Despite the fact that dolphins are incredibly intelligent, sociable, and sentient beings, we still choose to hunt them, either to death as part of traditional slaughters or to capture for display in marine parks and aquariums. Now, adding to the evidence that this practice is cruel and outdated, scientists are warning that the dolphins suffer severe physical and psychological trauma as a result.

Publishing their findings in the Journal of Applied Animal Welfare Science, an international team of researchers conducted an analysis of previous research focusing on Japan’s dolphin hunts. During these “drive hunts”, flotilla fishing vessels herd small cetaceans into shallow coves by chasing them with an “aversive wall of sound” created by banging hammers on trumpet-shaped metal poles.

The practice targets a variety of small cetacean species, which, once cornered, are either slaughtered for meat or taken from the ocean to be displayed in aquariums or to perform in shows. The hunted species include bottlenose, Risso’s, rough-toothed, and pantropical spotted dolphins, as well as false killer whales, short-finned pilot whales, and melon-headed whales.

The most infamous of the hunts takes place in Taiji, Japan, and was the subject of the Oscar-winning documentary The Cove. However, drive hunts also occur in the Faroe Islands and Solomon Islands.

One obvious stressor in the chase is the intense noise emitted by the hunters. This cacophony can damage the cetaceans’ ears and disrupt their ability to communicate, while also causing a damaging stress response. The paper’s authors note that the surge in stress hormones during the hunt can harm reproductive health and even lead to an early death. Stress hormones combined with the physical exertion of being chased can also lead to heart and muscle damage.

Having been corralled into a shallow cove, the dolphins or whales are usually held there for a number of days. They often suffer injuries, their breathing becomes rapid, and they can drown. They can also suffocate if they are being restrained. Those chosen for slaughter are dragged away by their tails to be killed. Hunters must stick to certain quotas, so some of their catch gets released back into the ocean, but these animals are sometimes so injured or psychologically traumatized that they either die or beach themselves over the next few days.

“Drowning or asphyxiation, resulting from forced restraint, would not be permitted in any accepted slaughter process for terrestrial mammals,” the authors write, noting that the practice disobeys slaughter guidelines set out by the World Organization for Animal Health.

Dolphins are known for their impressive intelligence. They use sponges as tools, have advanced social awareness, act altruistically, and live in complex and intricate social clans. Unfortunately, this braininess makes them even more susceptible to the trauma of the hunts.

"Sociality is an often overlooked aspect of wildlife welfare," study author Philippa Brakes told IFLScience. 

The animals can be distressed by witnessing fellow group members with whom they share a close bond be captured or killed. Meanwhile, mothers can be separated from their calves. If reunited, high levels of stress hormones can be transmitted through the mother’s milk, potentially damaging the health of the calf.

“There is compelling scientific evidence that the process of chase and capture is inhumane,” the researchers conclude. “Based on current knowledge of these animals and the high probability for injury and suffering resulting from pursuit, chase and herding, the authors assert that the drive hunt method cannot be conducted in a humane manner and should be abandoned.” 

Whether it is abandoned is in the hands of Japanese lawmakers who, despite mounting pressure, have yet to ban the practice.

"Considering Japan’s flagrant violation and abandonment of international whaling agreements, it appears that they are holding on to these last bastions of coastal whaling at all costs, despite the horrible suffering associated with these hunts, and the devastating impact to dolphin populations in the waters around Japan," lead author Courtney Vail told IFLScience.