The Great Survivors By Barry Moore
The outback, with its meagre and erratic rains, is a very unsympathetic environment for fish; few species survive there and those that do are only to be found in the most favourable places. However, one would hardly expect that the lush and well-watered rainforests of coastal tropical Queensland would pose similar problems, yet during the winter season of 1992, which was one of the driest on record, they did exactly that.
My property in this region forms part of an elevated ridge, for the most part covered in rainforest and attaining a maximum height of 550m, some 100 m above the surrounding (and largely settled) plain. The average yearly rainfall is about 1800 mm (72"), i.e. nearly three times as much as we get in Canberra. Numerous gullies carry temporary creeks during the wet summer season but these peter out as the rains decline and dry out completely during the winter, when the periodic light showers are not enough to provide the needed run-off to sustain them. Not surprisingly, fish are absent from these temporary creeks. However, at the base of the ridge, both on my side and the opposite one, on a friend's property, are spring-fed perennial creeks that I was for a while tempted to regard as permanent, and these present a very different picture.
To my delight, some years ago and soon after acquiring a toe-hold in the district, I detected thriving populations of the Northern Trout Gudgeon (Mogurnda mogurnda) in both creeks and of the Eastern Rainbow Fish (Melanotaenia splendida splendida), plentiful on my friend's place but with smaller numbers also on mine. Both species readily responded to a scattering of bread crumbs but the Gudgeon, being a bottom dweller rather than a free swimmer, seemed to prefer to feed on small pieces of cheese that immediately sank beneath the surface.
My irregular monitoring showed both species to have been present for several consecutive years until the drought commenced in mid-1992. Little by little, the flows decreased until, in August, they ceased altogether, at least upon the surface, and the creeks were reduced to a few isolated and rather murky-looking pools. By September the pools had also gone and the creek-beds appeared to be completely dry.
At this stage domestic water-bores were showing an ever descending water table and the rainforest trees responded with an unusually heavy leaf-fall. What, I wondered, had become of my treasured fishes?
The dry spell continued with little relief until December, when more than 500 mm (20") of rain suddenly renewed all systems and my creeks started to flow once more. I approached them with bated breath but the water was so cloudy that it was impossible to tell whether the fish had survived or not and I had to curb my curiosity until the end of the 1993 summer wet.
Now (August 1993), the creeks appear to be back to normal and I'm glad to report that thriving populations of the Gudgeon (including some quite large specimens) are still present, although the Rainbowfish have disappeared. The former, being bottom dwellers, presumably managed to survive in the few remaining damp spots under the creek beds but the free swimming Rainbowfish probably perished when the last pools dried out.
Although this drought was one of the worst on record, similar ones must have occurred in ages past and my creek has no doubt dried out many times before. Perhaps the Gudgeon has always been present, in active or passive form, but it seems likely that the populations of Rainbows come and go. Presumably they are replenished after such disasters by upstream migration from the safer havens of the larger river systems of the surrounding plain, for which the local creeks are merely feeders. I certainly hope so and I shall be keeping a keen lookout for the return of these beautiful fish.