Spatial variation in vital rates and population growth of thick-billed murres in the Atlantic Arctic

Abstract

Understanding spatiotemporal variation in vital rates and population growth rates is a central aim of population ecology, and is critical to conservation of migratory species where different populations may spend the non-breeding season in sometimes widely separated areas. However, estimating those parameters and identifying the underlying drivers of variation for species migrating to remote areas is challenging. The thick-billed murre Uria lomvia is a colonial seabird with a pan-Arctic distribution. Previous studies have documented large-scale spatial variation in population growth in the species’ Atlantic range, with eastern populations declining and western populations being stable, and suggested that this variation was linked to conditions in the wintering areas. We analyse variation in breeding success and adult survival from colonies throughout the Atlantic range, construct region-specific stochastic population models, and compare model predictions to observed colony growth rates. Breeding success was uniformly high in Greenland and Iceland, lower and more variable in Spitsbergen, Bjørnøya and Hudson Bay, and low at Jan Mayen. Adult survival was average or high in all colonies during the 2010s. Observed colony growth rates were lower than modelled growth rates for most populations. This suggests that pre-breeding survival or breeding propensity must have been lower than assumed in many of these populations. Low pre-breeding survival could be linked to poor feeding conditions in fall and winter, possibly influenced by large-scale oceanographic variation. Our results support the idea that seabird populations not subject to breeder mortality due to anthropogenic causes are regulated mainly through variation in pre-breeding survival.

Lower nutritional state and foraging success in an Arctic seabird despite behaviorally flexible responses to environmental change

“…Longer flights could represent a high energy search strategy (Norberg, 2021), suggesting murres could be tracking distant ice edges, cueing into foraging locations with higher prey availability when ice is still present. For example, in Iceland, thick-billed murres are cold-water specialists, selectively foraging in cooler waters in fjords and along the Marginal Ice Zone (Bonnet-Lebrun, Larsen, Frederiksen, et al, 2021;Bonnet-Lebrun, Larsen, Thórarinsson, et al, 2021). As we then observed a higher nutritional state (lower levels of non-esterified fatty acids) within a high ice regime during the chick-rearing stage, this further suggests prey availability may have been higher during a high ice regime.…”

“…Furthermore, recent findings suggest environmental conditions during the nonbreeding season (overwintering and prebreeding areas) are one factor driving major differences in population trends of murres observed across the Atlantic, in addition to mortality caused by hunting and oil spills (Frederiksen et al, 2016(Frederiksen et al, , 2021. Rapid population declines are occurring in eastern Atlantic populations (breeding colonies in Iceland, Svalbard, and southwest Greenland) that overwinter in waters around southwest Greenland and Iceland (Frederiksen et al, 2016(Frederiksen et al, , 2021. Meanwhile, western Atlantic populations (breeding colonies in Canada and northwest Greenland), which overwinter in waters off Labrador and Newfoundland, remain stable (Frederiksen et al, 2016(Frederiksen et al, , 2021.…”

“…Rapid population declines are occurring in eastern Atlantic populations (breeding colonies in Iceland, Svalbard, and southwest Greenland) that overwinter in waters around southwest Greenland and Iceland (Frederiksen et al, 2016(Frederiksen et al, , 2021. Meanwhile, western Atlantic populations (breeding colonies in Canada and northwest Greenland), which overwinter in waters off Labrador and Newfoundland, remain stable (Frederiksen et al, 2016(Frederiksen et al, , 2021. In addition to the effect of geographic location and environmental change on seabird breeding success in a changing Arctic, the overall size of breeding colonies is also expected to play an interactive role, as murre colonies can range in size across several orders of magnitude, from fewer than 500 breeding pairs (Merkel et al, 2014) to more than 800,000 breeding pairs (Hickey & Craighead, 1977), and recent work has shown that murre foraging range scales to colony size with an exponent of 0.33 (Patterson et al, 2022).…”

Canadian murre harvest management in the face of uncertainty: a potential biological removal approach

“…Thickbilled murre harvest in Greenland has declined from 200,000−250,000 birds in the mid 1990s to 60,000−80,000 birds annually in 2011 (Merkel et al 2014). In 2020 and 2021 harvest was approximately 30,000 birds per year in Greenland (Frederiksen et al 2021; N. Holm, Greenland Ministry of Fisheries, Hunting and Agriculture, personal communication) and <3,000 birds in Iceland (B. Jónsson, North West Iceland Nature Center, personal communication). In spite of these reduced harvest levels, renewed concern about the sustainability of murre harvests emerged in the 2010s (Frederiksen et al 2019(Frederiksen et al , 2021, as thick-billed murre populations throughout the Atlantic, including depressed populations in Greenland, were showing signs of decline (Descamps et al 2013, Merkel et al 2014.…”

“…In 2020 and 2021 harvest was approximately 30,000 birds per year in Greenland (Frederiksen et al 2021; N. Holm, Greenland Ministry of Fisheries, Hunting and Agriculture, personal communication) and <3,000 birds in Iceland (B. Jónsson, North West Iceland Nature Center, personal communication). In spite of these reduced harvest levels, renewed concern about the sustainability of murre harvests emerged in the 2010s (Frederiksen et al 2019(Frederiksen et al , 2021, as thick-billed murre populations throughout the Atlantic, including depressed populations in Greenland, were showing signs of decline (Descamps et al 2013, Merkel et al 2014. Further, tracking studies of thick-billed murre clarified important linkages between breeding colonies and harvest areas that were previously unquantified (Frederiksen et al 2016).…”