No. 20: Mar-Apr 1982
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?