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Fishery Bulletin 105(3) 



VA, diversity and evenness indices, multidimensional 

 scaling, and cluster analyses to assess the influence of 

 water depth, diel migration, temperature, and salinity 

 on the occurrence and concentration of dominant ich- 

 thyoplankton taxa and assemblages. This is the first 

 examination of diel variation in the vertical distribu- 

 tions of ichthyoplankton in the northern California 

 Current since Boehlert et al. (1985), and the only work 

 of its kind for an offshore assemblage. In addition, no 

 similar study has been conducted examining fish egg 

 diel vertical distributions and assemblages in this re- 

 gion. Results from this study are intended to supple- 

 ment previous spatial and temporal analyses of Oregon 

 coast ichthyoplankton (Richardson and Pearcy, 1977; 

 Auth and Brodeur, 2006) -analyses that were based on 

 samples collected along the Newport Hydrographic (NH) 

 line (44°39'N) over many years. 



Materials and methods 



Sampling procedures 



Ichthyoplankton samples were collected from a single 

 station (HH-05) approximately 69 km off of Heceta Head 

 (44°00'N, 125°00'W) along the central Oregon coast in 

 950 m of water. Sampling cruises in August 2000 and 

 2002 resulted in the collection of 74 depth-stratified 

 samples from nine diel hauls: five during the day and 

 four at night (Table 1). Samples collected after the begin- 

 ning of civil twilight (-0445 Pacific daylight-savings 

 time [PDT]) were considered day samples, whereas those 

 collected after the end of civil twilight (-2006 PDT) were 

 considered night samples. A multiple opening and clos- 

 ing net and environmental sensing system (MOCNESS; 

 Wiebe et al., 1976) with a 1.2-m- mouth opening and 

 333-pm mesh nets was used to collect ichthyoplankton 

 at 7-9 discrete depths. The MOCNESS was fished as 

 a continuous oblique tow from a depth of 350 m to the 

 surface at a retrieval rate of 20-30 m/min and a ship 

 speed of 1.0-1.5 m/s. Ship and retrieval speeds were 



continually adjusted during each tow so as to maintain 

 the mouth opening at a 45° angle for an effective mouth 

 opening of 1 m^ at all times. Mean water volume filtered 

 by each net was 210 m^ (standard error [SE] = 18.0), but 

 was always greater in nets from deeper strata and less 

 in nets fished in the upper 50 m. Because strata had 

 unequal depth ranges, towing times were different for 

 each stratum. Throughout the water column during each 

 tow, we recorded volume of water filtered, temperature, 

 salinity, depth of the net, length of wire out, and angle 

 of the net mouth relative to the geoid. 



Ichthyoplankton samples were preserved at sea in 

 a 10% buffered-formalin seawater solution. Fish eggs 

 and larvae from each sample were completely sorted, 

 counted, and identified to the lowest taxonomic level 

 possible in the laboratory with a dissecting micro- 

 scope. The lesser of either all larvae or a random 

 subsample of 50 individuals from each species in each 

 sample was measured to the nearest 0.1 mm standard 

 length (SL) (or notochord length for preflexon larvae) 

 using an ocular micrometer mounted on the sorting 

 microscope. 



It should also be noted that Sebastes spp. were not 

 identifiable below the generic level based on meristics 

 and pigmentation patterns (see Richardson and Pearcy 

 [1977] and Matarese et al. [1989] for a more complete 

 discussion of this problem); therefore no species-specific 

 inferences are intended for this taxon in this study. Re- 

 cent work has allowed the identification of rockfishes to 

 species level based on mitochondrial markers (Gray et 

 al., 2006), and this identification should enable future 

 researchers to discern specific patterns in larval rock- 

 fish distribution and abundance. 



Data analyses 



Fish egg and larval concentrations for each depth-strati- 

 fied sample (D,) were expressed as the number of indi- 

 viduals per 1000 m^. Weighted mean water-column 

 densities for each haul (D//„„/' were calculated according 

 to the following equation; 



