O'Connell and Carlile: Density of adult Sebastes ruberriums in eastern Gulf of Alaska 



305 



Fairweather Ground 

 Study Area 



Figure 1 



Study sites for submersible survey of yelloweye rockfish, eastern Gulf of Alaska, 1990 

 1991. 



Eleven dives were made on the Fairweather Ground 

 and nine dives were made off Sitka Sound. Eighteen 

 dives and 30 transects were completed off Sitka Sound 

 during 27 May-3 June 1991. One transect was repli- 

 cated at night to compare day and night effects. Transect 

 locations were chosen systematically to include sites 

 with a range of topographical relief. Bathymetric data 

 from the National Ocean Service Hydrographic and Ma- 

 rine Geophysical databases were used as an aid in site 

 location. 



In a typical dive in 1990, three transects were run 

 per dive with each transect lasting 30min. In 1991, 

 transect durations were extended to 1 h with two 

 transects run per dive. Deltas pilot attempted to main- 

 tain a constant speed of 0.5 kn and to remain within 

 lm of the bottom, terrain permitting. A predetermined 

 compass heading was used to maintain position along 

 a transect line. Periodic locational fixes of Delta along 

 each transect were recorded using a TRAK-POINT 

 navigation system aboard the support vessel, in com- 

 bination with a Loran (19901 or a global positioning 

 system (1991). The length of each transect (1, ) was 

 measured as the sum of distances between locational 

 fixes. 



The usual procedure for line- 

 transect sampling entails count- 

 ing objects on both sides of a 

 transect line. Due to the configu- 

 ration of the submersible, we 

 only counted fish on the right 

 side of each line. Horizontal vis- 

 ibility was usually good, 5-15 m. 

 All fish observed from the star- 

 board port were individually 

 counted and their perpendicular 

 distance from the line recorded 

 (Buckland 1985). The observer 

 used the lower and middle star- 

 board ports for viewing. An ex- 

 ternally-mounted video camera 

 was used to record both habitat 

 and audio observations of species 

 encountered and perpendicular 

 distances to fish. Yelloweye rock- 

 fish have distinct coloration dif- 

 ferences between juveniles and 

 adults, so observations of the 

 two were recorded separately, 

 and also on a back-up tape re- 

 corder. A Pisces Box data-logger 

 recorded depth of the submersible 

 and its distance from the bottom, 

 time of day, and temperature onto 

 the videotape at Is intervals. 

 These data were later downloaded onto a microcom- 

 puter spreadsheet. In addition to the video system, we 

 used a Photosea 35 mm camera with strobe to photo- 

 graph habitat and fish. Two lamps were mounted exter- 

 nally to provide lighting for the camera systems. 



Hand-held sonars were modified to obtain perpen- 

 dicular distance recordings. Two sonar models were 

 used: Manta and Scubapro. The end of each gun was 

 fit with a tight (rubber) reservoir cinched to the sonar 

 barrel. The reservoir was filled with water, and a sy- 

 ringe used to remove air bubbles. The end of the reser- 

 voir was kept damp by resting it on a wet sponge. A 

 digital read-out of the distance from the submersible 

 to its target was obtained by pressing the reservoir 

 end of the gun against the port, aiming the gun, and 

 pressing the trigger. To verify the accuracy of this 

 method, we confirmed readings by positioning a scuba 

 diver at intervals along a marked transect line. 



Six habitat categories were used: soft, gravel, cobble, 

 continuous rock, boulder, and broken rock. Other de- 

 scriptions of habitat were also recorded, including rock 

 type (e.g., basalt), invertebrate cover, and vertical re- 

 lief. To analyze depth differences, two depth intervals 

 were defined: shallow <108m, and deep >108m. 



