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Homing, dispersal and mortality after translocation of long-lived land snails Placostylus ambagiosus and P. hongii (Gastropoda: Bothriembryontidae) in New Zealand

Stringer, Ian Alexander Noel, Parrish, Glen Richard, Sherley, Gregory Howard
Molluscan research 2018 v.38 no.1 pp. 56-76
Gastropoda, cliffs, fauna, genetic variation, habitats, islands, mortality, philopatry, radar, snails, transponders, New Zealand
Between 1997 and 2003 mortality and yearly movements including homing (philopatry) of long-lived Placostylus ambagiosus and P. hongii land snails were studied when left in situ or exchanged between nearby sites in New Zealand. Harmonic radar transponders, attached to shells, increased recapture rates but might have increased emigration. Manipulation (translocation exchanges vs. control) caused no detectable changes but sample sizes were small. At Cape Maria van Diemen, 20% of P. ambagiosus homed after translocation although 90% died during widespread mortality. No P. ambagiosus snails homed at Surville Cliffs where 2.4% died and 26% emigrated. At Whareana Bay, 23% homed, 19% died, 8%–15% stayed where released and 58% emigrated. Mortality of P. hongii on Tawhiti Rahi Island, Poor Knights Islands, was 2% after 1 year. When transferred 10–84 m, 78% homed within a year, 2% went elsewhere and 20% were not found. However, 24% of those transferred 30–84 m returned to their release sites after homing. When left in situ, 60% remained nearby, 8% moved elsewhere and 30% were not found. There was an indication that habitat quality might influence emigration. Results are briefly discussed in relation to possible future translocations to conserve genetic variability and restore faunas.