The dolphins of Te Tai o Aorere / Tasman Bay.

Any trip out on the water is enriched by an encounter with marine mammals.  One of our most commonly asked questions is ‘will we see dolphins today?’.  Well the answer to that question is ‘I don’t know,  but if we’re not in it then we don’t win it!’  It’s a big sea out there and dolphins can be elusive creatures,  as with humans they have different patterns,  moods and levels of energy.   Some species are easy to spot,  such as the Bottlenose,  whereas Hector’s could go un-noticed from a few metres away.  Tasman Bay is one of the places in Aotearoa where you could come across any of the four commonly seen species of marine dolphin.  Here we will describe our local dolphins,  how we can co-exist with them better and what you can do to help in their conservation.  Happy reading!

Bottlenose dolphin / Terehu (Tursiops truncatus)

Aside from orca,  bottlenose are one of the largest dolphins at up to 3.5m long. They are a very cosmopolitan species,  with populations globally not exceeding 45 degrees towards the poles.  New Zealand is at the southern extreme of their range and they are  locally distinct and reasonably uncommon here with probably less than 1000 individuals.  In Te Tau Ihu (Nelson / Marlborough),  there is an estimated sub-population of around 380.  These can often be the easiest dolphins to spot as they move in large pods,  creating all sorts of commotion.  I have seen these dolphins leap up to 10m in the air,  which is kind of freaky when it is right next to the boat.  They typically feed on schooling and bottom dwelling fish,  and I have personally seen them eating kahawai and snapper,  it is likely that they follow the fish schools around and that is what governs their presence.  Females are sexually mature at 5 – 7 years and breed every 3 – 5 years.  Males can live to 45 years and females slightly older at 50.

Bottlenose are most commonly seen in the Abel Tasman from spring to Autumn,  they appear to love human interactions, and often seek out vessels.  Humans love to kick up wake in their boats for the dolphins to surf,  however this is considered bad practice as if you change direction or speed suddenly, they can get injured by the prop.  We see evidence of this all the time on bottlenose,  with missing dorsal fins and big scars, although a lot of these scars could be caused by sharks,  which are their most important natural predator.  It is thought that human presence alters the behaviour of these dolphins and may even distract them from important feeding,  socialising and resting opportunities.  These are certainly the roughest looking dolphins we encounter, but amazing to be around.  Always interact with dolphins on their terms, and if there is any sign of distress or disinterest,  please terminate the encounter,  or better yet,  go with someone who is trained in marine mammal interactions.

 

Short Beaked Common Dolphin / Aihe (Delphinus delphis)

We don’t often see common dolphins close to shore very often,  but when they do it can be spectacular, these sleek black,  grey and yellow creatures are master hunters,  and more often than not,  we see them feeding on small fish such as pilchards,  rounding them up into bait balls,  working together to clean up every last little fish.  We see them closer in winter,  often when the water is very clear, and they often associate with other species such as dusky dolphins, albacore tuna and NZ fur seals.  Commons can be seen in abundance if you venture further offshore,  and are renowned as more of a pelagic species.  We don’t really know how many common dolphins there are,  as their ranges are vast and they are often seen in pods of hundreds or thousands.

It is thought that commons can dive very deep,  up to 280 metres, and spend more than 8 minutes underwater,  although standard dive times are only a minute or two.  They feed on small fish and squid.  Males become sexually mature at 7 – 12 years and females 7 – 7 years.  They gestate for 11 months and can live up to 22 years of age.

Their threats range from tourism interactions to regularly mortality from seine nets,  set nets and trawls, as they are often associated with their prey species.  One of their greatest natural enemies are orca, and they have also been observed with shark bites.

One of the coolest experiences I’ve ever had was swimming with these incredible animals at Collingwood in Golden Bay with John Davis.  Check out the video below for some awesome footage.

Dusky Dolphin (Lagenorhynchus obscurus)

These small black and white countershaded dolphins can be identified by their almost blunt black dorsal fin and lack of a pronounced beak.  They are restricted to the Southern hemisphere,  between 26 and 55 degrees.  In Aotearoa,  their stronghold is Kaikoura,  where they can be reliably observed in huge super pods,  and a thriving dolphin swimming industry has been based around them.  They are very rare in Northern waters, being generally found South of East Cape.  We regularly see small pods of Duskies on their winter and early spring holidays in the Abel Tasman,  where they come to feed,  often mixing with Common  Dolphins.  Due to the variability in their pod sizes (from 2 – 1000) and their migration patterns from inshore to offshore,  the NZ population estimations are from 12,000 to 20,000 individuals.  Duskies feed on anchovies, hake and several squid species.

