A multi-method approach to monitor and categorize changes in diet composition in common guillemots in the Baltic Sea

• Main Authors: 3rd World Seabird Conference 2021, Berglund, Per-Arvid
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Underline Science Inc. 2021
• Subjects: Animal Science; Ecology; FOS Biological sciences; Ornithology; Berglund; common guillemot; Uria aalge; uria
• Online Access: https://dx.doi.org/10.48448/wfx9-cb83; https://underline.io/lecture/34793-a-multi-method-approach-to-monitor-and-categorize-changes-in-diet-composition-in-common-guillemots-in-the-baltic-sea

Abstract: Understanding seabirds' diets is key in understanding species reactions to current and future marine ecosystem changes. Finding appropriate and practical methods for diet sampling and ensuring comparability between historical and current studies is therefore essential. We studied the diet of common guillemot (Uria aalge) chicks at the Baltic Sea island of Stora Karlsö ((57° N, 17° E)) using a multi-method approach, combining dawn-to-dusk feeding watch studies (2005-2019), stomach content analysis (2008-2020), and nest sampling of discarded prey (1972-1976 + 2015-2021). Local chick diet composition was previously based on secondary data: prey dropped in nests not verified to represent consumed prey, and ocular feeding observations not allowing for distinction between sprat (Sprattus sprattus) and herring (Clupea harengus). By collecting 200+ chicks (deceased by unsuccessful landing during fledging), stomach content could be analyzed. This material was then compared with dropped prey of the same period. The material from the two sources matched, confirming the usefulness of dropped fish as an indicator of consumed prey. This allowed for a historical comparison of dropped fish, showing both some change in prey species composition and in prey size between the 1970s and today. Monitoring diet change over time can inform about both local seabird conditions, and marine ecosystem changes at large, and is fundamental in prey based models. Climate change, fisheries, eutrophication and population dynamics in all trophic levels possibly effect seabird diet composition and by comparing historical and current trends more can be known about links in marine ecosystems. Authors: Per-Arvid Berglund¹ ¹Baltic Seabird Project