Decline in an Atlantic Puffin Population: Evaluation of Magnitude and Mechanisms

Abstract

Determining which demographic and ecological parameters contribute to variation in population growth rate is crucial to understanding the dynamics of declining populations. This study aimed to evaluate the magnitude and mechanisms of an apparent major decline in an Atlantic Puffin Fratercula arctica population. This was achieved using a 27-year dataset to estimate changes in population size and in two key demographic rates: adult survival and breeding success. Estimated demographic variation was then related to two ecological factors hypothesised to be key drivers of demographic change, namely the abundance of the main predator at the study site, the Great Skua Stercorarius skua, and Atlantic Puffin chick food supply, over the same 27-year period. Using a population model, we assessed whether estimated variation in adult survival and reproductive success was sufficient to explain the population change observed. Estimates of Atlantic Puffin population size decreased considerably during the study period, approximately halving, whereas Great Skua population estimates increased, approximately trebling. Estimated adult Atlantic Puffin survival remained high across all years and did not vary with Great Skua abundance; however, Atlantic Puffin breeding success and quantities of fish prey brought ashore by adults both decreased substantially through the period. A population model combining best possible demographic parameter estimates predicted rapid population growth, at odds with the long-term decrease observed. To simulate the observed decrease, population models had to incorporate low immature survival, high immature emigration, or increasingly high adult non-breeding rates. We concluded that reduced recruitment of immatures into the breeding population was the most likely cause of population decrease. This study showed that increase in the size of a predator population does not always impact on the survival of adult prey and that reduced recruitment can be a crucial determinant of seabird population size but can easily go undetected.

Combined bottom‐up and top‐down pressures drive catastrophic population declines of Arctic skuas in Scotland

“…Driving seabird breeding failures in Orkney and Shetland have been shortages of postlarval sandeels during the chick‐rearing period (Miles et al., ; Oro & Furness, ; Phillips et al., ). Sandeels are high energy prey for seabirds (Rindorf, Wanless, & Harris, ; Wanless, Harris, Redman, & Speakman, ), and Shetland lacks suitable alternatives (Furness & Tasker, ).…”

“…Overall change in Arctic skua population size plotted against mean annual Arctic skua productivity for 20 colonies during 1992-2015 (see Supporting Information Table S1 for colony identities and number of years) (Miles et al, 2015;Oro & Furness, 2002;Phillips et al, 1996).…”

“…In the northeast Atlantic Ocean, great skua Stercorarius skua is a scavenger whose exploitation of anthropogenic food (fish discarded from fishing vessels) and reduced persecution helped fuel recent population growth (Furness, 1977;Jones, Smith, Williams, & Ramsay, 2008;Votier, Bearhop, Fyfe, & Furness, 2008). Increasingly since the 1980s, it is also a major predator of seabirds (Hamer, Furness, & Caldow, 1991;Miles et al, 2015;Votier, Bearhop, Ratcliffe, Phillips, & Furness, 2004). By contrast, at Scottish colonies, the smaller Arctic skua Stercorarius parasiticus eats mostly fish kleptoparasitised from terns (e.g., Arctic tern Sterna paradisaea), small gulls (e.g., black-legged kittiwake Rissa tridactyla) and auks (e.g., common guillemot Uria aalgae and Atlantic puffin Fratercula arctica) (Furness, 1977;Jones, 2002;Phillips, Caldow, & Furness, 1996).…”

“…These declines are a major conservation concern, due to global importance of Scotland's great skuas (57% of world population; BirdLife International, 2018) and extent of Arctic skua decline (Eaton et al, 2015). Since the late 1980s, seabirds in Orkney and Shetland have experienced frequent poor breeding success, leading to localised population declines (Miles et al, 2015;Mitchell, Newton, Ratcliffe, & Dunn, 2004). Similar seabird declines throughout the northeast Atlantic Ocean (Fauchald et al, 2015;Vigfusdottir, Gunnarsson, & Gill, 2013) are closely linked to reduced availability of lesser sandeels Ammodytes marinus (Miles et al, 2015;Oro & Furness, 2002;Phillips et al, 1996).…”

“…Since the late 1980s, seabirds in Orkney and Shetland have experienced frequent poor breeding success, leading to localised population declines (Miles et al, 2015;Mitchell, Newton, Ratcliffe, & Dunn, 2004). Similar seabird declines throughout the northeast Atlantic Ocean (Fauchald et al, 2015;Vigfusdottir, Gunnarsson, & Gill, 2013) are closely linked to reduced availability of lesser sandeels Ammodytes marinus (Miles et al, 2015;Oro & Furness, 2002;Phillips et al, 1996). Consequently, within Europe several seabird hosts of Arctic skuas are Endangered (e.g., Atlantic puffin), Near-Threatened (common guillemot) or Vulnerable (black-legged kittiwake), and thus, Arctic skua is Endangered within the European Union (BirdLife International, 2015).…”