Baseline Terrestrial Invertebrate Survey for the Alaoa Hydropower Dam Project, Apia, Samoa (Part 2 of 9)

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.

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:

______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.

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. This area encompasses the forested headwaters of the catchments that flow through Apia; the upper slopes, beyond the project site, are mapped as montane rainforest, and the lower slopes, at the project site, are mapped as disturbed forest (ADB 2013). The Vasigano catchment is also designated as an Important Bird Area (IPA). The nearest protected area to the project site is O Le Pupu-Pue National Park. The northern boundary of the National Park is approximately 3.8 kilometres to the south, and encompasses the reciprocal southern catchments of the high peaks from which the Vaisigano River also flows. The National Park includes entire catchments from the high points to the sea.

2.2 Butterfly fauna of Samoa

The butterfly fauna of the Samoan Archipelago is well known based on the survey work of the two main islands of Samoa and the island of Tutuila in American Samoa over the summer of 2008-2009 (Patrick et al. 2010). This intensive butterfly survey also resulted in a poster and supporting booklet (Edwards and Patrick 2010). Additionally, the butterfly fauna of Samoa was put in a regional context in a wellillustrated popular book that covered 14 countries and territories of the South Pacific (Patrick and Patrick 2012).

The Samoan Archipelago is of volcanic origin (Richmond 1992, McDougall 2010). The Fagaloa Volcanics that form the basement rocks of Upolu, one of the older islands in the group, have been dated to 2.15 million years old (McDougall 2010). The islands have a diverse biota containing relatively high levels of endemism amongst its flora and fauna. The archipelago has 31 butterfly species, all of which are indigenous, with nine species endemic to this part of the South Pacific (29% endemism). Within the archipelago the Republic of Samoa has 29 species of which five are confined naturally to these large islands of Upolu and Savai’i (Patrick et al. 2010).

The majority of the butterfly species of Samoa are confined to areas of indigenous forest, with fewer species in modified areas including farmed or suburban areas. The significant destruction of indigenous forest, particularly on the island of Upolu over the

2 © 2019 Contract Report No. 4816 past 60 years (Whistler 2004), has resulted in the rarity of many butterfly species and the local extinction of the largest species, the Samoan swallowtail (Papilio godeffroyi), which has a wingspan of 10 centimetres. All of the butterfly species are associated with specific indigenous plants on which the females lay their eggs and their caterpillars feed on. The demise of the Samoan swallowtail in Samoa had not been noticed until the survey work in 2008-2009 (Patrick and Patrick 2012). Its rediscovery on Tutuila in American Samoa in September 2008 was fortuitous as it was found there during a break in the survey work of Upolu. The Samoan swallowtail is now an IUCN Red Listed butterfly and its reintroduction to Samoa is being discussed by authorities in Samoa and American Samoa.

Table 1: List of the butterfly species endemic to the Samoan Archipelago and their distribution within the archipelago.

Species/Distribution Samoan Archipelago Samoa American Samoa Papilio godeffroyi (Endangered) ✓ - - Tirumula hamata melittula - ✓ - Tirumula hamata tutuilae - - ✓ Euploea algea schmeltzi - ✓ - Phalanta exulans - ✓ - Hypolimnas errabunda - ✓ - Melanitis leda hopkinsi ✓ - - Deudorix doris ✓ - - Oriens augustula alexina - ✓ -

Two butterfly species were observed in the eastern branch of the Vaisigano River (Eurema hecabe sulphurata and Tirumala hamata melittula) during surveys for an initial environmental survey for a different hydropower project in the Vaisigano catchment (Atherton et al. 2013).

2.3 Threat status of Samoan butterflies

Extensive clearance of indigenous vegetation has occurred on Upolu over the past 64 years (Whistler 2004). These accumulated losses have resulted in the local extinction of an indigenous butterfly and the rarity of other species (Patrick and Patrick 2012).

