Glaucous-winged gulls as sentinels for ecosystem change

This thesis discusses the Glaucous-winged Gull (Larus glaucescens) as an indicator of ecosystem change in the Salish Sea region.

Glaucous-winged Gull (Larus glaucescens). Photo courtesy of USGS.
Glaucous-winged Gull (Larus glaucescens). Photo courtesy of USGS.

Glaucous-winged gulls are generalist gulls found throughout the Salish Sea. Their populations have been studied since the mid-1800s, and in the 20th century researchers observed dramatic growth followed by a steep decline, which some models have attributed to decreasing consumption of forage fish. Seabirds have several traits that make them reliable indicators, including coloniality, competition with humans for fish, and sensitivity to environmental change. However, most studies take a short-term approach, and there is a lack of research investigating the causes of long-term shifts in seabird populations.

There is little data of fish populations in the Salish Sea that are not commercially exploited, but it is probable that forage fish now absent or scarce in the region, such as pilchard (Sardinops sagax) and capelin (Mallotus villosus) were once a significant component of gull diets. Using stable isotope analysis of feathers collected over 150 years, the study demonstrates links between declining forage fish populations and diet and population change in glaucous-winged gulls, and suggests that further analysis may shed light on long-term ecosystem changes and their potential effects on native species populations.

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