Influence of chlorophyll-a and environmental drivers on fish landings along the west coast of India

Abstract

Fish landings along the west coast of India account for ~ 65% of the country’s total marine catch, with regional contrasts. This study investigated how fish landings relate to chlorophyll-a and key environmental drivers including sea surface temperature (SST), wind velocity, and mean sea level anomaly using satellite data within 100 km of the shoreline from Gujarat to Kerala. In addition, in-situ sampling was carried out off Goa and Kochi (September 2022, December 2022, and March 2023) to show seasonal variability in water column temperature, dissolved oxygen, chlorophyll-a, and FlowCAM-based microplankton quantity. The results show that fish landings increased during the periods of elevated chlorophyll-a (> 2 mg/m³) and dissolved oxygen (> 4 ml/l), but declined under warmer SSTs (> 28.9 °C), strong winds (> 5.8 m/s). Robust regression analysis indicated a strong positive association between chlorophyll-a and fish landings (slope: 3.56 × 10⁴ tonnes/mg m − 3 , p < 0.001; n = 99). Chlorophyll-a concentrations were consistently higher in the northern Arabian Sea, while total landings were comparable between Gujarat (avg. 6.4 ± 1.4 × 10^5 tonnes/yr), Kerala (avg. 5.6 ± 1.2 × 10^5 tonnes/yr) and Karnataka (avg. 6.1 ± 2.3 × 10^5 tonnes/yr), suggesting similar reported landings despite contrasting environmental conditions and fishing pressure. Higher landings off Kochi were observed during seasons characterized by a dominance of larger autotrophs, whereas off Goa higher landings coincided with relatively greater heterotrophic plankton abundance. This study highlights the need for integrated monitoring that combines water column physics, plankton dynamics, wind forcing, fishing effort, fishing bans, and fleet mobility. Satellite, in-situ, and vessel tracking observations provide mechanistic insights into the match and mismatch between environmental conditions and fish landings, supporting sustainable harvests and evidence-based management along the west coast of India.