KEY POINTS:
Shark sightings causing alarm off New Zealand beaches are the result of normal migratory behaviour, says a Department of Conservation marine scientist.
Clinton Duffy said several shark species move into shallower waters from around October, usually starting with smaller species such as school and rig sharks.
They tend to be followed by larger predators such as bronze whalers and hammerheads, and then great whites.
"Unlike the other species, the white sharks don't seem to be in there to breed. They seem to be there to feed on the young sharks or the pregnant sharks and the fish and stingrays that are in those areas. Some then migrate away from New Zealand and then return again in the spring ... Most of the species are present all year round but generally just further offshore."
There are no more around this year than any other, Mr Duffy said.
Niwa scientist Dr Malcolm Francis said sightings tended to increase in summer because there were more sharks closer to the shore, and more people in or near the water. But attacks remain extremely rare.
"The risk of an attack is extremely low, but if there's a shark in the water, you're obviously wise to hop out, listen to the lifeguards and do what they tell you to do. Above all, be careful driving to the beach and be aware of drowning because they're much more likely to be dangers to you than a shark is."
The last fatal shark attack occurred in Te Kaha in the Bay of Plenty on January 1, 1976. The most recent serious shark attack was on February 27, 2003, when a scuba diver was attacked by a great white off Halfmoon Bay, Stewart Island.
Mr Duffy, who keeps New Zealand records on the voluntary International Shark Attack File, said about 25 people are killed each year by sharks worldwide. New Zealand's rate of attacks remains very low.
