Migration and Feeding

The annual migration of the gray whale extends from the lagoons of the Baja, the nursery grounds of the species, to the Arctic waters of the Bering, Chukchi and Beaufort seas. The 10,000-mile round trip migration is the longest of any mammal.

Grays travel in pulses, and females and males never travel together. After summer feeding, late-stage pregnant females leave the Arctic first to return to their winter home, followed by the non-pregnant females. The males take up the rear a distant third. On the return trip back north, the newly pregnant females start off first followed by the males, while the mothers and their newborn calves are the last to leave the lagoons.

On the northward leg, mother and calf swim close together for the survival of the calf. Killer whales (Orcas) are vicious enemies of the grays. Gray mother and calf are especially vulnerable to attacks by Orcas in Monterey Bay, Calif. This is a deep ocean canyon and if the grays decide to take a shortcut and cross it, rather than hug the shoreline, they are at serious risk. Cousteau notes that “In a coordinated hunt, the smaller killer whales (working in groups) separate the mother and calf and relentlessly attack, exhaust, and eventually drown the calf as the mother struggles to save it. One calf may feed up to 30 killer whales.” The Orcas are particularly after the calves’ tongue, a culinary delight.

Grays do not stay underwater for as long as most other whales. They submerge for about five minutes at a time. They swim and feed close to shore, staying in relatively shallow waters off the continental shelf. During migration, some individuals stop along the way in the shallows and bays of the US and British Columbia coastlines to opportunity feed before heading to the Alaskan waters.  Some individuals will not make the entire trip to the Arctic and take up summer residence in the secluded bays and estuaries of Oregon, Washington, and British Columbia.

Grays Feed on Ocean Floor

Click photo to see video
of gray feeding on seabed

Gray whales are the only cetacean that feeds on benthic (bottom-dwelling) crustaceans. They feed mainly on amphipods, tiny shrimplike crustaceans. They also feed on isopods, polychaete worms, and mollusks. Gray whales have also been observed munching on kelp. It is believed they are feeding on microorganisms that colonize the plant.

Gray whales feed primarily during the summer months in the Arctic seas. As the video at left shows, they swim slowly on their sides, skimming over the ocean floor and taking in sediment through the sides of their mouths. When filled, the mouths close, expelling water and sediment through the baleen which filters the prey. Not all sediment is expelled, however, as some winds up in the stomach.

The gray's feeding method is advantageous to the species. By stirring up the bottom sediment, benthic phytoplankton gets suspended in the water column. Amphipods which feed on the phytoplankton grow in greater abundance as a result, which in turn increases the whale’s food supply.

Summer is a crucial time for the females.  Since the mothers eat very little after the summer months, they must store up enough fat to last the year. By the time the whales return to their feeding ground, they have lost up to one-third of their body weight. It is one of nature’s wonders that female gray whales forgo feeding for so long a time, especially when they must travel thousands of miles and maintain enough energy to breed, give birth and nurse their offspring.