A shark expert believes more people being in the water is the likely reason behind the number of shark sightings this summer.
Swimmers at an east Auckland beach today are being warned to take care after sharks were spotted offshore, with another shark warning continuing over on a west coast beach. Last month, 19-year-old Kaelah Marlow died after apparently being attacked by a shark at Waihī Beach in the Bay of Plenty.
Marine scientist and shark researcher Riley Elliott said the increased number of sightings is not surprising with more people swimming at beaches after a hot summer and due to Covid-19.
He said there are far fewer sharks than previously, but a lot more people are going into the water than before.
"So you put all that into perspective - we cannot blame sharks for us encountering them more, we can only blame ourselves, we can only educate ourselves and we can only understand the environments that we go into and accept the risk if we're going to go into them."
But Elliot said every tragedy as a result of a shark needs to be investigated so we can learn from our mistakes.
"It should be recognised because we don't want this to continue, you need to learn from these, you need to react from these tragedies."
Elliott said it's vital to distinguish science from personal observations.
A major international report came out in the journal Nature a few weeks ago indicated that worldwide shark numbers have declined by 70 percent over the last 50 years due to an 18 fold increase in fishing pressure, he said.
"That is absolute scientific fact, so we have only 30 percent of the world's sharks left and that is a huge decline."
Elliot said many reports in the media or reports from fishers are personal observation.
"I'm looking at a couple here right in front of me saying 'oh because we stopped shark finning there's sharks everywhere' - that's personal observation."
Elliot said one person's personal observation does not count as fact or science.
"But when we have a unique tragedy like the unfortunate one in Waihī from a suspected white shark - that is something that stands out as an anomaly that we should be looking into because statistically and scientifically great whites in that area have not been a common thing."
He said last year there were sightings of great whites in Bowentown in Tauranga, as well as a great white biting a surfer's board at Pauanui beach, while this year there has been a fatality.
At this stage these are anomalies that are not yet statistically significant, he said.
"But any tragedy is statistically significant in my eyes as a shark biologist."
Australia's shark population
Elliot said Australia needs to be broken into two distinct areas in terms of shark attacks.
"West Australia has quite a lot fewer shark attacks but they're almost all fatal, where as the east coast of Australia has, I think it was 88 in the last 10 years, but a very small proportion of those are fatal."
He said on the West Coast there are mature sharks which are hunting seals and their hunting grounds overlap with the areas where surfers are.
"You just get a full-blown predatory attack, you know which results in fatalities cause these people are also far from medical help."
Elliot said there is a much larger population of small great whites on the east coast of Australia because estuaries and shallow water coastal systems there make good nurseries for sharks.
"You get a lot of nips, a lot of these young juvenile sharks that don't really understand what's going on yet, their diet shifting from fish to mammals, being seals not us, and they make mistakes."
Elliot said the east Australian sharks are part of the New Zealand shark population, with most of this country's shark population hunting around the southern islands of New Zealand.
But he said the sharks that have been seen in the North Island are juveniles.
"These are ones that live in our northern harbours, they get above two-and-a-half metres and they shift their diet from fish to seals and they start moving down the coasts or they start migrating."
Elliot said he is both curious and concerned to see whether New Zealand ends up with a situation such as that in east Australia where there is an increase in the number of juvenile sharks which potentially leads to increased encounters.
He said there have very low numbers of shark fatalities in New Zealand in the last decade, but because each death is a tragedy it's important to investigate what is happening further.
"So it's nothing to panic about but it's something that requires investigation for sure."
He said juvenile great whites have been protected since 2004 and that protection should lead to a growth in the population.
"But we've also increased fishery by-catch rates in that time, the fatalities of juvenile great whites has been 53 over the last eight years I believe and that's just what's reported."
Elliot said currently there is very little data on shark numbers, but useful information could be gleaned from fisheries if they were forced to better report their catch.
"The bottom line is unless the government starts allocating money to start researching this stuff, to enforce fisheries to better report their catch, we have no data."
Elliot said without that it is impossible to tell great white numbers and to ascertain whether they have "moved in their habitat and their behaviour".