FISHERY Bl'LLETIN: VOL. 76, NO. 4 



500 



D 1 



D 2 



N 1,2 



D 3 



N 3.4 



D 4 



Figure 9. — Vertical distribution ofChauliodus macouni at Sta- 

 tion Q, 1974. Scale represents 25 individuals/10'* m^. Sequence of 

 vertical series as in Figure 3B. 



Table 8. — Abundance fnumber'10,000 m^) of Stenohrachius 

 leucopsarus and Diaphus thcta in three series of half-hour sam- 

 ples collected in horizontal tows at 40-m depth during one night 

 at Station Q in the northeastern Pacific. Sampling commenced 

 after the migratory scattering layer had merged with the surface 

 reverberation and terminated after the scattering layer had 

 descended below the surface reverberation (0425). Time is when 

 net was opened. 



(Table 4), indicating that the distribution of this 

 fish probably extended below the normal limit of 

 sampling in the routine vertical series. At Station 

 Q, specimens of C. macouni ranged from 29 to 189 

 mm SL. Very large fish ( >100 mm) were usually 

 captured at night in the deepest samples, but for 

 fish <100 mm there was no clear trend of size- 

 dependent variation in vertical distribution. 



Other fish species (Table 2) occurred sporadi- 

 cally in the samples and were caught primarily at 

 night: the only daytime catches were below 300 m 

 (e.g., Lampanyctus ritteri in Table 4). Included in 

 the category "Others" in Table 2 were members of 

 the families Bathylagidae, Gonostomatidae, 

 Melamphaeidae, Opisthoproctidae, Paralepidi- 

 dae, and Scopelarchidae. 



Variability in Abundance of 

 Myctophids in Replicated Samples 



With a few exceptions, the estimates of abun- 

 dance of myctophids integrated over the water 

 column sampled did not vary by more than a factor 

 of 4 between vertical series within cruises (Table 

 3). At Station Q, three series of half-hour horizon- 

 tal hauls were made at 40 m throughout one night 

 (Table 8). Excluding the sample (0430) collected 

 after the scattering layer had descended, concen- 

 trations of S. leucopsarus varied by a factor of 

 about 4, those for D. theta by a factor of about 9. For 

 both species, there was a significant trend (P = 

 0.05, run test, Tate and Clelland 1957) toward 

 increased abundance during the night, and their 

 abundances were strongly correlated (rank differ- 

 ence correlation coefficient 0.74, P ~ 0.01, Tate 

 and Clelland 1957). Myctophids were abundant in 

 the surface layer until the migratory scattering 

 layer descended. 



Estimated Abundance and 

 Standing Stock of Fishes 



Our data for mean abundance of all fishes cap- 

 tured for the 3 yr ranged from 0.78 to 1.61/m^ for 

 the water column extending to between 385 and 

 460 m (Table 9). The three most abundant species 

 of myctophids combined accounted for 77-859r by 

 number of all fish collected. There was no consis- 

 tent difference between day and night estimates of 

 concentrations offish. 



Equations for the regression of dry body weight 

 on body length (Table 10) were used in conjunction 

 with the lengths and abundance offish from each 

 sample to calculate the population standing stocks 

 of S. leucopsarus, D. theta, and P. thompsoni for 



Table 9. — Estimated mean abundance and standing stock of 

 mesopelagic fishes at Stations P and Q in the eastern subarctic 

 Pacific Ocean. Myctophids includes only the three most abun- 

 dant species, Stenohrachius leucopsarus, Diaphus theta, and 

 Protomyctnphum thompsoni . Estimated mean abundance and 

 standing stock are based on average of all day and night vertical 

 series; values in parentheses are means for night vertical series 

 only. 



Table 10. — Equations for the regression of dry body weight, W 

 (grams), on body length, L (centimeters), for three species of 

 myctophids. 



762 



