Cetacea is often broken down into two suborders, Mysticeti (Baleen whales), and Odontoceti (the toothed whales). Many toothed whales feed on animals such as squid and fish, while the baleen whales usually feed on small invertebrates. A single blowhole or nasal opening on top of the head distinguishes odontocetes, whereas the mysticeti have a double blowhole. Though the divergence of the baleen and toothed whales is still not completely understood, the toothed whales pursued a carnivorous lifestyle, creating organisms with fairly larger brains and the ability for agile and quick movement. The teeth of the mysticetes never break through the gums, replaced by triangular horny plates called baleen (different from teeth in that they are derived from epidermal tissue, like hair), which hangs down from either side of the palate, serving as a net to catch Krill, their main food source. The baleen plates are about 6 mm thick and are lined up along the upper jaw. Frayed fibrous bristles cover the space between the plates, making an effective strainer for seawater, therefore allowing Krill to be captured.

There are several different species of both baleen whales and toothed whales that frequent the waters surrounding the Baja peninsula; the gray whale, the mighty blue whale, minke whales, some fin whales, common and bottlenose dolphins. Also, occasionally sighted are orca, humpback, and sperm whales.

Gray Whale - Eschrichtius robustus (Family Eschrichtiidae)
The gray whale can be identified by its large size (approximately 40-50 feet long), with a small head in proportion to the rest of the body. There is no dorsal fin, instead a series of six to twelve crenulations extending along the last third of the body. The body is gray with white mottling and colonized with barnacles and whale lice.

During the long summer days in the Arctic, the whales feed constantly, sometimes consuming up to a ton of food every day enabling them to grow and increase their supply of blubber. By September, ice begins to form and the whales begin migrating south. Females begin to ovulate in November and mate during fall migrations or at winter stays in lagoons. After swimming an average of 100 miles a day at 2-5 mph, the pregnant female whales reach the Baja Peninsula. Southbound pregnant females (those that will calve during this migration season) begin the migration first, and therefore are the first to appear in Baja.

The main activity upon reaching Baja California, Mexico is to calve. The gestation period for the gray whale is approximately thirteen months with nursing and weaning occupying another six to eight months. The mother nurses her calf until early March, causing her to lose an average of eight tons of body mass. In Mexico the major calving areas are Laguna Guerrero Negro (Magdalena Bay), Laguna Ojo de Mexico, Laguna San Ignacio, and Estero Soledad (the gray whales have been sighted elsewhere in Baja, but these areas are most prominent).

A few whales have been recorded traveling around Cape San Lucas to the southern shores of the Gulf of California. Primarily these organisms remain on the Pacific coast, probably for several reasons. The water in the Gulf of California can be fairly warm in the summer, too warm for these large mammals to thrive. Also, because of the long trip back to the Bering Sea, the calm coves and bays of the Pacific side make a suitable habitat for calving without necessitating an even longer migration event.
By around March to April the whales begin to migrate north again, with the newly pregnant females first and the females with new calves last, the peak passing Pt. Piedras Blancas, California, in early May.

When watching for Gray whales in Baja, the best time is February to March, when the whales are in the lagoons and can be seen fairly close to shore. One of the characteristic behaviors of the whale is called "spyhopping". There are several hypotheses explaining this behavior such as the whales looking for landmarks on shore, dislodging parasites from the skin or simple play.

Blue Whale - Balaenoptera musculus (Balenopteridae)

The blue whale is the largest of the mysticetes and the largest mammal alive today. These whales are bluish gray in color, with white undersides to the flippers. Blue whales are considered Nekton, which includes pelagic dwellers that can swim in directions independently of the ocean's currents. The blue whale is a filter feeder, feeding primarily on zooplankton, especially euphausids or krill. For these whales, the amount of phytoplankton (which feed on plankton) growing in the upper sunlit layers of the ocean governs the population density. There are three subspecies of blue whales; with the largest B. m. intermedia found in the Southern Hemisphere, the pygmy blue whale B. m. brevicauda found in subantarctic waters of the Indian Ocean and the medium sized B. m. musculus, located in the North Atlantic and North Pacific oceans. Therefore in Baja, when observing the blue whales, one is most likely to encounter B. musculus musculus, the second largest group of blue whales.

Most North Pacific blue whales tend to migrate from feeding grounds in the spring and summer (beginning in April and May) after wintering in subtropical and tropical waters off southern California, Baja California, Mexico and Asia. In the northward migration the blue whales are reported to move along the coast, splitting into two groups one group moving towards the Gulf of Alaska and the other heading west towards the Aleutian Islands.

Blue whales can be seen alone or swimming in groups of two or three groups, though large feeding groups have also been observed. Blowing and diving patterns will vary with activity level, though blue whales generally make 10-20 shallow dives at 12-20 second intervals, followed by a 10-30 minute deep dive. The blow is tall (6-12 meters), narrow, and vertical. On slow dives, the head and blowhole along with the tail stalk and fluke can be observed. On fast dives, the head disappears before the fluke emerges. In Baja, the Blue Whales can be observed from March to April in the Gulf of California feeding on phytoplankton.

Minke Whale - Balaenoptera acutorostrata (Balenopteridae)

The minke whale is the smallest and most common of the finback whales. The minke can be identified by its pronounced dorsal fin, and a small head, which appears triangular when viewed from above. The distribution of these whales ranges from the North Pacific to North Atlantic and into the Southern Hemisphere. In the northeast Pacific, minke whales range from Alaska to Islas Revillagigedos, Baja California, Mexico. Only occasionally are minkes sighted in the Gulf of California due to the increase in ambient water temperature.

Minke whales are fairly uncommon around Baja; instead their primary habitat along the North American coast is in the further north. The whales in both the east and west Pacific have northern coastal migrations in the summer and southern migrations in the autumn and winter. During summer months, there is much segregation between the whales with males and females remaining spatially distant while more mature animals travel to northern feeding grounds.

Common Dolphins- Delphinus delphis

Bottle Nose Dolphins - Tursiops truncates

Dolphins are a majority of the suborder Odontoceti, meaning that they have teeth instead of baleen to use for feeding. Killer and pilot whales are also considered dolphins though they are usually considered to be true whales. Dolphins can be distinguished from small porpises by their long, narrow, beak-shaped head.

The common dolphin prefers to be associated with large or small schools of other dolphins. This animal is a quite swift and agile swimmer and can often be found near ships, playing and swimming in the waves. Furthermore, due to their frisky nature the common dolphin can be seen playing with and around other marine organisms such as fish and turtles. Though D. delphis can swim to deep depths, it is usually found in shallow waters and participating in fairly shallow dives. The primary food source of the dolphin is located in these shallow waters and consists of small surface-living fish, but they can also be seen consuming small crustaceans, mollusks, and cuttlefish.

The bottlenose dolphin is larger than the common dolphin, both in length and circumference, and appears purplish-black on its back, fading all the way to white on the underside. The bottlenose prefers coastal waters to open ocean and appears less playful than the common dolphin.
Dolphins can be found all over Baja, both in the Pacific and in the Sea of Cortez. For example, one may stop to take a scenic picture at Bahia Concepcion and happen upon a huge pod of dolphins relaxing and playing in the water. Or, one may look out into the Pacific Ocean and see schools of fish flying out of the water followed quickly by a dolphin pod.