The effect of temperature on the vertical distribution of larval herring ( Clupea harengus L.)

The effect of temperature on the vertical distribution of herring ( Clupea harengus L.) larvae was investigated in a Perspex tank filled with sea water to a depth of 1.76 m. The vertical distributions of larvae subjected to artificial thermoclines were compared with those observed in homogeneous temperatures. All experiments were performed in complete darkness and larvae were observed with an infra-red sensitive television camera and light source. The activity of the larvae was restricted to alternating bouts of sinking and vertical swimming which resulted in many encounters with the temperature discontinuity. The larvae showed a preference for the higher temperature, in the upper part of the tank, when exposed to temperatures of up to 13 °C in the upper part of the tank and tended to accumulate near the thermocline.