Inter-annual climate variability affects foraging behavior and nutritional state of thick-billed murres breeding in the southeastern Bering Sea

Abstract

Sustainability within the fisheries of the commercially important European whelk Buccinum undatum has become a major concern because of over-exploitation and increased landings in many European coastal shelf seas due to the expansion of export markets to East Asian countries. Current management of B. undatum populations is difficult to achieve as several life history traits are problematic to accurately monitor. The current method of age determination for stock assessment has a low success rate and focuses on the use of putative annual rings on the surface of the organic operculum. Here, we validate an annual periodicity of growth ring formation in B. undatum statoliths that provides an alternative, reliable and accurate method for determining a whelk's age. Laboratory-reared juvenile B. undatum of known provenance and age deposited a hatching ring at the time of emergence from their egg capsule and a clearly defined growth ring during February of their first and second years. Stable oxygen isotope profiles from the shells of 2 adult whelks confirmed annual growth ring deposition by demonstrating seasonal cycles of δ 18O in the shell that matched the relative position and number of visible growth rings in the statolith. Validation of annually resolved statolith growth rings will, for the first time, provide fisheries scientists with a tool to determine the age structure of B. undatum populations and allow analytical stock assessments that will enable informed decisions for future management practices of whelk fisheries.

Variability in trophic level and habitat use in response to environmental forcing: isotopic niche dynamics of breeding seabirds in the southeastern Bering Sea

“…Whether a greater abundance of pollock is also beneficial for murres has been unclear, as water masses and prey at depth may be somewhat independent of the dynamics shaping the food web available to surface foragers (Byrd et al 2008b, Renner et al 2016. Our results, however, indicate that common and thick-billed murres shifted towards shelf-based prey on St. George and St. Paul Islands, suggesting that they may also be feeding on juvenile pollock in warm years (Sinclair et al 2008, Kokubun et al 2018. Although all 3 species in both colonies took advantage of more abundant shelf-based prey in warm years in some way, we found that isotopic niche dynamics in the 2 colonies were different between warm and cold years and among species.…”

“…The diets of murres and black-legged kittiwakes have been documented to be diverse, including forage fish and invertebrate species (Iverson et al 2007, Sinclair et al 2008, Renner et al 2012. To date, however, efforts to detect broad relationships in this region between the diet of murres and kittiwakes nesting at the Pribilof Islands and regional climate indices have failed to find any consistent trends (Renner et al 2012, 2014, but see Kokubun et al 2018 for thick-billed murres). In contrast, shifting patterns in habitat use have been documented from ship-based surveys at both seasonal and inter-annual time scales (Schneider & Hunt 1984, Renner et al 2016, Suryan et al 2016, Hunt et al 2018.…”

“…those breeding on St. George Island) were able to exploit additional prey sources in the vicinity of their breeding colony. Consuming more prey on the shelf would potentially reduce the cost of foraging for adults during the chick-rearing period (Kokubun et al 2018). While warm conditions in early summer have been linked to abundant young-of-the-year pollock in the upper water column of the shelf (Renner et al 2016), warm conditions in late summer and autumn result in low recruitment of the same young pollock (Hunt et al 2011, Mueter et al 2011.…”

“…These 2 islands are located 60 km apart (Byrd et al 2008a). Tracking studies have revealed that murres and kittiwakes rarely forage in the area between the 2 colonies, and that there is little overlap in their shelf and slope foraging locations (Harding et al 2013, Kokubun et al 2018.…”

“…In cold years, murres and kittiwakes breeding on the Pribilof Islands incurred relatively high levels of nutritional stress, suggesting that food was scarce or difficult to obtain (Paredes et al 2012, Satterthwaite et al 2012, Kokubun et al 2018. In warm years, however, they had relatively low levels of nutritional stress, indicating that food was abundant or more easily obtained (Benowitz-Fredericks et al 2008, Satterthwaite et al 2012, Harding et al 2013.…”