Relative importance of human activities and climate driving common murre population trends in the Northwest Atlantic

Seabird populations are affected by environmental and anthropogenic influences on a global scale. Many population-level responses to climate change have been shown, yet few studies have addressed the additive and/or relative impact of environmental and anthropogenic influences on seabird populations. Using a mixed model approach, we analyzed the trends in plot counts of common murres (Uria aalge) from a Low Arctic colony at Cape St. Mary’s, Newfoundland, across 26 years (1980–2006). We tested for associations between population change and various environmental and anthropogenic covariates: water temperature, winter North Atlantic Oscillation, hunting mortality, oil pollution, by-catch in fishing gear, and visitor disturbance. The number of murres occupying central plots decreased from 1980 to 1989 and increased from 1990 to 2006. Annual changes in the population were negatively associated with the estimated number of murres killed in the Newfoundland murre hunt and the high numbers killed in the early 1980s likely caused the observed population decline. The large number of gillnets set in Newfoundland waters during the 1980s, and associated incidence of drowning through by-catch, probably also contributed to the observed decline. Though a centennially significant cold-water perturbation in 1991 forced a regime shift in pelagic food webs, the effect of ocean climate variability on the population was not obvious. We conclude that management efforts should focus on assessing and mitigating the effects of human-induced influences and consider the potential additive effects of climate change.