Clear et a\: Validation of annual increments in otoliths of Thunnus maccoyii 



27 



Table 1 



Numbers of southern bluefin tuna released with yellow tags and numbers of SBT injected with SrClj and released with orange tags, 

 and a summary of yellow and orange tag returns from 1990 to 1996. The number of returned yellow and orange tags released in 

 each year of the tagging program, and the number of returned tags as a percentage of the total number released in the year (shown 

 in parentheses) are shown. (The years of release and recapture are from October of one year to September of the next.) NS = not 

 significant. 



Fish recaptured 

 1990-91 



1991-92 



1992-93 



1993-94 



1994-95 



1995-96 



1990-96 

 All recapture 

 years 



Difference 

 between yellow 

 and orange tag 

 returns 



1990-91 



1991-92 



1992-93 



1993-94 



1994-95 



1995-96 



1990-96 

 All release year.^- 



yellow orange 



tags tags 



«=6909 n=835 



yellow orange yellow orange yellow orange yellow orange yellow orange yellow orange 



tags tags tags tags tags tags tags tags tags tags tags tags 



H=4.543 n=3595 n=5907 n=5304 «=8253 fi=82.51 n=15,683 «=2219 n=2998 n=0 n=44,293 n=20,204 



183 25 — — — — — — — — — 



12.65) (2.99) 



180 19 84 55 — — — — — — — 



(2.61) (2.28) (1.8) (1.53) 



111 11 116 86 56 63 — — — — — 



11.61) (1.32) (2.6) (2.39) (0.95) (1.19) 



62 6 102 76 130 90 50 47 — — — 



(0.90) (0.72) (2.2) (2.11) (2.20) (1.70) (0.61) (0.57) 



29 6 43 36 177 116 171 168 67 20 — 



(0.42) (0.72) (0.95) (1.00) (3.00) (2.19) (2.07) (2.04) (0.43) (0.90) 



2 6 6 29 17 86 89 94 25 21 



(0.03) (0.13) (0.17) (0.49) (0.32) (1.04) (1.08) 0.60) (1.13) (0.70) 



567 67 351 259 392 286 307 304 161 45 



(8.22) (8.03) (7.68) (7.20) (6.64i (5.40i (3.72) (3.69) (1.03) (2.03) 



5.02(0.83) 3.17(0.94) 1.44(0.61) 3.22(0.40) 1.68(0.39) 



NS 



NS 



NS 



NS 



NS 



NS 



back-pack or attached to the tagging cradle ( WilHams, 

 1992). 



We injected the fish about 2 cm below the dorsal 

 midline, in line with the center of the first dorsal 

 fin. We occasionally obsei-ved a loss of the solution 

 from the muscle, especially in larger fish. When this 

 happened, we noted the loss and injected the fish a 

 second time. To minimize loss of solution we carefully 

 expelled all the air from the vaccinator so that air 

 bubbles were not injected into the muscle. 



To determine a suitable dosage rate for SBT, initial 

 tiials with strontium were made on thi-ee nontuna species 

 in captivity: silver trevally, Pseudocaranx dentex, sand 

 flathead, Platycephalus bassensis, and purple wrasse, 

 Pseudolabnis fucicola, the largest fish weighing 500 g. 

 The dosages were based on Brothers' (1990) immersion 

 and injection trials with strontium on trout — 100 mg/kg — 

 and Wild and Foreman's ( 1980 ) tetracycline experiments 

 on tuna — 0.3 mlVkg or 27.5 mg/kg of fish. Dosages 

 between 50 and 200 mg Sr/kg resulted in clear Sr 

 marks on otolith sections and no mortalities (CSIRO, 



unpubl. data^). In the field, the length of the fish was 

 measured to the nearest centimeter, but weight could 

 only be estimated. We therefore chose the required SrClj 

 dose according to length (Table 2). These dosages were 

 increased for fish longer than 90 cm when the marks 

 on the first otoliths recovered ft-om SBT of this size 

 showed up faintly, indicating low strontium absorption. 

 The dosages were adjusted so that at least 80 mg of Sr 

 was injected per kilogi'am of fish. 



Tag collection and otolith sampling 



A critical factor in the experiment was the sustained 

 effort, over many years, to recover otoliths from recap- 

 tured fish. An extensive campaign was conducted to 

 explain the objectives of the marking experiment to 

 the SBT fishing industiy and to develop a protocol for 



'' CSIRO (Commonwealth Scientific and Industrial Research Organi- 

 zation) unpublished data. 1989. CSIRO Marine Research, GPO 

 Box 1538, Hobait, Tasmania, 7001, Australia. 



