The Catlins
Coloburiscus

Daniel Agar fishes the peaty waters of New Zealand's deep south and finds mayflies aplenty.

Tell people you've been down to the Catlins and you'll most likely get a bemused look followed by "and where is that?" Well, this sparsely populated part of Otago in the bottom south-east corner of New Zealand is far from both the beaten tourist path and blue ribbon angling route.

It's an area rich in history and legend. Maoris say that the forest interior is inhabited by Maeroero, the wild men of the woods, and these mythical beings have shared the region with moa hunters, whalers, sealers, sawmillers and dairy farmers. Now, derelict buildings stand as testament to the past and as the lush wet climate fights back, pasture reverts to bush. These days the current growth in eco-tourism has seen a revival of sorts, and more are coming to see the spectacular coastline and dense silver beech and podocarp forests. Some even dangle a line in the region's rivers.

The names of these rivers - the Tahakopa, McClennan, Owaka and the Catlins reflect a shared Maori and European history. The dank smelling, peat-stained waters resembling strong black tea may not look so appealing for the angler, but this neglected region has its own special place in New Zealand's angling history. For it was here that one of our few original dry flies, the Owaka, was developed. All this at a time when New Zealand was swamped with traditional British patterns. Don't expect to find an Owaka in a Taupo tackle house, but this upwing quill tie is still a favourite of southern anglers schooled in the old ways.

Nowadays, most of the fishing takes place in the slower moving, lower reaches, where every year, during the whitebait runs, the locals take double figure fish. Large lures fished deep and slow during the hours of darkness also account for the odd trophy. But the real treats of this fishery are revealed in the middle to upper reaches, where surprisingly few anglers venture.

For those in the know, it's a golden experience, with the treasure being the mayflies belonging to the genus Coloburiscus. There is nothing quite like this region in spring, working your way up the river surrounded by the rich yellow native kowhai and intense broom flowers as the trout rise to hatching yellow mayflies. And for the many whose best mayfly experiences involve using tiny, drab imitations, the delights of fishing these large, colourful mouthfuls are obvious. But don't expect to hear a lot of Latin on your fishing trip. The New Zealand angler's love of colloquialisms means Coloburiscus is usually reduced to plain 'collie'.

Coloburiscus is a crawling mayfly that belongs to the family Siphlonuridae. It is closely related to the Australian Kosciuszko mayfly (Coloburiscoides species). Dark chocolate in colour, the nymph is often referred to as the spiny gilled mayfly due to its peculiar gill formation. It is also known as the hunchback nymph, as the mature larvae has a distinctive humped thorax to house the developing wing pad. Whilst in 'the drift', crawling mayfly species are easy targets for trout, owing to their poor manoeuvrability. Coloburiscus, however, takes the prize for the poorest swimmer because of its bulky gills.

The only specific nymph imitation, Carty's Coloburiscus, was designed by Murchison guide and fly-tier Peter Carty after streamside sampling in his home river, the lower Buller. As Peter informed me, "They were really prolific and I did not have anything in my box that I felt would do the job." Over the past ten years he has continued to improve the original. "I'm sure the secret is in the shape, you must have a flattened abdomen and trim off the ostrich herl on the top and bottom to accentuate the gills."

It is an excellent imitative nymph, looking just like a mature drifting collie when held under water. Fish it dead drift, in the faster ripply water, where the more active, mature nymphs are most likely to be. However, it also has the advantage of being a deadly impressionistic mayfly nymph. In fact these days Peter regards it as his favourite all-purpose nymph. "When you're not sure what to tie on it's seldom a mistake. I've had reports from all over the country and various parts of the world on its effectiveness. I even nailed a few on the Tongariro one winter."

Scientific and angling literature on the species concludes that most hatching occurs from late winter through to late spring. Emergence is similar to Deleatidium, in that the mature nymph floats to the surface to hatch. During my research, I was surprised to read an account describing how this mayfly crawls out of the stream via rocks to hatch. Thankfully this is not so, as New Zealand anglers are deprived of quality surface mayfly action as it is.

The colourful dun is not hard to recognise, as it stands out from New Zealand's other grey toned mayflies. Look for the faint yellow stripe along the front edge of the wing and the more prominent yellow spot at the base of the wing. The adult has three tail filaments with the middle one being much shorter.

To represent the natural, flies need to be on the large size, ranging between #10 and #14. The true adult representation is that quintessential New Zealand dry fly the Kakahi Queen, as outlined by Norman Marsh in Trout Stream Insects of New Zealand (1983). Most agree that this pattern was devised by Basil Humphrey, the postmaster of Kakahi, some time after the First World War.

