Using stable isotopes as a tool to understand the trophic relationships and movement of seabirds off Southern Africa

• Main Author: Barquete, Viviane
• Other Authors: Ryan, Peter G
• Format: Doctoral Thesis
• Language: English
• Published: University of Cape Town 2014
• Subjects: Zoology
• Online Access: http://hdl.handle.net/11427/6229

Includes abstract. === Includes bibliographical references. === Stable isotopes (SI) have been widely applied in ecology to investigate the trophic relationships of animals. Stable isotope analyses were used to augment our understanding of the foraging ecology and movements of three globally threatened seabirds: African Penguins (Spheniscus demersus), Cape Gannets (Morus capensis) and White-chinned Petrels (Procellaria aequinoctiallis). The diets of captive penguins were varied to estimate the 15N turnover rates and discrimination factors of toenails and blood fractions. Plasma δ15N showed a faster turnover rate (7.6 ± 0.7 days) than erythrocytes (14.3 ± 1.6 days). Discrimination factors varied among tissues. No shift in nail δ15N signature was detected after 5 months, suggesting that toenails are insensitive to short to medium-term diet shifts. Among wild penguins and gannets sampled across the Benguela region, tow different responses to the effects of fisheries were observed,due to different feeding strategies, Age, sex year and colony location accounted for isotopic variation. Age-based differences may be linked to limited foraging skills of juvenile birds and their wider dispersion. Female gannets apparently feed on more live natural prey whereas males take more fishery discards, although the sex-based difference was confounded by colony effect. Marked inter-colony variation probably results from regional differences in oceanic conditions between, prey availability and among gannets, variation in dependence on fishery discards. Inter-annual variation in SI signatures might be linked to variation in primary production (African Penguins), or variation in prey availability (Cape Gannets)...