The ecology and conservation of threatened damselflies Integrated catchment science programme Science report: SC040027/SR1 The Environment Agency is the leading public body protecting and improving the environment in England and Wales. It’s our job to make sure that air, land and water are looked after by everyone in today’s society, so that tomorrow’s generations inherit a cleaner, healthier world. Our work includes tackling flooding and pollution incidents, reducing industry’s impacts on the environment, cleaning up rivers, coastal waters and contaminated land, and improving wildlife habitats. This report is the result of research commissioned and funded by the Environment Agency’s Science Programme. Published by: Author: Environment Agency, Rio House, Waterside Drive, Katherine Allen Aztec West, Almondsbury, Bristol, BS32 4UD Tel: 01454 624400 Fax: 01454 624409 Dissemination Status: www.environment-agency.gov.uk Publicly available Released to all regions ISBN: 978-1-84911-093-8 Keywords: © Environment Agency – August 2009 Scarce Blue-tailed Damselfly, Ischnura pumilio, C. mercuriale, Coenagrion mercuriale, Ecology, All rights reserved. This document may be reproduced Conservation, Dispersal, Habitat, Population Size. with prior permission of the Environment Agency. Research Contractor: The views and statements expressed in this report are University of Liverpool those of the author alone. The views or statements Liverpool expressed in this publication do not necessarily L69 3BX represent the views of the Environment Agency and the Tel: 0151 794 2000 Environment Agency cannot accept any responsibility for such views or statements. 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Steve Killeen Head of Science ii Science Report – The ecology and conservation of threatened damselflies Executive summary Background This report presents the results of an autecological study of the Scarce Blue-tailed Damselfly, Ischnura pumilio (Odonata: Coenagrionidae) in south-west England. Ischnura pumilio has a sparse, localised distribution in the UK and is classed as “scarce” in the British Red Data Book of Insects. The aim of this study was to ,raise the ecological understanding of this species to a similar level to that of other threatened odonates such as the Southern Damselfly (Coenagrion mercuriale) with a view to better informing its conservation management. Fieldwork was conducted in the New Forest, Hampshire and at a variety of sites throughout Cornwall and Devon. Main objectives The primary aim of this study was to examine the dispersal potential, survival rates, population sizes and habitat requirements of I. pumilio in the south of England. Similar work on other species, such as C. Mercuriale, has been useful in guiding conservation efforts, but there are very few studies of I. pumilio. It is hoped that this study will inform conservation management and allow more effective monitoring and surveillance of this species. Results Intensive mark-release-recapture (MRR) studies were conducted at two sites during 2005 and 2006. These revealed that, despite a reputation as long range dispersers, I. pumilio were generally very sedentary with movement characteristics similar to those of other similar sized odonates. No movement between sites was recorded and 88 per cent of individuals moved less than 50m (net) in their lifetime. Movement distance was inversely dependent on population density, indicating a tendency to move towards conspecifics or areas of more suitable habitat. The presence of parasitic mites (Hydryphantes spp.) significantly increased movement distance. Males consistently moved further than females. Longer intervals between captures resulted in greater movement distances. Surveys of vegetation and environmental factors were conducted at 31 sites with I. pumilio records from the previous 10 years. The species occurred at sites with a range of water depths, management regimes and levels of pH, grazing, pollution and disturbance. Occupied habitats generally had slow-flowing water, some bare ground at the water’s edge and low levels of shade. A low overall count for odonate species was also associated with the presence of I. pumilio. Areas away from water were found to be important for the species and over 30 per cent of matings were recorded at least 10m from water. Existing sites should be actively managed up to 25m from water, and new habitat created, where possible, with dispersal potential in mind. Survival and recapture rates for Scarce Blue-tailed Damselflies and C. mercuriale were estimated using single and multistate MRR modelling techniques. The resulting rates were used to estimate population sizes for I. pumilio populations surveyed in 2005 and 2006, and two C. mercuriale populations in south England surveyed during 2001 and 2002. Survival generally decreased with age and time in the season and a negative effect of parasites was also indicated. Removing a leg for genetic analysis was not found to affect survival. The sex of mature individuals had no, or negligible effect on Science Report – The ecology and conservation of threatened damselflies iii their survival rates. Ischnura pumilio was found to exist in much smaller populations than C. mercuriale and so may suffer greater levels of inbreeding. A comparison of monitoring methods showed that transect walk estimates were a reliable method of estimating abundance and provided a good basis for further work to develop a predictive relationship. Conclusions and recommendations Despite the strength of some UK populations, such as Latchmoor, I. pumilio still requires conservation management at sites that have poorer quality habitat and smaller populations. Many populations are isolated, based on the range of movements observed in this study, and without dispersal to augment genetic diversity even strong populations are at risk of developing high levels of inbreeding. This study has examined several aspects of the species’ ecology and is the first large scale study of I. pumilio that has been conducted. This report presents estimates of dispersal potential, survival rates and habitat requirements and discusses these with respect to the species’ conservation management. Key findings and recommendations include: • The species was found at sites with a range of water depths, management regimes and levels of pH, pollution, grazing and disturbance. However, sites generally had slow-flowing water, with some bare ground in and around the water’s edge and were relatively open in terms of shade from tall vegetation. • Management of areas away from water should be incorporated into any habitat management plan, as different individuals may be present and may exhibit different behaviours. A buffer of 25m may be sufficient for the necessary roosting, mating and feeding requirements of I. pumilio. • A monitoring program to establish the current status of these and other key odonate sites across the UK would be beneficial. Monitoring of adult I. pumilio at existing sites may be achieved using transect walks, which are a useful method for large-scale monitoring. • The ability of I. pumilio to colonise newly formed habitat is still open to question. No long-range dispersal movements were recorded in this study and no upward flight behaviour was observed. • In this report, the estimated maximum population sizes for the two studies of C. mercuriale are among the highest recorded for any damselfly. However, I. pumilio populations were much smaller and as such may be more at risk of genetic effects such as inbreeding. iv Science Report – The ecology and conservation of threatened damselflies Acknowledgements I am deeply grateful