An ecological problem is possibly brewing along the west coast of Mexico, The U.S., and Canada. An unusual event first started in January 2019, resulting in 378 confirmed gray whale deaths from the eastern North Pacific population with much more unrecorded ones and many more of them found in very poor condition.
Now, as emaciated gray whales are being reported as they start their migration route, and scientists are fearing that the unusual mortality event (UME), a big number of marine mammal populations dying during an unforeseen phenomenon, will continue developing this year.
A new study from Aarhus University has found evidence that starvation is contributing to the unusual mortality event, the press release reports.
The study is published in the journal Marine Ecology Progress Series.
Body mass of gray whales documented
The gray whales (Eschrichtius robustus) take on an annual southward journey from their feeding grounds in the Bering, Chukchi, and Arctic seas each January to reach their breeding ground off the coast of Southern California and Mexico.
The first research on these magnificent animals was conducted from 1977 to 1982 in Laguna San Ignacio (LSI) in Baja California Sur, Mexico. Laguna San Ignacio Ecosystem Science Program (LSIESP) was initiated in 2006, where rigorous research on the body condition of gray whales with the use of drone photogrammetry, which involves the measuring of the body length and width of the animals from vertical photographs taken by drones, started in 2017. This enabled researchers to measure the relative body condition of individual whales.
In just two years, the researchers documented the decline in the body condition of juvenile and adult gray whales visiting the Mexico shores. In 2019, which the current UME started, the decline was also seen, coinciding with a drop in the number of mother-half pairs sighed. This indicates a decrease in the reproductive rate of female gray whales, per the press release.
While the decline has been highly documented, the reason why it is happening has not yet been determined. The reason for the current UME could be a decline in amphipods, which are the main preys for gray whales, in their main feeding grounds.
As amphipods decline in abundance and biomass as a result of the warming Arctic waters due to climate change, such UMEs might damage gray whale populations in the upcoming years.