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Fishery Bulletin 98(3) 



evidence of fishing activities, the large sizes of individual 

 fishes further support the concept of a natural harvest 

 refuge in these areas. Although overall mean length of 

 many species was similar and in some cases smaller in 

 Soquel Canyon when compared with those on Heceta Bank 

 (Stein et al., 1992), sizes were substantially larger for the 

 large benthic species in the canyon (i.e. S. ruberrinius, S. 

 paucispinis, S. babcocki, and O. elongatus). 



Aggregations of young rockfishes were absent at any 

 depth during our surveys of Soquel Canyon, leading us to 

 conclude that although the canyon is likely a refuge for 

 adult rockfishes it does not serve as a nursery ground. In 

 contrast, from submersible observations of dense schools 

 of young-of-the-year rockfishes associated with the shal- 

 low (100 m) ridge tops of Heceta Bank, Pearcy et al. (1989) 

 suggested that rocky portions of the bank function as a 

 nursery for young rockfishes. Heceta Bank is topograph- 

 ically isolated and located about 55 km off the Oregon 

 coast; it is likely that there are no suitable nursery areas 

 for rockfishes nearby. Soquel Canyon, however, is about 15 

 km offshore in Monterey Bay, and in close proximity to 

 shallow rock outcrops, cobble fields, and kelp forests that 

 function as nursery areas for many rockfish species (Carr, 

 1991; Johnson, 1997). 



Aside from changes in population numbers and sizes, 

 marine fisheries have been identified as one of the most crit- 

 ical environmental threats to marine biodiversity (Sobel, 

 1993; Boehlert, 1996), and it has been suggested that har- 

 vest refugia may contribute to the preservation of individ- 

 ual species, genotypes, and habitats (Bohnsack and Ault, 

 1996). Overall, the benthic fish assemblages in the vari- 

 ous habitats of Soquel Canyon are relatively diverse; total 

 species richness in the canyon was 52 (20 species compris- 

 ing 90'7f of the total abundance) compared with 38 spe- 

 cies on Heceta Bank (where only 10 species contributed 

 to 909f of the abundance; Stein et al., 1992). Species diver- 

 sity, as measured by H' (Fig. 8), clearly varied among habi- 

 tats; fish assemblages associated with complex habitats of 

 rock, cobble, and mud maintained the highest diversity, 

 whereas boulder habitats had lower diversity with a few 

 dominant species. There was no clear influence of relative 

 fishing activity on species diversity in the complex rock 

 habitats of the canyon, but there was an influence on the 

 relative abundance and sizes of the species themselves. 



We conclude that some heterogeneous rocky habitats 

 of high relief interspersed with soft mud in deep water 

 of Soquel Submarine Canyon support high numbers of 

 large adult rockfishes, in particular those species impor- 

 tant to regional fisheries. These fishes are likely protected 

 from excessive harvest because these habitat characteris- 

 tics make them difficult to locate and target. These areas 

 appear to function as a natural harvest refugium, poten- 

 tially contributing new recruits to adjacent fished areas. 

 We suspect that other such isolated high-relief rock hab- 

 itat, as yet undetected or described, exists elsewhere in 

 deep water on the continental shelf and slope of the west 

 coast. The challenge now is to identify and characterize 

 these habitats and associated fish assemblages, and to 

 relate these small scale patterns to larger geographic areas 

 relevant to benthic fishery stocks. 



Acknowledgments 



This multidisciplinary study required the time and effort 

 of many people. In particular, we acknowledge the assis- 

 tance of the following people: L. Browne, M. Ledbetter, 

 G. Moreno, P. Reilly, R. Starr, P Stipa, W. Wakefield, and 

 D. Watters with field logistics and data collection; D. Cas- 

 well (Pelagos Corp. I with the side scan sonar survey; M. 

 Boyle, T Chase, C. Degnan, H. Lucky, and C. Steele (USGS) 

 with geophysical data analyses and mapping; the captains 

 and crews of the RVs Jolly Roger, Cavalier, and Pt. Sur 

 for providing suitable research platforms; J. Barry and S. 

 Etchemendy (MBARI) for logistical support; and all per- 

 sonnel from Delta Oceanographies, especially R. Slater, D. 

 Slater, and C. Ijames, whose expertise and dedication pro- 

 vided for the safe and efficient use of the research submers- 

 ible Delta. J. Mason, V. O'Connell, R. Parrish, P. Reilly, and 

 three anonymous reviewers offered valuable comments on 

 earlier drafts of this manuscript. This study was partially 

 supported by NOAA's National Undersea Research Pro- 

 gram, West Coast and Polar Regions Undersea Research 

 Center, University of Alaska Fairbanks (grant nos. UAF- 

 92-0063 and UAF-93-0036). 



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