Diel cycles of zooplankton and fish vertical biomass movement in San Jorge Gulf

YVAN SIMARD; MIRTHA LEWIS; MARÍA VALERIA RETANA

Rimouski

Workshop; Workshop on the PROMESSe project: results and opportunities; 2017

UQAR-ISMER

We present the preliminary results of the echo sounder in the 3 legs of the mission and in particular the diel vertical migration of zooplankton at the fixed station in San Jorge Gulf during the Coriolis Missiion. As part of the goals of the working group, we analyzed the data from the echo sounder to detect zooplankton and fishes as potential preys of marine top predators. The distribution of the zooplankton was classified from the volume backscattering strength at 120 khz for 36 hs at the fixed station. During daytime, zooplankton was located below 65 m, except at the beginning of the second day where another zooplankton layer was located between 20 and 40 m (above the pycnocline). During night, most of them stayed in the upper water column but some were found at mid-water column. The zooplankton started to migrate to the surface at 20 Hs, one hour before the sunset, reaching the surface at 21:40 hs at a swimming velocity of ~1 cm/s. The zooplankton biomass (mean and maximum) was estimated from the sv at 120 khz using a general conversion coefficient from literature . the highest mean aerial (i.e. integrated over the water column) concentration of zooplankton reached 57.8 g/m3 at noon of the second day.