Giant Amazon fish 'locally extinct' due to overfishing
A 10ft (3m) long fish which used to dominate the Amazon river has been fished to extinction in a number of areas, scientists have revealed.
Arapaima populations were found to be extinct in eight of the 41 communities studied, and extremely low on average.
Fishermen were trained to count the fish as part of a large-scale survey.
Researchers concluded that the effects of fishing on tropical fish was worse than previously thought.
Study results are reported in Aquatic Conservation: Freshwater and Marine Ecosystems.
Arapaima can weigh more than 28st 8lb (181kg) and are among the largest freshwater fish in the world.
They are air-breathing and come to the surface every five to 15 minutes, making them easy to catch.
Their size means they are highly sought after and are landed by fishermen using harpoons and gillnets.
A century ago the giant fish dominated fisheries in the Amazon but the researchers say overfishing has dramatically reduced their numbers.
Previously, bio economic theory predicted that fishing does not cause extinctions because fishermen inevitably move away from depleted resources.
Scientists, led by Dr Leandro Castello, from Virginia Tech, US, wanted to know how healthy the arapaima populations in the Lower Amazon region were.
They also wanted to find out whether these fisheries supported bio economic predictions or the alternative fishing-down theory which predicts that large, high-value, easy-to-catch fish will be fished to extinction.
The researchers interviewed 182 fishermen, who were considered to be "experts" on fisheries by their colleagues, in 81 communities covering 401.5 square miles (1040 kilometres squared) of Amazonia floodplains.
Fish counts were also carried out in 41 of those communities where interviews had been carried out. Eight fishermen were trained to count the arapaima at the moment they surfaced for air.
The census revealed that arapaima populations were depleted in 57% of the survey area, locally extinct in 19%, over-exploited in 17%, and well-managed in just 5%.
In 2% of the communities they were un-fished.
In addition to the census results, more than three quarters of the fishermen questioned said that arapaima numbers had decreased in recent years.
Almost a quarter of the fishermen in each community fished arapaima regardless of the population's status.
The research team say the results contradict conventional economic thinking and instead support "fishing-down" predictions.
End Quote Dr Leandro Castello Virginia Tech
Many fishing-induced extinctions in the tropics are going unnoticed because of lack of data”
Dr Castello said: "Mainstream thinking has predicted that scarcity would drive up price, which would increase fishing costs and help save depleted species. But that is not what has happened."
He said because the tropics contain many species of fish living together, there is no way to avoid catching arapaima.
"Fishers continue to harvest arapaima regardless of population depletion. When the mature, large fish are gone, gill nets are used to harvest small fish and these capture juvenile arapaima as well. Eight communities report zero arapaima," Dr Castello added.
Only 27% of the communities studied have management rules for arapaima harvests. But those that did have rules that were followed by fishermen were found to have larger fish stocks.
"Many fishing-induced extinctions in the tropics are going unnoticed because of lack of data, illegal fishing, and lack of economic alternatives for the fishers," Dr Castello said.
"The time has come to apply local ecological knowledge to help assess populations, document practices and trends, and solve problems through user participation in management and conservation."
He added that community management for arapaima is now being developed and implemented in the region.
"There is willingness among fishers to implement management, but our efforts require more support from governmental agencies," he said.