Abstract
BackgroundWe investigated the feeding ecology and habitat use of 32 harbour porpoises by-caught in 4 localities along the Scandinavian coast from the North Sea to the Barents Sea using time-integrative markers: stable isotopes (δ13C, δ15N) and trace elements (Zn, Cu, Fe, Se, total Hg and Cd), in relation to habitat characteristics (bathymetry) and geographic position (latitude).ResultsAmong the trace elements analysed, only Cd, with an oceanic specific food origin, was found to be useful as an ecological tracer. All other trace elements studied were not useful, most likely because of physiological regulation and/or few specific sources in the food web. The δ13C, δ15N signatures and Cd levels were highly correlated with each other, as well as with local bathymetry and geographic position (latitude). Variation in the isotopic ratios indicated a shift in harbour porpoise's feeding habits from pelagic prey species in deep northern waters to more coastal and/or demersal prey in the relatively shallow North Sea and Skagerrak waters. This result is consistent with stomach content analyses found in the literature. This shift was associated with a northward Cd-enrichment which provides further support to the Cd 'anomaly' previously reported in polar waters and suggests that porpoises in deep northern waters include Cd-contaminated prey in their diet, such as oceanic cephalopods.ConclusionAs stable isotopes and Cd provide information in the medium and the long term respectively, the spatial variation found, shows that harbour porpoises experience different ecological regimes during the year along the Scandinavian coasts, adapting their feeding habits to local oceanographic conditions, without performing extensive migration.
Highlights
IntroductionWe investigated the feeding ecology and habitat use of 32 harbour porpoises bycaught in 4 localities along the Scandinavian coast from the North Sea to the Barents Sea using timeintegrative markers: stable isotopes (δ13C, δ15N) and trace elements (Zn, Cu, Fe, Se, total Hg and Cd), in relation to habitat characteristics (bathymetry) and geographic position (latitude)
We investigated the feeding ecology and habitat use of 32 harbour porpoises bycaught in 4 localities along the Scandinavian coast from the North Sea to the Barents Sea using timeintegrative markers: stable isotopes (δ13C, δ15N) and trace elements (Zn, Cu, Fe, Se, total Hg and Cd), in relation to habitat characteristics and geographic position
(page number not for citation purposes) http://www.biomedcentral.com/1472-6785/7/1 this study, we examined the spatial variation in composition of stable isotopes (δ13C, δ15N) and of six trace elements (Zn, Cu, Fe, Se, Hg, Cd) in harbour porpoises of relatively similar age (Table 1), collected along the Scandinavian coast from the North Sea to the Barents Sea, with regards to the local bathymetry and the latitude (Figure 1)
Summary
We investigated the feeding ecology and habitat use of 32 harbour porpoises bycaught in 4 localities along the Scandinavian coast from the North Sea to the Barents Sea using timeintegrative markers: stable isotopes (δ13C, δ15N) and trace elements (Zn, Cu, Fe, Se, total Hg and Cd), in relation to habitat characteristics (bathymetry) and geographic position (latitude). Harbour porpoises (Phocoena phocoena) are among the smallest cetaceans, and are widely distributed in cold waters of the temperate and sub-arctic northern hemisphere [1]. They occur primarily over continental shelves, some individuals are occasionally found in deeper waters [2]. Until now, the application of these techniques to harbour porpoises remains limited and geographically localized [5,6,7]. While these studies have revealed remarkable aspects of porpoise movements and diving capabilities, they can hardly be extrapolated from one area to another and they do not directly address feeding habits
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