Kedarnath Mahapatra

Variability of satellite-derived sea surface height anomaly, and its relationship with Bigeye tuna (Thunnus obesus) catch in the Eastern Indian Ocean

Abstract We analyzed the variability of sea surface height anomaly (SSHA), and its relationship with Bigeye tuna catch in the eastern Indian Ocean (EIO) off of Java Island (Indonesia). Both time series of SSHA and Bigeye tuna HR show dominant signals corresponding to the annual and inter-annual variability. During the southeast monsoon the wind blows along southern coast of Java and produces coastal upwelling. This causes sea level to drop due to an offshore Ekman transport, and thermocline becomes shallower. During El Niño and Indian Ocean Dipole (IOD) positive phase, upwelling is more intense and a large cold eddy forms in the EIO off Java. Generally, Bigeye tuna HR tends to increase during upwelling seasons and becomes even higher during El Niño and the positive phase of the IOD. The increased Bigeye tuna HR during the southeast monsoon, El Niño and the IOD positive phase can be attributed to the shallower thermocline depth and the enhancement of biological productivity due to development of eddies and strong upwelling in the EIO. The spatial distribution of SSHA indicates that Bigeye tuna catches are abundant in the frontal regions between cold and warm eddies.

Bio-optical relationships in southwest Atlantic sector of Antarctic Ocean

Optical and phytoplankton pigment data collected from around 80 stations in the south-west Atlantic sector of Antarctic Ocean between the Drake Passage and Antarctic Peninsula during three Antarctic Expeditions of Japan Fisheries Agency in Austral summer were analyzed for bio-optical characterization. Three optical water types were identified based on the spatial variability of phytoplankton pigment in the euphotic zone and corresponding profile of physical parameters along with total beam attenuation coefficient, ct(m-1) and diffuse attenuation coefficient, Kd(m-1). The derived pigment specific particulate beam attenuation coefficient and diffuse attenuation coefficients were effectively used to identify optical stations under dominant influence of non-chlorophyll substances. The pigment specific coefficients were compared with the coefficients reported from typical case I waters and polar waters as well. Significant variations from temperate model and agrement with polar region model are discussed. Chlorophyll remote sensing model was examined with two sets of reflectance, R((lambda) ) and sub-surface upwelling radiance, Lu((lambda) ) ratios. The typical case I water remote sensing algorithm and the algorithm derived from present analysis were implemented on the CZCS image, and satellite derived chlorophyll values were compared with in situ estimates available in the same area from the Polish BIOMASS-FIBEX expedition. The results point to the need of more critical study on the bio-optical aspects before implementation of local algorithms for this region on ocean color image.