Comparison of the MOCNESS and IYGPT pelagic samplers for the capture of 0-group cod ( Gadus morhua ) on Georges Bank

Abstract

Two samplers commonly used to capture pelagic 0-group gadids are the International Young Gadoid Pelagic Trawl (IYGPT) and the 10-m ² Multiple Opening and Closing Net Environmental Sensing System (MOCNESS). To evaluate the comparability of data collected by each sampler, a paired trawling experiment was conducted in June 1986 on the Northeast Peak of Georges Bank. This study compared the estimates of abundance, the length frequencies, and size of retention of Atlantic cod ( Gadus morhua ), 10–60 mm, by these two samplers. Over a 48-h period, 25 paired sets were completed, 14 during daylight and 11 at night. Between gears, standardized abundance estimates were statistically greater from the MOCNESS during the night but not during the day, indicating an undersampling of the 0-group cod at night by the IYGPT. Comparisons of the length frequencies show a trend for the IYGPT to catch larger individuals, both day and night, than the MOCNESS. However, vertical distribution studies and submarine observations suggest that a greater sampling depth by the IYGPT during these paired sets may be responsible for this increase in mean length. The lower size limit of retention by the IYGPT was found to be approximately 25 and 35 mm, day and night, respectively. The upper size limits of retention by the MOCNESS appeared to be obscured by the sampling design.