446
A. SUDA:
contrary to the general expectation that the center of distribution should shift southward during the northern hemisphere winter period. In the third and fourth quarters
of the year, the northern extreme of concentration of the fishes moves to the south
and a poor area of tunas seems to prevail along the western coast of India. During
N.----.-----,-----,----,-----,--,
Hooking rote (%)
N
20"
10"
30"
~ < 1.0
r& to - 3.0
• >3.0
Hooking rote (%)
< to
ti: to-3.0
~P1tijjntfm~.~> 3.0
50"
70"
8O"E
N.----.-----,-----r----.-----.-~
Hooking rote (%)
<1.0
~ 1.0 -3.0
• >3.0
Hooking rote (%)
< 1.0
~ 1.0 - 3.0
• > 3.0
Fig.Sb. Quarterly distribution of hooking-rate of bigeye tuna in the Arabian Sea, 1966-1968
the third quarter of the year, upwelling is reported along the Malabar Coast (CUSHING,
1969) and the above-mentioned southward spread of the area of poor productivity of
tunas seems to be attributable to this upwelling.
Thus, as far as the longline data from the Arabian Sea are concerned, rather poor
catches of yellowfin and bigeye in the upwelling zone are indicated.
On the other hand, the hooking-rate of the longline fishery in the waters south of the
Great and Small Sunda Islands, where the occurrence of upwelling is suggested, does not