Tracking Trout

Dr Gerry Closs
Dr Gerry Closs
Understanding the habits and behaviour of the wily brown trout is one of the great sports-fishing challenges of the South Island, attracting anglers from all over the world.

Some of this game fish's movements have been largely a mystery to science in the past, but recent advances in laser technology have given Department of Zoology fisheries scientists fresh insights into the life cycle and migration patterns of brown trout.

The key is a new technique of analysing trace element "fingerprints" from a crystal of calcium carbonate (otolith) in the heads of fish, that records the subtle changes in chemical composition of their environment throughout their lives. It is the first time the technique has been used for brown trout recruitment studies.

Fisheries scientist Dr Gerry Closs and his research students say understanding the movements of brown trout populations is crucial for making informed decisions about the fishery and habitats.

"It allows you to identify which are the important spawning streams within the fishery, migratory patterns, issues of fish passage, which streams are suitable for agriculture or hydro-electric power schemes and which streams you need to protect," he says.

"It gives a very precise picture of the way fish are moving around within a catchment, whereas before it would have been only guesswork. Now we actually have hard data."

Researchers have completed major studies on the Taieri and Motueka Rivers and have recently begun another study on the upper Clutha River catchment.

FUNDING
Fish and Game New Zealand
Clutha Fisheries Trust
University of Otago Research Grant

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