Search the SPREP Catalogue

Invasive rodents are successful colonists of many ecosystems around the world, and can have very flexible foraging behaviours that lead to differences in spatial ranges and seasonal demography among individuals and islands. Understanding such spatial and temporal information is critical to plan rodent eradication operations, and a detailed examination of an island’s rat population can expand our knowledge about possible variation in behaviour and demography of invasive rats in general. Here we investigated the movements and survival of Pacific rats (Rattus exulans) over five months on sub-tropical Henderson Island in the South Pacific Ocean four years after a failed eradication operation. We estimated movement distances, home range sizes and monthly survival using a spatially-explicit Cormack-Jolly-Seber model and examined how movement and survival varied over time. We captured and marked 810 rats and found a median maximum distance between capture locations of 39 ± 25 m (0–107 m) in a coastal coconut grove and 61 ± 127 m (0–1,023 m) on the inland coral plateau. Estimated home range radii of Pacific rats on the coral plateau varied between ‘territorial’ (median: 134 m; 95% credible interval 106–165 m) and ‘roaming’ rats (median: 778 m; 290–1,633 m). The proportion of rats belonging to the ‘roaming’ movement type varied from 1% in early June to 23% in October. There was no evidence to suggest that rats on Henderson in 2015 had home ranges that would limit their ability to encounter bait, making it unlikely that limited movement contributed to the eradication failure if the pattern we found in 2015 is consistent across years. We found a temporal pattern in monthly survival probability, with monthly survival probabilities of 0.352 (0.081–0.737) in late July and 0.950 (0.846–0.987) in late August. If seasonal variation in survival probability is indicative of resource limitations and consistent across years, an eradication operation in late July would likely have the greatest probability of success.

Rodent eradications in tropical environments are often more challenging and less successful than those in temperate environments. Reduced seasonality and the lack of a defined annual resource pulse influence rodent population dynamics differently than the well-defined annual cycles on temperate islands, so an understanding of rodent ecology and population dynamics is important to maximise the chances of eradication success in the tropics. Here, we report on the recovery of a Pacific rat (Rattus exulans) population on Henderson Island, South Pacific Ocean, following a failed eradication operation in 2011. We assessed changes in the rat population using capture rates from snap-trapping and investigated seasonality by using capture rates from live-trapping. Following the failed eradication operation in 2011, rat populations increased rapidly with annual per capita growth rates, r, of 0.48–5.95, increasing from 60–80 individuals to two-thirds of the pre-eradication abundance within two years, before decreasing (r = -0.25 – -0.20), presumably as the population fluctuated around its carrying capacity. The long-term changes in rat abundance may, however, be confounded by short-term fluctuations: four years after the eradication attempt we observed significant variation in rat trapping rates among months on the plateau, ranging from 36.6 rats per 100 corrected trap-nights in mid-June to 12.6 in late August. Based on mark-recapture, we also estimated rat density fluctuations in the embayment forest between 20.4 and 42.9 rats ha-1 within one month in 2015, and a much lower rat density on the coral plateau fluctuating between 0.76 and 6.08 rats ha-1 in the span of two months. The causes for the short-term density fluctuations are poorly understood, but as eradication operations on tropical and subtropical islands become more frequent, it will be increasingly important to understand the behaviour and ecology of the invasive species targeted to identify times that maximise eradication success.

The Pacific Ocean Pollution Prevention Programme (PACPOL) mission is to protect public health, safety, environment and natural resources of the Pacific Islands from the effects of ship sourced marine pollution

Marine pollution is widely recognised as one of the four major threats to the world’s oceans, along with habitat destruction, over-exploitation of living marine resources and invasive marine species. Spills of oil and other chemicals into the marine environment, both from ships and land-based sources, is a significant source of pollution.

Assisting the South Pacific Regional Environment Programme's (SPREP) island members to plan, prepare and respond to marine spills is one of the four activity areas of the Pacific Ocean Pollution Prevention Programme (PACPOL). PACPOL activities currently include a regional risk assessment regional and national contingency plans, formulation of a regional equipment strategy and facilitating regular workshop to discuss marine spill issues. The aim of this initial shipping risk study was to identify and quantify the shipping routes, frequency of voyages and types of cargoes transported in the region as well as to map shipping incidents, navigational hazards and assess the risk of marine pollution across the region, EEZs and at a port scale. The regional and EEZ distribution of risk potential showed clusters of high risk in Fiji, French Polynesia, Papua New Guinea and Solomon Islands. Smaller clusters occurred in Tonga, the Samoa's, Vanuatu and the corridor from Chuuk northward past Guam and the Northern Mariana Islands. Another potential marine pollution risk for the Pacific is the fuel oil and cargoes remaining on WWII shipwrecks deteriorating in the waters of the region. More than 1000 such wrecks have been identified amounting to over 3 million tons of shipping lost.

Report on the Strategic Environmental Assessment Oil Spill Incident USS Mississinewa, Ulithi Lagoon, Yap State, Federated States of Micronesia : Draft, 18th September, 2001 / by Trevor Gilbert