Trophic Niche Partitioning among Rorquals in the Gulf of St. Lawrence
In collaboration with Fisheries and Oceans (DFO) Canada, we are investigating trophic niche partitioning among the four sympatric rorquals species in the Gulf of St Lawrence using stable isotopes in the skin of the whales. In resource-limited environments, competition for food sources is potentially greatest among closely-related species with similar ecological requirements such as the blue, fin, humpback and minke whales all found in the Gulf of St Lawrence. However, there is a general lack of information regarding their ecological niches, which limits our comprehension of mechanisms facilitating their coexistence. So far we have found that blue whales occupied the lowest relative trophic position, followed by fin, minke and humpback whales. In addition, an evaluation of long-term resource use patterns revealed, that species with specialized diets (blue whales) effectively had the lowest degree of temporal dietary variation, whereas species known to have broader diets (fin, humpback and minke whales) showed dietary fluctuations over time. This temporal variation in resource use, particularly in humpback whales, may be a response to shifts in prey abundance or availability. Stable isotopes can also be used to monitor large environmental changes over time and we will continue to monitor the diet of the whales in the St. Lawrence.