Size structure, maturity size, growth and condition index of stone crayfish (Austropotamobius torrentium) in North-West Croatia

Abstract

Austropotamobius torrentium (Schrank, 1803), the smallest species of freshwater crayfish from the family Astacidae, is considered a vulnerable species, protected by international laws. Since it has never been economically important, it has not been frequently studied. Therefore, the results presented in this paper are a contribution to the knowledge on stone crayfish’s population size structure, size at maturity, growth, and condition index throughout the year, as a possible tool for evaluating protection and restocking measures of this threatened species. The research included three stone crayfish populations with 1492 specimens in the “Medvednica” Nature Park, north-west Croatia, during a period of 18 months. In all the populations studied, crayfish of a total length between 5 and 8 cm prevailed. Activity of different size classes had a seasonal pattern that could be connected to different crayfish activities throughout the year. Appearance of sexual maturity within the populations coincides with the crayfish total length between 5 and 6 cm, after which allometric growth of males’ claws was recorded. On average males gain 0.42–0.72 cm and 2.65–4.30 g per moult, while females gain 0.44–0.70 cm and 2.04–3.83 g. Crayfish condition varied throughout the year with, in general, both juvenile and adult males having higher condition indices than juvenile and adult females in all three populations. In addition, adult crayfish were in significantly better condition in the autumn, whereas juveniles had higher condition indices in the summer.

Keywords

• stone crayfish
• growth
• maturity size
• condition index
• Croatia