Unusual Mortality Event

Something is amiss in the NE Pacific. Half of the gray whales seen in the breeding lagoons of Mexico this winter were “skinny” (compared to the annual average of 10-12% of whales) and fewer calves have been seen as the whales migrate north again. The number of whales washing up dead along the coasts of Mexico, the US and Canada is also much higher than usual with over 170 counted so far this year. Many of the dead whales are thin and carrying high loads of parasites. As a result of this, the National Oceanic and Atmospheric Administration (NOAA) has declared gray whales in the NE Pacific to be undergoing an Unusual Mortality Event (UME) and a team of scientists has been tasked with investigating the matter.

Perhaps the whales couldn’t consume enough prey in their feeding grounds last summer and now lack the energy reserves to complete their migration? In truth, it’s probably not that simple. It’s not just about prey availability; factors such as disease or an accumulation of biotoxins can also affect whales’ feeding behaviour. Plus diseased or nutritionally stressed whales may be more likely to suffer fishery interactions or ship strikes. Picking apart the cause, or causes, of death is no easy task.

Eastern Pacific gray whales suffered another UME back in 1999-2000 when over 650 whales washed ashore, many of them emaciated. The proximate cause of death was only established for three whales and was different in each case. All three animals were emaciated, however. Whether the whales starved due to a lack of prey, or whether their illness prevented them from feeding, is not known.

For now the public has been urged to report any injured or dead whales to their local stranding network who will continue to collect and analyse samples from the stranded whales. These results will be passed to the investigative team working alongside NOAA’s working group for marine mammal UMEs and will hopefully shed light on what’s killing the gray whales of the NE Pacific.