Seasonal and spatial distribution of larval euphausiids from the shelf waters off southwest coast of India

Abstract

The annual mean value of euphausiid larval biomass in the southwest shelf waters of India has been numerically estimated to be 1,507 per 1000 m' of water. There was a well defined oscillation in the abundance of larvae mostly in relation to the changes in the environment brought about by upwelling. The June to October period was associated with intense upwelling in the study area. The process of upwelling started in the southern parts and gradually moved to the northern areas, according to which there was a seasonal and spatial shift in the larval abundance too. A monthly estimate revealed that while the larvae were least abundant in (June 36/1000 m') they were moderate in December, February and April (151-679/1000 m') and maximum in August and October (3,856 and 4,393/1000 m *). The larvae of Pseudeuphausia latifrons, Euphausia diomedeae, Nematoscelis gracilis and Stylocheiron armatum were more during the non-upwelling period of December to April. The larvae of Euphausia sibogae were abundantly present during the August-October period (of intense upwelling). The larvae of Stylocheiron affine were present almost throughout the year. The abundance of larvae of various species in different months was indicative of the breeding seasons.