OCEANOGRAPHIC ASSOCIATIONS OF NEUSTONIC LARVAL AND 

 JUVENILE FISHES AND DUNGENESS CRAB MEGALOPAE OFF OREGON 



Jonathan M. Shenker' 



ABSTRACT 



The larval and juvenile fishes and crabs inhabiting the neustonic zone within 50 km of the coast were 

 sampled biweekly from April through July 1984, with a Manta net (mouth 1.0 m wide x 0.7 m deep), 

 and a large neuston trawl (mouth 3.5 m wide x 1.0 m deep). The Manta net was an efficient sampler 

 for larval fishes and crabs, while the neuston trawl collected larger juvenile fishes that had rarely 

 been observed in previous studies. 



Nocturnal sampling accounted for nearly all the ichthyoneuston and zooplankton taken. Dunge- 

 ness crab megalopae were the most abundant species. Although present throughout the survey, the 

 great majority were found in very large aggregations along visible convergence zones or in association 

 with Velella velella. Discrete groups of abundant larval and juvenile fishes were found prior to 

 upwelling [Parophrys vetulu3 , Scorpaenichthys marmoratus , Hemilepidotus spinosus, Hexagrammos 

 sp., and A noplopoma fimbria ) and after its onset (Engraulis mordax and Sebastes spp.). These species 

 had distinct zonal (east-west) distribution patterns and were generally associated with, or affected by, 

 hydrographic characteristics such as convergences, upwelling, and the Columbia River plume. 



Recent studies of the ichthyoplankton off the 

 northwest coast of the United States have con- 

 tributed new information on the temporal and 

 spatial occurrences of larvae of coastal and 

 pelagic fish species (Richardson 1973; Richardson 

 and Pearcy 1977; Laroche and Richardson 1979; 

 Richardson et al. 1980; Kendall and Clark 1982a, 

 b; Clark 1984; Bates 1984; Mundy 1983; Brodeur 

 et al. 1985; Boehlert et al. 1985). These surveys 

 focused on larvae occurring below the surface 

 layer of the ocean, although concurrent neustonic 

 samples were occasionally collected (Kendall and 

 Clark 1982 a, b; Clark 1984; Bates 1984; Richard- 

 son^). Comparison of simultaneous surface and 

 subsurface samples demonstrated that many spe- 

 cies were found in both depth strata, while an 

 additional group of species was collected only 

 from the neustonic zone. Brodeur et al. (1987) 

 examined the larval fish and invertebrate compo- 

 nents of the neuston in the northeast Pacific, and 

 determined that these organisms were frequent 

 prey items of juvenile salmonids. 



^Oregon State University, College of Oceanography, Hatfield 

 Marine Science Center, Newport, OR 97365; present address: 

 University of California, Bodega Marine Laboratory, P.O. Box 

 247, Bodega Bay, CA 94923. 



2Richardson, S. L. Oregon's coastal ichthyoneuston - a pre- 

 liminary report. Unpubl. rep. Presented at American Soci- 

 ety of Ichthyologists and Herpetologists, Williamsburg, VA, 

 June 1975. 



Manuscript accepted November 1987. 

 FISHERY BULLETIN; VOL. 86, NO. 2, 1988. 



Standard plankton and neuston nets used in 

 these studies were effective in collecting the rela- 

 tively slow-moving early larvae. However, net 

 avoidance by larger larvae and juvenile stages 

 (Barkley 1972; Murphy and Clutter 1972) sug- 

 gests that use of traditional collecting gear is in- 

 appropriate for more mobile fishes. This paper 

 describes the results of a neustonic survey con- 

 ducted off the Oregon coast in the spring and sum- 

 mer of 1984 that focused on the larger ichthy- 

 oneuston. Conventional sampling gear and a new 

 net designed specifically for sampling juvenile 

 fishes were used to characterize the temporal and 

 spatial distribution patterns of both larval and 

 juvenile ichthyoneuston and Dungeness crab, 

 Cancer magister, megalopae. 



MATERIALS AND METHODS 



Sampling was conducted at approximately 

 2-wk intervals from early April through July 

 1984, on an east-west transect along the 44°40'N 

 parallel, 3 km north of Newport, OR (Fig. 1). Sta- 

 tions were located at distances of 1, 5, 10, 15, 20, 

 30, 40, and 50 km from shore. The stations were 

 occupied twice during each 24-h cruise, once dur- 

 ing the day and once at night. On one cruise (8-10 

 June), the 50 km station was occupied for 27 

 hours to assess diel variation in abundance of 

 neustonic organisms. In response to several 



299 



