FLANAGAN and HENDRICKSON: FISHERY AND REPRODUCTIVE BIOLOGY OF TOTOABA 



suppose that, as breeding adults reach the north- 

 ern end of the gulf, they immediately move up into 

 the channels at the mouth of the Colorado River. 

 The arrival of the largest population segment 

 would then be indicated by the peak catch. Alter- 

 natively, the peak catch may have signaled a peak 

 of spawning activity by an already-resident 

 breeding population, becoming more vulnerable to 

 the nets by virtue of spatial concentration and/or 

 behavior. While the data do not allow firm conclu- 

 sions, we favor the second alternative. 



A period of behavioral stimulation in schools to 

 induce the spawning act is suggested by the fact 

 that enormous numbers of individuals allegedly 

 used to gather in this relatively small area to 

 spawn (Jordan 1916; Berdegue 1955). Although the 

 population has been drastically reduced, the fish 

 apparently continue this habit. If the release of 

 reproductive behavior patterns depends upon 

 mutual stimulation within large aggregations 

 (consistent with their sound-producing air blad- 

 der; see Breder and Rosen 1966), the present small 

 population might be experiencing some break- 

 down in the behavioral sequence with consequent 

 lowered reproductive success. 



Although the significant yields of 21 and 22 

 March may indicate a peak in spawning activity, 

 this does not preclude the possibility that other fish 

 were later in arrival and that spawning also 

 occurred in April (during the closed season). The 

 Golfo de Santa Clara fleet's near-failure to catch 

 fish during the 25-31 March period, and our failure 

 to find adult fish during the April cruise lend doubt 

 to this possibility, but the existence of more than 

 one breeding population should not be ruled out. 



Juvenile Totoaba Distribution, 

 Habitat, and Diet 



The microhabitat and residence time of juvenile 

 totoaba on the nursery grounds are largely un- 

 known. Berdegue (1955) reported that juveniles 

 remain in the shallow waters near the Colorado 

 River mouth until they begin a southward migra- 

 tion to join the parent population. The Colorado 

 River Delta is heavily exploited by the shrimp 

 fishery during parts of the year (effort was ob- 

 served to be especially intense during April, May, 

 and June), and Berdegue first called attention to 

 the increased mortality of juvenile totoaba due to 

 shrimp trawling activity. 



In our experience, the juveniles captured in 

 shrimp trawls are individuals ranging in length 



from about 15 cm to about 45 cm. The holotype in 

 the U.S. National Museum is approximately 25 cm 

 long and was taken in 20 fathoms of water (Gilbert 

 1891). To our knowledge, the first collection of 

 really small juveniles (6-12 cm size range) which 

 were positively identified as totoaba was made in 

 1970 near San Felipe, B.C., and described by 

 Chavez (1973). We surveyed probable northern 

 gulf sites for the presence of such small juveniles 

 during May and June 1972 and 1973 (Figure 6). 



Substrate and depth appear to be more impor- 

 tant than either temperature or salinity in char- 

 acterizing the habitat of the captured juveniles. 

 For all sites, surface water temperatures ranged 

 from 25° to 29°C and salinities were recorded 

 between 35 and 407oo. Sites where we collected 

 juveniles were shallow as compared to the other 

 sampling locations, and none were collected from 

 depths greater than 1 m. Substrates were com- 

 posed of fine clay-silt sediments, devoid of sand; 



1972 



1973 



Golfo de 

 Santa Clara 



Figure 6.-Sites sampled in northern Gulf of California for 

 presence of juvenile totoaba in 1972 and 1973. Circled numbers 

 indicate offshore areas sampled by otter trawl. All other locations 

 are shore stations sampled by seine. Sites where juvenile totoaba 

 were found are indicated by stars. Numbers captured are shown 

 at upper right of each map. 



537 



