NOTE Smith et al.: Triakis semifasciata recaptured after 20 years 



197 



with extreme care, especially when examining band pat- 

 terns in older, slow-growing sharks. For these fish, less 

 precise preparation methods (such as examining whole 

 centrum faces) are probably inadequate for interpreting 

 narrow gi-owth bands that form later in life. Additionally, 

 in species like the leopard shark, the most recently depos- 

 ited band pair may only become clearly defined or fully dif- 

 ferentiated as new tissue after the accretion of subsequent 

 bands. Thus, although most band pairs seem to be rela- 

 tively well defined in this species (even in older specimens 

 such as this one), the peripheral bands can be indistinct or 

 incomplete. Beamish and McFarlane (2000), who recently 

 reported on a sablefish (Anoploporna fimbria) recaptured 

 up to 20 years after being injected with OTC, also warned 

 that the aging structures of long-lived fish require very 

 careful preparation and interpretation. 



In the vertebrae of the 1999 recaptured leopard shark, 

 substantial centrum growth occurred in the late 1980s, e.g. 

 the width of the 1987 growth zone (at 13 yr old) was over 

 twice that of annual growth zones adjacent to it. We cannot 

 explain why this period may have been so favorable for this 

 shark over previous and subsequent years, but it does sug- 

 gest that this species is capable of great interannual vari- 

 ability in growth, even at a relatively advanced age. Lenarz 

 et al. (1995) described mild El Niiio conditions off central 

 California in 1987-88, although temperatures were less el- 

 evated than during other El Nirio events, and only short pe- 

 riods of unusually high sea-level anomalies were observed. 

 Moser et al. (2002) classified 1985-87 as a "normal" oceano- 

 graphic period off California, between the warm 1982-83 El 

 Niiio episode and a cool-water 1988 La Nina episode. 



OTC fluorescence is known to fade with exposure to LFV 

 light; therefore samples are traditionally stored in dark- 

 ness and processed in dim light (Weber and Ridgeway 

 1962). The OTC mark in the leopard shark at liberty for 

 20 years was especially light-sensitive, disappearing after 

 a few minutes exposure, much more quickly than tetra- 

 cycline marks observed previously by one of the authors 

 in earlier recaptures from this study. This may be due 

 to diminishment of the phosphorescent properties of the 

 chemical, combined with compression of the mark within 

 the cartilage matrix over time. Therefore, when working 

 with cartilaginous fishes (especially those at liberty for 

 many years), it may be extremely important to obtain as 

 many vertebrae as possible, to keep OTC-labeled centra 

 away from light, to preplan microscope viewing sessions 

 carefully, and to process and photograph samples quickly. 



Previous studies have validated annual periodicity in 

 leopard sharks up through age 17 (Smith 1984; Kusher 

 et al. 1992). Beamish and McFarlane (1983) pointed out 

 that band periodicity must be established for a full range 

 of age classes to fully meet the requirement of age valida- 

 tion in fishes. This requirement is seldom met and has not 

 yet been achieved for any elasmobranch. The OTC-labeled 

 fish recaptured in 1999 measured 2 cm longer but was 8 

 years older than the oldest age-validated leopard shark of 

 Kusher et al. (1992). This latter fish, also a female, mea- 

 sured 122 cm TL and was estimated to be 17 yr of age. 

 It had been at liberty for 7.3 years — the longest duration 

 recorded in that study. Results of the present study extend 



age validation for this species to fish at liberty for up to 

 19-1- years, up to 124 cm TL, and up to 25 yr old. Longevity 

 of this species has been estimated at 25-30 years (Smith, 

 1984); thus full validation for this species spanning ages 

 through 25 is now complete. 



Acknowledgments 



We thank David Au, John Butler, Sandy McFarlane, and 

 anonymous reviewers for helpful comments on drafts of 

 this manuscript. We are also grateful to the anglers who 

 recaptured and returned to us the vertebrae of the fish 

 recaptured in 1999 (Jeff King of Fairfield, California, and 

 Howard Arnold, a cooperating volunteer for the California 

 Department of Fish and Game Shark Tagging Program), 

 and to Bretta Larson (Romberg Tiburon Center, SFSU) 

 and Bay Van To for return of tag recapture no. 337. 



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