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

A. Govender, S. L. Birnie

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

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

Fingerprint

Carcharhinus
shark
sharks
South Africa
fishing mortality
mortality
sheep
ear tags
fouling
beaches
ears
beach
Africa
rate

ASJC Scopus subject areas

  • Aquatic Science

Cite this

@article{8d18a5786ba74fe295f100b3dcc384be,
title = "Mortality estimates for juvenile dusky sharks Carcharhinus obscurus in South Africa using mark-recapture data",
abstract = "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.",
author = "A. Govender and Birnie, {S. L.}",
year = "1997",
language = "English",
pages = "11--18",
journal = "African Journal of Marine Science",
issn = "1814-232X",
publisher = "National Inquiry Services Centre Ltd",
number = "18",

}

TY - JOUR

T1 - Mortality estimates for juvenile dusky sharks Carcharhinus obscurus in South Africa using mark-recapture data

AU - Govender, A.

AU - Birnie, S. L.

PY - 1997

Y1 - 1997

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=0031372498&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0031372498&partnerID=8YFLogxK

M3 - Article

SP - 11

EP - 18

JO - African Journal of Marine Science

JF - African Journal of Marine Science

SN - 1814-232X

IS - 18

ER -