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Keywords:

  • beluga;
  • Delphinapterus leucas;
  • St. Lawrence;
  • population;
  • numbers;
  • trend;
  • surveys;
  • aerial surveys;
  • photographic surveys

Abstract

The belugas (Delpbinapterus leucas) inhabiting the St. Lawrence estuary were freely hunted until 1979 and thereby much reduced in numbers. In the late 1970s concerns for their future, and for the effect of contaminants, habitat modification, and marine traffic, became acute, and they were declared “Endangered” in 1983.

The numerical progress of the population has been monitored since 1973 by continued sample surveys. Nine of 10 surveys were aerial, and of those 9, 7 used high-altitude aerial photography. Published indices of population size showed an average increase of about 17 belugas per year (SE = 4) and a 1995 smoothed value of about 650 (SE = 40) belugas. This apparent temporal trend might be open to question owing to slight variation in survey methods and in the area covered by different surveys, so factors were developed to correct for differences in survey coverage and in treatment of data and for the effect of hunting on population trajectory. Revised assessments of the population trajectory and of the present smoothed index value changed little as a result. A series of total-count surveys in 1987-1992 estimated a decline of about 6 belugas per year, and when they were combined with sample surveys flown in 1984-1995, an increase of 10 belugas per year was estimated and a 1995 standardized index of about 640 (SE = 43). It appeared that hunting in the 1970s could have consumed all of, perhaps even slightly more than, the potential for natural increase of this population.