Recruitment and survival of immature seabirds in relation to oil spills and climate variability

Abstract

Summary 1.In long-lived animals with delayed maturity, the non-breeding component of the population may play an important role in buffering the effects of stochastic mortality. Populations of colonial seabirds often consist of more than 50% non-breeders, yet because they spend much of their early life at sea, we understand little about their impact on the demographic process. 2. Using multistate capture-mark-recapture techniques, we analyse a long-term data set of individually identifiable common guillemots, Uria aalge Pont., to assess factors influencing their immature survival and two-stage recruitment process. 3. Analysis of the distribution of ringed common guillemots during the non-breeding season, separated by age classes, revealed that all age classes were potentially at risk from four major oil spills. However, the youngest age class (0-3 years) were far more widely spread than birds 4-6 years old, which were more widely spread than birds aged 6 and over. Therefore the chance of encountering an oil spill was age-dependent. 4. A 2-year compound survival estimate for juvenile guillemots was weakly negatively correlated with winter sea-surface temperature, but was not influenced by oil spills. Non-breeder survival did not vary significantly over time. 5. In years following four oil spills, juvenile recruitment was almost double the value in non-oil-spill years. Recent work from Skomer Island showed a doubling of adult mortality associated with major oil spills, which probably reduced competition at the breeding colony, allowing increased immature recruitment to compensate for these losses. We discuss the implications of compensatory recruitment for assessing the impact of oil pollution incidents.

Effects of climate change and fisheries bycatch on Southern Ocean seabirds: a review

“…Southern Ocean seabirds are also increasingly exposed to marine debris, pollutants and chemicals, which may also potentially affect their physiology, behaviour and demography (Burger & Gochfeld 2002). For example, in common guillemots Uria aalge breeding in the North Atlantic there was a doubling of adult mortality associated with major oil spills in the wintering areas of the birds, and recruitment was higher in years following oil spills than following non-oil-spill years, probably through reduced competition and compensatory recruitment at the breeding colony (Votier et al 2008). Finally, increased freshwater input from melting glaciers and ice shelves acts to increase stratification along coastal margins, which, in turn, may affect phytoplankton blooms (Moline et al 2008) and release persistent organic pollutants into the ecosystem where they may accumulate in higher trophic level predators (Geisz et al 2008).…”

Seabirds and climate: knowledge, pitfalls, and opportunities

“…Testing hypotheses about the effects of climate on seabird ecology (e.g., diet, behavior, and phenology) is a first step toward making predictions regarding climate effects on population trajectories and to understanding the mechanisms linking patterns and processes, but this is just the first step. In general, we should move to a research devoted more toward forecasting the effects of global change (not only climate, but considering the synergetic effects of several agents of global change (e.g., Votier et al, 2008b;Finkelstein et al, 2010;Rolland et al, 2010;Lebreton, 2011), and to offer evidence that can help managers develop a roadmap of conservation actions (Jenouvrier, 2013). However, we need to collect the foundational information regarding links between demographics and climate, and the mechanisms that link them as we must have robust estimates of vital rates to build predictive models, and this constitutes a big challenge.…”

Using integrated land- and boat-based surveys to inform conservation of the Critically Endangered Balearic shearwater

“…Our identification of possible ageand/or colony-partitioning in the population, which was also tentatively suggested by Guilford et al (2012), identifies a potential risk of the loss of entire age cohorts or colonies from such catastrophic events. However, age partitioning, in particular, may be beneficial at the population level be cause if breeders and non-breeders are spatially segregated, this can provide the opportunity for compensatory recruitment should one cohort be im pacted by a catastrophic event (Votier et al 2008b, Péron & Grémil-let 2013.…”