Diadromous fish in Portugal: status, threats and management guidelines

Abstract

Diadromous fish evolved in a way to use two completely different environments during their life-cycle (i.e. river and sea), being divided in anadromous (e.g. sea lamprey, shads) and catadromous (e.g. eel, thinlipped grey mullet) species, if their reproduction occurs, respectively, in freshwater or marine environments. In Portugal, the high commercial value associated with these species makes them primary targets for traditional fisheries, which need proper management to avoid overfishing and guarantee the long-term survival of their populations. loss of river connectivity, caused by the construction of dams and other hydraulic infrastructures, also contributes to the decrease in population numbers of diadromous species, a scenario that is oen exacerbated by the associated river flow regulation, water scarcity and the climatic changes occurring at a global level but with special intensity in the Iberian Peninsula. e high complexity and territorial scope of these threats demand the development of suitable and integrated measures for the conservation and management of diadromous fish. e scientific component can act as a link between all the stakeholders involved in these processes, namely the local and central administration managing rivers basins and fisheries, commercial fishermen, private promotors and general public. e work being developed in the Mondego river basin for the past 20 years, and which recently begun to be replicated in the vouga river basin, represents a valuable and decisive contribution to the recovery of diadromous fish populations in Portugal. Habitat rehabilitation and management of commercial fisheries can act in synergy, allowing a sustainable exploitation of these valuable resources.