The Samoan swallowtail Papilio godeffroyi is locally extinct. The cause of its extinction in Samoa is not known for certain, but was probably the result of widespread forest clearance and the local extermination of its larval host plant. Fortunately, it was rediscovered on Tutuila, American Samoa, in September 2008, and is locally common on this comparatively small, but mountainous island (Patrick and Patrick 2012). Based on its demise over 90% of its former range, and its vulnerability to extinction on Tutuila, is has been given the threat ranking “Endangered” by the IUCN and placed on its Red List.

The other 28 indigenous butterfly species of Samoa appear to have reasonably strong populations in their natural habitats on both Upolu and Savai’i, although they will have suffered from the widespread forest clearance also. Most species were found to be

3. BASELINE SURVEY METHODOLOGY

3.1 Survey timing

A survey of the butterflies and other conspicuous invertebrates was completed at the study site (Figure 1) 1-5 November 2018 by entomologist and specialist lepidopterist Brian Patrick, assisted by Dr Tim Martin.

3.2 Lepidoptera

• Lepidoptera were swept from vegetation with a large net, netted in flight, and hand- collected. • Larval host plants present were recorded, and notes and photographs taken of damage by specialist feeders. • Specimens were carefully bottled, and stored in cool place prior to the setting, labelling and storage of representative samples. • Samples were identified using the latest literature, including Brian Patrick’s own dried collection, papers, and books.

3.3 Land snails

Land snails were collected from five locations within or adjacent to the project footprint. Four sites were located within mixed indigenous-exotic forest on hillslopes, and one from an area of cultivated crops on a river terrace, immediately below the confluence of the eastern and western tributaries within the inundation zone of the proposed dam. At each sampling site, the vegetation was described and undergrowth and ground tier was searched for land snails within a circle approximately 2.5 metres in radius of a recorded point.

Leaf litter layers were lifted and searched, and leaves, rocks and logs were overturned. Any decomposing logs that could be broken up by hand were internally searched. All land snails, except for the large African giant snail (Lissachatina fulica), were collected and placed in labelled vials for later identification.

Snails were identified to family, genera, or species level. Two taxa were only identified to family level (Subulinidae); this family is only represented in Samoa by exotic species, and identification of species is very difficult (Cowie et al. 2017). Similarly, for Lamprocystis and Succinea, taxa were only identified to genus level. In Samoa, these two genera are only represented by indigenous species.

While butterflies and moths were the target insect group, other conspicuous insects were also collected, e.g. stick insects, katydids, beetles, damselflies, dragonflies, caddisflies.

4. BUTTERFLIES

Overview

Nine indigenous species of butterflies within three families were recorded in the wider project area in early November 2018. Four of the nine species are endemic to the Samoan Archipelago. Table 2 lists all 16 species potentially present, and notes the localities where these nine species were found. Seven species were located within the two arms of the Vaisigano River which will be flooded by the proposed dam, five species were located at the site of the dam and associated infrastructure close-by, and seven species, including two species not found at the site of the proposed dam, were located in the catchment below the dam within the urban area of Apia.

Table 2: Butterfly survey results for the wider project site and the expected butterfly fauna for lowland habitats on Upolu, Samoa. Species seen during survey shown in bold, endemic species marked with an asterisk*.

Dam Wall Below Dam Family and Species Inundation and (suburban * Samoan endemic taxon Zone Associated Infrastructure Apia) PIERIDAE

Belenois java schmeltzi - - - Eurema hecabe sulphurata ✓ ✓ ✓ NYMPHALIDAE

Danaus plexippus - - ✓ Doleschallia tongana vomana - - - *Euploea algea schmeltzi ✓ - - Hypolimnas bolina pallescens ✓ ✓ ✓ *Hypolimnas errabunda ✓ - - Junonia villida villida - - - *Melanitis leda hopkinsi - - ✓ *Tirumala hamata melittula ✓ ✓ ✓ Vagrans egista bowdenia ✓ ✓ ✓ LYCAENIDAE

