What are belugas dying from (2015)

Every year, some 15 or so belugas are found stranded on the shores of the St. Lawrence. What are they dying from? Examination of these carcasses speaks volumes about the health of the population and can offer possible solutions for their recovery.

Study method

The beluga carcass recovery program was created in 1982; since then, 469 belugas have been found, mainly in the Estuary between April and November and peaking from May to August. View the beluga mortality toll in 2013

What have we learned?

Based on analysis of the 222 belugas examined between 1983 and 2012, it was determined that the most frequent causes of mortality in young belugas are infectious diseases of parasitic origin (32%), in particular verminous pneumonia. Infectious diseases of bacterial origin as well as cancers, especially those of the digestive system, are believed to be the main causes of mortality in adult belugas. However, cancers are declining; no beluga born after 1971 has died of this disease, which coincides with the implementation of measures to ban and better regulate a number of contaminants. Other causes of mortality are collisions with boats, inanition (food deprivation), entanglements in fishing gear, as well as saxitoxin poisoning produced by the algae Alexandrium tamarense.

The number of newborns found dead was exceptionally high in 2008 (8), 2010 (8) and 2012 (16) compared to 0 to 3 in previous years. In 2008, these mortalities were believed to be associated with a bloom of the toxic algae Alexandrium tamarense in the Estuary, a phenomenon known as a red tide. This algae produces paralyzing neurotoxins that can result in death by blocking the respiratory muscles. Numerous other marine animals (birds, fish, seals, harbour porpoises) also experienced unusual mortalities during this occurrence.

In 2010 and 2012, other factors are thought to have reduced young belugas’ chances of survival. This period coincides with a period of significant changes in terms of their prey, reduced ice cover in winter and higher water temperatures. In parallel, a rise in the number of females dying from birth-related complications (15%) has been observed since 2010, which suggests a problem related to reproduction. Lastly, mortality in adults did not show any temporal tendencies during the study period. The likelihood of finding an adult beluga carcass was the same regardless of the animal’s sex.

Also, the average age of the females recovered has been falling since the 2000s, i.e. females are dying younger. Dead belugas are aged based on the growth layers in their teeth.

Références bibliographiques

DFO. 2013. Status of beluga whales (Delphinapterus leucas) in the St. Lawrence River estuary. DFO Can. Sci. Advis. Sec. Res. Doc. 2013/076.

Lair, S., Martineau, D., Measures, L.N. 2013. Causes of mortality in St. Lawrence Estuary beluga (Delphinapterus leuca) from 1983 to 2012. DFO Can. Sci. Advis. Sec. Res. Doc. 2013/ 119. iv + 37 p.

Lesage,V., Mosnier,A., Measures,L.N., Lair,S., Martineau,D., and Béland,P. Mortality patterns in St Lawrence beluga whales,inferred from stranding characteristics, 1983-2012. 2013. DFO Can. Sci. Advis. Sec. Res. Doc. 2013/ 118. iv + 23 p.

Plourde, S., Galbraith, P., Lesage, V., Grégoire, F., Bourdage, H., Gosselin, J.-F., McQuinn, I., and Scarratt, M. 2013. Ecosystem perspective on changes and anomalies in the Gulf of St. Lawrence: a context in support to the management of the St. Lawrence beluga whale population. DFO Can. Sci. Advis. Sec. Res. Doc. 2013/ 129. v + 29 p.

Scarratt, M., Michaud, S., Measures, L., Starr, M., 2013. Phytotoxin analyses in St. Lawrence Estuary beluga. DFO Can. Sci. Advis. Sec. Res. Doc. 2013/ 124. v + 16 p.