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The use of epidermal mucus in elasmobranch stable isotope studies: a pilot study using the giant manta ray Manta birostris
Stable isotope analysis of tissues with different turnover rates allows for a broader temporal view of a species’ feeding habits. Epidermal mucus is a rapid to medium turnover ‘tissue’ in teleost fishes, but its utilisation in elasmobranch dietary studies is unknown. Here, we conduct stable isotope analysis on mucus and muscle from the giant manta ray, Manta birostris. Mucus δ13C values were depleted and closer to surface zooplankton δ13C values in comparison to muscle, whereas there was no significant difference in δ15N values between these two tissue types. Using diet tissue discrimination factors from the literature, there was no significant difference in the expected prey profile between muscle and epidermal mucus. However, a broader range in δ13C values of expected prey was shown for mucus in comparison to muscle. Results suggest that if M. birostris mucus is indicative of recent dietary intake, resource use during aggregative behaviour off Ecuador is broader, but with no obvious resource switching. This study is the first example of using mucus to investigate feeding ecology in elasmobranchs using bulk stable isotope analysis. The time-course for the change in mucus isotopic signature needs to be determined through controlled feeding studies in an aquarium setting.
MF16355 Accepted 05 December 2016
© CSIRO 2016