WIEBE ET AL.: AVOIDANCE OF TOWED NETS BY NEMATOSCKUS MEGALOPS 



Table 2.— The ratio (Night/Day) of night 1 m 2 and 10 m 2 MOC- 

 NESS catch of Nematoscelis megalops (no./m 2 ) divided by the 

 paired day catch at stations in the Slope Water and cold core 

 rings and the depth where the cumulated frequency of occur- 

 rence equals 50% in the night tow. Information about the tows 

 taken on Chain 125 and Knorr 53 is given in Ortner et al. 

 (1978). 



'Vertical distribution of N. megalops on these tows illustrated in figure 

 5 of Wiebe and Boyd (1978). 

 2 None present in day collection 



the water column. These values were obtained by 

 combining the stratified oblique hauls to form a 

 composite tow. Note that because the water col- 

 umn sampled is 1,000 m, the integrated number 

 per 1,000 m 3 for the column is identical to num- 

 bers per square meter. 



RESULTS 



Analysis of 1 m 2 and 10 m 2 

 MOCNESS Observations 



The vertical distribution of N. megalops at sta- 

 tions where pairs of 1 m 2 and 10 m 2 MOCNESS 

 tows were taken (Fig. 3) illustrates the large var- 

 iations in depth distribution that can occur in the 

 different hydrographic regimes and at different 

 times of year. As previously described by Wiebe 

 and Boyd (1978), this species generally has its 

 center of distribution above 300 m in Slope 

 Water. Exceptions in Slope Water are associated 

 with the presence of warm core rings. In young 

 cold core rings such as "Bob," the center of distri- 

 bution is also shallow. In most of the older rings 

 we have sampled, the distribution of N. megalops 



deepens as is evident in "Franklin" and "Emer- 

 son" (see also figure 5 in Wiebe and Boyde 1978). 



Very close agreement between the two net sys- 

 tems in the shape of the vertical distribution is 

 found, especially at night (Fig. 3). The night 1 m 2 

 and 10 m 2 MOCNESS tows also show significant 

 agreement in the integrated numbers caught per 

 square meter (r = 0.99; P<0.05). In contrast, the 

 paired day tow data are considerably more vari- 

 able and do not show significant agreement in in- 

 tegrated numbers per square meter (/• = 0.13; 

 F>0.05). 



Clearest evidence for differential day/night 

 net avoidance by N. megalops is found in the 

 catch data obtained by the 1 m 2 MOCNESS (Fig. 

 3). Without exception, for each of the eight day/ 

 night pairs of tows taken on Knorr 65 and Knorr 

 71, the day estimate of numbers per square 



t 



10 20 



NEMATOSCELIS MEGALOPS 

 TOTAL BODY LENGTH (mm) 



40 



Figure 2.— Relationship between total body length, carapace 

 length, and wet weight of Nematoscelis megalops. 



79 



