A great white shark discovered dead in a fishing net on Bowentown beach had probably been there for at least a couple of days, an examination has found.
The Ministry for Primary Industries (MPI) has said the set net appeared legal, but it and two shark experts say it was not used in line with good fishing practice — with one saying untended nets could become "indiscriminate killers" of marine life.
Marine biologist Melissa Kellett, who has been studying sharks in Tauranga for five years, performed necropsies on two great whites found on the beach on Monday.
She understood one of the sharks was found washed up and the other had been removed from a nearby set net by fisheries officers.
Kellett said the condition of the shark "indicated it had been caught in the net for at least a couple of days".
In her view, this was "poor fishing practice".
"It is advised that fishermen using set nets in the area deploy for a short soak time, and remain near their net and check it at regular intervals. This increases the chance of unwanted species in the nets being released alive if they are unintentionally caught."
She said both white sharks were males about 2m long and likely juveniles.
"The stomach of one of the sharks contained items such as fish bones and fish eye lenses, which was no surprise given the importance of bony fish to the diet of white sharks of this size."
She said vertebrae were taken to allow the sharks to be aged and to contribute to research on length-age models.
"Tissue samples were also taken to contribute to a revised genetic mark-recapture population estimate for the New Zealand - east Australian population."
Department of Conservation (DoC) technical advisor marine species Clinton Duffy said DoC would be looking into whether any offences had been committed under the Wildlife Act.
Great whites are protected under the Wildlife Act 1953, which means it is illegal to hunt, kill, or harm them.
It is not illegal to accidentally catch a white shark but it must be released without causing it further harm, and it is a legal requirement to report the capture.
Duffy said the shark in the net was in "a reasonably advanced stage of decomposition".
All the teeth had fallen out of the jaws and the shark was rotting, he said.
"There were a lot of fish and crabs in the net. Virtually all of the other fish were dead and decomposed or scavenged."
He understood the nets had been set on Thursday and were prevented from being cleared because "the seas came up".
"This sort of incident is a good example of what's not really good fishing practice.
"If you're setting set nets, you should remain within sight of them at all times so that if they do catch protected species - not just great whites but marine mammals, dolphins, seals, shags, other types of sea birds - [you're] in a position to release them alive ... and that you can retrieve them quickly if conditions change."
He said this was recommended best practice when fishing with a set net and it was not really "good form" to leave set nets overnight.
"That's what leads to these nets either fishing for days on end killing everything that blunders into them or being swept away and becoming ghost nets."
He said it was possible to fish "quite responsibly" with set nets but it was incidents such as this that resulted in "a lot of opposition" to set nets.
"It's when they're left like this they become basically indiscriminate killers."
Duffy said incidents such as this would happen "several times a year" in New Zealand and it was not just great whites but other protected species.
"It probably happens more than we're aware of."
MPI Bay of Plenty district team leader fisheries compliance Jodie Cole said the information collected to date by fishery officers in the field did not indicate an offence had been committed.
There was no restriction on how long a net could be in the water, Cole said.
"However, a short soak time reduces the possibility of damage or waste to the fish caught and reduces the chance of being caught out by the weather.
"In addition, unwanted or undersized fish, as well as birds or marine mammals, will have a greater chance of being released alive and unharmed if they are unintentionally caught."
These nets were set on the main surf beach which experiences large waves and currents, Cole said.
"MPI maintains that it is not good practice to set nets in an area like this as they can quickly become unreachable and can break free from their anchors."
Cole said MPI had received calls about set nets in this area and in "most cases" nets were set legally and correctly.
"Waihī is an area of concern, and fishery officers often visit the area – often very early in the morning and late in the evening in an attempt to identify any breaches outside of normal hours."
Details of sightings, captures or strandings should be reported to DoC firstname.lastname@example.org or to 0800 DOC HOT (0800 362 468).
- Additional reporting Emma Houpt
Rules for set netting
- Nets must not be baited.
- Set nets must not be longer than 60m.
- Nets must not be set within 60m of another net.
- Each end of a set net must have a surface float marked permanently and legibly with the fisher's initials and surname (only one float is required for fyke nets).
- You must not use nets in a way that causes fish to be stranded by the falling tide.
- Only one set net (maximum 60m) and one bait net (maximum 10m with a mesh size of 50mm or less) can be carried on a boat at the same time.
- You cannot use stakes to secure nets.
- No person may set or possess more than one set net.
- Nets (or setups with more than one net) must not extend across more than one quarter the width of any river, stream, channel, bay, or sound.
- Set nets are restricted in some areas.