Geoff Thomas: Terns give game away

The right fly pattern was the key to catching this White Island trevally. Photo / Herald on Sunday

The "kahawai birds" were fluttering among the splashes on the green harbour. Boats cut across the action, with people holding rods anxious for a strike. No rods bent.

The white terns, often referred to as kahawai birds, are drawn to the schools of kahawai when they corral swarms of tiny bait fish which squirt out of the water trying to escape the voracious feeders. But none escape, and those that reach the surface are snapped up by the swooping, squawking birds. It is typical of the symbiotic relationships so common in nature.

Another predator is attracted by the frantic activity - the angler, the fisherman who scans the sky hoping to pick up the flickering white flashes that signal birds wheeling and diving into the sea. He knows that where there are birds, he will find fish. And not just kahawai.

If the prey are small fish the predators will be kahawai. If the bait is anchovies or pilchards they may be joined by kingfish and dolphins.

There is also a different scenario which frustrates the angler.

The predatory fish will appear as a dense mass, snouts all facing the same way and moving slowly. This is when they are feeding on tiny organisms like plankton or krill. And the kahawai will usually be sharing the feast with another fish highly regarded by anglers - the trevally.

It is also when they prove frustrating for those trolling lures across and through the packed fish, and the fish ignore them. They are not interested in the flashing and wobbling lures.

They are focused on one item of food and anything which does not resemble their dinner in size and colour will not be viewed as something which should be swallowed.

There is a solution, and it has been referred to in these pages before. Take a leaf out of the trout angler's book.

They use delicate creations combining tufts of fur from a seal or possum with fibres from the wing of a bird, all secured around a wafer-thin hook with cotton thread and glue. The hooks may be no larger than a thumb nail but the steel is finely tempered and can hold a powerful 5kg trout in a mountain stream.

When matched with a hand-crafted fly rod 3m long, a balanced moulded line and a reel which has a finely machined drag system this super shark little hook can easily fasten in the gristle of a trevally's lip.

The art of fly fishing for trout in sparkling streams goes back 400 years, but in recent years it has been adapted to the saltwater and the tackle modified to withstand not only the corrosion of the sea water but also the power of fish like the trevally and kingfish. Compared to the delicate trout, these are brutes which will quickly destroy any tackle not up to the challenge.

So when the kahawai and trevally are found in a dense pack as they scoop up plankton, it is time to bring out the fly rod and cast a nymph at them.

The pattern is not as critical as when tempting a trout which is focused on size No18 mayflies. Something which is pink or grey will do the trick. But be prepared for a sizzling run as your fish tears line from the reel. The long, tapered leader designed for a pin-point delicate presentation is also not needed. A short length of 4kg monofilament is fine, just so long as it will go through the eye of the nymph.

If the angler is not practised in the art of casting a fly, it can be simply trolled slowly through the school of fish.

The fly rod can even be dispensed with if one is not easily to hand. It is just a question of being a little inventive.

The object is to place the nymph in front of the quarry. So a small casting outfit like a soft-bait rod with a spin reel and light line can be adapted by adding a small sinker with the nymph on a light trace half metre below the weight.

This can be easily cast at the fish and slowly wound back. It won't get very far if the fly on the end is roughly the right size. Usually a No6 is small enough.

One occasion at White Island involved a little Kiwi ingenuity for there were no trout nymphs in the fly box which was deep in the tackle bag. The usual ammunition for a foray out wide to places like White Island involves saltwater flies - streamer patterns designed and tied specially for species like kahawai and kingfish, and trevally will also often take such lures. They are much bigger than trout flies with stainless steel hooks and long, colourful tails.

But on this particular day the trevally were not interested in the saltwater flies. They were looking for smaller prey, so a little surgery on the smallest of the streamer flies removed the tail and much of the body, leaving only a few slim wisps of filmy material along the top of the hook - and it did the trick. Then the fun started.

The other important factor in tangling with speedsters like kahawai and trevally on trout or similar light tackle is to play them carefully, using the rod to bring them to the boat and not attempting to net the fish until it is tired out and lying on its side. By no means ever try and lift it into the boat as something will give.