Gray whale migration along North America's West Coast has continued to drop in recent years, according to a new NOAA Fisheries report.
The population is currently down 38% from its high in 2015 and 2016, while experts investigate the causes.
Gray whale numbers continue to decline
According to an accompanying analysis, the population also produced the fewest calves on record this year since counts began in 1994, as per ScienceDaily.
The 38% drop from a peak of over 27,000 whales in 2016 to 16,650 this year is consistent with previous oscillations in the eastern North Pacific population.
Southwest Fisheries Science Center researchers believe it is important to keep an eye on it.
Population counts for gray whales in the eastern North Pacific are usually done every two years.
However, NOAA Fisheries will add a third year to this study, from late December to mid-February 2023, to count gray whales that transit along the Central California Coast.
"Given the continued reduction in numbers since 2016, we need to actively monitor the population to better understand what is causing the trend," said Dr. David Weller, Director of the Science Center's Marine Mammal and Turtle Division.
In 2019, NOAA Fisheries declared an Unusual Mortality Event for the gray whale population, triggering an inquiry into the possible reasons.
Several potential contributors have been discovered as part of the ongoing inquiry.
According to recent studies released earlier this year, these include biological changes in the Arctic that impact the seafloor and the amphipods and other invertebrates dwelling in and above the sand and water column that gray whales graze on each summer.
According to Dr. Sue Ellen Moore, a University of Washington researcher who leads the UME team studying ecological factors, some gray whales may have struggled to locate food during those transitions.
She highlighted that gray whales consume a diverse spectrum of animals, so there might be numerous variables influencing how, when, and where they locate food.
While many of the 600 deceased whales identified between 2019 and 2022 seemed emaciated, others did not.
Some of the stranded whales had evidently perished from other causes, such as ship strikes or predation by killer whales. The number of strandings increased in 2019 but subsequently decreased in succeeding years.
This implied that the majority of the gray whale population loss happened in the years following the declaration of the UME.
There is no one factor that may explain all of the strandings, according to Deborah Fauquier, Veterinary Medical Officer in NOAA Fisheries' Marine Mammal Health and Stranding Response Program, who is in charge of the UME study, "It looks like there are several aspects that we are currently trying to grasp."
Gray whales are well-known for their annual journey along the West Coast.
The population has varied significantly in the past, including a comparable decline of nearly 40% from the late 1980s to the early 1990s.
Later, the population recovered to a new peak. Gray whales in the eastern Pacific Ocean have recovered completely from commercial whaling and were removed from the endangered species list in 1994.
A similar increase in strandings resulted in the designation of an earlier Unusual Mortality Event in 1999 and 2000 when the population dropped by around 25%.
It later returned to a high in 2015 to 2016.
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Calf numbers are also decreasing
NOAA Fisheries researchers count southbound whales headed towards Mexico to determine the population size of gray whales, as per News Wise.
They track calf production by counting moms and calves as they migrate north each spring from Baja California lagoons where some whales give birth.
The most recent census, which ended in May, estimated total calf output this year to be around 217.
This was a decrease from 383 calves the previous year and the lowest number since the census began in 1994.
The number of calves born each year has varied, as has the gray whale population as a whole. Before recovering, low calf numbers were observed for periods of three to four years.
Two of the previous three episodes of low calf production corresponded with Unusual Mortality Events and population decreases.
The investigation on calf numbers finds that the same variables that impact gray whale survival likely also affect their reproductive.
Aerial images of gray whales in Mexican lagoons revealed reductions in the bodily condition of several adult whales, highlighting that link.
"Depending on the age of the whales, this lower body condition may have resulted in delayed reproduction and lower calf numbers, as well as poorer survival in skinny whales," researchers said.
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