Temporal trends in non-indigenous freshwater species records during the 20th century: a case study in the Iberian Peninsula

Galicia (NW Spain) is a region with a high number of freshwater endemics, and probably the best preserved area concerning fish populations in the Iberian Peninsula, where records of non-indigenous freshwater species are recent when compared to the rest of the Peninsula. Detailed analysis of introductions of those species with records after 1900 present in both areas shows that delays were up to 100 years for species introduced on the Iberian Peninsula at the beginning of the twentieth century, but the tendency adjust to a decreasing linear regression, with species introduced after 1995 being almost immediately present in Galicia. We underline the outstanding role of aquarium trade on these results. Analysis of temporal trends highlights several periods with numerous introductions, and shows a different trend in the last decade depending on the group of organisms, with a clear deceleration in introduction rates of vertebrates, but a continuous growing trend for invertebrates. Recent educational programs might be responsible for the reduction in the inflow of vertebrates, but there is still a need for the control of less conspicuous but equally harmful invertebrates and plants, as it will take longer to make both stakeholders and public aware of their detrimental effects on their new habitats.