Exotic species, fisheries and conservation of freshwater biodiversity in tropical Asia: the case of the Sepik River, Papua New Guinea

Abstract

1. Development of effective conservation strategies for freshwater biodiversity must take account of the trade‐off between species preservation and human use of ecosystem goods and services. The latter cannot be prevented, and attempts to manage ecosystems that focus solely on maximizing biodiversity will fail. 2. A compromise position of management for ecosystem functioning and human livelihoods — rather than preservation of every species — will provide a better basis for biodiversity conservation. This has implications for the management of exotic species. 3. There are some situations, in lentic habitats in Sri Lanka, for example, where the establishment of exotics has increased fishery yields without apparent detriment to native biodiversity. The Sepik River in Papua New Guinea provides another illustration of potential compromises between human livelihoods and biodiversity conservation. 4. The Sepik supports a relatively unproductive fishery. Two fish stocking projects (in 1987–93 and 1993–97), representing a partnership between the Papua New Guinea Government and the United Nations (UNDP/FAO), led to the introduction of a suite of exotic fish into the Sepik. Species were selected on the basis of their potential to occupy niches not filled by native fish. Unfortunately, the outcomes of these introductions are poorly documented, although there is preliminary evidence both of increased human use of exotic fish as well as declines of some native species associated with the spread of exotics. 5. Better understanding of the results of the Sepik fish introductions is important, because the pressures of burgeoning human populations in most of tropical Asia make it impossible to preserve near‐pristine environments such as the Sepik. While attempts to conserve natural or near‐natural systems must remain a priority, there is a need to develop strategies for the management of damaged or degraded ecosystems, which may contain exotics, with the aim of maintaining ecosystem functioning and, if possible, maximizing the persistence of native biodiversity. Copyright © 2006 John Wiley & Sons, Ltd.

Diet shift of Red Belly Pacu Piaractus brachypomus (Cuvier, 1818) (Characiformes: Serrasalmidae), a Neotropical fish, in the Sepik-Ramu River Basin, Papua New Guinea

“…Species interactions across taxonomic groups are rarely accounted for when predicting and evaluating the effects of species introductions (Herbold & Moyle, 1986;Spencer et al, 1991). The absence of follow up studies after the introduction of P. brachypomus in the Sepik-Ramu system (Dudgeon & Smith, 2006;Gehrke et al, 2011) precludes our understanding of how the species became established in this new environment. We do not know if the diet shift occurred gradually or abruptly, however it is likely that trophic plasticity has played a pivotal role in allowing the species to use available food resources and obtain energy necessary to survive, reproduce and become established.…”

“…The Sepik is the longest river in Papua New Guinea (PNG, 1100 km long, 78000 km 2 catchment) and its lower reaches are interconnected with the lower Ramu River through channels and a shared floodplain (Dudgeon & Smith, 2006). The Sepik-Ramu River Basin is a nearpristine system containing 78 species of diadromous and primary freshwater fishes, most of which are derived from marine lineages (Dudgeon & Smith, 2006).…”

“…The Sepik is the longest river in Papua New Guinea (PNG, 1100 km long, 78000 km 2 catchment) and its lower reaches are interconnected with the lower Ramu River through channels and a shared floodplain (Dudgeon & Smith, 2006). The Sepik-Ramu River Basin is a nearpristine system containing 78 species of diadromous and primary freshwater fishes, most of which are derived from marine lineages (Dudgeon & Smith, 2006). This relatively low fish diversity, nearly half of that of the Fly River in southern PNG, is likely the result of a recent geological history and the lack of estuarine areas that are important as nursery grounds (Coates, 1993b;Dudgeon & Smith, 2006).…”

“…The Sepik-Ramu River Basin is a nearpristine system containing 78 species of diadromous and primary freshwater fishes, most of which are derived from marine lineages (Dudgeon & Smith, 2006). This relatively low fish diversity, nearly half of that of the Fly River in southern PNG, is likely the result of a recent geological history and the lack of estuarine areas that are important as nursery grounds (Coates, 1993b;Dudgeon & Smith, 2006). Despite having an extensive floodplain (35000 km 2 , Coates, 1997) covered with diverse aquatic macrophytes (Osborne, 1993) and swamp grasses and forests (Paijmans, 1975;Mitchell et al, 1980), few native fish species in the basin have adapted to exploit floodplain resources, another potential cause for markedly low fish yields (Coates, 1993b;Gehrke et al, 2011).…”

“…Although this introduction was extensively planned, and the benefit for the local people heavily weighted (Coates, 1997), the evaluation of environmental risks is largely controversial (e.g., Paxton, 1989;Coates, 1993aCoates, , 1993b. To date, there are no follow-up studies looking at the fate of P. brachypomus after its introduction in the Sepik-Ramu River (Dudgeon & Smith, 2006;Gehrke et al, 2011). The frequency with which P. brachypomus has been introduced worldwide gives broad relevance to ecological data from populations that are established outside their native range.…”