Whale composting: Letting bacteria do the hard work of specimen defleshing

Bones and skeletons are key parts of a natural history collection, used by researchers from archaeologists to zoologists. Usually, preparing these osteological specimens starts with removing the flesh. No big deal for small animals.

But, a couple of years ago, Canadian Museum of Nature collections staff faced a whale-sized specimen preparation challenge.

We wanted to deflesh hundreds of kilograms of preserved whale specimens. They had been collected during commercial whaling off the coast of Newfoundland from the late 1960s until 1972, when commercial whaling in Canada was ended.

These specimens weren’t just big (up to 25 kilograms) they had also been changed by the preservation process.

Before being transferred into ethanol in the late 1990s, the whale parts had been stored in formalin which hardens animal tissues. This meant they’d require additional preparation, such as ammonia soaks or peroxide treatments, to break down the tissues so that they could be physically removed.

We calculated that manually removing the skin, blubber and muscle to preserve the bones would take years.

Our short-cut alternative? Compost the whale pieces and let bacteria and fungi do the hard work of defleshing.

Whale specimens in the museum’s special compost bin prior to being covered with sawdust and manure. Image: Shalini Chaudhary © Canadian Museum of Nature.

So, in the summer of 2017 we created a compost station on the grounds of the museum’s research and collections facility in Gatineau.

Efficiently composting large whale pieces requires creating a compost pile with the right mix of carbon (sawdust) and nitrogen (manure) to achieve the ideal temperature for microorganisms, and then giving it time.

During the summer, we did five 18-day composting cycles. During each cycle, we adjusted the sawdust to manure ratio to try and achieve the ideal temperature, which varied between 27°C and 43°C. Sometimes we added water to optimize the humidity levels for the microorganisms. After the last cycle, we removed the largely defleshed whale pieces from the compost pile and moved them into the collections lab.

The compost-based defleshing process did not go as quickly, or work as completely, as we’d anticipated. This was in part because we’d struggled at times to reach optimal composting temperatures. So, to get rid of the remaining flesh we simmered the bones in almost-boiling water, a technique called hot macerating. Then, residual oil was removed by soaking in ammonia. Finally, a peroxide soak bleached the bones which had darkened in the composting process.

A chart of ambient air temperature vs. the internal compost temperatures over three months during whale specimen composting. The most efficient composting occurred when there was the largest gap between the two temperatures. Image: Marie-Hélène Hubert © Canadian Museum of Nature

This combination of multiple preparation techniques worked well and saved the museum time, money and effort. Osteological, or bone, specimens are important components of natural history collections. They are used by many researchers, from archaeologists and palaeontologists to comparative anatomists and zoologists. So, there will always be work preparing these specimens.

Our whale composting experiment has led us to think that we might well be heading back to the compost heap for the preparation of future zoological specimens.

Fin whale (Balaenoptera physalus) skull bones before (left) and after (right) composting. The initial weight was 25 kg; after composting and cleaning, 18.7 kg. Image: Marie-Hélène Hubert © Canadian Museum of Nature.