Development of in situ Sr isotope analyses in shark vertebrae (Old ID 27633)

Chief Investigator

Accurately ageing sharks underpins sustainable harvest and population recovery. The conventional ageing technique consists of counting growth bands in vertebrae, however, this approach suffers errors associated with over- and under-counting due to misidentifying periodic features and in-complete. More recently, element-to-element ratios have been explored as complementary tools for determining age and migratory, and in this context Mn:Ca shows promise as an age-specific fingerprint, and Sr:Ca has shown promise as one of the most prominent indicators of fresh/estuarial vs. marine environment (along with Ba:Ca), because marine environments typically have significantly higher Sr (and lower Ba) concentrations. This means that Sr:Ca—alongside Mn:Ca and Ba:Ca—can potentially be used as an annual marker, in particular for female sharks that annually return to freshwater environments to pup. It is well-known from fish otoliths (a calcified part of the inner ear) that marine and freshwater environments display distinct Sr isotope signatures (87Sr/86Sr ratios), and that fresh vs marine signatures can be readily distinguished at requisite length-scales (e.g. 50 microns) using in situ (“in place”, i.e. non-destructively) laser ablation multi-collector inductively coupled plasma mass spectrometry (or LA-MC-ICP-MS). Moreover, it is well-established that 87Sr/86Sr ratios can be determined in situ in bio-apatite (calcium phosphate or bone, such as that in fish vertebrae), and 87Sr/86Sr ratios in bio-apatite can be used to determine sub-annual mobility. And yet to date, Sr isotopes have never been investigated in shark vertebrae towards these ends. This study will combine in situ elemental compositions and 87Sr/86Sr ratios in the vertebrae of sharks to determine their ultimate viability as complementary ageing, environmental and migratory reconstruction tools.

01 Jan 2022 - 31 Mar 2023

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