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Istiophorus platypterus (Shaw, 1792) is the most common billfish species in the Arabian Sea and contributes more than
50% of the total billfish landings in India. The abundance of I. platypterus was more off Maharashtra and Gujarat in the
northern Arabian Sea and in Lakshadweep islands with higher catches during March, April and December. The aim of
the study was to predict the suitable habitat of occurrence and potential fishing ground of I. platypterus by correlating the
spatial catch rates with environmental parameters along the Arabian Sea. Generalised Additive Modelling (GAM) showed
significant relationship between the catch and the predictor variables [sea surface salinity (SSS), sea surface temperature
(SST), sea surface height anomaly (SSHa), current speed (CS) and chlorophyll (Chl)]. SSS from 32 to 36 ppt had a positive
effect on the expected abundance. Similarly, SST showed a positive effect from 25 to 28°C and thereafter had a negative
effect on catch rate. The highest catch values associated with the SSHa was >0.4 m and partial effect of SSHa on catch was
negative below 0.4 m. Current speed higher than 0.4 m s-1 showed negative effects on catch rate and lower Chl-a values
which ranged between 0.04-2.14 mg m-3 in the study area showed a positive effect. All explanatory variables (SST, SSHa,
CS, Chl) except SSS were found to be highly significant covariates (p<0.01, p<0.01, p<0.001 and p<0.05 respectively) and
38.2% of variance was explained by the model with these variables. The paper discusses the fishery and trend of billfish
landings along the Indian coast in relation to various remotely sensed data and defines the optimum habitat suitability for
I. platypterus.
