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The Honolulu Advertiser
Posted on: Monday, February 24, 2003

HAWAI'I'S ENVIRONMENT
Diversions may take toll on aquatic life

By Jan TenBruggencate
Advertiser Columnist

What happens to a stream when you divert water from it?

That's been a subject of a great deal of controversy in the Islands. Clearly, there's less volume downstream and thus less habitat for downstream fishes. Water temperature is likely to be a little warmer. Less water is available for downstream users, such as taro farmers.

On the other end of the balance, the diverted water can improve the economy across large areas, opening dry areas to large-scale agriculture and making possible residential and industrial uses that might not otherwise work in those areas.

A new study suggests the costs to the natural world of stream diversions may be greater than many people may have guessed.

Eric Benbow, a Michigan State University researcher working with Earthwatch Institute volunteers and others, conducted studies in Maui's '?ao Stream, and published their results late last year in the journal River Research and Applications.

From April to August 2000, they found that 92 percent to 97 percent of the stream's daily flow was being diverted out of the stream bed. They found that for those forms of life called macroinvertebrates — insects, crustaceans and snails — abundance below the major diversion was much different than above it.

Several groups of creatures existed above the diversions, but disappeared below it. They include the shrimp known as 'opae kala'ole, a small fly and a kind of tiny crustacean called an amphipod.

The aquatic forms of other small creatures, the most common of which were a midge and two species of caddisfly, were found both above and below the diversions, but the density of streamlife below the diversions was less than half of that above the diversions, the researchers found.

"Reduced stream flow lowers the velocities and depth important for many of the endemic and native stream species that are rheophilic, preferring fast-moving water, such as fly larvae," Benbow said.

Benbow says most folks don't care much about midges and amphipods, which he calls uncharismatic. By contrast, folks like larger creatures such as the edible native stream fishes — several varieties of gobies collectively known as 'o'opu.

A variety of factors may be responsible for the decline in the once-famous abundance of 'o'opu in Hawaiian streams. Benbow's work suggests diversions are significant issues in streams.

"When the densities of these non-charismatic critters are reduced, this has negative effects on the food resources for the more charismatic critters, such as fish found nowhere else in the world but Hawai'i," he said.

Jan TenBruggencate is The Advertiser's Kaua'i bureau chief and its science and environment writer. Reach him at (808) 245-3074 or jant@honoluluadvertiser.com.