MEPS 208:265-271 (2000)  -  doi:10.3354/meps208265

ABSTRACT: Stable-isotope ratios of carbon (δ¹³C) were determined in liver samples from a number of procellariiform seabirds from New Zealand. Generally, δ¹³C values were low (depleted in ¹³C) and there was a significant degree of intra- and inter-specific variation. We suggest that the pelagic versus inshore/benthic foraging model for δ¹³C values in marine consumers is insufficient to explain the intra- and inter-specific variation. Nor can observed δ¹³C values of procellariforms be linked to variation in foraging distances. We propose that carbon relatively depleted in ¹³C derived from dietary lipids is incorporated into proteins. Support for this hypothesis is provided by depleted δ¹³C signatures we measured in lipids extracted from liver tissue, which were always lower than δ¹³C signatures in liver tissue (by 4.2 to 6.8‰, depending on species). Additionally, δ¹³C values were determined in a small number of stomach-oil samples; these too were relatively depleted and lower than δ¹³C values measured in liver tissue. Incorporation of dietary lipids, relatively depleted in ¹³C, into protein could explain both intra- and inter-specific variation in δ¹³C signatures in procellariiforms and may represent an additional explanation for relatively low δ¹³C values in pelagic consumers.

KEY WORDS: Stable isotopes · Diet · New Zealand · Seabird · Foraging