Studies on the round-mouthed whorl snail Vertigo genesii (Gastropoda: Vertiginidae) in northern England: observations on population dynamics and life history

Studies were carried out to investigate the wide-scale and small-scale distribution of Vertigo genesii (Gredler, 1856) in an area of Widdybank Fell in northern England over the period 2000 to 2003, to identify the critical features of the habitat that are essential to the survival of the snail, and to investigate the life history of V. genesii, in particular to determine significant times of the year for reproduction. This paper presents the results on the part of the project covering life history studies. There was an increase in abundance of V. genesii from August through to November in both 2000 and in 2002 although there was considerable variation throughout the study period. There was no defined time of year for a major reproductive event. Juveniles were present throughout the year and on average they comprised 55% of the population. Juvenile mortality was high. There does not appear to be a strong correlation between weather conditions and the species' reproductive cycle.