Title: Standardization of fishing gears used for stock assessment in Lake Victoria

Abstract

Designs and theoretical performance of bottom and pelagic trawls for fish stock assessment in Lake Victoria (East Africa) were studied in order to evaluate their present standardization. Three nations cooperate in assessing the fish stocks in Lake Victoria and standardization of gears and methods is of importance for reliable and consistent sampling. The trawl plans from the net manufacturers, together with the ones provided in the standard operating procedures (SOPs), were investigated by direct measurements and calculations. The trawl plans were re-drawn to scale, compared and their resistances in relation to the towing powers of the used research vessels evaluated. Comparison of the plan and rigging of two bottom trawl nets (the old one supplied in 1997 and the new one obtained in 2010), and two pelagic nets (old and new) were done. The two bottom trawls differed in the fore openings, twine area, belly size and sweep line lengths. Calculations showed that changes in these parameters resulted in changes in trawl resistance and the area swept. The old and new pelagic nets showed minimal difference in total resistance and can be towed at approximately 2 knots using the power of the current vessels. The lack of standardization reduces reliability in stock assessment surveys. In this project, I propose a guide to standardize the sampling gears for stock assessment in Lake Victoria.