Analysis of stable isotope ratios in blood of tracked wandering albatrosses fails to distinguish a δ¹³C gradient within their winter foraging areas in the southwest Atlantic Ocean

Abstract

International audienceRATIONALE: The main limitation of isotopic tracking for inferring distribution is the lack of detailed reference maps ofthe isotopic landscape (i.e. isoscapes) in the marine environment. Here, we attempt to map the marine δ13C isoscape forthe southwestern sector of the Atlantic Ocean, and assess any temporal variation using the wandering albatross as amodel species.METHODS: Tracking data and blood and diet samples were collected monthly from wandering albatrosses rearingchicks at Bird Island, South Georgia, during the austral winter between May and October 2009. The δ13C and δ15N valueswere measured by mass spectrometry in plasma and blood cells, and related to highly accurate data on individualmovements and feeding activity obtained using three types of device: GPS, activity (immersion) loggers and stomachtemperature probes.RESULTS: The tracked birds foraged in waters to the north or northwest of South Georgia, including the Patagonianshelf-break, as far as 2000 km from the colony. The foraging region encompassed the two main fronts in the SouthernOcean (Polar and Subantarctic fronts). The δ13C values varied by only 2.1 ‰ in plasma and 2.5 ‰ in blood cells, andno relationships were found between the δ13C values in plasma and the mean latitude or longitude of landings or feedingevents of each individual.CONCLUSIONS: The failure to distinguish a major biogeographic gradient in δ13C values suggest that these values in thesouth Atlantic Ocean are fairly homogeneous. There was no substantial variation among months in either the δ13C or theδ15N values of plasma or blood cells of tracked birds. As birds did not show a significant change in diet composition orforaging areas during the study period, these results provide no evidence for major temporal variation in stable isotoperatios in consumer tissues, or in the regional marine isoscape in the austral winter of 2009

Age‐related variation in non‐breeding foraging behaviour and carry‐over effects on fitness in an extremely long‐lived bird

“…However, there was no latitudinal shift in distribution of the tracked birds from South Georgia with age, in contrast to our prediction. As we found no correlation between average δ 13 C and latitude (matching results for breeding birds; Ceia et al., ), we suggest that changes in δ 13 C might reflect different habitat preferences or diets of older males, as depletion in 13 C can also reflect greater reliance on offshore than inshore, or pelagic than benthic prey (Phillips, Bearhop, et al., ). It has been hypothesized that old males forage further south to take advantage of stronger winds, thereby reducing flight costs (Jaeger et al., ; Lecomte et al., ).…”

Stable Isotope Dynamics (δ13C and δ15N) in Neritic and Oceanic Waters of the North Atlantic Inferred From GPS-Tracked Cory’s Shearwaters

“…Thus, we were able to assess their interconnectivity and show which variables should be more prone to drive isotopic values. Some of these (or related) variables have been applied in other studies on stable isotope patterns in the marine environment both spatially and temporally (e.g., Chouvelon et al, 2012;Ceia et al, 2015b;Quillfeldt et al, 2015;Oczkowski et al, 2016). Due to the peculiarity of the existence of a large canyon very close to the colony of Berlenga (Nazaré canyon), the distance to this feature was considered as a potential explanatory variable.…”

“…According with Magozzi et al (2017) the transfer of temporal variations in baseline levels to consumer tissues decreases with increasing trophic level, potentially leading to the averaging of temporal baseline variations in high-trophic level organisms. In general, seabirds such as the Cory's shearwater are top consumers that feed on mid-trophic level prey that integrate (and then buffer) spatio-temporal isotopic variations (especially at a local scale) that could weak the seasonal effect effectively present in prey (Ceia et al, 2015b).…”

“…In addition to the typical and strong spatial influence overall, isotopic values are often influenced by environmental and temporal drivers (Laakmann and Auel, 2010;Quillfeldt et al, 2015;Oczkowski et al, 2016). However, in some instances no major biogeographic gradients and temporal variations were found at a consumer level in regional areas of fairly homogeneous isotopic values (Roscales et al, 2011;Ceia et al, 2015b).…”

“…There is also some information regarding the dynamics of stable isotopes only for specific marine environments in the North Atlantic, for the Bay of Biscay (Chouvelon et al, 2012), the North Sea (MacKenzie et al, 2014), the Gulf of Maine (Oczkowski et al, 2016), the Northwest Atlantic (Ceriani et al, 2014), and the oligotrophic North Atlantic waters (Montoya et al, 2002). However, local and regional maps of marine isoscapes in the Atlantic Ocean for high-trophic level organisms such as seabirds are still scarce and mainly limited to the Southern Atlantic (e.g., Jaeger et al, 2010;Quillfeldt et al, 2010Quillfeldt et al, , 2015Ceia et al, 2015b). Marine isoscapes can be a powerful tool to study migrations, wildlife movements and trophic interactions in the region of the North Atlantic (Roscales et al, 2011;Ceriani et al, 2014), but to our knowledge no detailed reference maps are available nor studies focusing in the stable isotope dynamics of high-trophic level organisms at both local (i.e., dozens of km) and regional (i.e., hundreds of km) scales, comprising both oceanic and neritic waters.…”