Gray whales ( Eschrichtius robustus) are medium-sized baleen whales known for their long migrations and unique feeding habits. These marine mammals undertake some of the longest migrations of any mammal, regularly traveling 10,000 miles round-trip and sometimes up to 14,000 miles annually. Their diet and feeding behaviors are crucial to understanding their ecological role and conservation needs.
Physical Characteristics and Identification
Gray whales are easily identifiable by their dark slate-gray color and characteristic gray-white patterns. These patterns are scars left by parasites that drop off in their cold feeding grounds. Individual whales are typically identified using photographs of their dorsal surface, matching the scars and patches associated with parasites that have either fallen off or are still attached. Gray whales measure from 4.9 m (16 ft) in length for newborns to 13-15 m (43-49 ft) for adults, with females tending to be slightly larger than adult males. Newborns are a darker gray to black in color.
Notable features that distinguish the gray whale from other mysticetes include its baleen, which is variously described as cream, off-white, or blond in color and is unusually short. Small depressions on the upper jaw each contain a lone stiff hair, but are only visible on close inspection. Its head's ventral surface lacks the numerous prominent furrows of the related rorquals, instead bearing two to five shallow furrows on the throat's underside. The gray whale also lacks a dorsal fin, instead bearing 6 to 12 dorsal crenulations ("knuckles"), which are raised bumps on the midline of its rear quarter, leading to the flukes. This is known as the dorsal ridge.
Feeding Mechanisms and Diet Composition
Gray whales are baleen whales, with fringed plates, or baleen, as part of their upper jaw. Unlike other baleen whales, gray whales are mainly bottom feeders, getting their food by scraping the side of their head along the ocean floor and scooping up sediment that’s crawling with those small invertebrates they love. The gray whales expel the sediments and water through the baleen, while the invertebrates remain trapped behind for the whale to ingest. Gray whales are the only whale species known to feed extensively on benthic animals. When feeding, the whales use the brush-like baleen in their mouths to strain out the tiny animals from the water they draw in.
Benthic Feeding
Gray whales feed on the bottom of the ocean, stirring up clouds of mud and sediment. These clouds contain important nutrients that will then be stirred up and more accessible to other feeding life. It will also stir up larger creatures such as crabs that may rise high enough for predators such as birds to reach.
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The whale feeds mainly on benthic crustaceans (such as amphipods and ghost shrimp), which it eats by turning on its side and scooping up sediments from the sea floor. This unique feeding selection makes gray whales one of the most strongly reliant on coastal waters among baleen whales. It is classified as a baleen whale and has baleen, or whalebone, which acts like a sieve, to capture small sea animals, including amphipods taken in along with sand, water and other material.
Opportunistic Feeding
Not all gray whales stick to the migration route. Some drop off the route and feed along the Oregon Coast on mysids (another shrimplike creature that lives in kelp beds) and plankton, among other tiny, nutrient-dense ocean creatures. You may see gray whales also eating plankton, when they skim-feed at the surface, their upper jaws visible.
When mysids are abundant gray whales are present in fairly large numbers. Despite mysids being a prey of choice, gray whales are opportunistic feeders and can easily switch from feeding planktonically to benthically. When gray whales feed planktonically, they roll onto their right side while their fluke remains above the surface, or they apply the skimming method seen in other baleen whales (skimming 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, (like blue whales, gray whales seem to favor rolling onto their right side) and 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. Mostly, the animal feeds in the northern waters during the summer; and opportunistically feeds during its migration, depending primarily on its extensive fat reserves.
Unusual Feeding Behaviors
Gray whales (Eschrichtius robustus) evolved to suction feed on benthic invertebrates and typically do not consume adult fish. Yet, these whales are flexible foragers, occasionally skim feeding on planktonic invertebrates and rarely lunge feeding on fish, the latter according to anecdotal accounts.
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Researchers documented the unusual phenomenon of multiple gray whales predating dense schools of anchovy over a sustained period (22 days) in June 2022 at Pacifica, California, in the Gulf of the Farallones. Analysis of 11,265 photos and 11 video clips (totaling 4 min 16 s) for behavior and whale identification resulted in a total of 165 foraging events by six identified gray whales. Attribution of foraging behavior to the most active individuals was achieved by matching left pectoral fins, visible during lateralized feeding behavior. Whales rolled onto their right sides in 96% of near-surface side-swimming bouts. Another behavior, first photographed here, was dynamic surface lunge feeding by one gray whale.
Five gray whales interspersed fish feeding with benthic suction feeding evidenced by sediment streaming: prey type switching was executed rapidly, in less than 1 minute in several instances, the shortest intervals reported for a baleen whale. Similar results were obtained for foraging behavior switching (continuous side-swimming or intermittent lunging) in pursuit of fish. Four photo-identified Pacifica whales were sighted in San Francisco Bay/Gulf of the Farallones, one of which was also matched to the Pacific Coast Feeding Group. Such local and regional connections warrant efforts to determine whether gray whales use this area as a migratory stopover site or for summer foraging, or both.
