Boaties using the Hauraki Gulf this summer need to take greater care in sharing the water with marine mammals, Massey University researchers say.
The call comes as they release information and shocking images on the impact of collisions between vessels and marine mammals in the area.
In a paper published this month in the New Zealand Journal of Marine and Freshwater Research, the impact of a boat propeller injury on a bottlenose dolphin was reported, with dismaying results.
Coastal-Marine Research Group (C-MRG) PhD student Sarah Dwyer of Stanmore Bay was lead researcher for the paper describing severe propeller strike injuries sustained by an immature bottlenose dolphin.
"In this instance, the bottlenose dolphin sustained injuries that penetrated to the bone. Considering the severity of the wounds, it was surprising these injuries weren't immediately fatal," she says.
The young dolphin was observed with a huge open wound behind its dorsal fin and two evenly spaced parallel wounds on the tail consistent with propeller strike.
It was first sighted in May 2010 with an adult bottlenose dolphin presumed to be its mother.
They were photographed together for the next two and a half years.
Thereafter the mother was spotted alone and it is believed she would not abandon her injured offspring.
C-MRG director Dr Karen Stockin says the probability of vessel strike decreases when speed is reduced.
"We need boaties to be acutely aware they're sharing the waters with other marine mammals and, more importantly, to immediately report any incidents of vessel strike," Dr Stockin says.
Research on dead marine mammals show many die as the result of blunt force trauma after colliding with a vessel or being struck by propellers.
Juvenile dolphins are most often hit because they are slower swimmers, spend more time in shallower waters and are naturally inquisitive.
The Hauraki Gulf is home to one of the busiest ports and shipping lanes in New Zealand, with a marked increase in recreational traffic during weekends.
It's also shared with marine mammals, including species of dolphins and whales using the waters to feed and nurse their young.
Marine mammals in New Zealand are legally protected under the Marine Mammal Protection Act (1978) and anyone who accidentally kills or injures one is required to report the incident to a fishery officer or the Department of Conservation within 48 hours.
The Marine Mammal Protection Regulations covers commercial whale and dolphin watching activities, and recreational interaction.
Under this law, vessels must avoid rapid changes in both speed and direction and not exceed speeds faster than the slowest mammal within 300 metres.
"We need people in all kinds of vessels - from commercial ships to motor boats, yachts, jet-skis and kayaks - to be considerate of other species sharing the waterways," Dr Stockin says.
- © Fairfax NZ News
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