194 



Age-validation of a 



leopard shark (Triakis semifasciatd) 



recaptured after 20 years 



months; and parturition takes place in 

 spring (April-May peak) in San Fran- 

 cisco Bay (Smith and Abramson 1990; 

 Kusheretal, 1992). 



Susan E. Smith 



Southwest Fisheries Science Center 



National Manne Fishenes Service. NOAA 



8604 La Jolla Shores Dnve 



La Jolla, California 92037 



E-mail address: susan.smith@noaa gov 



Robert A. Mitchell 



26530 Grant Street 



St. Clair Shores, Michigan 48081 



Dan Fuller 



Inter-American Tropical Tuna Commission 

 8604 La Jolla Shores Dnve 

 La Jolla, California 92037 



On 10 July 1999, vertebrae bearing 

 an oxytetracycline (OTC) time mark 

 were retrieved from a tagged leopard 

 shark (Triakis semifasciata ) recap- 

 tured in San Francisco Bay, CA, after 

 being at liberty for almost 20 years. 

 An additional long-term leopard shark 

 tag return was received in June 2001, 

 for which growth information (but 

 not vertebrae) was obtained. The first 

 recapture is significant in that it rep- 

 resents the longest at-liberty period 

 for an age-validated (OTC-injected) 

 shark, extends and completes age 

 validation for this species, spanning 

 all age classes up to its estimated 

 average maximum ago, and provides 

 an example of the persistence of the 

 OTC time mark in an elasmobranch 

 at liberty for almost 20 years. The 

 recaptured leopard shark made in 

 2001 also provides valuable informa- 

 tion on long-term growth from time of 

 release to time of recapture. Findings 

 are documented here so that other 

 researchers are aware that validation 

 is complete for this species, to pres- 

 ent pertinent evidence of considerable 

 interannual variability in growth in 

 this species, and to report observations 

 on processing difficulties relating to 

 the ephemeral nature of the 20-yr-old 

 OTC mark 



Earlier results from the tagging 

 study that led to these recaptures were 

 published by Smith (1984), Smith and 

 Abramson (1990), and Kusher et al. 

 (1992). These authors concluded that 

 one pair of vertebral growth bands 

 (one opaque, one translucent) is pro- 

 duced each year in this species for the 

 age classes they examined (up to 17 

 years). Opaque bands are deposited 

 primarily in late spring and summer 

 (mainly in August in the San Francisco 

 Bay area); translucent bands, presum- 

 ably representing minimum growth 

 periods, are deposited primarily in late 

 fall and winter (Kusher et al., 1992). 

 Average annual growth of recaptured 

 leopard sharks examined in these 

 studies ranged from 0.0 cm per year to 

 4.0 cm per yr (mean of 2.14 cm per yr); 

 centra grew proportionately to shark 

 length over all size classes sampled. 



The leopard shark occurs from 

 Baja California, Mexico, to Oregon; 

 maximum confirmed size is 180 cm 

 TL (Kato et al., 1967), but fish over 

 146 cm TL are uncommon off central 

 California (Herald et al., 1960; Kusher 

 et al., 1992). Age and size at which 

 females first reach maturity have 

 been estimated at approximately 13 

 yr and 110 cm TL, respectively; the 

 gestation period is estimated at 10-12 



Methods 



The recaptured sharks were from a 

 group of 948 leopard sharks tagged and 

 released off Hunteris Point (37°44'N 

 lat., 122°21'W long.) in South San 

 Francisco Bay between 26 July and 

 13 September 1979. All were injected 

 with oxytetracycline hydrochloride 

 (OTC), tagged on the dorsal fin with 

 yellow plastic livestock rototags, and 

 released as described by Smith (1984). 

 The shark returned in 1999 was 

 caught on 10 July off Oakland Airport 

 in San Francisco Bay by a recreational 

 angler fishing -8 km east of the original 

 release point. The fish was measured 

 and the vertebrae removed and later 

 frozen. In the laboratory, the vertebrae 

 were sectioned and mounted as de- 

 scribed by Smith ( 1984). Various verte- 

 bral section widths (from 0.4 mm to 1.3 

 mm wide) were tested to determine the 

 best thickness for interpreting narrow 

 band patterns near the centrum edge. 

 The transverse sections were viewed 

 illuminated alternately by ultraviolet 

 UV (365 nm) and transmitted light. 

 Micrographs were taken with a Leica 

 DMLB microscope with a Diagnostic 

 Instruments SPOT CCD (charged 

 coupled device) digital camera coupled 

 through a 0.6x phototube, multiplied 

 by the ocular magnifications of 1, 5, 

 and lOx to obtain a total magnification 

 of 0.6, 3, and 6x. The three magnifica- 

 tions were evaluated for the best pos- 

 sible counting path. The images were 

 then analyzed with Media Cybernetics 

 Image Pro Plus image analysis soft- 

 ware (Media Cybernetics, 1998), with 

 which increments were enhanced with 

 an edge-sharpening filter After the 

 application of the filter the images 

 were evaluated and counts from the 

 OTC mark to the margin were made. 

 An annulus was defined as the distal 

 edge of each translucent band in the 

 corpus calcareum, at the distal edge 

 of each band pair (e.g. Kusher et al. 

 1992; Branstetter and Stiles 1987 and 



Manuscript accepted 19 August 2002. 

 iM.sh. Bull. 101:194-198 (2()():ii. 