Unlike other patterns that come and go, this attractive dry fly is still hugely popular today, although this has nothing to do with the synchrony and density of collie hatches. For even though collies rank behind Deleatidium as the most commonly found mayfly in New Zealand, dense daytime hatches are by no means common.

Coloburiscus is typical of most New Zealand stream invertebrates in that it hatches in dribs and drabs. This is further compounded by the trout's apparent disinterest in the adult. Peter Carty, who has guided in classic collie country for well over a decade, reports that trout rarely get stuck into the adult. "I've seen the fish really home in on the adults on only a few occasions. I distinctly remember Tony Entwistle and some customers landing 25 on the Karamea when the fish were on collies."

So is there an explanation for this? Well, most anglers know that the majority of trout feeding occurs subsurface. Few however, realise how introduced trout have impacted on native fauna such as mayflies. Indeed recent studies have shown that as trout depend on visual cues to feed, they are more likely to forage during the day. Mayflies such as Coloburiscus have adapted to avoid predators by drifting, feeding (at least on the top of the substrate) and hatching less during the daytime.

This is what makes the Catlins so special - not only are there dense daytime hatches but also plenty of surface action. I was lured to the region on the advice of David Orr, who stumbled upon it a few years ago whilst looking for fishable early season water. A look at David's last season diary entries showed fast and furious collie action. And so it was to be. During my mid October visit, I fished a variety of Catlins rivers on no less than seven days, with each day providing collie angling like I had never seen before.

A look at the substrates of the Catlins rivers gave some clues to the hatches. The bulky Coloburiscus nymph was by far the most dominant invertebrate in the fast flowing cobbly sections of the rivers. A large proportion were mature late instar larvae with darkened wing pads indicating imminent emergence. But why do these rivers have such a healthy, numerous Coloburiscus population? Key factors must include the regular and reliable rainfall, ideal water temperature, a bouldery stable riverbed, and a reasonably unmodified catchment.

I encountered sparse numbers of duns on the water mid morning, but the hatch didn't really kick in until about 2 pm and gradually petered out several hours later. The best dun fishing was on overcast days, when the mayflies remained on the water longer to dry their wings. But it was not just wave after wave of duns sailing down and taking off, on the warm windless days the smooth slick pools were thick with spinners as well. If you ignored the trout for a minute and looked closely at the insects, you could see a distinctive bright orange egg sac beneath the female's tail.

And the trout played their part. Favourite areas to scan for rises were at the base of ripples just before the smooth glides where drifting nymphs tended to congregate. Various patterns were tried, from the traditional Kakahi Queen through to a yellow Humpy and a Royal Wulff tied with yellow floss. It seemed that the secret was in the touch of yellow. Indeed a gut analysis and several stomach pumps proved the obvious; the Cat-lins trout were feeding on various stages of the collie life cycle - nymphs, emergers and duns, wings crushed but yellow blotch obvious, even bright yellow broom flower buds.

Brown trout show plenty of colour and pattern variation and these were the prettiest fish imaginable; gleaming gold and bronze bars, with a smattering of brilliant red spots. Fish were taken up to 5 pounds with the average just under three. None of the monsters of the lower reaches, but the quality of fishing more than made up for it. Plenty of scrappy one pound trout too, although the decent fish occupied prime feeding positions and had obvious rise forms.

Given the colour of the water it's not easy to polaroid, so look for the rises. For those who arrive early, prospect the likely water with a nymph. I was there to enjoy the collies to the fullest and preferred to use patterns representing the mayfly's life cycle. A lightly weighted #12 Carty's Coloburiscus nymph provided great initial action - of course I did switch to a dry once the hatch proper began. My companion however, fished a dry throughout. These trout share a characteristic with their southern cousins; they are free risers and can usually be brought to the surface.

Don't be put off by the fishing guidebooks that point to the lower reaches or talk of logistical problems. Go and explore, there is miles of water, most easily accessible. It's a robust, healthy fishery with enough deep shaded pools to provide sanctuary during the infrequent summer droughts. But from what I hear the summer ushers in a new phase for the dry fly angler and as the mayfly hatches taper off, the terrestrial action really heats up. Apparently all the native bush cover and overhang leads to outstanding fishing, but then again, that's another story.

Carty's Coloburiscus

HOOK: TMC 3761 #12 (also #10 & #14, but #12 is the closest to the natural)
THREAD: Black
TAIL: Black Hackle Fibres
RIB: Dark Copper Wire
UNDER BODY: Lead wire, flattened
BODY: Dark brown dyed ostrich herl trimmed on the top and the bottom to accentuate the gills
WING CASE: Black Flexi Body or Umpqua Thin Skin
THORAX: Fine brown dubbing
LEGS: Black Accent Flash or Krystal Flash