Merluccius capensis spawn in Namibian waters, but do M. paradoxus?

  • P Kainge National Marine Information and Research Centre, PO Box 912, Swakopmund, Namibia
  • OS Kjesbu Institute of Marine Research, Nordnesgaten 50, PO Box 1870 Nordnes, N-5817 Bergen, Norway
  • A Thorsen Institute of Marine Research, Nordnesgaten 50, PO Box 1870 Nordnes, N-5817 Bergen, Norway
  • AG Salvanes Department of Biology, University of Bergen, PO Box 7800, N-5020 Bergen, Norway

Abstract

Spawning time and areas, and the length of the spawning season of shallow-water (Merluccius capensis) and deepwater (M. paradoxus) hake, were investigated from bottom trawl collections taken in Namibian waters between September 1998 and October 2000 and from August to November 2001. The gonadosomatic index (GSI) and the incidence of advanced maturity stages of M. paradoxus were low along the entire coast throughout the year, but with a few exceptions in the south (between Lüderitz and Orange River). By contrast, M. capensis spawn in the area throughout the year, but mainly between July and October. Evaluating the accuracy of visual maturity staging by comparing results with those of image and histological analyses revealed few errors in classifications of maturity stage in the field, with the exception of Stage 5 (spent and resting) in M. paradoxus. Specific GSI values were intercalibrated with the appearance of developing oocytes. As the GSI is quickly estimated, this new concept, designated here as a ‘maturity reference line', could enhance understanding of the spawning biology of other species with a similarly complex, indeterminate spawning strategy. It is concluded that M. paradoxus do not appear to spawn in Namibian waters.

Keywords: GSI, hake, image analysis, maturity staging, Namibia, spawning time

African Journal of Marine Science 2007, 29(3): 379–392
Published
2008-02-07
Section
Articles

Journal Identifiers


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