White shark research has been conducted arguably since the last 1960’s, but in New Zealand it has only been ongoing for the last 10 years. Initial studies commenced at the Chatham Islands in 2005. At that time white sharks were known to frequent the Chatham Islands and it was considered a potential ‘aggregation’ site. However popular opinion was that white shark sightings elsewhere in New Zealand were individuals that had strayed off course from Australia and there was no ‘resident populations’.
The research project that initially kicked things off was a joint venture between the National Institute of Water and Atmospheric Research (NIWA) and the Department of Conservation (DoC), headed up by Dr Malcolm Francis (NIWA) and Clinton Duffy (DoC). The reason for the interest in white sharks in New Zealand was driven by ongoing international concern about their conservation status, particularly their listing on Appendix 1 and 2 of the Convention on Migratory Species, and the almost complete lack of any robust information on the species in New Zealand waters. Knowledge of their low reproductive and growth rates also suggested that reported levels of fishing mortality could be causing their population to decline. Little is known about the habitat requirements of white sharks, their seasonal behaviour patterns, or their interactions with fisheries. It was felt that an improved understanding of where they are at what times, and their migratory patterns would allow strategies for reducing bycatch to be developed. The initial objectives of the project were:
- Describe the movements and habitats of these sharks in New Zealand and the SW Pacific.
- Identify areas of overlap with fisheries inside and outside New Zealand’s EEZ
- Investigate the use of photo-ID as a fishery independent method of monitoring population trends.
The Chatham Islands posed a number of obstacles the scientists had to contend with, rough weather and their remote location being the biggest issues.
Four pop-off archival satellite tags provided by Dr Ramon Bonfil and the Wildlife Conservation Society, NY, were deployed at the Star Keys in 2005 and numerous other large white sharks were observed. Those early tags quickly opened new insight into migratory movements of New Zealand white sharks, most notably that the sharks tagged at the Chathams were not migrating between South Australia and New Zealand as expected. All of the tagged sharks moved north of New Zealand to the Louisville Ridge and New Caledonia. Based upon the success of that expedition it was possible to secure funding for further satellite tagging and eventually expand the programme to other parts of New Zealand, notably Stewart Island.
Research commenced at Stewart Island in 2007 and has been ongoing there ever since. Initially, the programme focussed on satellite tagging but was expanded to include photo-identification of individual white sharks using their markings, and acoustic tagging to study fine scale movements. Among other things, it is hoped that the photo-identification project will enable estimation of population size and trend at Stewart Island, removing reliance on traditional tagging methodologies and fisheries by-catch data. The acoustic tagging study involved the deployment of an array of acoustic receivers around the Titi Islands, Ruapuke Island and Paterson Inlet.
Satellite tagging of Stewart Island sharks confirmed they also undertake a seasonal migration to subtropical and tropical regions of the southwest Pacific. Perhaps most importantly the tagging undertaken at the Chatham Islands and Stewart Island has shown that sharks do not appear to move between these locations, although they mix off northern New Zealand and outside New Zealand waters.
Meanwhile, Clinton Duffy also became interested in the movements of juvenile white sharks which were occasionally reported by commercial and recreational fishermen around the upper North Island, in particular the Manukau and Kaipara harbours. The first satellite tag deployment was on a 2.1 m TL male in Manukau Harbour in February 2006, and this was eventually followed by another deployments on a 3.2m TL female named Kate off Gisborne in September 2009. Unfortunately both tags came of the sharks prematurely. However, both were recovered and provided detailed information on the short-term diving behaviour of both sharks.
In 2011 the first shark was successfully tagged in the Manukau with a SPOT and PAT tag. The 2.4m TL female (Marina) was tracked out of the Manukau and up the west coast to Cape Maria Van Diemen and Cape Reinga where her SPOT tag ceased to transmit (possibly due to the battery going flat).
Clinton Duffy attaches the PAT Tag to Marina’s Dorsal Fin
Her PAT tag continued to function and it detached off the East Coast of Australia and was recovered on a beach in southern Queensland. The tag was returned to Clinton and the information is currently being analysed. We hoped to hear about her movements in detail this year but unfortunately there has been insufficient time to start analysis.
