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Whale Blog 10: Project updates and more on the Minke

Posted on 29-11-2017 by Becky Desjardins

The vertebrate department has undertaken the task of cleaning our dirty cetacean skeletons over the next few years before they are moved to their space in our new collections storage building. In this blog we will be documenting some of the techniques we use as well as some of the cool things we find while doing this project. It is sure to be a whale of a job!

I returned from my North Carolina adventures earlier in November, but a few things kept me from really diving back into the whale bone cleaning project until this week. One of the things I had to work on was a bit of paperwork, namely: how many specimens have we cleaned so far, and how many do we still have to go?

In that regard there is good news and bad news. The good news is, that we already have done 60 whales!  Yay! Woo! The bad news is… there are still more than 200 to go. Awhh.  Up to this point mostly we have cleaned the mounted skeletons, which tend to be smaller species.  The really large whales are mostly loose bones stored in crates.  But, I feel optimistic. Many of the mounted skeletons that we have prepared have needed restoration of wires and other structural issues. This always takes a lot of time. So, we shall see if having to vacuum lots of large bones is equal in time to rewiring broken ribs. 

Photo 1: The next stage of the whale project: loose bones stored in cranes.

Photo 2: Does wiring takes more time than cleaning with a vacuum?

There are few other things going on in whale land these days, one of which is that we had a recently deceased minke whale to process (Read about it here and here). It was the second pregnant female in 2 years that we have worked on, which was killed by a collision from a ship. It made us wonder  how big a problem this is for minkes, and if shipping lanes should be altered or speed limits controlled during migration to avoid strikes. This what was done on the east coast of the USA to prevent harming northern right whales.  After spending a few hours researching this topic, I think that this is not a big problem. We just don’t know enough about minke whale migration or where our whales are coming from to say for sure where they are getting hit.  But, I did learn a few things about great whales in the North Sea.

While most whales that wash up on the coast of the Netherlands are male,  most minkes are female. Looking at the ratio of male to female minkes on walvisstrandingen.nl, there had been 12 females and only 6 males stranded (though more than half were not determined to be either male or female. In total 40 strandings where recorded from 1862 to 2017).  Compare this to fin whales, which are the other common great whale species to show up the Netherlands. In fin whale stranding records, there were 12 males and only 7 females (again, with more than half fin whales of undetermined gender). 

 

Living minkes are found swimming in the North sea usually once or twice a year, though according to Waarnemingen.nl these sightings are usually in the spring and summer. Although it is a very low sample size, we can assume that minkes are not running into trouble in the North Sea itself. More likely, the problem is that minkes are hit somewhere north or west of Scotland and drifting into the North Sea (the currents that come in from the north are the strongest).  In the North Atlantic, the minke population is divided into 5 breeding groups found in Newfoundland, Greenland, Iceland, off the coast of Norway, and Spitsbergen/Barents Sea. From mid-October to Early November they leave these summer grounds and start to head to the winter grounds, which include the Canary Islands, Caribbean Islands, off the SE US coast, and in the middle of the Atlantic ocean between the Canaries and Caribbean.  Minkes tend to migrate solo or in very small  groups (2-3 animals), and it is unknown if they follow the same migratory route or wander a bit. Regarding ship strikes during migration, walvisstrandingen.nl and the museum database indicate fall migration is dangerous: November has the most fatalities of minke whales with 8 deads.  Most other months had only 3 or 4. February was the only month without strikes.

Photo: A minke whale in the Arctic ocean

It is interesting that so many more female than male minkes are hit by ships and end up in the North sea. Perhaps this implies that females have a different and more dangerous migration route.  But, the sample size is too small and there are too many unknowns to make any conclusions. There is also the issue that not all whales are killed by ship strikes, some get stuck in fishing nets or otherwise get in trouble. Happily, for now, world populations of minke whales appear to be stable. However, if we start adding multiple female minke whales every year from the Dutch coast to the Naturalis collection, we will easily be able to see that there is a problem in the population.

References

Risch D, et al. (2014), Seasonal migrations of North Atlantic minke whales: novel insights from large-scale passive acoustic monitoring networks. Movement Ecology 2014 2:24 https://doi.org/10.1186/s40462-014-0024-3

Hill, A. N., Karniski, C., Robbins, J., Pitchford, T., Todd, S. and Asmutis-Silvia, R. (2017), Vessel collision injuries on live humpback whales, Megaptera novaeangliae, in the southern Gulf of Maine. Marine Mammal Science, 33: 558–573. doi: 10.1111/mms.12386