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.