10 
Fishery Bulletin 108(1 ) 
c 
46°N 
44 q N 
42"N 
40°N 
152°E 154"E 156°E 158°E 160°E 162=E 164°E 
Figure 8 
The spatial distribution of fishing effort for Ommastrephes bartramii from the Chinese squid jigging fleets in (A) August, 
(B) September, and (C) October 2005 overlaid on the habitat suitability index (HSI) map generated from the arithmetic 
mean model with three environmental variables (sea surface temperature, sea surface height anomaly, and chlorophyll-o 
concentrations). 
and 15-16°C SST, 33.3-33.4 psu SSS, and 0.3-0.4 mg/ 
m 3 chi a in October. The results are the same as those 
in previous findings (Chen and Chiu, 1999; Chen, 1997; 
Tian, 2006) and indicate that the dynamics of high O. 
bartramii aggregations were influenced by the progres- 
sion of seasonal cooling (thermal and SSS front), and 
that the movement of the chl-a front can be predicted 
by using the specific levels of the proxy variables. These 
proxy indicators appear to play a critical role in formu- 
lating and patterning potential O. bartramii habitat and 
migration routes. 
The SSHA field is coupled with the dynamics (cur- 
rents) and thermodynamics (heat balance) of the upper 
ocean. Convergences and divergences of the water mass 
transport in the surface layer of the ocean result in 
positive and negative sea level anomalies, respectively 
(Zagaglia et al., 2004). Variations in water density, 
which are dominantly controlled by changes in tem- 
perature or in heat storage (changes in the mixed layer 
depth or its temperature), also give rise to sea level 
anomalies (Polito et al., 2000). It is natural, therefore, 
to expect that changes in SSHA can be related to varia- 
tions in the CPUE and O. bartramii distribution. Each 
species has a salinity preference and congregates at ver- 
tical salinity breaks, as at horizontal salinity “fronts” 
(Chen, 2004). We found that O. bartramii distribution 
is closely related to the environmental variables, SST, 
SSS, SSHA, and chi a. Of the four environmental vari- 
ables considered in this study, SST, SSHA, and chi a 
can be easily obtained in near real-time from remote 
