RICHARDSON: LARVAL FISHES OFF OREGON 



occurring deeper. Myctophids, scorpaenids, 

 bathylagids, and cyclopterids had a much higher 

 frequency of occurrence in deep tows. 



Species Composition 



Positive samples (207 out of 287) yielded 

 28,489 fish larvae from all deep tows (Table 1). 

 Of the 40 taxa, 28 were identified to species and 

 6 to genus. Twenty-two families were repre- 

 sented. 



Ninety-eight percent of all larvae (individ- 

 uals/1,000 m^) in combined samples were in 

 four families: 



68.4% Engraulidae in 29.6% of all samples 

 25.3% Myctophidae in 96.9% of all samples 

 4.2% Scorpaenidae in 34.1% of all samples 

 0.4% Osmeridae in 4.2% of all samples 



Other families represented in over 5% of the 

 samples were: Pleuronectidae, 19.5% of all 

 samples; Cyclopteridae, 15.7% ; Bathylagidae, 

 14.3% ;Bothidae, 13.6% ;Chauliodontidae,9.8% ; 

 and Paralepididae, 7.3% . 



During the sampling period, abundance of 

 larvae per 1,000 m^ estimated from combined 

 samples (Table 1) peaked in July-August and 

 was lowest in October. Results from the MN 

 indicated greatest abundance in May and 

 June. The MN collected many small E. mordax 

 in June and S. leucopsarus in May and June 

 (Table 5). By the July-August cruise, larvae of 

 these two species were still abundant, however 

 the larger specimens were not as readily cap- 

 tured by the more slowly hauled MN. 



Dominance 



Dominant taxa for each type of gear during 

 each cruise were determined by a ranking sys- 

 tem (biological index, BI) modified from Fager 

 (1957). By this method, the most numerous 

 species in each sample is given 5 points, the next 

 4, etc. Scores for each taxa are summed for all 

 positive samples for each cruise and each type of 

 gear and divided by the total number of samples 

 (positive and negative) on that cruise by that 

 gear. Both abundance and frequency of occur- 

 rence are considered in this determination. 



BI values from each type of gear and all gear 



combined for combined cruises indicated the 

 same four taxa were most dominant, E. mordax, 

 S. leucopsarus, T. creiiulans, and Sebastes spp., 

 although not necessarily in that order (Table 6). 

 S. leucopsarus had a higher BI value than E. 

 mordax in MN samples and combined samples. 

 Sebastes spp. ranked above T. croiularis in 

 IKMT samples. A drop in BI value, indicating a 

 lower degree of dominance, existed between the 

 fourth and fifth highest ranked taxa for each 

 gear, particularly MN and IKMT, and com- 

 bined gears. Only the bongos agreed with taxa 

 shown to be in the top 11 by combined gears, 

 although not in the same order. 



Some of the discrepancy among gear types 

 may be explained by size of organisms captured. 

 The high BI values of osmerids; rex sole, Glypto- 

 cephalus zachirus; and Lestidium ringens in 

 IKMT samples was in part due to the large size 

 of most specimens which would avoid the smaller 

 types of gear. None of these taxa was captured 

 by the MN and generally few were taken by the 

 bongos. Some of the higher ranked taxa from 

 bongo and MN samples. Pacific vipei-fish, Cha- 

 uliodus macouni, and Bathylagus ocliotensis, 

 are very slender forms which may escape readily 

 through the IKMT net. Specimens of pinpoint 

 lampfish, Lampanyctus regalis, taken by the 

 MN in June were small, mostly 3 to 4 mm, and 

 may have been extruded out of the bongos be- 

 cause of the fast tow speed. BI values indicate 

 that the IKMT captured more large organisms, 

 the MN captured more small or slender forms, 

 and the bongos were intermediate. 



The most dominant (BI) taxa in May (all gear 

 combined) were Sebastes spp. and S. leucop- 

 sarus; in June, S. leucopsarus and T. crenularis; 

 in July-August, E. mordax and S. leucopsarus; 

 in August and September, S. leucopsaims, E. 

 mordax, T. crenularis; and in October, Sebastes 

 spp. and E. mordax (Table 7). All had a 

 BI > 1. All taxa below these had a BI< 1, usually 

 with a considerable drop in BI value from the 

 most dominant taxa. S. leucopsarus, T. crenu- 

 laris, and Sebastes spp. consistently ranked in 

 the top five from May through September (Table 

 5). E. mordax became the most dominant species 

 in July-August and remained dominant through 

 October. 



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