After spending several days in the region of Montreal, the humpback whale is found dead: A collision with a boat is suspected.

The humpback whale before its death. We can observe the presence of a large amount of material covering the skin of the whale. This material is mainly composed of Saprolegnia sp., an oomycete normally found in fresh water.

A humpback whale has been observed since May 27 in the St. Lawrence River in the Montreal region. The Réseau québécois d’urgence des mammifères marins (RQUMM) set up a monitor program to follow the level of activity of the animal and make boaters aware of the animal’s unusual presence in this area. The objective of this program was to minimize the risk of disturbances and collisions by boats. The unusual presence of this whale in the heart of the Montreal metropolitan area has attracted the attention of many city dwellers.

The remote observation of the animal indicated that it was a whale of about 2 years of age with an adequate body condition. Over time, the appearance of the animal’s skin has gradually deteriorated, which is not unexpected for a cetacean exposed to fresh water. The activity level of the animal, which swam vigorously face in the current and breached numerous time per day, seemed on the other hand good. Although this type of incursion of baleen whales in freshwater remains unusual, similar cases have been reported in North America and Europe. The reasons that led this whale to venture into freshwater more than 400 km away from its usual habitat remain unclear. Young cetaceans may tend to explore new areas. In some cases, this exploratory behavior is possibly associated with the movements of schools of fish that are part of the whale’s diet. Some have suggested that the presence of the animal in the fluvial portion of the St. Lawrence could coincide with a significant runs of shad. Is it possible that this followed potential preys in the St. Lawrence River? Hard to say.

The carcass of the humpback whale is moved on dry dock to enable the realization of a post-mortem examination by the CWHC team.

The whale, which had remained in the same area for a few days, was lost on the morning of June 7 after it was last seen at the eastern tip of the Island of Montreal. After 48 hours without news of the whale, its carcass was found in Varennes. In order to determine the cause of death of the animal, a necropsy was performed by the CWHC – Quebec Region at the Sainte-Anne-de-Sorel dock. On examination, this 10.2 m juvenile female humpback whale showed adequate body condition. A significant proportion of the surface of the skin was covered by the proliferation of downy material frequently forming circular lesions. Although this accumulation of material was mostly superficial, in some areas, the full thickness of the epidermis appeared to be involved. The first evaluation of this material suggests that it is mainly an infection with Saprolegnia sp. (saprolegiosis). This microorganism is an opportunistic oomycete naturally present in fresh water, which can colonize skin wounds in fish and is known to invade the skin of cetacean frequently fresh water. This type of skin change is frequently observed on the skin of cetaceans spending some time in fresh water. The impact of these spectacular skin lesions on the health of the animal remains unclear. It has been observed that this type of change quickly disappears when the animal returns to salt water. Macroscopic examination of the whale revealed hemorrhagic areas suggestive of bruises in the subcutaneous tissues and in the surface of the muscles. Although these areas were present on both sides of the carcass, the left flank was by far the most affected. The presence of these bruises could suggest a collision with a boat. This observation, which will have to be confirmed following more complete analyzes, makes us believe that the death of this whale could have been caused by a collision with a large vessel. This abrupt death could explain the sudden disappearance of the animal.

It as to be pointed out that this diagnosis is preliminary at this time. The CWHC – Quebec Region team should submit a detailed report of the event over the summer. Collisions with boats are one of the main causes of death for large baleen whales. For some species, such as the right whale, these collisions actually represent a significant cause of decline.

The unusual presence and death of this whale in an urban center was associated with unprecedented media attention; several interviews having been carried out. This clearly shows the interest of the Quebec population towards the health of wildlife.

The CWHC – Quebec Region would like to thank all the partners who participated in the monitoring and necropsy of this humpback whale, especially the RQUMM team who took care of the logistics of this complex operation and the municipality of Sainte -Anne-de-Sorel.

Stéphane Lair

CWHC – Quebec Region

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