Their spectacular aerial displays are thought to be part of their feeding synchronisation behaviours,  and we often see jumping duskies,  side slapping the water to scare fish into tighter shoals for predation.  The usual suspects,  orcas and sharks are their predators.  Human threats are typically from set nets,  it is unknown how many have been killed by nets,  also planned aquaculture development in Admiralty Bay in the Marlborough Sounds is a threat to their breeding habitat.

Hector’s Dolphin / tutumairekurai, aihe, papakanua, upokohue, tukuperu, tūpoupou, pahu, pōpoto and hopuhopu.

Hector’s dolphins are endemic to Aotearoa, these tiny dolphins get no bigger than 1.5m long.  They are distinguished by their round dorsal fin. They are resaonably short lived at 20 years maximum, and they inhabit very shallow and often turbid waters.  It can be very hard to spot a Hector’s as they make very small splashes, and can often be mistaken for a seal.  Since I started work in the Abel Tasman in 2002,  I had probably seen less than 10 Hector’s.  This has changed in the last couple of years,  we are seeing pods of Hector’s much more regularly at all times of year, with my largest sighting of 25 at once.  When the government banned set netting around parts of the country to protect the Hector’s and Maui Dolphin populations,  Te Tau Ihu (Top of the South) was ignored as there was not enough data to suggest that they are present here.  Hector’s are little homebody dolphins,  with a linear range of around 50km of coast.  This means that local populations can be genetically distinct,  with the gene pool being enriched by the occasional errant roamer from another rohe (area).

The abundance of Maori names for the Hector’s dolphin suggests that this species was once much more abundant than it is today.  An old waitaha proverb states “He tu te Pahu, He tu te Tai – If the dolphin is well, so too are our coasts”.  There are many such signs and indicators of Hector’s dolphin behaviour that indicated weather and fish abundance,  told down through the generations.  Hector’s are a taonga or treasured species to Maori.  As one of the world’s rarest and geographically isolated dolphins,  they are also of international significance,  and the world is watching New Zealand to see how they fare under our guardianship.  They have attracted attention from the Sea Shepherd Conservation Society, who are concentrating their efforts on policing the set net ban on the East Coast of the South Island.  See https://www.operationpahu.nz/  for details. 

So how do we really know how many Hector’s there are?  In 1970 there were estimated to be around 30,000, and the last published estimate was just over 7,000.  The North Island sub-species, the Maui dolphin is estimated to be down to the last 55 – 75 individuals over one year of age.  A live one hasn’t been sighted in quite a while,  however a pregnant female was washed up on a Raglan beach in October 2018 and probably died of blood poisoning due to the premature death of it’s unborn calf.  With these low numbers,  this is a massive blow to the population.  One of our staff is a fisheries observer in the winter and has not seen any sign of Maui dolphin in their home range.  It is actually now thought that the Top of the South Hector’s population could potentially interbreed with Maui,  being the lifeline to this vulnerable population.  Work needs to be done in this area,  genetic sampling through biopsy to identify any connection between the two populations.

 

Conservation

hectors-dolphins-sightings

Gemma McGrath of the Whale and Dolphin conservation Trust is the champion for these little characters, based in the deep South of New Zealand, in a Hector’s hotspot,  her focus is on the plight of our local Top of the South Hector’s.  Once a year she comes up to Te Tau ihu to engage with communities here to help her protect the Hector’s.  Our Non-profit organisation Tasman Bay Guardians,  Forest and Bird, and other passionate locals assist by organising forums for Gemma to deliver her messages.  She is the creator of the Hector’s Dolphins Sightings App  (click to download).  Through this App, it has emerged that there are a lot more Hector’s here than were once thought.  The set net ban was rejected here in bay due to lack of information, this App is helping to prove that Hector’s are resident here,  and will go towards efforts to estimate their population.  If you are a boatie in New Zealand,  please download the app and record sightings of any dolphins you see,  as this information is very important.  Of course commercial fishermen spend the most time on the water,  and their knowledge is invaluable to the conservation of the species,  it is also unfortunately certain fishing methods that contribute to the mortality of all dolphins, so working with fisherman is key to their conservation.

