Comparison of Euphausiid Collections — Jerde 
were counted. Because the samples taken with 
the micronekton net were very large, it was 
necessary to use aliquots in all cases; these ali- 
quots ranged from 2.75% to 50% depending 
upon the size of the sample. A Folsom plankton 
splitter (McEwen, Johnson, and Folsom, 1954) 
was used for fractionating the samples, with the 
exception of the micronekton sample at station 
41. For this sample the animals in a gallon jar 
were kept in suspension by agitation, and a 
portion of animals and fluid was poured out; 
"wet” displacement volume of the animals was 
determined, and subsequently the euphausiids 
were measured and counted. 
After the actual catch of euphausiids was 
estimated, the numbers were standardized for 
each size category to numbers per 500 m 3 of 
water (Table 1). Blackburn (MS) estimates 
that the amount of water actually filtered by the 
micronekton net at a speed of 5 knots, using the 
above mentioned filtration coefficient, is 1000 
m 3 per 3.69 minutes. In this study micronekton 
standardized volumes, or numbers, per 500 m 3 
were calculated by the following formula: 
actual vol. or number 
ml or number/500 m 3 = X 1-85 
number of minutes 
Brinton (1962) has denoted as plentiful 
species those which occur in concentrations 
greater than about 25 specimens per 1000 m 3 
of water. Of the euphausiid species which 
mature at 7> 9 mm, only one, Euphausia eximia, 
was plentiful in the 64-1 and 64-2 collections, 
and this species was the predominant euphausiid 
in the samples. For each collection, in the por- 
tion of the sample counted, the length of each 
E. eximia was measured to the nearest mm, from 
the tip of the rostrum to the tip of the telson. In 
addition to other station data, the percentage of 
each sample which was counted and measured 
is noted in Table 1. Excluding station 41, the 
remainder of each sample was scanned under 
the microscope for rare species. 
DISCUSSION AND SUMMARY 
Wilcoxon’s signed-rank test (Tate and Gel- 
land, 1957), a nonparametric statistical method, 
was employed to test for differences in euphau- 
siid catching ability between the two nets. The 
data in Table 1 indicate that there is no sig- 
179 
nificant difference between the nets with respect 
to estimated volume of total euphausiids per 
500 m 3 . However, it is clear that the nets differ 
with regard to ability to catch different species 
and ontogenetic stages. It is evident that the 
micronekton net does not quantitatively sample 
larval or juvenile Euphausia eximia , and that 
those animals which are less than 13 mm long 
escape readily through the larger mesh. In the 
size range 13-21 mm there appears to be no 
significant difference in number of E. eximia 
per 500 m 3 , but there may be such a difference 
in the 22-28 mm size range; the micronekton 
net appears to catch more euphausiids in this 
size range than does the 1-rn net. This difference 
in the 22-28 mm category may be interpreted 
as evidence of avoidance of the 1-m net by the 
larger euphausiids. However, when all adults 
(13-28 mm) are grouped together there is no 
significant difference between the nets with re- 
gard to the estimated density of E. eximia. Evi- 
dence of avoidance of towed nets by zooplank- 
ton has been presented by Fleminger and Clutter 
(1965). 
In terms of the number of euphausiid species 
found at a station, there was no significant dif- 
ference between the two nets when adults alone 
were considered (Table 1). When larvae and 
juveniles, as well as adults, were used to deter- 
mine the total number of species present at a 
station, there was a significant difference be- 
tween the catches of the two nets. The 1-m net 
caught more euphausiid species than the micro- 
nekton net, because it retained more larvae and 
juveniles than the micronekton net (Table 1) 
and also retained more adults of the smaller 
species (adult at <9 mm in length, Table 2). 
Table 2 shows a comparison of the two nets 
with respect to presence or absence of adults of 
different euphausiid species at nine stations. For 
the larger species (adult at 7> 9 mm) the micro- 
nekton net as a sampling device is as good as 
or better than the 1-m net with regard to pres- 
ence or absence of species (Table 2). Of the 
smaller species, with the exception of E. dis- 
tinguenda (Table 2), presence of adults was 
observed more often in the 1-m net than in the 
micronekton net. Thus, for qualitative euphau- 
siid studies, the 1-m net provides almost as 
much or more information for one-third of the 
ship time. 
