FROST and McCRONE; MESOPELAGIC FISHES IN THE EASTERN SUBARCTIC' PACIFIC 



Analysis of Samples 



All organisms in the nekton samples were 

 counted. Fish were identified from descriptions in 

 Hart (1973) and Wisner (19761. The standard 

 length (SL) (distance from the tip of the snout to 

 the end of the vertebral column) of each fish was 

 measured to the nearest millimeter. Among the 

 invertebrates collected in nekton samples, only 

 euphausiids and decapod shrimps were consis- 

 tently captured in substantial numbers. The 

 numbers offish and shrimp were standardized to 

 number per 10,000 m-' of water. 



Myctophid fish, preserved for about 3 yr, were 

 sorted from samples for determination of body 

 length and dry body weight. Intact, undamaged 

 specimens were dried to constant weight at 65°C 

 on glass slides in a drying oven. Drying usually 

 took 3-4 days, but up to 10 days for some of the 

 largest fish. Dried fish were weighed to the nearest 

 milligram. The relationship between standard 

 body length and dry body weight for each species of 

 myctophid was determined by linear regression 

 analysis of logarithmically transformed mea- 

 surements. 



RESULTS 



The vertical series of nekton samples collected 

 at Stations P and Q yielded nine species of myc- 

 tophids, one abundant species of chauliodontid, 

 and one relatively raremelanostomiatid. All other 

 families combined made up only 2-Wi of the total 

 catch by number (Table 2). In addition to fish, the 



samples contained considerable numbers of 

 euphausiids and decapod shrimps. Other inver- 

 tebrate groups, such as siphonophores and squids, 

 were only sporadically captured. The more com- 

 mon fishes had similar relative abundances at the 

 two stations. More than 80^- of the myctophids 

 consisted of three species (Stenobrachius leucop- 

 sarus, Protoniyctophum thompsuni , and Diaphus 

 thetu ) whose vertical distributions were generally 

 well bracketed by the sampling. The other species 

 of myctophids were either rare or appeared to be 

 distributed below the usual range of sampling; 

 therefore, emphasis in this study was placed on 

 the above three, abundant, relatively shallowly 

 distributed species. 



Vertical Distribution of Fish 



The most abundant fish in our samples was S. 

 leucopsarus. Its only congener, S. nannuchir. was 

 rarer (Table 2). As discussed later, with the excep- 

 tion of the very deep vertical series ( 782-440 m ) in 

 1975, only small specimens ( <35 mm) of S. nan- 

 nochir occurred in the vertical series. The fish 

 caught at Station P in 1973 were in such poor 

 condition that it was not possible to discriminate 

 the smaller specimens of the two species of Steno- 

 brachius. However, there is evidence (presented 

 below) that S. nannochir was extremely rare at 

 Station P in 1973, much rarer than at Station Q or 

 Station P in 1975 (Table 2). Redesign of the cod 

 ends, after the 1973 cruise, provided us with good 

 specimens which permitted discrimination of the 

 two congeners. 



T.ABLE 2. — Composition of the total fish catch in vertical series of nekton samples in the 

 northeastern Pacific. Data for each station combine all vertical series. 



Family and species 



Myctophldae: 

 Stenobrachius leucopsarus 

 S nannochir 



Protomyctophum thompsoni 

 Diaphus Iheta 

 Tarletonbeania crenulans 

 Lampanyclus regalis 

 L. ritteri 



Notoscopelus japonicus 

 Symbolophorus californiense 



Chauliodontidae: 

 Chauliodus macouni 



Melanostomiatidae: 

 Tactostoma macropus 



Others 



Totals 



57 



1.129 



5.0 



147 



6.4 



2.288 



84 



935 



9.0 



'Due to the poor condition of the fish caught at Station Pin 1973. it was impossible to discriminate the smaller 

 specimens of the two species of Stenobrachius It is possible that some of the fish listed here as S leucopsarus 

 •Mere in fact S, nannochir. but for reasons described in the text, we do not believe this to be the case. 



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