Tuna Fisheries and their Resources in the Indian Ocean
445
relationship between upwelling and concentration of tunas. Here, a remarkable upwelling
in the Arabian Sea is considered as an example. As shown in Fig. 5 a and b, longline data
do not necessarily cover the whole area of upwelling. Still, remarkable features are
suggested regarding seasonal changes in the distribution of hooking-rates of yellowfin
and bigeye in the area:
N,----.-----.-----r----,-----~,
Hooking rate 1%)
< 10
~ 1.0 -3.0
• >3.0
Nr----.-----.-----r----.-----,--,
Hooking rate (%)
< 1.0
111.0-3.0
~mr-r-,..,,,-...n:I • > 3.0
Hooking rate (%)
S < 1.0
X · 1.0 - 3.0
• > 3.0
Fig. 5 a. Quarterly distribution of hooking-rate of yellowfin tuna in the Arabian Sea, 1966 -1968
a) The coastal area of Somalia and SE Arabia, where the upwelling is located, is
characterized by poor longline catches of the tunas, at least in the second and third
quarters of the year, when the upwelling is more intense.
b) Concentration of the tunas takes place in the area away from the Somalian coast
during the first and second quarters of the year. In the fourth quarter of the year, it tends
to approach the coast.
c) Northward expansion of fish concentrations of high density appears in the first
and second quarters of the year, and is especially remarkable in the first quarter,
445
relationship between upwelling and concentration of tunas. Here, a remarkable upwelling
in the Arabian Sea is considered as an example. As shown in Fig. 5 a and b, longline data
do not necessarily cover the whole area of upwelling. Still, remarkable features are
suggested regarding seasonal changes in the distribution of hooking-rates of yellowfin
and bigeye in the area:
N,----.-----.-----r----,-----~,
Hooking rate 1%)
< 10
~ 1.0 -3.0
• >3.0
Nr----.-----.-----r----.-----,--,
Hooking rate (%)
< 1.0
111.0-3.0
~mr-r-,..,,,-...n:I • > 3.0
Hooking rate (%)
S < 1.0
X · 1.0 - 3.0
• > 3.0
Fig. 5 a. Quarterly distribution of hooking-rate of yellowfin tuna in the Arabian Sea, 1966 -1968
a) The coastal area of Somalia and SE Arabia, where the upwelling is located, is
characterized by poor longline catches of the tunas, at least in the second and third
quarters of the year, when the upwelling is more intense.
b) Concentration of the tunas takes place in the area away from the Somalian coast
during the first and second quarters of the year. In the fourth quarter of the year, it tends
to approach the coast.
c) Northward expansion of fish concentrations of high density appears in the first
and second quarters of the year, and is especially remarkable in the first quarter,