some districts, the decline prompted a temporary ban on mink hunting to let the population recover. In the early 20th century, 40–60,000 European minks were caught annually in the Soviet Union, with a record of 75,000 individuals (an estimate which exceeds the modern global European mink population). In Finland, annual mink catches reached 3000 specimens in the 1920s. In Romania, 10,000 minks were caught annually around 1960. However, this reason alone cannot account for the decline in areas where hunting was less intense, such as in Germany. Decline of crayfish The decline of European crayfish has been proposed as a factor in the drop in mink numbers, as minks are notably absent in the eastern side of the Urals, where crayfish are also absent. The decline in mink numbers has also been linked to the destruction of crayfish in Finland during the 1920s-1940s, when the crustaceans were infected with crayfish plague. The failure of the European mink to expand west to Scandinavia coincides with the gap in crayfish distribution. Competition with the American mink and disease The American mink was introduced and released in Europe during the 1920s–1930s. The American mink is less dependent on wetland habitats than the European mink and is 20-40% larger. The impact of feral American minks on European mink populations has been explained through the competitive exclusion principle and because the American mink reproduces a month earlier than the European species, and matings between male American minks and female European minks result in the embryos being reabsorbed. Thus, female European minks impregnated by male American minks are unable to reproduce with their conspecifics. Disease spread by the American mink can also account for the decline. Though the presence of the American mink has coincided with the decline of European mink numbers in Belarus and Estonia, the decline of the European mink in some areas preceded the introduction of the American mink by many years, and there are areas in Russia where the American species is absent, though European mink populations in these regions are still declining. Diseases spread by the American mink can also account for the decline. Twenty-seven helminth species are recorded to infest the European mink, consisting of 14 trematodes, two cestodes and 11 nematodes. The mink is also vulnerable to pulmonary filariasis, krenzomatiasis and skrjabingylosis. In the Leningrad and Pskov Oblasts, 77.1% of European minks were found to be infected with skrjabingylosis.