Stephen D. Gregory

Island prioritization for invasive rodent eradications with an emphasis on reinvasion risk

Invasive rodents occur on over 80% of the world’s island groups, invasions are continuing, and rodent impacts on insular wildlife have been well demonstrated. The extent of this problem calls for tools to aid large-scale prioritisation among the many candidate eradication operations. As conservation funds are limited, biologists have responded with prioritisation systems based on financial cost-effectiveness. Instead, we claim that long-term conservation gain should be the primary focus when prioritising islands for invasive rodent eradication. This concept is embodied mainly by invasive rodent reinvasion risk, which we categorise as natural or anthropogenic, based on the mechanism of reinvasion and our ability to mitigate the risk. The result is a first-pass triage system that prioritises eradication programmes by their long-term conservation potential, not their immediate value for money. To construct a prioritization list, we group islands into units for simultaneous eradication, to minimize inter-island reinvasion risk, and then assign weights to levels of unit reinvasion risk and unit conservation value. The choice of parameter weights may depend on capacity for biosecurity action (i.e. reduction in reinvasion risk) and a choice of tertiary filter variables can further discriminate within priority ranks. We illustrate our prioritization framework with a case study on rodents in New Caledonia but explain how our system can be adapted to suit any invasive rodent species or island configuration.

Long-Term Field Data and Climate-Habitat Models Show That Orangutan Persistence Depends on Effective Forest Management and Greenhouse Gas Mitigation

Background Southeast Asian deforestation rates are among the world’s highest and threaten to drive many forest-dependent species to extinction. Climate change is expected to interact with deforestation to amplify this risk. Here we examine whether regional incentives for sustainable forest management will be effective in improving threatened mammal conservation, in isolation and when combined with global climate change mitigation. Methodology/Principal Findings Using a long time-series of orangutan nest counts for Sabah (2000–10), Malaysian Borneo, we evaluated the effect of sustainable forest management and climate change scenarios, and their interaction, on orangutan spatial abundance patterns. By linking dynamic land-cover and downscaled global climate model projections, we determine the relative influence of these factors on orangutan spatial abundance and use the resulting statistical models to identify habitat crucial for their long-term conservation. We show that land-cover change the degradation of primary forest had the greatest influence on orangutan population size. Anticipated climate change was predicted to cause reductions in abundance in currently occupied populations due to decreased habitat suitability, but also to promote population growth in western Sabah by increasing the suitability of presently unoccupied regions. Conclusions/Significance We find strong quantitative support for the Sabah government’s proposal to implement sustainable forest management in all its forest reserves during the current decade; failure to do so could result in a 40 to 80 per cent regional decline in orangutan abundance by 2100. The Sabah orangutan is just one (albeit iconic) example of a forest-dependent species that stands to benefit from sustainable forest management, which promotes conservation of existing forests.

Is bigger really better? Towards improved models for testing how Atlantic salmon Salmo salar smolt size affects marine survival: S. SALAR SMOLT SIZE AND MARINE SURVIVAL

A general framework is presented that should enhance our understanding of how intrinsic factors, such as body size, and extrinsic factors, such as climate, affect the dynamics and demographics of fish populations. Effects of intrinsic factors, notably studies relating juvenile Atlantic salmon Salmo salar body size to their probability to return as an adult, are often context-dependent and anecdotal, due to data constraints. By merit of its flexible specification, this framework should admit datasets with a range of situation-specific nuances, collected using different approaches, and thereby deliver more general and robust findings for more effective population management.

Under what circumstances does the capture and tagging of wild Atlantic salmon Salmo salar smolts affect probability of return as adults

Adult return rates for wild Atlantic salmon Salmo salar smolts captured in a rotary screw trap and tagged with coded wire (CW) tags were compared with a control group, using detections from passive integrated transponder (PIT) antennae systems over 7 years in a small chalk stream in southern England, U.K. Compared with control smolts, capture and CW-tagging of experimental smolts affected detected return rates only under certain conditions, with a decreased return probability for smolts caught and tagged following mild winter river temperature anomalies and during the night. Similarly, analysis of the experimental smolts revealed that capture and CW-tagging following mild winters decreased their probability of return as adults. There were also marginal positive effects of length at PIT-tagging as parr and length at CW-tagging as smolts, on individual probability of return as adult. The results support the hypothesis that the effect of procedures involving the capture and tagging of migrating wild S. salar smolts will vary with the circumstances under which they are performed. The implications of the findings are considered in the context of ongoing investigations to derive and report marine return rates for S. salar in support of national and international stock assessments and in developing best practice.