It is early fall in the northern hemisphere as I write this. By now a significant number of California gray whales (Eschrichtius robustus) have reached the coastal waters of the Pacific Northwest on their southward journey from their feeding grounds in the Bering and Chukchi Seas to a series of coastal lagoons off the west coast of Mexico’s Baja peninsula — about a 5,000-mile commute, each way‚– where they will mate, calve and spend the winter. 

Shearwater TERN
By late fall and early winter many of these same whales will be passing through California waters, and once again the annual appearance of this iconic species will bring great joy to many. 
Despite their massive size, California gray whales are usually wary of divers. Thus, the odds of encountering a California gray whale underwater on any given dive are very low. But every year a number of lucky souls look up during a dive only to see one of these 40 foot-long giants looking back at them. And many of us will see a pod of gray whales from the surface from coastal outcroppings and as we travel to and from dive sites. 
This article is intended to provide insights into the natural history of these magnificent whales so that you might get the most from any encounter should good fortune smile on you.
The Big Picture
All of the world’s approximately 78 species of whales, dolphins and porpoises are classified as cetaceans. Taxonomists divide cetaceans into two suborders: Mysticeti, the baleen, or filter feeding, whales, and Odontoceti, the toothed whales. Although specialists debate the numbers, there are approximately 11 species of baleen whales and 67 species of toothed whales.
As is the case with the blue, fin, minke, northern and southern right, and humpback whale, the California gray whale is a baleen whale. Toothless animals, baleen whales feed primarily on planktonic organisms and a variety of small bony fishes. When feeding, these behemoths swim open-mouthed through dense concentrations of their prey or scoop their prey in shovel-like fashion off the sea floor in areas where the bottom is soft. After gathering the prey in its mouth a baleen whale closes its mouth to expel water as tough, flexible, horny sheets of modified hair called baleen trap the prey. The baleen bears some resemblance to a synthetic fiber, and a mouthful of baleen looks like some sort of natural-bristle toothbrush. 
Species Description
The California gray whale is characterized by its streamlined body, tapered head, and mottled coloration. The upper jaw is curved and slightly overlaps the lower jaw. The outer skin of the upper jaw is populated with a number of dimple-like depressions with each depression holding one stiff hair. A series of two to five grooves are present on the lower part of the throat. As is the case with all baleen whales, California gray whales are equipped with two blowholes. In contrast, all toothed whales have a single blowhole.
Distinct scratches are present on the skin of adult gray whales as are unevenly distributed patches of barnacles and orange-tinted whale lice. The bodies of most newborn calves are dark gray to black, but some display prominent white markings.
Gray whales lack a dorsal fin, but do display a prominent dorsal hump located roughly two-thirds of the way back toward the tail on the top of the body. To the rear of this hump are a series of 6 to 12 knuckles that extend along the back toward the tail. The knuckles are especially prominent during the southern part of the whales migration because the adults have gone without any significant feeding for an extended period of time, and the less they weigh, the more prominent the knuckles become.
Somewhat pointed near the tips, gray whale flippers are paddle shaped. The tail of an adult is 10 to 12 feet across with a deeply notched mid-point. The tips of the fluke are pointed. 
Full-grown adult females attain proportions of almost 50 feet and 40 tons. Full-grown males are usually a few feet shorter, but they, too, can weigh as much as 40 tons. 
A migrating gray displays a fairly regular breathing pattern with a whale inhaling and exhaling three to five times in intervals of 15 to 30 seconds before lifting its tail and making a three to five minutes-long dive. Gray whales can remain submerged for up to 15 minutes. 
Life Cycle
California gray whales spend the late spring, summer and early fall in the Northern Hemisphere feeding on benthic amphipods in prolific northern waters. In the fall they head south as they begin their astonishing 10,000 mile-long roundtrip migration, the second longest mammal migration known to science. Groups of migrating whales typically consist of only two or three animals, but pods sometimes number as many as 15 animals. 
