Following last Wednesday's fatal shark attack at Muriwai Beach, we thought our readers might have some questions about sharks they'd like answered.
NIWA fisheries scientist and fish biologist Dr Malcolm Francis is New Zealand's foremost shark researcher. Francis has been a scientist, diver and underwater photographer for more than 30 years and is a representative to the IUCN Shark Specialist Group.
In 2008 he was awarded the prestigious New Zealand Marine Sciences Society Award for his "continued outstanding contribution to marine science in New Zealand".
Here Francis answers the second batch of questions from readers (read part one here).
It has been my understanding that the Great White is more of a threat to water goers in Australia than when in NZ waters as they are in breeding mode here, and during this period hunt less and are less aggressive. How far is this supported by research? Do large sharks exhibit different behaviours in NZ and Australian waters which has an impact on the incidence of shark-related injuries? (Simon Mowatt)
New Zealand definitely has fewer great white attacks than Australia, but it is not clear why. It may be related to the relative numbers of sharks, or teh numbers of people going into the sea for a range of purposes. It is unlikely to be related to breeding condition as very few mature female white sharks are seen in either country (although small juveniles do occur in coastal waters of both countries). I'm not aware of any other behavioural differences between Australian and NZ sharks.
Is surfing at Auckland east coast beaches safer than west coast beaches? And what kind of reactions are required if we see a shark fin while surfing? (Tetsuya Totsuka)
Given that there have been very few fatal attacks on humans in NZ (the last confirmed one was 37 years ago), and occasional non-fatal attacks, beaches throughout NZ have a very low risk of shark attack. Sharks should always be treated with a healthy respect - leave the water if you see one while surfing.
I was stunned to hear that the shark that killed Mr Strange was not only very aggressive but then fought to retain the body. According to statements made by rescuers, the shark stayed with Mr Strange for 20 minutes and refused to relinquish him even after taking shots and being hit over the head. I have never heard of this kind of defensive behaviour before. The presence of multiple sharks is also unusual. Clearly this was not a case of "mistaken identity" in which a Great White bites once and then departs, but true predation. I would be very interested to hear what you make of this unusual behaviour. (Irene Castle McLaughlin)
I have not yet seen a comprehensive account of the attack so I can't say much about it. Predatory attacks do occur but they are relatively rare compared with non-predatory attacks in which a person is bitten and then the shark leaves.
Like an increasing number of NZers I take to the water on a regular basis in a kayak. Sometimes I fish from the kayak and have always been very careful to contain fish juices and to subdue my struggling catch. But if a 4m Great White looks like it wants to taste test me what am I best to do - make a stand and try to smack it with the paddle? Or try to paddle away sedately as possible? (Dave Adams)
There have been an increasing number of interactions between sharks and kayakers in the last decade or two, both in NZ and overseas. This is undoubtedly because of the increasing popularity of kayaking and kayak fishing. Struggling and bleeding fish are a shark attractant because sharks have acute senses of smell and hearing.
Sharks investigating floating objects like a kayak are likely to try and bump them to find out if they are alive or dead, and worth tasting. If the shark is not making a fast aggressive rush, then stay calm, and still, keeping your body weight low to reduce the chances of being tipped over. But if the shark is attacking your kayak, by all means try to defend yourself with the paddle or paddle away to safety.
Apparently it has been confirmed that Adam Strange was attacked by two sharks - a great white and a bronze whaler. Is it unusual for two different types of sharks to hunt together? (Paul Harper)
Identifying shark species in the water under the circumstances occurring at Muriwai is tricky and I haven't heard the basis for the identifications reported recently. Different shark species do not typically hunt co-operatively together, and attacks on humans that involve more than one species are very rare.
If two species were involved in this attack, it is likely that they were both attracted independently to the area by the same stimulus, for example schools of fish aggregating in shallow waters. Great white and tiger sharks have been seen feeding on the same whale carcasses a number of times, probably because they were both attracted by the same food source.
We are hearing that NZ waters host quite a number of sharks, including the great white, yet we don't think of NZ as being similar to the Mediterranean, Australia, South Africa or USA for being a natural great white habitat. What research has been done on the reasons and when they come to NZ waters? Is it to breed, nurse young, feed or just "hang out" at certain times of the year? Is there certain parts of NZ that the Great Whites "hang out" at more or are they widespread all around NZ? (Zoe Juniper)
New Zealand is part of the normal range of great white sharks. Tracking of sharks of all sizes shows that most of them (except for small juveniles) migrate to tropical waters north of NZ in winter-spring: they have been tracked to the Great Barrier Reef and New South Wales in Australia, New Caledonia, Vanuatu, Fiji and Tonga.
So "our" white sharks are actually part of a mobile south-west Pacific population. They spend about 5-8 months each year in NZ waters and the rest overseas. While in NZ the sharks feed intensively on fish and marine mammals. Young white sharks occur mainly around the northern North Island but it is not clear whether they are born there or somewhere else - only two pregnant female white sharks are known from NZ waters, and mature females, which are longer than 4.5 - 5 m, are rarely seen. But NZ is an important nursery area for white sharks. Subadult and adult sharks occur throughout NZ waters, but are most abundant around large seal colonies such as at Stewart Island and the Chatham Islands.