By Jan TenBruggencate
Advertiser Columnist

Twenty-five years ago, it seemed that Hawai'i might be covered with inland ponds growing prawns.

The big, tasty crustaceans seemed to grow well, sold at a good price, and ponds were being dug on most of the islands — sometimes on a big commercial scale and sometimes in back yards.

The ponds were a concern to some folks because of their demand for fresh water and the issue of the nutrient-rich outflows, although a few growers added papaya fields and other crops to make the rich wastewater for irrigation and save on fertilizer costs.

Where have the ponds gone?

University of Hawai'i professors Arlo Fast and PingSun Leung, in a paper published in the journal "Reviews in Fisheries Science," said that by 1983, sales reached $3.3 million statewide, with more than 800,000 pounds of production.

Only four years later, even as prices for prawns continued to rise, the production collapsed to 100,000 pounds, and had dropped to the neighborhood of 40,000 pounds in recent years.

Fast and Leung said a lot of the pond operations were based on the assumption that you could get close to 3,000 pounds per acre a year from the prawns. Even at the 20-years-ago price of $3.50 a pound, that meant a 10-acre farm could gross more than $100,000.

But when people got into growing the prawns, they found that in most places, they couldn't achieve anywhere near those yields. They averaged less than half the promised yields — enough of a difference that lots of prawn farmers dropped out of the business. Even when prices nearly doubled, most farms weren't profitable, Fast and Leung concluded.

Researchers achieved the high yields on small test ponds in the early 1970s, but when production was ramped up to a commercial scale, yields dropped.

Plus, growing prawns wasn't any easier than most other kinds of farming. There were problems with birds eating the prawns, with tilapia getting into ponds and competing with the prawns, with growth rates dropping when water temperatures dropped, and with tail flesh softening if not handled very carefully.

Ultimately, too, markets preferred marine shrimp to the freshwater version.

"If the original yields had materialized, the industry would have made it, I think," Leung said.

The remaining prawn farms in the state tend to be small operations, with specific markets such as restaurants.

"There is room for a small niche market," he said.

Most operators have another crop or another job to make ends meet, Leung said.

If you have an issue, question or concern about the Hawaiian environment, drop a note to Jan TenBruggencate, The Advertiser's Kaua'i Bureau chief and its science and environment writer. Reach him at at jant@honoluluadvertiser.com or (808) 245-3074.