In the summer of 2012 tagging expeditions continued in the Kaipara with one shark a 1.8m TL male named Scotty successfully PAT tagged and a number of other small white sharks seen. In January 2013 a 1.5 m TL male was SPOT tagged in Kaipara Harbour but no transmissions were ever received. The reason for this is unknown. No sharks were tagged off the North Island in 2014. From 2010 through to the summer of 2015 a number of white sharks were encountered on each expedition however tagging success was low. This was attributed to the very low water clarity and the method of capture that was being deployed during this time period. However the annual expeditions to Stewart Island proved extremely fruitful both in terms of the tagging studies but also the development of the photo ID database, which now includes more than 120 individuals. The team deployed acoustic tags and set up an acoustic array to further investigate fine scale movements of sharks in the research area. 60 sharks received acoustic tags and the fine scale study revealed some interesting information of their movements. One such revelation was the fact that the acoustic array set up around a local salmon farm actually got no hits at all. It was expected that the nets, and any escapees would attract seals and so also attract white sharks. This was not the case.
The Kiapara expeditions were assisted by IGFA member and expert sport fisherman, Scott Tindale on the Red October. Scott applied his years of experience with game fishing and developed a new method of catching the sharks which was put into practice in 2015. In addition to Scotts help with a new rig the expedition took a different approach exploring the Kaipara harbour and tried a different location – less the 5 km from Shelly Beach. This changes in catch approach and location brought a change in success and on the first day out a total of 8 white sharks were seen, six were actually hooked by us, and three were tagged. The first to be tagged was a 2.2m TL male (Thomas D). This shark was tagged with both a SPLASH and a PAT tag. He was quickly followed by a 2.1m TL female (Caitlin) which was tagged with a SPOT tag.
Catlin’s dorsal fin and SPOT tag
The last, tagged towards the end of the day, was a 3.4m TL female. She was tagged with a PAT tag and given the name ‘Sue’.
Sue with PAT tag
The following day a further three sharks were hooked but no tags were deployed. Two weeks later another three sharks were hooked with two being successfully tagged – a 2.5m TL female named ‘Lea’ which was tagged with a SPOT and a mini-PAT tag, and a 3.3m TL female named Cindy that was PAT tagged.
There have been no further white sharks successfully tagged this year, however tracking the ones tagged in January provided interesting data. Catlin was the shark that ‘reported back’ most and she was tracked throughout the year travelling. Initially she appeared to be heading toward Pandora Bank or possibly Spirits Bay.
Catlin’s movements along Ninety Mile Beach in 2015.
However she returned to the Kaipara in June, travelling from Pandora Bank averaging a travelling speed of 3.24 km p/hr. Clinton was particularly interested to see if she would stop sending signals once she entered the harbour as it could indicate a change to more bottom-orientated foraging behaviour which snapper also do in turbid water.
The 2.5 m female (Lea) tagged on Jan 8th proved to be rather secretive. The first fix on her tag was received north of the Graveyard off Lake Wairere on Jan 14th followed by a single fix 4.7 km outside the bar. Thereafter the were no signals to indicate where she was. Equally nothing heard from the 3.3 and 3.4 m females that were PAT tagged. This is not to say the tags were not working as often a lack of signals can be due to the wet/dry sensor or aerial being fouled, or simply due to the shark spending only very brief periods of time at the surface. With a lack of regular report backs, recovery of the tag is vital.
‘Cindy’, the 3.3 m TL female on 8 Feb 2015 released her pop-off tag earlier than expected and started transmitting from over the Tonga Trench about 260 km southeast of Tongatapu, water depth a bit shy of 6000 m in August 2015. This has allowed for some data to be transferred, however as the tag has not been recovered, there is no detailed report of her movements.
Sue, the 3.4 m female caught in Kaipara River on 17 January however the tag started transmitting from a position 219 km southeast if Isle Hunter (Hunter Island) on Hunter Ridge; 707 km Southeast of New Caledonia and 739 km Southwest of Viti Levu, Fiji.
Finally, the mini-PAT tag on Lea, the 2.5 m female started transmitting four days later than expected in November. There were no position fixes from the transmissions and the tag then went silent again after three days before Clinton obtained a position fix from this tag in the Tasman Sea 114 km west of the Challenger Plateau (619 km west of Cape Egmont). This shark’s SPOT tag last transmitted close to Pandora Bank, off Cape Maria Van Diemen. It looks like it may be on its way back to New Zealand from eastern Australia so it was hoped the tag continued to transmit in order to reconstruct its track to confirm that the theory.
We were hoping to assist in deployment of another 6 tags before the end of the year, however weather conditions this spring and summer so far have prevented any opportunity to get back out on the water.