Population‐level effects of lead fishing tackle on common loons

Poisoning from lead fishing tackle has been identified as the leading cause of mortality in adult common loons (Gavia immer). As a K‐selected species, adult survival is a critical component in the population demography of loons, but the population‐level effects of mortality from ingested lead tackle on loons have not been quantified. We used a long‐term dataset (1989–2012) on common loon mortality in New Hampshire, USA, to describe the types of lead tackle ingested by loons, investigate methods of ingestion of lead tackle, document the number and rate of adult mortalities resulting from lead tackle, and test for a population‐level effect of lead tackle on the loon population in New Hampshire. Nearly half (48.6%) of collected adult mortalities resulted from lead toxicosis from ingested lead fishing tackle, representing an adjusted annual mortality rate of 1.7 ± 0.6% (SD) of the statewide population. Jigs accounted for 52.6% and sinkers for 38.8% of the archived lead tackle objects removed from loons, a higher proportion of jigs than has been reported in previous studies. The timing of lead tackle mortalities and a high incidence of accompanying non‐lead associated fishing gear (hooks, fishing line, leaders, swivels, wire), which peaked in July and August, suggest that loons obtain the majority of lead tackle from current fishing activity rather than from a reservoir of lead tackle on lake bottoms. To project the statewide loon population in the absence of lead fishing tackle as a stressor, we constructed a retrospective population model, which re‐inserted loons that died from lead tackle into the population, and used linear regression to test for a population‐level effect. We defined a population‐level effect as a difference in the population growth rate (λ). We estimated that lead tackle mortality reduced the population growth rate (λ) by 1.4% and the statewide population by 43% during the years of the study. This study suggests that replacing lead fishing sinkers and jigs weighing ≤28.4 g with non‐toxic alternatives would result in an immediate benefit to the loon population in New Hampshire. © 2017 The Wildlife Society.