New records of nonnative signal crayfish Pacifastacus leniusculus in Nagano Prefecture with implications for multiple translocation pathways

Abstract

The North American signal crayfish Pacifastacus leniusculus was newly found in six waterbodies of Nagano Prefecture, central Japan, from 2011 to 2020. The waterbodies with new introductions included reservoirs, farm ponds and low-gradient streams within the altitude range of 670 - 1300 m. Analyses of ectosymbiotic branchiobdellidan (Annelida: Clitellata) species composition and mitochondrial DNA sequences of the crayfish suggest that the new invasions arose due to translocation via multiple pathways from inside and outside of Nagano Prefecture. Efforts to eradicate the newly established signal crayfish populations should be undertaken. At the same time, further efforts to stop illegal stocking are needed to prevent range expansions of signal crayfish.