diel vertical migration. Hatchet fishes and myctophids were found 

 below 250 m by day but were found in the upper 100 m at night. 

 Snipe eels ( Nemichthyidae ) were found deeper than 350 m by day 

 but move up into the upper 100 m at night. Paralepidids were 

 found somewhat deeper, >450 m, by day but were found above 250 m 

 at night. 



Melanostigma atlanticum , which we nicknamed the "Cheerio" 

 fish because it was mostly seen motionless, curled in a circle, 

 also showed some evidence of a diel vertical migration. During 

 the day it was found at a minimum depth of 600 m but this 

 decreased to 400 m at night. Other common fishes, e.g., 

 Cyclothone spp. and Stomias boa ferox apparently did not 

 vertically migrate or they had a reverse migration since their 

 minimum day depth was slightly shallower than their night depth. 



There is some evidence to suggest that some midwater taxa 

 may be more abundant just above the bottom (Wishner, 1980; Smith, 

 1983). During 1987 we found that on some dives there was an 

 increased number of gelatinous zooplankton near the bottom. 

 Nanomia , an undescribed red cydippid, Beroe , and trachymedusae 

 were sometimes most numerous near the bottom. On several dives 

 Nanomia were so numerous within 10 m of the bottom that many 

 could be seen at any time. Euphausiids sometimes occurred in 

 dense swarms near the bottom at depths of 400 to 600 m. Also the 

 numbers of fishes was sometimes higher near the bottom where 

 midwater and benthopelagic species co-occurred. 



DISCUSSION 



For the invertebrate macroplankton and micronekton it was 

 evident that the fauna was dominated, both in terms of species 

 and individuals, by those that were found at depths in excess of 

 400 m. Only about 20% of the species were observed at depths of 

 less than 300 m and 50% were only seen below 600 m. 



Only a single species ( Pelagia noctiluca ) was found to only 

 occur in surface waters (<300 m). Most of the species which were 

 found in the upper 100 m were eurybathic species e.g., Beroe 

 cucumis , Bolinopsis inf undibulum , Meqanyctiphanes norveqica, 

 which also were found much deeper and generally were more 

 abundant at greater depths. Thus the midwater invertebrate 

 macroplankton and micronekton fauna in slope waters south of 

 Georges Bank was mostly mesopelagic and although some species 

 occupied a relatively broad depth range the fauna was most 

 diverse at greatest depths. 



For medusae, the results of two previous studies of the 

 midwater fauna of the North Atlantic can be compared with the 

 present study. Thurston (1977) and Roe et al. (1984) working in 

 the eastern North Atlantic, at 53-60° N 20° W and 44° N 13° W 

 respectively, both employed discrete depth open-closing midwater 



276 



