Changes in abundance of the northern Benguela sardine stock during the decade 1990 – 2000, with comments on the relative importance of fishing and the environment

  • DC Boyer National Marine Information and Research Centre, Ministry of Fisheries and Marine Resources, P.O. Box 912, Swakopmund, Namibia
  • HJ Boyer National Marine Information and Research Centre, Ministry of Fisheries and Marine Resources, P.O. Box 912, Swakopmund, Namibia
  • I Fossen Formerly Institute of Marine Research, Private Bag 1870 Nordnes, 5817, Bergen, Norway; now Møre Research Section of Fisheries, P.O. Box 5075, N-6021 Aalesund, Norway
  • A Kreiner National Marine Information and Research Centre, Ministry of Fisheries and Marine Resources, P.O. Box 912, Swakopmund, Namibia
Keywords: environmental effects, fishing effects, northern Benguela, recruitment, sardine

Abstract

The northern Benguela stock of sardine Sardinops sagax used to be considered one of the major clupeoid stocks of the world; it supported an average annual catch of >700 000 tons throughout the 1960s. The stock has been in a depressed state for more than two decades, as demonstrated by annual catches that averaged around 50 000 tons between 1978 and 1989 and only slightly more in the 1990s. It has experienced fluctuations in abundance of several orders of magnitude during the most recent decade. Population size increased until 1992, when the acoustic estimate of biomass was about 750 000 tons. Catches increased accordingly, averaging 100 000 tons between 1992 and 1995, but from 1992 to 1996 the stock was in decline and the lowest annual catch in the history of the fishery was taken in 1996. Although there was a small increase during the last three years of the decade, the stock remains seriously depleted. Survey-based recruitment indices suggest that the changes in the 1990s were initiated by fluctuations in recruitment, but the decline was almost certainly exacerbated by continued fishing. Poor recruitment and decreasing catch rates between 1993 and 1996 in a number of other key resources suggest that system-wide environmental changes were an important factor in the decline of the sardine stock at that time. Anomalous oceanographic conditions, such as extensive hypoxic shelf waters in 1993/94 and a Benguela Niño in 1995, support this conclusion.

Keywords: environmental effects, fishing effects, northern Benguela, recruitment, sardine

African Journal of Marine Science 2001, 23: 67–84
Published
2006-10-23
Section
Articles

Journal Identifiers


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