GRAY WHALE: CHARACTERISTICS, MIGRATION, FEEDING, REPRODUCTION - BIOLOGY - 2025

The gray whale (Eschrichtius robustus) is a whale of the Eschrichtiidae family. She is the only representative of this family. The name of the genus is dedicated to the Danish zoologist Daniel Eschrich. It bears the specific epithet "robustus" due to the robustness of its body. Gray whales have the shortest and thickest baleen among the baleen whales.

Until recently, they were widely distributed in the Northern Hemisphere. However, only two populations remain in the Pacific Ocean as those in the North Atlantic became extinct due to the activities of whalers.

Gray whale (Eschrichtius robustus) By Merrill Gosho, NOAA

This whale is the one that grows closer to the continental coasts compared to other species. In addition, they are the ones that carry out the longest migration, between 15 and 20 thousand kilometers round trip, from the primary feeding areas to the winter breeding areas.

Migration lasts about two months, with pregnant females generally leaving first, followed by other adults, immature females and finally males.

Few natural enemies possess these whales. However, there are many attacks suffered by killer whales that are generally not lethal and are evidenced in bite marks or scratches on the skin of adults. Orcas generally target the calves, which are affected during the migration north after birth.

As for the feeding of the gray whale, they generally capture their prey (mainly krill) at depths that vary between 4 and 120 meters.

General characteristics

Gray Whale Blowhole By striped-belly

These whales of the group of the mysticetes (Mysticeti), also known as baleen whales in conjunction with other species, are distinguished by being quite robust and slow-moving animals.

In appearance, they are more slender than the right whales and more robust than the fin whales with which they are closely related. These whales reach a maximum length of approximately 15.3 meters.

Its color is greyish, which is why it is called the gray whale. In addition, it has irregular white spots on the body and in general, the skin is always plagued with barnacles and similar crustaceans.

These whales do not have a dorsal fin, instead, they have a hump that is continued by a series of fleshy bulges later. They have beards of a yellow or pale cream color.

The folds present in the throat contrast with those of other whales, since they are few (between 2 and 7), short and longitudinal. The head is triangular, not as telescopic as that of other whales, and is relatively short relative to the total length of the skeleton.

A characteristic feature of these whales is the presence of a cyst or gland on the ventral surface of the caudal peduncle, the function of which remains unknown.

Migration

Gray whales are observed in large groups in winter in the vicinity of lagoons or in coastal lakes of the west coast of Baja California and the Gulf of California on Mexican coasts.

Migration begins in autumn. During migration some young may be born as they head south, however the rest of the young are born around the shallow lagoons where they gather in Baja California.

In spring they migrate to areas with shallow and productive waters in the northeast of the Bering Sea and the southern seas of Chukchi and Beaufort and even further west in Russian locations.

This return migration occurs in a first stage where newly pregnant females travel first, followed by other adults and males.

In a second phase, the females that gave birth with their young return. This occurs because the small calves spend 1 to 2 months in their area of ​​birth together with their mothers, the purpose being to strengthen and grow before making the long journey north.

Other gray whales spend the summer along the Pacific coast of North America from California to Kodiak, Alaska, forming feeding groups.

Migration of the Asian population

On the other hand, the Asian gray whale population returns each year (including mothers with calves and pregnant females) to Sakhalin, a feeding site, and then migrate to the eastern Pacific during winter. Also some gray whales, which feed in the Okhotsk Sea, migrate to Japanese waters and possibly further south in the winter.

The migration routes of the Asian population remain poorly understood.

Taxonomy

The evolutionary history of this family of whales is practically unknown, with few representatives in the fossil record.

The family Eschrichtiidae, including the fossil record, groups only three genera, the oldest record being the genus Eschrichtius from the late Pliocene (1.8 to 3.5 million years ago).

According to recent studies, these whales are more related to fin whales (Balaenopteridae family) with which they form the monophyletic clade Balaenopteroidea.

Habitat and distribution

Gray whale skeleton By Emőke Dénes

The gray whale occupied much of the oceans of the northern hemisphere. However, it became extinct in the Atlantic Ocean, leaving relict populations in the neritic and productive waters to the north of the Pacific Ocean and adjacent waters of the Arctic Ocean.

The populations of the Atlantic and the Pacific were communicated during the interglacial periods being separated when the ice sheets formed in the Hudson Bay and the Beaufort Sea to the northeast of Canada.

Currently there are two large populations of gray whales, one called the California population, which is located between the eastern Arctic Ocean of the North Pacific and Amerasia. The second population is in the western North Pacific, also known as the Asian population located off the Asian continent.

