Sunday, January 29, 2023

Why did the sperm whale die? That's not yet clear, but myriad possibilities

 It will likely be weeks or longer before we know why a big sperm whale washed ashore on Kauai, or we may never know.

Some folks have already been suggesting theories, but without doing the science, it’s guesswork.

There are many known causes of sperm whale strandings—many natural and some involving human activities.

Veterinarians and other wildlife experts are doing the hard work to conduct a necropsy on the more than 50-foot sperm whale that washed up at Lydgate Beach Park in Wailua, Kaua’i, on the morning of January 28.

But let’s look at some of the possibilities.

Whales do get old and die. They get viruses and other diseases. They can be affected by parasites. There is some evidence that climate change can impact navigation and food availability. They can be injured by natural (think big sharks) or human (think container ship impacts) causes. Noise can disorient them, and that noise can be from natural causes like undersea earthquakes, or human causes like deep sea mining exploration, sonar and noisy big ships.

The options really are too numerous for guesses to be taken seriously. Some recent strandings have had various causes.

One sperm whale that beached in the Florida Keys last year was very thin. On investigation, it had ingested marine debris, which had interfered with its ability to feed.

A 30-foot sperm whale that washed up this month in Oregon had injuries consistent with being hit by a ship.

This 2018 study suggests that some North Sea strandings may simply have been because the healthy but young sperm whales inadvertently swam into shallow water and couldn’t get back into the deep. 

Sperm whales, like many others, can become engangled in marine debris like ropes and buoys, and can be weakened by having to drag all that weight. Entanglement in fishing gear like buoys can make it difficult for whales to submerge for feeding.

This 2005 study and this 2009 study suggested that sunspot activity and even changes in the Earth’s magnetic field could impact sperm whale stranding. 

As we reported recently at Raising Islands, roughly half of recent stranded whales of various were associated with a newly described virus. 

In some cases, there are multiple things going on, such as skin disease, liver disease, parasites, viral infections, bacterial infections, fungal infections, high concentrations in blubber of man-made chemicals like pesticides and PCBs, and having ingested plastic while feeding. In many cases, it is not possible to determine which, if any, of these was the cause of the stranding.

And then there is the whole issue of climate change, which can impact marine life in numerous ways, including forcing animals into unfamiliar feeding territories, impacting feeding for juvenile animals, and much more. This Australian study from 2013 suggested: “Reductions in the extent of key habitats, changes in breeding success, a greater incidence of strandings in dugongs and cetaceans, and increased exposure of coastal species to pollutants and pathogens are likely.” 

In one month last year, 17 whales of several different species stranded off Norway. The cause is not known, and as the authors of this paper wrote, “Whale strandings are common globally, although to date there are still many challenges in identifying their cause.” 

© Jan TenBruggencate 2023

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