Fishery Bulletin 91 f I). 1993 



58N 



56N 



Materials and methods 



Study area 



This study was conducted in Au- 

 gust 1988 and 1989 on the outer 

 continental shelf in the eastern 

 Gulf of Alaska (Fig. 1). Study 

 sites extended over a 300 km 

 range to include a wide range of 

 habitats and population densities 

 of Pacific ocean perch. Dive sites 

 were selected from coordinates of 

 previous trawl and sonar stud- 

 ies: (1) Sites north of lat. 56° N 

 from studies by the Auke Bay 

 Laboratory, Alaska Fisheries Sci- 

 ence Center, National Marine 

 Fisheries Service, in July 1987 

 and 1988 using bottom trawls, 

 midwater trawls, and sonar to 

 locate high and low densities 

 of rockfish at high-relief (un- 

 trawlable) and low-relief (trawl- 

 able) sites; and (2) sites south of 

 lat. 56° N from studies by 

 Leaman & Nagtegaal ( 1986) who 

 used sonar to locate high densi- 

 ties of rockfish at untrawlable 

 sites. 



Submersible 



The submersible Delta was char- 

 tered for all dives. This battery- 

 powered two-man submersible is 

 4.7 m long, dives to 365 m, and 

 travels 2-6 km/h for 2-4 h. It is 

 equipped with ten 150 W exter- 

 nal halogen lights, internal and 

 external video cameras, a 35 mm 

 external camera, magnetic compass, directional gyro 

 compass, underwater telephone, and transponder that 

 allowed tracking of the submersible from the surface 

 vessel Wm. A. McGaw. 



Submersible transects were charted from the 

 Wm. A. McGaw. The surface vessel tracked the sub- 

 mersible and recorded LORAN fixes at the beginning 

 and end of a transect, and every 5-15 min during a 

 transect. In 1988, a transect consisted of a single com- 

 pass heading followed for 60 min. The transect pattern 

 was changed in 1989 to facilitate trawl comparisons, 

 and consisted of four parallel compass headings fol- 

 lowed for 15 min each. The four parallel transects were 

 each separated by 5 min of travel. 



CAPE SPENCER 



DIXON ENTRANCE 



140W 



Locations of submers 

 1989 (•). 



136W 



132W 



Figure 1 



ble dive sites in the eastern Gulf of Alaska, 1988 ▲ and 



A pilot and one of the two observers were aboard 

 the submersible on each dive. The pilot maintained 

 the submersible within 0.5 m of bottom at 3-4 km/h 

 while the observer made observations through a star- 

 board porthole; external cameras were mounted on the 

 starboard side, and the side portholes provided the 

 widest range of view. Observations included rockfish 

 species identification, number, size, grouping behavior, 

 orientation, position relative to the sea bottom, habi- 

 tat affiliations, and reactions to the submersible. Addi- 

 tional observations included identification and enu- 

 meration of other fish species, and estimates of current 

 direction and velocity based on the bending of sea pens 

 and drift of silt. The pilot sat above the observer in a 



