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Students Ask and Experts Answer

Ecology

A jar of shrimplike amphipods — a gray whale's favorite food!

Q. What do gray whales eat?
A. Gray whales feed on small crustaceans such as amphipods, and tube worms found in bottom sediments. They feed primarily during the summer months of long daylight hours in the cold Arctic waters of the Bering and Chukchi seas. A whale will swallow approximately 70 metric tons of food during that time. They may eat a ton a day of shrimplike amphipods.

Q. How do gray whales eat?
A. Gray whales have no teeth. They capture and strain their food thorugh a fringed "curtain" of baleen, which hangs from the roof of the mouth. Grays are the only bottom-feeding whales. To feed, a whale dives to the bottom, rolls on its side and gulps mouthfuls of mud. As the whale closes its mouth, water and sediments squirt out through the baleen plates. This leaves the tiny amphipods stuck to the baleen inside their mouths. Whales then use their tongues to loosen the amphipods from the baleen, and swallow them.

Baleen

Q. What are baleen plates?
A. Baleen whales have a series of 130-180 fringed, overlapping baleen plates hanging like curtains from each side of the upper jaw where teeth might otherwise be found. Baleen is made of a fingernail-like material called keratin. The fringe-like plates are off-white in color and about 2-10 inches (5-25 cm) long. When whales take huge gulps of ocean water, the baleen work like giant combs to trap food in as the whale "squeezes" the water back out.

Q. How fast do gray whales travel during migration?
A.
Grays traves at about 3-6 miles per hour (4.8-9.6 km/hr). The can cover nearly 100 miles (161 km) a day. They can cover the distancel from Unimak Pass in Alaska to the lagoons of Baja California Mexico in an average of 55 days. The pace is slightly slower on their journeys north, particularly for mothers with new babies.

Q. Do all gray whales migrate?
A. Not all. Some individual gray whales can be seen year round on the coasts of British Columbia, Washington, Oregon, and California. People who live in those areas call them "resident whales," and look forward to seeing them. The resident whales join up with the migration south in the fall or winter, butthey don't return all the way back to the Arctic in the spring.

Q. When do gray whales make their yearly migration?
A.
In October, the whales begin to leave their feeding grounds in the Bering and Chukchi Seas. They swim south during the fall and winter to their mating and calving lagoons in Baja California, Mexico. The southward journey takes 2-3 months. The whales return north during the late winter and spring (mid-February to early June).

Q. How do the whales know when to migrate?
A.
No one knows for certain, but it's probably several things: fewer hours of daylight, changes in water temperature, changes in food supply as the northern pack ice increases, or changing hormones involved in breeding. Experts believe the whales keep time with an inner biological clock. Whatever the reason, gray whales leave their feeding grounds in late summer and begin the journey south.

Q. Why do the gray whales swim all the way down to Mexico to have their babies? Why don't they stay were they are because they have enough fat to keep them warm?

A. The moms do have plenty of fat to keep them warm, but the babies don't! When gray whales are born they have practically no fat on their bodies. In fact their skin hangs in folds along their bodies and they look like little tadpoles. So it is much better for these babies to be born in warmer waters away from the cold of the Arctic where mom can nurse them until they get nice and fat for the return trip to Alaska. Baby gray whales gain weight very quickly and grow about 9 feet by the time they are weaned.


Q. When whales head south, where are they going?
A.
Gray whales migrate to their winter breeding and calving grounds. This means the warm, shallow, salty lagoons of Mexico's Baja California coast. The three main lagoons where most of the whales go are Bahia Magdalena, Laguna Ojo de Liebre, and Laguna San Ignacio.

Q. Do all the whales go at the same time?
A.
Gray whales travel in groups. First to head south are pregnant females (cows), who want to reach the lagoons before giving birth. The other adults and juveniles follow about a month later. When whales return north, the males and newly pregnant cows head north first. Next are adult males and young whales from previous years. The last to leave are the new mothers and calves.

Q: Why do gray whales migrate along the coast?
A.
The coastline may help them navigate the long distance. And being benthic (bottom) feeders, they have evolved with an orientation toward the seafloor where their food is located.

Watching for Whale Spouts Through Binoculars

Q: How far from the coast do they usually travel?
A.
Along linear coastlines like in California, gray whales migrate within 2.5 miles of the shore. In narrow Unimak pass, while turning the corner around the Alaska Peninsula, the whales pass within 1.6 miles of the shore. Gray whales may pay more attention to water depth than distance from shore. As a result, the whales pass close to shore where the continental shelf is steep, and when it is shallow they spread over a greater distance. Bays, islands, and straits may confuse their travel. This might explain why in some places they are observed farther offshore.

Q. Do whales eat while in their winter breeding grounds?
A.
Not much. During the months of migrating and socializing in the lagoons of Baja California, gray whales survive almost entirely on fat reserves built up in the summer feeding grounds. Some observers believe that gray whales eat nothing from the time they leave the Arctic in autumn until their return there in the spring. Recent research at Laguna Ojo de Liebre has shown that there are critters in the muddy bottom upon which the whales may feed.

Q. Do gray whales lose a lot of weight while in their breeding grounds?
A.
A 30-ton whale will expend so much energy on the migration to the Baja lagoons that it may lose fully eight tons of its blubber. It eats little or nothing in the breeding grounds. But by early summer, most gray whales are back at their northern feeding grounds. Then they feast! Over the next five months they will gain back an estimated 16 to 30 percent of their total body weight.

 

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