FISHERY BULLETIN: VOL. 87, NO. 4, 1989 



Back-Calculation 



Back-calculated size at time of first ring deposi- 

 tion was 52.1 and 53.2 cm for females and males, 

 respectively. These values correspond closely to 

 observed sizes of C. Iimbatns at birth, further 

 supporting the first translucent ring being a birth 

 ring. Back-calculated size was inspected for 

 "Lee's Phenomenon," which appeared to occur at 

 some ages; however, no consistent trend was 

 identified (Table 3). Mean back-calculated size at 

 age was consistently lower than observed and 

 predicted data (Figs. 6, 7). 



Growth curves for both sexes were derived 

 using observed data from sharks with 1-11 ver- 

 tebral rings. As shown in Figures 6 and 7, ring 1 

 (birth ring) and ring 2 are shown to be one year 

 apart. In actuality, the second translucent ring is 

 deposited approximately 7-8 months after the 

 formation of the birth ring. However, because 

 83.4% of these sharks were captured during the 

 summer months of May-September, sharks with 



two translucent rings are more likely to be at 

 least one year older than those with only the 

 birth ring. 



Age-Weight 



The nonhnear relationship between shark age 

 and weight was significantly fit with a logistic 

 gi'owth equation {P < 0.05). The relationship for 

 females (W^), and males {W),„ was 



(W)^= 42.68/1 + e.xp-'»-M0*'->-3.i4 

 r = 0.962, A^ = 69 



{W),n = 27.83/1 + exp-<0-550*'-)-2.58 

 r = 0.974, A^ = 48 



where W = weight in kg, and r = number of 

 translucent rings (Figs. 8, 9). Growth in length 

 and weight of C. limbatus appears to reach an 

 asymptote, and blacktips gi'eater than 10 years 

 old probably gi'ow very little each year. 



Table 3. — Mean back-calculated total lengths (cm) at age, for female and male blacktip shiarks captured in tfie 



Tampa Bay area of Florida. 



Rings 



Number Mean 



SE 



10 



101.0 

 114.4 125.9 



96.5 113.1 126.4 



87.9 104.8 119.8 133.0 



88.0 103.6 119.2 133.9 144.2 



96.1 111.9 126.9 138.2 149.9 159.5 



85.4 100.7 114.1 127.0 137.9 138.8 158.6 

 86.9 102.2 116.0 128.6 139.1 150.6 162.7 168.8 

 87.9 103.1 119.3 131.0 140.8 149.8 157.9 170.3 



93.2 107.4 121.4 133.5 144.5 154.7 159.6 169.4 

 34 29 28 27 25 23 11 5 

 14.2 14.0 12.1 11.0 10.2 4.9 9.8 7.1 



101.1 

 103.6 125.6 



97.3 117.3 130.4 



95.3 109.0 120.3 132.8 



96.6 111.2 119.5 128.7 140.2 



93.1 110.3 120.7 132.8 141.4 148.3 

 89.6 103.6 118.4 127.1 137.5 144.4 151.4 



95.0 110.6 118.4 126.2 134.0 140.0 148.0 154.3 

 97.8 112.0 122.3 129.9 138.4 144.2 150.3 154.3 

 22 13 12 9 6 4 3 1 



14.2 9.4 7.6 8.5 5.8 6.1 4.5 



176.5 



176.5 



2 



852 



