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Radion1etric Ageing of Sharks

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Radion1etric Ageing of Sharks Radion1etric Ageing of Sharks Dr G.E. Fenton FIS HERIE S RESEARCH & DEVELOPMENT UNIVERSITY OF TASMANIA CORPORATIO N Project No. 94/021 2001 FINALREPORT Radiometric Ageing o{Sharks Table of Contents Acknow ledgments ...................................................................................... 3 1. Non-technical Summary............ ................................................ ...4 2. Background.. ... ......................................................................................... 5 2.1 Radiometric analysis .................................................................... 6 2.2 Shark Species Studied .................................................................. 8 a) School shark Galeorhinus galeus ........................................ 8 b) Spotted Dogfish Squalus acanthias .................................... 9 c) Golden Dogfish Centroscymnus crepidater .......................... 9 d) Southern Dogfish Centrophorus uyato.... ........................... 10 3. Need ...........................................................................................................11 4. Objectives................................................................... ...............................11 5. Methods .....................................................................................................11 5 .1 Collection of shark vertebrae ....................................................... 11 5.2 Dissection and Cleaning vertebrae ..............................................12 5.3 Second Dorsal Spine ..................................................................... 13 5.4 Radionuclide Analysis .................................................................. 14 5.5 Trace Element Analysis ...................................................... 14 6. Results .......................................................................................................14 6.1. Vertebrae morphometrics ............................................................ 14 a) School shark G.galeus .......................................................... 14 b) Spotted Dogfish S.acanthias ................................................ 15 c) Golden Dogfish C.crepidater ................................................ 15 d) Southern Dogfish C.uyato .................................................... 16 6.2. Second Dorsal Spine S.acanthias ................................................ 16 6.3. Stable element analysis ............................................................... 17 1 FINALREPORT Radiometric Ageing ofSharks a) Calcium levels ...................................................................... 17 b) Strontium levels .................................................................. 18 c) Barium levels.. ...................................................................... 19 d) Lead levels ............................................................................ 20 6.4. Radioactive Isotopes .................................................................... 21 a) 210pb levels .......................................................................... 21 b) 226Ra levels ......................................................................... 23 c) 210pb/226Ra Activity ratios.. .............................................. 24 6.5. Estimation of shark age................... ............................................ 25 7. Age Estimation Results and Discussion ................................................ 25 8. Benefits..................... ................................................................................. 26 9. Further Development...... .......................................................................... 30 10. Conclusion.. ............................................................................................ 31 11. References.. ............................................................................................ 32 Appendix 1 :Intellectual property arising .................................................... 37 Appendix 2: Staff................................................... ....................................... 37 2 FINAL REPORT Radiometric Ageing ofSharks Acknowledgements Thanks are extended to Dr Terry Walker and colleagues at the Marine Science Labs (now MAFRI) Queenscliff for assistance collecting school shark, to Dr John Stevens and colleagues at CSIRO for assistance with collecting shark vertebrae and commenting on a draft of this report. Thanks are also extended to Matt Healey for his enthusiastic assistance measuring vertebrae and spines, particularly after I had resigned from the University to take up a position working for the Tasmanian Department of Primary Industries, Water and Environment. The analytical skills of Rob Chisari, from the Australian Nuclear Science and Technology Organisation are gratefully acknowledged forconducting the radiometric analyses. The support of Laura Denholm from the Research Office and to Prof. Craig Johnson and Barry Rumbold from the School of Zoology University of Tasmania was appreciated during a rather complicated process of completing this research after leaving the University. Finally thanks to the support and patience of my family during the write up of this project given it was entirely an "after-work and kids-bedtime" exercise. 3 FINAL REPORT Radiometric Ageing ofSharks 1. Non-technical Summary Determining the age of sharks 1s difficult. A reliable independent method of validating age estimates is needed, apart from relying on tag return data. The success of radiometric analysis for bony fish overseas and in Australia suggested that it would be worth trying the method on sharks. Four species were chosen for this study, school shark Galeorhinus galeus, white­ spotted dogfish Squalus acanthias, and two deepwater sharks golden dogfish Centroscymnus crepidater and the southern dogfish Centrophorus uyato. The results of the study were quite different from previous radiometric analyses of fish otoliths. Age estimates have been made using the in-growth of 210Pb. The age estimates for G.galeus range from 22 to 55 years. These age estimates are remarkably similar to the known tag return ages for this species, but are very different from the ages estimated by the alizarin red method used on vertebrae from each of the individuals radiometrically analysed here. The alizarin red method gave ages up to a maximum of 11 years. The problems with the alizarin red method were already known, and this was part of the reason why the radiometric method was applied to school sharks. The age estimates for S.acanthias using the radiometric method range from 40 to 78 years. These ages do not match the age estimates from counting bands in sections of the second dorsal spine, where the maximum age recorded here was 23 years. However this species has been widely reported to be long-lived, in the order of 70 years. The ages estimated for C.crepidater ranged from 26 to 43 years, this small range in ages reflecting the small size range of sharks available foranalysis. This is the firstestimate of age for this species. The radiometric age method estimated the age of C.uyato ranging from 34 to 46 years. Again the smaller size range of individuals was reflected in similar ages. This is also the first estimate of age for this species. 4 FINAL REPORT Radiometric Ageing ofSharks The technique was also applied to a range of teleost and other shark species where 210Pb values were available. The results of this analysis also indicate the validity of this method for age determination. In summary the project has been successful in fulfilling the objectives of the study, and importantly the method looks very promising to offer an alternate method of ageing and a validation tool. The results of this study point to further development of this method for sharks, including analysing vertebrae from tag­ return individuals which have been at liberty for many years. 2. Background Resource assessment is important for management of shark fisheries in Australia. One of the key requirements for this assessment is accurate estimation of age. However accurate age determination remains difficultfor sharks. There are many techniques that have been used for ageing sharks, but verification/validation of the ages still remains difficult. Shark ageing methods have generally involved counting opaque and translucent bands present in vertebrae and finspines. However, few studies have attempted to determine the periodicity of these bands. A review by Cailliet (1990) found that age had been validated in only 6 species. Many studies have however, at least partially verified their age estimates. Where verification is defined as the process of confirming an age estimated by comparison with other indeterminate methods and validation is proving the ages are true by comparison with a determinate method and this must be conducted for all size classes. Cailliet (1990) listed 7 methods that have been used to estimate age and verify the periodicity of band formation in elasmobranchs: 1. back calculation and calculation of growth model parameters (neither qualify as verification); 2. size frequency analysis 3. centrum or spine edge dimensions, histological characteristics, and/or elemental analysis; 5 FINALREPORT Radiometric Ageing ofSharks 4. radiometric dating 5. laboratory growth studies 6. tag recapture studies fromthe field; and 7. tetracycline marking both in the field and laboratory. The main methods of verification/validation have included using tetracycline and tag
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