FISHERY BULLETIN: VOL. 71, NO. 2 



with respect to the seasonal peak in production 

 of food. 



In many of the abundant species, the seasonal 

 changes in abundance and size composition 

 were quite pronounced. When these were com- 

 bined with size-dependent differences in migra- 

 tion habits, the depth-abundance profile also 

 changed with season. Consequently, samples 

 from only one period may give a misleading 

 picture of vertical distribution and abundance. 

 This would be particularly true in the tropics 

 where, as opposed to longer-lived species at 

 higher latitudes, several different size classes 

 are not often present in abundance at all 

 seasons. 



Interspecific Relations 



Many species of myctophids, including some 

 congeners that are very similar morphologically, 

 occur together in the water column yet must be 

 ecologically segregated. From this study it is 

 possible to examine several relevant factors: 

 depth distribution, size range, and size changes 

 with depth and season. Owing to better data for 

 some of these aspects for the nighttime, only 

 night distributions will be considered. There are, 

 however, some data (Backus et al., 1968 

 Barham, 1970) that suggest that myctophids 

 are rather inactive during the day and that 

 interspecific patterns at night are probably 

 more meaningful ecologically. 



In Figure 12, depth-size patterns are dia- 

 grammed for 16 of the 19 most abundant 



species. For each species, a straight line is 

 drawn connecting the size-depth coordinate 

 for smallest size-shallowest depth with that for 

 largest size-deepest depth. Symbolophonis ever- 

 manni, which showed no trend, and the Hy- 

 gophus species, which will be discussed separ- 

 ately, have been omitted. Extremes of depth of 

 capture and size range have been ignored; 

 consequently, the ranges shown in Figure 12 

 are, in some cases, narrower than those given 

 in Table 1. The straight lines are of course only 

 a rough approximation to the actual patterns 

 of size and depth; it is realized that more data 

 would probably result in polygons for each 

 species. 



The species can roughly be separated into 

 three groups. The first group includes eight 

 species whose young occur principally at about 

 25 m and the adults between 75 and 125 m, 

 depending on size. In the second group of three 

 species, the pattern is similar except that the 

 young occur principally at 80-100 m and the 

 adults down to 150-250 m, again depending on 

 size. The third group includes four species 

 with sharper gradients in size with depth where 

 juveniles occur around 50 m and larger fish are 

 mostly between 150 and 200 m. Two of the 

 rarer species, Myctophum selenoides and 

 Lampadena lumuiosa, appear to have patterns 

 like those of the third group. Diaphus anderseni 

 has a depth-size pattern different from any of 

 those illustrated, but two rarer species, Taan- 

 ingichthys nmiimus and Boludchthys supra- 

 lateralis, appear to have similar patterns. 



100 



a. 



UJ 

 Q 



200 



STANDARD LENGTH (mm) 

 10 30 50 70 90 

 —I 1 I I I I I I i_ 



Figure 12. — Depth-size profiles (see text) in 

 the upper 250 m at night for 16 species of 

 myctophids: Diaphus schniidii (A), Diapluis sp. 

 A (B), Beiuhoscina siihorhitule and Triphoiiirus 

 iiii^ri'scens (C), Bolinichthys lon^ipcs (D), Diaphus 

 eliicens (E), Ceratoscopehis wuniuniii (F), Luni- 

 panycms nohilis (G), Diaphus rolfbolini (H), 

 Diaphus sp. B (I), Laiupanyctus nifier (J), Noio- 

 lychmts valdiviac (K), Diaphus anderseni (L), 

 Lobianchia ^emellari (M), Diaphus hrachyceph- 

 alus (N), and Lampanycius steinbecki (O). 



428 



