Hector's dolphin surveys

Kaikoura 

This two-year study focused on the identity, population structure, and abundance of Hector's dolphins inhabiting the Kaikoura coastline. Biopsies were collected during a total of 15 boat surveys in 2014 and 2015 from two local populations, north and south of the Kaikoura canyon.

Kaikoura biopsy team look out for Hector's dolphins

• The Hector’s dolphins north and south of the Kaikoura Canyon form two local populations with low levels of individual exchange and interbreeding.
• Oceanographic features, such as the deep waters of the Kaikoura Canyon, might be limiting individual movements, and therefore breeding, between the two populations.
• The low level of connectivity that exists between the two populations is important for maintaining the genetic diversity and evolutionary potential of such small local populations.
• The abundance of the two Kaikoura populations combined, estimated using genetic mark-recapture methods, was 480 (95% CL: 342-703;CV = 0.29).

Download the report (PDF, 4,634K)

Te Wae Wae Bay 

There have been three vessel based surveys conducted in Te Waewae Bay - two used line transect methods and the most recent one used mark-recapture method. Both methods can be used to gain a robust population estimate but are different both in terms of the method and length of survey period.

1988

The first population estimate of Hector’s dolphins in Te Waewae Bay (Dawson & Slooten 1988) was conducted as part of a nationwide coastal strip-transect survey to estimate total abundance of the dolphins. Dawson and Slooten (1988) estimated the population of the bay at approximately 341 dolphins, with no confidence intervals provided.  

1998/99

Photographing Hector's dolphin 'Sky', Te Waewae Bay
Image: Rosalind Cole | DOC 

A later survey in 1998/99 (Dawson et al. 2004) provided a population estimate of Te Waewae bay of 89 dolphins (CV = 0.324; 95% CI = 36-218) as part of a wider study to provide a population estimate for an area between Farewell Spit and Long Point.

2004-2005

Vessel-based surveys were conducted in Te Waewae Bay, Southland during 2004 and 2005 (Green et al. 2007). The aims of the study were to provide an abundance estimate and document the distribution of the Hector’s dolphin population that used the bay.

The method used in this study was photo-ID mark recapture. This involved taking photos of dolphins over two separate time periods and comparing how many individuals were seen in one or both years.

An alternative method of mark-recapture is using genetic tissue samples. This is the method used for Māui dolphin abundance estimates. Read more about Māui dolphin genetic mark recapture.

Key findings:

• The study estimated that the population that used Te Waewae Bay in the Autumn of 2004 was 259 (CV = 0.171; 95% CI = 185-361) and in the summer period, 403 (CV = 0.121; 95% CI = 280-488).
• 282 hours were spent on the water over 38 days of study with a total of 2,462 km travelled.
• Dolphin distribution was concentrated along the inshore coastal section of the bay (less than 5.6km from shore) and dolphins were sighted less at the western and eastern extremes of the bay.
• 16.1% of the sighted dolphins in the Autumn period were sighted further than 5.6 km from shore and in summer 2.1% were sighted further than 5.6 km from shore, showing some indication of seasonal inshore-offshore movement.

Download the report (PDF, 1,003K)

Important note: Due to the considerable difference in the methods between line-transect and mark-recapture surveys, the results do not indicate any trend such as an increase in the Hector’s dolphin population of Te Waewae Bay.