Silber: Phocoena sinus in the northern Gulf of California 



343 



Figure 5 



Phocoena sinus sighting rate (individuals/ 100 km) relative to water 

 depth. 



Figure 6 



Phocoena sinus sighting rate (individuals/100 km) relative to distance 

 from nearest shore. 



affiliations that probably represent utilization of a simi- 

 lar habitat by two or more species rather than active 

 association. Twice, Bryde's vfha\es Balaenoptera edeni 

 were seen < 1 km from P. sinus, and three times com- 

 mon dolphins Delphinus delphis were observed <1.5 

 km from the porpoise. Numerous times black storm- 

 petrels Oceanodroma melania and Bonaparte's gulls 

 Larus Philadelphia dipped into the wake of surfacing 

 vaquita. Manta rays Mania birostris were seen once 

 near porpoises. 



In addition to vaquita, five other marine mammal 

 species were common within the study area, including 

 bottlenose dolphins Tursiops truncatus, common dol- 

 phins, fin whales Balaenoptera physalus, Bryde's 

 whales, and California sea lions Zalophus californi- 

 anus. There appeared to be a general segregation by 

 location and water depth among the three most com- 

 mon odontocet species. The distribution of P. simis 

 overlapped that oi Delphinus and B. edeni, but not that 

 of Tursiops and B. physalus (Silber et al. In prep.). 

 Bottlenose dolphins were consistently seen in more 

 shallow water than were vaquita, and common dolphins 

 were generally seen in greater, but comparable, water 

 depths as vaquita. Data on sympatric marine mammals 

 will be presented in greater detail elsewhere (Silber et 

 al. In prep.). 



Unconfirmed sightings and 

 fishermen interviews 



In February and April 1983 cetaceans that may have 

 been P. sinus were seen near Cerralvo Island (24°10'N; 

 109°55'W) by a scientist who has extensive experience 

 with marine mammals and Gulf of California fauna (G. 

 Notarbartolo di Sciara, Piazza Duca d'Aosta 4, 20124 

 Milano, Italy, pers. commun., May 1984). In both sight- 

 ings, the animals were 10-50 m from the observer. 



They were described as being small, possibly possess- 

 ing a blunt rostral profile, and surfacing "unobtrusive- 

 ly" in small groups. They were "quite distinct from 

 Tursiops, Delphinus, or Lagenorhynchus" (G. Notar- 

 bartolo di Sciara, pers. commun.. May 1984). If true, 

 these unconfirmed sightings occurred in an area >850 

 km south of our southernmost sightings, and extend 

 the present known range considerably. 



Based on these observations, the decision was made 

 to interview fishermen in the southern Gulf about the 

 presence of vaquita. In 1987, 17 fishermen from La Paz 

 were interviewed about their fishing practices and their 

 knowledge of the vaquita (Table 2). In most cases the 

 fishermen had spent considerable time on the water 

 (fishing 4-6 days/week. 3-12 months/year, for 5-51 

 years; x = 20.6 yrs). Fishermen in the La Paz area 

 generally had no knowledge of vaquita; however, one 

 man was familiar with the porpoise and indicated that 

 he had seen it several times near San Jose Island 

 (25°00'N; 110°40'W), 80 km north of La Paz. Unlike 

 others interviewed, this man was one of two who had 

 been fishing for over 50 years and he had worked in 

 an area (the coast near San Jose Island) different from 

 the other fishermen. In addition, his knowledge of the 

 natural history of marine mammals was regarded as 

 being accurate by the interviewer (D. Aurioles, Cen- 

 tro de Investigaciones, Biologicas B.C.S., APO Postal 

 128, La Paz, Baja California Sur, Mexico, pers. 

 commun., June 1987). One fisherman described netting 

 near San Jose Island a small cetacean that had rounded 

 ("acorn-like") teeth, a feature characteristic of the 

 genus Phocoena. 



All fishermen interviewed in San Felipe (n = 7) 

 expressed a knowledge of vaquita, and two said that 

 they had entangled the porpoise while fishing for 

 totoaba. Although taking totoaba is illegal, three men 

 indicated that they continue to use gillnets for totoaba. 



