946 



Fishery Bulletin 97(4), 1999 



frequency analysis. No OTC-injected individuals 

 were included in these calculations. 



Tag-recapture with OTC injection 



During 1985-97, more than 650 tiger sharks (59 to 

 291 cm FL) were measured, injected with a 25 mg/ 

 kg body weight dose of OTC (Gruber and Stout, 1983), 

 tagged, and released. To determine the effects of OTC 

 on growth, data from recaptured OTC-injected fish 

 were analyzed separately from those of noninjected 

 recaptured fish. Only those OTC-injected specimens 

 measured at both tagging and recapture and at liberty 

 for at least 0.9 years were included in the analysis. For 

 comparison of growth of injected fish to gi'owth of 

 noninjected fish, the growth rates fi-om OTC-injected 

 individuals were plotted with the von Bertalanffy 

 growth function ( VBGF) ft-om the tag-recapture analy- 

 sis. The size at tagging was used as a guide to estimate 

 age at tagging with the VBGF. The time at liberty de- 

 termined the distance along the :*:-axis, and sizes at 

 recapture determined the slope. The growth of the OTC- 

 injected individuals was then compared graphically 

 with the growth curves for long-term (>0.9 yr) tag-re- 

 captured sharks and monthly growth estimates. 



Monthly growth 



Data for tiger sharks measured and subsequently 

 tagged from the defined nursery area were analyzed 

 for monthly growth. Data on measured fish were 

 available by month from June 1988 to August 1994. 

 Data were organized into 5-cm intervals. The modes 

 for the 1988, 1989, 1990, 1991, 1992, and 1993 year 

 classes were followed progressively from the birth 

 mode until the last visible mode for that year class. 

 Where modes were not clear (i.e. single fish at more 

 than one interval) the mean was taken as the mode. 

 Previously tagged individuals were not included in 

 this data set. Length-frequency histograms were 

 developed for each month of each year for modal 

 analysis. To determine if the data from the six year 

 classes could be combined, the modes of each year 

 class were plotted by month and compared graphi- 

 cally and through an analysis of covariance. Growth 

 per year was calculated by subtracting the June birth 

 mode from the June one-year mode and the June one- 

 year mode from the June second-year mode. To com- 

 pare the growth of these fish to tagged noninjected 

 fish and tag-recaptured OTC-injected fish, month- 

 per-year growth rates were plotted against the VBGF 

 from the recapture analysis and the growth rates 

 from the individual tag-recaptured OTC-injected fish. 

 The initial positioning of the modes on the jc-axis 

 assumes birth takes place in June^ so that the first 



point of the monthly growth was fixed on the monthly 

 tag-recapture curve for June. The monthly growth 

 values were fixed on the curve on the basis of month 

 they were calculated for (i.e. June, birth; June, year 

 1; June, year 2). Graphical comparisons enabled us 

 to determine whether growth based on the tag-re- 

 capture analysis was distinct from growth based on 

 a method without tagging (represented by monthly 

 growth). In addition, we compared Branstetter et al.'s 

 ( 1987) vertebral growth curve to these data. 



Results 



Tag-recapture data 



Information on 42 recaptured tiger sharks, measured 

 at both tagging and recapture and at liberty for at 

 least 0.9 years, was used to produce values of L_ and 

 k of the VBGF (Table D.The Gulland and Holt (1959) 

 method produced the most biologically plausible es- 

 timates of VBGF parameters (Table 2). The Fabens 

 ( 1965 ) analysis underestimated L^ with known maxi- 

 mum size estimates, and the value for k was high. 

 Therefore, further analysis was based on the results 

 from the method of Gulland and Holt ( 1959). Age at 

 maturity, based on lengths at maturity from 

 Branstetter et al. ( 1987), for female (265 cm FL) and 

 male (258 cm FL) tiger sharks is 7 years (Fig. 2; Table 

 3). Maximum age was estimated to be 27.3 years 

 (335-1- cm FL > 997r of L^). 



Tag-recapture with OTC injection 



Analysis of the gi'owth of the four OTC-injected speci- 

 mens recaptured >0.9 years after tagging indicates 

 that individuals grew at appro.ximately the same rate 

 as predicted by the tag-recapture data (Fig. 3). 

 Growth calculated for the first year (growth/year of 

 two individuals tagged at <100 cm FL) was 42.3 and 

 48.4 cm/yr. and 39.4 and 48.7 cm/yr. for the second 

 year (gi-owth/year two individuals tagged at >100 cm 

 FL) (Table 1). These four individuals were at liberty 

 between 0.94 and 1.19 years. 



Monthly growth 



Modes were clearly visible in the length-frequency 

 histograms for small tiger sharks of all year classes 

 from birth to 1.5 years. The modes for 1.5-2 years 

 were less distinct owing to decreased sample sizes 

 at the larger sizes (Fig. 4). Differences in growth rates 

 among the six year classes were statistically signifi- 

 cant (ANCOVA, P>0.05) so we did not combine the 

 monthly length frequencies for all years (Fig. 4). In 



