A giant Amazon fish that was once extremely prevalent has gone extinct in certain fishing communities. 

To make their findings the Virginia Tech research team compared mainstream bioeconomic theory (which has been largely relied on to protect fish populations) with the less popular "fishing down" theory (which predicts that large, high-value and easy to catch fish can be driven to extinction). 

"Bioeconomic thinking has predicted that scarcity would drive up fishing costs, which would increase price and help save depleted species," said study leader Leandro Castello, an assistant professor of fisheries in Virginia Tech's College of Natural Resources and Environment. "If that prediction were true, extinctions induced by fishing would not exist, but that is not what has happened."

The research was conducted on the giant arapaima, which is typically about 10 feet long and can weigh as much as 400 pounds. 

"Arapaima spawn on the edges of floodplain forests and come to the surface to breathe every [five] to 15 minutes, when they are easily located and harpooned by fishers using homemade canoes," said Caroline C. Arantes, a doctoral student in wildlife and fisheries science at Texas A&M University and an expert on fish biology and fishery management.

The fish dominated the local fishing industries a century ago, but three of the five species have completely disappeared for decades. The research was based on 182 fishers in 81 communities. The data suggested the fish are extinct in 19 percent of communities and approaching extinction in 57 percent. 

"Fishers continue to harvest arapaima regardless of low population densities," Castello said. 

When the large fish are not available fishers use gill nets to capture smaller species, and can remove juvenile arapaima as well. On the bright side, some communities have been implementing fishing rules to protect this species, such as imposing minimum capture size and restriction gill net use; only 27 percent of the communities surveyed have these rules. 

"Because tropical regions suffer from widespread illegal fishing and a lack of data, these findings suggest that many similar fishing-induced extinctions likely are going unnoticed," Castello said. "There is also a lack of economic alternatives for the fishers."

The researchers hope the trends can be reversed in the future. 

"Many previously overexploited arapaima populations are now booming due to good management. The time has come to apply fishers' ecological knowledge to assess populations, document practices and trends, and solve fisheries problems through user participation in management and conservation," Castello said.

The findings were published in this week's edition of Aquatic Conservation: Freshwater and Marine Ecosystems