The origin of the Saharan Bank cephalopod fishery

The Saharan Bank (West Africa, between 21 degrees N and 26 degrees N latitude) has been fished since the fifteenth century. Bottom trawls were introduced during the Second World War. Catches of cephalopods were very limited until the 1960s, when a spectacular increase was observed in their landings. The apparent replacement of finfish by cephalopods has been attributed to a change in the ecosystem due to overexploitation of Sparidae, but the hypothesis has never been quantitatively confirmed. The evolution of the profile of Spanish catches from the region from 1933 to 1996 shows a decreasing trend in the numbers of Sparidae, which virtually disappeared from landings at the beginning of the 1970s, with a simultaneous sharp increase in cephalopod catches. However, results from surveys carried out on the bank in 1942, 1962, 1974, and 1990 are not entirely consistent with the replacement hypothesis. The data suggest that there may have been some adjustment in the faunistic communities in response to fishing, but that the change has by no means been of the magnitude suggested by fishery statistics. We suggest that the changes observed are caused by a combination of factors, including economic incentives as well as oceanographic variations and competition for food, which have ultimately favoured benthic cephalopod populations at the cost of most finfish populations. (C) 2000 International Council for the Exploration of the Sea.