Sharks & Rays
Daily Activity Cycle
- Recording the movements of tagged sharks suggest that most sharks undergo daily activity rhythms. Their greatest activity occur during the twilight and dark hours.
- Although sharks and batoids are basically asocial, many species demonstrate various degrees of social behavior. For instance, hammerhead sharks commonly school.
Hammerhead sharks are periodically observed schooling in large groups.
- Pilotfish (usually Naucrates ductor, but there are others) often travel with sharks, for unclear reasons. The relationship may be due to the natural schooling behavior of the pilotfish, or the pilotfish may conserve energy by riding the hydrodynamic bow wake of the shark. Pilotfish also eat small amounts of food scraps released as the shark feeds.
- Several species of small fishes, notably the cleaner wrasse (Labroides dimidiatus), are "cleaners" that pick debris and parasites from sharks.
- Remora (several species in the family Echeneidae) commonly attach themselves to sharks and batoids or ride their hydrodynamic bow wakes. In addition, they may eat parasites off sharks and batoids.
A remora's dorsal fin is a modified sucking disc
that it uses to attach itself to large animals.
- Parasites of sharks and batoids are mainly copepods and flatworms.
- Only 32 species of sharks have been identified with attacks on humans or boats. These species have three features in common: they prey on fish or marine mammals, grow to a large size, and frequent warmer coastal waters where swimmers are apt to be.
- In 1958, the U. S. Office of Naval Research and the American Institute of Biological Sciences set up the Shark Research Panel - a union of scientists that gathered documentation on shark attacks and compiled the information into the Shark Attack File. The Shark Research Panel documented the following:
- Humans become prey by accident. Most shark attacks involved people handling hooked or snared sharks or spearfishermen handling wounded fish. Through sight or sound, a shark may confuse swimmers or divers for prey.
- Sharks may also attack from a territorial drive, with no intention to feed. A characteristic swimming pattern called agonistic display usually precedes attacks out of territoriality. The shark shakes its head and swims erratically with a hunched back, pectoral fins pointing down, and snout pointing up.
- An analysis of 1,000 recent shark attacks world-wide showed that well over 50% of the attacks were not feeding-related.
- Up to 60% of shark attack injuries are slashes of the upper jaw teeth. This behavior is typical of courtship advances by some male sharks.
- Sharks may also injure victims by bumping them vigorously, but mostly sharks move in cautiously when attacking.
- A great white shark rushes towards its prey, attacking from beneath and behind. These sharks rely on stealth and surprise to prey on seals, sea lions, and other marine mammals.
- After a great white shark bites its victim, it swims a short distance away, waiting for its victim to bleed to death.
- Great white shark populations may be increasing along the coasts of California and Oregon due to increasing populations of seals and sea lions. Marine mammal populations are increasing as a result of federal protection. Populations of predators naturally increase as food becomes more readily available.
- Swimmers and skindivers at the surface are prone to attack more than scuba divers in the water. At the surface, a swimmer's or diver's silhouette resembles that of a seal. Great white sharks may not be able to make the distinction.
At the surface, a diver's silhouette resembles a seal's.
- California has one of the highest great white shark attack rates in the world, yet fatalities average only one every eight years. Most humans survive attacks by great white sharks and sharks in general.
- In False Bay, South Africa, great white sharks attack more boats in this one area than in all other places in the world combined. No one understands why this phenomenon occurs at False Bay.
- Great whites are usually listed as the most dangerous shark for attacks on humans. Strangely, 80% of reported attacks are in tropical waters where great whites are rare. The tropics are home to large, potentially dangerous species such as bull, tiger, and mako sharks (Isurus spp.). It is possible the great white shark is misidentified in many attacks.
Because they look fierce, sand tiger sharks are feared and killed around the
world, but this species is generally not dangerous unless first provoked.
- In 1997, there were 61 worldwide shark attacks reported (11 being fatal).
- From 1990 to 1996, there were 49 unprovoked attacks reported per year with 6.3 deaths on average. This is consistent with the belief that there are between 50 to 100 shark attacks with only 5 to 10 fatalities per year.
- More people are killed every year by bees, elephants, dogs, lightning bolts, and pigs than by sharks.
- There is no known effective shark deterrent.
- A chain mail suit made up of 400,000 tiny, interlocking stainless steel rings proved effective against bites of smaller sharks. The suit costs around $5,000.
- The Shark Screen is like a plastic sleeping bag that floats in the water. Most shark attacks occur on easier to bite targets like arms and legs. A person inside the Shark Screen appears as one mass and offers no easy target for a shark to bite. Body chemicals and blood cannot escape into the water as well.
- The only natural shark repellent known comes from the Moses sole. When a shark attempts to bite a Moses sole, its mouth seems to become paralyzed. Human attempts to synthesize the Moses sole defense mechanism have not been successful.