volunteers conduct surveys every two to four weeks. Surveyors document living and dead wildlife; restoration recovery; visitor-use patterns, wildlife disturbance and violations; chronic and catastrophic oil pollution; and detection of ecosystem changes such as El Niño and upwelling events.

Tagging of Pacific Pelagics (TOPP)
Since 2000, TOPP had been exploring the Pacific Ocean using a carefully selected group of animals to gather data about their world. A pilot program of the Census of Marine Life, it is an international endeavor to determine what lives, has lived and will live in the world’s ocean. Ultimately, scientists will draw upon their data to build models of Pacific ecosystems.

Collaborative Survey of Cetacean Abundance and the Pelagic Ecosystem (CSCAPE)
West Coast CSCAPE is a collaboration between National Oceanic and Atmospheric Administration (NOAA) Fisheries and the National Marine Sanctuary Program to assess the abundance and distribution of marine mammals and to characterize the pelagic ecosystem out to approximately 300 nautical miles off the U.S. West Coast.

Structure of Populations, Levels of Abundance and Status of Humpbacks (SPLASH)
SPLASH is an international cooperative effort to understand the population structure of humpback whales across the North Pacific and to assess the status, trends and potential human impacts to this population.

NOAA Fisheries Gray Whale Stock Assessment
This ongoing project conducts annual surveys of the gray whale population on its northward and southern migrations along the U.S. West Coast. Aerial surveys assess the health of cow-calf pairs, and land-based biologists observe group dynamics, behaviors and feeding activities.

Wind to Whales 
This project, through the Center for Integrated Marine Technologies (CIMT) at the University of California Santa Cruz, uses emerging technology to assess the processes underlying the dynamics of the coastal upwelling ecosystems along the California coast. The project includes study of primary production, nutrient flux, harmful algal blooms and the effects of these on the distribution, abundance and productivity of organisms at higher trophic levels, including squid, fishes, seabirds, sea turtles, pinnipeds and whales.

Table 1. Marine Mammal Species Common in the Coastal and Pelagic Zones of the Sanctuary

* federally listed as Endangered Species
” federally listed as Threatened Species
^ breeds on Farallon Islands

Table 2. Marine Mammal Species Less Frequently Observed in the Greater Farallones

* federally listed as Endangered Species
” federally listed as Threatened Species