The southward journey extends into winter months and brings the whales close to coastal outcroppings along North America’s Pacific coast. The whales reach Baja in early winter. Although some whales swim all the way around Baja and into the Sea of Cortez, most stop at Scammons Lagoon, San Ignacio Lagoon or Magdelena Bay, a series of shallow, well-protected bodies of water tucked into the seclusion of the Baja wilderness. Conditions there help create ideal settings for the whales to court, and for pregnant females to give birth, usually to a single calf, and for calves to spend the early vulnerable days of their lives.
Mating typically occurs in groups of three: one female and two males. The role of the second male is a subject of debate. Some specialists believe he is present to learn the finer points of courtship, while others suspect that he is there to steady the female so the first male can achieve penetration. Courtship takes place mostly at the surface and often lasts for several hours.
Calves are born in early winter after a 13 month-long gestation period. At birth the calves are 12 to 17 feet long, and weigh in excess of 3,000 pounds. While that is large for starters, the calves are capable of gaining an astonishing 10 pounds an hour for the next several months as they feed on the rich milk of their mothers. 
In late winter and early spring the whales begin their northbound journey back to their feeding grounds. This part of their migration usually takes the whales farther out to sea. Exactly how the whales maintain their bearings and successfully navigate such long distances is not well understood. 
When the whales reach their feeding grounds they gorge themselves on a variety of small crustaceans and worms found in bottom sediment. When feeding, a gray whale dives to the bottom, rolls onto its side and takes bottom sediment and water into its mouth. Then the whale closes its mouth causing the water and sediment to get expelled through the overlapping series of baleen plates. The baleen traps the food on the inside near the tongue, and the food is then swallowed. 
Surface Sights
Gray whales are often seen holding their head as high as 10 feet out of the water in an act known by several names; spy-hopping, sparring, and spying-out. Some authorities believe the whales are trying to visually orient themselves with prominent coastal features, but others believe the whales’ above-water vision to be too poor. 
Gray whales can also be seen leaping almost entirely out of the water in a dramatic maneuver known as breaching. Swimming at speeds of close to 30 miles an hour the whales launch themselves skyward. Researchers have multiple theories about breaching; it might help dislodge parasites; be a form of intra-species communication; a means of establishing dominance; serve other purposes, or “all of the above.” The fact is, there’s just a lot we don’t know about gray whales. 
Not too many years ago there were three healthy populations of gray whales in the world; a now extinct North Atlantic population, a Korean (western Pacific stock) that is now on the brink of extinction, and the eastern Pacific population. It is the whales in the eastern Pacific population that are commonly known as California gray whales. Over-hunting eliminated the North Atlantic population, and severely threatened the other two groups. 
The California gray whale was hunted to near extinction in the middle of the nineteenth century after their calving lagoons were discovered, and again in the early 1900s with the advent of factory ships that could process slaughtered whales at sea. In 1937 gray whales were given partial protection, and ten years later full protection, by the International Whaling Commission. The current-day population of the California gray whale is believed to be close to its pre-hunting numbers. 
The common name gray whale is a reference to the mottled coloration of these whales that results from a combination of gray patches and white markings on their natural blackish skin. Their taxonomic name, Eschrichtius robustus, is derived from a reference intended to honor the 19th century Danish zoologist D.F. Eschricht, and the Latin “robustus” meaning oaken or strong. 
Are Gray Whales Friendly? 
Gray whales are often described as being “friendly” toward humans. Some specialists argue that the word “friendly” anthropomorphizes the whales, and that whales have no concept of friendship, especially with members of another species. 
People on both sides of the issue can make good arguments, but what is known without question is that gray whales in the Baja lagoons routinely approach boats filled with exuberant whale watchers. The whales not only approach the boats, but they nudge the boats and appear to enjoy the physical contact with the people that reach over the side and scratch, rub, pet, brush or otherwise touch the whales. Whether or not the term friendly is too anthropomorphic remains open to debate, but clearly the encounters are thrilling for the people who experience the up close and personal nature. 
A number of operators lead whale-watching expeditions in the lagoons. By law, no scuba diving or snorkeling is allowed, but topside encounters are often spectacular.
California Diving News