Sterilization of the invasive crayfish Pacifastacus leniusculus (Dana, 1852) (Decapoda: Astacidea: Astacidae) through pleopod removal: persistence and potential for improvement

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Abstract
The signal crayfish, Pacifastacus leniusculus (Dana, 1852), has become established as an invasive species in freshwater ecosystems worldwide, causing severe ecological impacts. While effective control measures are urgently needed, sterilization via pleopod removal may represent a practical option. This study aimed to 1) evaluate the persistence of sterilization achieved through pleopod removal and 2) test whether the procedure could be simplified by unilateral removal (left side only), which approximately halves handling time. Because females rely on pleopods for brooding, we hypothesized that pleopod removal would persistently impair brooding, and that unilateral removal would still produce strong effects. Laboratory experiments were conducted using crayfish collected from the Toyohira River, Sapporo, Hokkaido, Japan between July 2023 and January 2025. Brooding ability declined markedly following pleopod removal. The evidence suggests persistent inhibition of brooding, with egg-carrying reduced by 97.0% in the first reproductive season and showing sustained suppression in the second. This sustained inhibition is attributed to incomplete pleopod regeneration through molting (3.5% in the first year and 40.2% in the second). Females dropped most eggs immediately after oviposition and lost all eggs within two weeks. Partial pleopod removal was technically inadequate, as its sterilization effect relative to effort was inferior to that of complete removal. These findings suggest that complete pleopod removal is a promising sterilization method for invasive crayfish, but further field studies are required to evaluate its effectiveness under natural conditions.

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