Marine Megafauna: Ngā Kōrero Webinar Recap
The third webinar of the Ngā Kōrero series put a spotlight on ‘Marine Megafauna’ - the big creatures that live in the sea. Our guest speakers for this webinar were three New Zealand experts in marine megafauna who are particularly knowledgeable about humpback whales, southern right whales, and sharks (amongst lots more!)!
We’d like to say a huge thanks to our wonderful speakers; Dr. Rochelle Constantine and Dr. Emma Carroll from The University of Auckland - Waipapa Taumatau Rau and Clinton Duffy, Department of Conservation – Te Papa Atawhai.
Marine megafauna are highly mobile – they don’t recognise human boundaries, and that creates a huge challenge when it comes to safeguarding them. The work of these scientists revealed how many technological advancements, over time, have increased our understanding of the movement ecology of many wide-ranging marine animals. Their work highlights the importance of collaboration in finding answers to some big questions that can help to inform effective global and local conservation management actions. Below we’ve tried to summarize the main points of their presentations.
Humpback Whales: tracking their movements and measuring recovery
First, we heard from Dr. Rochelle Constantine, a distinguished marine ecologist and international whale and dolphin researcher. Constantine is a professor at the University of Auckland and she leads the Southern Ocean Research Partnership - International Whaling Commission ‘Humpback Whale Connectivity Programme’, amongst many other initiatives. Rochelle’s presentation gives incredible insight into the humpback whale research that she’s been involved in. It gives details of what they have learned about the recovery of whales since whaling days in the 1900’s; many whales were hunted, more than 2 million whales were killed, over 208,000 were humpback whales.
The recovery of some populations of whales is remarkable but not all humpback whale breeding stocks have been recovering at the same rates. Interestingly, their recovery has been quite inconsistent across various regions of the oceans. Rochelle reveals how in Eastern Australia the humpbacks seem to have fully recovered, but in Oceania, humpbacks are still at about 50% of pre-whaling numbers. To learn more about why this could be, the Southern Ocean Research Partnership - International Whaling Commission pulled resources together to go to the Southern Ocean. In 2010 the team deployed satellite tags and identified 112 individuals (through photographs and genetics) but didn’t find any of the Oceania whales down there.
Their next trip to learn about these humpbacks was to Raoul island, where they tagged 24 whales, took tissue samples, and photographed flukes. Over time they accumulated data from the satellite tags on those whales and discovered that some whale individuals had an estimated total migration (from breeding ground to feeding ground and return) over 18,200km!!! An interesting finding was how mothers and calves have different use of feeding grounds compared to whales without calves (the mums have a shorter migration path!) Rochelle goes even further to describe the interesting evidence of the difference between the population of ‘Southern’ and ‘Northern’ whales and remarks on how technology is taking us to inaccessible places; telemetry (from satellite tag data), genetics and photographs are revealing important information. This indicates what areas are most utilised by the whales and thus signalling to scientists where it’s important to implement protection. This valuable spatial data can be incorporated into the design of protected areas. Check out the ‘Humpback Whale Connectivity Project’ for more on humpback whales.
Tracking Tohorā: uncovering changes in whale culture over time
Next up was Dr. Emma Carroll, a Rutherford Discovery Fellow at the University of Auckland. Carroll is leader of Team Tohorā, an international group of researchers studying the recovery of southern right whales – tohorā – in the context of climate change. Historically, right whales were given their name since they were the ‘right’ whales to hunt; large and slow moving creatures, ideal targets for the early hunters who sought after them from around 1825. Over time hunters drastically reduced the numbers of tohorā; from a population of roughly 30,000 whales, contrasted with a more recent estimate of their population of around 2,000. The dramatic change in population size totally changed the distribution of tohorā in New Zealand waters – leaving scientists wondering ‘why?’.
