KEY POINTS:
Snapper live in the sea, which is their "source". They move into and populate hotspots, known as "sinks". Remove snapper from the sinks and others move in to keep the numbers up.
Why? Niwa wants to know. What makes the sinks so popular? The more scientists know about them, the better snapper stocks can be conserved and the better the fishing will be.
To this end, Niwa scientists will be spending nine days, starting on Monday, tagging 4000 snapper from two commercial longliners in the inner Hauraki Gulf.
Fishers who return tags go in a year-long monthly draw for two prizes of rod/reel combos worth $350 each. Niwa's telephone number is on each tag.
All the information Niwa receives from the tagging programme will go towards "looking after the underpinning ecosystem that supports the Hauraki Gulf fishery", says scientist Mark Morrison, who is leading the study.
The information will be used to get a picture of snapper movements in the gulf to show what makes the population tick. In particular, Niwa wants to test ideas about sources and sinks.
"The idea is that hotspots for snapper are population 'sinks' - as snapper are caught, their numbers are replenished by snapper moving in to 'replace' them from surrounding 'source' areas," says Morrison.
"The premise is that something about the sink areas makes them more attractive as habitats for snapper than the source areas."
He suspects the reason is a combination of snapper preferences for more complex seafloor structure - such as shells, rocks, sponges and worm-tubes - currents and abundant food sources.
Information from returned tags will also give the Niwa scientists insight into how to protect sinks, especially from sedimentation caused by activities on land, which has filled in some sinks.
The sinks are where the snapper are, and a healthy sink means a healthy fishery. Where else on the planet can you catch large, healthy snapper in the middle of a major city?
Many claim the Hauraki Gulf is the best snapper fishery in the world. The Niwa scientists wants to keep it that way. They need those tags back.
The tagging is being supplemented by night video surveys of snapper grabbing 40 winks in their little seabeds, providing information on their abundance and size in source and sink areas.
The tagging programme is part of a four-year study, now in its second year, investigating the interaction of recreational fishing and tourism with marine ecosystems.
Anglers reporting a tagged fish will be asked where and when it was caught - including whether it was over sand or reef - its length and to give GPS co-ordinates of the catch site if possible.
Niwa will also be collecting data on recreational fishing from aerial boat counts and boat-ramp surveys, data that will help to show the movement of snapper from sources to sinks.
The tagging programme comes as snapper schools are closing in around the gulf to begin spawning.
Skippers have reported bigger fish in close at the 30m line. On any good weekend from now on, up to 400 boats could be out fishing the gulf's sinks.
On the trout-fishing scene, the Ohau Channel at Rotorua is still giving up monsters to anglers prepared to hang in there till midnight or go out at 5am.
The biggest landed in the past two weeks were 6.8 kg and 7.8kg.
Catch of the week has to have been the one taken by a Tongariro angler who was playing a good fish when he saw the butt of a fly rod emerge above the surface. The trout had become tangled in a lost rod. The angler landed them both.
The rod was a Penn Gold Medal and, with the reel and line attached, is worth about $700. Not a bad score. The owner can make inquiries at Sporting Life in Turangi.
