Does krill influence the dispersal of fin whales?
The Lower St. Lawrence Estuary is a major plankton traps. Large quantities of krill can be found in this area. Krill is the prey of several species of baleen whales, including the fin whale. Is there a relationship between krill abundance and the dispersal of fin whales?
To go through the looking glass
Every year since 1994, a team from Fisheries and Oceans Canada has been conducting an oceanographic mission to evaluate the abundance and biomass of krill in the Lower St. Lawrence Estuary. Forty eight stations spread over eight sections located between Les Escoumins in the Lower St. Lawrence Estuary and Sept-Îles in the north-western Gulf are sampled every year. Researchers harvest zooplankton using a Bioness, a device equipped with nine plankton nets. In the laboratory, researchers identify and evaluate the abundance and respective biomasses of the species collected. Simultaneously, a programme to document whale-watching activities at sea has been systematically recording the presence of whales in the Estuary since 1985 from aboard whale-watching boats. Research assistants note the position, species and number of animals within a radius of 2000 metres every 10 minutes
Recorded krill abundance data combined with fin whale dispersal data demonstrates that the more abundant the krill, the more the fin whales are scattered. Krill is relatively easy to hunt; it drifts with the current. Consequently, fin whales do not have to congregate to optimize hunting efficiency. On the other hand, the less abundant the krill, the more the fin whales congregate. In fact, it is not uncommon to see groups of a dozen fin whales in years of low krill abundance, such as 1996 and 1998. In these two years of low krill abundance, fin whales were likely feeding on another prey species: capelin. A better swimmer than krill, capelin is harder to hunt. In this case there would be an advantage to fin whales hunting in groups to increase their chances of gleaning a good meal.
Although this model proved valid for a number of years, it does not explain what has been happening since 2002; krill has not been very abundant and fin whales have been very dispersed. There is a possibility that less capelin was available in these years. This would have made the Estuary less interesting as a buffet for fin whales—fewer of which showed up. In order to verify this alternative hypothesis, a researcher from the Maurice Lamontagne Institute is studying the diet of fin whales by examining the biopsy samples extracted from fin whales every summer.
Fisheries and Oceans Canada, Saguenay—St. Lawrence Marine Park, AML Cruises
GIARD, J. R. MICHAUD, M. HARVEY, AND J.A. RUNGE. (2001) Fin whales tune their dispersion and grouping pattern on krill standing stock biomass. European Cetacean Society, 15th annual conference, Rome, 6-10 may 2001.
Ministère des Pêches et Océans du Canada 2002. État de l’océan en 2001 : Les conditions chimiques et biologiques dans l’estuaire et le golfe du Saint-Laurent. Rapport du MPO sur l’état des stocks G4-03 (2002).
M. HARVEY, J.F. ST-PIERRE, PIERRE JOLY AND G. MORRIER (2002) Oceanographic conditions in the Estuary and the Gulf of St. Lawrence during (2001). Rapport du MPO sur l’état des stocks 2001/117, 19 p.
Ministère des Pêches et Océans du Canada. 2001. Les conditions océanographiques dans le golfe du Saint-Laurent au cours de l’an 2000. Rapport du MPO sur l’état des stocks G4-01 (2001).
HARVEY, M., R. MICHAUD, J.A. RUNGE, J.F. SAINT-PIERRE, P. JOLY. 2001. Interannual variability of the krill standing stock biomass in the Lower St. Lawrence Estuary: impact on fin whales dispersion. American Society of Limnology and Oceanography, 2001 Aquatic Sciences meeting, 12-16 February 2001, Albuquerque, New Mexico, USA.