Stranding of a live humpback whale in the Magdalen Islands

On March 25^th, 2018, the stranding of a live juvenile humpback whale (Megaptera novaeangliae) on a beach of the Magdalen Islands was reported to the Réseau québécois d’urgences pour les mammifères marins (RQUMM). The evaluation of pictures taken by a volunteer revealed an advanced state of emaciation of the animal. Following consultations with experts it was determined that it would not be wise to attempt a rescue of the whale due to the very poor survival prognosis and to the high risks associated with such a complex procedure. The death of the animal a few hours after its stranding confirmed its advanced state of weakness. Two CWHC teams (Atlantic and Quebec) were dispatched to the Magdalen Island to conduct a full necropsy, thanks to the collaboration of RQUMM volunteers and the support of Environment Québec and the Department of Fisheries and Oceans Canada.

Figure 1: Juvenile humpback whale stranded on a Magdalen Islands beach on March 25th, 2018. Photo credit: Sophie Beauchemin.

The carcass was in excellent preservation condition. This female had a length of 8.8 meters which confirmed that it was approximately one year of age,¹⁰ and therefore probably weaned quite recently. Weaning of humpback whales begins when they are about 6 months old and usually ends at the end of their first year of life,² when they reach approximately 8 meters in length.⁹ A marked emaciation, characterized by diffuse muscular loss and marked thinning of the subcutaneous adipose panniculus, was noted at the necropsy. No sign of recent feeding was observed. A small number of attached barnacles as well as many barnacle marks were observed on the head, the pectoral fins and the tail. These crustaceans attach themselves to the humpback whales’ skin while they are in the warm waters of breeding and calving grounds. The barnacles fall when whales arrive in the cold waters of the feeding grounds. The presence of these crustaceans and marks indicate that the arrival of this whale just in the Gulf of St. Lawrence was fairly recent. Gulf frequentation during winter by humpback whales is poorly documented and is limited to anecdotal observations.⁵ Thus, it is difficult to determine whether the presence of this whale around the Magdalen Island at the end of March was unusual or not. However, on April 3^rd (9 days after the stranding), three humpback whales were sighted in Mont-Louis (northeast of the Magdalen Islands).⁴ 

Two sets of superficial curvilinear whitish scars were also visible on the tail. The pattern of these scars is indicative of rake marks caused by killer whale (Orcinus orca)⁷. Some killer whale ecotypes are known to attack large cetaceans,⁶ including the Artic bowhead whales (Balaena mysticetus), in which approximately 8% of whales harvested by subsistence hunters have signs of killer whale aggression.³ The frequency of killer whale rake marks on humpback whales varies by region and appears to be significantly higher in Canadian waters (between 15.9 and 18.9%)⁶ and in eastern Australian waters (17.0%)⁷ compared to humpback in Maine, West Greenland, Iceland and Norway waters⁶. Since these marks are superficial and completely healed, they probably had no impact on the health of this animal. No pathological condition that could explain the emaciation was identify on the macroscopic examination of the carcass. In addition, there were no signs of traumatic injuries that could have been caused by a collision with a boat or by an entanglement in fishing gear. The current hypothesis to explain this stranding is that this recently weaned juvenile humpback whale was not able to meet its nutritional needs and therefore suffers from chronic malnourishment. Its stranding appears to be secondary to a state of generalized weakness associated with a negative energy balance. However, histological examination of tissues taken during the necropsy will need to be done if we want to rule out infectious diseases.

Figure 2: Barnacle marks (on the left) and killer whale rake marks (on the right) on the tail of the stranded humpback whale.

Finally, an increase in humpback whale mortality has been observed on the Atlantic coast (from Maine to Florida) since January 2016. Nine mortalities have been reported since the beginning of the current year, bringing the number of carcasses to 68 since January 2016. An Unusual Mortality Event of humpback whales has thus been decreed by the National Oceanic and Atmospheric Administration. Necropsies were performed in about half of these mysticetes and the cause of death could be attributed to collisions with boats or entanglements in fishing gear in 50% of cases. The cause of death could not be established in other whales and investigations are still ongoing.⁸

References:

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2. Clapham, P. J. (1996). The social and reproductive biology of humpback whales: an ecological perspective.Mammal Review, 26(1), 27-49.
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7. Naessig P.J., Lanyon J.M. (2004). Levels and probable origin of predatory scarring on humpback whales (Megaptera novaeangliae) in east Australian waters. Wildlife Research, 31, 163-170.
8. National oceanic and atmospheric administration (NOAA) Fisheries. (2018). 2016-2018 Humpback whale unusual mortality event along the Atlantic coast. Retrieved from:http://www.nmfs.noaa.gov/pr/health/mmume/2017humpbackatlanticume.html.
9. Society for Marine Mammalogy. (1993). Appearance of juvenile humpback whales feeding in the nearshore waters of Virginia. Marine mammal science, 9(3), 309-315.
10. Stevick, P. T. (1999). Age-length relationship in humpback whales; a comparison of strandings in the Western North Atlantic with commercial catches. Marine Mammal Science, 15(3), 725-737.

Karine Béland and Stéphane Lair, CWHC – Quebec