Jamides argentina - - - Lampides boeticus - - - Nacuduba dyopa dyopa - - - Zizina otis labradus ✓ ✓ ✓ Zizula hylax dampierensis - - -

Pieridae

The Common Sulphur butterfly Eurema hecabe sulphurata is a bright yellow butterfly species and was commonly observed flying low over riverside, forest edge, and trackside herbage within the footprint of the proposed dam, and below the dam. It is one of the most widespread and common butterflies across the Samoan Archipelago. It has probably only colonised Samoa over the last few decades, arriving from islands further

west where it is known from Tonga and Fiji, and then westwards as far as tropical Africa (Patrick and Patrick 2012).

Nymphalidae

The Monarch butterfly (Danaus plexippus) is a large orange species that has colonised the islands of the Pacific from its North American homeland over the past 150 years. It was seen in small numbers below the site of the proposed Alaoa Dam and in the upper suburbs of Apia.

The Blue Tiger butterfly (Tirumala hamata melittula) is very common and widespread in the project area and in the lower reaches of the Vaisigano River. The large fastflying adults were commonly observed on forest edges feeding on nectar and moving swiftly through the area. This taxon is endemic to Samoa but is abundant at low altitude throughout the country.

The Samoan Crow butterfly (Euploea algea schmeltzi) is endemic to Samoa. It is one of the commonest butterflies in the lowlands including villages and suburban Apia. It was found in the footprint of the proposed dam flying slowly over riparian vegetation.

The Blue Moon butterfly (Hypolimnas bolina pallescens) is endemic to a large area of the south Pacific where it is generally one of the commonest butterflies at low altitude in both natural and suburban environments. It was common across the project area and in the catchment below, flying over forest edge, sunbathing on foliage, and taking nectar from various flowering plants.

The Samoan Eggfly butterfly (Hypolimnas errabunda) is endemic to Samoa where it is locally common from lowland to upland areas. It was seen twice in forested areas in the dam footprint.

The Evening Brown butterfly (Melanitis leda hopkinsi) is endemic to the Samoan Archipelago and was found in the Vaisigano River catchment below the proposed dam. It is a widespread and generally abundant species across the islands of Samoa.

The Tailed Rustic butterfly (Vagrans egista bowdenia) is a widespread and common tropical species, and the subspecies V. egista bowdenia is endemic to many islands of the South Pacific. It was common throughout the project area and below the proposed dam site into the upper suburbs of Apia.

Lycaenidae

The Common Blue Zizina otis labradus was observed in small numbers flying over low- growing vegetation across the project site and in the catchment below the proposed dam site. This is one of the commonest and most widespread butterflies in the lowlands of the South Pacific.

4.1 Land snails (Mollusca)

Four to five species of land snail were identified at each of the sampled sites (Table 3). The African giant snail was present at all sites, and was very abundant at some sites, with several individuals per square metre of ground. Exotic and indigenous snails were found at all sites, and at all sites, the number of exotic species (2-4) was higher

than the number of indigenous species (1-2).

Table 3: Land snail survey results for the project footprint. Numbers of exotic and indigenous species identified at each site shown in brackets.

Sampling Location Vegetation Land snails 1. Eastern arm above upper limit Forest c.30 metres tall with Pometia pinnata Exotic (2): Lissachatina fulica, Subulinidae (two species). of inundation. and the exotic Castilla elastica. Indigenous (2): Pleuropoma fulgora, Lamprocystis species. 2. Hillslope on edge of eastern Forest c.20 metres tall with Myristica and Exotic (3): Lissachatina fulica, Subulinidae (two species). arm. Ficus species. Indigenous (2): Succinea species, Lamprocystis species 3. Hillslope on edge of western Forest c.30 metres tall with Castilla elastica Exotic (3): Lissachatina fulica, Subulinidae (two species). arm. and Ficus species. Indigenous (2): Succinea species, Lamprocystis species 4. Hillslope on ridge at junction Forest c.30 metres tall with Pometia pinnata, Exotic (3): Lissachatina fulica, Subulinidae (two species). of eastern and western arm. Ficus species, Myristica, and Castilla. Indigenous (1): Succinea species. 5. River terrace immediately Cultivated land with banana (Musa species), Exotic (4): Lissachatina fulica, Bradybaena similaris, below confluence of eastern taro (Colocasia esculenta), breadfruit Subulinidae (two species). and western tributaries. (Artocarpus communis), and a ground cover Indigenous (1): Lamprocystis species. of Mikania.

