Regulation of lead fishing weights results in mute swan population recovery

Abstract

Legal regulation of human activities is a key mechanism for alleviating anthropogenic impacts on wildlife populations. Conservationists frequently request the regulation of toxic substances such as lead, which can be harmful to animals even at low levels of exposure. However, without assessments of the effectiveness of legislation, such regulations may be undermined or revoked and opportunities to make amendments to improve the legislation may be missed. Here we carried out a population-level study of the effectiveness of regulating the use of lead. We show that the increase in population size of a charismatic waterbird (the mute swan Cygnus olor) in Great Britain over 39 years was best explained by the regulation of lead fishing weights, rather than by changes in food supplies, habitat quality, or winter temperature. The proportion of individuals dying of lead poisoning dropped following regulation, from 0.34 to 0.06, suggesting that higher survival rates were the demographic driver of increased population size. Legal restriction therefore succeeded in alleviating, although not eliminating, the impact of poisoning on mute swans. Restrictions on the use of toxic substances, and their release into the environment, would provide an effective conservation mechanism for reducing negative effects of human activities on wildlife populations. At a time when many policy makers prefer to rely on voluntary actions or market forces to achieve change, our study highlights that legal regulations on human activities can be an effective means of alleviating anthropogenic impacts on wildlife.