Population estimates of Pacific coast groundfishes from video transects and swept-area trawls

Abstract.-Demersal fish surveys are used for two purposes: to detect trends in multispecies communities for environmental assessment and to provide fishery independent stock assessments for management. We compared remotely operated vehicle (ROV) and swept-area trawl surveys to evaluate their strengths and weaknesses for these two purposes. ROV abundance estimates tended to be higher and have lower coefficients of variation than did trawl abundance estimates. This trend is greatest for benthic species and particularly so for small, cylindrically shaped fishes. For patchily distributed, off-bottom fishes such as rockfish, Seba8te8 spp., sablefish, Anoplopoma fimbria, and Pacific whiting, Merlucciu8 productu8, the results vary between ROV and trawl estimates. For environmental assessment, the ROV estimates are superior because, for most species, abundances are higher and smaller changes can be detected. For fisheries management of commercially important species, the results are divided. Dover sole, Micro8tomu8 pacificu8, and thomyheads, Sebastolobu8 spp., have higher ROV abundance estimates and lower coefficients of variation than the trawl. Sablefish, which exhibit more offbottom behavior, have higher trawl estimates at two of three depths. The ROV and trawl provide different types ofinformation not available from other gear. Much of the difference between the two types ofsurveys stems from the nature of the sampling gear and from the behavior, body shape. and size of the fishes