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We studied life cycle of stone crayfish for 18 months in three streams on Medvednica Mountain, located above city of Zagreb. Sampling of animals was carried out with baited traps twice a month and various physiological functions were recorded. Sex ratio of trapped crayfish was 1:1, but it fluctuated during the year. Animals were active from early spring until the beginning of November when their activities significantly decreased. In this period we noticed three peaks of higher activity. The first one after winter starvation in March, the second one after egg hatching (June/July) and the third one during mating period (end of September - beginning of November). The maximal recorded weight for female was 38 g while the heaviest male was 55 g. The longest female was 9.28 cm and male 10.30 cm. Development of glair glands started from the end of July, mating occurred at the end of October and the juveniles hatched until mid-June. Freshly moulted animals were found from mid-May until mid-October. Main injuries were claw and limb loss. We noticed the presence of burn spot disease and Branchiobdella parasita Henle within studied populations. Correlation with five different physico-chemical parameters of water showed that animals’ activity is positively correlated to water temperature, conductivity, pH and hardness and negatively to oxygen concentration.

The presence of the signal crayfish, Pacifastacus leniusculus, in waterbodies of Europe is of high concern due to its potentially major ecological impact on invaded ecosystems and native crayfish. In this study, we examined population characteristics and spatial dynamics of a recently established signal crayfish population near the edge of its invasive range in the Mura river (Croatia), by analyzing population density, fecundity, and sex and size structure, as well as movement patterns. The obtained results revealed that the examined population is characterized by relatively low population density, balanced sex and size structure of adult crayfish, and high spatial activity of examined individuals, with an average daily movement of 28 m/day. Pleopodal fecundity was in a similar range to other signal crayfish populations in Europe. The large minimal size of caught mature females (85 mm total length), coupled with the estimated low population density (0.8–1.2 crayfish.m-2), suggested that the examined population has not reached its maximum density yet. Obtained results represent baseline information for the development of monitoring procedures and management strategies aimed at signal crayfish control within the Mura and Drava catchments and also highlight the importance of understanding local factors controlling invasive species’ population dynamics and productivity.