Is the change in distribution and abundance of blue whales related to the groundfish collapse in the northern Gulf of St-Lawrence?
The Gulf of St. Lawrence is a summer feeding ground for the blue whale and other marine mammal species. Blue whale (Balaenoptera musculus) sightings in the northern part of the gulf have declined since the early 1990s, while the number of humpback whales (Megaptera novaeangliae) has increased since then. Over the same period, abundance of many Atlantic cod (Gadus morhua) and groundfish stocks in the Northwest Atlantic declined to low levels due to overfishing. With this decrease in biomass, the ensuing predation pressure on small pelagic fishes (capelin (Mallotus villosus) and Atlantic herring (Clupea harengus)) was quantitatively lower and could have led to an increase in their abundance and geographical distribution throughout the Gulf of St. Lawrence in the 1990s. Blue whales are specialists, feeding only on krill (zooplankton). Consequently, any increase in the capelin population, which mainly feed on zooplankton, would amplify potential competition with the blue whale for the same resource. However, the more opportunistic humpback whales, which target both zooplankton and fish, might be favored by this pattern, thus explaining their increased abundance. All these findings support the assumption that a striking change in the ecosystem food web could explain the observed variations in distribution and abundance of rorquals in this region.
Comtois, Sophie; Savenkoff, Claude; Bourassa, Marie-Noëlle; Brêthes, Jean-Claude; Sears, Richard. 2009. Is the change in distribution and abundance of blue whales related to the groundfish collapse in the northern Gulf of St-Lawrence? Oral presentation to the Eighteenth Biennal Conference on the Biology of Marine Mammals, Quebec, Canada.
Is the change in distribution and abundance of blue whales related to the groundfish collapse in the northern Gulf of St-Lawrence? PDF (1.64 MB)