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Retired fisherman and shark hunter Laurie Waters has issued a warning to Dunedin swimmers.
He said swimmers were more vulnerable to attacks by white pointer sharks at this time of the year because the small fish they ate were closer to the shore and there were fewer fish to eat than before, so sharks were hungrier than ever.
''They'll attack whatever they can to get a feed. This is a bad time of the year for sharks to be in close at Dunedin beaches.''
Sharks could sense a storm and were more likely to ''violently'' attack anything edible before the storm hit.
Sharks attacked four hours before a ''strong southwest wind change'' on a hot day with northwest wind, he said. Swimmers and surfers should beware of the forecast change in weather.
''Each shark attack has been at this critical time.''
He had helped kill a shark in Dunedin after a spear fisherman was killed by a shark at Aramoana in the 1960s.
Mr Waters said he started his career as a commercial fisherman in 1950 when he was aged 15 and he set the first shark nets in Dunedin in the 1960s.
Dunedin City Council parks manager Mick Reece said shark nets were expensive and ineffective and would not be returning to Dunedin beaches.
University of Otago marine science senior lecturer Associate Prof Stephen Wing had not heard the theory of a four-hour shark feeding frenzy prior to a storm, but said sharks were more active in summer, especially in seal pup season.
''The best advice I've heard is: don't swim in open water near seal colonies.''