University of Pretoria
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Stable isotope analysis of Southern Ocean myctophids using faecal otoliths

posted on 2023-07-10, 11:04 authored by André van TonderAndré van Tonder

The tables and figures in this dataset represent the development of a method to estimate the stable isotope values of myctophids when only otoliths from faecal samples of predators (or sedimentary samples) are available. Otoliths from wild myctophids were collected from faecal samples of fur seals at Marion Island in the Southern Ocean, and were cleaned using NaOCl (bleach) before obtaining the stable isotope values of the otoliths' organic component. The cleaning step required correction which was done by establishing a correction curve based on the amount of otolith material to be cleaned.The next step involved establishing an offset value between otoliths and muscle that could be applied to otolith stable isotope values to estimate muscle values in the absence of fresh fish samples (only faecal or sedimentary otoltihs available). The offsets were calculated by measuring paired otolith and muscle values of Antarctic fish, while ensuring control for lipid content in muscle.

With the offsets applied to the cleaned and corrected Marion Island samples, the utility of the method is demontrated by comparisons with published counterparts, and used in the stable isotope dietary mixing models of Marion Island predators including various southern elephant seal classes and killer whales. Analyses were done using R software. Juvenile southern elepehant seal diet modelling was improved, first models for sub-adult, adult female and adult male seals are now available, and killer whale modelling remains unresolved.



Zoology and Entomology

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