Effects of small-scale hydrographical change on the occurrence of larval Indian oil-sardine (Sardinella longiceps) at the coast of Oman (Arabian Sea)

Larvae of the clupeid species Sardinella longiceps (Indian oil-sardine) were found in the ichthyoplankton along the coast of Oman (Arabian Sea) between March and April 1987 (premonsoon period). A grid consisting of 25 stations (50 × 100 nautical miles) was sampled twice during a 2-week period. Depth stratified stations were sampled by the use of a modified MOCNESS-1 down to 150 m depth. Hydrographical data were obtained by a CTD-system on each station. Results show that short time hydrographic changes like the lateral advection of a different water mass can be responsible for high variability in abundance and distribution of fish larvae on or off the narrow shelf at the coast of Oman during the premonsoon season. The shift from a coastal to a more oceanic characterized water mass seems to have limited the occurrence, but increased the abundance, of sardine larvae in the study area. In spite of the absence of a strong hydrographic stratification, larvae were exclusively distributed in the upper 30-35 m of the water column. A slightly stronger stratification due to the intrusion of the oceanic water may have led to a concentration of sardine larvae in the upper part of the pycnocline