Drivers of productivity in a subarctic seabird: Arctic Terns in Iceland

Thesis abstract Marine ecosystems are changing rapidly in response to anthropogenic and environmental stresses, and seabird populations that depend on marine resources are in decline in many areas of the world. Iceland supports internationally important populations of many seabird species and, although fishing pressures in Icelandic waters are relatively low, the impacts of current climatic and oceanic changes are predicted to be particularly severe at high latitudes, including Iceland. However, little is known about the current status and demography of Icelandic seabird populations. In this thesis, I explore the breeding demography of Arctic Terns, Sterna paradisaea, at colonies throughout the W and NE of Iceland, between 2008 and 2011. Although Arctic Tern productivity varied among colonies, it was generally low in both regions, primarily because of very low chick survival rates. Low chick survival was primarily a consequence of low growth rates throughout the pre-fledging period, and the application of forensic ecology techniques showed that chick mortality occurred throughout each breeding season and at all ages. Prey composition and prey delivery rates varied regionally and among colonies. The main high quality marine prey are sandeels, Ammodytes spp., In W-Iceland and capelin, Mallotus villosus, in NE-Iceland, but non-marine prey of low nutritive value comprised a large proportion of chick diet in both regions. While productivity in W-Iceland increased with prey delivery rates, in NE-Iceland prey delivery was either inconsistent or low in quality, and productivity was always low. A suite of changes in marine prey communities appears to be impacting Icelandic Arctic Terns. These may include fishing impacts on capelin abundance and/or oceanic and climatic influences on the abundance and availability of sandeels, which are not fished in Iceland. These changes may also be impacting other seabird species in Iceland, for which there is also some evidence of recent low productivity