I recently watched a documentary involving mako sharks where the researchers used a kind of conditioned response test to gauge the mako's intelligence or lack thereof. The makoes quickly "learned" which action would produce bait and which action would not. The researchers would lower bait when the mako bumped a certain object in the water. Has any testing similar to this been conducted on white sharks?

Kate Holly
Fresno, CA
kate@agrilaw.com

Lemon sharks (Negaprion brevirostris) were the first sharks to be trained. They were fed at a target that, when pressed, caused a submerged bell to ring. The ringing of the bell then induced the sharks to approach the target. The learned response has been used as a probe by many researchers since then to ascertain what frequencies of sound, wavelengths of light, and magnitudes of electric fields to which sharks are sensitive. Learning experiments have yet to be conducted on white sharks since they have yet to be successfully kept in captivity, where such tests are more easily conducted.

Clark, E. 1959. Instrumental conditioning of lemon sharks. Science, 130:217-218.

How long do hammerheads live and what is the size of the record caught by weight?

Walter Polk
Kannapolis, NC
wpolk@ctc.net

There are nine species of hammerhead sharks. The largest is the great hammerhead (Sphyrna mokarran). The largest reported by Compagno in his species description is 610 cm long (20.0 feet). However, most adults are not longer than 341 cm (11.2 feet). Large individuals are rarely weighed.

It is more easy to determine how rapid sharks grow than their maximum range. The oldest individuals are rare in a population as most individuals are caught before they reaching their natural life span. The age of a shark can be determined by counting the rings of more and less dense cartilage deposition on a vertebrae. Staining the vertebrae with a dye, called tetracyline, that is fluorescent under ultraviolet light makes it easier the discern the rings. Male scalloped hammerhead sharks reach a length of 140 cm (5.6 feet) in eight years. These sharks certainly grow considerably older. The largest free-swimming hammerhead that I measured using a stereocamera was 361 cm (11.8 feet). Yet one can not simply extrapolate an age for this individual as the growth per year decreases as a shark gets larger. An Australian soupfin shark (Galeorhinus australis) tagged in the mid 1950s and estimated to be at least five years old was recaptured in the mid 1990s, giving an age of 35 years. This species is a member of the reef shark family Carcarhinidae, which is closely related to the hammerhead family Sphyrnidae.

Klimley, A.P. and S.T. Brown. 1983. Stereophotography for the field biologist: measurement of lengths and three-dimensional positions of free-swimming sharks. Marine Biology, 74:175-185.

Schwartz, F.J. 1983. Shark ageing methods and age estimation of scalloped hammerhead, Sphyrna lewini, and dusky, Carcharhinus obscurus, sharks based on vertebral ring counts. Pp. 167-174 in Prince, E.D. and L.M. Pulos (Eds.), Proceeding sof the International Workshop on Age Determination of Oceanic Pelagic Fishes: Tunas, Billfishes, and Sharks. NOAA Tech. Rep. NMFS 8.

What is the average length of an adult hammerhead shark?

Adam Berry
Lenoir, NC
adamberry@webtv.net

There are nine species of hammerheads. The smallest is the bonnethead, Sphyrna tiburo, with an average adult size of 120 cm (3.9 feet). The great hammerhead, Sphyrna mokarran, is the largest species with adults averaging 300 cm (9.8 feet). Females grow larger than males because a greater size enables them to give birth to more young. For sizes for the different species, consult the following reference volume:

Compagno, L.J.V. 1984. FAO Species Catalogue. Vol. 4, Part 2, Sharks of the World. An Annotated and Illustrated Catalogue of Shark Species Known to Date. United Nations Development Programme. Food and Agriculture Organization of the United Nations.