Aspects of the biology and fisheries of an economically important sparid Dentex macrophthalmus (Bloch 1791) in the Namibe province, Angola

  • WM Potts
  • LA Inácio
  • CV Santos
  • TJ Richardson
  • WHH Sauer

Abstract

The sparid Dentex macrophthalmus is a widespread, important fishery species along most of the West African coast from southern Namibia to the Mediterranean. In southern Angola it is an important artisanal species targeted predominantly by handline fishers. A biological and fisheries study was conducted on this species in southern Angola between June 2008 and July 2009. It was the dominant species in the artisanal fishery, accounting for 99% of the sparids captured and 67% (by mass) of the total catch. The life history of D. macrophthalmus was characterised by slow growth (females: Lt = 309[1 - e-0.06(t + 5.43)], males: Lt = 248[1 - e-0.16(t - 1.77)]), advanced age at maturity (females: 7.4 years, males: 6.0 years) and high longevity (females: 36 years, males: 38 years). The sex ratio was 1:1 male:female. The length- and age-frequency distributions and macroscopic observations suggested that the species is a late gonochorist. Males and females reached 50% maturity at 151 and 166 mm fork length respectively. Although individuals with ripe gonads were found during most of the year, the peak spawning period appeared to be in December and January. Despite a life history that renders D. macrophthalmus vulnerable to overexploitation, only 38% of artisanal fishers noticed a decline in the catches of this species. Potential reasons for this include: technology creep; limited pressure on the juvenile portion of the stock as a result of late recruitment (above the length of 50% maturity); the ‘basin affect’, whereby depleted areas are reseeded by areas (e.g. deeper water) inaccessible to the linefishery; and a deep-water reserve of large individuals. It is recommended that precautionary management strategies be implemented until the age estimates are revised by the countries in which this species forms significant fisheries.

Keywords: growth, large-eye dentex, management, mortality, reproduction, Sparidae

African Journal of Marine Science 2010, 32(3): 601–611

Author Biographies

WM Potts
Department of Ichthyology and Fisheries Science, PO Box 94, Rhodes University, Grahamstown 6140, South Africa; South African Institute of Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa
LA Inácio
Faculdade Ciências da Universidade Agostinho Neto (FCUAN), Avenida 4 de Fevereiro nº 71, Luanda, Angola
CV Santos
Faculdade Ciências da Universidade Agostinho Neto (FCUAN), Avenida 4 de Fevereiro nº 71, Luanda, Angola
TJ Richardson
Department of Ichthyology and Fisheries Science, PO Box 94, Rhodes University, Grahamstown 6140, South Africa
WHH Sauer
Department of Ichthyology and Fisheries Science, PO Box 94, Rhodes University, Grahamstown 6140, South Africa
Section
Articles

Journal Identifiers


eISSN: 1814-2338
print ISSN: 1814-232X