Species

Gray whale

Content Cover Image

Gray whale. Source: NOAA

The only member of the Eschrichtiidae family, the Gray whale (Eschrichtius robustus), is a very large marine mammal, in the family of Rorquals (Balaenoptera), part of the order of cetaceans.

caption Gray whale barnacled rostrum at two meter range. @ C.Michael Hogan The Gray Whale is a baleen whale, meaning that instead of teeth, it has long plates which hang in a row (like the teeth of a comb) from its upper jaws. Baleen plates are strong and flexible; they are made of a protein similar to human fingernails.  Baleen plates are broad at the base (gumline) and taper into a fringe which forms a curtain or mat inside the whale's mouth. Baleen whales strain huge volumes of ocean water through their baleen plates to capture food: tons of krill, other zooplankton, crustaceans, and small fish.

The Gray Whale has numerous unique behavioral and physical features. This whale makes the longest migration out of any mammal known (up to 20,400 kilometers), and is the sole cetacean species that feeds by filtering sediment on the bottom of the sea floor using baleen. Despite feeding solely by filtering small invertebrates (molluscs, worms and bottom-dwelling crustaceans), this marine mammal can grow to a massive length. An adult E. robustus  ranges  from 11 to 13 meters in length, and can achieve a body mass of up to 40 tons. Because of the ferocity of mothers separated from their calves, whalers refer to Gray whales as devil-fish.

 

 

 

 

caption Gray whale relative size to an adult human.

 

Conservation Status caption Gray whale. Source: Pacific Wildlife Foundation

Scientific Classification

Kingdom: Animalia (Animals)
Phylum:--- Chordata
Class:------ Mammalia (Mammals)
Order:-------- Cetacea (Cetaceans)
Family:-------- Eschrichtiidae
Genus:----------Eschrichtius
Species:----------- Eschrichtius robustus (lilljeborg, 1861)

The Gray whale is alternatively known as California Gray Whale, Grey Whale, Devil-fish, Gray back, Hard head, Mussel Digger, Pacific Gray Whale and Rip Sack.

Originally, an Atlantic population of the Gray whale once existed; however, hunting drove this stock to extinction sometime in the late 19th to early 20th centuries. While regulations on hunting set in 1946 by the International Whaling Commission bolstered the eastern Pacific stock of whale to Least Concern, the western Pacific stock remains Critically Endangered.

Physical description

The Gray whale is mottled dark to light gray in color and is encrusted with patches of barnacles and whale lice. The species lacks a dorsal fin and instead has a series of bumps along a dorsal ridge on the final third of the back.

Gray whales lack teeth, and instead use a baleen structure (homologous to teeth) for feeding. There are two deep grooves on the throat, which allow the mouth to expand when feeding, and the baleen, which is used to filter food, is cream-white in color. When surfacing, the blow produced is distinctly bushy, short and forked, or heart-shaped, as it arises from two blowholes. Females tend to be larger than males, but otherwise the two sexes are similar in appearance.

Reproduction

The Gray whale makes the longest migration of any mammal. Each autumn and spring, they travel between their Arctic summer feeding grounds and the warm lagoons near the equator where females give birth. In this annual round trip, individuals can travel up to 20,400 kilometers. Sexual activity mostly occurs during the southward migration; however, sexual activity may occur at any time of the year.

Little is known about the mating strategies of this species moreover, the breeding cycle occurs over two years. Gestation (pregnancy) lasts about 13 months, and the single calf is then suckled for a further seven months. At birth, the calf's exterior is smooth compared to the encrusted adults. The calf also lacks sufficient blubber needed for survival in Arctic waters. During the first few hours following birth, the mother often holds the calf near the surface to help it breathe.

Observing teeth is the primary method for identifying lifespan in mammals. Because of a lack in teeth,  the Gray whale's lifespan is difficult to determine. Maximum longevity is estimated to be 77 years in the wild.

 

caption Chief morphological features of the Gray whale.

 

Distribution

caption Distribution of the Gray whale.

The gray whale makes the longest migration of any mammal known. Each autumn and spring, they pass between their Arctic summer feeding grounds and the warm lagoons near the equator where females give birth. Each year, individuals may travel up to 20,400 kilometers because of this trip. The Gray whale is most commonly found within a kilometer of the coastal shore in waters typically no deeper than 100 meters.

There are two main stocks (related groups) of gray whales. One stock exists along the eastern Pacific coast from Baja California to the Bering and Chukchi Seas. The second stock occurs in the western Pacific, from South Korea to the Okhotsk Sea. The eastern Pacific stock migrates annually from Arctic feeding grounds to breed in Mexican waters, while the western Pacific stock migrates along the east coast of Russia. An Atlantic Ocean stock once existed, but was hunted to extinction about 150 years ago.

Predation

Killer whales are the only non-human predator of the Gray Whale. Attacks directed toward calves have been observed. Adult grays will often protect the young by positioning themselves between the killer whales and the calf. The gray whales also head for shallow waters and kelp beds in order to take refuge from attackers.

