Southern Papua New Guinea Research Articles

Papua New Guinea: A Potential Refuge for Threatened Indo–Pacific River Sharks and Sawfishes

The conservation of threatened elasmobranchs in tropical regions is challenging due to high local reliance on aquatic and marine resources. Due primarily to fishing pressure, river sharks (Glyphis) and sawfishes (Pristidae) have experienced large population declines in the Indo-Pacific. Papua New Guinea (PNG) may offer a refuge for these species, as human population density is low, and river shark and sawfish populations are thought to persist. However, few data are available on these species in PNG, and risk posed by small-scale fishers is poorly understood. This study observed elasmobranch catches in small-scale fisheries in riverine and coastal environments in the East Sepik (northern region), Gulf, and Western Provinces (southern region) of PNG. Surveys were conducted over a period of weeks to months in each region, during the dry season across seven field trips from 2017 to 2020. We observed a total of 783 elasmobranchs encompassing 38 species from 10 families. River sharks made up 29.4% of observations in the southern region, while sawfishes made up 14.8 and 20.3% in the northern and southern regions, respectively. River sharks were commonly caught by small-scale fishers in lower riverine environments in southern PNG, while sawfishes were generally less common and mainly observed through dried rostra. The primary threat to river shark and sawfish populations is their capture by small-scale fishers targeting teleosts for swim bladder. Persisting populations of river sharks and sawfishes indicate that PNG is the second known nation with viable populations of multiple species in the Indo-Pacific. However, populations are declining or at high risk of decline, and fisheries management and conservation are required to realize the potential of PNG as a long-term refuge.

Local knowledge surveys with small‐scale fishers indicate challenges to sawfish conservation in southern Papua New Guinea

Abstract Sawfish (Pristidae) are considered to be among the most threatened families of elasmobranch (sharks and rays). There is a need to gather information on the status of poorly known sawfish populations to assist in global recovery initiatives. This study used interviews with local fishers to investigate the presence of sawfish in southern Papua New Guinea (PNG) and their interactions with and uses and values for small‐scale fishers. A range of sawfish size classes are still encountered throughout southern PNG, while juvenile largetooth sawfish Pristis pristis were additionally reported in the freshwater reaches of all rivers surveyed. Reports of large size classes in estuarine and marine environments provide an optimistic outlook that sawfish populations persist throughout southern PNG. Most fishers that catch sawfish retain them for various uses including consumption and for the sale of meat, fins and occasionally rostra. Negative population trends including decreases in catch frequency and/or size classes were reported by 66% of interviewees, with the largest declines being reported in the Kikori River. The increasing technical capacity of small‐scale fishers, their preference for gillnetting and the emerging market for teleost swim bladder (a high‐value fishery product) present a major ongoing threat to sawfish in southern PNG. Furthermore, the tendency of fishers to kill or remove rostra from entangled sawfish results in high fishing mortality regardless of any use by the fisher. This study indicates that considerable community engagement will be necessary to manifest any legislative actions or increased enforcement on international trade regulations for sawfish in PNG. This is due to traditional land and waterway ownership values throughout PNG and the local perception of sawfish as a traditional food resource rather than an animal of intrinsic biodiversity value as perceived by global conservationists. Future research should consider exploring culturally appropriate conservation initiatives that are likely to achieve engagement and participation from local fishers.

The intrusion of polluted Fly River mud into Torres Strait

There is a concern that the Fly River plume from Papua New Guinea (PNG) may be delivering mine-derived polluted mud along the southern PNG coast into the northern Torres Strait, which is the northernmost extent of the Great Barrier Reef. To quantify this threat, the mud transport dynamics along the southern PNG coast were studied using the SLIM model. The model was qualitatively verified using historical field data on sediment dynamics and compared with more recent satellite-derived turbidity data. During strong south east winds and spring tides, about 5.4% of the Fly River mud discharge enters the Torres Strait, in agreement with previous field-derived results. The annual net movement of mud is westward, thus polluted Fly River mud progressively intrudes into Torres Strait. This intrusion is slow and may take a century to reach in significant quantities at Saibai Island, the nearest Australian island to the Fly River. Field data are needed to fully validate the model and provide greater confidence in these results.

