The diel vertical movement of deep scattering layers monitored by the drogue-site 
                       acoustic method in the I-Lan Bay, Taiwan

                 Shih-Chin Chou*, Ming-Anne Lee* and Kou-Tien Lee*

* Department of Fishery Science, National Taiwan Ocean University, Taiwan 202.

      The drogue-site  method with  a 38kHz  scientific echo  sounding system was 
used to  monitor the diel  vertical movement of  deep scattering layers  in the I-Lan 
Bay, Taiwan,  April 13-15 and  June 12-14, 1997.  At the  time of the  monitoring, a 
IKMT  sampler was  used  to  collect biological  samples  to determine  the  species 
composition of  the layers. The  dominant species were  Systellaspis pellucida, Sergia 
lucens and  Pasiphea japonica.  They occupied more  than 90.6% the  weight of  total 
samples. The  deep scattering layers  showed a distinct  nocturnal migration with  an 
ascent at  speeds of  1.52-1.90 m/min around  17-18 pm  and a descent  at 1.42-1.67 
m/min around 4 am.

Key  words :  deep scattering  layers, drogue-site  acoustic  monitoring, diel  vertical 
movement