Jagielo et al.: Demersal groundfish densities in trawlable and untrawlable habitats off Washington 561 



scale. Although our study was subject to the limitations of 

 the visual transect method, we assumed that the method 

 could reliably estimate (with a catchability of 9=1.0) the true 

 density of selected demersal bottomfish in both trawlable 

 and untrawlable habitats for evaluation of the habitat bias 

 present in the trawl-survey approach (which does not allow 

 for sampling in untrawlable habitat). We do not feel that 

 this assumption was severely violated, although we have 

 no objective measure of the potential biases of the method, 

 and thus we cannot estimate the consequences of assump- 

 tion failure. We did recognize clearly that difficulties in fish 

 identification limited the number of species that we could 

 quantitatively sample with this technique. Technological 

 improvements in underwater videography and image rec- 

 ognition software are likely to enhance the capabilities of 

 the visual transect survey technique in the future. 



In conclusion, it is clear that relatively large-scale sur- 

 veys are needed to assess bottomfish densities in habitats 

 that are not accessible to trawl survey gear. For some spe- 

 cies, it may be possible to derive an area-specific trawl-sur- 

 vey bias correction factor, but for many other species it is 

 likely that there will be no substitute for direct estimation 

 of densities in untrawlable habitat on a routine and synop- 

 tic basis. In either case, stratified random sampling designs 

 should be employed with sample sizes sufficient to ensure 

 acceptable levels of statistical power At present, the in situ 

 visual transect submersible survey method appears to be a 

 useful tool for this purpose, and the utility of this method 

 will likely improve further with technological advances. 



Acknowledgments 



We would like to thank Farron Wallace and Brian Culver 

 for help during the submersible dive survey and with fish 

 identification on the videotapes; Cindy Knudsen for video- 

 tape area-swept data collection; Kevin Redman and Colin 

 Stewart (Williamson and Associates) for geophysical data 

 analysis and mapping, and Mike Famam, and Brian Bunge 

 (USN) for geophysical data acquisition; the captains and 

 crews of the USN Agate Passage and FW Auriga for excel- 

 lent support vessel services; D. Slater, C. Ijames, and J. Lilly 

 of Delta Oceanographies for safe and efficient use of the 

 Delta submersible; Victoria O'Connell and Waldo Wakefield 

 for advice on field logistics and data collection; and Marion 

 Larkin (FV Larkin), for his insights regarding trawlable 

 and untrawlable habitat obtained from many years of fish- 

 ing experience in the study area. This study was supported 

 by the NOAA National Undersea Research Program, West 

 Coast and Polar Regions Undersea Research Center, Uni- 

 versity of Alaska Fairbanks (grant no. UAF 98-0045), the 

 Washington Department of Fish and Wildlife, and the 

 National Marine Fisheries Service. 



Literature cited 



Adams, P. B., J. L. Butler, C. H. Baxter, T. E. Laidig, K. A. Dahlin, 

 and W. W, Wakefield. 



1995, Population estimates of Pacific coast groundfishes 



from video transects and swept-area trawls. Fish. Bull. 

 93:446-455. 



Alverson, D. L. 



1951. Deep water trawling survey off the coast of Washing- 

 ton (August 27-October 19, 1951) Commercial Fisheries 

 Review 13:11. U.S. Dep. Fish. Wild. Serv., Sep. 292. 



Auster, P. J., L. L. Stewart, and H. Sprunk. 



1989. Scientific imaging with ROVs: tools and techniques. 

 Mar. Technol. Soc. J. 23(3):16-20. 



Butler, J, L., W. W Wakefield, P B. Adams, B. H. Robison, and 



C. H. Baxter 



1991. Application of line transect methods to surveying 

 demersal communities with ROVs and manned sub- 

 mersibles. Proceedings of the Oceans 91 Conference, 

 Honolulu, Hawaii, 1-3 October 1991, p. 689-696. Marine 

 Technology Soc, Columbia, MD. 

 Cailliet, G. M., A. H. Andrews, W W. Wakefield, G. Moreno, and 

 K. L. Rhodes. 



1999. Fish faunal and habitat analyses using trawls, camera 

 sleds and submersibles in benthic deep-sea habitats off cen- 

 tral California. Oceanol. Acta 22(6):579-592. 

 Caimi, F. M., J. H. Blatt, B. G. Grossman, D. Smith, J. Hooker, 



D. M. Kocak, and F. Gonzalez. 



1993. Advanced underwater laser systems for ranging, size 

 estimation, and profiling. Mar. Technol. Soc. J. 27(1):31^1. 



Cohen, J. 



1988. Statistical power analysis for the behavioral sciences, 

 2"'' ed., 567 p. L. Erlbaum Associates, Hillsdale, NJ. 

 Dark, T A., and M. E. Wilkins. 



1994. Distribution, abundance, and biological characteris- 

 tics of groundfish off the coast of Washington, Oregon, and 

 California, 1977-1986. U.S. Dep. Commer Nat. Mar. Fish. 

 Serv., NOAA Tech. Rep. NMFS 117, 73 p. 



Davis, D. L., and R. F. Tusting. 



1991. Quantitative benthic photography using laser calibra- 

 tions, 5 p. Undersea World, San Diego, CA. 

 Dixon, W. F., and F. J. Massey. 



1957. Introduction to statistical analysis, 2"'' ed., p. 244—255. 

 McGraw-Hill, New York, NY. 

 Greene, H. G., M. M. Yoklavich, R. M. Starr, V. M. O'Connell, W. 

 W. Wakefield, D. E. Sullivan, J. E. McRea, Jr, and 

 G. M. Cailliet. 



1999. A classification scheme for deep seafloor habitats. 

 Oceanol. Acta 22(6):663-678. 

 Gregory, R. S., J. T. Anderson, and E.L. Dalley. 



1997. Distribution of juvenile Atlantic cod Gadus mor- 

 hua relative to available habitat in Placentia Bay, New- 

 foundland. Northwest Atl. Fish. Organ. Sci. Counc. Stud. 

 29:3-12. 

 Krieger, K. J. 



1993. Distribution and abundance of rockfish determined 

 from a submersible and by bottom trawling. Fish. Bull. 

 91:87-96. 

 Krieger, K. J., and D. H. Ito. 



1999. Distribution and abundance of shortraker rockfish, 

 Sebastes borealis, and rougheye rockfish, S. aleutianus, 

 determined from a manned submersible. Fish. Bull. 97: 

 264-272. 

 Kulbicki, M., and L. Wantiez. 



1990. Comparison between fish bycatch from shrimp trawl- 

 net and visual censuses in St.Vincent Bay, New Caledonia. 

 Fish. Bull, 88:667-675. 



Matthews, K. R., and L. J. Richards. 



1991. Rockfish (Scorpaenidae) assemblages of trawlable 

 and untrawlable habitats off Vancouver Island, British 

 Columbia. N. Am. J. Fish. Manage. 11:312-318. 



