The Giant Arapaima fish, a large, commercially-important species in the Amazon Basin, is now locally extinct in many regions around the area, according to biologists.

Bioeconomic theory is often used by national and local officials to determine how best to protect endangered fish populations. An international team of researchers compared this system to "fishing-down theory," which is premised on the idea that large fish that are easy to catch and valuable to humans can be harvested beyond the ability of the species to repopulate.

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

Three of the five known species of Arapaima have not been seen in the Amazon for several decades. The giant fish can grow to be 10 feet long and weigh up to 500 pounds. They spend between five and 15 minutes underwater at a time, after which the fish come to the surface to breathe. In that precarious position, the animals are often killed by fishermen hunting the highly-valuable animals. They were common in fisheries along the Amazon in the first years of the 20th Century, before populations plummeted.

Researchers interviewed 182 people known for being experts in local fish populations in 81 communities in the Amazon basin. Those volunteers report the animal has disappeared from 19 percent of the areas. Populations are depleting in 57 percent of the regions and the animals are being over-fished in 17 percent of the areas surveyed. Just one in 20 locations had well-managed populations of Arapaima, and only one in 50 regions was not utilized for fishing.

"Many previously over-exploited 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.

Researchers found populations of the giant fish were up to 100 times higher in areas where harvesting of the animals is regulated, compared to regions without such laws.

Regulations to protect the species are in place in just 27 percent of the locations examined in the study. São Miguel, one of the areas studied, prohibited the use of gill nets 20 years ago, and has the highest populations of the animals seen in the study.

Study of Arapaima populations was detailed in the journal Aquatic Conservation: Freshwater and Marine Ecosystems.