trawls to examine vertical distributions. The overall vertical 

 distributions are similar for the three geographic areas although 

 there are differences. The major difference in the studies is 

 that even though Roe et al . , (1984) worked at 44° N their data 

 showed a more shallow distribution for most medusae (the 

 exception was Periphylla periphylla which was taken at the 

 surface at 53-60° N) than does ours at 40°N. All three studies 

 found highest species diversity and greatest numbers of 

 individuals at depths of 600 m and greater. Some of the 

 differences among these studies is due to numbers of samples 

 taken and their depths. 



Thurston (1977) and Roe et al . (1984) found evidence for 

 diel vertical migrations, up to 200 m, for a number of midwater 

 medusae including Atolla vanhoef f eni , Pantachogon haeckeli , and 

 Periphylla periphylla . But others e.g., Atolla wyvillei and 

 Halicreas minimum did not migrate. 



The most abundant midwater coelenterate off the Grand Banks 

 was the physonect Nanomia cara . Previously N. cara was known to 

 be abundant at shallower depths in this region (Rogers et al., 

 1978) but its importance at mesopelagic depths was unknown. 



We found evidence that midwater siphonophores undertook diel 

 vertical migrations of up to 150 m. Previous studies in the 

 North Atlantic have documented similar diel migrations but this 

 was mainly for calycophorans (Pugh, 1977, 1986). 



Because of the extreme fragility of ctenophores almost 

 nothing is known about their existence in midwater (Madin and 

 Harbison, 1978; Harbison, 1986). For example, in one of the most 

 comprehensive studies of the midwater community in the North 

 Atlantic, Roe et al., (1984) only listed a single ctenophore 

 species, Beroe cucumis . Until about a decade ago only three 

 ctenophore species were definitely known to occur in the deep-sea 

 (Madin and Harbison, 1978). However recently, direct 

 observations using submersibles (Madin and Harbison, 1978; 

 Youngbluth, 1984; Mackie, 1985; Harbison, 1986) has shown that 

 the number of midwater ctenophores is large and, in fact, 

 Harbison (1986) states that "the vast majority of ctenophores 

 live in the deep-sea." Our results supports Harbison's 

 conclusion. 



Here we found that midwater fishes were mainly below 400 m, 

 day and night. Backus et al., (in preparation) working in the 

 same area found that midwater fish were concentrated in the 400- 

 800 m zone regardless of time of day. We also noted that at 

 night, hatchet fishes, myctophids, and snipe eels occurred above 

 100 m. Other studies have documented mesopelagic concentrations 

 of midwater fishes and diel vertical migrations (Badcock, 1970; 

 Clarke, 1973, 1974; Roe, 1974; Pearcy et al., 1977; Howell and 

 Krueger, 1987; Karnella, 1987). In some regions 50% of the 



277 



