Baseline Terrestrial Invertebrate Survey for the Alaoa Hydropower Dam Project, Apia, Samoa (Part 2 of 9)
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Environmental Impact Assessment Project Number: 52111-001 February 2020 Samoa: Alaoa Multi-purpose Dam Project Volume 2: Baseline Terrestrial Invertebrate Survey for the Alaoa Hydropower Dam Project, Apia, Samoa (Part 2 of 9) Prepared by Entura for the Asian Development Bank. This environmental impact assessment is a document of the borrower. The views expressed herein do not necessarily represent those of ADB's Board of Directors, Management, or staff, and may be preliminary in nature. Your attention is directed to the “terms of use” section on ADB’s website. In preparing any country program or strategy, financing any project, or by making any designation of or reference to a particular territory or geographic area in this document, the Asian Development Bank does not intend to make any judgments as to the legal or other status of any territory or area. BASELINE TERRESTRIAL INVERTEBRATE SURVEY FOR THE ALAOA HYDROPOWER DAM PROJECT, APIA, SAMOA R 4816 BASELINE TERRESTRIAL INVERTEBRATE SURVEY FOR THE ALAOA HYDROPOWER DAM PROJECT, APIA, SAMOA Samoan Eggfly butterfly (Hypolimnas errabunda). This species is endemic to Samoa and is widespread but generally uncommon in areas with indigenous forest remnants. Contract Report No. 4816 May 2019 Project Team: Dr Tim Martin - Field survey and report author Brian Patrick - Field survey and report author Roger Bawden - GIS Prepared for: Entura 89 Cambridge Park Drive Cambridge Tasmania 7170 AUCKLAND OFFICE: 12 NIXON STREET, GREY LYNN, AUCKLAND 1021 P.O. BOX 46-299, HERNE BAY, AUCKLAND 1001, Ph 09-360-6083 HEAD OFFICE: 99 SALA STREET, P.O. BOX 7137, TE NGAE, ROTORUA Ph 07-343-9017; Fax 07-343-9018, email [email protected], www.wildlands.co.nz EXECUTIVE SUMMARY A baseline terrestrial invertebrate survey of the proposed footprint of the Alaoa Dam and reservoir, Upolu, Samoa, was undertaken 1-5 November 2018. Most of the project footprint is highly modified. Exotic vegetation covers most of the site, and the terrestrial invertebrate fauna also reflects the degree of modification. The butterfly fauna is relatively depauperate, with only seven indigenous species found within the proposed footprint, and these were all species that are widespread on Upolu. One species, the Samoan eggfly butterfly (Hypolimnas errabunda), whilst widespread, is endemic to Samoa and has a localised distribution. The land snail fauna is dominated by indigenous and exotic species that are tolerant of disturbed habitats. The proposed project footprint encompasses less than two percent of the catchment above the point of the proposed dam. Within the area of proposed inundation there are small remnants of older indigenous or mixed indigenous-exotic forest that met the definition of natural habitat. These forest remnants include both indigenous and exotic canopy species, and, whilst partially modified, nevertheless provide habitat for indigenous invertebrates. These remnants provide a range of larval host plants and nectar sources for indigenous butterflies, and are habitat for indigenous land snails. No areas within the project footprint were identified as critical habitat with regards to terrestrial invertebrates. If unmitigated, the project will result in further reductions in habitat, albeit minor, for the endemic Samoan eggfly butterfly, and a suite of butterflies, snails, and other invertebrates that are characteristic of disturbed habitats. To address likely effects on indigenous terrestrial invertebrates, the loss of natural habitat, including indigenous and mixed indigenous-exotic forest vegetation, should be quantified. The actual extent of loss should then be reassessed post construction. Mitigation planning should then include plantings to ensure that there is no net loss of indigenous forest within the middle reaches of the Vaisigano River, and to include within these plantings species that provide important resources for indigenous invertebrates. This compensation for habitat loss should be accompanied by measures to reduce impacts on the habitats to be retained, including clear demarcation of habitats close to but beyond the construction footprint, and ensuring that strict biosecurity measures are developed and implemented. This should include the management of disturbed areas to prevent the proliferation of invasive plants or exotic invertebrates, and should include the planting of indigenous species and the control of invasive plant species. Mitigation for the project could also include a partnership with a local initiative to reintroduce the locally extinct Samoan swallowtail butterfly (Papilio godeffroyi). This reintroduction, while not a core part of the mitigation approach, would be complementary to other mitigation components for the dam, including restoration of indigenous forest to compensate for lowland forest loss. If the mitigation measures described above are implemented successfully, the likely minor effects of construction and operation of the proposed Alaoa Dam on terrestrial invertebrates will be addressed adequately. © 2019 Contract Report