BIOECONOMIC EVALUATION OF CHANGES IN FISHING TECHNOLOGY OF SHRIMP-TRAWL NETS IN SHALLOW WATERS OF THE COLOMBIAN PACIFIC COAST

Abstract

With active participation of the fishing industry, the biological and economic effects of technological changes in shrimp trawling fishing on the Colombian Pacific coast were evaluated to reduce bycatch and fuel consumption. Two boats were used simultaneously in experimental fishing surveys that compared the performance of a trawl net prototype and the conventional trawl net used by the fleet, quantifying in both cases the effects of the turtle excluder device (DET) and two fishing grounds (central-north and centralsouth). The performance fishing variables used to test the effect of changes in fishing technology on the target catch (CO) and the bycatch [incidental catch (CI) and discard (D)], were the relative fish or shellfish abundance, individual sizes, net revenues and fuel consumption by boat. Effects of fishing grounds, trawl net type, presence of device and the interaction between these factors, were evaluated using a three way ANOVA. The effect of new technologies on lengths of organisms from the catch components (CO, CI and D), was evaluated by comparison of the length frequency distributions using the Chi-square test and by modeling size selectivity of the trawl net prototype. Differences in fuel consumption between types of trawl nets of each boat were evaluated by t- test. Totals of CO, CI and D were 1436, 12163 and 15428 kg, respectively, with a global proportion between target catch and bycatch of 1:19. The bycatch was composed by 217 taxa, of which 32 families, mainly fishes, made up the CI and 52 were part of discard (fish, crustaceans and mollusks). The CO showed greater abundance on the central-north fishing ground than on the central-south one, whereas a contrary tendency showed the CI and D, in response to resources availability provided by oceanographic conditions and habitat. The prototype trawl net reduced in 34.8% the CO, 16.3% the CI and 28.7% the D (45% of bycatch), being significant the reductions of CO and D; whereas the DET reduced significantly the CI and D, without affecting the CO mainly in the conventional trawl net. Lengths frequency distributions of CO, CI and D differed between trawl net types, with a clear tendency to that the prototype trawl net selected greater lengths of shrimps and fishes. The use of the trawl net prototype implied a non significant reduction of the net revenues by haul (23.4%), whereas the use of the DET represented a significant reduction in net revenues of 77 %, mainly in the conventional trawl net. The prototype trawl net with prototype trawl doors reduced the fuel consumption in 36%, whereas the same net with conventional trawl doors reduced 23 %, which represents a saving in variable costs per fishing trip between $ 10`125 000 and $ 6`468 750 (Colombian pesos in 2005). The adoption of new fishing technologies by the industrial shrimp fleet from the Colombian Pacific has scientific evidence that it demonstrates the reduction of byctach without putting at risk the economic benefits derived from a selective fishing