A Brief Guide to Partial Necropsy

Why am I telling you about the macroscopic examination of a porpoise carcass? Because Méduline and I are about to dismember and inspect, from the blowhole to the tail, the body of this harbour porpoise to perform a “partial necropsy” of the animal.

This exercise was devised in the event it proves impossible to recover a carcass and the veterinarians are unable to travel to perform a necropsy in the field. Although mobile teams will now be trained to collect more information from carcasses, the expertise of veterinarians is irreplaceable.

Dressed in our personal protective equipment and equipped with sharp knives, tweezers and surgical scissors, off we go! As we dissect the cetacean, we remain on the lookout for the presence of anything abnormal in the body. These anomalies will guide our sample collection. Our amateur eyes look for any tissue showing signs of bruising, hemorrhages, edema, necrosis, hematomas, hemothorax as well as the presence of any fractures, abnormal masses, signs of malnutrition, scoliosis, parasites, unusual exudates (an organic fluid that oozes from an inflamed surface) and so on and so forth.

What does a carcass tell us?

Although veterinary pathologists are able to analyze the tissues we recover to paint a comprehensive picture of the animal, we are still able to extract important tidbits of information during our initial analyses.

For example, the absence of teeth in this porpoise leads us to conclude that it is an older individual. Dissecting the trachea reveals that a large amount of foam has accumulated in the respiratory tract and that significant accumulation is also present in the bronchial tubes of the lungs. “This foam suggests that this porpoise may have drowned,” confirms Laura Bourque. On the other hand, no signs of entanglement were noted during the macroscopic examination. How did it drown? The samples we’ve taken may reveal additional information once we get back to the laboratory. Continuing our exploration toward the gastrointestinal system, we are impressed by the presence in the animal’s stomach of a large colony of nematodes, a type of parasitic worm. “Completely normal,” explains Dr. Laura Bourque. “They can live quite well with large quantities of worms!” With the tissue samples we collect, Dr. Bourque will be able to determine whether certain changes in the animal’s body took place antemortem (before death) or postmortem (after death). Preserved in formaldehyde or stored in a freezer, the tissues taken from the porpoise carcass will also enable Laura Bourque and her team to focus on histology (study of the microscopic structure of the tissues) and thereby confirm the cause(s) of the animal’s death.

I am impressed with the complexity of the work and the effort required to compile important data on marine mammals in the St. Lawrence. Each stakeholder in the process represents an important link in the knowledge acquisition chain. As soon as an incident involving a stranded, drifting or vulnerable marine mammal is reported, the gears of a well-oiled machine are set in motion. Everyone plays their part in obtaining data that will inform major marine wildlife conservation decisions in Canada. We can be proud to be a part of this process as we strive to better understand in order to better protect.

Patrick Weldon

Patrick Weldon joined the GREMM team as UMM supervisor in 2022. He now holds the position of responsible at the Quebec Marine Mammal Emergency Response Network (QMMERN). An anthropologist by training, it is his strong connection with the ocean that sparked his desire to get involved in protecting the marine ecosystem.