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

ABSTRACT

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.

KEYWORDS:

• Conservation
• harmonic radar
• home range
• long-term monitoring
• site fidelity

Acknowledgements

We are grateful for field assistance from the following: at Te Paki Farm Park Tristan Armstrong, Maria Boger, Fabrice Brecia, Dianne Gleeson, Ruth Henry, Katrina Hansen, Tracy Harris, Maree Hunt, Yens Jorgenson, Cathy Lake, Gary Land, Megan McLean, Graeme Murtagh, Kahori Nakagawa, Richard Overwijk, Gerard Pilon, Christine Reed, Aileena Sucich, Catherine Yong; and on Tawhiti Rahi Island Christine Reed, Leigh Honnor, Katrina Hansen, Maree Hunt, Megan McLean, Paul Barrett and Suzanne Bassett. We thank Kenny Anderson, Joroen Jongejans and Peter Saul for transport to Tawhiti Rahi Island. Our work at Te Paki was assisted greatly by the Department of Conservation (DOC) Te Paki Field Centre staff and we thank Trevor and Gail Bullock, Simon Job and Aileena Sucich for their generous and unfailingly cheerful help. We thank Maria Minor for Russian translation, Murray Potter and Gary Barker for critically reviewing the manuscript and Sandra Parkkali for preparing the figures.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was supported by the DOC [grant number 2386] and the Massey University Research Fund.