CLARKE: ECOLOGY OF LANTERNFISHES 



a greater overall advantage than the increased 

 "stealth" of the larger CT. 



The full-new moon series indicated that most 

 species occurred deeper at full moon and that 

 several avoided the trawl better at full moon. 

 The Hygophum species appeared to do just the 

 opposite. The changes suggest that it is best 

 overall to sample the upper 200 m at new moon 

 only. A mixed sampling program can result in 

 some populations being sampled twice and the 

 depth range and abundance overestimated, or 

 most of the population being missed and 

 abundance underestimated. 



Most species appeared to occur 50-75 m 

 deeper at full moon. Data presented by Clarke 

 (1970), however, indicate that in clearest ocean 

 water, the depths of isolumes at full moon are 

 about 200 m greater than at new moon. This 

 suggests that the fishes occurred at higher light 

 levels at full moon and may explain the in- 

 creased avoidance noted then. The data of 

 Blaxter and Currie (1967) indicate that this is 

 possible. They observed that the depth of a 

 sonic scattering layer was depressed by artificial 

 light but to a light level about 10 times brighter 

 than that at which the layer normally occurred. 



Intraspecific Variations in 

 Migration 



Most myctophid larvae appear to occur in the 

 upper layers (Ahlstrom, 1959). Whether they 

 descend just prior to or just after metamorphosis 

 is not known, but at least some species do not 

 begin to undertake regular, extensive diurnal 

 migrations immediately after metamorphosis. 

 The data indicate that the recently meta- 

 morphosed juveniles of Benthosema suborbitale, 

 Lampanyctus niger, L. nobilis, and Cerato- 

 scopelus warmingi, and possibly Hygophum 

 proximum, Symbolophorus evermanni, and 

 Bolinichthys longipes, do not regularly migrate. 

 More thorough sampling of the deeper layers at 

 night with opening-closing devices may show 

 this to be a general feature of myctophids. 



Nafpaktitis (1968) has suggested that gravid 

 females of some myctophids do not migrate. 

 No evidence of this was found. The larger males 

 of Diaphus brachycephalus and the larger 

 individuals of Bolinichthys supralateralis ap- 



peared to remain at depth both day and night, 

 but in both cases data were too few to be 

 certain. In the latter species, there was no 

 clear relation to maturity or reproductive 

 condition. Most of the "nonmigrating" B. su- 

 pralateraliH were immature. 



Large fractions of the populations of three 

 species, Notolychnus valdiviae, Lampanyctus 

 niger, and Triphoturus nigrescens, appeared to 

 remain at the day depth during the night on 

 some occasions. It is unlikely that the deep 

 night catches were due to contamination, i.e., 

 encountering aggregations in the upper layers 

 on the way up or down. The numbers caught at 

 depth during the December 1970 series were in 

 all cases considerably larger than those caught 

 in short oblique tows made during the same 

 series. Also it seems unlikely that patches 

 would be encountered only by tows made to the 

 same depths where the species were found during 

 the day. Finally, the day and night calculated 

 totals and size frequencies agreed well for all 

 three species in December. If the deep night 

 catches had been contaminants, the night totals 

 would have been much larger than those for 

 the day. 



There were no obvious differences between 

 the migrating and nonmigrating fractions of 

 the populations. The nonmigrating fraction of 

 Lampanyctus niger tended to be smaller and 

 that of Notolychnus valdiviae, larger in Sep- 

 tember 1970, but there was considerable overlap 

 between both fractions of the populations in 

 both cases. For Triphoturus nigrescens and 

 N. valdiviae in December 1970, both fractions 

 of the populations were nearly identical in size 

 composition. Thus the difference in behavior 

 was not entirely a function of size. There was no 

 case where shallow and deep night samples 

 differed in sex ratio or percentage of ripe 

 females. The number of specimens involved was 

 rather large in all cases, so it is doubtful that 

 more data would produce clearer trends or any 

 explanation related to the parameters measured 

 here. 



Most species showed significant differences 

 in size composition with depth. Symbolophorus 

 evermanni was the only species present in 

 abundance for which all sizes appeared to occur 

 throughout the depth range. In the great 



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