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Fishery Bulletin 102(1) 



linkage function was applied to arrange the nekton spe- 

 cies assemblages and stations into cluster groups. The 

 cutoff level to form optimal groups within the species 

 and station dendrograms was based on several criteria: 1) 

 biological meaning; 2) significance tests of groups using 

 a multi-response permutation procedure (MRPP); and 3i 

 comparison of cutoff level MRPP results with those groups 

 obtained from one cutoff level below and above the level of 

 interest. A nonparametric procedure, MRPP compares the 

 a priori groupings from AHCA and tests the hypothesis 

 of no difference between the groups. For cluster analysis 

 of stations, indicator species analysis (ISA) was used to 

 determine nekton species strongly associated with indi- 

 vidual groups. ISA assigns indicator values to each spe- 

 cies according to relative abundance and frequency, then 

 tests the significance (Monte-Carlo permutation test) of 

 the highest species-specific indicator value assigned to a 

 particular group. 



Nonmetric multidimensional scaling (NMS; Kruskal, 

 1964) was used to ordinate sample units in species space 

 and to compare station cluster groups to environmental 

 gradients. NMS was chosen for this analysis because it is 

 robust to data that are non-normal and that have high 

 numbers of zeros. Initial runs of NMS from both cruise da- 

 tasets resulted in three-dimensional solutions. Subsequent 

 reapplication of NMS using a three-dimensional solution 

 (Sorensen distance, 400 maximum iterations, and 40 runs 

 with real data) was applied for the final ordinations. To 

 examine the environmental or station factors associated 

 with each NMS axis that may have affected the distribu- 

 tion of the dominant taxa, we correlated the NMS station 

 and species scores to a suite of environmental variables 

 including water depth, distance offshore, latitude, surface 

 temperature, surface salinity, chlorophyll-a concentration, 

 and neuston zooplankton settled volumes. Pearson and 

 Kendall correlations with each ordination axis were used 

 to measure strength and direction of individual species and 

 environmental parameters. 



Results 



Distribution of juvenile salmon and other species 



We collected a total of 18,852 nekton individuals: two ceph- 

 alopod, one agnathan, two elasmobranch, and 57 fish taxa 

 from 163 surface trawls (see Table 1 for scientific names 

 of all species). With the exception of market squid in June 

 and blue shark in August, most of the nonteleost nekton 

 occurred in only a few collections. Substantially fewer fish 

 were caught in the June cruise than in the August cruise, 

 but the diversity was much higher in the June cruise. The 

 catch in June was dominated by forage fishes such as 

 Pacific herring, surf and whitebait smelt, and juvenile rock- 

 fishes, sablefish, and flatfishes. Salmonids, mainly juvenile 

 chinook and coho salmon and steelhead, comprised a rela- 

 tively minor proportion of the catches (only 114 juvenile 

 salmonids; 1.9 % of the total). 



The August cruise was dominated by several large 

 catches of Pacific sardine (Table 1 ). Jack mackerel was the 



most common nonsalmonid caught. Many of the juvenile 

 fish taxa caught during the June cruise were absent during 

 the August cruise; those that did occur ( sablefish. rex sole) 

 were much lower in abundance. Mesopelagic fishes of the 

 family Bathylagidae and Myctophidae were collected only 

 during the August cruise, mainly because of the inclusion 

 of more offshore stations and occasional collections during 

 nondaylight hours. As in the earlier cruise, salmonids com- 

 prised a relatively minor percentage of the catch (3.19f ) but 

 were more common and abundant during this survey. 



Juvenile chinook salmon were broadly distributed lati- 

 tudinally during both cruises, but their distribution was 

 mainly restricted to nearshore stations within the 100-m 

 isobath (Fig. 3). Coho salmon juveniles were more common 

 north of Cape Blanco during both cruises and were found 

 generally farther offshore than chinook salmon juveniles 

 (Fig. 3). In contrast, steelhead juveniles were found mainly 

 south of Cape Blanco, especially in June, but their zonal 

 distribution overlapped that of coho salmon juveniles. 



Size and condition of juvenile salmon 



Fork length of yearling chinook salmon averaged 227 ±42 

 mm FL in June and 230 ±30 mm FL in August and aver- 

 aged 135 ±12 mm FL for subyearling chinook salmon in 

 August, whereas juvenile coho salmon averaged 162 ±32 

 mm FL in June and 286 ±46 mm FL in August ( Table 2 ). No 

 significant differences in fork length of juvenile chinook or 

 coho salmon north or south of Cape Blanco were evident. 



Juvenile coho salmon weighed significantly more on a 

 wet-weight basis for a given fork length in the region north 

 of Cape Blanco compared to juveniles captured south of 

 Cape Blanco (Fig. 4). This pattern was also similar and 

 significant when evaluated on a dry-weight basis (bioen- 

 ergetic growth). Although the stock composition in the two 

 regions could account for some of these differences, the 

 growth responses likely reflect habitat-specific features in 

 the region north of Cape Blanco that benefit coho salmon. 

 No difference in condition of yearling chinook salmon cap- 

 tured north or south of Cape Blanco, on either a wet- or dry- 

 weight basis, was evident (Fig. 4). Information regarding 

 size and condition of subyearling chinook salmon are not 

 presented because few subyearling chinook salmon were 

 caught in June and all but one subyearling chinook salmon 

 in August were caught in the region south of Cape Blanco, 

 OR. Insufficient subyearling chinook salmon were avail- 

 able for an analysis comparable to that done for yearling 

 chinook and coho salmon. 



Proportions of wild and hatchery coho salmon 



Most of the juvenile coho salmon caught during the plume 

 study north of Newport, Oregon, originated in hatcher- 

 ies (Table 3). In June and September 2000 we estimated 

 that wild fish comprised only W9i and 25 r < . respectively, 

 of the catch. Wild fish, however, comprised a proportion- 

 ally much higher percentage of the catch of coho salmon 

 in the GLOBEC study area in June north of Cape Blanco 

 (67$ I, and in August south of Cape Blanco (619! I, than in 

 the plume study area farther to the north. Most jacks and 



