The Freshwater Ichthyofauna of Bougainville Island, Papua New Guinea!

Tailings disposal from the Bougainville Copper Limited open-cut porphyry copper mine on Bougainville Island, Papua New Guinea (1972-1989) impacted the ichthyofauna of the Jaba River, one of the largest rivers on the island. To assess the 'extent of this impact, comparative freshwater ichthyological surveys were conducted in five rivers on the island during the period 19751988. Fifty-eight fish species were recorded, including one introduction, Oreochromis mossambicus. The icthyofauna is dominated by euryhaline marine species consistent with that of the Australian region, but more depauperate. There are more than 100 species present on mainland New Guinea that are absent from Bougainville streams. Oreochromis mossambicus was the most abundant species in the sampled streams, accounting for 45% of the catch. The most abundant native fishes were the mainly small Gobiidae and Eleotridae. There were few native fish of potential value as food and these were restricted to an eleotrid gudgeon (Ophieleotris aporos), tarpon (Megalops cyprinoides), eel (Anguilla marmorata), and snappers (Lutjanus argentimaculatus and Lutjanus fuscescens). Fish production in the rivers is limited by the morphology of the streams and the depauperate ichthyofauna. Fish yield from the Jaba River in its premining state is estimated to have ranged from 7 to 12 t/yr. The population living in the Jaba ,catchment in 1988 (approximately 4,600 persons) shared this resource, resulting in an extremely low per-capita fish consumption rate of less than 3 kg/yr. ' most seven-eighths of the world's primary freshwater fishes (Darlington 1957), so the absence of the group from the New Guinea mainland has left the freshwater ichthyofauna depauperate (Haines 1983) and limited in capacity for freshwater fisheries production (Coates 1985). It is well known that faunal diversity on islands (including the freshwater fauna) is naturally depressed, depending in part on island area (MacArthur 1972) and the distance of the island from the nearest continental land mass (Usinger 1963). The combined effects of reduced area, remote location, and the absence of ostariophysan fishes suggest severe reduction of the freshwater ichthyofauna of the Papua New Guinea island groups. It is surprising that there has been relatively little freshwater ichthyological study of the New Guinea islands except for records provided by Munro (1967), Kailola (1975), and Allen (1989, 1991) for both marine and 346 THE FRESHWATER ICHTHYOFAUNA of the Australian region, which includes Australia, mainland New Guinea, and associated island groups, is unique because the dominant groups of primary freshwater fish (Ostariophysi) are not represented (Roberts 1978). This has been confirmed by a number of ichthyological surveys of several major rivers on the New Guinea mainland, including the Fly (Roberts 1978), Laloki (Berra et al. 1975), Angabanga (Hyslop 1996), and Purari Rivers (Haines 1983) to the south; the Gogol (Parenti and Allen 1991), Ramu (Allen et al. 1992), Upper Yuat (Jenkins 1997), and Sepik Rivers (Allen and Coates 1990) to the north; as well as rivers in Irian Jaya (Allen and Boeseman 1982). The ostariophysan fishes account for al1 Manuscript accepted 10 February 1999. 2 Environmental Management and Planning Services Pty. Ltd., P.O. Box 406, Samford, Queensland, 4520, Australia. The Freshwater Ichthyofauna of Bougainville Island, Papua New Guinea-PoWELL AND POWELL 347 freshwater fishes. Gressitt (1982) excluded freshwater fishes from his treatment of the ecology of New Guinea, and Choy (1986) concluded that freshwater ecology in the Pacific Islands had been largely overlooked. Environmental issues associated with industrial development in Papua New Guinea have imposed a requirement for management and political decisions in the absence of detailed knowledge of local freshwater environments. An example on the Papua New Guinea mainland is the Ok Tedi copper and gold mine (Allen 1991) and the Bougainville Copper mine on Bougainville Island (Ellis 1988). Bougainville Copper Limited operated the large open-cut porphyry copper mine on Bougainville Island (6 00' S, 155 30' E) from 1972 until 1989, when civil unrest forced premature mine closure. The mine was situated at an altitude of 900 m in Panguna in the headwaters of the Jaba River in the Crown Prince Range of Bougainville Island, North Solomons Province, Papua New Guinea (Figure 1). During the period 1972-1989, and with government approval, Bougainville Copper Ltd. discharged tailings at rates up to 140,000 tjday into the JabajKawerong River system. The tailings were discharged into the headwaters of the Kawerong River, and approximately 60% of the input entered the sea 35 km downstream. Sedimentation on this scale severely changed the morphology of the river and resulted in total loss of ichthyofauna in the main channel and partial loss in tributaries. The Jaba River tributaries were not directly influenced by sedimentation, but were isolated from the sea by high suspended-solid loading in the main channel. To evaluate the extent of this impact and to assist Bougainville Copper Ltd. with ongoing negotiations for loss of natural resources resulting from its operations, ichthyological surveys of five streams on Bougainville Island were conducted during the period 1975-1988. The purpose of this paper is to document the freshwater ichthyofauna of Bougainville Island in a biogeographical context and provide information about a largely unknown resource on a remote tropical Pacific Island. The importance of freshwater fishes as a source of high-quality protein to the indigenous inhabitants of the island is also assessed.