Climatic and marine environmental variations associated with fishing conditions
of yellowfin tuna (Thunnus albacares) of the equatorial Atlantic Ocean
Kuo-Wei Lan1, Ming-An Lee1, Hsueh-Jung Lu1, Wei-Juan Shieh2
1
Department of Environmental Biology and Fisheries Science, National Taiwan Ocean
University. 2 Pei-Ning Rd., Keelung 20224, Taiwan R.O.C.
Email: D96310002@mail.ntou.edu.tw
2
Taiwan Ocean Research Institute, National Applied Research Laboratorie. 3F, No. 106,
Ho-Ping E. Road, Sec. 2, Taipei 106, Taiwan R.O.C.
In this study the Taiwanese longline fishery (LL) data were divided into two
types: regular LL and deep LL. Furthermore, we collected environmental variables
such as sea surface temperature (SST), subsurface temperature, chlorophyll-a
concentration (Chl-a), net primary production (NPP), wind speed and the North
Tropical Atlantic SST Index (NTA) during the period of 1998-2007 to investigate the
relationship between LL catch data and oceanic environmental factors using principal
component analysis (PCA).
After the daily LL was separated into two types of LL, the results indicated that
the deep LL was the major fishery to catch yellowfin tuna (YFT) in the equatorial
Atlantic Ocean. The spatial distribution of the nominal CPUE by deep LL exhibited
that the YFT mostly aggregated in warm water above 24-25°C. The SST decreased on
the west coast of Africa and the YFT migrated to the west of 20°W in the third quarter
of the year. The results of PCA displayed that higher sub-surface water temperature
led to a deeper thermocline and resulted in a higher CPUE of YFT, but the influence
of NTA index for the CPUE of YFT seemed to be inconspicuous. In the equatorial
Atlantic Ocean, the 5-7 month lag of Chl-a and NPP may influence the activity of
YFT because of the availability of its forage material and a lag effect of trophic
transformation. The time lag of Chl-a and NPP related to the CPUE suggests that the
forage concentration is an important factor which causes the aggregation of tuna
schools, and consequently influences the spatial distribution and migratory patterns of
the YFT.