Based on what scientists know about ‘social learning’, which is the learning of information or behaviours from others, it’s apparent that some behavioural traditions can be passed down through generations. All types of behavioural traditions from simple to complex behaviours, which we know as ‘culture’, are not limited to humans, primates, or mammals – they are widespread, found throughout the animal kingdom. There are many examples of ‘whale culture’ around the world – and it’s even more complex in other species like killer whales and sperm whales. It is what makes pods or ‘clans’ of the same species a bit different from each other. It appears that southern right whale mothers are incredibly dedicated to the survival of their calves- justifiably so, as they only have one baby every three years after reaching sexual maturity. In the first year of its life, the calf learns its mother’s favourite feeding grounds, and travels with her mum to these feeding and breeding grounds, learning these patterns for the future. Maternally directed learning of migratory destinations – migratory culture; is seen in other species too, humpbacks, sperm whales, and killer whales.
To give examples of the data revealing the significance of these learned behaviours, Carroll shares a bit about the research they’ve done at the Auckland Islands (Maungahuka). Over the winter months the team travelled to the remote archipelago to deploy more satellite tracking tags and to take skin biopsy samples. Through this work they found that over the span of one year, Wiremu (Bill), the southern right whale undertook the longest journey known of any tagged southern right whale - 15,000km round trip! The satellite tag of just this one whale gave amazing insight into how far tohorā can travel and showed that Bill visited several different foraging grounds before returning to the Auckland Islands. Tohorā can traverse the whole of the southern hemisphere – feeding from about 30 degrees south all the way to the ice edge. Data from 17 southern right whales, tagged over the span of 2 years, shows the similarities and differences of their tracks – you can see this for yourself at: www.tohoroavoyages.ac.nz
Tracking data has provided evidence of how the feeding behaviour of tohorā has changed; their current movement patterns are the opposite of the patterns from the times of historical whaling catches. Overall, there has been dramatic changes in movement patterns in these whales over time. Furthermore, there has been changes in maternal lineages, behavioural traditions, seen in the genetics research. Using a genetic marker that is maternally inherited from mother to calf, like the learned migratory behaviours, DNA taken via skin biopsy samples and from historical whale bones found throughout NZ) revealed maternal lineages
Dr. Carroll concludes with explaining that combining the various data types shows significant changes not just in tohorā abundance and distribution, but in their migratory traditions. It seems that the tohorā that used to inhabit areas near mainland NZ to calve inshore were wiped out. Therefore, the knowledge and behaviour of the tohorā which used to visit the eastern coastal region of NZ was lost in the whole population. This is an example of how we (humans) have played an important part in shaping how their population has changed. Closing with this thought, Carroll points out that if we want the whales to come back and start using the mainland waters we have to make sure we leave some space for them.
Large-scale movements of New Zealand Sharks
Our final guest speaker, Clinton Duffy, from the Department of Conservation, shared some of his knowledge about sharks. Clinton is an experienced scientific diver and DOC scientist, member of the IUCN Shark Specialist Group – Australia and Oceania, marine research associate at Auckland Museum, director of the Tindale Marine Research Charitable Trust, and lots more. He’s got an interest in understanding how shark populations are structured and learning about their critical habitats. The research he does provides data to inform risk assessments of the overlap of shark and ray habitats with commercial fishing grounds – an activity which has one of the largest impacts on shark and ray populations. The research he’s been involved with has benefited greatly from the advances in technology of a variety of electronic tags; acoustic tags, satellite tags, fin mounted tags and clamp on cameras.
Using a combination of information from different devices they can see that adult white sharks are extremely good navigators, often returning to the same places year after year traveling upwards of 3,000 km in 22-25 days. Mako sharks are highly migratory as juveniles and seem to be spending a lot of time in New Zealand waters. Making long forays into the Pacific, turning around and returning to NZ – going straight to places they know were good foraging grounds. Despite being highly migratory mako sharks are spending a lot of time within NZ’s exclusive economic zone (EEZ). Duffy, along with several others, have also been studying the occurrence of the oceanic manta ray in New Zealand and scientists are constantly learning new things about their movement patterns and how they utilize NZ waters. There is so much more to learn about these mysterious creatures that often evade our sight, mostly keeping below the surface.
All of our speakers want to encourage the public to participate in citizen science and report sightings via iNaturalist and the DOC website’s marine mammal sighting form. Be observant, get underwater, if and whenever you can - and share your sightings and photos! Thanks to all the supporters of Seaweek and in particular those which have made this webinar series possible: the New Zealand National Commission for UNESCO and the Live Ocean Foundation. Finally, if you missed our previous webinars in this series they are all online and this is the playlist.