Organochlorine residues in Antarctic snow

DDT is a useful model compound for studying the circulation of a toxic pollutant in the global environment1,2. An understanding of this process could in future be related to potentially more hazardous materials. Present models of the dynamics of DDT circulation can account for only a small fraction of the amounts of DDT and DDE which are known to have been released into the environment. Major unknowns include the extent to which the atmosphere and oceans act as reservoirs and the transfer rate of these residues from the atmosphere to the oceans where, according to present ideas, they may be removed from circulation by transfer to the abyss3. Such atmospheric and oceanic transport mechanisms may carry pollutants into the ecologically protected area of Antarctica and it is necessary to assess the extent to which this is occurring and the relative importance of alternative input routes. The atmosphere has been assumed to play the major role in the transport cycle but there is a lack of supporting data. We report here levels of DDT and metabolites in Antarctic snow which suggest that the role of the atmosphere in the transport of DDT may have been overemphasised

Evaluating the effects of population management on a herbivore grazing conflict

Abundant herbivores can damage plants and so cause conflict with conservation, agricultural, and fisheries interests. Management of herbivore populations is a potential tool to alleviate such conflicts but may raise concerns about the economic and ethical costs of implementation, especially if the herbivores are ‘charismatic’ and popular with the public. Thus it is critical to evaluate the probability of achieving the desired ecological outcomes before proceeding to a field trial. Here we assessed the potential for population control to resolve a conflict of non-breeding swans grazing in river catchments. We used a mathematical model to evaluate the consequences of three population management strategies; (a) reductions in reproductive success, (b) removal of individuals, and (c) reduced reproductive success and removal of individuals combined. This model gave accurate projections of historical changes in population size for the two rivers for which data were available. Our model projected that the River Frome swan population would increase by 54 %, from 257 to 397 individuals, over 17 years in the absence of population control. Removal of ≥ 60 % of non-breeding individuals each year was projected to reduce the catchment population below the level for which grazing conflicts have been previously reported. Reducing reproductive success, even to 0 eggs per nest, failed to achieve the population reduction required. High adult and juvenile survival probabilities (> 0.7) and immigration from outside of the catchment limited the effects of management on population size. Given the high, sustained effort required, population control does not represent an effective management option for preventing the grazing conflicts in river catchments. Our study highlights the need to evaluate the effects of different management techniques, both alone and in combination, prior to field trials. Population models, such as the one presented here, can provide a cost-effective and ethical means of such evaluations