Population structure, morphometry and individual condition of the non-native crab Rhithropanopeus harrisii (Gould, 1841), a recent coloniser of the Gulf of Gdańsk (southern Baltic Sea)**This research was funded by the Polish National Science Centre, grant No. 3016/B/P01/2011/40.

The aim of this study was to characterise the introduced North American Harris mud crab Rhithropanopeus harrisii, which occurs in the Gulf of Gdańsk, Poland (southern Baltic Sea). Of the 920 specimens caught between 2006 and 2010, males and females made up 44 and 40% respectively, whereas juveniles (< 4.4mm carapace width) comprised 16%. Overall carapace widths ranged from 1.96mm to 21.40mm (mean 9.03±4.11mm). Ovigerous females (mean 11.12±2.76mm) were present in the population from June to October. Most of the adult specimens collected (n=158) had carapace widths between 10.1 and 12.0mm. The wet weight of R. harrisii varied from 0.005 to 4.446g (mean 0.410 ± 0.569g). Females exhibited a negative allometric increase in weight (b=2.77), males an isometric increase in weight (b=3.02). The condition factor (K) in R. harrisii varied from 0.02 to 0.08 (mean 0.05±0.01)