Why are so many whales getting stranded on US beaches?

In the past three months, nearly two dozen large whales have washed ashore on beaches on the east coast of the US. The surge in strandings has experts worried about the already vulnerable species, and has spurred speculation over the potential causes behind the deaths.

Are these whale strandings unusual?

Since 1 December 2022, there have been 22 large whale strandings along the US Atlantic coast, according to the US National Oceanic and Atmospheric Administration (NOAA). These include 15 humpback whales, three sperm whales, two North Atlantic right whales, one sei whale and one minke whale. Whale deaths in the first two months of 2023 are already rivalling last year’s totals. “It’s an alarming surge,” says Sheila Dean at the Marine Mammal Stranding Center in New Jersey.

This latest wave of whale deaths is part of a larger trend beginning in 2016. NOAA has been investigating the seven-year-long unusual mortality event, but notes that this number of deaths so early in the calendar year is abnormal.

Which whale species are at risk?

Of the five species washed up in recent months, three are considered vulnerable or endangered: North Atlantic right whales, sperm whales and sei whales. Humpback whales (Megaptera novaeangliae) and North Atlantic right whales (Eubalaena glacialis) are the species most commonly stranded on the US Atlantic coast, though humpbacks typically account for the bulk of strandings, which may be because they are the most abundant whale in the area.

The situation is dire for North Atlantic right whales, which have fewer than 350 individuals remaining. The death of two right whales within weeks of each other was an especially concerning blow to the species. More than 20 per cent of the population has been affected by the unusual mortality event since 2016, according to NOAA.

What is killing the whales?

There is no one cause responsible for every whale stranding, though most beached whales are sick or injured. In some cases, there are clear clues: multiple whales beached in New Jersey had deep gashes probably caused by a boat propeller. In other cases, marine biologists must perform necropsies – a careful dissection similar to a human autopsy – on the whales to try to find a cause of death. Some necropsies this year have pointed to trauma from collisions with ships, while other animals were too decomposed by the time they reached the shore to be dissected.

Of the 178 humpback whale deaths that NOAA has investigated as part of the unusual mortality event, around half underwent necropsies. “Of the whales examined, about 40 per cent had evidence of human interaction, either ship strike or entanglement,” said Lauren Gaches at NOAA in a press conference on 18 January.

Unusual winds, tidal patterns and ocean currents can increase the chances that whales will become stranded on a beach, and such changes could be exacerbated by climate change.

Some blame the unusually high mortality events on the noise created by surveying equipment for offshore wind turbine installations, though NOAA says there is no evidence to support the claims that such noise impedes whales’ ability to navigate and communicate. “There are no known connections between any of this offshore wind activity and any whale stranding regardless of species,” said Benjamin Laws at NOAA in the 18 January press briefing. Protesters have recently called on New Jersey government leaders to halt the expansion of offshore wind until more research can be done into potential links between underwater noise and whale deaths.

Are there any other explanations?

The food source for humpback whales is increasing. In New Jersey, a small, silvery fish called Atlantic menhaden (Brevoortia tyrannus) has been on the rise in recent years as commercial fishing waned. But that means humpbacks have been hanging around their feeding grounds for longer than usual as a result, which puts them in the path of a major shipping route. “Their food stayed here, and so did they,” says Dean. Changing when, where and how quickly ships travel could be part of the solution.

Another explanation for the surge in beached whales could be that some species are recovering from the edge of extinction, leading to a greater overall number of stranding events. Whaling bans and fishing regulations have allowed humpback whales to balloon from around 400 individuals in the 1980s to more than 80,000 today – a dramatic recovery, but still shy of their numbers before whaling.

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