Cowie et al. (2017) characterises the typical habitats for the land snail species present as modified or disturbed lowlands, including disturbed forests, or edges of plantations. The exception is Pleuropoma fulgora (Figure 3), with a habitat described as “in forest litter”. This species was only found above the limit of proposed inundation in the eastern tributary (Land Snail Sample Point 1, Figure 1), and may be scarce or absent from more modified habitats within the project footprint.

4.2 Other invertebrate groups

4.2.1 Dragonflies and damselflies (Odonata)

Two species of Odonata were common in the project area:

• A medium-sized dragonfly Diplacodes bipunctata, red in colour, was abundant in both branches of the Vaisigano River. It is a widespread and common Samoan species that has aquatic larvae in various types of water body. • A smaller and paler damselfly Amorphostigma armstrongi was also abundant over the dry riverbed and edges of the flowing river. It is also an abundant and widespread species throughout the lowlands of Samoa (Marinov et al. 2013).

4.2.2 Orthoptera (katydids)

An indigenous katydid of unknown identity was common in the footprint of the proposed dam. It was swept from low-growing vegetation using a net. It is a widespread species across the Samoan Archipelago based on surveys over the summer of 2008- 2009 (BP, pers. obs.).

4.3 Presence of vulnerable or endangered invertebrate species

None of the nine species of butterfly and two odonata found above or below the proposed dam site are classified as threatened species.

5. NATURAL AND CRITICAL HABITAT ASSESSMENT

Natural Habitat is defined as “land and water areas where biological communities are formed largely by native plant and animal species, and where human activity has not essentially modified the area’s primary ecological functions”. Small, localised areas of ‘natural habitat’, dominated by indigenous plant species, occur on the lower hillslopes and river terraces within the inundation zone; cumulatively these are likely to extend over less than two to three hectares (the total area within the zone at full supply level is 20 hectares). These areas include the mature forest patches at land snail survey Sites 1- 4 (Figure 1), where indigenous plant species comprise more than 50% of the canopy tree species. These forest areas support native terrestrial invertebrates 1 and their

1 Noting that most indigenous Lepidoptera species are dependent on indigenous plant species for part of their lifecycle. Non-indigenous plants may also provide supplementary nectar sources for adults.

ecological function as forest is largely intact. The existing road network will be used to access the project site and these traverse urban and disturbed forest habitats

dominated by exotic trees. Any works required to upgrade existing roads that require removal of tree species should be surveyed for the presence of natural habitat once the required works have been confirmed.

Mapping and quantification of the extent of natural habitats is not possible as a desktop exercise for the inundation area and the construction footprint. The proportion of native to exotic tree species present within a forest area determines whether this definition is met, and the native and exotic trees are of similar colour and texture when viewed using aerial photographs. The location and extent of natural habitats would be best determined by a field survey of the project site.

Critical habitat is a subset of natural and modified habitat, including:

• Habitat required for the survival of critically endangered or endangered species; • Areas having special significance for endemic or restricted-range species; • Sites that are critical for the survival of migratory species; • Areas supporting globally significant concentrations or numbers of individuals of congregatory species; • Areas with unique assemblages of species or that are associated with key evolutionary processes or provide key ecosystem services; • Areas having biodiversity of significant social, economic, or cultural importance to local communities; • Areas either legally protected or officially proposed for protection, such as areas that meet the criteria of the World Conservation Union classification, the Ramsar List of Wetlands of International Importance, and the United Nations Educational, Scientific, and Cultural Organization’s (UNESCO) world natural heritage sites.

