Effect of tow duration on catch rate and size composition of Northern shrimp (Pandalus borealis) and Greenland halibut (Reinhardtius hippoglossoides) in the West Greenland Bottom Trawl Survey

The standard towing time in the annual West Greenland Bottom Trawl Survey for shrimp and fish has initially been 60 min. Shorter tow durations have been gradually introduced over time and a mixture of 30 and 15 min tows have been used in the recent years. From the surveys conducted since 1999, 15 and 30 min tows have been analysed to examine whether a reduction of tow duration to 15 min influences the catch per swept area (CPUE), its precision and the size composition of Northern shrimp and Greenland halibut. For both species, neither total biomass density nor numerical densities of different size groups differed significantly (p < 0.05) between 15 and 30 min tows. No indication was found that 15 min tows give less precise estimates than 30 min tows. Furthermore, tow duration had no significant (p < 0.05) effect on mean size and maximum length of both species. The results suggest that the mixture of 15 and 30 min tows can be replaced by 15 min tows on all stations of the survey without impact on the continuity of the time series and the gain in survey time should be used to increase the total number of stations.