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- Development of New Methods for Quantifying Fish Density Using Underwater Stereo-video Tools
- The use of video camera systems in ecological studies of fish continues to gain traction as a viable, non-extractive method of measuring fish lengths and estimating fish abundance. We developed and implemented a rotating stereo-video camera tool that covers a full 360 degrees of sampling, which maximizes sampling effort compared to stationary camera tools. A variety of studies have detailed the ability of static, stereo-camera systems to obtain highly accurate and precise measurements of fish; the focus here was on the development of methodological approaches to quantify fish density using rotating camera systems. The first approach was to develop a modification of the metric MaxN, which typically is a conservative count of the minimum number of fish observed on a given camera survey. We redefine MaxN to be the maximum number of fish observed in any given rotation of the camera system. When precautions are taken to avoid double counting, this method for MaxN may more accurately reflect true abundance than that obtained from a fixed camera. Secondly, because stereo-video allows fish to be mapped in three-dimensional space, precise estimates of the distance-from-camera can be obtained for each fish. By using the 95% percentile of the observed distance from camera to establish species-specific areas surveyed, we account for differences in detectability among species while avoiding diluting density estimates by using the maximum distance a species was observed. Accounting for this range of detectability is critical to accurately estimate fish abundances. This methodology will facilitate the integration of rotating stereo-video tools in both applied science and management contexts.
- Denney, Fields, Gleason, Starr
- Changes in size composition and relative abundance of fishes in Central California after a decade of spatial fishing closures
- Rockfish Conservation Areas (RCAs) were implemented in 2000 to 2003 along the West Coast of the United States to reduce fishing mortality on rockfish (Sebastes spp.) and other groundfish species that had recently been declared overfished. In 2012, we initiated a study to compare recent catch rates, species compositions and length frequencies of fishes inside and outside the RCAs with data collected in central California between 1995 and 1998. At all sites surveyed, total catch rates from the new surveys (2012–14) were significantly higher than catch rates from before RCA implementation (1995–98). The majority of the differences were due to the increased relative abundance of yellowtail rockfish (Sebastes flavidus), although other species, including the overfished canary rockfish (Sebastes pinniger), also increased. Differences in the size composition of species between the two time periods reflected both the increased survival of older fishes and higher recruitment success in the past decade. © 2015, Scripps Institution of Oceanography. All rights reserved., published
- Marks, Fields, Starr, Field, Miller, Beyer, Sogard, Wilson-Vandenberg, Howard