With regards to terrestrial invertebrates, none of the areas identified within the survey area meet the definition of Critical Habitat.

6. ANTICIPATED EFFECTS ON INVERTEBRATES

6.1 Overview

Most of the project area, including the footprint of the proposed dam and associated infrastructure, is highly modified in terms of its natural habitats and vegetative cover.

Exotic plant species, of relatively low value as terrestrial invertebrate habitat, are dominant over large areas. This is the likely cause of the relatively depauperate insect fauna recorded for the project area, compared to other more natural areas of Upolu. This is indicated by only nine butterfly species being found there during the five day survey, out of the 16 species that potentially could be present at the site, based on altitude and the range of habitats present (Patrick and Patrick 2012). Similarly, only three species of indigenous land snails were recorded. The butterfly and land snail fauna of the project area, because it is so tightly tied to the vegetation, directly reflects the high degree of modification of the vegetation and habitats present, and abundance of exotic plant species.

Of the seven indigenous butterfly species found at the site of the proposed dam and reservoir, one species, the Samoan Eggfly Butterfly (Hypolimnas errabunda), is of conservation or biodiversity significance. It is endemic to Samoa (Table 1) and whilst widespread in Samoa’s indigenous forested areas, it has a local distribution. This species was not seen at surveyed sites downstream of the proposed dam, but may be present in the upper catchment, beyond the area surveyed for this assessment. Tamafalu (Micromelum minutum), the host plant for the Samoan swallowtail, was not seen during the survey, but has previously been recorded in the upper catchment. The Samoan swallowtail would have formerly been present in the catchment, before modification or loss of lowland forest, and the loss of its host plant.

Potential effects of the proposed dam on terrestrial invertebrates can be summarised as:

• Localised loss of remaining patches of indigenous vegetation, that meet the definition of “natural habitat” and their associated indigenous invertebrates. • Further fragmentation and degradation of the remaining indigenous forest and the associated vegetation. • An increase in forest edge leading to an increase in abundance of invasive invertebrate species.

6.2 Effects of construction

Construction of the dam and associated infrastructure will inundate two vegetated valleys of the Vaisigano River. The area of inundation comprises less than two percent of the catchment upstream of the dam. Anticipated impacts on indigenous terrestrial invertebrates include:

• Habitat loss for seven indigenous butterfly species. Small areas of older or remnant indigenous vegetation that provide larval host plants and or adult nectar sources will be inundated by the proposed reservoir. This may further decrease their populations, in addition to the reductions in range that have occurred with forest clearances of the recent past (Whistler 2004). • If the Samoan eggfly butterfly (Hypolimnas errabunda) is not present in forested habitats upstream of the proposed dam, it is possible that this species could be lost from the middle reaches of the Vaisigano River catchment due to the proposed dam

and associated inundation. However this is considered unlikely due to the small proportion of the catchment within the proposed area of inundation (less than two percent). • Construction activities may result in further disturbance of already modified habitats, and without mitigation, may further favour the establishment of exotic over indigenous vegetation. This may result in further reductions in the current terrestrial invertebrate fauna present in the area at present. The shift of habitats from being largely terrestrial, to largely aquatic, within the project footprint, is likely to result in population increases for invertebrates that complete part of their lifecycle within aquatic habitats (e.g. Odonata). Construction activities, including vegetation clearance and earthworks, may also result in increased abundance of exotic terrestrial invertebrates such as paper wasps (Polistes species) that favour open disturbed environments (Clapperton et al. 1996). If, like the Asian paper wasp (Polistes olivaceous), these species prey on invertebrates, this could lead to further declines in indigenous terrestrial invertebrates at the project site.

6.3 Effects of operation

Operation of the dam, including ongoing maintenance of roads and structures, will produce ongoing disturbance to any remnant butterfly populations on the margins of the surviving forest. This additional disturbance may further favour invasive plants, and in particular vines, which would result in further reductions in indigenous invertebrate habitats and their populations.

