A team of anglers competing in the Counties One Base fishing contest have helped tag and release a great white shark which is providing valuable research information.
Michael Grey, Ethan James and Braden Olsen caught the shark while fishing in Manukau Harbour. Following advice provided at the competition briefing by DOC shark researcher, Clinton Duffy, they secured the shark alongside their boat ‘On It’ and motored slowly ahead to keep it alive. They called in the capture by cell phone and the news was relayed to Clinton by the One Base radio operator and the crew of a nearby jet ski.
20 minutes later Clinton and his helpers arrived to attach two types of satellite tags – A fin mounted SPOT (smart position and temperature) tag that transmits each time the shark surfaces; and a PAT tag (pop-up archival transmitting tag) that will stay on the shark for a year and archive depth and temperature data.
The SPOT tag transmits information when the shark surfaces and allows Clinton to track her movements
The PAT tag (pop-up archival transmitting tag) will stay on the shark for one-year and archive depth and temperature data
“The animal was tagged in a part of the Manukau Harbour not far from Auckland International Airport,” said Clinton. “Great white sharks, including pregnant females, are regularly reported in the Hauraki Gulf, and the Manukau and Kaipara Harbours also appear to provide important habitat, particularly for juveniles.”
Clinton Duffy attaching the SPOT (smart position and temperature) tag to a white shark in Manukau Harbour
The shark measured at 2.4 metres in length and was identified as a juvenile great white female, with an estimated weight of 143 kg. She was given the name ‘Marina’ after a member of the White Shark Conservation Trust that helped tag her.
Since then, Marina has been on the move and her tag has yielded valuable information for Clinton and his research. She was picked up outside the Manukau Harbour on the 7th Feb for the first time after she was released. On the 16th of Feb she swam from a position close to the Manukau Bar to, just north of Port Waikato, and back again. By 25 Feb Marina had been up to the entrance of the Kaipara Harbour and headed north.
The latest track on Marina was only yesterday (3rd of March) and incredibly she was recorded off the northern tip of New Zealand at Cape Maria Van Diemen! Which means since leaving Hamilton’s Gap south of the Manukau Harbour on the 15th of February she has covered a minimum distance of 355 km, not including her meanderings in between. Clinton was confident she would be feeding on fish, particularly kahawai, trevally, kingfish, school shark and snapper.
Map generated from Marina's tag showing her movements in Manukau Harbour
Map generated from Marina's tag showing her movements off the Kaipara Harbour
As of yesterday Marina was tracked off Cape Maria Van Diemen at the Northern tip of New Zealand
It was the fifth year running that Clinton has been involved with the sport fishing event which is held each year during Waitangi weekend. He is co-leader of a research project on great white sharks (Carcharodon carcharias) in New Zealand involving the Department of Conservation, NIWA and the University of Auckland. The primary objectives of this research are to investigate:
- Movements of white sharks between New Zealand and the wider pacific.
- Movements and habitat use within New Zealand waters
- The use of photo-identification as a means of monitoring the white shark population
In 2007 white shark were listed as a protected species under the Wildlife Act 1953 and DOC is working along side international scientists to learn more about them. Part of this work relies on assistance from the public for reports of sighting and animals that are hooked on fishing lines.
Special thanks go out to the Counties Sport Fishing Club, particularly Michael, Ethan and Braden for assisting with the tagging of Marina. Like the fishermen from Auckland, there are things you can do to help white shark. The DOC website has some tips on how you can help.
I like the Great White track. Rather perturbed where she crosses onto land at Cochranes gap, or is that the human Marina setting out for the day?
Hi there,
The shark’s position is estimated using the information obtained from the transmissions from its tag and a mathematical formula. In rough conditions, or when the tag only briefly breaks the surface as the satellite passes over, very few transmissions are received and the resulting estimate of the shark’s position can be subject to a lot of error. Each estimated position received from Argos is assigned a class indicating its accuracy. The best positions have an accuracy of plus or minus 350 m, the worst can be thousands of km out. Many of this shark’s positions have been in the highest quality classes – the ones on land however are low quality fixes and will be discarded from the final data set.
For more information on how the system works follow this link to the Argos website: https://argos-system.cls.fr/html/system/how_it_works_en.html
Clinton