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Public help sought as hammerhead shark does bit for science

People fishing in the Bay of Islands are being asked to keep a look out for a young hammerhead shark, nicknamed Orokawa.

Photo by Scott Tindale

Orokawa is providing scientists with information on his whereabouts after becoming the first electronically tagged hammerhead to provide useful data in New Zealand waters.

The young shark, just 137cm long, was tagged last Sunday near Deep Water Cove in the Bay of Islands by fisherman Scott Tindale.

“We were anchored within casting distance of the rocks and saw a hammerhead swimming towards us on the surface,” Mr Tindale said.

“I cast a bait towards him and he took it straight away. Because he was small we were able to get him in the boat, oxygenate his gills with seawater from a deck hose, and tag and release him within five minutes.”

NIWA shark expert Dr Malcolm Francis has been contracted by the Ministry for Primary Industries to find out more about the biology, behaviour and stock status of hammerhead sharks in a bid to determine whether they are threatened by overfishing.

Dr Francis and Mr Tindale plan to tag a number of hammerheads – recognisable by their bizarre head shape - in the coming year to determine whether they are resident or migratory and what they do.

Little is known about the species, its habitat or abundance in New Zealand and Dr Francis says the young hammerheads are vulnerable to capture by set nets, longlines and trawls.

“They seem to be very sensitive to capture and most of them die before they can be ret
urned to the sea.”

Since being tagged, Orokawa has crossed the outer Bay of Islands and travelled around the north side of the Purerua Peninsula.

“He is moving around a lot but not going far. He makes a lot of inshore/offshore movements, almost reaching the shore at times,” Dr Francis said.

“This is the first time detailed information on hammerhead shark movements has been obtained in New Zealand waters.”

The only other New Zealand tagged hammerhead to provide useful information was a 2m female tagged with a plastic gamefish tag near Cuvier Island in 2011. It was recaptured east of Vava’u, Tonga, almost two and a half years later and more than 2200 km away.

Dr Francis thinks that this indicates that medium to large hammerheads may be highly migratory, though small juveniles are probably resident in New Zealand waters for the first few years of life.
Despite being common in northern New Zealand waters, hammerheads are rarely seen.

Dr Francis is asking fishers to be on the lookout for Orokawa and if they catch him, to release him as soon as possible.

If he is found dead, the tag on his dorsal fin should be removed and returned to Dr Francis at NIWA.

Orokawa was named after Mr Tindale’s boat and means calm seas.

The tag used on Orokawa is called a SPOT tag. It transmits messages to orbiting satellites whenever the dorsal fin, and the tag’s aerial, break the surface of the sea. The satellite estimates the position of the tag and sends that information via the Argos ground station in France, from where Dr Francis can download the data to his office in Wellington.


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