Range extension in 1967 of the alien amphipod, Gammarus tigrinus Sexton, 1939, in the Netherlands

The range extension of Gammarus tigrinus in The Netherlands slowed down in 1967 to a gain of no more than 2 or 3 kilometers in the north – eastern and south – eastern parts of the distribution area, and to some 18 kilometers in the south – western part. The invader reached in 1967 the provinces of South Holland and Utrecht.