Behaviour of recurving cyclonic storms in Arabian Sea as a response to atmospheric interactions

During the year 1998, Arabian sea witnessed two distinct and unusual cyc\onic systems. The very severe cyclonic storm of June 1998 was the most severe storm since last fifteen years as far as Arabian Sea systems are concerned; while October 1998 system was unique for, Its unusual and sudden easterly track after almost touching Saudi Arabia coast, (ii) Very high speed of movement and (iii) Interaction and merger with another vortex present in Arabian Sea off Saurashtra coast. This study is an attempt to understand the peculiar behaviour of the systems in Arabian sea which do not intensify beyond cyclone stage or even show a tendency to weaken before crossing coast as a response to atmospheric interactions. All the cyclonic systems in Arabian Sea since 1975 (Satellite era) have been examined in detail and the main findings of the study are : (i) Interaction between cyclonic disturbances of different intensities simultaneously present, appears to be the key factor in determining the further intensification or not of the systems. (ii) Track prediction for the systems upto marginal cyclone stage appears to be governed mainly by middle level atmospheric forcing. (iii) Upper level wind steering is found to be important for movement of systems from severe cyclonic storm stage onwards. The above results have direct relevance to operational cyclone forecasting.

Reproductive biology and feeding habits of the common dolphinfish Coryphaena hippurus (Linnaeus, 1758) off Saurashtra coast, India

The present study analysed reproductive biology and feeding habits of the common dolphinfish Corphaena hippurus, along the Saurashtra coast of India. The study is based on an investigation of 295 specimens caught using drift gillnet at Veraval. The samples were collected on a monthly basis between March 2015 and February 2016. The sex ratio was 1:1.75 with a significant dominance of females in the population. The size at maturity for females was 593 mm FL (fork length). Absolute fecundity of the individuals ranged from 1,07,813 to 15,50,400 having ova diameter range of 0.3-1.96 mm. C. hippurus spawned throughout the year with its reproductive activity peaking in April and December. Thus the dolphin fish has an extended spawning season; during which it laid eggs almost continuously. A total of 128 stomachs of C. hippurus, whose fork length FL ranged from 380 to 1250 mm were examined during the one year period of this study. Tunas were found to be the common dietary component of the dolphinfish.

Optical dating of late Quaternary carbonate sequences of Saurashtra, western India

Bioclastic carbonate deposits that formed because of a combination of nearshore marine, fluvial, and aeolian processes, occur along the Saurashtra coast and in the adjacent interior regions of western India. Whether these carbonates formed by marine or aeolian processes has been debated for many decades. The presence of these deposits inland poses questions as to whether they are climate controlled or attributable to postdepositional tectonic uplift. In particular, the debate centres on chronologic issues including (1) appropriate sampling strategies and (2) the use of 230Th/234U and 14C ages on the bulk carbonates. Using traces (<1%) of quartz grains trapped in carbonate matrices, optically stimulated luminescence (OSL) dating of quartz grains, deposited along with the carbonate grains, provides ages for the most recent deposition events. The OSL ages range from >165 to 44 ka for the shell limestones, 75–17 ka for the fluvially reworked sheet deposits, and 80–11 ka for miliolites deposited by aeolian processes. These are younger than the 230Th/234U and 14C ages and suggest that the inland carbonate deposits were reworked from older carbonate sediments that were transported during more arid phases.

GIS based mapping of spatio-temporal distribution pattern of ribbonfish Trichiurus lepturus (Linnaeus, 1758) along Saurashtra coast, India

Identification of spatio-temporal distribution of fish species represents fundamental information for stock assessment which in turn is essential for formulation of fishery management plans as well as for GIS based decision making. This study investigated the spatio-temporal distribution and abundance of different life stages of ribbonfish, Trichiurus lepturus (Linnaeus, 1758) off Saurashtra coast. Geographical coordinates of fishing and allied information on the time of fishing, depth of the fishing area as well as catch details were collected using a structured schedule, from selected trawlers operated from Veraval. Information was mapped using a GIS software to get the spatio-temporal distribution of the species. It was observed that juveniles were more abundant along the south Saurashtra coast whereas subadults and adults showed a discontinuous distribution with abundance in the waters off south Saurashtra as well as north Saurashtra coasts.