Marine ecosystems are under increasing pressure due to the intensification of human activities, particularly fishing and maritime traffic. This is particularly evident in key regions like the Gulf of St. Lawrence, one of the most important feeding grounds for fin and humpback whales. These anthropogenic pressures lead to injuries and changes in the physical condition of these cetaceans.
A team of researchers affiliated with Laval University and the Sept-Îles Education and Research Center has developed a non-invasive assessment tool to analyze the health of whales. Published in the journal Animalstheir study draws on physical data collected between 2016 and 2021 to link physical signs, such as injuries, to the impacts of human interactions. This work provides an in-depth understanding of the challenges these marine mammals face and should then guide conservation policies in this critical environment.
A growing threat to cetaceans
Fin whales (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) are two emblematic species that migrate each year to the Gulf of St. Lawrence to feed. The fin whale, the second largest animal after the blue whale, is distinguished by its impressive size and speed. Mainly piscivorous, it feeds on small fish and zooplankton in large quantities. The humpback whale, best known for its complex songs and spectacular social behaviors, also adopts collaborative hunting techniques to capture fish and krill. These characteristics make the Gulf a critical area for their survival, particularly because of the richness of its ecosystem.
Search area in the Sept-Îles and Port-Cartier region. Humpback whales (n = 50) are represented by circles and fin whales (n = 50) by triangles. © A. Boileau et al., 2024
However, visiting this region is associated with increased risks. Fin whales, often found in shipping lanes, are highly exposed to collisions with ships. Humpback whales, which often swim near the surface, are frequently entangled in fishing gear. These interactions with human activities, combined with changes in their habitat, compromise their well-being and their ability to feed effectively. Studying these mammals in the context of an anthropized environment is therefore essential to better understand the pressures they experience and consider appropriate solutions.
Visual tools for precise assessment
To assess the well-being of these animals in the Gulf of St. Lawrence, researchers implemented a systematic method based on the visual analysis of the physical characteristics of cetaceans. Aboard a research boat, the team observed each animal for up to two hours. When an individual was spotted, the boat positioned itself parallel to its body at a distance of at least 50 meters. High quality photographs were then taken from different angles, including the sides and fins.
And for humpback whales, the tail fins. Indeed, the latter often expose them when they dive. This contrasts with fin whales, which generally do not raise their tail fins above the water. When an individual exhibited avoidance behaviors, such as rapid diving, observation was interrupted to limit stress.
These photographs were then sorted. The images retained made it possible to evaluate four indicators: body condition, skin lesions, wounds and parasitic loads. The researchers analyzed more than 6,400 images (3,251 for humpback whales and 3,152 for fin whales). They covered observations made between 2016 and 2021. The researchers then used collaborative databases, such as Happy Whale, to cross-reference the identities of the individuals observed.
They relied on public databases from the Canadian government to extract environmental data. They focused on temperature, salinity and dissolved oxygen levels. These abiotic parameters were correlated with physical indicators of cetaceans using statistical models. The authors aimed to establish a clear link between environmental conditions and anthropogenic impacts on the health of these marine mammals.
Contrasted well-being
The results of the study then highlight significant disparities between fin whales and humpback whales. According to the researchers, 60% of the humpback whales were in good body condition. Compared to only 46% of fin whales. Anthropogenic injuries include scarring from entanglement in fishing nets or impacts from ship strikes. They showed a direct link with a degraded body condition.
According to Anik Boileau, it is impossible to determine the origin of the difference between the body states of the two species. In addition, it could be larger than estimated, because researchers cannot have visual access to the entire body of the fin whale.
“ These injuries, often chronic, reduce the physiological capacities of cetaceans to feed or move. They affect their long-term survival », Explain the authors. Note that 50% of fin whales and 48% of humpback whales studied had visible scars. They then confirm the extent of the pressures exerted by human activities. Anik Boileau specifies: “ Humpback whales have very long pectoral fins, often covered in barnacles. Entanglements in fishing gear then seem more complex than in the other species. “.
Statistical analyzes also revealed that the intensity and frequency of these injuries varied between years. It therefore seems that there are more critical periods. Particularly in 2017, serious injuries were particularly high. But for Anik Boileau, it is impossible to explain the reason at present.
Revealing skin
Another crucial aspect concerns the condition of the whales' skin, which has provided a better understanding of the links between the health of cetaceans and their environment. Skin lesions, such as pale skin patch syndrome, were often correlated with high nitrate levels and low water oxygenation, signs of eutrophication. “ These lesions are not just visual markers. They demonstrate prolonged environmental stress and degraded living conditions for these animals. », underline the researchers.
Parasitic loads (diatoms or lamprey bites) also influenced skin condition. There are notable impacts on the overall condition of individuals. Among fin whales, 74% of individuals showed bite marks, compared to 36% for humpback whales. Finally, the abundance of fish, although essential for the diet of these cetaceans, did not show a direct correlation with their body condition. This observation highlights the complexity of interactions between environmental and anthropogenic factors.
Towards informed conservation of cetaceans and marine ecosystems
This research strongly highlights the importance of rigorous monitoring and precise methodologies to assess the increasing impacts of human activities on cetaceans. The physical indicators validated by this study offer valuable tools for understanding the health status of whales and the pressures they experience in highly anthropized environments such as the Gulf of St. Lawrence.
By demonstrating the links between human-caused injuries, environmental degradation and the physical condition of cetaceans, researchers highlight the need for increased regulation of human practices, particularly in critical areas for the feeding and survival of these species. .
Positive correlations of the four measurement scales for the two species (n = 50). © A. Boileau et al., 2024
In a global context of accelerated degradation of marine habitats, these results go beyond the local framework. They call for stricter management of maritime activities, but also for the integration of animal welfare indicators into conservation policies on an international scale. Protecting cetaceans does not just mean preserving these emblematic species.
This must also guarantee the resilience of marine ecosystems on which a large part of ocean biodiversity depends. By pursuing this approach, it will become possible to build sustainable conservation strategies. Strategies adapted to a world where human pressure on the oceans continues to grow.
Source: Boileau, A.; Blais, J.; Van Bressem, M.-F.; Hunt, K.E.; Ahloy-Dallaire, J. “Physical Measures of Welfare in End (Balaenoptera physalus) and Humpback Whales (Megaptera novangliae) Found in an Anthropized Environment: Validation of a First Animal-Based Indicator in Mysticetes”. Animals 2024, 143519.
https://doi.org/10.3390/ani14233519
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