These whales occupy neritic habitats, that is, areas close to the coast that do not come into contact with the transition between the continent and the marine ecosystem. They also occupy environments such as estuaries.

Conservation

Gray whales are generally above the population threshold to be considered in any IUCN threat category. However, this is only applicable to the population of California, which has been increasing in number over the last three generations.

The reproductive population of the North Atlantic is extinct.

The western population of gray whales in the Pacific Ocean, a genetically distinct or self-contained group relative to the Californian population, is in danger of extinction mainly due to over-capture by whalers. This population has around 250 reproductive individuals, which represents a critical population threshold.

Climate change and declining productivity of the seas where gray whales feed pose a great threat.

There have already been several events of decline in eastern Pacific populations attributed to high whale mortality due to resource deficiencies. In fact, whales with skinny rather than stocky bodies have been observed during migrations south.

Faced with a possible increase in food shortage conditions due to global climate change, the survival of these whales will depend on their adaptation to transitions.

Sensitivity to human activities

Gray whales tend to respond negatively to loud underwater noises and generally change their swimming direction to avoid them. On the other hand, the incidence of these noises during reproductive activities tends to alter them.

They have been documented to change course and swimming speed when followed by observation boats. They have also been affected by oil spills on their migration route.

Given these facts, it seems that the baleen of gray whales show resistance to damage from contact with oil, just like their skin. However, other chemicals can be absorbed by the crustaceans on which they feed and could adversely affect them when consumed.

On the other hand, a large number of whales are injured or mortally injured by collision with large vessels. A fact that could influence the long-term stability of reproductive populations.

Feeding

Gray whale with its calf By Carlos Valenzuela

These whales feed primarily by intermittent sucking. The number of food items are varied and complex. They generally take their food from the benthos, consuming organisms that live and develop on or near the seabed such as benthic amphipods.

They are capable of opportunistically ingesting plankton and nect from medium and surface waters and perhaps some plants, as well as other small organisms.

Capture strategies consist mainly of intermittent suction. However, they can make opportunistic gulps and rubs to capture non-benthic resources. The water is extracted mainly from its dams that contain on average between 60 and 80% water.

Feeding is concentrated over 5 months. From May to October in the Californian population and from June to November in the Asian population, when they are in waters with high productivity. Feeding activities occur throughout the day

Due to climatic changes, the productivity of the feeding grounds of these whales in the north of their range has decreased by up to 75%. The latter has caused the whales to spend more time in these areas or to roam alternative feeding areas. This video shows how a gray whale feeds:

Reproduction

Reproduction among gray whales occurs primarily during migration, usually mid-journey. However, reproductive events are also frequent in shallow winter gathering ponds.

Pregnant females use coastal lagoons on the west coast of the Baja California peninsula and the California coast as their calving area.

Most calves are born near or within the Ojo de Liebre Lagoon, San Ignacio Lagoon, or Magdalena Bay. Other coastal lagoons are no longer used in the breeding season.

Only mothers and young occupy these areas. The rest of the whales are distributed along nearby shores.

Breeding events can also occur during migration, but the general rule is that breeding occurs in the immediate vicinity of rearing ponds. The following video shows the mating of two gray whale specimens:

References

1. Cooke, JG 2018. Eschrichtius robustus. The IUCN Red List of Threatened Species 2018: e.T8097A50353881. http://dx.doi.org/10.2305/IUCN.UK.2018-2.RLTS.T8097A50353881.en. Downloaded on 28 October 2019.
2. Dunham, JS, & Duffus, DA (2002). Diet of gray whales (Eschrichtius robustus) in Clayoquot Sound, British Columbia, Canada. Marine mammal science, 18 (2), 419-437.
3. Fleischer, LA (2013). The gray whale: Mexican by birth. Fund of Economic Culture.
4. LeDuc, RG, Weller, DW, Hyde, J., Burdin, AM, Rosel, PE, Brownell Jr, RL, Würsig, B. & Dizon, AE (2002). Genetic differences between western and eastern gray whales (Eschrichtius robustus). Journal of Cetacean Research and Management, 4 (1), 1-5.
5. Moore, S., & Clarke, JT (2002). Potential impact of offshore human activities on gray whales (Eschrichtius robustus). Journal of cetacean research and management, 4 (1), 19-25.
6. Perrin, WF, Würsig, B., & Thewissen, JGM (Eds.). (2009). Encyclopedia of marine mammals. Academic Press.
7. Rugh, DJ, Hobbs, RC, Lerczak, JA, & Breiwick, JM (2005). Estimates of abundance of the eastern North Pacific stock of gray whales (Eschrichtius robustus) 1997-2002. Journal of Cetacean Research and Management, 7 (1), 1.