OPTIMIZING THE DESIGN OF GIANT SCALLOP (PLACOPECTEN-MAGELLANICUS) SPAT COLLECTORS - FLUME EXPERIMENTS

Flume experiments were carried out in 1993 with specially designed col lectors and inert particles to optimize the effect of various structur al components of scallop spat collectors. The structural components co nsidered were monofilament diameter and density, and mesh size of exte rnal bags. Results showed that abundance of particles trapped in silic one treated collectors did not vary significantly with monofilament di ameter. The heterogeneous arrangement of monofilament also proved to b e an important factor. Combinations of monofilament of three different diameters (0.17, 0.55 and 0.90 mm), the thinnest being the upstream o ne, collected at least twice as many particles than all other single o ne-sized monofilament collectors. Particle abundance decreased with de creasing density of monofilament, and the densest arrangement of monof ilament captured over four times more particles than the least dense a rrangement. Collectors with an external bag of intermediate mesh size (0.4 x 0.5 cm) were the most efficient at collecting particles. The ef fect of flow speed was also investigated. Particles were trapped in si gnificantly greater numbers at flow velocities of 5 cms(-1) than at lo wer or higher velocities. These results are consistent with results of field experiments carried out to optimize the design of scallop colle ctors. Enhancement of spat collection is possible by modifying collect ors. Results from both field and flume experiments confirm the hypothe sis that larvae of the species collected in the field are passive at s ettlement at the scale of the collectors.