No. 4816 CONTENTS EXECUTIVE SUMMARY 6 1. INTRODUCTION 1 2. LITERATURE REVIEW 2 2.1 Protected natural areas near the project site 2 2.2 Butterfly fauna of Samoa 2 2.3 Threat status of Samoan butterflies 3 3. BASELINE SURVEY METHODOLOGY 4 3.1 Survey timing 4 3.2 Lepidoptera 4 3.3 Land snails 4 3.4 Other invertebrates 5 4. BUTTERFLIES 8 4.1 Land snails (Mollusca) 10 4.2 Other invertebrate groups 13 4.2.1 Dragonflies and damselflies (Odonata) 13 4.2.2 Orthoptera (katydids) 13 4.3 Presence of vulnerable or endangered invertebrate species 13 5. NATURAL AND CRITICAL HABITAT ASSESSMENT 13 6. ANTICIPATED EFFECTS ON INVERTEBRATES 14 6.1 Overview 14 6.2 Effects of construction 15 6.3 Effects of operation 16 7. OPPORTUNITIES TO AVOID, REMEDY OR MITIGATE POTENTIAL 16 ADVERSE EFFECTS ON INVERTEBRATES 16 7.1 Minimise loss of older indigenous vegetation 16 7.2 Restoration of areas of lowland forest vegetation 16 7.3 Minimise increases in the abundance of exotic species within disturbed areas and forest edges 17 7.4 Biosecurity measures for equipment 17 7.5 Opportunity to facilitate reintroduction of a locally extinct endemic butterfly 17 8. MONITORING AND REPORTING REQUIREMENTS 18 9. CONCLUSIONS 19 ACKNOWLEDGMENTS 20 REFERENCES 20 Reviewed and approved for release by: © 2019 Contract Report No. 4816 _______________________ W.B. Shaw Director/Principal Ecologist Wildland Consultants Ltd Wildland Consultants Ltd 2019 This report has been produced by Wildland Consultants Ltd for Entura. All copyright in this report is the property of Wildland Consultants Ltd and any unauthorised publication, reproduction, or adaptation of this report is a breach of that copyright. © 2019 Contract Report No. 4816 1. INTRODUCTION Entura are leading the detailed feasibility assessment for the proposed Alaoa multipurpose dam project, upstream of Apia, Samoa. The project area consists of a 59.6 metre high dam wall located on the combined eastern branch of the Vaisigano River 6.5 kilometres upstream from where the river discharges into Apia Bay. At full supply level (FSL) the dam will inundate 0.2 km2 (20 hectares) of riverbed, valley floor, and hillslope habitats in the middle region of the Vaisigano Catchment, including a 1.3 kilometre length of the middle-eastern branch and a 1.1 kilometre reach of the eastern branch of the Vaisigano River. The area of inundation is less than two percent of the catchment area upstream of the proposed dam. A penstock will run 360 metres downstream from an outlet on the dam along the right bank of the river to the new power station. The existing Alaoa Power Station discharges into the Vaisigano River 80 metres upstream from the proposed new power station but is located on the opposite bank. It is assumed that material for construction of the dam will be obtained from within the inundated area, removing the need for offsite borrow areas. The Contractor may base his administration buildings outside the inundation area but the footprint will be small and impacts managed through normal site practices. It has been assumed that storage and processing areas will be located inside the inundation area. Transport of imported construction materials, between the Port and the construction site, will be on the existing road network. The dam will reduce flood risk during the wet season, provide raw water supply security in the dry season, and some “run of river” hydropower capacity. A reconnaissance survey of the project site was carried out by the EIA team in July 2018, and determined that a site survey was needed by a terrestrial entomologist with experience of Pacific Island terrestrial ecology. To this end, Entura commissioned Wildland Consultants Ltd to carry out a baseline terrestrial invertebrate survey for the proposed Alaoa Dam project. This survey focused on Lepidoptera (butterflies and moths) as this insect order is tightly tied to the prevailing indigenous vegetation and habitats. As such, Lepidoptera will be the most informative group to survey. Additionally, this insect group is well-documented in Samoa and their ecology, life history, distribution, and threat status are well known (Patrick & Patrick 2012). Of the 29 butterfly species in Samoa, many are good candidates for ongoing monitoring as they are responsive to vegetation changes and are conspicuous in flight. This report is intended to be incorporated into the overall Environmental Impact Assessment for the project, and includes: • A baseline assessment of the terrestrial invertebrate populations present or likely to be, present in the affected area, including the potential presence of vulnerable, 1 © 2019 Contract Report No. 4816 endangered, and/or critically endangered species or the presence of natural or critical habitats for invertebrate species as defined by the Asian Development Bank (ADB) Safeguard Policy Statement 2009 (SPS) • An assessment of the impacts of the construction and operation of the proposed Alaoa Dam on terrestrial invertebrates • Proposed mitigation measures as well as monitoring and reporting requirements. 2. LITERATURE REVIEW 2.1 Protected natural areas near the project site The Alaoa power scheme lies within the Apia Catchments Key Biodiversity Area.