We all know those targeted and organised research projects, where scientists go into the field and collect specific data. But not everything in the scientific realm is as plannable as that. Some events, such as cetacean strandings, are unpredictable and may only happen a few times per year. Still, there can be valuable data to collect of you know what to look for!
Sperm whale strandings in New Zealand
Sperm whales (Physeter macrocephalus) are the largest species of odontocetes (toothed whales). They live in the waters around New Zealand and you can usually see them in the deep waters off Kaikoura, South Island. a
The 2018 mass stranding
In May 2018, 13 male sperm whales stranded in Taranaki, North Island. One month later, another male sperm whale stranded at Clifford Bay, South Island. With the permission of iwi (local tribes of Maōri, the indigenous people of New Zealand), we took some small skin samples in order to learn more about the individuals, as well as the species as whole. We also took these events as an incentive to analyse the existing records of sperm whale strandings in New Zealand.
When we collect skin samples from stranded animals, we can gain information about how individuals are connected to one another, like a family tree. There is a particular type of DNA called mitochondrial DNA (mtDNA) that is passed down from mother to calf. On this mtDNA, we can find specific groups of alleles (certain DNA sequences) called “haplotypes” which we can use as indicators of any connections or differences that sperm whales have to each other. We found 7 haplotypes from the 14 male sperm whales that we assessed. One of these was a brand new haplotype that had not been recorded anywhere else previously in the world. Another one had not been previously found in New Zealand sperm whales before.
Stable isotope results
Skin samples collected from strandings also allow us to find out information about sperm whale feeding habits! While it is very informative to look at the stomach contents of dead animals, with large whales this is not always feasible, plus stomachs of stranded animals are sometimes empty. Instead, we used stable isotope analysis of skin samples, which is based on the principle that different isotopes of elements differ in their molecular weights. We use two types: stable isotopes of carbon tells us about the feeding habitat, and stable isotopes of nitrogen tell us roughly how high up the food chain a whale has been feeding.
In our case, we found that the whale that stranded in Clifford Bay had very different isotopic values compared to the other whales that stranded a few weeks earlier. This confirmed our suspicion that this single whale did not belong to the group that stranded earlier. Instead, it was likely a solitary animal which is very common for adult male sperm whales. By comparing the fluke of the male who stranded at Clifford Bay to photos of males taken at Kaikoura, the stranded male was confirmed to be a regular visitor to Kaikoura. His name was Kaha and he was well known locally by tour operators and researchers.
When we analysed all available stranding records from New Zealand, we found that sperm whales stranded all around the New Zealand coast. However, females did not often strand below 42 degree latitude, which matches the global distribution of female sperm whales where they tend to stay in warmer waters with their calves. As stranding locations relate to where sperm whales are likely hanging out, this is really important information. We know that male sperm whales spend a lot of time feeding in the Kaikōura Canyon, but previously we didn’t know much at all about female sperm whales in New Zealand. We also found that mass strandings occurred mainly on the North Island and on Chatham Island, but single strandings occurred along the entire coastline of New Zealand. Single strandings also seemed to be more common in summer, which is a general peak time for strandings of whale and dolphins in New Zealand.
What’s next for New Zealand sperm whales?
There are still more data we have not yet analysed, for example we could extract DNA from cultural artefacts such as scrimshaw or pendants made of tooth and bone, to look at how genetic connectivity has changed over time. While our results have answered some questions regarding the spatial and demographic trends of New Zealand sperm whale stranding, we are still just scratching the surface of everything there is to know about these magnificent animals!
Palmer E, Alexander A, Liggins L, Guerra M, Bury SJ, Hendriks H, Stockin KA, Peters KJ (2022). A piece of the puzzle: analyses of recent strandings and historical records reveal new genetic and ecological insights on New Zealand sperm whales. Marine Ecology Progress Series 690: 201-217. https://doi.org/10.3354/meps14051
We (DOC) are legally responsible for implementing the Marine Mammals Protection Act 1978. This means that we are in charge at marine mammal stranding events. As the lead decision maker, our responsibilities include:
- protecting the welfare of stranded animals
- disposing of any dead marine mammals
- ensuring the health and safety of staff, volunteers, and the public
- enabling cultural protocols – this involves consulting with local iwi and hapū through every step of the stranding, including rescue, euthanasia, sampling and disposal
- enabling research, eg through the collection of scientific samples.
Find out more here