FLANAGAN and HENDRICKSON: FISHERY AND REPRODUCTIVE BIOLOGY OF TOTOABA 



2 000 -, 



^ f LO W YE ARS 1936 196 



Carchtog r p 



I - 5 <_39 6 > 05 



.4 4 9 < 5 



1,600 - 



lA 

 (0 



>• 800 



Z 



o 



t- 



< 400 



o 



'— 



1033 - 606 X 



6 



7 

 8 

 9 

 10 



459 <05 



50 3 <.0 5 



550 < 1 



4 5 4 < 5 



10 



1 2 



13 



Figure 9.-Plot of annual totoaba 

 yield (metric tons) 9 yr following the 

 annual recorded flow, for the 1936-60 

 period. This plot displays the sug- 

 gested relationship between flow and 

 recruitment level. Linear regression 

 calculations employing lag times from 

 1 to 10 yr are significant only for those 

 years corresponding to estimated 

 ages of recruitment (6-10 yr). 



FLOW (10 acrefeet) 



resources, both of which are directly related to 

 substrate and shallowness, and indirectly related 

 to flow. 



The final cause suggested for the decline in 

 totoaba stock is overfishing of the breeding 

 population. We have examined the relationship of 

 catch with catch n years later. If catch is a good 

 indicator of population size, then we would expect 

 a linear, positive relationship between population 

 size and the size one recruitment age later. Alter- 

 natively, if catch is partially a function of 

 sociopolitical constraints (e.g., enforcement of a 

 preserve area and closed season resulting in a 

 catch which significantly underrepresents the 

 population size), we might expect a more com- 

 plicated plot with a distinct cluster of years 

 corresponding to periods of fishing regulations. 

 We have analyzed plots of catch against catch for 

 recruitment periods ranging from 6 to 10 yr and 

 have found significant relationships which satisfy 

 both of the above predictions. Graphs for all 

 estimated ages of recruitment from 6 to 10 yr 

 showed essentially the same pattern (Figure 10). 

 However, we note inconsistencies which advise 

 against drawing strong conclusions of either 

 overfishing or the demonstrated worth of enforced 

 regulatory measures. For example, increases in 

 catch occur 2-3 yr earlier than is consistent with 

 our assumption that regulatory measures were not 

 enforced until 1955, given that the minimum age 

 of recruitment is 6 yr. The question of a change in 



gear efficiency, effecting a realized increase in 

 effort, serves to confound the analysis; although 

 catch would increase, this factor alone could not 

 explain recovery of catch to such high levels. We 

 can visualize a combination of factors giving rise 

 to the significant second peak in totoaba produc- 

 tion (increase in gear efficiency acting on an 

 increased population size following the period of 

 regulation) but lacking effort data throughout the 

 period, our hypothesis must remain speculative. 



Support for the overfishing hypothesis may lie 

 in the recent trend of the relative catches of the 

 three main totoaba fishing fleets. Historically, the 



1,200 



800 



400 - 



Y: 182.9 • .194X 

 r : .497 p < 05 



400 



800 



1,200 

 CATCH 



1.6 00 



2/)00 



Figure lO.-Totoaba catch plotted against catch 8 yr previous. 

 This examines for evidence of reduction in breeding stock by 

 overfishing. All data are from Figure 1, in metric tons. Points 

 above dashed line are for the 1952-59 period. The breeding 

 sanctuary was established in 1955 and the points corresponding 

 to the years 1955-59 may reflect enforcement of this regulation 

 (see text). 



541 



