We saw in the last post that whales are particularly difficult animals to study, and that biologists have been very creative to find ways to track and understand them. But how do their unique characteristics influence the relationship that cetaceans have with their environment?
The oceans of the 21st century are full of dangers for marine life: ever more ships that are larger and faster, chemical pollution, plastic waste, ropes and fishing gear, climate change... Whales were perfectly adapted to the oceans in the pre-industrial era, but they are vulnerable to these rapid changes in their environment. These are problems that are invisible to most people, being hidden beneath the surface, far off the coast in rarely visited seas. Even ship strikes, where humans are by definition present at the time of the accident, often go undetected, and it is estimated that only one in ten entangled whales are recorded. Furthermore, it is difficult for humans, utterly visual creatures, to understand how sensitive whales are to their sound environment, and we are only starting to address this crucial problem for cetaceans.
The fact that whales consume large amounts of food during their lifetime exposes them to bioaccumulation of environmental contaminants. As predators that consume other carnivorous animals such as seals and large fish, killer whales are particularly affected by this phenomenon. In St. Lawrence belugas, which consume invertebrates living in contaminated mud, this could explain the high perinatal mortality rate. Toothed whales such as sperm whales and Cuvier's whales can swallow large quantities of plastic debris, which seriously impedes their digestion.
The vulnerability of whales to fast-appearing ocean disruptions is due in part to their long life cycle, which limits their demographic resilience. Indeed, even under ideal conditions, it is difficult for a population to rebound quickly from a disturbance that causes high mortality, as large whale species mature slowly and often space out their calvings by several years. For this reason, when thinking about whale conservation, one must consider that not all individuals are equally important to the survival of their species. In an endangered population where the reproduction rate is insufficient to ensure demographic growth, the survival of a young female has more impact on the future of her group than that of a male or an older individual.
But several cetacean species live in complex groups that can range from a family unit to several hundred dolphins: the value of an individual is not only based on its reproductive potential, but also on its social role. In killer whales and pilot whales, females help their sons to reproduce and take a leadership role when they reach menopause.
The fact that many whales exhibit social learning mechanisms, which many researchers equate with culture, is a double-edged sword for their preservation. On the bright side, the ability to quickly learn a survival strategy may be the key to exploiting a new resource and adapting to a changing reality. For example, sperm whales have learned to take advantage of the increased presence of fishermen to help themselves directly on their hooks. On the other hand, this knowledge can be lost with the death of key individuals, or when populations are too fragmented to allow cultural transmission. For sperm whales, which live in matrilineal groups, losing an older female also means losing a social marker, which is the repository of knowledge on migration routes, feeding and communication. Additionally, some groups may specialize their behaviors much more than required by their physiological disposition, to the point where they become dependent on one resource. This is the case for the southern resident killer whales on the west coast of North America, which feed almost exclusively on salmon and are severely struggling as stocks are declining. Meanwhile, on overlapping territories, their anatomically identical transient cousins eat marine mammals of all sizes and do not experience such malnutrition problems.
If even their intelligence, their sensitivity to the environment, and their ability to learn from each other and cooperate can work against them, is there hope for the future of cetaceans? Certainly, yes, as their charisma and uniqueness capture the attention of researchers, the public, and marine industry stakeholders more and more each year. We now have a better understanding of the role that whales play in ocean-wide nutrient cycles, and we know that their preservation is critical to the balance of systems that are crucial to maintaining marine and terrestrial ecosystems as we know them. So what are the particular challenges of cetacean conservation, and how can Whale Seeker contribute to this daunting mission? That is what we will see in the next post.