Title: A surplus production analysis of the Cape horse mackerel (Trachurus capensis) midwater trawl fishery in Namibia.

This paper examines the optimal yield and stock development of the Cape horse mackerel (Trachurus capensis) fisheries. Surplus production analysis based on the Gordon-Schaefer (1954) bioeconomic model was applied to the Cape horse mackerel midwater trawl fishery in Namibia, using empirical yearly data from 2009-2020. Cost of capital was observed to be relatively low and was adjusted to the long-term average capital cost of the Icelandic pelagic industry. Effort was measured as trawling duration and CPUE as catch per hour trawled. The findings support model theories and concepts that the maximum economic yield (Y_MEY) is estimated to be 327,091Mt, lower than maximum sustainable yield, Y_MSY, at 342,115Mt. The respective corresponding efforts were estimated to be 23,455 and 29,673 hours of trawling. There is a small margin between the two static reference points and therefore, overfishing could cause a sudden decline in profits. The results suggest that effort exerted in 2020 was sufficient to achieve maximum sustainable yield, however that was not obtained due to an unresponsive fishing allocation. The use of bioeconomic modelling can inform fisheries management to determine optimal fleet sizes and fishing effort, giving Namibia an advantage to maximise the potential benefits from the Cape horse mackerel fishery. However, bioeconomic analysis is fundamentally driven by effort parameters and therefore, further research may be required to develop a consensus on an accurate effort measure and other dynamic factors that affect the Cape horse mackerel fishery.