313 



Abstract — We examined the diel ver- 

 tical distribution, concentration, and 

 community structure of ichthyoplank- 

 ton from a single station 69 km off the 

 central Oregon coast in the northeast 

 Pacific Ocean. The 74 depth-stratified 

 samples yielded 1571 fish larvae from 

 20 taxa, representing 11 families, and 

 128 fish eggs from 11 taxa within nine 

 families. Dominant larval taxa were 

 Sebastes spp. (rockfishes), Stenobra- 

 chius leucopsarus (northern lampfish), 

 Tarletonbeania crenularis (blue lan- 

 ternfish), and Lyopsetta exilis (slender 

 sole), and the dominant egg taxa were 

 Sardinops sagax (Pacific sardine), 

 Icichthys tockingtoni (medusafish), 

 and Chauliodus macouni (Pacific 

 viperfish). Larval concentrations 

 generally increased from the surface 

 to 50 m, then decreased with depth. 

 Larval concentrations were higher at 

 night than during the day, and there 

 was evidence of larval diel vertical 

 migration. Depth stratum was the 

 most important factor explaining 

 variability in larval and egg con- 

 centrations. 



Diel variation in vertical distribution 



of an offshore ichthyoplankton community 



off the Oregon coast 



Toby D. Auth (contact author)' 

 Richard D. Brodeur^ 

 Kathleen M. Fisher^ 



Email address lor T, D, Auth: toby.authiSnoaagov 



' Cooperative Institute for Marine Resources Studies 

 Oregon State University, Hatfield Marine Science Center 

 2030 Marine Science Dnve 

 Newport, Oregon 97365 



^ Northwest Fishenes Science Center 

 NOAA Fisheries, Hatfield Marine Science Center 

 2030 Marine Science Drive 

 Newport, Oregon 97365 



^ National Ocean Service 

 NOAA, The Center for Operational Oceanographic Products and Services 

 1305 East-West Highway 

 Silver Spnng, Maryland 20910 



Manuscript submitted 15 August 2006 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 25 October 2006 by the Scientific Editor. 



Fish. Bull. 105:313-326(2007) 



Early life stages of fishes have long 

 been studied to gain insight into 

 adult spawning locations and bio- 

 mass (Hunter et al., 1993), trophic 

 interactions between fish larvae and 

 their surrounding zooplankton and 

 piscivore communities (Hunter and 

 Kimbrell, 1980), and the relationship 

 between early life processes and sub- 

 sequent recruitment success (Brad- 

 ford. 1992; Houde, 1997). Knowledge 

 of the diel vertical distribution offish 

 eggs and larvae is critical to under- 

 standing the structure and ecological 

 interactions of ichthyoplankton com- 

 munities, and for the development of 

 appropriate sampling strategies ( Gray, 

 1998). Furthermore, variation in the 

 diel vertical distributions of different 

 larval fish taxa and their associated 

 predator and prey fields may influence 

 the occurrence, degree, and timing of 

 competitive, trophic, and environmen- 

 tal interactions (Neilson and Perry, 

 1990). In addition, an understanding 

 of the differences in ichthyoplankton 

 depth distribution and concentration 

 is essential for accurate quantitative 

 estimates of whole water-column abun- 

 dance when the depth to be sampled 

 is limited (Ahlstrom, 1959; Comyns 

 and Lyczkowski-Shultz, 2004). Also, 

 because in many surveys sampling is 



conducted during both night and day, 

 it is often necessary to separate diel 

 (e.g., visual net avoidance by larvae 

 during daylight conditions) and depth 

 effects when analyzing variable ich- 

 thyoplankton distributions (Ahlstrom, 

 1959; Boehlert et al., 1985). 



Larvae of many fish species are 

 known to perform diel vertical mi- 

 grations (Ahlstrom, 1959; Neilson 

 and Perry, 1990). These migrations 

 can follow several different patterns; 

 the most common is movement into 

 the upper water column during night 

 and into deeper water during the day 

 (Shoji et al., 1999; Tsukamoto et al., 

 2001). However, the reverse pattern 

 has also been observed (Lyczkowski- 

 Shultz and Steen, 1991; Brodeur and 

 Rugen, 1994). In addition, some fish 

 larvae have been found to disperse 

 during the night and aggregate dur- 

 ing the day (Brewer and Kleppel, 

 1986; Munk et al., 1989). 



In the present study the diel varia- 

 tion in vertical distributions and con- 

 centrations of fish eggs and larvae 

 was examined by repeatedly sampling 

 fish eggs and larvae from a single off- 

 shore station off the central Oregon 

 coast in the northeast Pacific Ocean. 

 We used univariate and multivariate 

 statistical techniques such as ANO- 



