Description: Highlights: • A combination of methods is necessary to assess the foraging ecology of avocets. • Marine fish make up a higher proportion of the diet than previously assumed. • Telemetry data indicate that intertidal channels are important foraging grounds. • Avocet behaviour implies high fish densities in intertidal channels. • Protected areas are important habitats for breeding, resting and foraging avocets. Abstract: Pied avocets (Recurvirostra avosetta) breeding in the Wadden Sea typically forage in shallow water, using their characteristic upward-curved bill to feed on macrozooplankton in the water column and prey items in the uppermost centimetre of the sediment. Former studies on prey choice based on droppings and visual observations of feeding behaviour suggested that ragworms were the main prey items of avocets. The present study combined different methods to assess the foraging ecology of breeding avocets in the eastern Wadden Sea. Important foraging grounds were identified using GPS telemetry. Diet was analysed from droppings and stable isotope signatures of whole blood samples from breeding avocets at two different colonies in April–June 2014 and 2015. Analysis of droppings confirmed the former results, but stable isotope analysis suggested that marine fish comprised the highest proportion of the avocet diet by mass. Telemetry data indicated that intertidal channels close to the breeding areas were used as the main foraging grounds. Avocets performed short foraging trips (maximum distance: 0.3–5.9 km) mainly during the daytime. Logger data and diet analysis thus implied the existence of high fish densities in intertidal channels, underlining the importance of this saltmarsh habitat as foraging areas for breeding avocets.

Description: Body condition and energy reserves are important indicators of organism health, habitat suitability and predictors for the reproductive success in fish. In Greenland waters, Atlantic cod (Gadus morhua) inhabits different habitats in shallow and deep parts on top of the shelf and along slopes, where diet composition differs. We investigated the influence of habitat heterogeneity and trophic niche on body condition using organosomatic indicators, e.g. the morphometric index K, hepatosomatic and gonadosomatic indices, and biochemical indicators, e.g. lipid content and fatty acid compositions, of mature female cod. Body condition differed between sites and peaked in north-eastern regions in depths below 300 m towards the slope of the northern Irminger Sea. Trophic niches as indicated by stable isotope values and stomach composition data varied between sites, which was likely related to depth and differences between benthic and pelagic feeding regimes. Total lipid content and fatty acid profiles important for reproduction were associated with a pelagic diet comprised of mesopelagic fish and crustaceans. Interestingly, consumption of capelin was not linked to highest energy reserves as indicated by traditional body condition indices, such as K and the hepatosomatic index, but lowest ratios of eicosapentaenoic acid to arachidonic acid in gonads, which are known to be beneficial for high egg production. This shows that body condition on biochemical level can differ from conventionally used indices, which emphasizes the need to take fatty acid composition into account, when investigating condition and reproductive potential in cod. Our results emphasize that the factor habitat cannot be ignored for population replenishment of the cod stocks in Greenland waters and indicate that capelin as part of an Arcto-boreal diet benefits reproductive success in cod.