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... Science Frontiers ONLINE No. 104: Mar-Apr 1996 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects The Magnetic Mountain To find the "magnetic mountain," you must venture out into the Gulf of California about 15 miles east of the Baja Peninsula. Out there, beneath the boat, you can find a basaltic mountain named Espiritu Santo. Next, you don your face mask and descend toward the submerged peak. At about 70 feet, you will likely find yourself surrounded by scores, possibly hundreds, of scalloped hammerheads, some as long as 13 feet. They will ignore you and the teeming fish as they slowly wheel passively around the submerged mountain. Why do these big sharks congregate in this spot? Marine biologists have been asking this for years. (SF#20) A.P . Klimley and his colleagues decided to find the answer. First, by direct observation, they determined that the sharks' main purpose was not pro-creation, although some mating did occur. Mainly, the hammerheads just idled away the daylight hours. At dusk, they disappeared. Klimley et al next implanted some sharks with transmitters and followed them at night. This was their feeding time, they swam 10-15 miles to deep waters where they gorged on squid. At daybreak, they were back drifting around Espiritu Santo. Apparently, the mountain was just a place to rest. But how did the hammerheads find their way back so unerringly? Furthermore, by tracking the tagged fish, the researchers found the sharks often ...
Terms matched: 1 - Score: 91 - 15 May 2017 - URL: /sf104/sf104p05.htm
... Science Frontiers ONLINE No. 65: Sep-Oct 1989 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Why the hammer head?You probably thought, as we did, that the function of the hammerhead shark's weirdly shaped head was to separate the eyes and thus improve binocular vision. This is not the case. The visual fields of the hammerhead's eyes do not overlap at all. Each eye presents the brain with a separate, completely different image to integrate. What, then, could be the purpose of the hammer head? No one really knows, but three suggestions are as follows: The head acts as a hydrofoil and gives the heavier-than-water, swimbladderless shark better swimming control. Grooves on the hammer head channel water toward the nostrils, providing "stereoscopic sniffing." The head is a platform for electromagnetic sensors that help locate prey. Stingrays are a favorite food of the hammerhead, and the shark may de-tect them electromagnetically, as surmised by the author of this article in the following encounters: "I have observed great hammerheads swimming close to the bottom, swinging their heads in wide arcs (a motion common, in a lesser degree, to all large sharks) as if using the increased electroreceptive area of their hammer like the sensor plate of a metal detector. Sometimes, these animals would doubleback to scoop up one of several stingrays hiding in the bottom silt. The minute electrical pulse that keeps the stingray's heart and spiracles operating betrays their presence to a hungry ...
Terms matched: 1 - Score: 65 - 15 May 2017 - URL: /sf065/sf065b06.htm
... Science Frontiers ONLINE No. 20: Mar-Apr 1982 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Puzzling Group Behavior Of Sharks For some unknown reason, sharks often congregate in immense groups. Approximately 2,000 sharks took over 24 kilometers of the surf zone near Corpus Christi during June 1977. Some courageous divers decided to study large groups of the scalloped hammerhead that regularly gather in the Gulf of California. Happily, the hammerheads were not aggressive when so occupied and could be approached closely. They swam pointed in roughly the same direction, maintaining about the same spacing through the groups, which sometimes numbered 100 or more. They did not feed, mate, or do anything collectively; but once in a while an individual would suddenly engage briefly in acrobatic behavior -- one common type was dubbed the "shimmy dance." The researchers concluded that these shark groups had no obvious purpose and that, for reasons beyond the ken of man, this behavior somehow contributed to their evolutionary success. (Klimley, A. Peter; "Grouping Behavior in the Scalloped Hammerhead," Oceanus, 24:65, Winter 1981/1982.) Comment. The sharks might be much "farther along" without complex, time-wasting group behavior. What do sharks know about evolution anyway? From Science Frontiers #20, MAR-APR 1982 . 1982-2000 William R. Corliss ...
Terms matched: 1 - Score: 42 - 15 May 2017 - URL: /sf020/sf020p08.htm
