FISHERY BULLETIN: VOL. 78, NO. 3 



culosis. At no time did deaths due to disease 

 approach epidemic levels in any population. Fre- 

 quency of disease symptoms, deaths attributable 

 to disease, etc., for each population may be found 

 in Hankin (1978b). 



Phase II (Weeks 36-58) 



Long-Term Controls: Populations 5, 6, and 12 



Total population biomass of control guppy popu- 

 lations during weeks 36-58 confirmed the earlier 

 speculation that populations were near their max- 

 imum biomass by week 36. Net changes in total 

 biomass from week 36 to week 58 were +0.5, + 0.1, 

 and +0.9 g in populations 5, 6, and 12. Minor 

 asynchronous fluctuations in biomass occurred 

 throughout Phase II in all control populations. 

 Logistic-based estimates of maximum supportable 

 biomass made at week 36 were 30.6, 32.4, and 

 31.1 g and agreed remarkably well with actual 

 biomass levels at termination, 28.3, 30.7, and 

 30.7 g. 



Control populations showed no signs of conver- 

 gence in total population numbers nor of parallel 

 fluctuations. Although total numbers in the three 

 control populations differed greatly, total num- 

 bers and weights of reproductive females (size 

 categories Ag-Ag) were similar. In populations 

 5, 6, and 12 there were 37, 36, and 42 such females 

 at termination with corresponding total weights 

 of 20.6, 17.6, and 20.0 g. Since fecundity is roughly 

 proportional to female weight, the three popula- 

 tions had nearly equal reproductive potentials in 

 spite of large differences in total numbers. Adult 

 females accounted for from 57 to 72% of total 

 population biomass. No uniformity in numerical 

 or biomass densities was noted for adult males. 



Treated Populations 



BIOMASS DYNAMICS.— Total population bio- 

 mass increased in all treated guppy populations 

 during Phase II (Figure 9). At termination, mean 

 population weights of the three treatment groups 

 were not found significantly different in pairwise 

 comparisons (Student's t tests). Since greatest 

 differences in mean biomass among treatment 

 groups occurred at week 58, there were probably 

 no statistically significant differences in mean 

 biomass throughout Phase II. Alteration of refuge 

 fence spacing had no apparent effect on population 

 biomass growth. 



36 



40 



44 48 



WEEKS 



52 



56 



Figure 9. — Mean total biomass in treatment groups of guppies 

 during Phase II. 



Mean total weights of mature females (size 

 categories Ag-Ag) differed significantly among 

 treatment groups (Student's t tests). The mean 

 percentage of total population biomass accounted 

 for by adult females was consistently higher in 

 the 5.5 mm group (71%) than in the 4.5 mm 

 group (56%). 



NUMERICAL DYNAMICS. — Although bio- 

 mass growth was roughly equal for all treated 

 guppy populations, treatment groups diverged 

 rapidly in total numbers (Figure 10). Smallest 

 population numbers were maintained in the 

 5.5 mm group, intermediate but highly variable 

 numbers in the 5.0 mm group, and largest num- 

 bers in the 4.5 mm group. At termination mean 

 total numbers in the 4.5, 5.0, and 5.5 mm treat- 

 ment groups were 249, 160, and 128. Mean net 

 additions during Phase II, in the same order, were 

 172, 86, and 47. 



M 

 E 

 A 

 N 



N 

 U 

 M 

 B 



E 

 R 

 S 



36 



40 



44 48 



WEEKS 



52 



56 



Figure 10. — Mean total numbers in treatment groups of guppies 

 during Phase II. 



566 



