From the sea to the lab: the journey of a beluga carcass (3/3)

“For example, if the beluga has a bacterial infection, inflammation will be visible in the tissue,” says Stéphane Lair of the Faculty of Veterinary Medicine. Depending on what is found during the analysis of the tissue slides, the samples will then be submitted to specialized teams at the bacteriology or virology labs.

Dr. Lair and his assistants published results in this regard in 2015. Of the 222 beluga carcasses studied between 1983 and 2012, infectious diseases – which were identified as the leading cause of mortality in the population – were responsible for one-third (32%) of beluga deaths. In juvenile belugas, verminous pneumonia was the cause of death in 52% of the animals. A total of 31 belugas died as a result of infection from malignant tumours, i.e. 20% of belugas aged 19 years or older. One of the hypotheses put forward to explain the unusually high frequency of some of the pathological conditions observed in belugas is the chronic exposure to environmental contaminants.

Heavily contaminated

Based on fat and skin samples, biologist Jonathan Verreault, associate professor at UQAM’s Department of Biological Sciences, is currently developing a portrait of the toxins found in belugas. While the presence of contaminants in beluga tissues has been the subject of long-term investigations, the nature of these contaminants has changed. In the early years of the carcass recovery project, an unusually high number of cancer cases were found in the animals studied. Indeed, St. Lawrence belugas are amongst the most heavily contaminated marine mammals in the world. “When we look at what was present in their environment, the blame often fell on polycyclic aromatic hydrocarbons (PAHs), an important source of which was aluminum production,” explains Dr. Lair. Since the 1970s, PAH concentrations in sediment of the Saguenay have decreased as industrial processes have evolved.

“In addition to the 38 PBDE congeners, we analyze nearly a dozen emerging flame retardants that are substitute compounds for the PBDEs that have been banned in consumer products. We also intend to analyze other emerging compounds and possibly also classical organochlorines such as PCBs, DDTs, HCBs, etc.,” explains Jonathan Verreault.

DNA in the skin

Skin samples are also being sent to the Maritimes. Beluga skin, in addition to contamination-related information, contains valuable data on the whale’s genetic profile. Likewise, if the DNA profile is available, it may be possible to match the carcass to a known living animal.

The beluga’s skull is detached in pieces during the necropsy. The lower jaw is sent to the Maurice Lamontagne Institute of Fisheries and Oceans Canada (DFO). There, lab technician Yves Morin will attempt to determine the age of the animal.

There are many steps and the techniques are constantly evolving. Once the teeth have been extracted and cleaned, an approx. 50 mm thick sliver must be cut lengthwise, polished, and digitized with a high-resolution scanner or a binocular microscope equipped with a digital camera. The photos are then edited to bring out the contrasts in order to better discern the growth rings. A single growth layer represents one year of life. Belugas can live up to sixty years.

Saxitoxin under the researchers’ microscope

Toxic and harmful microalgae are naturally present in the habitat of the St. Lawrence beluga. This phytoplankton varies in abundance from one summer to the next, sometimes creating a “red tide”.

The alga A. tamarense produces a powerful family of so-called paralytic toxins capable of causing a quick death by asphyxiation. In humans, the phenomenon is known as “paralytic shellfish poisoning” (PSP) and is generated by the accumulation of saxitoxin and its derivatives in filter-feeding bivalves. In the case of the beluga, the phenomenon is caused by an accumulation of the toxin in their prey.

The biggest container taken out of the necropsy room will also be sent to DFO’s Maurice Lamontagne Institute, this time to Véronique Lesage’s laboratory. A large icebox containing stomach contents will help determine what the beluga consumed before it died.

The contents of the stomach are washed and sieved. Researchers look for prey residues such as squid beaks, crystallized fishbones, otoliths (small crystals from the ears of some fish) and the hooks of polychaetes (bristle worms living in the sediment).

Thanks to this content, researchers can gain insight into the food sources that constitute the diet of the St. Lawrence beluga and thus study the evolution of this aspect of the species’ biology.