Modelling a Multispecies Schooling Fishery in an Upwelling Environment, Mauritania, West Africa.
Date of Award
Doctor of Oceanography and Coastal Sciences (POCS)
Oceanography and Coastal Sciences
Richard F. Shaw
Off Mauritania, Northwest Africa, small pelagic fish have long been a valuable target of a large and diverse international fleet. In the early 1990's, average annual catch was about 400,000 metric tons in which three to four families were frequently represented: carangidae (Trachurus trachurus, T. trecae and Decapterus rhonchus); clupeidae (Sardina pilchardus, Sardinella aurita and S. maderensis); scombridae (Scomber japonicus); and lately, trichiuridae (Trichiurus lepturus). Using empirical orthogonal function analysis, it was shown that the study area is a transition zone between permanent upwelling in the north (20-25$\sp\circ$N) and regions with seasonal upwelling in the south (10-16$\sp\circ$N). Also, from 1985 to 1993, a warming in the southern EEZ was identified as a part of a long-term successive cooling and warming trends of sea surface temperature (1946-1988). These trends were also reflected in coastal station data and suggest strong associations between physical processes at local stations and the large-scale processes in the Northwest African coast. Univariate and multivariate time series analyses performed on catch per effort (CPUE), hydrographic seasons, north and south fishing zones, and fishing vessel types indicated considerable temporal and spatial patterns in species yields. These variations are shown to be closely associated with hydrological conditions. For instance, carangidae dominated catch composition particularly during transitional water seasons while, Sardina was most abundant during the cold water season and in the northern fishing zone. Further investigations of the CPUE computation suggested that proportional allocation of the fishing effort among the individual species groups was a better alternative to computing CPUE based upon the whole catch which is presently the case. This method used a nonequilibrium Schnute's version of the Schaefer model, for which a new formula was derived that allows computing confidence intervals around the maximum sustainable yields. The results indicate that proportional allocation of the effort and the multivariate regression model considerably enhanced the fit of the model. Given the complexity of the fishery and species interdependence in species catch, the techniques and procedures presented are highly recommended tools to model the fishery.
Ould dedah, Sidina, "Modelling a Multispecies Schooling Fishery in an Upwelling Environment, Mauritania, West Africa." (1995). LSU Historical Dissertations and Theses. 6149.