Surface Swarming of Euphausiids — Komaki 
437 
Fig. 2. Daily landings of Euphausia pacifica 
( solid line ) from Kinkazan waters and daily change 
of aggregate number of fishing boats ( dashed line) 
yielding euphausiids (1959). 
the like, but there were no apparent relation- 
ships. The yield on a calm day is likely to 
be more abundant than that on a rough day, 
but this is caused essentially by the relative 
difficulty of the fishing operation. The time 
of swarming throughout a given day is not 
definite. It occurs in early morning on some 
days, while on other days it takes place in the 
afternoon even in bright sunshine. 
Swarming Season 
The fishing season of euphausiids corre- 
sponds with the swarming season in the area 
where the euphausiid fishery is carried out. As 
shown in Figure 2, the swarming season during 
1959 in the Kinkazan waters started in the 
middle of March and terminated at the end 
of May. The season, however, changes slightly 
from year to year. The swarming season in the 
Kinkazan waters ranges between late February 
and late May in maximum extent. 
Figure 3 shows the general aspect of the 
swarming season along the coasts of the Sea 
of Japan. The rectangles in Figure 3 show the 
range of the swarming season in the zones indi- 
cated by the numbers in Figure la. Figure 3 
was derived from replies of fishermen to the 
question, "In what month (s) do you usually 
observe the euphausiid swarming in your favor- 
ite fishing grounds?" The three degrees of 
swarming intensity of euphausiids were fixed 
as follows: 1-3 affirmative response (s) from 
a certain zone in a given month were expressed 
by a white area, 4-6 affirmative responses by 
a shaded area, and more than 7 by a black area. 
Actually, each month expressed by a black area 
represents more than 15 affirmative responses. 
Figure 3 also indicates that the major swarm- 
ing regions in the coastal areas of the Sea of 
Japan are around Sadogashima (zone 8), in 
Wakasawan and vicinity (zones 15 and 16), 
off Sanin district including Oki (zones 18-21), 
and on the east side of the Tsushima Gunto 
(zone 24). 
There seems to be a tendency for swarming 
to take place earlier in the year in the southern 
part of the Sea of Japan. Thus, in the north 
of Kyushu (zones 23-25), the most intensive 
swarming is observed in February and March; 
in the Wakasawan and Sanin districts (zones 
15-21), the most notable swarming season is 
in March and April (also in May in some 
zones) ; and in the area surrounding Sadoga- 
shima (zone 8), the euphausiids aggregate 
most actively in April through June. According 
to the fishermen’s information, the swarming 
season in each zone changes from year to year, 
as in the Kinkazan waters. The beginning, 
peak, and terminating times of the swarming 
are different from year to year. The swarming 
season along the coasts of the Sea of Japan 
occurs between January and June. 
Seasonal Change of Water Temperature 
Figure 4 shows the mean surface tempera- 
ture and salinity cycles throughout a year at 
three representatives coastal points in the Sea 
of Japan. All temperature records for a given 
month, taken over a period of 26 years, were 
averaged. The same was done with salinity 
determinations. 
Upon comparing Figure 4 with Figure 3, it 
may be seen that the occurrence of swarming 
is closely associated with colder water tempera- 
tures. Swarming starts at a slightly higher tem- 
perature than the local minimum, continues 
with increasing temperature, and then termi- 
nates as the temperature exceeds 16°C. The 
