The retrospective geolocation of free-living marine organisms using stable isotapes

Abstract

Isoscapes are spatially explicit models describing isotopic variability due to spatial differences in physical, chemical and biological processes across natural environments. Marine isoscapes are being increasingly developed to address a range of ecological questions, from better understanding space use and foraging behaviours to determining individual trophic feeding positions and assigning animals or animal products to their origin. However, many marine isoscapes lack suitable data coverage and resolution or explicit measures of variance, necessary for assignment. This research aims to advance isoscape prediction methodologies and develop isoscape assignment techniques to benefit marine conservation and management.

I have demonstrated two different methods of isoscape prediction. The first, ordinary kriging of in situ 13C and 15N measurements of lion’s mane jellyfish (Cyanea capillata) across the North Sea, producing highly accurate isoscapes. The second, a Bayesian hierarchical modelling approach incorporating multiple species of in situ jellyfish samples and additional environmental data to produce highly precise 13C, 15N and 34S UK shelf sea isoscapes. Both techniques provided greater than 80% assignment accuracy to areas representing 40% of each isoscape. North Sea assignments were comparable to light based data loggers and UK shelf sea assignment accuracy was approximately 80% when assigning to ICES subareas. I also demonstrated marine isoscape use in seabird foraging behaviour research, by refining over winter feeding positions during the vulnerable moult period of UK breeding guillemots (Uria aalge), razorbills (Alca torda) and Atlantic puffins (Fratercula arctica). The three sympatric species frequented slightly different areas and fed over different trophic positions, with high individual variability. Foraging responses also differed between winters with contrasting environmental conditions, with razorbill and puffin populations displaying different adaptation strategies.

This study addresses current limitations of sample collection constraints in marine isoscape predictions and highlights the potential of animal assignments to isoscapes as a useful tool to aid conservation, fisheries management and traceability.

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ORCID for Clive Trueman: orcid.org/0000-0002-4995-736X

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