Postmortem examination of a humpback whale by CWHC-Quebec
Humpback whale carcass stranded near Mont-Saint-Pierre in Gaspésie (photo credit: RQUMM).
On October 25 the Réseau d’urgences mammifères marins (RQUMM) contacted the Centre québécois sur la santé des animaux sauvages (CWHC-Quebec) following the stranding of a dead humpback whale (Megaptera novaeangliae) near Mont-Saint-Pierre on the Gaspésie Peninsula. Intervention options to determine the cause of death of this individual were jointly examined, with the support of Fisheries and Oceans Canada and the MELCCFP – Région du Bas-Saint-Laurent, de la Gaspésie et des Îles-de-la-Madeleine.The location of the stranding did not allow for intervention supported by heavy machinery, and access was only possible at low tide. Despite these logistical challenges, a post-mortem examination was conducted on the morning of October 27 by the teams from the CQSAS (RCSF-Québec) and RQUMM.
An external assessment of the carcass was conducted before beginning the process of removing the skin and blubber from the whale’s body. This stage of the necropsy is the longest but also one of the most important as it allows for the evaluation of potential indications of a collision with a vessel and access to the whale’s internal structures. After approximately 3 hours of work on the carcass, several internal organs were identified and sampled for subsequent analyses. It is worth noting that morphometric measurements had already been taken by the RQUMM team during a previous low tide, once again to maximize the time spent working directly on the carcass on the day of the necropsy.
Personnel from CQSAS (CWHC-Quebec) and RQUMM starting the post-mortem examination of the humpback whale at low tide, under the supervision of Émilie L. Couture
This intervention as a whole revealed that this whale was a juvenile male measuring 10.7 meters with an estimated age between 3 and 5 years (Boye et al. 2020, Stevick 1999). A photo identification was conducted, revealing that this humpback whale had been last seen in the Tadoussac region by the GREMM research team on September 27th, in the company of two other individuals. During the assessment of the carcass, no evidence of entanglement in fishing gear was observed, with the limitation of position of the carcass not allowing for an evaluation of the base of the right pectoral fin. This preliminary investigation also did not reveal any injuries that could be associated with blunt trauma, but the possibility of a collision with a vessel cannot be conclusively ruled out given the partial assessment of structures that could be affected in a collision. Since the anatomical landmarks normally used in evaluating body condition in whales were not visible during the necropsy, it was not possible to assess the nutritional condition of this humpback whale accurately. Nevertheless, as the animal’s body condition had been assessed as adequate during the last observation a month prior, we do not believe that this individual died from starvation.
The microscopic evaluation of the collected tissues could help us paint a more precise picture of what may have led to the death of this individual. The information obtained during the necropsy, although partial, along with the logistical experience gained in the context of intervention with limited access, remain important assets that justify this type of procedure when field conditions permit.
Although the humpback whale is considered a ‘least concern’ species by the International Union for Conservation of Nature (IUCN), a recent study suggests a link between a decline in reproductive success and environmental variations affecting the availability of food resources for the species in the Gulf of St. Lawrence, which is a major summer feeding ground for this species (Kershaw et al. 2020). Furthermore, since 2016, there has been an ongoing investigation into unusual humpback whale mortalities on the east coast of the United States, with no published conclusions on the precise causes of mortality so far, except for some cases of vessel collisions (NOAA).
This necropsy was made possible through the partnerships established between CQSAS/RCSF, GREMM/RQUMM, and Fisheries and Oceans Canada. Thanks to the field team that faced darkness and suboptimal access conditions to attempt to elucidate the cause of death for this individual.
References:
Boye TK, Garde E, Nielsen J, et al (2020) Estimating the Age of West Greenland Humpback Whales Through Aspartic Acid Racemization and Eye Lens Bomb Radiocarbon Methods. Frontiers in Marine Science. 6:811.
Kershaw J. Ramp CA, Sears R, Plourde S, Brosset P, Miller PJO, Hall AJ (2020) Declining reproductive success in the Gulf of St. Lawrence’s humpback whales (Megaptera novaeangliae) reflects ecosystem shifts on their feeding grounds. Global Change Biology. 27(5):1027-1041.
NOAA. https://www.fisheries.noaa.gov/national/marine-life-distress/2016-2023-humpback-whale-unusual-mortality-event-along-atlantic-coast
Stevick PT (1999) Age-length relationships in humpback whales: A comparison of strandings in the Western North Atlantic with commercial catches. Marine Mammal Science. 15(30): 725-737.
Benjamin Jakobek, Émilie L. Couture, CWHC-Quebec
