Fish feeding study revises int'l understanding of rivers: New Zealand scientists

Taking water from rivers for farming and other uses ends up starving freshwater fish, New Zealand scientists said Friday.

A study by the independent Crawthron Institute, which found that rivers act like a "conveyor belt" delivering food to fish, had global implications for water use, project leader and Crawthron freshwater fisheries scientist Dr John Hayes said.

The 15-year study of the stream flow requirements of trout, which drift-feed on small aquatic and terrestrial invertebrates drifting in and on the water, showed that these fish had higher flow requirements than present models allow for.

The principles also applied to other drift-feeding fish, such as juvenile salmon, Hayes said in a statement.

"We've now shown that as flow declines, the diminished power and transport capacity of a river results in less drifting food. A new computer model that our team developed predicts that this translates to fewer, or more slowly growing, fish," he said.

The new knowledge had global implications for irrigation and hydro-electric development, and recreational fishing.

"The environmental, social and economic consequences are far-reaching," said Hayes.

"Now that we've advanced the ecological realism of modelling potential flow requirements of fish, we now need to tackle the really difficult question of how to measure the carrying capacity (food and space) of rivers and when and where fish are abundant enough to fill the carrying capacity," he said.

"The rationale being, that if factors other than low flow are limiting the numbers of fish, then there is scope to allocate water out of streams without harming the fish." Endit