Gray Whale

The gray whale is a baleen whale which is the sole member of the genus Eschrichtius. It is a large whale which can reach sizes of 15 meters and weigh up to 40 tons. This species lives mostly in the North Atlantic Asian coastline and in few numbers on the North American coastline.

Taxonomy

By the scientific name Eschrichtius robustus, this whale is the only member of its genus and family Eschricthiidae. Firstly described by John Edward Gray in 1865, this whale is closely related to rorquals of the family Balaenopteridae such as the fin whale and the humpback whale and to a lesser extend to minke whales.

Anatomy

The popular name of the gray whale comes from the characteristic gray patterns that can be observed on the skin. These are either ecto-parasites such as crustaceans and

whale lice or the scars left by such parasites when they drop off as the whales reach cold waters during their annual migration. These whales can measure from 13 to 15 meters in length, with females being slightly larger than males. These whales can reach 40 tons in weight. The baleen plates are unusually short and they are adapted to the unique feeding habits of scooping the sediments at the bottom of the coastal waters. The whales lack a dorsal fin but they have between 6 and 12 dorsal crenulations or so-called knuckles.

Feeding

Opposite to most other baleen whales which feed by swimming with their mouths open to capture large amounts of prey and water, these whales are benthic feeders. This means that they rely almost exclusively on crustaceans that live in the sediments on the sea floor. When feeding, the whales turn to one side which is usually the right one and scoop up large amounts of sediment along with crustaceans. This turning usually leads to eyesight loss on the side used for feeding. This unique feeding behavior is also the reason why the gray whale is more reliant on coastal waters than most other baleen whales. The main feeding waters are in the Northern parts of the Pacific Ocean, with the warmer Southern parts being reserved for giving birth.

Reproduction of the gray whale

The breeding behavior of these whales is complex, and it has been observed from late November to early December. Females usually reach oestrus synchronously and the male testes also grow in size during this period. The females breed biannually, and it is common for them to have more than one mate. The females give birth to calves after a 13 months and a half gestational period. The calf measures 4 meters at birth. After feeding on the high energy 53 percent fat milk in quantities between 700 and 1100 liters per day, the calve will be weaned after 7 months.

Migration

The ovulation period of the females usually occurs according to this species patterns of annual migration. These whales typically travel between 8 and 11 thousand kilometers to cold waters where they feed and to warmer waters to give birth. Thus, the gray whale has the longest annual migration known for mammals, amounting between 16,000 and 22,000 kilometers on a year-long round trip.

This post was last modified on May 17, 2017, 10:21 pm