Feeding habits

This species is the only cetacean known to feed by straining the sediment on the sea floor. An individuals rolls onto their sides after diving to the bottom, taking large amounts of sediment into his mouth. As the whale rises to the surface, the contents of the mouth are strained through the baleen, leaving a trail of mud and sand behind it. The invertebrate prey; consisting of bottom-dwelling crustaceans, worms and molluscs, are isolated by the strain and swallowed. A number of seabirds are attracted to feeding gray whales, and take advantage of invertebrates that escape the filtering process.

Sufficient fat reserves are built up during their stay in the feeding grounds, enabling individuals to go without food during the breeding season. On return to the feeding grounds, approximately one third of the body weight may have been lost. In relation to the ecosytem, numerous seabirds are attracted to feeding Gray whales, and take advantage of invertebrates that escape the filtering process

Lifespan

Estimates of lifespan in the wild range from 25 to 80 years of age, with many first hand family accounts of Mexican observations tracking the same individuals for over five decades. Mortality rates are highest for juveniles, with an average annual calf mortality of 5.4%. Appproximately three fourths of first-year calf deaths occur during the first fourteen days subsequent to birth. Annual adult mortality is estimated to be between one and five percent per annum. Due to their large size and resultant specialized and high feeding requirements, Gray whales are not deemed suitable for captivity.

Conservation status

caption Gray whale. Source: Alaska Fisheries Science Center/Encyclopedia of Life

In 1946, the International Whaling Commission (IWC) legally protected Gray whales from commercial whaling. The eastern Pacific stock has shown a remarkable recovery, increasing from the brink of extinction to around 21,000 individuals today; as a result, he eastern Pacific stock is classified as Lower Risk / Conservation Dependent (LR/CD) However, the western Pacific population which migrates along the east coast of Russia is Critically Endangered, and remains in very small numbers.

Whale watching, particularly in southern California and Mexico, has developed into a popular tourist attraction. This attraction allows people to appreciate these awesome creatures in their natural environment while providing additional value to their conservation.

Threats

The main threat to the gray whale has been hunting. Humans have exploited the species for its oil, hide, baleen and meat. Massive over-exploitation in the 19th and 20th Centuries drove at least one stock of Gray Whale to extinction, and critically endangered the rest of the species. While hunting is now banned, a small quota is permitted to indigenous hunters. Also, an unknown level of illegal hunting still occurs.

Shipping and industrial activities in the coastal migratory routes increase the risk of collisions with ships, entanglement in fishing nets, and pollution. Furthermore, habitat degradation resulting from drilling and dredging also threatens the species.

References

  • Eschrichtius robustus, Encyclopedia of Life (accessed August 27, 2009)
  • Myers, P. 1999. http://animaldiversity.ummz.umich.edu/site/accounts/information/Eschrichtiidae.html Eschrichtiidae] (On-line), Animal Diversity Web. Accessed August 28, 2009
  • Heyning, J. 1995. Whales, Dolphins, Porpoises: Masters of the Ocean Realm. Seattle, WA: University of Washington Press. ISBN: 0295974877.
  • Thomas A. Jefferson, Marc A. Webber, Robert Pitman and Brett Jarrett, 2007. Marine Mammals of the World Academic Press ISBN: 0123838533.
  • Evans, P.G. 1987. The Natural History of Whales & Dolphins. Facts on File Publications, New York. ISBN: 0816017328.
  • Grzimek, B. 1975. Grzimek's Animal Life Encyclopedia. Van Nostrand Reinhold Company, New York. ISBN: 0787653624.
  • Herman, L.M. 1980. Cetacean Behavior: Mechanisms and Functions. John Wiley & Sons, New York. ISBN: 0894642723.
  • Nowak, R. M.2003. Walker's Marine Mammals of the World. The Johns Hopkins University Press, Baltimore. ISBN: 0801873436.
  • NOAA. National marine mammal laboratory
  • Gray. 1864. Eschrichtius. Ann. Mag. Nat. Hist. 3 (14): 350.
  • A.Lang. 2011. Demographic distinctness of the Pacific Coast Feeding Group of Gray Whales (Eschrictius robustus). NOAA Fisheries Service, Protected Resource Division, Southwest Fisheries Science Center.
  • James G.Mead and Robert L.Brownell Jr. 2005. Order Cetacea (pp. 723-743). In Wilson, Don E., and Reeder, DeeAnn M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press, 2 vols. 2142 pp. ISBN 978-0-8018-8221-0
  • William F.Perrin, Bernd G.Würsig, J.G.M. Thewissen. 2009. Encyclopedia of marine mammals. Academic Press. ISBN 980123735539.
  • S.B.Reilly, J.L.Bannister, P.B.Best, M.Brown, R.L.Brownell Jr., D.S.Butterworth, P.J.Clapham, J.Cooke, G.P.Donovan, J.Urbán J & A.N.Zerbini. 2008. Eschrichtius robustus. IUCN Red List of Threatened Species.
  • D.W.Rice. 1998. Marine Mammals of the World. Systematics and Distribution. Special Publication Number 4. Lawrence, Kansas: The Society for Marine Mammalogy.
  • A.B.Van Deinse. 1937. Recent and older finds of the gray whale in the Atlantic. Temminckia 2: 161–188.
Glossary

Citation

(2011). Gray whale. Retrieved from http://www.eoearth.org/view/article/51cbede87896bb431f694a48

0 Comments

To add a comment, please Log In.