Provenance and supply of Fe-enriched terrigenous sediments in the western equatorial Pacific and their relation to precipitation variations during the late Quaternary

Iron (Fe) deposition in the equatorial Pacific has important implications for the global carbon cycle, while the provenance of Fe supply and its change remain highly debated. Here, we geochemically characterize the provenance of terrigenous sediments deposited on the pathways of the Equatorial Undercurrent (EUC) and the New Guinea Coastal Undercurrent (NGCUC). The Fe-enriched sediments in the western equatorial Pacific are mostly derived from fluvial inputs of Papua New Guinea (PNG), while nearly negligible impact from eolian dust could be detected. Variability of the terrigenous Fe-enriched deposition (7.4–13.4%) for core KX21-2 in the western equatorial Pacific over the past 380ka shows dominant precession periods, superimposed on a clear glacial–interglacial trend with higher input during glacials. The precession periods are correlated with the precipitation over PNG, in response to the local summer insolation (5°S, March) and meridional migration of the Intertropical Convergence Zone (ITCZ). The glacial–interglacial trend is induced by sea level fluctuations that significantly influence the fluvial input from southern PNG. The different expressions of precession periods between glacials and interglacials in core KX21-2 are tightly associated with the undercurrent. The subdued precession periods during interglacials can be attributed to the weakness of the NGCUC, which may link to La Niña-like conditions. The enhanced precession periods during glacials should result from increased input from southern PNG on one hand, and an intensified NGCUC on the other hand, due to the El Niño-like conditions. Compared to Fe, the proxy ln (Ti/Total) (XRF log-ratio of Ti/Total counts) for core KX21-2 preferentially indicates the northern PNG input, and therefore could be used to reflect the glacial changes in the NGCUC. Our records imply that the NGCUC was particularly stronger in MIS 6 and 10, and weaker in MIS 8.

Holocene pollen records from Caution Bay, southern mainland Papua New Guinea

This study presents new palynological data from Caution Bay, south-central Papua New Guinea (PNG). It explores Holocene mangrove transitional events along a tide-dominated shoreline, and expands reconstructive detail for the wider southern PNG lowlands. Coinciding with recent regional archaeological research, this study also holds implications for interpretations of the Holocene settlement of Caution Bay and long-term people–landscape interactions. Data demonstrate a late-Holocene mangrove to mudflat transition, with vegetation patterns largely a function of low sediment loading, sedimentary redistributions and salinisation upon sea level decline c. 2000 cal. yr BP. These trends appear unique to Caution Bay, highlighting a variety of Holocene shoreline vegetation changes along the PNG south coast, each dependent on geomorphologic setting and hydrological fluxes. Further work is required to elucidate vegetation change inland of the coastal zone. Greater understanding of burning patterns and an archaeological collaboration are required to determine more concisely dryland plant spatial and temporal variability.

Cold Water Flow and Upper-Ocean Currents in the Bismarck Sea from December 2001 to January 2002

Abstract The authors investigated the upper-ocean currents in the Bismarck Sea and related oceanic thermal changes in the western equatorial South Pacific for December 2001–January 2002; during this period, coastal upwelling occurred along the Papua New Guinea (PNG) coast. Southeastward and northwestward coastal currents toward the central PNG coast appeared along northern and southern PNG, respectively. In addition, westward currents extended toward central PNG in the southern part of the Bismarck Sea. A northeastward outflow toward the equator from the PNG coastal area, which is compensated for by such flows, was also found. Volume budget analysis in the upper ocean showed that, during the analysis period, the northeastward outflow ranged from +1.0 to +2.0 Sv (1 Sv ≡ 106 m3 s−1). This northeastward outflow brought relatively cool coastal water, which is related to PNG coastal upwelling, to the western equatorial South Pacific near PNG during this period. In addition, the upper-ocean temperature in this region showed a cooling tendency in line with a negative heat transport from the PNG coastal region. The present results indicate that northeastward transport of the cold water is related to the complicated upper-ocean currents in the Bismarck Sea and may have strongly affected the upper-ocean thermal change in the western equatorial Pacific near PNG for December 2001–January 2002.

Phylogeography of colour polymorphism in the coral reef fish Pseudochromis fuscus, from Papua New Guinea and the Great Barrier Reef

Body colour has played a significant role in the evolution of coral reef fishes, but the phylogenetic level at which colour variation is expressed and the evolutionary processes driving the development and persistence of different colour patterns are often poorly understood. The aim of this study was to examine the genetic relationships between multiple colour morphs of Pseudochromis fuscus (family Pseudochromidae), both within and among geographic locations. Pseudochromis fuscus is currently described as a single species, but exhibits at least six discrete colour morphs throughout its range. In this study, P. fuscus from Papua New Guinea (PNG) and the Great Barrier Reef (GBR), Australia, formed three genetically distinct clades based on mitochondrial DNA (control region) sequence data: (1) yellow and brown morphs from the GBR and southern PNG, as well as an orange morph from southern PNG; (2) a pink morph from southern PNG; and (3) all three morphs (pink, orange and grey) found in Kimbe Bay, northern PNG. The three groups showed deep levels of divergence (d=14.6–25.4%), suggesting that P. fuscus is a complex of polychromatic species, rather than a single widespread species with many different colour morphs. Population genetic analyses indicate that the three clades have experienced unique evolutionary histories, possibly from differential effects of sea level fluctuations, barriers to gene flow and historical biogeography.