Environmental Impact Assessment Project Number: 52111-001 February 2020 Samoa: Alaoa Multi-purpose Dam Project Volume 2: Aquatic Biodiversity and Habitat Assessment (Part 4 of 9) Prepared by Hydro-Electric Corporation 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. ALAOA MULTI- PURPOSE DAM PROJECT Aquatic biodiversity and habitat assessment 7 September 2019 Prepared by Hydro-Electric Corporation ABN48 072 377 158 t/a Entura 89 Cambridge Park Drive, Cambridge TAS 7170 Australia Entura in Australia is certified to the latest version of ISO9001, ISO14001, and OHSAS18001. ©Entura. All rights reserved. Entura has prepared this document for the sole use of the client and for a specific purpose, as expressly stated in the document. Entura undertakes no duty nor accepts any responsibility to any third party not being the intended recipient of this document. The information contained in this document has been carefully compiled based on the client’s requirements and Entura’s experience, having regard to the assumptions that Entura can reasonably be expected to make in accordance with sound professional principles. 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Document information Document title Alaoa Multi-Purpose Dam Project Aquatic biodiversity and habitat assessment Client organisation Asian Development Bank Client contact Jean Williams ConsultDM number E307132 Project Manager Will Elvey Project number P513660 Revision history Revision 1.0 Revision description Prepared by Will Elvey Reviewed by Andrew Taylor/Dr Andrew Storey Approved by Andrew Taylor/Dr Andrew Storey (name) (signature) (date) Distributed to Jean Williams Asian Development Bank (name) (organisation) (date) Error! Unknown document property name. - Error! Unknown document property name. Revision No: Error! Unknown document property name. Error! Unknown document property name.Error! Unknown document property name. Glossary Term Comment Amphidromous Adults breed in freshwater, larvae flow to the sea and juveniles return to freshwater to complete the life cycle Benthic/benthos Occurring at the bottom of a body of water Catadromous Adults live in freshwater and migrate to sea to spawn with juveniles returning to freshwater to complete the life cycle Cascade Small waterfall occurring over sudden changes in stream gradient producing broken turbulent flow over course substrate Dissecting microscope A low-magnification stereomicroscope used especially for examining or dissecting biological specimens Decapod crustaceans A crustacean of the order Decapoda, such as a crab, prawn, or shrimp Detritus Decaying plant matter (leaves, branches etc) which provided habitat and food sources Backpack electro-fisher Uses direct current electricity flowing between a submerged cathode and anode. This affects the movement of the fish so that they swim toward the anode, where they can be caught Estuarine Partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it Fishway A structure built into or adjacent to an instream barrier enabling fish to pass upstream Fyke net A long, bag-shaped fishing net held open by hoops Geomorphological Study of the nature and origin of landforms, particularly erosion processes Glide habitat Slow moving non-turbulent flow, too shallow to be a pool but slower flow than a run Headpond Storage reservoir located to create head (elevation) for a penstock and hydro- power station Littoral zone Habitat at the edge of the river channel or lake between the high and low water mark Macroinvertebrate An invertebrate that is large enough to be seen without a microscope Opera trap Small folding net with a single baffled entrance for capturing crustaceans and small fish Penstock Pipe used to transfer water from a storage reservoir to a power station Primary production New organic matter produced by photosynthesis Riparian Terrestrial vegetation that fringes a watercourse Riffle habitat Areas of fast, turbulent flow over coarse substrate Run habitat Areas of relatively fast, shallow non-turbulent flow Taxa A taxonomic group of any rank, such as a species, family, or class Taxonomic The classification of organisms in an ordered system that indicates natural relationships Trophic Ecology of or involving the feeding habits or food relationship of different organisms in a food chain Error! Unknown document property name. - Error! Unknown document property name. Revision No: Error! Unknown document property name. Error! Unknown document property name.Error! Unknown document property name. Executive summary The Asian Development Bank (ADB) commissioned Entura to carry out a baseline aquatic values survey for the proposed Alaoa Multi-Purpose Dam Project. This report is intended to be incorporated into the overall social and environmental impact assessment (SEIA) for the project, and includes a literature review, outcomes of the dry and wet season baseline aquatic surveys, assessment of natural and critical habitats, potential impacts arising from operation and potential options to mitigate those impacts. Baseline values and regional biodiversity significance The fauna recorded during the dry (September 2018) and wet season (May 2019) surveys are consistent with previous surveys undertaken in the Vaisigano River and what would be expected given what is known about Samoa’s freshwater biodiversity. The highest fish diversity occurs in the lower reaches of the river where access to the riverine habitat is not restricted by waterfalls or weirs. Upstream of the first significant waterfall, the fish and crustacean fauna is restricted to species which can climb up or around instream barriers. The majority of these climbing species are also obligatory migratory fauna which move between freshwater and marine habitats to complete their life cycle. The reaches within and upstream of the inundation zone include six species of migratory fish and seven species of migratory crustacean. The migratory fish species includes the endemic goby, Stiphodon hydoreibatus. The majority of the freshwater species recorded in the river are common and widespread in the Indo-Pacific region. No aquatic species recorded during the aquatic surveys for this project, or in previous surveys of any Samoan freshwater watercourse, are listed as near threatened, vulnerable, endangered or critically endangered by the International Union for Conservation (IUCN) Red List. The endemic fish Kuhlia salelea was recorded in the lower reaches of the river during the dry season survey in 2018 but is unlikely to be negatively affected by the scheme and may benefit if an outcome of the project was mitigation in the form of an environmental flow released from Samasoni Weir. The migratory goby Stiphodon hydoreibatus was recorded during wet season survey and is endemic to Samoa, American Samoa, and Futuna. There is no information on the population size, life history or trends of this species as it has not been commonly found and it may be naturally rare. The lack of information about the requirements of Stiphodon hydoreibatus, its apparent restricted distribution and rarity raises the significance of any negative impacts of the project on this species compared to the other more common migratory species. Few freshwater surveys have been conducted in Samoa and the full diversity of Samoan freshwater fauna is uncertain. The discovery of new species is therefore possible during future surveys. Natural and critical habitat assessment The lower Vaisigano River catchment, within the wider Apia Catchments key biodiversity area (KBA), is highly modified by existing urban, hydro-electric and water supply infrastructure. The lower, middle and upper reaches of the river are affected differently by these developments and will be affected differently by the proposed Alaoa Multi-Purpose Dam Project (the project). As defined in the Asian Development Banks (ADB) Social Safeguard Policy (2009), the aquatic habitat in the Vaisigano River downstream from the project area is modified by land use and flow regulation, vii Error! Unknown document property name. - Error! Unknown document property name. Revision No: Error! Unknown document property name. Error! Unknown document property name.Error! Unknown document property name. particularly the lower Vaisigano River below Samasoni Weir which is in very poor condition as no environmental flow is currently released downstream of Samasoni Weir. Thus the river channel is dry from the weir to Samasoni Power Station (approximately 4.2 kilometres downstream) for weeks