Direct observations of particle kinematics within a scallop (Placopecten magellanicus) spat collector by means of video endoscopy

Previous field and flume studies have shown that scallop spat collection in the field can be enhanced by modifying the structural design of collectors. In this study we examine, in a flume, how structural components of collectors and water velocity might influence larval collection. Spherical plastic particles (200 μm) were used to mimic larvae. Structural components considered were monofilament diameter, heterogeneity in the arrangement of monofilament, and mesh size of external bags. Particle speed, deflection ratio, and the number of contacts with a monofilament strand were the response variables measured by means of video endoscopy and image analysis. With increasing monofilament diameter particle speed decreased while the deflection ratio and number of contacts with monofilament increased. The number of contacts per unit area, however, increased with decreasing monofilament diameter. Particle speed, deflection ratio, and number of contacts with monofilament (as well as contacts expressed per unit area) were greater in heterogenous collectors. Particle speed decreased with decreasing mesh size of external bags. Deflection ratios were more variable. In general, highest deflection values were observed closer to the external bag with increasing mesh size. The number of contacts with monofilament peaked at intermediate mesh size. Accordingly, the number of vortices observed immediately downstream of external bags was greater using intermediate mesh size than with other mesh sizes. Overall, our results showed that the number of particles trapped by spat collectors is a complex function resulting from the interaction between particle speed and the capture efficiency of monofilament strands used inside collectors. The ultimate objective of the study was to provide the scallop industry criteria to improve collector design to maximize scallop spat collection.