|Growth rate of juvenile dusky sharks, Carcharhinus obscurus (Lesueur, 1818), from southwestern Australia estimated from tag-recapture data|
Simpfendorfer, C.A. (2000). Growth rate of juvenile dusky sharks, Carcharhinus obscurus (Lesueur, 1818), from southwestern Australia estimated from tag-recapture data. Fish. Bull. 98(4): 811-822
In: Fishery Bulletin. US Government Printing Office: Washington, D.C.. ISSN 0090-0656, more
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Tagged neonate and small juvenile Carcharhinus obscurus were released between March 1994 and June 1996 in southwestern Australia. Length and time-at-Iiberty data from 304 usable recapture data were used to examine growth rates of male, female, oxytetracycline injected, noninjected, and all individuals combined. Recaptures were made up to 4.7 years after release. Four methods of analysis were employed: Gulland and Holt, Fabens, Francis, and length-at-age. Length-at-age analysis was possible because the majority of the animals released had open umbilical scars and so were of known age. The four methods produced varying results. One method was not able to estimate growth parameters, another produced inaccurate estimates of von Bertalanffy growth parameters, and two methods indicated that a linear growth model described growth better than the von Bertalanffy model. Although each produced different results, the three successful methods estimated that the growth rate up to age 5 ranged from 8 cm/year to 11 cm/year. These growth rates agreed closely with those reported for young C. obscurus. Length-at-age analysis indicated significant differences in the growth rates between males and females, and between oxytetracycline-injected and noninjected males. Results from the Francis method did not show significant differences between males and females, or injected and noninjected animals. The coefficient of variation of growth variability ranged from 0.24 to 0.40, mean measurement error ranged from 0.0 cm to 0.94 cm, and the standard deviation of measurement error ranged form 2.1 cm to 2.4 cm. The usefulness of each of the methods is discussed-the more detailed meth- ods providing a better understanding oftag-recapture data.