Do cetaceans interact with sharks?

Relations between cetaceans and sharks are far more complex than the popular image of a simple confrontation between predator and prey would suggest. Depending on the species, the context and the region of the world, these interactions range from outright predation to remarkable defensive strategies, by way of peaceful coexistence and even certain forms of active avoidance. Understanding that diversity means entering one of the most fascinating chapters of marine ecology.

When killer whales hunt sharks

The most spectacular example is that of the killer whales that hunt great white sharks in South Africa. Since 2017, two male killer whales nicknamed Port and Starboard (after the opposite lean of their dorsal fins) have ranged along the South African coast and specifically targeted Carcharodon carcharias. Their particularity: they eat only the liver, an organ especially rich in lipids and therefore in energy, and leave the rest of the carcass.

The techniques used are remarkably precise. The killer whales generally begin by ramming the shark to destabilise it, then turning it onto its back. This inversion triggers a state of temporary paralysis known as tonic immobility, a physiological reflex peculiar to sharks when they are upside down. During that state, they can extract the liver with surgical precision. In one documented case, Starboard killed a 2.4 metre juvenile white shark on her own in under 2 minutes.

The ecological impact has been spectacular: the sustained presence of Port and Starboard in an area has driven great whites away for months. Several South African bays historically frequented by great whites (False Bay, Mossel Bay) have seen their populations collapse. This “ecological fear” even has knock-on consequences for seals and other usual prey of great whites.

Cooperative hunting and other techniques

Killer whales of other ecotypes also hunt sharks, with varying techniques. The offshore killer whales of the North-East Pacific have specialised in Pacific sleeper sharks, which they attack in deep water, and their teeth show characteristic wear linked to the rough skin of those sharks. In New Zealand, some killer whales have been observed hunting stingrays right up onto the beaches.

Sperm whales, too, can attack sharks, particularly the large solitary males of the high latitudes. The megamouth shark, the basking shark, the blue shark and the sleeper shark occasionally feature on the menu of these giants. With their powerful teeth and colossal strength, sperm whales can prevail even against sharks of large size.

When sharks hunt cetaceans

The relationship is reversed for small cetaceans. The calves of large species, isolated dolphins and porpoises are regular prey for several large sharks. The tiger shark (Galeocerdo cuvier) and the bull shark (Carcharhinus leucas) are particularly formidable for young dolphins. The semi-circular scars left by the triangular teeth of these sharks are visible on many adult dolphins, evidence of attacks survived.

The basking shark and the whale shark, despite their gigantic size, are plankton feeders, harmless to cetaceans, and coexist peacefully with them in feeding areas rich in zooplankton.

The defensive strategies of dolphins

Faced with a shark, dolphins are not defenceless. When a large shark threatens a group of common bottlenose dolphins, several collective defence strategies have been observed. The most effective is the coordinated attack: several dolphins surround the shark and strike it in turn with their rostrums, targeting the liver and the gills in particular. The rigid rostrum of an adult common bottlenose dolphin (200-300 kg) can inflict serious injuries even on a large shark.

When a calf or a juvenile is attacked, the adults often form a protective circle around it, keeping it at the surface where it can breathe while barring the shark’s access. These protective behaviours are observed in many dolphin species and show a genuine collective solidarity.

An ecological division

Beyond direct interactions, cetaceans and sharks often occupy complementary ecological niches. Basking sharks and baleen whales exploit plankton swarms in the same places without competing directly. Sperm whales and deep-sea sharks hunt in superimposed layers of the ocean. On whale carcasses (whale falls), sleeper sharks, megamouth sharks and other scavengers of the abyss coexist with other species in a genuine ephemeral ecosystem.

These two lineages of large marine predators, which appeared long before humans and are in places separated by 400 million years of evolution, have had ample time to develop a full range of interactions, from the most violent confrontations to the most peaceful coexistence. Far from the simple “shark versus dolphin” of adventure films, their relationship is one of the richest in the marine world.

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Further reading