Cancer in Beluga from the St. Lawrence Estuary. (Correspondence).

Martineau et al. (2002) reported that St. Lawrence beluga (SLB) have high cancer rates. Unfortunately, errors in their interpretation of the data have led them to overstate the importance of cancer and its links to environmental sources.

Martineau et al. (2002) compared mortality patterns between the beach-cast, naturally dead animals in the protected, predation-free SLB population with those from a hunted Alaskan beluga population, which were also subject to natural predation (Burns and Seaman 1985). This analysis is incorrect because it compares the raw frequency distribution of ages at death of SLB with an age structure reconstructed by fitting a model to the Alaskan age and reproductive data from the harvest, under the assumption of constant natural mortality (Burns and Seaman 1985). A correct analysis (Burns and Seaman 1985) of the SLB data shows that mortality rises continuously from about 6 years of age. There is no peak in the 20s, and no difference in standing population at 21-25 years of age between Alaskan beluga [8%: Table 7 in (Burns and Seaman 1985)] and SLB [8.1%: stranding data 1982-1998 (Martineau et al. 2002)].

Martineau et al. (2002) estimated an annual cancer rate (AR) among SLB beluga using

AR = (SL[B.sub.with cancer] / t) x (100,000 / population size)

where t is 17 years. The authors used an aerial survey index estimate of 650 whales, which incorporates a conservative 15% correction factor to account for animals that were below the surface on transect lines and therefore unseen (Kingsley 1999). Our concern is the author's failure to recognize the importance of this correction to their conclusions. Kingsley (1999) applied a factor of 2.09, developed specifically for SLB (Kinglsey and Gauthier. In Press), to the average of five surveys using similar methods between 1988 and 1997, and hence estimated a mean fully corrected population size of 1,100 [+ or -] 113 (mean [+ or -] SD) whales. Using this estimate of population size reduces the cancer rate from 163 to 96 (95% confidence interval, 88-105).

Martineau et al. (2002) asserted that the rate of winter stranding is as high as or higher than that during the rest of the year because of harsh weather conditions, but that these carcasses are not recovered and adjust their calculations accordingly. These adjustments may be inappropriate for two reasons. First, the beluga is an Arctic species adapted to ice and cold water, and is unlikely to be stressed by winter conditions in the St. Lawrence; mortality rates could in fact be lower during this period. Second, animals that die in winter could freeze into the ice and be beach-cast and thus recovered after breakup. A more appropriate estimated minimum with cancer (EMC) can be estimated from the observed stranding rate as a minimum, resulting in an EMC of 47, or as one end of a range of 47-63. The adjusted estimated annual rate (AAR) of cancer for a complete year,

AAR = (EMC / t) x (100,000 SLB / 1,100),

would then be 251 instead of the value of 570 presented by Martineau (2002). The AAR of cancer in SLB is then no longer the highest of the seven species they tabulated.

Martineau et al. (2002) argued that epidemiologically the SLB data resemble human data more than that from domestic animals because population size is known; however, they then cited incorrect population estimates for the SLB. They also stated that rates among pets are overestimated because pets are protected from other causes of death. Cancer rates in pets are not overestimated; they are high because death is inevitable, and mortality from predation, trauma, and malnutrition is nearly nonexistent--just as is the case for the SLB.

The absence of malnutrition as a cause of death and the generally good body condition of recovered carcasses from this unhunted, predator-free, wild population is unusual. The small number of juvenile carcasses recovered, prima facie indicates a bias toward older adults, whereas the absence of emaciated carcasses may indicate a bias against animals in poor condition that are likely to sink. The beach-cast sample of carcasses is clearly incomplete and must be assumed to be biased. The direction and size of this bias is unknown, but it may increase the apparent significance of cancer.

Martineau et al. (2002) suggested that bottom invertebrates from the sediments of the Saguenay Fjord are important in the diet, and a significant source of contamination with polycyclic aromatic hydrocarbons (PAHs), leading to high cancer rates. However, the Saguenay River is not used extensively by all SLB, particularly west of the Baie Ste. Marguerite area, for which PAH data are available. Furthermore, the only existing diet data come not from the Saguenay, but from collections made elsewhere in the St. Lawrence over 60 years ago (Vladykov 1946).

The SLB population is unique in its accessibility and in its geographic isolation from Arctic conspecifics. The incidence of cancer among a sample of beach-cast animals is interesting, but failure to make the proper links between a sample with unknown bias and the population means that the importance of cancer in this population and links to environmental conditions are overstated.

Mike O. Hammill
Veronique Lesage
Department of Fisheries and Oceans Canada
Mont Joli, Quebec, Canada
E-mail: [e-mail]
Michael C.S. Kingsley
Greenland Institute of Natural Resources,
Nuuk, Greenland

REFERENCES

Burns JJ, Seaman FA. 1985. Investigations of belukha whales in coastal waters of western and northern Alaska. Contract NA 81 RAC 00049. Fairbanks, AK:Alaska Department of Fish and Game, 129.

Kingsley, MCS. 1999. Population indices and estimates for the belugas of the St. Lawrence Estuary. Can Tech Rep Fish Aquat Sci 2266:27.

Kingsley MCS, Gauthier I. 2002. Visibility of St. Lawrence belugas to aerial photography, estimated by direct observation. In: Belugas in the North Atlantic and the Russian Arctic (Heide-Jergensen M-P, Wiig O, eds). NAMMCO Scientific Publications, Vol. 4. Tromso, Norway:North Atlantic Marine Mammal Commission, 259-270.

Martineau D, Lemberger K, Dallaire A, Labelle P, Lipscomb TP, Michel P, et al. Cancer in wildlife, a case study: beluga from the St. Lawrence Estuary, Quebec, Canada. Environ Health Perspect 110:285-292.

Vladykov, VD. Etudes sur les Mammiferes aquatiques IV. Nourriture du Marsouin Blanc ou Beluga (Delphinapterus leucas) du Fleuve St-Laurent. Quebec, Canada:Departement Pecheries du Quebec. 1946.