Henrik Thurfjell of SLU ArtDatabanken said measures begun in the 1960s and 1970s have allowed the otter to be classified as viable and that the white-tailed eagle and the long-legged frog have also been reclassified as viable.The latest Red List update notes that the otter's recovery reflects decades of conservation while warning that high levels of environmental pollutants measured in otters and lingering uncertainties about reproduction leave the species' long-term trajectory unclear.Several other species are in much worse condition: the European eel remains critically endangered, herring, salmon and trout have been added as near threatened, and several common butterfly species were red-listed after rapid declines; the Red List was compiled by the Swedish University of Agricultural Sciences with about one hundred experts.