BARNETT ET AL.: DISTRIBUTION OF ICHTHYOPLANKTON OFF SAN ONOFRE, CALIF. 



ed among the 10 most abundant in any of the 5 sam- 

 pling blocks. Fourteen taxa showed significant 

 differences among the strata which were resolved 

 into spatial patterns (Table 1, Fig. 3). Taxa with cen- 

 ters of abundance nearest shore tended to be concen- 

 trated in either the epibenthic or the neustonic layer. 

 Of the five epibenthic taxa, four (Gibbonsia Type A, 

 Seriphuspolitus,Gobiesox rhessodon, and Goby Type 

 A [consisting of Ilypus gilberti and Quietulay-cauda]; 

 Fig. 3A-D) had centers of abundance within 2 km of 

 shore. The fifth, Genyonemus lineotus, was most 

 abundant out to about 4 km (Fig. 3E). Atherinidae 

 (Fig. 3F) were neustonic and most abundant within 2 

 km of shore. Hypsopsetta guttulata (Fig. 3G) was 

 abundant in the neustonic and midwater layers out to 

 2 km. It had the most nearshore pattern of any mid- 

 water taxon. Hypsoblennius spp. were concentrated 

 in the neustonic and midwater layers out to about 5 

 km and in the neustonic layer beyond 5 km from 

 shore (Fig. 3H). 



The remaining six taxa with discernible patterns 

 were all most concentrated in midwater. The centers 

 of abundance of Engraulis mordax and Paralichthys 

 californicus (Fig. 31, J) extended from 2 to ~5 km 

 from shore, while those of Pleuronichthys verticalis, 

 Citharichthys spp., Sebostes spp., and Stenobra- 

 chius leucopsarus appeared to extend seaward of the 

 sampling area (Fig. 3K-N). 



Five taxa (Chromis punctipinnis, Parolobrax spp., 

 Porophtys vetulus, Peprilus simillimus, and Pleuro- 

 nichthys ritteri) were not shown to have patterns by 

 this analysis. 



Vertical Migration 



Because the basic study plan called for nighttime 

 sampling, the patterns described would pertain to 

 nighttime distributions. The preliminary study found 

 little evidence of daily vertical migration; neverthe- 

 less, we conducted a further small study of vertical 

 migration to test whether the vertical component of 

 the patterns remained the same during daylight 

 hours. The study was conducted at two inshore 

 locations (Fig. 1). A description of the vertical study 

 is given in the Appendix. 



There was no indication of vertical migration at the 

 8 m station, but at the 13 m station two taxa, Hyp- 

 soblennius spp. and Paralichthys californicus, 

 showed significant (P < 0.05) vertical shifts 

 downward in the water column during the day (Fig. 

 4). The low probability (0.055) of the F value for 

 Gobiesox rhcssodon (App. Table 2), though higher 

 than the customary rejection level of 0.05, suggests a 

 daily change in vertical distribution. The data indi- 



cate this species may, like Paraclinus integripinnis in 

 the preliminary study, tend to migrate or settle from 

 midwater into the epibenthic layer at night. 



Onshore-Offshore Abundance 



The analysis of cross-shelf pattern assumes that lar- 

 vae are uniformly distributed throughout each mid 

 water stratum, an assumption that becomes in- 

 creasingly untenable with depth of stratum. Layering 

 of ichthyoplankton within the midwater zone will 

 cause an apparent decrease in density in the seaward 

 blocks, as more of the volume used in the density 

 calculations comes from deeper waters where a 

 species may be rare. To eliminate bias in the cross- 

 shelf patterns due to inclusion of noncontributing 

 depths in the density calculations, one-dimensional 

 abundances were calculated based on the estimated 

 number of larvae under a unit ( 1 00 m 2 ) of sea surface 

 in each offshore block 



jV 



3 



z 



rtjdi 



where n = larvae/ 1 00 m- 1 in stratum i and d — vertical 

 thickness of stratum i in meters (0.16 m, neustonic; 

 0.50 m, epibenthic; depth of water column — 1 m, 

 midwater). 



The one-dimensional patterns, which emphasize 

 numbers of larvae (Table 2), provide a useful com- 

 parison to the two-dimensional patterns which 

 emphasize larval density (Table 1, Fig. 3). All 

 epibenthic and neustonic taxa had similar onshore- 

 offshore centers of abundance as determined by both 

 methods. This was expected, since their cross-shelf 

 abundance patterns were essentially one- 

 dimensional. Gibbonsia Type A, Seriphus politus, 

 Gobiesox rhessodon, Goby Type A, and Atherinidae, 

 all with abundance centers within 2 km of shore in the 

 two-dimensional analysis (Fig. 3), likewise had one- 

 dimensional maxima shoreward of 2 km. With the 

 exception of S. politus, these taxa were less than half 

 as abundant beyond 2 km. Genyonemus lineatus, 

 most concentrated in the epibenthic layer within 

 about 4 km of shore, had a one-dimensional max- 

 imum at 2-4 km but remained abundant (>V£ max- 

 imum) out to ~5 km. 



Of the eight midwater taxa, only two had one- 

 dimensional patterns which differed from their two- 

 dimensional patterns Engraulis mordax appeared 

 more abundant farther offshore in one dimension (cf. 

 Table 2 and Fig. 31). The steady increase in abun- 

 dance of E. mordax with distance from shore is at 

 odds with its two-dimensional pattern (Fig. 31) and 



103 



