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Whale Blog 12: Why Do Whales Strand?

Posted on 07-02-2018 by Becky Desjardins

Becky Desjardins about the progress of the whale project and the why behind whale strandings.

I am happy to report that all of the mounted skeletons have been cleaned, and now we are beginning work on the large whales, most of which are not mounted but instead the bones are stored in enormous wooden boxes. This is a sign of progress on this big project! Currently we are working on a whale that washed up in 2012, a humpback nicknamed Johanna by the press. What made this stranding different was that unlike most of the long dead whales that float to our shores, she was still alive when she washed up.  She died a few days later after multiple attempts to try and get her off the beach.

Photogallery: crates full of whale skeletons, and the bones of whale Johanne. Becky Desjardins

Why do whales strand, anyway? What would cause a seemingly healthy animal to get washed onto the beach? There are many, many different theories including disease, interference from underwater sonar related to military activities, pollution in the water which can sicken a whale, undersea noise, weather, and a change in magnetic activity of the earth.  Also, within pods of some species (including sperm and pilot whales) the bonds are so tight the cries of one distressed animal might lead the rest of the pod to strand. This could be the reason for some of the mass strandings of pilot whales in the southern hemisphere, such as the 600 that died in new Zealand in early 2016.  Ship strikes and entanglement in fishing lines can cause injuries which lead to a whale not swimming well and getting into trouble in shallow water. But sometimes scientists just don’t know. Which makes whales such as 2012’s humpback or the recent sperm whale in Domburg that had no obvious injuries more intriguing.

The 2012 humpback had plastics in her stomach, but they were so small researchers don’t think that they would have affected her overall health.  Her muscles were damaged, but it was hard to say if that was from laying on the beach or if it happened before.  Whales are buoyant in the water but once they are on the beach gravity takes over and the organs can collapse under the weight of the animal. They also suffer from sunburns and dehydration.  Her exact cause of death remains unknown.

The Domburg potvis was covered with long, deep scratches, and it is theorized that they were from washing against an oyster or musselbank, though it is unknown if this injury  was pre or post mortem. The animal also had an infection in his intestine. Perhaps he was so ill that he could not navigate properly anymore.  Perhaps it was a combination of getting ill and being lost that caused him to beach. At this point, it is still a mystery as to why he stranded.

Photo: the sperm whale that stranded December 2018, attracked a lot of attention.

One of the most interesting cases were the six sperm whales that stranded on Texel in 2016. These belonged to a larger pod of which twenty-nine in total washed up dead across the coasts bordering the North Sea. Sperm whales do not normally occur in the North Sea and it is suspected that this pod got lost as they were migrating from Norway to their wintering grounds near the Azores. Whales migrate using the geomagnetic field of the earth, and a recent German paper suggests that severe solar storms affected the earth's geomagnetism a few weeks prior to the strandings. This interruption may have caused the whales to get lost and enter the North Sea instead of into the Atlantic Ocean. The shallow shifting sands of the North Sea caused further hindered navigation and eventually these animals became trapped.

These were all young males, and externally they appeared healthy. Gut analysis revealed that some of them had large amounts of plastic in the stomach: mostly fishing lines and nets with some trash. However, only nine out of twenty two sampled had these plastics, so it is hard to theorize if that caused them to strand.  Perhaps the unhealthy animals led the healthy whales accidentally to strand.  The actual cause of death remains again unknown.

Photogallery: in 2016 a group of six sperm whales stranded on the beach of Texel.

Though there are still many questions about strandings, there is a lot of research being done as well. Recently, there was a long term study published about sperm whale strandings in Australia, the first of its kind, which illuminated some trends in whale death.  Stranding research in the US led to laws enacted that limit ship speed limits with the aim of reducing whale strikes.  And here in the Netherlands the University of Utrecht has a dedicated mammal stranding team, part of their work is  to puzzle out the causes of strandings. Hopefully all of this work will result in solutions that will prevent whale strandings going forward.

 

Literature

MacDonald, J. (2017 April 23) Why do Whales Strand Themselves. Retreived from https://daily.jstor.org/why-do-whales-strand-themselves/

Unger, B., Rebolledo, E. L. B., Deaville, R., Gröne, A., IJsseldijk, L. L., Leopold, M. F., Siebert, U., Spitz, J., Wohlsein, P. & Herr (2016)  Large amounts of marine debris found in sperm whales stranded along the North Sea coast in early 2016  Marine Pollution Bulletin, Volume 112, Issues 1–2, 15 November 2016, Pages 134–141. DOI:10.1016/j.marpolbul.2016.08.027

Vanselow, K., Jacobsen, S., Hall, C., & Garthe, S. (2017). Solar storms may trigger sperm whale strandings: Explanation approaches for multiple strandings in the North Sea in 2016.International Journal of Astrobiology, 1-9.