CLARKE and WAGNER: VERTICAL DLSTRIBUTION OF MESOPELAGIC FLSHES 



were taken at night within the daytime depth 

 range, suggesting that a small fraction of the 

 population does not migrate. 



We examined the gonads of 127 specimens. Of 

 39 females (19-74 mm), those less than 50 mm were 

 clearly immature, 2 56-mm fish were nearly ma- 

 ture, and 8 of the 10 largest (57-74 mm) carried 

 well-developed ova. The 88 males were 18-60 mm. 



There were too few mature females to consider 

 any seasonal trends in ripeness. Juveniles (7-12 

 mm) were taken in March, June, and September, 

 and made up the largest fraction of the catch (59*%) 

 in March. There were other peaks in size- 

 frequency distributions at all seasons, but none 

 could be clearly traced from season to season. 



Poromitra crassiceps (Gunther) (57; 16-130 mm) 



All sizes of P. crassiceps occurred shallower at 

 night than during the day. Day catches were 

 between 750 and 1,000-1,200 m. No specimens over 

 60 mm were caught above 900 m. At night, two 

 small fish were caught near the day depth, the 

 remaining small fish (19-51 mm) at 150-400 m, and 

 the larger fish (84-128 mm) between 340 and 825 m. 



The seven smallest fish (16-25 mm) were taken 

 in March, June, or July, and 16 intermediate-sized 

 individuals (27-35 mm) were all taken in Sep- 

 tember. The others (39-130 mm) were scattered 

 seasonally. Twenty-four specimens were 80 mm or 

 larger. Nineteen of these (80-101 mm) were males; 

 several of those over 90 mm appeared, subjective- 

 ly, to be mature or nearly so. The five females were 

 97-130 mm, and none were mature. 



Poromitra mega/ops (Liitken) (56; 13-41 mm) 



All but one P. megalops were either 13-21 mm or 

 28-41 mm. Four of the small fish were caught at 

 625-1,000 m during the day. At night, five were 

 taken at 250-380 m. and five at 690-775 m. Of 

 the large fish, 27 were taken at 725-1,000 m during 

 the day and 13 at 640-850 m at night. Thus some of 

 the small fish undertake a fairly substantial up- 

 ward migration at night, but the large fish appear 

 to shift upwards only slightly, if at all. There were 

 no obvious seasonal trends in size composition of 

 the catches; specimens of both size groups were 

 present at all seasons. 



Of the 34 specimens sexed, there were 18 

 females (26-41 mm) and 16 males (28-39 mm). The 5 

 smallest females (26-35 mm) were immature, 

 while the 13 large ones (37-41 mm) appeared 



mature. Ebeling and Weed (1973) reported the size 

 range of mature P. megalops as 45-62 mm. Possi- 

 bly, P. megalops matures at a smaller size in 

 certain parts of its range. (Ebeling and Weed did 

 not give specific geographic data for their mature 

 specimens.) 



Poromitra oscitans Ebeling (19; 44-71 mm) 



Poromitra oscitans is a deep-living, nonmigrat- 

 ing species (Ebeling 1975). It occurred only at the 

 lower edge of the depth range sampled in detail. 

 One specimen each was taken at 750 and 850 m; the 

 others were caught in nine tows all of which fished 

 below 1,000 m. Four of these were taken in open- 

 ing-closing TT tows which fished only below 1,350 

 m. Three were males (44-53 mm), and the others, 

 immature females (45-71 mm). 



Scopeloberyx opisthopterus (Parr) (93; 14-38 mm) 



Scopelohergx opisthopterus was taken between 

 540 and 1,200 m during the day. Night catches by 

 the IK were at 650-1,175 m, and one specimen was 

 taken by the TT fished open between 1,300 and 

 1,450 m. There was thus no evidence of any diel 

 change in depth range. Most small specimens (<25 

 mm) were taken above 800 m and most large ones 

 below 750 m. 



Out of 55 specimens (25-38 mm) sexed, there 

 were 10 immature females (26-30 mm), 24 mature 

 females (31-38 mm), 7 males (27-33 mm), and 4 

 (25-29 mm) that were too small to sex with cer- 

 tainty but which were probably males. Mature 

 females were taken at all seasons except 

 December (when only four 5. opisthopterus were 

 taken). There were two rough size groups in the 

 catch; all but seven specimens were either 14-20 

 mm or over 26 mm. Representatives of the smaller 

 group were absent from samples taken in July and 

 nearly absent in June, suggesting possible sea- 

 sonality in recruitment. 



Scopeloberyx robustus {Gunther) (120; 12-31 mm) 



Scopeloberyx robustus was taken at 550-1,200 m 

 during the day. With the exception of three small 

 (14-20 mm) specimens taken at 340-425 m, the 

 night depth range was similar-600-1,175 m. Thus 

 there is no indication that any but the small S. 

 robustus vertically migrate. There was a distinct 

 increase in size with depth. With few exceptions, 

 fish less than 20 mm were caught above 800 m, 



639 



