Stable carbon and nitrogen isotope ratio profiling

Authors: Sónia Mendes Jason Newton Robert J Reid Alain F Zuur Graham J Pierce

Publish Date: 2006/11/24

Volume: 151, Issue: 4, Pages: 605-615

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Abstract

Teeth from male sperm whales Physeter macrocephalus stranded in the Northeastern Atlantic were used to determine whether chronological profiles of stable isotope ratios of C δ13C and N δ15N across dentine growth layers could be used to detect known ontogenetic benchmarks in movements and trophic ecology Profiles showed a general decrease in δ13C median = 191‰ and an increase in δ15N median = 242‰ with age A marked decline in δ13C occurred for all 11 teeth around 9–10 years and again for six individuals around 20 years After the early twenties the δ13C continued to decline with age for all teeth These results are consistent with males segregating from natal groups in low latitudes with the onset of puberty between 4 and 15 years and gradually dispersing poleward into 13Cdepleted temperate waters Penetration into further depleted productive high latitudes after the age of 20 might facilitate the spurt of accelerated growth rate observed around this age Breeding migrations back to lower latitudes were not reflected in the δ13C profiles possibly due to being short compared to the time spent feeding in high latitudes The timings of marked isotopic change in the δ15N profiles reflect those of the δ13C profiles suggesting a link between dietary changes and movements The observed increase in δ15N with age is likely to be caused by a trophic level increase as males grow in size probably feeding on larger prey An additional explanation could be that in the higher latitudes of the North Atlantic the main prey source is the high trophic level squid Gonatus fabricii Also the lower latitudes from where males disperse are depleted in basal 15N Profiles of δ13C and δ15N in sperm whale teeth gathered from different regions sexes and periods in time could provide a unique way to understand the ecology of this species across different oceansWe thank Colin MacLeod Jennifer Learmonth Patricia Lastra Gabriele Stowasser and David Mackenzie at the University of Aberdeen for help with sample preparation and Dave McNamara Donegal County Council for the provision of the Irish tooth We thank Colin MacLeod and two anonymous reviewers for useful comments on the manuscript S M was supported through a PhD studentship by the Portuguese Foundation for Science and Technology grant SFRH/BD/5466/2001 and the stable isotope analyses were carried out at the NERC Life Sciences Mass Spectrometry Facility application no EK7411/04

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