Investigating stock structure and trophic relationships among island-associated dolphins in the oceanic waters of the North Atlantic using fatty acid and stable isotope analyses

Abstract

International audienceShort-beaked common dolphins (Delphinus delphis) and Atlantic spotted dolphins (Stenella frontalis) are the two most abundant cetacean species in the oceanic waters of Madeira and the Azores. They are of similar size, occur in similar habitats and are regularly observed in mixed-species groups to forage together. Genetic analyses suggested that, within each species, dolphins ranging around both archipelagos belong to the same panmictic population. We tested the hypotheses that (1) within each species, individuals from the two archipelagos belong to a single ecological stock; (2) between species, common and spotted dolphins have distinct trophic niches; using fatty acid (FA) and stable isotope (SI) analyses. Fatty acids and stable isotopes were analysed from 86 blubber and 150 skin samples of free-ranging dolphins, respectively. Sex-related differences were not significant, except for common dolphin FA profiles. In S. frontalis, FA and SI differences between archipelagos suggested that individuals belonged to different ecological stocks, despite the existence of gene flow between the two archipelagos. In D. delphis, differences were more pronounced, but it was not possible to distinguish between stock structure and a seasonal effect, due to differential sampling periods in the Azores and Madeira. Inter-specific comparisons were restricted to the Azores where all samples were collected during summer. Differences in FA proportions, noticeably for FA of dietary origin, as well as in nitrogen SI profiles, confirmed that both species feed on distinct resources. This study emphasizes the need for an integrated approach including both genetic and biochemical analyses for stock assessment, especially in wide-ranging marine top predators

Variation in δ15N and δ13C stable isotope values in common dolphins (Delphinus spp.) worldwide, with particular emphasis on the eastern North Atlantic populations

“…Stable isotopes constitute a useful tool for investigating diet, habitat use and distribution patterns of animals and in cetaceans they have been widely used to infer population structure . Stable isotopes of carbon (measured as δ 13 C values) and nitrogen (measured as δ 15 N values) have been used mostly as dietary tracers based on the fact that the isotopic composition of these elements present in the tissues of an animal depends on that of its food sources and therefore offers an integrated measure of the prey assimilated over a comparatively protracted period of time .…”

Potential use of stable isotope and fatty acid analyses for traceability of geographic origins of jumbo squid (Dosidicus gigas)

“…For example, several studies have shown that sea surface temperature and food availability may influence D. gigas energetic requirements for growth or reproduction . As the functional storage lipids, SFAs are synthesized to provide an adequate energy source for growth and survival of marine organisms . Hence, geographic variations in SFAs are probably due to the different energy demands of squid inhabiting distinct oceanographic areas.…”

“…Biochemical tracers, such as fatty acid (FA) profiles and stable isotope ratios, have proven to be powerful indicators to identify the geographic origin of food products . FAs are an important energy source for the growth and survival of marine organisms, and regional differences in FA profiles have been reported at the intraspecific level . These differences are generally associated with the divergent environmental conditions (e.g.…”

Macro- and micro-geographic variation of short-beaked common dolphin’s whistles in the Mediterranean Sea and Atlantic Ocean

“…A recent study (QUÉROUIL et al 2013) reveals faint stock differences among oceanic dolphins using fatty acid and stable isotope analyses. Our results show little variation between the Azores and Canary archipelagos and between the Bay of Biscay and the Mediterranean Sea.…”