Diet characterization of Hudson Bay ringed seals in a changing sub-arctic marine environment

Abstract

Rapid environmental change in the Arctic can influence food web structure and dynamics. Ice- obligate species, such as ringed seals (Pusa hispida), are particularly vulnerable to decreased sea ice extent. In this thesis, I examined the patterns and foraging plasticity of ringed seals in Hudson Bay, an ecosystem undergoing rapid ecological change, to make inferences on possible changes to the Arctic marine food web dynamics. To examine ringed seal diet, I used muscle and liver tissues from subsistence harvested seals, and vibrissae segments from live captured ringed seals. Specifically, I investigated spatial, temporal, and within-individual variation in the diet of ringed seal populations. I used long-term datasets from two Nunavut communities over the years of 2003 – 2017 to quantify the general increase in isotopic niche breadth for seals in western Hudson Bay and a decrease in eastern Hudson Bay, despite having similar diet proportions. Using chronological tissue sampling, I then revealed high variation among individuals rather than within individuals of seals in the same age and sex class, indicating that these generalist feeders are foraging with individualized strategies. Lastly, I compared ringed seal diet signatures with two other Hudson Bay phocid species and indicated that ringed seal diets do not generally overlap with harbour seals (Phoca vitulina). I then determined reliable estimates of sympagic and pelagic algal carbon sources to the diets of the three seal species and found that ringed seals have more pelagic algal content and less sympagic algal carbon in their diet compared to harbour seals and bearded seals (Erignathus barbatus). Overall, this thesis highlights the limits to foraging plasticity and spatio- temporal feeding patterns of ringed seals in a changing environment.