Reproductive performance of Helix pomatia (Gastropoda: Pulmonata: Helicidae) and survival of its hatchlings under farm conditions

The reproductive ability of 1254 breeding individuals of Helix pomatia originating from a local wild population were studied. Reproduction was carried out in a greenhouse at a stocking density of 51.2 breeding snails per m2. The reproductive season was 83 days long. From 30 May to 21 August 2003 almost all the snails laid eggs at least one time, but 25.1% of the snails laid eggs twice, and 5.2% laid eggs three times. The mean number of eggs per clutch for all the breeding snails was 41.7. Because of the multiple laying of eggs, the number of eggs laid in the 2003 season averaged 61.5 per breeding snail, and the eggs' total biomass constituted 38.5% of the biomass of all breeding individuals. A significant (P < 0.05) increase in egg laying was found from 30 May to 21 July. This period was followed by a rapid decline in reproductive intensity, until egg laying ceased on 21 August. Breeding snails laid 77100 eggs, out of which 40000 eggs hatched. From the hatched eggs 27000 two-to-three-week-old hatchlings were obtained. Of the obtained hatchlings 15000 were released into a greenhouse; 32.0% of these individuals survived winter hibernation in a pen. In May of the next year, the 4800 hatchlings were released into a field pen, at a density of 260 specimens per m2. They reached a mean body mass of 19.1 g and mean shell diameter of 30.1 mm in July. The rapid rate of growth observed under farm conditions allows us to propose a two-year farming cycle for this species, from hatching to the stage of sexual maturity.