Limnetica 35

We examined the past, present and predictable status of diadromous fishes on the Iberian Peninsula, with a focus on the species inhabiting the Minho River. Data on six diadromous species (five anadromous, one catadromous) were collected. Due to population extinction and abundance reductions, many species are now classified as threatened or endangered. Many populations persisted at only drastically reduced abundance levels. Habitat loss (especially damming), overfishing, pollution and, increasingly, climate change contributed to this decline of diadromous fish. Although there is still limited information on the conservation status, migratory behaviour, biology and ecology of diadromous fish in the Iberian Peninsula, and except for Sea lamprey, which have shown a recent rise in population size in some rivers, it is clear that diadromous fish populations are showing a general trend towards decline. Overall, Iberian diadromous species have suffered a great decline since the 20th century. Although Iberian Sea lamprey populations are not critically endangered or endangered, they are facing a high risk of extinction in the wild in the medium-term future. Atlantic salmon populations experienced the first serious decline in the 19th century, and the decline has continued during the 20th century. Despite the importance of Sea trout in Galician (NW Spain) and North Portugal, to date, few studies have been performed. The reduction in the Portuguese Sea trout populations may have reached 98% of the number of mature individuals. Allis and Twaite shads were, at times, of large economic importance, but currently, some Iberian populations are severely extirpated. For example, in the Minho River, the catches have decreased by about 90% since the 50th decade of the 20th Century. In the Iberian Peninsula, eel disappeared from important Iberian catchment areas, and during the 1980s, commercial fishing showed a downward trend. As most of the larger Iberian rivers cross international borders, the management and conservation of migratory fish species on transboundary rivers should be based on international cooperative and concerted efforts.