Mortality estimates for juvenile dusky sharks Carcharhinus obscurus in South Africa using mark-recapture data

A. Govender, S. L. Birnie

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A maximum likelihood model is developed, using mark-recapture data, to estimate total and fishing mortality rates for the dusky shark Carcharhinus obscurus in South Africa. The model accounts for tag-shedding, nonreporting of recaptured tags, the multiple release and single recapture nature of the study and the usage of two different types of tags (sheep-ear and ORI tags). Tag shedding was quantified as tags washed up on beaches and fouling of tags in protective shark nets, which amounted to 17% of all tags recovered between 1986 and 1993. The ORI tag had a higher tag-shedding rate than the sheep-ear tag. Assuming a 75% reporting rate for recaptured dusky sharks, an instantaneous fishing mortality rate was estimated to be 0.27·year-1, with a 95% confidence level ranging between 0.19 and 0.44·year-1.

Original languageEnglish
Pages (from-to)11-18
Number of pages8
JournalSouth African Journal of Marine Science
Issue number18
Publication statusPublished - 1997


ASJC Scopus subject areas

  • Aquatic Science

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