Gray whale populations continue to decline

According to a new assessment by the National Oceanic and Atmospheric Administration (NOAA), gray whales which migrate along the West Coast of North America continued to decline over the past two years, the population being now down 38 percent from its peak in 2015 and 2016. Moreover, as an accompanying report explained, the whales also produced the fewest calves this year since counts began in 1994.

Although this decline from a peak of about 27,000 whales in 2016 to 16,650 this year resembles past fluctuations in the eastern North Pacific population, it warrants continued monitoring. “Given the continuing decline in numbers since 2016, we need to be closely monitoring the population to help understand what may be driving the trend,” said David Weller, the senior author of the reports and director of the Marine Mammal and Turtle Division at NOAA. “We have observed the population changing over time, and we want to stay on top of that.”

A significant increase in gray whale strandings led NOAA Fisheries to declare an “Unusual Mortality Event” (UME) in 2019, prompting an investigation into the possible causes of this population decline. According to the scientists, some of the contributors include changes in the Arctic seafloor and the amphipods and other invertebrate species that gray whales feed upon in the summer, predation by killer whales, or accidents involving ships. Since the number of strandings spiked in 2019 and subsequently fell, most of the gray whale population decline probably occurred in the years before the UME was declared.

“There is no one thing that we can point to that explains all of the strandings,” said Deborah Fauquier, a Veterinary Medical Officer at NOAA Fisheries’ Marine Mammal Health and Stranding Response Program, who coordinates the UME investigation. “There appears to be multiple factors that we are still working to understand.” 

Since many gray whales migrate between their feeding grounds in the Arctic during summer and lagoons in Baja Mexico in the winter where they nourish their newborn calves – a 10,000 miles-long roundtrip – they most likely encounter many stressors along the way, a factor which led to population declines in previous decades too. These stressors affecting whale survival also had a major impact of their reproductive capacities, leading to lower calf production.

Fortunately, after most of the previous declines, the number of gray whales increased again. “The population has rebounded multiple times from low counts in the past,” said Tomoharu Eguchi, the lead author of the reports and an expert in Cetacean Health at NOAA. “We are cautiously optimistic that the same will happen this time. Continued monitoring will determine whether and when they rebound.” 

 “What we hope to see in the next few years is that the abundance stabilizes and then starts to show signs of increase. We will be watching closely,” concluded co-author Aimee Lang, a research scientist at NOAA.

Image Credit: NOAA Fisheries

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By Andrei Ionescu, Earth.com Staff Writer