Is Overfishing the Main or Only Factor in Fishery Resource Decline? The Case of The Magdalena River Fishery and Its Correlation with Anthropic Pressures.

Overfishing has been historically considered as the main cause of fish stock depletion worldwide. This paradigm has oriented fishery management towards a classical approach, under which externalities to fisheries were not considered as they were difficult to assess and measure. The aim of this study is to describe the dynamics of different environmental, economic, and demographic variables (water flow, forest cover, gold production, population growth, stored water volume, and sediments) in relation to the behavior of the fishery production in the Magdalena-Cauca river basin from 1980 to 2015. Generalized Additive Models were used to determine the variables that best explain fishery production. The findings confirmed that environmental deterioration of the Magdalena River basin explained at least 60% of the reduction in fishery production. Thus, we concluded that the traditional approach of making fishers responsible for the decline of fish production was a misguided argument, and before implementing restrictions on fishing activity, a better understanding of the overall system is crucial. Hence, fishery management should involve the economic and social sectors that affect the offer of ecosystem services within the basin, including fishing.