SCIENCE & RESEARCH SERIES NO.77 ECOLOGICAL RESEARCH AND MONITORING OF THE PROTECTED GRASSHOPPER Brachaspis robustus IN THE MACKENZIE BASIN by E.G. White Published by Head Office, Department of Conservation, P 0 Box 10-420, Wellington, New Zealand ISSN 0113-3713 ISBN 0-478-01641-7 November 1994, Department of Conservation This publication originated from work done under Department of Conservation contract No.943, and was approved for publication by the Director, Science and Research Division Department of Conservation, Wellington. Cataloguing-in-Publication data White, E. G. (Edwin Graeme), 1938- Ecological research and monitoring of the protected grasshopper Brachaspis robustus in the Mackenzie Basin / by E.G. White. Wellington, N.Z. : Dept. of Conservation, 1994. 1 v. ; 30 cm. (Science & Research series, 0113-3713 ; no. 77.) Includes bibliographical references. ISBN 0478016417 1. Brachaspis robustus. 2. Grasshoppers--New Zealand. 3. Mackenzie District (N.Z.) I. Title. II. Series: Science & research series ; no. 77. 595.726099369 20NZ zbn94-090549 Keywords: Brachaspis robustus , rarity, distribution, recognition, biology, ecology, predation, hydroelectric development, vulnerability, history, status, protection, risks CONTENTS ABSTRACT ............................................ 1 1. INTRODUCTION ........................................ 1 2. METHODS............................................. 5 2.1 Reconnaissance 5 2.2 Monitoring 5 2.3 Extended monitoring 6 2.4 Vegetation analyses and diet 7 2.5 Life cycle and ecology 7 2.6 Hydroelectric river releases 8 3. RESULTS AND DISCUSSION ............................... 9 3.1 Reconnaissance 9 3.1.1 Lower (southern) Basin 9 3.1.2 Central and Upper Basin 9 3.2 Monitoring 10 3.3 Extended monitoring 13 3.3.1 Sawdon Stream 13 3.3.2 Mackenzie River 13 3.3.3 Snow River 15 3.4 Vegetation analyses and diet 15 3.5 Life cycle and ecology 17 3.5.1 Field recognition of Brachaspis robustus 17 3.5.2 Field recognition of growth stages 17 3.5.3 Life cycle 18 3.5.4 Dispersal 20 3.5.5 Activity thresholds and general behaviour 20 3.5.6 Habitat preference 21 3.6 Predation 24 3.6.1 Invertebrate predators 24 3.6.2 Reptilian predators 24 3.6.3 Bird predators 25 3.6.4 Mammalian predators 25 3.7 Drought 26 3.8 Hydroelectric river releases 27 4. CONCLUSIONS AND RECOMMENDATIONS .................29 4.1 Current status of B. robustus populations 29 4.2 Natural history and vulnerability 30 4.2.1 The indigenous predators 30 4.2.2 The introduced predators 31 4.3 Risks of disaster 32 4.3.1 Natural disasters 32 4.3.2 Induced disasters 33 4.4 Suggested scenario to explain B. robustus abundance 35 4.4.1 Predation and pest control 35 4.4.2 Vegetation change 37 4.4.3 Hydroelectric development 37 4.5 Recommendations 37 4.6 Addendum, June 1994 39 5. ACKNOWLEDGEMENTS .... .. ........ .. ......... ..... 39 6. REFERENCES .... ... .... .. .. .. ......... .... ...... 40 APPENDIX 1 Grid refs for Brachaspis robustus search areas 41 APPENDIX 2 Vegetation composition of population centres in Mackenzie Basin 42 APPENDIX 3 Field recognition of Brachaspis robustus instars 44 APPENDIX 4 Known minimum ages and minimum movements 47 APPENDIX 5 Effects of Gate 22 spill tests 48 ECOLOGICAL RESEARCH AND MONITORING OF THE PROTECTED GRASSHOPPER BRACHASPIS ROBUSTUS IN THE MACKENZIE BASIN by E.G. White 74 Toorak Avenue, Christchurch, New Zealand ABSTRACT The distribution, abundance and natural history of the rare Robust Grasshopper has been assessed throughout it present range in the central and upper Mackenzie Basin, Canterbury. Reconnaissance suggests that it has recently disappeared from the southern basin, but it survives further north in some river channels and their outwash areas as small and often isolated populations. Regular monitoring of selected populations has clarified aspects of species biology and ecology, including growth stage longevities, dispersal, diet and habitat preferences. Only one moderately large population centre is known (estimate: 250-300 adult recruits per year), and all populations appear to face periodically heavy predation from a suite of predators, indigenous and introduced. Annual losses of adult females before breeding appear to be the most critical survivorship factor. Populations in river channels in addition face periodic losses from natural flood events or large hydroelectric river releases. The risks of natural and induced disasters are assessed in evaluating the current status of the species, and a suggested long-term scenario is presented to explain the virtual lack of species records before the 1980's. It draws together five key elements: rabbits, pest control, predation, vegetation change and hydroelectric develop- ment. Four recommendations are proposed to improve species and habitat protection. 