CLARKE: ECOLOGY OF LANTERNFISHES 



Within the first two groups, similar sizes of 

 the species tend to occur at similar depths. The 

 depth-size patterns of four species in the first 

 group — Be)tthoHema siiborbitale, Diapliu.s 

 schmidti, D. sp. A, and Tnphotimis nigre- 

 scens — are nearly identical. Within the third 

 group, the juveniles co-occur with similar- 

 sized individuals of the first group and the 

 adults with larger fish of the second group. 



Judging from the seasons of peak juvenile 

 abundance (Table 1) most species in group one 

 have similar reproductive cycles; large numbers 

 of juveniles were present in the June or July 

 samples. Juveniles were present in substantial 

 numbers also in September for Diaphus scIiDiidti, 

 D. sp. A, and Bolinichthys longipes. D. eluce}ts 

 showed a peak in September only. BentJiosema 

 suborbitalc and Ceratoscopelus warmhigi 

 showed large numbers of juveniles also in March. 

 In group two, Notolyclutus valdiviae and the 

 smallest Lampauyctus steinbecki co-occur in 

 summer and fall. L. niger, in spite of its apparent 

 later season of maximum recruitment, is re- 

 cruited at a larger size and co-occurs with 

 similar sized L. ateinbecki over much of the 

 year. Thus there is a good deal of overlap in 

 time as well as depth and size range for these 

 species. 



In general, congeners and closely related 

 species, except Hygophum spp., have different 

 size-depth patterns at night. Within each of the 

 above groups, there are few congeners, and the 

 co-occurring congeners are rather dissimilar. 

 The four species of group one whose patterns 

 are closest are of three genera, and the two 

 congeners, Diaphus schmidti and D. sp. A, are 

 quite different morphologically. Similarly, in 

 group two, the Lampauyctus spp. belong to 

 different groups within the genus. 



Taa)niigichthys miximus and T. bathyphilus 

 differ in that only T. minimus migrates. 

 Bolinichthys lo)tgipes and B. supralateralis 

 differ not only in morphology, size, and depth 

 distribution but also in overall abundance. The 

 two most similar Lampauyctus species, L. 

 stei)ibecki and L. uobilis, which were present 

 in abundance, have different night depth ranges 

 and different sizes at maturity. Among the 

 Diaphus species, closely related or similar 

 species-pairs are distinctly separated even 



though most species appear to have similar 

 reproductive cycles with peak juvenile abun- 

 dance in June or September and nearly the 

 same day depths. D. rolfboliui and D. eluceus 

 have different depth distributions at night. D. 

 sp. A and D. sp. B differ in depth distribution 

 and also in size at maturity. The species-pair 

 of D. a)iderseni and D. brachycephalus differs 

 similarly. 



The depth -size patterns of the different species 

 suggest that closely related species differ in 

 their responses to physical factors and that 

 genera or groups within genera have different 

 biological requirements. Strong gradients in 

 temperature, salinity, and light exist in the 

 upper 250 m, particularly for temperature and 

 salinity between 100 and 250 m. These are the 

 most obvious factors to explain the differences 

 in patterns of closely related species. Within 

 each group, however, similar-sized individuals 

 of dissimilar species co-occur under identical 

 physical conditions. For them to co-exist, it 

 would seem that they must be specialized with 

 respect to biological factors. 



A likely hypothesis is that the species within 

 a group have different food preferences. Morpho- 

 logical differences between species within the 

 groups include many features probably related 

 to finding or capturing food; relative size of the 

 eye and gape and the number, spacing, and 

 structure of gill rakers. Closely related species 

 of different groups are often rather similar in 

 these respects. 



The behavior of the Hygophum species 

 appeared to be different from that of the other 

 myctophids. The change in size-depth pattern 

 between new and full moon was unique. The 

 juveniles of H. proximum co-occurred with 

 those of species of the second group at new 

 moon and occurred shallower than those of 

 the first group at full moon. The changes 

 in avoidance with moon phase were also unique 

 and suggest that the Hygophum species re- 

 sponded to something besides the visual stimulus 

 of the trawl. 



The Hygophum species were the only two 

 congeners that occurred together in even 

 roughly comparable numbers [see Note (Added 

 in press) under Laiupauyctus uiger]. The two 

 species are quite similar morphologically. H. 



429 