7. OPPORTUNITIES TO AVOID, REMEDY OR MITIGATE POTENTIAL ADVERSE EFFECTS ON INVERTEBRATES

7.1 Minimise loss of older indigenous vegetation

Areas of older forest vegetation close to the footprint of works that include indigenous species such as tava (Pometia pinnata), fua fua (Kleinhovia hospita), and indigenous Ficus species, should be identified and physically marked prior to vegetation clearance and construction. This will minimise the loss of natural habitats for terrestrial invertebrates where they occur close to, but beyond, the proposed works footprint.

7.2 Restoration of areas of lowland forest vegetation

Within the footprint of the dam and the associated infrastructure, the actual extent of indigenous forest loss, and mixed indigenous-exotic forest loss (where indigenous species are a common canopy component) needs to be mapped. This will need to include any additional, unexpected losses that occur during construction, and so should be reassessed once the full extent of works is known. Restoration plantings should then be undertaken in modified areas of the Vaisigano River catchment to ensure, in the longer term, no net loss in the extent of indigenous vegetation. The high degree of modification of habitats adjacent to the dam, for example on hillslopes downstream of the proposed

dam, means that there is sufficient land in close proximity to the project site for this habitat restoration to occur in the same catchment, and to be “like for like” for the vegetation types within the proposed works footprint .

If these plantings also included species that are important food sources for indigenous invertebrates, but are now absent or uncommon within the local area, the value of these plantings for indigenous terrestrial invertebrates would be maximised. Plantings could include species such as tamafalu (Micromelum minutum) and species in the family Urticaceae, which are important food sources for butterflies, and species that form long- lived canopy trees.

7.3 Minimise increases in the abundance of exotic species within disturbed areas and forest edges

Construction activities will create new areas of disturbed ground, and new edges to existing areas of vegetation. To minimise the invasion of exotic plants within these areas, or increases in exotic invertebrates, plantings to establish desirable vegetation and the control of invasive plant species are both likely to be needed. Tamafalu and Urticaceae species should be included in plantings undertaken to seal forest edges that are created by the project; they will establish under a canopy, and are of high-value as host plants for indigenous Lepidoptera. To facilitate natural regeneration along forest edges post-disturbance, control of invasive species should particularly address invasive vine species, including fue lautetele (Merremia species) and fue saina (Mikania micrantha).

Plantings to restore disturbed areas to indigenous vegetation, with a focus on forest edges, are the best strategy to manage this risk: it directly counters the adverse effect (increased light and exposure on the forest edge) and is of long-term effect. The control of paper wasps is not recommended. Trials have shown that removal of adult wasps from populations (e.g. by trapping) has little or no effect on population size (Toft and Harris 2004), and subsequently predation pressure on indigenous invertebrates. Control of nests is not feasible as they are typically small, and hard to locate.

7.4 Biosecurity measures for equipment

Terrestrial indigenous invertebrates on Upolu are vulnerable to the effects of a wide range of invasive organisms, such as ants (e.g. fire ants - Wasmannia auropunctata, crazy ants - Paratrechina longicornis), snails, wasps (e.g. Asian paper wasp - Polistes olivaceous), and plants. All of these taxa could feasibly be transported to the site on construction equipment or other materials, either from elsewhere on the island, or overseas, if construction equipment is to be imported. Strict biosecurity protocols, including biosecurity checks of all construction equipment and materials brought to the site, should be implemented to reduce this risk.

7.5 Opportunity to facilitate reintroduction of a locally extinct endemic butterfly

The Samoan Swallowtail (Papilio godeffroyi) (Figure 2), now locally extinct, was formerly widespread on Upolu, including the Alaoa catchment. Plans are being developed for the reintroduction of this butterfly to Samoa. The Samoan Swallowtail population could be established on Upolu by translocation from the island of Tutuila in American Samoa. Whilst the four measures described in Sections 7.1-7.4 above collectively form the mitigation that is required, the reintroduction of this species to the Vaisigano catchment, could be an additional part of the mitigation package to address the loss of butterfly habitat.

