I Swim With Sharks
I Swim With Sharks
©Text and photography by Marty Snydeman
Upon first consideration, it seems like swimming or otherwise living in close association with toothy sharks would be the last place you would ever find smaller fishes. But Mother Nature has other ideas as several species of bony fishes including remoras, the rainbow runner, pilotfish, golden trevally and bluefin jack live in close association to some large fish-eating sharks.
The common names remora, diskfish, sharksucker, suckerfish, and hitchhiker fish are all used to label the eight fish species described in the family Echeneidae. It is quite common for all of these fishes to attach themselves to or otherwise accompany a variety of sharks and other larger host animals.
The relationship between remoras and the host animals they accompany is not completely understood. But it is likely that the relationship benefits both the remoras and hosts. The remoras gain protection by associating with large hosts as potential predators are likely deterred from pursuing a fish that is attached to the body of or swimming with a large shark.
Remoras also benefit by being supplied with food as they are known to feed on a variety of parasites that are found on the skin of their hosts, on scraps of food that they are quick to grab when their hosts capture their prey, and on some organisms that parasitize their hosts. In addition, at least two species of remoras acquire nutrition by eating the feces of their hosts, a feeding strategy known as coprophagy.
But there is a price to be paid by the remoras as their remains are routinely found in the stomach contents of sharks.
The rainbow runner (Elagatis bipinnulata) inhabits wide segments of offshore and coastal waters in tropical and subtropical seas. Rainbow runners have routinely seen “dive bombing” a number of species of sharks including silkies, gray reef, whitetip reef and blacktip reef sharks as these jacks aggressively rub themselves against the sharks’ rough skin. It is believed that the rainbow runners do so in an effort to dislodge parasites from their skin.
Fast swimmers, rainbow runners appear to easily keep pace with the sharks. The sharks, on the other hand, often appear to be irritated by the rainbow runners’ efforts to rub against them.
Another jack that routinely swims in close proximity to a variety of open water sharks is the pilot fish, Naucrates doctor. An oceanic species found in tropical and subtropical waters worldwide, pilotfish often tuck themselves in very close to a shark’s body or fins, and it is not uncommon to see them swimming within one foot or so of a shark’s snout.
Early day mariners believed pilotfish led sharks to food, hence their common name “pilot”. However, modern science suggests that pilot fish take up their position as a means of saving energy by swimming in the pressure wave created by a swimming shark. In addition, pilotfish receive the benefit of being protected against an attack from other predators simply because they are swimming so close to a potentially menacing shark. And pilotfish sometimes pick up scraps when their host shark makes a kill.
It is likely that the sharks do not benefit from the presence of the pilotfish.
Golden Trevally And Bluefin Jack
Juvenile golden trevally, Gnathanodon speciosus, are often seen as they swim only a few inches in front of the heads of fish-eating sharks. It is generally accepted that these youngsters gain protection from the mere fact that very few other creatures are likely to try to capture a golden trevally that has a toothy shark as a bodyguard.
The interaction between the bluefin trevally, Caranx melampygus, and whitetip reef shark, Triaenodon obesus, illustrates yet another relationship shared by jacks and sharks. During daylight hours, bluefin trevally commonly feeds on the mid-water plankton feeders known as Pacific creolefish. When the marauding jacks rush the creolefish, the creoles often seek cover in the latticework of the reef below. The frenetic swimming activity often excites the sharks, and they react by trying to pick off confused creolefish. In turn, the jacks benefit from the sharks’ pursuit of the creolefish as the further panicked creolefish become easier targets for the jacks.