hectors-dolphins-sightings-top-of-the-south
Hector’s Dolphins sightings in the Top of The South. 2018 (Gemma McGrath)

 

There are three recognised mitigation techniques to reduce bycatch of Cetaceans (whales and dolphins).  Primarily,  the removal of that fishing method (in this case set nets) from the area,  eliminates the danger to the species,  and also to sea birds and fish.  This is obviously popular with conservationists,  but not fishermen.  Secondly, the use of mitigation techniques such as seasonal closures, when the dolphins are less likely to be present, and physical techniques such as sonic pingers, that may discourage the dolphins from swimming into the nets.  This requires rigorous testing and is not 100% fool proof.  It may have detrimental impacts on the fishing effort for the target species aswell.   Thirdly, a Sustainable Bycatch limit can be set, where the fishery is closed once a pre-set number of the bycatch species are killed.  This relies on robust science of the population and also discourages misreporting.  An example of this is the Southern Squid fishery,  which is run on a Sea Lion Mortality quota.  In the mid water trawl fishery,  methods such as increasing the length of the headline can significantly reduce dolphin by catch.

Bycatch References –

Management-of-gillnet-bycatch-of-cetaceans-in-New-Zealand.pdf

review-of-mitigation-techniques-in-setnet-fisheries-paper.pdf

Common dolphin bycatch in New Zealand Trawl Fisheries

 

The government could fund a feasibility study on the transition to more sustainable fishing methods, both to mitigate dolphin mortality and protect habitat that supports.  Methods such as set netting (recreational and commercial)  threaten not just dolphins but all manner of by catch species such as sharks and rays.  Trawling damages the seafloor and re-suspends sediment,  making larval settlement harder and increasing the turbidity (murkiness) of the water.  Methods such as potting and bottom long lining,  using by-catch mitigation methods produce higher quality product, with much less bycatch and habitat destruction.  However the small-scale inshore fisherman generally does not have the capacity or inclination to change methods.  This would need research,  funding and a champion from fisheries to really see change to our inshore fishing methods.  See our library of scientific papers discussing the environmental issues in Tasman Bay.

 

 

dead-heactors-dolphin-in-net
Dead Hector’s Dolphin Caught in a net. (Steve Dawson)

The latest death of a Hector’s dolphin was in March 2018 at rabbit island (not far from Abel Tasman).  A necropsy confirmed that it was caught in a set net (likely recreational).  Also in the same month,  a commercial set-netter caught five Hector’s in one net,  he subsequently stopped fishing due to emotional trauma.  If you want to investigate dolphin deaths for yourself,  visit DOC’s Dolphin Incident Database. Obviously, as a nation, we need to address this issue,  and in early 2019 the Hector’s and Maui Dolphin Threat Management Plan will be reviewed.  This is the chance to have your say and submit on what you’d like to see happen to protect our precious Taonga species in Aotearoa.

 

seal-eating-kahawai
A NZ Fur Seal and Mollymawk fight over a kahawai killed by a pod of bottlenose dolphin who have swum off to the left of the shot. In the distance a coastal set netter sets his nets, right in the path of the approaching pod. (Stew Robertson)

 

smart-operator-logo

As commercial operators,  we have to have a marine mammal watching permit to take people to see marine mammals.  Every three years,  all of our staff must go through a course to ensure that they know exactly how to responsibly operate around marine mammals.  Abel Tasman EcoTours were the first SMART operator in the park,  and we are proud to be NZ marine mammal permit holders.  Since this programme was implemented by the Department of Conservation, the marine mammal experience has been much better in the park,  with quality interactions and responsible behaviour from the operators.  Click here for more information on the SMART Operator programme.

 

Abel Tasman EcoTours formed Tasman Bay Guardians in 2017,  creating a strategy that addresses a selection of ecological stressors on the Tasman Bay ecosystem.  These include issues such as sedimentation, habitat degradation, marine debris,  freshwater issues, our taonga species and threats to biodiversity from population increase.  We focus on positive collaborations on project based initiatives, public engagement and education programmes – Experiencing Marine Reserves and Whitebait Connection.  See our full strategy and kaupapa at Tasman Bay Guardians.

We thanks you for reading and hope you enjoyed this blog.

Nga mihi nui

 

Stew Robertson

 

General dolphin information taken from:

Personal observations

https://www.doc.govt.nz/nature/native-animals/marine-mammals/dolphins/

https://fs.fish.govt.nz

https://www.operationpahu.nz/

 

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