June 13, 2011
Aquatic Conservation: Marine and Freshwater Ecosystems - early view
- Science and policy worldwide are influenced by predictions from bioeconomic theory that fishing cannot lead fish populations to extinction because fishing effort inevitably moves away from depleted resources. Yet such predictions contradict evidence of fishing-induced extinctions and in particular a model, called ‘fishing-down’, that explains historical reductions in mean size of harvested species in tropical multispecies fisheries through the gradual depletion and extinction of large-bodied species.
- This study analysed data on fisheries for Arapaima spp., the most historically important and overexploited fishes of the Amazon Basin, to evaluate whether they supported bioeconomic or fishing-down predictions. The evaluation was based on census data on arapaima populations and interview data from 182 fishers with respect to fishing practices and management regulations, which were collected in 81 fishing communities covering 1040 km2 of Amazonian floodplains.
- Arapaima populations were found to be ‘depleted’ in 76% of the fishing communities, ‘overexploited’ in 17%, ‘well-managed’ in 5%, and ‘unfished’ in only 2%. Population densities were zero (i.e. locally extinct) in 19% of the communities. Twenty-three per cent of the fishers in each community harvested arapaima regardless of population status. Similarly, the percentage of the catch in compliance with the size regulation did not vary with population status, but compliance with the season regulation in communities with ‘overexploited’ or ‘depleted’ populations (72%) was lower than in communities with ‘well-managed’ or ‘unfished’ populations (97%).
- These results support fishing-down predictions that fishing pressure continues to occur even when fish populations are depleted. The fishing-down process appeared to occur because of low gear selectivity and larger body-size of target species as well as high species value and low fishing costs. These results and available data elsewhere suggest that fishing-induced extinctions are more common than previously thought, endangering biodiversity and ecosystem functioning. Such extinctions are probably going unnoticed because high levels of illegal fishing, geographic heterogeneity, and data scarcity make their identification difficult.
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