548 



Fishery Bulletin 101(3) 



Figure 3 



Schematic diagram of the study area divided into 800 m by 800 m sample units and 

 classified a priori as untrawlable (shaded) and trawlable (unshaded) habitat types. 

 The numbered sites represent the eight sample units selected at random from each 

 habitat type, which were numbered sequentially for the cruise plan. 



was inferred from locations with good hauls and unevent- 

 ful chain drags; untrawlable bottom was inferred from bad 

 hauls, short hauls, skipped hauls, and chain snags. On the 

 side-scan mosaic layer, untrawlable locations were typi- 

 cally darker than surrounding areas, indicating boulder 

 fields or hard, rocky bottom. Such areas often showed high 

 bottom relief as evidenced by shadows on the mosaic, and 

 bathymetric contours that indicated abrupt topographic 

 features, such as sharp ridges or pinnacles. A sample unit 

 was classified as untrawlable habitat when 1 ) NMFS sur- 

 vey events within the unit indicated rough bottom, or 2) the 

 mosaic or bathymetric layers of the unit resembled other 

 units that were classified as untrawlable, or 3) a sample 

 unit of unknown habitat type was completely surrounded 

 by untrawlable habitat. A sample unit was classified as 

 trawlable habitat when 1 ) NMFS survey events indicated 

 successful trawl tows in the unit or 2) when the mosaic or 

 bathymetric layers of the unit resembled other units that 

 were classified as trawlable. Our trawlable and untraw- 

 lable habitat assignments agreed well with information 

 obtained from knowledgeable fishermen. Each sampling 

 unit in the entire mapped area was examined visually in 

 detail according to the above procedure and was classified 

 accordingly as trawlable or untrawlable habitat. 



We selected the eastern portion of the mapped area 

 for the submersible survey (Figs. 2 and 3t. Our focus was 

 restricted to this section to minimize the difference in bot- 

 tom depths between the trawlable and untrawlable areas 

 as a factor, and for logistical convenience to complete the 

 most submersible dives possible within our survey budget. 

 Because the 800 m by 800 m sampling units were too large 

 to be surveyed in their entirety, we sampled using the strip 

 transect method at each location. Logistically, this was 

 accomplished by conducting 2-3 ncmoverlapping passes 

 across the sampling unit and by pooling these segments 

 together to form a single transect for analysis. 



Submersible survey 



We used the submersible Delta to conduct the fish survey 

 with the support vessel FV Auriga in July of 1998. The 



Delta is 4.7 m long, accommodates one observer and one 

 pilot, and has a maximum operating depth of 365 m. An 

 acoustic Trak- Point system was used with differential GPS 

 and WinFrog navigational software (Thales GeoSolutions 

 (Pacific), San Diego, CA) to track and log the position of 

 the submersible from the support vessel. The Delta was 

 equipped with halogen lights, external video cameras, an 

 external Photosea 35-mm camera with strobe, and a Pisces 

 Box data-logging system that recorded 1 ) the time of day, 2) 

 depth of the submersible, 3) its distance from the bottom, 

 and 4) sea temperature at 5-second intervals. Strip tran- 

 sects were conducted 1-2 m off bottom at a cruising speed 

 of approximately 2.5 km/h. All dives were made during 

 daylight hours. 



To quantify fish density, each strip transect was docu- 

 mented with a high 8-mm video camera mounted exter- 

 nally on the bow of the Delta, and pointed forward. The 

 camera was equipped with two parallel lasers, spaced 20 

 cm apart, which were used for estimating the area that was 

 swept. The scientific observer onboard the Delta verbally 

 annotated the videotape record with observations taken 

 through the submersible viewing ports, to help identify fish 

 and interpret the videotapes during subsequent analysis. 

 The high 8-mm tapes were copied to S-VHS format to 

 facilitate videotape analysis. The transect area that was 

 swept (m-) was estimated as the product of average area 

 swept per second (m-/min) and the total transect duration 

 in minutes (see Appendix I for details). The average area 

 that was swept per second (m'^/min) was determined from 

 a set of 30-second samples randomly selected from the 

 transect. On average, approximately 29'7r of each transect 

 was subsarapled in this manner. Bottom habitat type was 

 also visually characterized for the transect subsamples. 

 Following the method of Stein et al. (1992) and using the 

 classification criteria developed by Greene et al. ( 19991, we 

 categorized bottom microhabitat type (mud, pebble, cobble, 

 boulders, and rock ridge) as primary (at least 50% of the 

 area viewed) or as secondary (>20% of the area viewed). 

 The bottom-type measurements observed directly in the 

 transect subsamples were expanded to estimate microhabi- 

 tat coverage for each transect. 



