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.
N1 - Funding Information:
We thank our colleagues Ms E. Bullen for diligently maintaining the tagging database and Me N. Kistnasamy who provided many answers to our persistent queries on early dusky shark research at OR!. Drs L. E. Beckley (ORl), K. L. Cochrane (F. A. 0., Rome) and A. E. Punt (CSIRO, Australia) and Me S. T. Fennessy (ORI) commented on an early draft of the manuscript. Equations 1-4 were developed from suggestions by Drs Punt and Cochrane and Me B. Wareham is thanked for his information on recreational fishing for dusky sharks. This work was undertaken under the auspices of a special programme on modelling of KwaZulu-Natal fisheries and funded by the South African Foundation for Research Development. Partial funding was also obtained from the University of Natal Research Fund. Mr J. A. A. de Oliveira of the Sea Fisheries Research Institute and an anonymous reviewer are thanked for their comments, which enhanced this paper considerably.
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
U2 - 10.2989/025776197784161027
DO - 10.2989/025776197784161027
M3 - Article
AN - SCOPUS:0031372498
SN - 1814-232X
SP - 11
EP - 18
JO - African Journal of Marine Science
JF - African Journal of Marine Science
IS - 18
ER -