Soft substrate fishes included all other taxa listed. During ROV 

 deployment #1 in 1987, agonids appeared to be the most common 

 taxon occurring on all soft bottom. During ROV #2, although 

 agonids were still common, zoarcids (probably L^ cortezianus ) 

 were relatively more common. Individual Sebastolobus alascanus , 

 which appear to be quite sedentary, occurred in shallow pits. 

 Whether the fish excavate these or simply take advantage of 

 existing irregularities is unknown. 



DISCUSSION AND CONCLUSIONS 



The reason for dense invertebrate aggregations we observed 

 is unknown. Food concentration, reproductive behavior, or 

 gregarious interactions could be the causes of these. Although 

 there was no apparent environmental difference where box crabs, 

 ophiuroids, and echinoids were clumped, currents or eddies may 

 have caused concentrations of particulate organic materials in 

 the bottom water layer or at the sediment-water interface. 

 Reproductive pheromones released in the water by sexually mature 

 individuals could be the cue for clumping behavior. 



Our results demonstrate that upper subduction zone venting 

 can have a significant effect on distributions and occurrences of 

 benthic invertebrates and shelf fishes. Nehalem Bank is a soft- 

 bottom bank similar to others off Oregon. However, the extensive 

 past venting there has produced rock outcrops of a variety of 

 morphologies in the midst of a more or less soft bottom region. 

 These outcrops are of three basic types: donuts (chimneys), 

 jumbles, and flat slabs (Kulm and Suess, submitted). The rock 

 jumbles clearly provided a different habitat used by rockfishes 

 and encrusting epifauna in large numbers. 



The fish (typically sharpchin rockfish and rosethorn 

 rockfish) often extended their ranges out over the nearby mud. 

 The donuts and flat slabs (which typically appeared as small 

 ledges protruding from the sediment) harbored few fish. If any 

 fish were present, there were only one or two sheltering 

 alongside the rock. These results are not unexpected. They are 

 similar to the fish distributions described by Pearcy et al . (in 

 press) from Heceta Bank, Oregon. In both situations an isolated 

 patch of hard substrate can attract and apparently maintain an 

 isolated group of rockfish. 



However, the widespread occurrence of calcium carbonate 

 slabs and chimneys, a product of active vents in the past, has 

 probably changed the patterns of occurrence of a variety of fish 

 species, primarily rockfishes, and hard substrate invertebrate 

 epifauna. Active liquid and gas venting at shallow depths may be 

 occurring now elsewhere on the Oregon shelf. If this is the 

 case, venting could have additional effects on the structure and 



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