SEDIMENT PREFERENCE IN JUVENILE PACIFIC FLATFISHES

Behavioural preference tests were used to determine if sediment select ion played a role in habitat choice. Four species of juvenile pleurone ctids were given a choice of eight sediments in a carousel and final c hoices were recorded after 20 h. Juvenile flatfishes demonstrated stro ng selection for sediments less than 500 mu m. Juvenile starry flounde r (Platichthys stellatus) selected larger particles with increasing fi sh size. Starry flounder under 25 mm in length chose mud, 50-80 mm fis h chose mud and mixed mud sediments and larger juveniles (> 150 mm) co nfined themselves to fine sand. Juvenile halibut (Hippoglossus stenole pis) at 50-80 mm preferred a combination of mud and fine sand and were spatially segregated. Yellowfin sole (Pleuronectes asper) at 50-80 mm showed a slight preference for mud and mixed mud sediments over sand, a selection that became stronger in larger (> 150 mm) fish. Juvenile rock sole (Pleuronectes bilineatus) at 50-80 mm preferred substrata of sand and mixed sand nearly 90% of the time. All species seldom select ed sediments which were too coarse to allow the flatfishes to bury the mselves, such as granular or pebble substrata. The results of these la boratory studies can be used to predict the distribution of juvenile f latfishes in a nursery area.