Gillnet selectivity for the north African catfish, Clarias gariepinus (Actinopterygii: Siluriformes: Clariidae), from the Upper Okavango Delta, Botswana

• Autorzy: Bokhutlo T. , Mosepele K.
• Języki publikacji: EN

Abstrakty

EN

Background. Successful fisheries management requires estimation of gillnet selectivity for optimum exploitation of the resource. In the Okavango Delta, no study has assessed the selectivity of gillnets for Clarias gariepinus (Burchell, 1822) which is an important component of both the subsistence and the commercial gillnet fishery catch. The aim of this study was to simulate the harvesting pattern of the commercial gillnet fishery and provide gillnet selectivity parameters for C. gariepinus. This will help fishery managers with information on the appropriate mesh sizes needed for sustainable utilisation of the catfish resource. Materials and Methods. Monthly gillnet sampling was conducted over a period of 8 years from 2001 to 2009. The SELECT method was used to estimate gillnet selectivity for C. gariepinus using catch data from four mesh sizes (73 mm, 93 mm, 118 mm, and 150 mm). Results. The 93 mm and 118 mm mesh sizes were the most efficient when capturing C. gariepinus accounting for 44.6% and 21.9% of the total catch, respectively. Mean fish length increased with increasing mesh size and was significantly different between mesh sizes (P < 0.001). The modal fish lengths for the four mesh sizes were estimated at 41.63 cm, 53.23 cm, 66.35 cm, and 85.54 cm in order of increasing mesh size. Conclusion. The modal fish lengths for meshes 93 mm and 118 mm are greater than the size at maturity and therefore the current commercial gillnet fishery which uses 100 mm mesh size may not be a threat to the C. gariepinus population in the Upper Okavango Delta. Future studies should aim to conduct fishery dependent selectivity studies in the lower Okavango Delta to determine if selectivity changes with location and gear. Moreover, a comprehensive age-based stock assessment is required to establish the mesh size that optimizes yield without adversely depleting the spawning stock biomass.

• Wydawca: -
• Czasopismo: Acta Ichthyologica et Piscatoria
• Rocznik: 2015
• Tom: 45
• Numer: 2
• Opis fizyczny: p.133-141,fig.,ref.

Twórcy

autor

Bokhutlo T.

• Botswana International University of Science and Technology, Palapye, Botswana

autor

Mosepele K.

• Okavango Research Institute, University of Botswana, Maun, Botswana

Bibliografia

• Baremore I.E., Bethea D.M., Andrews K.I. 2012. Gillnet selectivity for juvenile blacktip sharks (Carcharhinus limbatus). Fishery Bulletin 110 (2): 230–241.
• Bokhutlo T., Weyl O.L.F., Mosepele K., Wilson G.G. 2015. Age and growth of sharptooth catfish, Clarias gariepinus (Burchell, 1822) (Clariidae), in the Lower Okavango Delta, Botswana. Marine and Freshwater Research 66 (5): 420–428.DOI: 10.1071/MF13322
• Butterworth D.S., Rademeyer R.A., Brandão A., Geromont H.F., Johnson S.J. 2014. Does selectivity matter? A fi sheries management perspective. Fisheries Research 158: 194–204.DOI: 10.1016/J.FISHRES.2014.02.004
• Carlson J.K., Cortés E. 2003. Gillnet selectivity of small coastal sharks off the southeastern United States. Fisheries Research 60 (2): 405–414.DOI: 10.1016/S0165-7836(02)00135-2
• Dos Santos M.N., Gaspar M., Monteiro C.C., Erzini K.2003. Gill net selectivity for European hake Merlucciusmerluccius from southern Portugal: Implications for fishery management. Fisheries Science 69 (5):873–882. DOI: 10.1046/J.1444-2906.2003.00702.X
• Hothorn T., Bretz F., Westfall P. 2008. Simultaneous inference in general parametric models. Biometrical Journal 50 (3): 346–363. DOI: 10.1002/BIMJ.200810425
• Hovgård H., Lassen H., Madsen N., Poulsen T.M., Wileman D. 1999. Gillnet selectivity for North Sea Atlantic cod (Gadus morhua): Model ambiguity and data quality are related. Canadian Journal of Fisheries and Aquatic Sciences 56 (7): 1307–1316.DOI: 10.1139/F99-070
• Hulson P.-J.F., Hanselman D.H. 2014. Tradeoffs between bias, robustness, and common sense when choosing selectivity forms. Fisheries Research 158:63–73.DOI: 0.1016/J.FISHRES.2013.12.016
• McCarthy T.S., Bloem A., Larkin P.A. 1998. Observations on the hydrology and geohydrology of the Okavango Delta. South African Journal of Geology 101 (2): 101–117.
• Merron G.S. 1993. Pack-hunting in two species of catfish, Clarias gariepinus and C. ngamensis, in the Okavango Delta, Botswana. Journal of Fish Biology 43 (4): 575–584.DOI: 10.1111/J.1095-8649.1993.TB00440.X
• Millar R.B., Fryer R.J. 1999. Estimating the size-selection curves of towed gears, traps, nets and hooks. Reviews in Fish Biology and Fisheries 9 (1):89–116.DOI: 10.1023/A:1008838220001
• Millar R.B., Holst R. 1997. Estimation of gillnet and hook selectivity using log-linear models. ICES Journal of Marine Science 54 (3): 471–477.DOI: 10.1006/JMSC.1996.0196
• Mmopelwa G., Mosepele K., Mosepele B., Moleele N., Ngwenya B. 2009. Environmental variability and the fishery dynamics of the Okavango delta, Botswana: The case of subsistence fi shing. African Journal of Ecology 47 (Suppl. s1): 119–127.DOI: 10.1111/J.1365-2028.2008.01058.X
• Mosepele K., Nengu S. 2003. Growth, Mortality and length–weight parameters of selected fishes of the Okavango Delta, Botswana. ACP-EU Fisheries Research Report 14: 67–74.
• Psuty I., Draganik B., Blady W. 2007. Gillnet selectivity to roach, Rutilus rutilus from the Szczecin Lagoon, Poland. Acta Ichthyologica et Piscatoria 37 (1): 17–23.DOI: 10.3750/AIP2007.37.1.03
• Ramberg L., Hancock P., Lindholm M., Meyer T., Ringrose S., Sliva J., Van As J., VanderPost C. 2006.Species diversity of the Okavango Delta, Botswana.Aquatic Science 68 (3): 310–337.DOI: 10.1007/S00027-006-0857-Y
• Richardson T.J., Booth A.J., Weyl O.L.F. 2009. Rapie biological assessment of the fishery potential of Xonxa Dam, near Queestown, South Africa. African Journal of Aquatic Science 34 (1): 87–96.DOI: 10.2989/AJAS.2009.34.1.9.734
• Van der Bank H., Smit N. 2007. Large allozyme variations within populations and isozyme differences between Clarias gariepinus and C. ngamensis from the Okavango Delta, Botswana. African Journal of Aquatic Science 32 (3): 311–315. DOI: 10.2989/AJAS.2007.32.3.12.311
• Wallace K.M., Leslie A. 2008. Diet of the Nile crocodile (Crocodylus niloticus) in the Okavango Delta, Botswana. Journal of Herpetology 42 (2): 361–368.DOI: 10.1670/07-1071.1
• Wilson K.H., Andrew J.H. 1987. Infl uence of gill net hang ratio on the catch of salmon in the Fraser River.Canadian Technical Report on Fisheries and Aquatic Sciences No. 1516.

Identyfikatory

DOI

10.3750/AIP2015.45.2.03