Protecting Hector’s – Decades of data reveal a concerning shift    

This is the third blog in the Protecting Hector’s series – a deep dive into a collaborative research project trying to find out how we can coexist sustainably with this rare taonga species.  

Tucked on the south side of Te Pātaka o Rākaihautū (Banks Peninsula) is the peaceful and unique Akaroa Harbour, home to the world’s smallest, and one of New Zealand’s most at threat dolphin species, the Hector’s dolphin. 

DOC is working alongside local tour operators, Rūnanga, researchers and the regional council to study the impacts of cruise ships, dolphin tourism and general vessel traffic in the Akaroa Harbour.  

Researcher Will Carome looks at how the distribution of the Hector’s dolphins has changed over a 20 year period.  

There is probably no other harbour on the planet where someone can get in a boat and go from one end to the other and be virtually guaranteed of seeing a dolphin. 

How have the dolphins fared in a changing harbour? 

As mentioned in our first installment, Akaroa Harbour has experienced substantial changes over the last two decades. Cruise ship visits more than quadrupled in summer 2011–2012 following the Christchurch Earthquakes and dolphin tourism grew substantially, in part to meet the growing cruise tourism market.

  

We’ve known for over a decade that the dolphin tours at Akaroa significantly alter the normal behaviour of these endangered dolphins. The challenge for us researchers is in interpreting what short-term changes in individual behaviour could mean for the long-term health of the population.  

I aimed to tackle this task by examining whether the distribution of the dolphins (i.e., where they choose to be) has been influenced by human pressures during the last twenty years. 

Answering this question began with poring over every standardised dolphin survey conducted at Akaroa Harbour between 2000 – 2020. This amounted to 369 surveys, with 2,335 dolphin encounters over 8,732 kilometres of boating. Dolphin research sounds like sunny days on glassy water, and we do get more than our fair share of that, but in reality this analysis was months of desk time.  

Mapping a change in distribution

I wanted to see what areas of the harbour are most important to Hector’s dolphins. To do this, I used a technique called kernel density estimation. Essentially, we input data from sightings in mapping software to create a heatmap showing how likely one would be to find dolphins in a given area.  

This method also shows us core use areas for the dolphins, known as hotspots. These are outlined in black in the heatmaps. To examine whether distribution has changed at Akaroa, I divided the study period into 2000 – 2011 and 2012 – 2020, before and after the increase in annual cruise ships. As you can see below, dolphin distribution shifted southward following a quadrupling of annual cruise ship visits to Akaroa. 

The distribution of dolphins has changed. What might this mean? 

Akaroa Harbour has always been important habitat for these dolphins. The shift in distribution raises concerns for both the dolphins and the health of the harbour ecosystem in general.   

Could the cruise ships be displacing the dolphins?  

The correlation between increased cruise ship visitation and changes in Hector’s dolphins’ presence/distribution in Akaroa Harbour does not necessarily mean cruise ships were the cause of the changes. Other potential drivers, such as changes in sea temperature or prey distribution, could have played a role in the shift.  However, there are certainly impacts associated with cruise ships that could influence dolphin habitat preference. These include increased noise, increased vessel traffic, and damage to the seafloor that may impact species that Hector’s dolphins eat.

It’s in the collective interest that the dolphins thrive at Akaroa. We were given opportunity to further examine sustainability of vessel interactions with the dolphins in the harbour to make careful, research-informed recommendations on minimising our impact.  

In the next installment, we narrow our focus to one hotspot, for both dolphins and boats, over one summer to better answer how we may be influencing where these dolphins choose to be. 

Read more: Protecting Hector’s – The dolphin, the place and the research