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Tagged Hector's dolphins transmitting crucial information

Massey University

10th August 2004

Researchers in the University’s New Zealand Wildlife Health Centre are in the process of analysing information on three Hectors dolphins caught near Banks Peninsula and tagged with satellite transmitters.

Marine mammal expert Dr Padraig Duignan says the preliminary data shows the dolphins were in good health and that they did not get stressed by the capture and handling.

From capture to release each dolphin was held for an average of 27 minutes for a health and physiological examination and their heat-rate and respiration measured throughout.  Dr Duignan says all three dolphins maintained a steady heart-rate of around 130 -140 beats per minute with little change in the rate.  He says because the dolphins are boat-friendly they do not need to be chased and consequently their heart-rates did not rise after they were captured and held out of the water.

Blood tests taken to check cell characteristics and to determine the health of vital organs also showed low levels of plasma cortisol (a hormone).  Cortisol levels are an indication of stress and the Hector’s dolphins cortisol levels were similar to those reported for bottlenose dolphins maintained in captivity and much lower than reported for free-living beluga whales captured for blood sampling.  The most disturbing finding for the health screening was that Puari, the oldest female, appears to have been infected by Brucella, a bacterium that can cause abortion in dolphins.  This could be why reproductive success is so low in Hector’s dolphins and may even explain the rapid decline of Maui’s dolphins in the North Island.  However, more research is needed on this disease before its impact can be assessed.

Dr Duignan says the most disturbing finding from the health screening was that Puari, the oldest female, appears to have been infected by Brucella, a bacterium that can cause abortion in dolphins.  He says this could be significant in an already endangered species.

Dr Duignan says the steady heart-rates, and the low plasma cortisol levels suggest that Hector’s dolphins may not perceive capture and handling as particularly stressful.  This is the first time a health assessment has been done on living, free-ranging dolphin species in New Zealand and an invaluable opportunity to build on the limited bank of information about the mammals.

Since 1996 the Wildlife Health Centre has autopsied ten Maui’s dolphins and over 60 Hector’s dolphins.  Dorsal fins from dead dolphins were studied to find the best hydrodynamic design for a satellite transmitter and to find the best way to attach them to the captured dolphins.  Both topical anaesthetic and intravenous pain relief were used to minimalise discomfort during the process, in which the tags were attached using two nylon pins to the dorsal fin.

Dr Duignan says the dolphins’ strongest reaction throughout the tests was to the ultrasound examination, because they could hear the wavelength.  The ultrasound was used to measure blubber depth as a general indicator of the mammals’ body condition.

Transmission signals have been monitored from the two female and one male dolphin caught.  The first dolphin caught, Puari, was monitored from March 4 until July 17.  The signals provide information on seasonal migrations, on the distance travelled during the day, and night-time movements.  Puari’s signals showed she spent a lot of time outside of the Marine Mammal Sanctuary around Banks Peninsula originally established to protect the dolphins from fishing vessels and set nets.

Dr Duignan says it is the first time satellite telemetry has been used to assess the daily and seasonal movements of the endangered dolphins and the information could be crucial to their survival.  Satellite telemetry has been used to learn about the movements of New Zealand sealions for several years, and the method is widely used on marine mammals in North America, South America and Europe and Australia.

The ground-breaking research is led by Dr Greg Stone from the New England Aquarium in Boston, who pulled together the team of experts, including Dr Duignan and Gareth Jones from Massey.  The Department of Conservation in Akaroa, the Natural Environmental Research Institute in Denmark, and the Department of Biological Sciences at Auckland University, and Wellington Zoo are also involved.

The research trial was given full support by Ngai Tahu.