Feeding Grounds and Migration
Gray whales undertake the longest migration of any mammal, regularly traveling 10,000 miles round-trip and sometimes up to 14,000 miles annually. Each October, as the northern ice pushes southward, small groups of eastern gray whales in the eastern Pacific start a two- to three-month, 8,000-11,000 km (5,000-6,800 mi) trip south. Traveling night and day, the gray whale averages approximately 120 km (75 mi) per day at an average speed of 8 km/h (5 mph).
By late December to early January, eastern grays begin to arrive in the calving lagoons and bays on the west coast of Baja California Sur. These first whales to arrive are usually pregnant mothers looking for the protection of the lagoons to bear their calves, along with single females seeking mates. Throughout February and March, the first to leave the lagoons are males and females without new calves. Pregnant females and nursing mothers with their newborns are the last to depart, leaving only when their calves are ready for the journey, which is usually from late March to mid-April. Often, a few mothers linger with their young calves well into May.
Summer Feeding Grounds
The Artic feeding grounds in the southern Chukchi Sea and the northern Bering Sea teem with these shrimp-like amphipods in concentrations of about 12,000 to 20,000 per square yard on the sea floor.
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Most of the eastern North Pacific stock gray whales spend the summer feeding in the northern Bering and Chukchi seas, but some feed along the Pacific coast during the summer, in waters off of Southeast Alaska, British Columbia, Washington, Oregon, and northern California.
Migration Route
En route to summer feeding grounds in the Bering Sea and other northern waters, gray whales often navigate the coastal waters of the Olympic Peninsula. Some even enter the Strait of Juan de Fuca and stay to feed for days or weeks.
The eastern Pacific stock begins migrating north from late February to May, staying close to the coast from California to Alaska. They enter the Bering Sea, primarily through Unimak Pass, mostly in April and May, and continue moving along the coast of Bristol Bay. After passing Nunivak Island, they head toward St. Lawrence Island and the Bering Strait. The whales disperse to spend the summer feeding in shallow waters (usually less than 200 feet (60 m) deep) of the northern and western Bering Sea and the Chukchi Sea.
Gray whales begin their southward migration in mid-October, passing through Unimak Pass between late October and early January, arriving in Baja California, Mexico in December and January.
Conservation Status and Threats
Prior to protection measures in the last 60 years, gray whale population numbers were critically low due to over-harvesting. As one of the main migrating whale species off the Olympic Peninsula, they are a sought-after sight along the rocky coasts.
Gray whales face a number of known or potential threats, such as entanglement in fishing gear and marine debris, ship strikes, human-generated marine sound, and climate change. These could adversely impact the Western North Pacific population because of its small size and precarious conservation status. The Pacific Coast Feeding Group is also a concern due to its small size and the substantial level of uncertainty pertaining to its possible status as a separate stock under the Marine Mammal Protection Act Resource information collection needs.
Conservation Efforts
NOAA Fisheries works to conserve gray whales through collaborative management, integrated science, partnerships, and outreach. Scientists use a variety of innovative techniques to study, protect, and rescue gray whales in distress (e.g., disentanglement and stranding response). NOAA Fisheries estimates the population size (also called a stock) for gray whales in its stock assessment reports.
All gray whale stocks are protected under the Marine Mammal Protection Act. The eastern stock or Distinct Population Segment (DPS) was once listed as endangered under the Endangered Species Act but successfully recovered and was delisted in 1994. The western stock or DPS remains very low in number and is listed as endangered under the ESA and depleted under the Marine Mammal Protection Act.
Climate Change Impacts
Due to their migratory patterns and broad range of habitat, gray whales are unlikely to be physiologically sensitive to changes in ocean temperature or chemistry. However, their sensitivity will most likely be driven by potential alterations in prey abundance.
A combination of increasing ocean acidity, increasing ocean temperatures, and other changing oceanographic patterns could lead to declines in the small benthic invertebrates that gray whales feed on (mainly amphipods, clams, and krill), as well as disrupt the timing and distribution of prey. Gray whales have extended their summer feeding range farther north of the Bering Strait in recent years in response to reduced sea ice coverage and greater prey availability in the Arctic Ocean. It is unclear how climate change may affect gray whales during migration or on their calving grounds in Mexico, when feeding does not occur.
Stranding Events
Gray whales regularly strand in Washington. Necropsies of stranded individuals should continue to monitor causes of death, animal condition, and physical health of the stock.
On May 30, 2019, NOAA Fisheries declared the elevated rate of gray whale unexpected strandings on the West Coast an ‘Unusual Mortality Event’ (UME), triggering a scientific investigation into the cause. Between 2019 and early 2021, over 200 gray whales had stranded on the coasts of California, Oregon, Washington and Alaska in this event, the most since 2000, when more than 100 whales stranded in what was also determined to be a UME.