US researchers say the number of gray whales off western North America has continued to dwindle during the last two years, a decline that resembles previous population swings over the past several decades but is still generating worry.
According to a National Oceanic and Atmospheric Administration Fisheries assessment released Friday, the most recent count put the population at 16,650 whales – down 38% from its peak during the 2015-16 period. The whales also produced the fewest calves since scientists began counting the births in 1994.
An increase in the number of whales washing up on west coast beaches prompted the fisheries agency to declare an “unusual mortality event”, or UME, in 2019. Researchers are still investigating the die-off, but they say factors likely include climate change, its effects on sea ice and the location as well as availability of prey.
Many – but not all – of the whales that washed up appeared malnourished, the assessment said.
According to the Noaa, some of the stranded whales died from other causes such as being hit by ships or getting hunted by killer whales. The amount of stranded whales peaked in 2019, only to then decrease in the following years, suggesting that most of the population decline likely happened in the years shortly after the declaration of the UME.
“There is no one thing that we can point to that explains all of the strandings,” said Deborah Fauquier, a veterinary medical officer in Noaa Fisheries’ Marine Mammal Health and Str