The knowledge of the common dolphin in New Zealand is very less, and very little authentic information is available for the species which occur in Hauraki Gulf. Delphinus sp.,the common dolphin species, native to New Zealand, have been misunderstood in terms of habitat use and demographics which has led to inadequate recognition and management of New Zealand Delphinus. These dolphins are the most abundant cetacean species in the Hauraki Gulf and this study was undertaken by Karen A Stockin and associates understand the effects of diel, season, depth, sea surface temperature, group size, and composition and dolphin behaviour. The activity budget of the dolphins was studied with respect to their activity stages- forage, mill, rest, social and travel and the compared with the earlier studies done by Dirk R. Neumann in 2001.
A semi-enclosed body of temperate water, of 60m maximum depth, was chosen as the study area, which is on the east coast of North Island (Hauraki Gulf, NZ). Due to the subtropical East Auckland Current, it as believed to be highly productive area with high levels of nutrients and large diversity of biological fauna. The studies were done on 92 samples analysed for 577 base pairs of the mtDNA control region. The samples from New Zealand were then compared with the published results from eight other populations around the world. Data was collected from Feb 2002 to Jan 2005.
The data was collected in relation to seasonal patterns in the activity budget and environmental variables were taken into account. Water depth and temperature was analysed in raw data. Behaviour studies were recorded by taking the initial and the lagged behaviours of the dolphins were taken into account (Lagged- after 30 minutes of viewing the dolphin).
A semi-enclosed body of temperate water, of 60m maximum depth, was chosen as the study area, which is on the east coast of North Island (Hauraki Gulf, NZ). Due to the subtropical East Auckland Current, it as believed to be highly productive area with high levels of nutrients and large diversity of biological fauna. The studies were done on 92 samples analysed for 577 base pairs of the mtDNA control region. The samples from New Zealand were then compared with the published results from eight other populations around the world. Data was collected from Feb 2002 to Jan 2005.
The data was collected in relation to seasonal patterns in the activity budget and environmental variables were taken into account. Water depth and temperature was analysed in raw data. Behaviour studies were recorded by taking the initial and the lagged behaviours of the dolphins were taken into account (Lagged- after 30 minutes of viewing the dolphin).
The results showed that behavioural data was collected for 686 groups out of total of 719 dolphin encounters. The activity budget for forage and travel were the most recorded states and social and rest were the least recorded behavioural states. Foraging was most recorded in winter and spring whereas resting was recorded in winter and autumn. Behaviour varied with the depth, foraging groups were observed in deepest, resting groups in shallowest, and travel and socialising groups were observed in median water depths. It was observed that the temperature also played a role in their behaviour. The foraging groups were observed in coolest (17.9°C), resting groups in warmest (20.3°C) and travelling, socializing and milling groups were observed in median temperature of 19.3°C.
Common dolphins observed in the Hauraki Gulf, New Zealand during assumed copulation. Photograph by Karen Stockin.The results concluded that the behaviour of the common dolphins were most influenced by water depth and food availability (46.8%) and determines their activity budget.
This paper presents the evidence that common dolphins occur in Hauraki Gulf due to availability of food and dolphins inhabit this area for other biological processes. This study shows that it is an important area for the Zealand Delphinus as it allows them to spend little time travelling and getting food and get more time in foraging, resting, breeding and tending calves. More deepening ecological studies will provide a platform to develop more action oriented strategies to wise management of the marine resource which is under stress from the local urban density and its use for recreation.
For more information: Marine Mammal Science, Volume 25 (2), April 2009
great picture!! It would be interesting to see how these dolphins differ in behaviour from the hector's and maui dolphins.
ReplyDeleteDoes this mean that fishing must be restricted in the gulf, to protect this valuable site for common dolphins?
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