Are Gulf of St. Lawrence rorqual whales contaminated?
The St. Lawrence drains a heavily industrialized area, which explains the presence of numerous toxic contaminants. It has been demonstrated that beluga whales, which are permanent residents of the St. Lawrence, accumulate significant quantities of contaminants in their tissues. But what about the rorqual whales that spend several months feeding in the St. Lawrence every summer?
To go through the looking glass
Biopsy samples collected from the four species of St. Lawrence rorqual whales have been analyzed to detect the presence of contaminants and determine concentration levels. Samples taken from 21 minke whales, 15 fin whales, 6 blue whales and 8 humpback whales in 1991 and 1992 were analyzed in an initial study. A second study carried out between 1992 and 1999 focused on blue whales and humpback whales. In this study 38 biopsy samples from male blue whales and 27 biopsy samples from female blue whales, along with 12 biopsy samples from female humpback whales and 13 biopsy samples from humpback whale calves were analyzed.
Sample analyses led to the detection of a wide variety of contaminants in the four species of St. Lawrence rorquals, including certain highly toxic chlorinated organic contaminants such as PCBs, DDT, HCH and Mirex. Certain contaminant levels fluctuated according to species. The minke whale, for example, presented lower DDT levels and higher Mirex levels than the other species. Blue whales, on the other hand, presented the highest proportions of DDT. These variations could reflect either metabolic differences or variances in the diet of these four species—minke whales and humpback whales tend to eat small fish, while fin whales and blue whales eat more krill.
On average, contaminant levels were higher in males than in females, which could be explained by the transfer of contaminants from the female to its offspring during gestation and nursing. Comparable concentrations were measured in both female humpback whales and young humpback whales. This indicates that the young whales rapidly accumulate contaminants during gestation and lactation.
J. M. Gauthier of Environmental and Resources Studies at Trent University, Chris Metcalfe, Brenda Koenig and Tracy Metcalfe of Water Quality Centre at Trent University, Gordon Paterson of the Great Lakes Institute for Environmental Research at the University of Windsor and Richard Sears of the Mingan Island Cetacean Study (MICS).
Fisheries and Oceans Canada, WhaleNet Program of Wheelock College, Natural Sciences and Engineering Research Council of Canada and the Fonds pour la Formation de Chercheuses et Chercheurs et l’Aide à la Recherche (FCAR), ministère de l’Environnement du Québec.
Gauthier, J. M., Metcalfe, C. D. et Sears, R. 1997. Chlorinated organic contaminants in blubber biopsies from northwestern Atlantic balaenopterid whales summering in the Gulf of St. Lawrence. Marine Environmental Research. 44, 201-223.
Metcalfe, C. D., Koenig, B., Metcalfe, T. Patterson, G. et Sears, R. 2004. Intra- and inter-species differences in persistent organic contaminants in the blubber of blue whales and humpback whales from the Gulf of St. Lawrence, Canada. Marine Environmental Research. 57, 245-260.