Small fish are often seen swimming closely alongside sharks. This association highlights a unique aspect of ocean ecosystems. Understanding why these fish accompany sharks reveals interesting ecological relationships.
Identifying the Small Fish
The small fish observed with sharks are primarily remoras and pilot fish. Remoras, sometimes called suckerfish, have a distinctive, oval-shaped suction disc on their heads. This modified dorsal fin allows them to firmly attach to the shark’s skin. Pilot fish are smaller, slender fish with prominent dark vertical stripes, and they do not possess a suction disc. Both species stay close to sharks, but their association methods differ.
Benefits for the Fish
The small fish accompanying sharks gain several advantages from this association, particularly concerning food acquisition. Remoras often feed on leftover scraps from the shark’s meals and graze on parasites and dead skin cells found on the shark’s body. Pilot fish similarly benefit from discarded food particles and may also consume external parasites on the shark.
Beyond sustenance, safety is a significant factor for these fish. Associating with a large predator like a shark offers protection from their own predators. Many marine animals avoid approaching a shark, providing a safe zone for the accompanying fish. This allows them to forage and travel with reduced risk.
Transportation is another benefit, especially for remoras. By attaching to a shark, remoras conserve energy they would otherwise spend swimming. They are transported across oceanic distances without effort. Pilot fish, while not attaching, often swim in the shark’s slipstream, benefiting from reduced drag and expending less energy during travel. This allows both types of fish to cover wide ranges and access new feeding grounds.
Benefits for the Shark
The common perception that sharks gain substantial benefits from these accompanying fish is largely a misconception, as the relationship is primarily commensal. While remoras do consume external parasites and dead skin from the shark’s surface, this service is generally not considered critical for the shark’s overall health. Sharks are robust predators with their own natural defenses against parasites, and remoras do not provide a vital cleaning service.
Pilot fish also consume parasites and food scraps, but their contribution to the shark’s well-being is similarly minor. The shark does not actively seek out or rely on the pilot fish for any essential function. The relationship is largely one-sided, where the smaller fish benefit significantly without providing a substantial advantage to the shark.
Sharks typically tolerate the presence of these fish, showing little to no aggression towards them. This tolerance is likely due to the minimal impact the fish have on the shark’s well-being or hunting efficiency. The close association is more a testament to the adaptability and opportunistic behavior of the remoras and pilot fish rather than a mutually beneficial partnership for the shark.
The Mechanics of the Relationship
Remoras possess a specialized suction disc, a modified first dorsal fin, allowing them to adhere firmly to the shark’s skin. This disc contains lamellae that create a vacuum, enabling powerful adhesion. Remoras can attach to various parts of the shark’s body and can easily detach and reattach as needed. Their ability to release quickly helps avoid entanglement during rapid movements.
Pilot fish, lacking a suction device, maintain their close association by swimming in precise positions relative to the shark. They often position themselves in front of the shark’s snout, near the pectoral fins, or around the tail. By swimming in these areas, they use the hydrodynamic forces created by the shark’s movement, reducing their own energy expenditure. This allows them to keep pace with the larger shark without expending excessive energy.