The California gray whale, Eschrichtius robustus, is a marine mammal known for its extraordinary journey. These baleen whales undertake one of the longest migrations of any mammal on Earth. Their annual trek connects the frigid feeding grounds of the Arctic with the warm, sheltered lagoons of Baja California, Mexico.
Physical Characteristics and Adaptations
California gray whales have mottled gray skin, often covered with white barnacles and orange whale lice. They can reach lengths of about 49 feet and weigh approximately 90,000 pounds, with females often slightly larger than males. Their streamlined bodies feature a narrow, tapered head and broad, paddle-shaped pectoral flippers.
Instead of a dorsal fin, they have a prominent dorsal hump about two-thirds of the way back on their body, followed by a series of 6 to 12 small bumps or “knuckles” extending towards their tail flukes. The tail flukes are nearly 10 feet wide with S-shaped trailing edges and a deep median notch. They have 130 to 180 coarse, cream-colored baleen plates on each side of their upper jaw, made of keratin, which are used for filtering food. A thick layer of blubber insulates them and provides energy reserves for their extensive migrations.
Annual Migration and Habitat
The annual migration of the California gray whale covers 12,000 to 14,000 miles round-trip each year, making it among the longest of any mammal. The journey begins in the nutrient-rich feeding grounds of the Arctic, primarily in the Bering and Chukchi Seas, where they spend summer and early fall. As temperatures drop and food becomes scarcer, they commence their southbound migration.
From September to December, these whales travel along the North American coast, often staying close to shore, making them visible from land. Their destination is the warm, shallow, and protected lagoons of Baja California, Mexico, such as Magdalena Bay, San Ignacio Lagoon, and Scammon’s Lagoon. These lagoons serve as breeding and calving grounds, offering a safe environment for birthing and nursing newborn calves. The northbound return journey begins around February, with mother-calf pairs being the last to leave the lagoons, staying closer to the coast for protection against predators like killer whales.
Diet and Foraging Behavior
California gray whales are unique among baleen whales due to their specialized bottom-feeding strategy. Their diet consists of small crustaceans, such as amphipods, along with other benthic (seafloor) and epibenthic (above seafloor) invertebrates and polychaete worms found in the sediment. They feed during the summer months in the cold Arctic waters.
To feed, a gray whale rolls onto its side and sucks sediment and prey from the seafloor. They then filter this material through their coarse baleen plates, trapping the food while expelling water and mud. This process often leaves behind characteristic “feeding pits” on the seafloor and visible plumes of sediment at the surface. While their main diet is benthic, they are opportunistic feeders and have been observed feeding on pelagic zooplankton like krill and even schooling fish, demonstrating their dietary flexibility.
Reproduction and Life Cycle
California gray whales reach sexual maturity between 6 and 12 years of age. Females give birth to a single calf every two to three years. The gestation period lasts approximately 12 to 13 months.
Birthing occurs in the warm, protected lagoons of Baja California, Mexico, between late December and early February. Newborn calves are dark gray to black, measuring approximately 14 to 16 feet long and weighing about 2,000 pounds. Calves nurse for about seven months on their mother’s milk, which is rich in fat (50-60%), allowing them to gain significant weight, often 60 to 70 pounds per day, to build a thick blubber layer for the long journey north. This strong mother-calf bond is sustained as they begin their first migration back to the Arctic feeding grounds. The average lifespan for gray whales is 50 to 60 years, though some individuals may live up to 70 or even 80 years.
Conservation and Current Status
Historically, commercial whaling brought the eastern North Pacific population of California gray whales to the brink of extinction. Due to international conservation measures and protections like the Marine Mammal Protection Act (MMPA) in the United States, this population recovered and was delisted from the Endangered Species Act in 1994. Despite this success, gray whales continue to face ongoing threats.
Current challenges include entanglement in fishing gear, collisions with ships, and the impacts of underwater noise pollution. Climate change also poses a concern, as it can affect the availability of their primary food sources in the Arctic feeding grounds. The western North Pacific gray whale population remains endangered, highlighting the need for continued global conservation efforts.