Yoklavich et al : Habitat associations of deep water rockfishes 



629 



sites for fish and habitat surveys. The bathymetry 

 indicated that Sequel Canyon is steeper and more 

 rugged than previously interpreted from NOAA's 

 Seabeam data. From the 3.5-kHz bottom profiles 

 we identified large slumps along both walls and 

 in the axis of the canyon. These areas had a hum- 

 mocky surface with little or no sediment cover 

 and were bounded by sharp relief on either side 

 (e.g. Fig. IC); these characteristics indicated likely 

 rockfish habitat. 



Five study sites were defined ( Fig. 2 ) on the basis 

 of a series of side-scan images identified along the 

 canyon walls. These images were interpreted as 

 rock outcrops representing approximately 35 ha of 

 the total area surveyed in Soquel Canyon. Area of 

 rock outcrop in the five study sites ranged from 1.4 

 ha of isolated rocks in about 200 m water depth 

 at site 5 to 19.6 ha of extensive rock in 90-350 

 m water depth at site 3. We considered these 

 estimates to accurately represent the amount of 

 exposed outcroppings within our study area. 



From submersible observations we verified our 

 interpretation of these reflectors as well-bedded 

 rock outcrops of various resistance, lithologies, and 

 bottom morphology (e.g.. Fig. 3, A and B). Cres- 

 cent-shaped slump scarps were imaged along the 

 upper walls of the canyon, and extensive rockfalls 

 comprising large (meters in diameter) angular 

 to sub-rounded (having rounded corners but not 

 spherical) blocks and smaller boulders (0.25-1.0 

 m diameter) were concentrated at the base and in 

 the axis. Well-layered, friable sedimentary rocks 

 were differentially eroded into overhangs (>90°), 

 crevices, and caves. These rocks occurred as iso- 

 lated outcrops (Fig. 3A), and as more extensive 

 rock exposures (Fig. 3C) interspersed with soft 

 mud along very steep walls from at least 150 to 

 330 m water depth. 



36°50' 



■122° -12r59' •12r58' -12r57' 



Figure 2 



Schematic map constructed from interpretations of side-scan sono- 

 gi'aphs of rock outcrops (stippled areas) in Soquel Canyon. Submers- 

 ible track lines during quantitative transects are mapped (lines), and 

 tlie five main study sites are labeled. 



Fish and habitat associations 



Thirty-three submersible dives were made at five sites to 

 assess rockfish assemblages and habitat associations in 

 Soquel Canyon. We counted 6208 nonschooling fishes, rep- 

 resenting at least 52 species (see Table 1 for both "scientific 

 and common names), from 83 10-min strip transects that 

 covered an estimated 33,754 m-. Rockfishes represented 

 779f of the total number of individuals, and included a 

 minimum of 24 species. The 20 most abundant taxa (QOVf of 

 total abundance) included 4540 individual rockfishes rep- 

 resenting at least 12 species. Nonrockfish species were rep- 

 resented primarily by six species, which comprised 17.2'7f 

 of the total abundance: Microstomiis pacificus, Ophiodon 

 elongatus, Sebastolobus alascanus. Eptatretus stouti, Mer- 

 luccius productus. and an unidentified species (or possibly 

 a complex of species) in the family Agonidae (most likely 

 Xeneretmiis spp.). 



Major rockfish habitat types in Soquel Canyon included 

 vertical cliffs with joints, fractures, and overhangs, small 

 and large ledges, talus slopes, cobble, and boulder fields 



of exposed sandstone and mudstone interspersed with soft 

 mud. Most rockfishes of all sizes were associated with 

 some structure, including invertebrates such as crinoids, 

 sea anemones and sponges, debris, and simple shallow 

 depressions in the mud. 



Cluster analysis (Fig. 4), which grouped standardized 

 abundance of each fish species (number per 100 m'-') by 

 bottom type, resulted in six habitat guilds. Most distinct 

 were guild I. having small species found on uniformly mud 

 bottom of flat or low relief, dominated by S. saxicola (42'7f ) 

 and to a lesser degree by M. pacificus. Agonidae, and S. 

 alascanus. and guild VI, a rock-boulder habitat of low-to- 

 high relief largely at 75-175 m depth, dominated by S. wil- 

 soni (429^ ), and with less representation by S. paucispinis. 

 S. pinniger, and S. chlorostictus. 



The remaining four habitat guilds (guilds II. Ill, IV, 

 and V; Fig. 4) were grouped two each into two clusters at 

 Euclidian distances 0.058 and 0.063. Guilds II and III were 

 ' characterized by combinations of mud and large-grain cob- 

 bles and pebbles that were of mostly flat or low relief (72'^ 

 occurrence). These assemblages were relatively diverse, 



