TAXONOMIC STATUS AND BIOLOGY OF 

 THE BIGEYE THRESHER, ALOPIAS SUPERCILIOSUS 



S. H. Gruber' and L. J. V. Compagno^ 



ABSTRACT 



This paper reviews the life history, taxonomic status, abundance, distribution and habitat, reproduc- 

 tion, feeding habits, scientific and economic importance, and Hterature of the bigeye thresher, Alopias 

 superciliosus; and presents new information on morphometries, vertebral counts, tooth counts, 

 denticles, size, age, and growth from 22 specimens. We found A. profundus is a junior synonym of 

 A . superciliosus , and we have extended the geographic range of the latter to the Mediterranean Sea and 

 New Zealand. Alopias superciliosus is a wide-ranging, circum tropical species between the latitudinal 

 limits of 40° north and 40° south. 



Thresher sharks (family Alopiidae, genus 

 Alopias), instantly recognizable by their tremen- 

 dously elongated caudal fins (the upper lobe of the 

 caudal fin about as long as the rest of the shark), 

 have been known since antiquity. According 

 to Salviani (1554), Aristotle was familiar with 

 thresher sharks and described their behavior. 

 Bonnaterre (1788) proposed the first valid specific 

 name for a thresher, Squalus vulpinus (the com- 

 mion thresher), while Rafinesque (1809) proposed 

 the genus Alopias for the same species, which 

 he termed Alopias macrourus. More recently 

 Tortonese (1938), Bigelow and Schroeder (1948), 

 and Bass et al. (1975) reviewed the systematics of 

 the genus Alopias. 



Lowe (1839) described new fishes from Madeira 

 in the eastern Atlantic. Among these was a very 

 brief diagnosis of a new thresher. Alopecias super- 

 ciliosus, which he characterized as follows: "At 

 once distinguished from the only other known 

 species of the genus, Carcharias vulpes, Cuv, by 

 the enormous eye and its prominent brow. I have 

 at present only seen a single young example." 



This shark, the bigeye thresher, was not men- 

 tioned by name in the literature until Fowler 

 (1936) erroneously synonymized it with Alopias 

 vulpinus (Bonnaterre 1788). The species was ap- 

 parently overlooked in the reviews of Dumeril 

 (1865), Giinther (1870), Garman (1913), White 

 (1937), and Tortonese (1938). Bigelow and Schroed- 



' Biology and Living Resources, Rosenstiel School of Marine 

 and Atmospheric Science, University of Miami, 4600 Ricken- 

 backer Causeway, Miami, FL 33149. 



^Tiburon Center for Environmental Studies, San Francisco 

 State University, Tiburon, CA 94920. 



er (1948) resurrected Lowe's species and gave the 

 first detailed diagnosis and description of Alopias 

 superciliosus, based on Floridian and Cuban speci- 

 mens. Earlier, Grey (1928), Nakamura (1935), and 

 Springer (1943) reported specimens of the bigeye 

 thresher under different scientific names, but 

 all of these writers overlooked Lowe's obscure 

 account. More recently, Cadenat (1956), Strasburg 

 (1958), Fitch and Craig (1964), Kato et al. (1967), 

 Telles (1970), Bass et al. (1975), and Stillwell and 

 Casey (1976) have presented descriptive accounts 

 as well as morphometric, meristic, and other 

 quantitative data on the species. 



Thresher sharks are peculiar in that their 

 elongated tails are the only known structure in 

 sharks, other than jaws and teeth and the armed 

 rostrum of sawsharks ( Pristiophoridae), that func- 

 tion in killing or immobilizing prey (Springer 

 1961). An Indo-Pacific orectoloboid, the zebra 

 shark, Stegostoma fasciatum (family Stegostoma- 

 tidae), also has a greatly elongated caudal fin, but 

 is not known to use it as a weapon. 



Bigeye threshers are noteworthy in having 

 enormous, dorsally facing eyes and unique head 

 grooves, structures which may reflect specialized 

 habits of the species that differ from the other two 

 species of thresher shark. 



The impression gained in most of the taxonomic 

 literature is that A. superciliosus is a widespread 

 but rare species. However, the works of Gubanov 

 (1972), Guitart Manday (1975), and Stillwell 

 and Casey (1976) indicate that it can be locally 

 abundant and of importance in pelagic longline 

 fisheries of the west-central Atlantic and north- 

 western Indian Ocean. 



Manuscript accepted June 1981. 



FISHERY BULLETIN: VOL. 79, NO. 4, 1981. 



617 



