NOTARBARTOLO-DI-SCIARA: NATURAL HISTORY OF MOBULA 



California is presented as an aid to future studies 

 of mobulids from this region. 



Working relationships were established with 

 the local fishing communities, and their activities 

 were intermittently monitored between 1981 and 

 1984. Captured rays were examined and mea- 

 sured before their pectoral fins were filleted; 

 stomach contents and reproductive organs were 

 examined later. Information was gathered on 

 size, weight, sex ratios, life history, seasonality, 

 feeding habits, habitat, behavior, and symbionts 

 of four species of rays belonging to the genus Mob- 

 ula (M. thurstoni, M. japanica, M. munkiana, 

 and M. tarapacana ). Detailed descriptions and 

 morphometries of those species are given by 

 Notarbartolo-di-Sciara (1987). The manta ray, 

 Mania birostris, was also occasionally captured 

 (Notarbartolo-di-Sciara in press), but is not 

 treated in the present study. 



METHODS 



Although mobulids are locally said to be abun- 

 dant on both sides of the southern Gulf of Califor- 

 nia, for logistic convenience collecting trips were 

 made only to the peninsular coast (Fig. 1). The 

 fishing cooperative based at Punta Arena de la 

 Ventana was selected as the prime collecting site, 

 because mobulids were caught there more consis- 

 tently than at other localities. Fishing camps on 

 Isla El Pardito, at Cueva de Leon, Ensenada de 

 los Muertos, and Bahia de los Frailes were also 

 sources of study material. Other fishing commu- 

 nities, such as Juncalito, San Evaristo, El Sar- 

 gento. La Ventana, and San Jose del Cabo were 

 occasionally visited, but yielded no data because 

 mobulids were not specifically sought by the fish- 

 ermen. Seven field trips were made. Six were 

 short-term (24 January-8 February 1981, 25 

 November 1981, 16-21 December 1981, 20-23 

 December 1982, 19-26 January 1984, and 28 Oc- 

 tober- 1 November 1984); one lasted almost six 

 months (26 January-15 July 1983). 



Mobulids of all available species and sizes are 

 caught with nets and harpoon; their meat is fil- 

 leted out of the pectoral fins for human consump- 

 tion and used as shark bait. Gill nets are either 

 strung just under the surface or are set on the 

 bottom perpendicular to shore, usually at depths 

 between 10 and 200 m. Fishing vessels were 5-7 

 m fiberglass launches, locally called "pangas", 

 powered by an outboard engine. Fishing occurred 

 within a radius of about 15 km from a base camp. 

 Nets are checked once a day, early in the morn- 



ing. Rays weighing up to approximately 100 kg 

 were hauled on board, larger specimens were 

 towed ashore. Rays that were dead in the nets, 

 after several hours (i.e., three unsexed specimens 

 of Mobula thurstoni), were often partially de- 

 stroyed by gammarid amphipods (locally called 

 "plaga"), and were unmarketable. 



Specimens were weighed and measured before 

 being processed by the fishermen. Weights (WT) 

 were taken with calibrated spring-scales. Rays 

 lighter than 20 kg were weighed to the nearest 

 pound with a 50-lb scale; weights were subse- 

 quently converted to kg. Heavier rays were 

 weighed to the nearest kg with a 150 kg scale. 

 Specimens which exceeded 150 kg (all postnatal 

 M. tarapacana ) were cut in four pieces and 

 weighed separately. Ten percent was then added 

 to the total weight to compensate for body fluid 

 loss. All the specimens could not be weighed, as 

 occasionally a large number of rays were beached 

 simultaneously, and because of the intense heat 

 the fishermen could not delay their processing. 



A set of 29 measurements was taken for mor- 

 phometric analysis and systematic purposes. 

 Methods and results are presented in 

 Notarbartolo-di-Sciara (1987). Measurements 

 relevant to the present paper were disc width 

 (DW), greatest dimension between outermost tips 

 of pectoral fins, pelvic fin length, from anterior 

 margin of vent to tip of pelvic, and clasper length, 

 from anterior margin of vent to tip of clasper. 

 Most specimens were discarded after measuring 

 and sampling. All preserved specimens were 

 deposited in the Marine Vertebrate Collection of 

 the Scripps Institution of Oceanography. Raw 

 data listing all specimens examined and pre- 

 served can be found in Notarbartolo-di-Sciara 

 (1985). 



The size and shape of the testes were inspected 

 in male specimens, and the ducti deferentes were 

 cut slightly above the genital papilla. Presence or 

 absence of seminal fluid was determined by 

 running a finger in the caudal direction over the 

 ducts anterior to the cut. Clasper length in 

 thousandths of disc width (DW) was plotted 

 against DW to determine size at maturity, and 

 the presence or absence of seminal fluid was 

 noted. Relative size and contents of uteri and 

 nidamental glands were examined in female spec- 

 imens, and right and left ovaries were compared. 

 The diameter of the largest ovum was plotted 

 against DW to determine size at maturity of fe- 

 male Mobula. Eggs were extracted from the 

 germinative epithelium and their greatest di- 



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