LOEB: VERTICAL DISTRIBUTION OF LARVAL FISHES 



versity at 25-50 m, possibly related to the bottom 

 of the mixed layer. A distinct change in species 

 composition and relative abundances occurred 

 below 75 m. This involved a shift from dominance 

 by Cyclothone alba, Vinciguerria nimbaria, and 

 lampanyctine myctophids to other gonostomatid 

 species, myctophine myctophids, and other 

 families. Ahlstrom (1959) previously had found 

 groups of species (in the California Current) to be 

 either predominantly within the mixed layer and 

 upper thermocline or mostly within or below the 

 thermocline. 



None of the abundant larvae were taken only in 

 one 25 m interval, and most were found over at 

 least a 75 m depth range. However, almost all 

 species taken in the upper 100 m had distinct 

 maxima of catch frequency and abundance within 

 one of the 25 m depth intervals sampled; for many 

 species, despite high catch variability due to 

 patchiness, the abundances in replicate tows 

 within this interval were significantly higher 

 than in any other interval. Almost twice as many 

 larvae and half again as many kinds were found in 

 100-225 m samples as in 100-350 m samples, indi- 

 cating that most deeper species may be distributed 

 above 225 m. 



Significant changes were found in cumulative 

 size-frequency distributions with depth for many 

 of the abundant species. There was a general trend 

 for those species with peak abundance in the upper 

 50 m to have significant increases in larval size 

 with depth. Species with maximum abundance 

 below 50 m tended to exhibit no size-depth 

 changes, or had significant decreases in size with 

 depth. With these deeper larvae, the apparent lack 

 of size change with depth may be the product of 

 small sample sizes outside the depth of maximum 

 abundance and the broader depth ranges sampled 

 below 100 m. 



The gonostomatids exhibited two different dis- 

 tributional patterns. Cyclothone spp., V. nim- 

 baria, and Diplophos taenia occupied the topmost 

 50 m. The other seven species were distributed 

 below 75 m, with maximum abundances in the 

 75-225 m range. The nighttime depth distribution 

 patterns of juveniles and adults (from Clarke 

 1974) of the migratory gonostomatid species rela- 

 tive to each other are, with the exception of Gono- 

 stoma elongatum, generally the same as for the 

 larvae (Figure 9). Both larval and adult Dip/op/ios 

 taenia had the shallowest distribution and Valen- 

 ciennellus tripunctulatus the deepest distribution 

 within the family. Also, except for G. elongatum , 



DEPTH (m) 

 50 100 150 200 250 



Diplophos i'-\ larvae 



foenio 



Vinciguerria 

 nimbaria 



Vinciguerria 

 poweriae 



Ichthyococcus 

 ovafus 



Valenciennellus 

 tripunctulatus 



Gonostoma 

 atlanticum 



Gonostoma 

 elongatum 



Figure 9. — Larval (upper bar) and adult (lower bar) nighttime 

 depth distributions for migratory gonostomatid species taken in 

 late summer near lat. 28° N, long. 155° W (North Pacific central 

 gyre). Hatched larval depth range indicates intervals where 

 >90% of the estimated water column abundance occurred. Adult 

 depth distributions from Clarke (1974). 



the upper depth distributions of the adults (usu- 

 ally small adults; Clarke 1974 ) tend to overlap the 

 lower ranges of peak larval abundance. Although 

 Clarke's (1974) adult information is from a differ- 

 ent oceanic regime (offshore Hawaiian waters), 

 his general patterns of depth distribution may still 

 be valid for the central gyre adults. 



The night depth patterns of larval and adult 

 myctophid species are more complex than those of 

 the gonostomatids. The larvae of subfamily Lam- 

 panyctinae generally occupy shallower depths 

 than do those of subfamily Myctophinae (Figure 

 6b). The opposite is generally true of the night 

 distributions of the adults from the two sub- 

 families. Clarke ( 1973) presented adult depth dis- 

 tributions for 46 myctophid species taken near 

 Hawaii. Of the 15 myctophine species he listed, 8 

 had upper night distribution limits at 0-25 m (5 of 

 these were taken in substantial numbers by dip 

 nets); 2 others occurred at 25-50 m. In contrast, 

 only 10 of the 31 lampanyctine species listed by 

 Clarke (1973) were caught in the upper 50 m. 

 Ahlstrom and Stevens (1976) also found that neus- 

 ton (surface) samples taken in the California Cur- 

 rent caught only myctophine juveniles and adults 

 and lampanyctine larvae. 



Different night adult and larval depth patterns 

 are apparent for the two subfamilies (Figure 10). 

 Lampanyctine adults, generally overlap, or are 

 distributed below, their depths of maximum larval 

 abundance. The shallowest lampanyctine indi- 

 viduals (which share the larval depth range) are 

 usually small adults or juveniles (Clarke 1973). 

 This contrasts strongly with myctophine adults 



791 