Figure 2: The Samoan Swallowtail is a large, high-flying and attractive butterfly that is now locally extinct in Samoa, but was rediscovered on the island of Tutuila, American Samoa in September 2008.

A conservation plan would be required that includes translocation methods, plantings to establish the butterfly’s host plant and nectar sources, and monitoring of the success or otherwise of the translocation. Whilst it is acknowledged that the proposed dam will not have an adverse effect on this species, it was historically present at the site, and is locally extinct due to the effects of human settlement, and forest loss. Construction of the dam, and associated mitigation activities such as forest plantings, may provide an opportunity to facilitate the reintroduction of this species to Upolu. This would require dialogue between the appropriate persons in Samoa and American Samoa to carefully plan the project in terms of logistics, funding, publicity, biological considerations, and timing. Government biodiversity staff from both territories have been in discussion regarding this project for the past decade. The Vailima Botanical Gardens in Apia is a potential partner. It is a well-established botanical facility with the expertise and space to be part of the team both growing the host plant and supporting a population of the butterfly. Additionally, because it is a facility open to the public it is a suitable place to allow the public to see the butterfly and tell its story through interpretation.

8. MONITORING AND REPORTING REQUIREMENTS

To ensure the anticipated impacts on terrestrial invertebrates are adequately addressed, the following monitoring and reporting is required:

• Quantification of the extent of lowland forest loss (where indigenous tree species are common or dominant).

• Quantification of areas of indigenous plantings, to ensure that no net loss of indigenous forest occurs due to the project.

• Pre-construction monitoring to determine the current presence, absence, and abundance of invasive terrestrial invertebrates in the project area (e.g. fire ants crazy ants, Asian paper wasp).

• Post-construction monitoring and survey to assess success of indigenous plantings, any changes to the suite or abundance of exotic invertebrates present, and the actual mitigated effects of the project for indigenous terrestrial invertebrates, particularly in relation to endemic butterflies, and the species only confirmed as being present within the proposed footprint of the dam (the Samoan eggfly butterfly).

If translocation of the Samoan Swallowtail is also pursued as a part of the mitigation for the project, this would require a Translocation Plan. This would provide monitoring plan to assess the success or otherwise of the reintroduction of this iconic species back to Samoa. The plan would need to detail the actions to be taken based on the results of the monitoring. While the Alaoa Dam project could fund or co-fund the monitoring, it could be undertaken by qualified staff of MNRE with input from a qualified lepidopterist, and results shared with the operational staff of the dam project, the relevant partners in American Samoan, the IUCN, and the South Pacific Regional Environment Programme.

9. CONCLUSIONS

Construction of a dam on the Vaisigano River will result in the inundation of approximately 0.2 square kilometres of river bed and terrestrial vegetation; this area encompasses less than two percent of the catchment upstream of the proposed dam, and most of the project footprint is highly modified. Exotic vegetation covers most of the site, and due to their dependence on indigenous flora, the terrestrial invertebrate fauna also reflects this state of modification. The butterfly fauna is relatively depauperate: seven indigenous species were found within the footprint of the proposed dam, and these were all species of widespread distribution on Upolu. One species, the Samoan Eggfly butterfly, whilst widespread, is endemic to Samoa and has a localised distribution; this species, within the extent of the survey, was only confirmed as being present within the project footprint, but may occur in the upper catchment. The land snail fauna comprises indigenous and exotic species that are tolerant of disturbed habitats.

Within the proposed dam and reservoir footprint, there are small remnants of older forest that meet the definition of natural habitat. Whilst these forest remnants include both

indigenous and exotic canopy species, they provide a range of larval host plants and nectar sources for indigenous butterflies, and are habitat for indigenous land snails, with an understorey including loose rocks and deep leaf litter. None of the habitats within the project footprint met the definition of critical habitat with regard to terrestrial invertebrates.

