Large numbers of gray whales start starving and dying in the Pacific

As early as January, the first gray whales from the Pacific Ocean population began arriving at the nesting lagoons in Nizhnyaya

California, Mexico.Since the start of their southward migration from their high-latitude feeding grounds (where the whale eats off after wintering), several cases of emaciated gray whales have been observed along their migration route.

This has caused concern among scientists aboutthe fact that an unusual mortality event (UME is an unexpected event during which a significant number of marine mammals die), which began in January 2019 and led to 378 confirmed deaths of gray whales, and possibly many more unrecorded, has lasted for the third year ...

Gray whales make annual migrations betweenfeeding grounds in the Bering, Chukchi and Arctic Seas; and breeding grounds from the Gulf of Southern California to lagoons along the Pacific coast of Baja California, Mexico.

During the summer feeding season, from May toOctober, whales accumulate large reserves of energy, mainly in the form of fat, to support energy costs during migration and while living in breeding grounds. Adequate energy reserves are critical for the reproduction and survival of gray whales that do not feed during the migration and breeding season.

In 2017 LSIESP (Special Relief Projectand Whale Research) began to study the body condition of gray whales using drone photogrammetry. This method involves measuring the length and width of animals from vertical photographs taken by drones, from which an estimate of the relative health (or fatness) of individual specimens can be obtained.

Already in the second year of sampling, researchersfound a marked deterioration in the physical condition of juvenile and adult gray whales visiting the San Ignacio Lagoon. The decline was also noticeable in 2019, at the start of the current UME. The deterioration in body condition also coincided with a decrease in the number of mother-calf pairs found in the San Ignacio Lagoon, indicating a decline in the fertility of female gray whales.

A similar UME was in 1999-2000.when 651 gray whales were found dead along the west coast of North America. During this two-year event, the gray whale population declined by about 25% from about 21,000 in 1998 to about 16,000 in 2002. It is not yet known what impact the current UME is having on the population of the eastern North Pacific.

Although research suggests that the declineThe survival and reproductive rates of gray whales during the current UME were caused by starvation, the main factors that caused this decline in body condition have not yet been determined. The fact that gray whales in 2018 and 2019 arrived at their breeding sites in Mexico already in significantly worse body condition indicates that this decline must have occurred either during the previous feeding season or during a southward migration.

“It seems that a large number of gray whalesleave their feeding grounds already in poor condition, and by the time they complete their breeding season in Mexico, they are depleting their energy reserves and starving to death. "

Dr. Fredrik Christiansen

Thus, the most likely explanationthe current UME is the decline in the availability of prey in the main feeding grounds. Since the late 1980s, there has been a decline in the abundance and biomass of amphipods, the main prey for gray whales, in the central part of the Chirikov Basin, the main feeding area for gray whales in the Bering Sea. This, in turn, is believed to be caused by warming of Arctic waters as a result of natural and / or anthropogenic climate change. If so, such UMEs could become more frequent, which could lead to a decline in gray whales in the coming decades or their complete extinction.

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