Research project: Movement patterns in pelagic sharks: stable isotope evidence
Currently Active:
Yes
Pelagic marine predators' abundance has drop by > 90% in the last 25 years due to overfishing and by catch. Conserving the remaining populations requires a thorough understanding of their spatial ecology. Migratory predators' movements however are difficult to reconstruct. Despite recent advances, electronic tags are expensive and only a few large individuals can be studied. Stable Isotope Analysis (SIA) allows reconstructing movements indirectly, but currently requires a better understanding of the isotopic variability in marine environments.
Project Overview
Intra-annual variability
Background
Static isoscape methods involve measuring baseline isotope values at known locations and interpolating between points, and assume negligible temporal variation. Regression-based methods identify and use the relationships between tissue isotopes and environmental variables to build predictive isoscapes.
Alternatively, geolocation can be achieved without using isoscapes: areas of highest correlation between contemporary time series of tissue isotopes and environmental variables are the most likely locations of isotopic assimilation.
coupling physiological measures of stable isotope fractionation by phytoplankton into global biogeochemical models (e.g. NEMO)
2) Use these models to reconstruct movement patterns in pelagic, highly migratory sharks:
Sampling of essential amino acids in shark skin, muscle and blood;
Coupling models of tissue turnover time into global biogeochemical models;
Testing inferred movement patterns using smart-tagged sharks.
Global Biogeochemical Models
Marine isotopic gradients are extremely dynamic compared to terrestrial ones, complicating the interpretation of stable isotopes. Global biogeochemical models predict likely isotope values in carbon-containing components ([CO
2aq
], DIC and POM) based on SST, [CO
2aq
] and phytoplankton growth rates. Despite being still insufficiently accurate to predict actual isotope values, these models provide tools to explore temporal stability of spatial isotopic gradients, and thus to assess the feasibility of using SIA for geolocation in specific marine systems.
