A direct comparison of MOCNESS and Video Plankton Recorder zooplankton abundance estimates: Possible applications for augmenting net sampling with video systems

A Video Plankton Recorder (VPR) was mounted on the frame of a 1- m 2 Multiple Opening and Closing Environmental Sensing System (MOCNESS) with 333- μ m mesh nets during May 1997 on a cruise to the southern flank of Georges Bank. Comparison of data from the two gears used a series of sampling hauls taken along a hydrographic mooring line encompassing the tidal front. To maximize species sampling overlap, a second study compared data from the VPR to data from a 1 4 - m 2 MOCNESS with 64- μ m mesh nets. Data sets were modified due to taxa abundance, organism size, or susceptibility to net damage, to contain only zooplankton that both gears sampled quantitatively. Taxa proportional contribution to the total Copepoda abundance was not affected by differing gear. Mean proportional differences ranged from 7% for Calanus to 15% for Pseudocalanus and the other copepoda taxa categories. The VPR produced standardized abundances that averaged two times higher than the MOCNESS nets. The differences in abundance may be decreased by a more accurate calibration of the VPR field of view or adjusted by a calibration factor. Gear comparison results were affected by net mesh size and oceanographic conditions. Results were not influenced by simultaneous, sequential or delayed timing between the samples that were compared. Consideration was given to the improvements possible to plankton surveys, larval feeding studies, and coupled bio-physical modeling, from VPR integration with net samplers.