Long-term studies on sex and size structures of the non-native crab Eriocheir sinensis from Polish coastal waters

The Chinese mitten crab Eriocheir sinensis is a non-native species that appeared in European waters more than 100 years ago. Size and sex structure as well as biological condition of populations of Eriocheir sinensis sampled annually between 1999-2014 from the eastern Baltic Sea coast (1999-2007 Gulf of Gdansk and 2008-2014 Vistula Lagoon, Poland) were analysed. Males were dominant over females, with a sex ratio of 1.6:1. Carapace width of all collected specimens (n = 467) ranged from 33.3 to 89.1 mm and the mean values for specimens from Gulf of Gdansk and Vistula Lagoon were 62.4 +/- 8.1 mm (n = 171) and 66.6 +/- 7.7 mm (n = 296) respectively. There were no statistically significant differences in carapace width between males and females. It is important to note that there were no individuals with a carapace width less than 30 mm, which may indicate a lack of an established population of this species from the eastern Polish coast. The wet weight of all specimens ranged from 30.9 to 321.9 g and the mean values for all specimens from the Gulf of Gdansk and the Vistula Lagoon were 119.4 +/- 45.2 g (n = 101) and 141.8 +/- 47.9 g (n = 223), respectively. The wet weight of an individual was significantly correlated to carapace width and the exponent b reaching values close to 3 may indicate their good condition.