FISHERY BULLETIN: VOL. 72, NO. 2 



ebelingi, and Eustomias gibbsi, were taken in 

 roughly the predicted ratios, and the other two 

 species of Eustomias treated here were clearly 

 sampled better by the CT. Size ranges, of course, 

 were greatly influenced by just one large indi- 

 vidual, but in general the CT caught considerably 

 larger individuals of the five species which it ap- 

 peared to sample relatively better in terms of 

 numbers. Although not shown by the figures in 

 Table 1, large Astronesthes indicus were also 

 apparently sampled better by the CT (see above). 



Of the 47 species considered here, only 

 Danaphos oculatus and Malacosteus niger clearly 

 did not migrate to shallower levels at night. All 

 the other abundant species migrated to the upper 

 layers at night and, in spite of the fact that no 

 opening-closing device was used, even the data on 

 many of the rarer species are consistent with mi- 

 grations of several hundred meters. It is, of course, 

 possible that, as in the case of Photostomias 

 guernei, a small percentage of some species may 

 not migrate at any given time. Diurnal vertical 

 migration has been shown to occur in a few of the 

 species considered here (e.g., Badcock, 1970; 

 Krueger and Bond, 1972), but due to limited data 

 it had been only "suspected" for many others. Pos- 

 sibly because of the deeper mixed layer and ther- 

 mocline and greater transparency of the water, 

 migrations in the tropics are greater in extent and 

 thus more easily detected than elsewhere. 



As with several species of myctophids (Clarke, 

 1973), there was evidence that some of the 

 stomiatoids did not regularly migrate during the 

 winter. For Vinciguerria nimbaria, Gonostoma 

 elongatum, Astronesthes indicus, and I diacanthus 

 fasciola, night catches within the day depth range 

 during December 1970 were higher than expected 

 if due to contamination and indicated that a frac- 

 tion of the population remained at depth. Too few 

 of the latter two species were taken to permit 

 consideration of any differences between the mi- 

 grating and nonmigrating fractions. The evidence 

 for nonmigration was weak for G. elongatum but 

 suggested that the large fish did not migrate. 

 There were no obvious differences in the two frac- 

 tions of the population of V. nimbaria. Thus as 

 with the myctophids, there is no explanation for 

 the apparent change in behavior. 



Many of the species showed trends for increased 

 size with depth both day and night. Similar trends 

 were noted for many species of myctophids 

 (Clarke, 1973), and qualitative reports (e.g.. Bad- 

 cock, 1970) indicate that this trend is shown by a 



variety of mesopelagic species. The trend was 

 clearest for the abundant vertically-migrating 

 gonostomatids, Diplophos taenia, Vinciguerria 

 spp., Gonostoma spp., and Valenciennellus 

 tripunctulatus, but was also evident for 

 Chauliodus sloani, Astronesthes indicus and 

 Thysanactis dentex. 



The size-depth patterns at night of 10 species 

 are shown in Figure 5 by straight lines connecting 

 the coordinates for the smallest size, upper limit of 

 depth range with those for the largest size, lower 

 limit of depth range (extremes of size and depth 

 have been ignored). These are only rough 

 approximations of the size-depth patterns; in real- 

 ity the patterns are rather complex polygons. The 

 straight lines serve mainly as a basis for consider- 

 ing the possible interactions of the various species. 



STANDARD LENGTH (mm) 



Figure 5. — Depth-size profiles (see text) for 10 species in the 

 upper 300 m at night: Vinciguerria nimbaria (A), Vi. poweriae 

 (B), Valenciennellus tripunctulatus (C), Diplophos taenia (D), 

 Chauliodus sloani (E), Thysanactis dentex (F), Gonostoma elon- 

 gatum (G),G. ebelingi (H), Astronesthes indicus (I), andG. atlan- 

 ticum (J). 



Two very similar species, Vinciguerria nim- 

 baria and V. poweriae, showed distinctly different 

 size-depth patterns. As with many similar species 

 of myctophids, individuals of similar sizes were 

 well separated in the water column. Where the 

 depth ranges overlapped, at 100-125 m, the larger 

 V. nimbaria co-occurred with the smaller V. pow- 

 eriae. Vinciguerria nimbaria generally co- 

 occurred with similar-sized or slightly larger in- 

 dividuals of several abundant species of myc- 

 tophids in the upper 100 m, while V. poweriae 

 co-occurred with the deeper living myctophids 

 (Clarke, 1973). 



Although their size-depth patterns were 

 slightly different, similar-sized individuals of 

 Gonostoma elongatum and G. ebelingi, two very 

 similar species, co-occurred over much of their 

 depth ranges. G. atlanticum , in addition to being 

 rather different from its congeners in size range, 

 color, and several morphological aspects, also had 



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