1. INTRODUCTION The Robust Grasshopper, Brachaspis robustus Bigelow, is a protected species endemic to New Zealand. It is a montane grasshopper belonging to the family Acrididae (short- horned grasshoppers) in which the antennae are of similar length to the face (Figure 1). The usual colour is slate-grey but varies between individuals, and especially between habitats of different background colours. Hence, earthen browns are more prominent in some areas, and richly patterned black and grey individuals may be found in prominent lichen areas. Light yellowish patterns on the thorax (and occasionally orange) add to the cryptic colouring of a few individuals, and the species' flash-display colourings on the inner side of the hind-legs provide an intense combination of red and indigo-violet. This latter combination is more dramatic than in any other New Zealand grasshopper. 1 Photo: Robin Smith Figure 1 Brachaspis robusttts adult female. The grasshopper is known from stony floodplain terraces, fluvioglacial outwash localities, recent fluvial outwash and rocky braided river systems of the Mackenzie Basin, Canterbury (Figure 2). Until 1984, only three specimens deposited in the Canterbury Museum, Christchurch, were known to science: two undated individuals labelled simply ' Kurow' (located on the Waitaki River that drains the Mackenzie Basin) and a 1963 adult labelled 'Ahuriri River, North Otago' (located at the southern limits of the basin) (see Bigelow 1967 for details and a species description). In 1954, several specimens were observed in Fork Stream at Balmoral Station, towards the northern limits of the basin (John Dugdale, pers. comm. 1993), and in 1971-72, the species was common by the Tekapo A Powerhouse (Pat Quinn, pers. comm. 1993). New discoveries of the species followed from 1984 onwards in the upper Mackenzie Basin (recorded in part by Davis 1986) and one further specimen was added to the Canterbury Museum collection. Despite any earlier 'common knowledge', a meagre 10 observa- tions had been scientifically recorded by 1984, but by 1990, Davis had added 80 further sightings to Canterbury Conservancy records. The current investigation spanned November 1991 to May 1993, and its observations have been complemented by further new records supplied by Canterbury Conservancy staff (Mark Davis, Ken Hughey, Richard Maloney, Ron Nilsson, Bert Rebergen and Lynn Adams). The contributions of these observers is gratefully acknowledged. 2 Figure 2 River and outwash systems of the Mackenzie basin. Arrows indicate known records of Brachaspis robustus. 3 The objectives of the present study were to explore locations and monitor the abundance of Brachaspis robustus in the Mackenzie Basin, spring-autumn 1991-92, 1992-93 as follows: To progressively mark and record grasshoppers on first capture and re-record at subsequent sightings To piece together a biology and life-history from completed marking/re-sighting records To estimate minimum population sizes and survival prospects, using formal analyses if data permit To relate observed grasshopper behaviour to habitat reqirements including, if possible, identification of food plants by faecal analysis To define known site locations To prioritise sites for recommended conservation effort, assuming the case for special effort is upheld. The study was carried out subject to the conditions of an authority to catch, handle, transfer and release absolutely protected wildlife (DoC Permit 12/23). The conditions stipulated minimised disturbance of B. robustus populations; minimised stress of captured, handled and marked individuals; and the most humane holding conditions for individuals temporarily held in the field for the collection of voided faeces. The authority did not allow the removal of animals from the field. Species protection is established in the Seventh Schedule of the Wildlife Ammendment Act 1980. Ramsay et al 1988 considered the species as possibly at risk from habitat modification and perhaps vertebrate predation. Sherley 1989 assigned it tentatively to 'Research Rank 1', that is, immediate research is essential. 4 2. METHODS Monthly field visits were made November 1991 - May 1992, and September 1992 - May 1993. Reconnaissance sought to identify as many Brachaspis robustus sites as possible while monitoring sought to assess population ecology at selected sites. 2.1 Reconnaissance Rocky braided river systems were not a known habitat type until 1991, and this discovery by Canterbury Conservancy staff greatly enlarged the potential species area to be searched. So also did the author's early discovery of B. robustus at a distance of 1 km from a current river channel. All 1984-90 sightings in the upper Mackenzie Basin had been adjacent to rivers and streams or within