NATURAL HISTORY OF THE RAYS OF THE GENUS MOBULA 



IN THE GULF OF CALIFORNIA 



Giuseppe Notarbartolo-di-Sciara1 



ABSTRACT 



Mobulid rays, which abound during summer in the southern Gulf of California, southern Baja 

 California, Mexico, were monitored for a period of four years during a study of their biology. A total 

 of 262 specimens belonging to four species of Mobula were examined. Mobula thurstoni was the most 

 abundant l58'/f of the catch), followed by M. japanica (30%), M. munkiana (9'5f ), and M. tarapacana 

 (3'^). The study area served as a nursery ground for M. thurstoni, a summer feeding and mating 

 ground for M. thurstoni and M. japanica, and a wintering ground for M. munkiana and young 

 M. thurstoni ; M. tarapacana was rare. Data on size, weight, sex ratio, life history, seasonality, feeding 

 habits, behavior, habitat, and symbionts are presented for each species. Size segregation was a 

 common feature of M. thurstoni , M. japanica , and M. munkiana ; sex segregation was not evident. An 

 extreme degree of feeding specialization was noted: summer prey were almost exclusively the eu- 

 phausiid Nyctiphanes simplex: the mysid Mysidium sp. dominated in the winter. A key to the genus 

 Mobula in the Gulf of California is presented as an aid for species identification. 



This paper reports on natural history aspects of 

 rays of the genus Mobula (Mobulidae), a poorly 

 known group of elasmobranchs commonly called 

 manta rays or devil rays, frequent in the Gulf of 

 California. A good early overview of the family 

 Mobulidae was given by Gill (1908). Cadenat 

 (1960) described the natural history of the mobu- 

 lids of tropical west African waters, based on 

 specimens which were occasionally captured by 

 the local fishermen. However, with the exception 

 of observations carried out with some regularity 

 by Coles (1910, 1913, 1915, 1916a, 1916b) of Mo6- 

 ula olfersi (= M. hypostoma ) and Manta birostris 

 off North Carolina, most of the available litera- 

 ture is purely anecdotal and deals with occasion- 

 ally encountered or harpooned specimens. Long- 

 term field investigations of devil ray ecology and 

 behavior are wanting. As a result, mobulids are 

 among the least known of the batoid taxa. This 

 was recognized by Bigelow and Schroeder (1953) 

 in their comprehensive review of the knowledge 

 of this family. No major contribution to the 

 understanding of any aspect of mobulid biology 

 has since been published. 



Regular fisheries for mobulids were not known 

 to exist, because mobulid meat is generally con- 

 sidered of little market value. However, in 1981, 

 during a reconnaissance trip to the southern Gulf 



iScripps Institution of Oceanogi'aphy, University of Califor- 

 nia, San Diego, La Jolla, CA 92093; present address: Museo 

 Civico di Storia Naturale, corso Venezia 55, 20121 Milano, 

 Italy. 



Manu.script accepted October 1987. 

 FISHERY BULLETIN: VOL. 86, NO. 1. 1988. 



of California (Mexico), in the vicinity of La Paz, 

 Baja California Sur, a regular, seasonally impor- 

 tant fishery was discovered. This activity afforded 

 the opportunity to study several aspects of the 

 natural history and the ecology of these batoids. 

 Preliminary oral interviews revealed that local 

 fishermen in the Gulf of California knew of, and 

 routinely captured, four species of devil rays, in 

 addition to the well-known giant manta ray, 

 Manta birostris. This information contrasted 

 with the scientific literature, where only two 

 mobulid species, Manta birostris and Mobula lu- 

 casana, were reported for the area (Beebe and 

 Tee-Van 1941; Fowler 1944; Castro-Aguirre 

 1965). The confusing state of mobulid taxonomy 

 demanded a revisionary work of the genus Mob- 

 ula (Notarbartolo-di-Sciara 1987), and a discus- 

 sion of the systematics of Manta in the eastern 

 Pacific (Notarbartolo-di-Sciara in press). Such ef- 

 fort permitted designation of names for all species 

 of Mobula found in the Gulf of California: M. 

 thurstoni (Lloyd 1908), of which M. lucasana 

 Beebe and Tee Van (1938) is a junior synonym; 

 M. japanica (Miiller and Henle 1841); M. tara- 

 pacana (Philippi 1892); and M. munkiana 

 Notarbartolo-di-Sciara (1987), which had not 

 been described before. Many of the reports of 

 M. lucasana { = M. thurstoni ) from Central and 

 South America (Beebe and Tee- Van 1941; Fowler 

 1944; Nichols and Murphy 1944; Barton 1948; 

 Castro-Aguirre 1965; Chirichigno 1974; Pequeno 

 1983) undoubtedly refer to other species of Mob- 

 ula . A key to the genus Mobula in the Gulf of 



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