60 



Fishery Bulletin 93(1), 1995 



population increased at 4.5% per year and doubled 

 about every 16 years. 



The predicted stable age distribution (Cj for the 

 best case scenario (Fig. 1) suggested that about 80% 

 of the population was composed of immature indi- 

 viduals. Because of the lack of data on sizes and ages 

 at first capture in the recreational and commercial 



2 3 4 5 6 7 8 



Age Class ( years ) 



Figure 1 



Predicted stable age distribution of the Atlantic sharpnose 

 shark, Rhizoprionodon terraenovae , under the best case 

 scenario presented in Table 1, assuming geometric growth 

 (with r=0.044) and constant age-specific mortality and fer- 

 tility rates. 



fisheries, the actual proportion of the population sub- 

 ject to fishing is unknown. Likewise, no size or age com- 

 position of this population is available from surveys, 

 precluding any comparisons with the theoretical C . 



Results of the sensitivity analyses indicated that 

 doubling age-specific natality, m x , had a distinct ef- 

 fect (a 286% increase) on the population's rate of in- 

 crease, r (scenario 4), and would allow the popula- 

 tion to double in only 4.1 years or 3.8 times faster 

 than in the best case scenario (Table 2). Generation 

 length, G, remained the same, while net reproductive 

 rate per generation, R o , increased 100% (Table 3). 



Decreasing age at maturity, t mat , by one year (sce- 

 nario 5) produced a smaller change in r, t x2 , and R o 

 (Tables 2 and 3) than doubling m x , but decreased G 

 by 12% (Table 3). Further decreasing t mat by another 

 year (scenario 6) produced almost the same values 

 of r and t x2 as those obtained in scenario 4 (Table 2), 

 although R o increased only 5% and G decreased by 

 20%. The combined effect of decreasing t mat and dou- 

 bling m x together (scenarios 7 and 8) produced in- 

 creases in r up to near 700% and t x2 values up to 8 

 times shorter than in the best case scenario (Table 

 2). Under scenarios 7 and 8, R o also increased by up 

 to more than 200%, while G decreased by up to 20%. 



Increasing first year survivorship, S o , by 10% (sce- 

 nario 9) yielded a value of r 39% higher and a value 

 of t x2 1.4 times shorter than in the best case scenario 

 (Table 2), affected R o very little (a 10% increase only), 

 and had no effect on G (Table 3). A further increase 



