Biology and Ecological Niches in the Gulf of the Farallones 



Marine Mammals 



Jan Roletto 



Many people are attracted to the Gulf of the 

 Farallones by the variety and abundance of 

 marine mammals that can be seen there. In 

 the gulf, they reign as both apex predators 

 and high-profile or "heroic" species. Some 

 marine mammals migrate through the gulf, 

 whereas others come there to "haul out" on 

 land, rest, and (or) rear their young. They 

 are attracted to the gulf because of the high 

 biological productivity of its waters and the 

 variety of prey species that are distributed 

 and retained there by oceanic circulatory 

 patterns and intense upwelling of nutrient- 

 rich water. 



The gulf attracts at least 33 species of 

 marine mammals. Of the 1 1 species that 

 dominate the coastal and pelagic (open 

 ocean) zones, the humpback whale and blue 

 whale are Federally listed as endangered 

 species and the Steller sea lion is listed as a 

 threatened species. The other dominant spe- 

 cies are the gray whale, Pacific white-sided 

 dolphin, harbor porpoise, Dall's porpoise, 

 California sea lion, northern fur seal, north- 

 ern elephant seal, and harbor seal. 



From the shore, the gray whale is 

 the most commonly seen of the cetaceans 

 (whales, dolphins, and porpoises) in the 

 gulf. Gray whales annually migrate 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. They can be seen migrating 

 southward through the gulf beginning in 

 November, and peak sightings are during 

 January and March. A few juveniles may be 

 seen year round. Gray whales are "baleen" 

 whales instead of teeth, they have numer- 

 ous long overlapping strips of elastic fin- 

 gernail-like material (baleen) hanging from 

 their upper jaws that they use to filter out 

 food. Gray whales feed primarily on the 

 shallow bottom (less than about 400 feet 

 deep), where they swim on their sides while 

 shoveling up mouthfuls of mud and water to 

 strain out small crustaceans, such as amphi- 

 pods, and other animals living in the sedi- 

 ment. They also feed in the water column 

 on euphausiid shrimp (krill) and a few fish 

 species, such as herring. 



Humpback whales are the most acro- 

 batic of the baleen whales seen in the gulf. 

 They use the gulf and Cordell Bank to the 

 north as feeding grounds during the summer 

 and fall months. Their prey consist primar- 

 ily of the krill species Thysanoessa spi- 

 nifera and Euphausia pacifica, and they also 

 feed on schooling fish, such as herring, 

 juvenile rockfish, and anchovy. 



Blue whales migrate to the Gulf of the 

 Farallones during the late summer and are 

 found there throughout the fall. As adults, 



these giant whales generally weigh more 

 than 100 tons and may be the largest ani- 

 mals that ever lived on Earth, possibly 

 exceeded only by the dinosaur Ultrasaurus. 

 These baleen whales feed primarily on krill 

 and, infrequently, red pelagic crabs. Red 

 pelagic crabs are found in the gulf only 

 during warmer-water conditions, such as 

 occur when El Nino events affect the gulf 

 (see chapter on Current Patterns Over the 

 Continental Shelf and Slope). 



The most familiar of the pinnipeds (seals 

 and sea lions) in the gulf is the California 

 sea lion. During its nonbreeding season 

 from August through May, males, juveniles, 

 and some females of this species are abun- 

 dant in the gulf. During that period, 10 

 to 40 percent of the total local population 

 are females. The sea lions are seen locally 

 on docks, on nearshore rocks, and in large 

 numbers on the Farallon and Ano Nuevo 

 Islands, along the Point Reyes headlands, 

 and at Bodega Rock. 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. 



Also common in the Gulf of the Faral- 

 lones is the northern elephant seal, one of 

 the deepest-diving marine mammals. Adult 

 female elephant seals can dive to depths of 



4,000 feet and males to 5,700 feet. While 

 at sea, these seals are submerged 80 to 90 

 percent of the time. Hunting, feeding, and 

 sleeping all take place underwater. They 

 come on land only to breed and molt. Their 

 breeding season begins during December 

 and ends in mid-March. Deep-water fish 

 and invertebrates squid, octopus, hagfish, 

 ratfish, hake, and rockfish are their pri- 

 mary foods. 



Other marine mammals observed in the 

 gulf include four species Federally listed 

 as endangered fin whale, sei whale, right 

 whale, and sperm whale. Two other species 

 are listed as threatened Guadalupe fur 

 seal and southern sea otter. Many addi- 

 tional species of marine mammals have 

 been observed in the gulf. Apart from the 

 minke whale, which is a baleen whale, 

 these species are all members of the group 

 known as "toothed whales." They include 

 the northern right-whale dolphin, short- 

 beaked common dolphin, long-beaked 

 common dolphin, bottlenose dolphin, 

 striped dolphin, spotted dolphin, Risso's 

 dolphin, killer whale, short-finned pilot 

 whale, pygmy sperm whale, dwarf sperm 

 whale, Cuvier's beaked whale, Baird's 

 beaked whale, Hubb's beaked whale, and 

 Blainville's beaked whale. 



48 Biology and Ecological Niches in the Gulf of the Farallones 



