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St. Lawrence beluga population size and trends

The earliest documented St. Lawrence belugas population survey was carried out in 1973. At the time, Sergeant and Hoek estimated the population at 443 animals. Between 1975 and 1985, six additional surveys have suggested a population of approximately 500 animals.

Table 1

These estimates represent approximately 10 % of the population at the turn of the century. Based on the number of barrels of oil collected at the time of the hunt and an estimate of population size at the end of the hunt (approximately 500 animals between 1970 and 1980), Reeves and Mitchell (1984) estimated by calculating backward that the population would have been between 4000 and 5000 at the end of the 1800s.

The most recent population estimates were derived from a series of five systematic aerial surveys, which began in 1988 and used standardized techniques of high-altitude aerial photography (see Table 2). These surveys establish the population between 491 and 705 animals. To obtain these estimates, the number of belugas photographed during a survey is multiplied by a factor of approximately 2 to account for the fact that photographs cover approximately 50 % of the summer range (systematically distributed). This number is then multiplied by a correction factor that takes into account submerged animals and the partial overlap of photographs.

Until recently, a 15 % correction factor was used to adjust population estimates. This correction factor, considered to be conservative, was recently re-evaluated. Based on aerial surveys carried out using helicopters, Micheal Kingsley and Isabelle Gauthier (2002) estimated that St. Lawrence belugas spend 44 % of their time below the surface making them invisible during aerial surveys. This estimate is comparable to others carried out in the Canadian Arctic using radio telemetry. With this new information, they calculated a correction factor of 109 %. (In fact, the correction factor calculated by Isabelle Gauthier is 122 %, but Michael Kingsley uses 109 % to account for the partial overlap of photographs.)

This new data had a considerable effect on population estimates (See Table 2). By using a correction factor of 15 %, population estimates from surveys carried out between 1988 and 2000 were between 491 and 705. Using the new correction factor, considered to be more realistic, these estimates are now 892 and 1281.

Table 2

(1) Values presented here are the original values as used by the main author (M. Kingsley) in recently published articles: Lesage and Kingsley (1998) and Kingsley (1998).

Is the population growing?

Obviously the upward revision of the correction factor applied to beluga population surveys does not mean that the population has grown. It does imply, however, that since 1973 we seem to have under-estimated its size. This is very good news just the same. The bigger an animal population, the less vulnerable it is to catastrophes like viral or bacterial epizootics (epidemics that attack animals) or toxic spills.

Unfortunately, due to numerous differences in the methodology used, the results of surveys carried out before 1988 cannot be compared to the results of more recent surveys. It is therefore impossible to determine whether the population has increased since the first survey in 1973. Moreover, the margin of error incorporated into the results of the most recent aerial surveys (1988-2000) is such that starting from 1988, 20 years would be required in order to detect a significant annual increase of 3 % (optimistic scenario), and nearly 40 years would be needed to detect an increase of 1 % (pessimistic scenario).

The results of the most recent surveys of the St. Lawrence beluga population and the upward revision of the correction factor are encouraging. There appear to be more belugas in the St. Lawrence than we at first believed. Although it seems unlikely that the population is in decline, it would be premature and rash to conclude that the population has recovered.

Works cited

• Béland, P., R. Michaud, and D. Martineau. 1987. Recensements de la population de bélugas (Delphinapterus leucas) du Saint-Laurent par embarcations en 1985. Report presented to the Department of Fisheries and Oceans Canada.
• Gosselin, J.-F., V. Lesage and A. Robillard. 2001. Population index estimate for the beluga of the St Lawrence River Estuary in 2000. Research Document 2001/049 of the Canadian Science Advisory Secretariat of Fisheries and Oceans Canada. 21 p.
• Kingsley, M. C. S. 1993. Census, trend, and status of the St. Lawrence beluga population in 1992. Canadian Technical Report of Fisheries and Aquatic Sciences 1938.
• Kingsley, M. C. S. 1996. Estimation d'un indice d'abondance de la population de bélugas du Saint-Laurent en 1995. Rapport Technique Canadien des Science Halieutiques et Aquatiques 2117.
• Kingsley, M. C. S. 1998. Population index estimates for the St. Lawrence belugas, 1973-1995. Marine Mammal Science 14(3) : 508-530.
• Kingsley, M. C. S. and I. Gauthier. 2002. Status of the belugas of the St Lawrence estuary, Canada. NAMMCO Scientific Publications 4:239-258.
• Kingsley, M. C. S. and M. O. Hammil. 1991. Photographic census surveys of the St. Lawrence beluga population, 1988 and 1990. Canadian Technical Report of Fisheries and Aquatic Sciences 1776.
• Lesage, V. et M. C. S. Kingsley. 1998. Updated status of the St. Lawrence River population of the beluga, Delphinapterus leucas. Canadian Field-Naturalist 112(1) : 98-114.
• Lynas, E. M. 1988. Transect estimators of cetacean abundance: theory and practice. Scientific Commitee Meeting of the International Whaling Commission, San Diego.
• Pippard, L. 1985. Status of the St. Lawrence River population of beluga, Delphinapterus leucas. Canadian Field-Naturalist 99(3) : 438-450.
• Reeves, R. R. et E. Mitchell. 1984. Catch history and initial population of white whales (Delphinapterus leucas) in the River and Gulf of St. Lawrence, Eastern Canada. Le Naturaliste Canadien 111: 63-121.
• Sergeant, D. E. et W. Hoek. 1988. An update of the status of white whales Delphinapterus leucas in the Saint Lawrence Estuary, Canada. Biological Conservation 45: 287-302.