Range extension of the alien amphipod Gammarus tigrinus Sexton, 1939, in The Netherlands, in 1971

After the introduction of the Gammarus tigrinus in the Netherlands around 1964, the species developed explosively in the IJssellake and invaded large parts of the surrounding provinces. The dispersal was carefully recorded in previous papers. A survey in 1971 showed considerable range extension in the northern provinces, in the lake district of Loosdrecht (prov. of Utrecht), and in the isle of Voorne (prov. of South – Holland).