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Mighty Migration of the Gray Whale

The Eastern Gray whale migrates off the west coast of the US from Alaska to Mexico. They stay close to shore to feed in shallow water.  I encountered them in a summer marine field course in the Sea of Cortez where they breed and calve.  When they are ready, mothers and their new calves hug the shore as they journey north.  There is also a critically endangered western subspecies in the Pacific which migrates between Russia and China.  Their status reminds us about the vulnerability of these large mammals; we need to appreciate and conserve both species. 

Fossil records show gray whales even once existed in the Atlantic Ocean.  They have migrated between the Pacific and Atlantic during periods when temperatures were higher in the Arctic. The National Oceanic Atmosphere Association (NOAA) conducts surveys and estimates there are approximately 19,000 gray whales in existence.  Ship strikes and entanglement in fishing gear are two direct ways in which humans threaten the population. Since 1972, the Marine Mammal Protection Act has prohibited the ‘’taking” of marine mammals- which bans harassment, hunting, capturing, collecting or killing in U.S. waters, by U.S. citizens.

Gray whales can be distinguished from other whales by a hump and ridge of 6-12 sharp bumps called crenulations or knuckles along their backs. They have five shallow furrows on the underside of their throat and baleen- bristly structures in their mouth, to filter food from the water. Their baleen acts like a sieve helping them capture small sea animals like amphipods and shrimp-like mysids. Whales feed mainly on benthic crustaceans, which they eat by turning on their side and scooping up sediments from the sea floor. For this reason, these whales rely on coastal waters. When gray whales feed planktonically, they roll onto their right side while their fluke remains above the surface, or they skim the surface with their mouth open. This skimming behavior mainly seems to be used when gray whales are feeding on crab larvae. Gray whales feed benthically, by diving to the ocean floor and rolling on to their side to suck up prey from the sea floor. Gray whales seem to favor feeding planktonically in their feeding grounds, but benthically along their migration route in shallower water. 

This species is dark slate-gray in color and with careful observation individuals can be identified by scars left by parasites which drop off in their cold feeding grounds.

During the breeding season, it is common for females to have several mates. Ovulation coincides with the species’ annual migration patterns, so births occur in warmer, southern waters in the winter, like the Sea of Cortez for the eastern species.  Calves are born tail first, measuring about 14–16 ft in length, weighing around 2,000 lbs.  Females lactate for approximately seven months following birth, at which point calves are weaned and maternal care begins to decrease. The shallow lagoon waters in which gray whales reproduce are believed to protect the newborn from sharks and orcas. 

Mostly, the animal feeds in the northern waters during the summer; and opportunistically during migration. Feeding areas during migration include the Gulf of California, Monterey Bay and Baja California Sur. The gray whales round trip migration is believed to be the longest annual migration of any mammal. I have viewed gray whales in the Sea of Cortez during the summer of 1988 while conducting research as part of a graduate course at the University of Arizona with Thomas who wrote the guide to the fish of the Sea of Cortez. 

The International Whaling Commission was instituted in 1949 to manage stocks. Then the Marine Mammal Protection Act of  1972 added further protections for whales in US waters, extending 200 miles into the ocean. Threats to the eastern North Pacific population of gray whales include: increased human activities in their breeding lagoons in Mexico, climate change, acute noise, toxic spills, aboriginal whaling, entanglement with fishing gear, boat collisions, and possible impacts from offshore fossil fuel exploration and extraction. Disturbance from underwater industrial noise may displace whales from critical feeding habitat. Physical habitat damage from drilling and dredging operations, combined with possible impacts of oil and chemical spills on benthic prey communities also is a concern.

This print is part of a series entitled Conservation of California Coastal Critters.

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