IN SITU MEASUREMENTS BY INSTRUMENTED GREY SEALS (HALICHOERUS GRYPUS) REVEAL FINE-SCALE OCEANOGRAPHIC PROPERTIES AND ENVIRONMENTAL INFLUENCES ON MOVEMENT PATTERNS

Abstract

The influence of oceanographic conditions on the movements of large marine predators has been demonstrated in diverse taxa. However, obtaining subsurface data that are spatio-temporally relevant to the decisions made by benthically-foraging species can be challenging. Between the years 2009 and 2015, 117 grey seals (Halichoerus grypus) were captured on Sable Island, NS and instrumented with Mk10-AF FastlocTM GPS devices. A bio-optical model for the estimation of chlorophyll-a using light attenuation was developed by performing a replicated experiment in the Bedford Basin. This model was applied to data collected in situ by grey seals and, along with other oceanographic conditions, mapped across the Scotian Shelf, providing high spatio-temporal coverage. Behavioural states were estimated from location data using the hidden Markov movement model. Generalized linear mixed-effects models indicated that grey seal behaviours are influenced by the fine-scale chlorophyll-a and environmental conditions they encounter across the oceanographically heterogeneous Scotian Shelf.