Contrasting Population Trends at Two Razorbill Colonies in Atlantic Canada: Additive Effects of Fox Predation and Hunting Mortality?

• Main Authors: Lavers, JL, Jones, IL, Robertson, GJ, Diamond, AW
• Format: Article in Journal/Newspaper
• Language: English
• Published: Resilience Alliance Publications 2009
• Subjects: Biological Sciences; Ecology; Ecology not elsewhere classified; Canada; Gannet Islands; Alca torda; Alopex lagopus; Razorbill; Seal Island; uria
• Online Access: http://www.ace-eco.org/articles/322.html; http://ecite.utas.edu.au/77908

We developed a stochastic, stage-based, matrix-projection population model to assesspopulation viability and estimate the impact of mortality caused by hunting, illegal and incidental to themurre (Uria sp.) hunt, and fox (Alopex lagopus) predation on Razorbill (Alca torda) populations breedingon the Gannet Islands, Labrador, the affected population, and Machias Seal Island, New Brunswick, theunaffected population. We estimated the potential population growth rate in the absence of anthropogenicmortality sources by using juvenile survival estimates from the relatively unaffected Machias Seal IslandRazorbill population. We used data collected on fox predation on the Gannet Islands from 19782009 toestimate the change in productivity as a result of fox presence. The intrinsic growth rate (l) of the stochasticmatrix based on vital rates from the Gannet Islands was 0.9570.008 and 1.0580.005 for Machias SealIsland. Hunting mortality reduced the predicted Gannet Islands population growth rate by 0.033, while foxpredation reduced population growth rate by 0.017. These sources combined reduced the baseline populationgrowth rate by 0.050. According to our model, the Razorbill population on Machias Seal Island appearsto be growing rapidly. In contrast, the Gannet Islands population may decline, likely because of hunting.However, oceanographic differences between the two areas and uncertainty regarding dispersal behaviorin this species may also contribute to the disparity between populations. Based on our findings, we makeseveral recommendations for the conservation and management of Razorbills in Atlantic Canada.