The National Institute of Water and Atmospheric Research says an increase in shark sightings each summer is mainly a result of more people being out at sea.
NIWA scientist Malcolm Francis says there is no evidence to suggest there are more sharks than normal hunting in New Zealand waters.
"There are a lot more people out there spending a lot more time looking in areas where they might see sharks."
Mr Francis says some species come into very shallow water in summer to feed on small schooling fish such as jack mackeral and kahawai, but most are harmless.
"But the sharks involved are mostly quite small - a metre and a half to two and a half metres - and harmless species."
Mr Francis says there have been 40 recorded shark attacks in New Zealand waters since 1840, and 11 fatalities, mostly involving Great White sharks.
He says the last serious shark attack was in the mid 1990s, in the Chatham Islands.