To address the anticipated effects on indigenous terrestrial invertebrates, the loss of natural habitat, including indigenous and mixed indigenous-exotic forest vegetation, should be quantified. Mitigation planning should then include plantings to ensure that there is no net loss of indigenous cover within the middle reaches of the Vaisigano River, and 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, ensuring that biosecurity measures are developed and implemented, and the management of disturbed areas to prevent the proliferation of invasive plants or exotic invertebrates, including plantings and the control of invasive plant species.

Mitigation for the project could also include partnering with a local initiative to reintroduce the locally extinct Samoan Swallowtail butterfly. This reintroduction would be complementary to other mitigation components for the dam, including restoration of indigenous forest to compensate for lowland forest loss. If these mitigation measures described in Section 7.1-7.4 are successfully implemented, the adverse effects of the construction and operation of Alaoa Dam on terrestrial invertebrates, whilst regarded as minor, will be addressed adequately.

ACKNOWLEDGMENTS

William Elvey (Entura) and Andrew Taylor (Envision 2020) provided client liaison. Toeolesulusulu Cedric Schuster provided useful local context and site information. Milen Marinov (Ministry for Primary Industries New Zealand) provided identification and information on the two species of dragonfly and damselfly.

REFERENCES

Atherton J., Jenkins A. and Stirnemann R. 2013: Rapid Assessments of the Biological environment of Small Hydropower Sites in Samoa - Alaoa HPP. James Atherton and Associates. 35 pp.

ADB 2013: Initial environmental examination for new SHPP schemes. Samoa Renewable Development and Power Rehabilitation Project Preparation Technical Assistance - 46044-002 Prepared by STR + P&P for the Asian Development Bank. Atherton J. and

Jeffries B. 2012: Rapid Biodiversity Assessment of Upland Savai’i, Samoa. SPREP, Samoa. 173 pp.

Clapperton B.K., Tilley J.A.V., and Pierce R.J. 1996: Distribution and abundance of the Asian paper wasp Polistes chinensis antennalis Perez and the Australian paper wasp P. humilis (Fab.) (Hymenoptera: Vespidae) in New Zealand. New Zealand Journal of Zoology 23(1): 19-25.

Cowie R., Rundell R., and Yeung N. 2017: Samoan Land Snails and Slugs - An Identification Guide. Department of Marine and Wildlife Resources, American Samoa Government, Samoa.

Edwards E. and Patrick B.H. 2010: Butterflies of Samoa. Poster and booklet. Samoan Government and JICA, Apia, Samoa. Marinov M., Chinn W., Edwards E., and Patrick B.H. 2013: A revised and updated Odonata checklist of Samoa (Insecta: Odonata). Faunistic Studies of Southeastern Asian and Pacific Island Odonata 5: 1-21.

McDougall I. 2010: Age of volcanism and its migration in the Samoa Islands. Geological Magazine 147(5): 705-717.

Patrick B.H., Edwards E. and Patrick H.J.H. 2010: Butterflies of the Samoan Archipelago. Butterflies 54: 13-26. Butterfly Society of Japan, Tokyo, Japan.

Patrick B.H. and Patrick H.J.H. 2012: Butterflies of the South Pacific. University of Otago Press. 240 pp.

Richmond B. 1992: Coastal geology of Upolu, Western Samoa. In: Keating B.H. and Bolton B.R. (Eds) Geology and Offshore Mineral Resources of the Central Pacific Basin. Circum-Pacific Council for Energy and Mineral Resources Earth Science Series Vol 14. Springer, New York. 101-125.

Toft R.J. and Harris R.J 2004: Can trapping control Asian paper wasp (Polistes chinensis antennalis) populations. New Zealand Journal of Ecology 28(2): 279-282.

Whistler A. 2004: Rainforest Trees of Samoa. A guide to the common lowland and foothill forest trees of the Samoan Archipelago. Book and poster. Isle Botanica, Honolulu, Hawaii.