Fisheries research has ‘global implications’ for water use

New freshwater fisheries research has ‘global implications’ for water use
– Trout and native fish need more water than we think, research finds.

Science has now provided evidence for what many anglers have suspected for years: taking water from rivers is risky for some fish, and we may have been short-changing them and their food sources in the past.

For the past 15 years a team of Cawthron Institute freshwater scientists has been investigating the stream flow requirements of trout, which drift-feed on small aquatic and terrestrial invertebrates (such as mayflies) drifting in and on the water. Their research shows that these fish have higher flow requirements than present models allow for. The principles learnt also apply to other drift-feeding fish, including juvenile salmon and native species – such as some whitebait.

“The aim of this research is to provide knowledge and predictive models for assessing the effects of flow change on trout, and other drift-feeding fish, to assist decision making on minimum flow and water allocation limits setting,” project leader and Cawthron freshwater fisheries scientist Dr John Hayes says. “A river acts like a conveyor belt delivering the drifting food to the waiting fish. 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.” Read full article on Cawthron Institute website

Global implications

The teams’ findings were published in April this year in an international scientific journal of the American Fisheries Society. Dr Hayes says the new knowledge has global implications for irrigation and hydro-electric development, and recreational fishing. In New Zealand, regional councils may need to revise minimum flows upward and water allocation limits downward.

“The environmental, social and economic consequences are far-reaching,” he says. “Fish & Game and the Department of Conservation have a better case for arguing for precautionary flow decisions, but tighter limits on taking water will be challenging for farmers and a government committed to sustainable economic growth.”

Southland and Otago regional councils have already begun to use the model, dubbed the ‘Hayes drift-NREI’ (net rate of energy intake) model, to revise their minimum flow rules. Dr Hayes says freshwater fisheries scientists in the United States have also been quick to realise its potential, using it in a multi-million dollar research programme on endangered salmonid populations, and how to restore them, in the Columbia River catchment.

Dr Hayes says while they have closed the gap in knowledge there is still some work to do if we want to be sure we are using our water efficiently.

“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 says. “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. If we can develop models that do that, then these tools together will enable much more precise minimum flow and water allocation limits setting in the future.”

A team effort
Dr Hayes worked with Cawthron colleagues Karen Shearer, Eric Goodwin and Joe Hay on the project, as well as scientists from the United States.
The research has been supported by the Ministry of Business, Innovation and Employment, Fish & Game New Zealand, University of Alaska Fairbanks, Bureau of Land Management Fairbanks; Environment Southland; Cawthron Institute; and more recently NIWA has been a major funder under its core-funded Sustainable Water Allocation Programme. Cawthron and NIWA are currently collaborating on developing further models.

Find out more:
Read full article on the Cawthron Institute website
Watch this 7 second video clip of a trout feeding
View the research published in the Journal of the American Fisheries Society

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