Using a Small ROV to Estimate the Abundance of Sensitive Rockfishes and Benthic Marine Fishes in a Broad-Scale Regional Survey

Many benthic marine fishes such as rockfishes (Sebastes spp.) live in restricted habitats, have sensitive life history characteristics, or are otherwise difficult to assess and manage.  Lethal sampling methods such as trawls and hook-and-line may impact population viability or inadequately sample abundance for bocaccio, canary, and yelloweye rockfishes that are now endangered or threatened species.  Over the past 20 years, staff of the Washington Department of Fish and Wildlife (WDFW) has developed non-lethal, videographic methods for estimating the abundance of rockfish and other sensitive species. A drop-camera system was used between 1994 and 2002, but its use was limited.  In 2004 and 2005, WDFW used a small remotely-operated vehicle (ROV) to conduct small-scale surveys in San Juan channel, with results confirming its utility as a quantitative survey tool.  In 2008, a region-wide study of rocky habitats in the San Juan Islands was conducted resulting in population estimates for 42 common and rare species.  This depth stratified and randomized survey resulted in standard errors ranging from 8 to 14% for common rocky habitat species. 

The federally-protected rockfishes have been rare in trawl surveys with six encounters of yelloweye rockfish and 24 encounters of canary rockfish among 1,612 trawl samples in Puget Sound,  However, 39 yelloweye rockfish, one canary rockfish, and four bocaccio were encountered among 207 ROV transects in 2008.  To evaluate the efficacy of the ROV as a survey tool for benthic fishes regardless of habitat type, the WDFW conducted another survey of the San Juan Islands in 2010-11.   We used stratified systematic adaptive sampling to lower the uncertainty of the estimates. In addition, stereological survey was employed to correct the bias the edge effect in the spatial sampling. Changes in equipment configuration greatly improved our ability to image flatfish and other small fishes that were rarely detected in previous surveys.