There was a great turn out at Te Papa last night to listen to Dr Ingrid Visser discuss her research on NZ Orca. This event was hosted by the Wellington City Council as part of our Year of the Coast. Ingrid has been studying Orca in NZ and around the world for 20 years.
There are ~200 Orca in New Zealand waters but from later discussion we don’t really know if this is a stable population or if this population size is appropriate for our waters. We do know that Orca are apex predators (at the top of the food chain – like lions in Africa) so we would expect smaller numbers when compared to their prey populations.
Ingrid and her fellow researchers can use photos to ID their subjects as each Orca has individual features – just like us. The shape of their dorsal fin (in adult males this can reach 2m long), the colour and shape of the grey saddle behind this fin amd the white patches near the eyes can all help identify individual Orca. So if you see Orca please try to get these photos so that they can determine which Orca are visiting which areas at what time of the year. In general Orca move south during the summer months when we are most likely to see them here in Wellington Harbour or along the South Coast then head back north over winter.
As apex predators Orca also accumulate toxins as they move up the food chain and unfortunately Ingrid’s research as shown that NZ Orca have more toxins in their bodies than other populations in the Southern Hemisphere so our clean green image needs some work as we monitor what poisons enter our waterways.
Under the Department of Conservation’s classifications NZ Orca are classed as ‘Nationally Critical” which is the highest ranking possible. Around the world only 1 other population of Orca, in the Americas, has this classification – mainly due to lack of research and understanding of Orca populations. As apex predators Orca can act as an ‘umbrella species’ which means that if we protect Orca and their habitats we also work to protect the species below them in the food chain.
So what do our Orca eat?
Elasmobranchs!! (Sharks & rays) Our Orca have developed strategies for hunting these species. As divers we have all seen rays lying on or under the sand with their tails out for protection. Unfortunately for rays their barb is close to the base of the tail and Orca can pick up a ray by the tip of the tail then swim over to another Orca who then bites the ray to disable it and then they food share. Talk about team work and cooperation!
One Orca has learnt to hunt sharks by swimming past them, turning away and slapping the shark with his tail to disable it – presumably to avoid damage to the Orcas face as it hunts sharks which are also apex predators and have sharp pointy teeth!! Orca have been recorded eating Thresher Sharks, Mako, Blue Sharks and Great Whites. They have also been observed eating dolphins!
Different Orca populations around the world have different strategies and prey that they learn from other Orca. In Argentina they rush up on the beach to eat sea lions, in Norway they form balls of herrings by releasing bubbles or flashing their bellies they then slap the water stunning or killing the fish.
Orca are very social animals and in NZ are often found in groups of 6-12 individuals though these groups are fluid over an individual’s life time (on average 70-80 years). Orca communicate with each other and scientists can detect regional dialects between populations and Ingrid played recordings of Antarctic Orca with a lot of high pitched squeaking (think Orca on helium!) then kiwi Orca with a very different accent and a lot more clicking. Ingrid has observed one female Orca with very evident propeller damage. She is a 1/3rd smaller than other Orca her age and her group travel a 1/3rd slower so she can keep up. She is unable to hunt so her group leave her with a babysitting, go hunting and then bring back food for the 2 of them. There is nothing quite like family.
Another unique feature of our Orca is the number of recorded strandings, 1 a year, compared to Australia which has 1 every 14 years. Fortunately Orca seem to cope well with these events with some assistance of course. If you would like to know more about helping during marine mammal strandings then visit www.projectjonah.com and if you are interested in the Marine Mammal Medic Course let us know and we can organise one here in Wellington.
It was a very entertaining & educational talk on our local Orca – if you would like to learn more about these amazing creatures, how you can get involved or how you can help Ingrid and her team continue their great work please visit www.orcaresearch.org