Diel vertical migration of the bigeye thresher shark (Alopias superciliosus), a species possessing orbital retia mirabilia

The bigeye thresher shark (Alopias superciliosus, Lowe 1841) is one of three sharks in the family Alopiidae, which occupy pelagic, neritic, and shallow coastal waters throughout the altropics and subtropics (Gruber and Compagno, 1981; Castro, 1983). All thresher sharks possess an elongated upper caudal lobe, and the bigeye thresher shark is distinguished from the other alopiid sharks by its large upward-looking eyes and grooves on the top of the head (Bigelow and Schroeder, 1948). Our present understanding of the bigeye thresher shark is primarily based upon data derived from specimens captured in fisheries, including knowledge of its morphological features (Fitch and Craig, 1964; Stillwell and Casey, 1976; Thorpe, 1997), geographic range as far as it overlaps with fisheries (Springer, 1943; Fitch and Craig, 1964; Stillwell and Casey, 1976; Gruber and Compagno, 1981; Thorpe, 1997), age, growth and maturity (Chen et al., 1997; Liu et al., 1998), and aspects of its reproductive biology (Gilmore, 1983; Moreno and Moron, 1992; Chen et al., 1997).