Marine Mammals of San Carlos

Order Cetacea - Whales and Dolphins

This large order is broadly differentiated into one extinct and two extant suborders. The two extant suborders are mysticeti - baleen or mustached whales, and odontoceti - the toothed whales. Both suborders are represented by numerous species within the Sea of Cortez.

Suborder Mysticeti - The Baleen Whales

The giants of the sea are the filter-feeding baleen whales. These are frequent visitors to the San Carlos area, owing to the tremendous amount of plankton that depends on the Midriff Islands upwelling zone for nutrients.

Fin Whales, Balaenoptera physalus - Although it is estimated that there are only about 400 fin whales within the Sea of Cortez, these are still one of the most commonly observed whales in the region. These are the second largest whales in the world, after the blue whale. For decades it was debated whether the Sea of Cortez fin whales were a localized population that are permanent residents of the Gulf, or whether they were members of the larger Pacific groups that might periodically enter the Gulf. In 2002, this debate appeared to be settled with analysis of mitochondrial DNA that indicated that the Sea of Cortez fin whales were indeed a unique permanent population that did not mix with the Pacific whales.


Blue Whales, Balaenoptera musculus - The largest of the whales, average blue whales are 24-24m in length, and weigh 100,000kg (about 80 feet and 200,000 pounds)! Even the pygmy subspecies of this whale is as large as a fin whale. These whales are found throughout the Sea of Cortez and are most abundant in the winter and spring.

Bryde's Whales, Balaenoptera edeni - The Bryde's whale is another common resident throughout the Gulf of California. Often confused with the larger fin whales, the Bryde's whale may be identified by its dorsal fin. In the Bryde's it is tall and curved like a sickle. It also rises steeply from the back of the whale. In the fin whales, the dorsal fin rises from the back at a gentler angle.

Humpback Whales, Megaptera novaeangliae - After spending summers feeding in the rich cold waters of the high latitudes, humpback whales move to warmer waters to mate and calve. While approximately 60% of the Alaskan humpbacks head for Hawaii, a significant number enter into the Sea of Cortez over the winter. They are found more frequently in the Southern Gulf, but have been seen as far north as the Midriff Islands.

 

Suborder Odontoceti - Toothed Whales and Dolphins

Orcas, Orcinus orca - It is generally believed that the orcas found in the Sea of Cortez are members of a resident population. Traveling in pods of typically 5-15 animals, they can occasionally be seen as they cruise near the shores of San Carlos Bay. More often they have been sighted near San Antonio Point and San Pedro Point. An apex predator, they have been observed feeding in the Sea of Cortez on fin whales, blue whales, and whale sharks. As an apex predator, they are more prone to accumulation of pesticides, heavy metals and other poisons through the process of bio-amplification, and may be the most heavily contaminated animals on Earth.

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Sperm Whales, Physeter macrocephalus are relatively common in the Sea of Cortez. As the deepest divers of all the cetaceans, they can reach depths of 3000ft/915m on a single breath. In most regions, they are hunting the giant squid found at these tremendous depths. There is no information about the abundance of giant squid in the Sea of Cortez, but several of the sperm whales that have been observed in the region bear the characteristic scars of such encounters. There are also large numbers of the smaller humbolt squid in the region. With the Guaymas trench reaching astounding depths of over 2000m, there is much that is not known about life in the very deep regions of the Sea of Cortez

Dolphins and Porpoises - Common dolphins, (both short and long-beaked, Delphinus delphis and D. capensis respectively), spotted dolphins, Stenella attenuata and bottlenose dolphins, Turisops truncates, are by far the most common species in the central Gulf, although it has been estimated that as many as 30 species of dolphins and porpoises are found in the Sea of Cortez. The Northern Gulf also has the auspicious honor as being the home to what is considered to be the smallest and most endangered marine cetacean, the Vaquita, Phocoena sinus.

 

Order: Carnivora, Suborder: Pinnipedia - Sea Lions (also seals and walruses worldwide)

California sea lions, Zalophus californianus are abundant throughout the Gulf now that protective measures are preventing them from being hunted. It is estimated that there may be as many as 30,000 in the Gulf. Despite protective legislation, humans may still be the primary cause of mortality in young sea lions. Accidental entanglement in lost fishing nets is a common occurrence and some fishermen still shoot or club sea lions as they believe that they are competing for fish and damaging their nets. The sea lions however remain curious and friendly to humans and are eager to play with scuba divers and snorkelers. They are most common on offshore islands where terrestrial predators such as coyotes and wild dogs are not present to feed on their pups. Dominant males, distinguished by a prominent protrusion on their brow, establish a beachhead and vigorously protect interlopers from sneaking into the harem. Even divers should be aware of the patrols of the bulls, as they will not hesitate to give an intruding scuba diver a rough shove.

 
 
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