FISHERY BULLETIN; VOL. 74, NO. 3 



Table 2.- Prime season catch,' in metric tons, of the three 

 principal totoaba fishing ports, 1964-75. Data for 1965-70 period 

 are from Arvizu and Chavez (1972). Data for 1971-75 were 

 provided by H. Chavez (pers. commun.). The 1974-75 data are 

 preliminary but are not expected to increase by more than 10*^ 

 from these figures. 



'Catch is calculated by adding January-April yields as recorded 

 in the official statistics. 



Puerto Penasco fleet catches fewer totoaba than 

 either the San Felipe or Golfo de Santa Clara fleets 

 (Table 2). This is a logical result of the fishing 

 methods and areas worked by the three fleets. 

 However during the last 3 yr, Puerto Penasco has 

 equalled or exceeded the other ports in recorded 

 totoaba yield despite no apparent increase in 

 eff'ort. Our interpretation of this new trend is that 

 the migrant population, encountered first by the 

 Puerto Penasco fleet along the Sonora shore, is 

 being decimated before reaching the spawning 

 grounds. 



CONCLUSIONS 



Our review of the history of exploitation of the 

 stock, our data on spawning concentrations, 

 breeding migration, and juvenile habitat, and our 

 analyses of proposed hypotheses for the decline of 

 the fishery have emphasized points of population 

 vulnerability. Fleets of the three major ports are 

 highly skilled at finding the migrant schools of 

 totoaba. They have, in a sense, specialized to 

 exploit the ascent, resident, and descent phases of 

 the breeding migration, both by nature of their 

 vessels and their port facilities, and by con- 

 sequence of their geographic locations. This level 

 of exploitation is possible only because the fishers 

 are able to predict with accuracy the migration 

 pattern. In the past, the commercial population 

 level was high and the temporal nature of the port 

 specializations was not a factor in the ranking of 

 port yields. Now, when the population level has 

 reached an all-time low, the Puerto Penasco fleet 

 seems to have some new advantage. 



The totoaba breeding behavior we describe 

 serves to render the resident spawning population 

 especially vulnerable to fishing effort. Frenzied 

 spawning in dense aggregations following a pe- 

 riod of behavioral stimulation insures that when a 

 net is encountered, the capture rate will be par- 

 ticularly high. Our capture incidence, daily catch, 

 and gonadal maturation data confirm the con- 

 sequences of these attributes. The bathymetry of 

 the delta restricts the spawning schools to highly 

 limited areas. These areas, or channels, are the 

 prime fishing sites for the Golfo de Santa Clara 

 fleet. They appear to lie (by our estimate) partially 

 within the breeding sanctuary established by the 

 Mexican Government. 



We reiterate here the artificial fishing mortality 

 suffered by juveniles in their forced crossing of the 

 near-delta waters as they make their way south 

 from the nursery grounds. We have documented 

 some known nursery sites and have suggested 

 characteristics of the juvenile habitat which may 

 have predictive value in future surveys of the area. 



We have examined the three most probable 

 factors responsible for the decline in totoaba stock. 

 Subject to the limitations of our catch and flow 

 data, our results suggest that overfishing has 

 played the most significant role during the pre- 

 1958 catch period. We speculate that the low yields 

 of the 1956-59 period may have been due to en- 

 forcement of the breeding sanctuary regulation 

 and that this partial temporary relief from exploita- 

 tion may, together with increased gear efficiency, 

 have been responsible for the second peak in 

 totoaba production. If this is true, then the power 

 of regulatory measures for recovery of this com- 

 mercial stock has been demonstrated. The cor- 

 relation of annual yield with annual Colorado 

 River flow, though weakened by statistical ir- 

 regularities, attests to the importance of some 

 flow-related quality of the spawning grounds. 

 Degradation of the spawning grounds, possibly in 

 the ability to provide olfactory cues, also may have 

 resulted in a decline of the commercial population. 

 According to our results, degradation of the nur- 

 sery grounds, through deterioration of some un- 

 known flow-related quality, has probably not 

 played a significant role in the fishery's decline. 



Although it may be possible to ignore statistical 

 analyses and the conclusions therefrom, one can- 

 not deny that the annual yield in 1975 was the 

 minimum recorded in the history of the fishery, a 

 mere 2.5% of the highest recorded catch. The area 

 of the fishery has shrunk to a small fraction of its 



542 



