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IN LITTLE STREAMS
Anglers focus on bigger streams when in pursuit of trout because this is where they live. Any water course less than about 3 meters wide and 50 centimeters deep holds very few large trout in the summer. In the winter large trout find their way into these rivulets to lay their eggs. In doing so they expose themselves to risk from predators from above. They need to find streams with some shelter so they can hide while they are going about the business of laying eggs.
Big trout need to make this journey into danger because little trout hatch from their eggs and these fish need little streams. There they find plenty of edge habitat - overhanging vegetation and places to shelter from the current and a stream of food traveling by only a few centimeters away. In these streams the water needs to be shallow and fairly swift, with biggish rocks, again to hide amongst and where lots of stream insects live. Few little trout are found in big rivers because that is where big trout live and big trout eat little trout. Other big things eat little trout too. Big eels and kokopu, shags and herons. But where the stream is narrow and swift, shallow and rocky these big animals cannot fit. They cannot see the little trout amongst the bustle of the water's flow so little trout are safe.
Safe at least from traditional enemies. Enemies they have learned to live with for millions of years. But when little streams become polluted or dried up, or warmed up, or cut off altogether little trout die. These fish can live in very high densities, maybe 30 or 40 in ten metres of stream. If a hundred metres of stream is cut off from its flow hundreds of trout die. Often little native fish live amongst the trout. River galaxiids, cousins of the whitebait, and upland bullies, freckle faced, with orange fringed fins, all finding a home in the swift shallow water for the same reasons trout do. If a bulldozer pushes the riverbed about and redirects the flow more trout die than can be eaten by a dozen shags, or big dark eels.
Little streams can become filled with plants; water weeds growing in profusion, under bright sun which warms and energises their production system. These plants smother the swift parts of the stream and turn it into a deep, slow, silty channel. They drive little trout out, as well as blocking farmers' drains. But shady trees growing along the river bank starve the plants of sunlight and allow riffles to remain, along with their trout.
Little streams are the lifeblood of our trout fisheries, when they glisten trout anglers' hopes grow, and they tell the world that we care about the land we live in.
Maurice Rodway
Southland, New Zealand E-mail: fishgame@southnet.co.nz Article ©1998 Maurice Rodway, All Rights Reserved. |
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