Effects of seeding density, substrate depth, and tray type on the growth and survival of juvenile Pacific geoduck clams <i>Panopea generosa</i> in suspended nursery culture

ABSTRACT Objective Nursery culture of Pacific geoduck clams Panopea generosa involves placing hatchery-produced juveniles in trays of sand in the field for grow out to a size at which they can be transplanted to the benthos for intertidal/subtidal grow out to market size. A 5-month experiment was conducted in Deep Bay, British Columbia, Canada, to determine the effects of nursery tray type (two types), sand depth (two levels), and initial seeding density (two levels) on the growth and percent survival of young Pacific geoduck clams. Methods Hatchery-produced juveniles (shell length [mean ± SD] = 5.8 ± 0.1 mm; wet weight = 32.9 ± 1.8 mg) were placed in two types of trays (black plastic oyster trays [OTs] or specially designed experimental aluminium trays [ATs]) at two sand depths (10 cm [10D] or 20 cm [20D]) and at two seeding densities (low [LD] = 1,615 individuals/m2 or high [HD] = 3,230 individuals/m2). The deeper sand depth could not be accommodated in the OTs, leading to six treatments: OT/LD/10D (n = 18), OT/HD/10D (n = 18), AT/LD/10D (n = 21), AT/HD/10D (n = 17), AT/LD/20D (n = 19), and AT/HD/20D (n = 17). The effects of those factors on shell length, wet weight, and percent survival were examined after 5 months of tray deployment. Results Tray type, sand depth, and initial seeding density all significantly affected the growth of the juvenile clams. The 20D and LD treatments produced significantly larger (shell length) and heavier (wet weight) individuals than the 10D and HD treatments. The ATs produced significantly heavier (but not larger) individuals than the OTs. Percent survival was relatively high (88.3–97.6% in the various treatments) and was not significantly impacted by any of the studied variables. Conclusions The study showed that ATs seeded with a density of 1,615 individuals/m2 in a sand depth of 20 cm resulted in the greatest shell length and individual wet weight for the systems tested for rearing juvenile Pacific geoduck clams during the nursery phase. The results will be useful in optimizing standard nursery practices in the Pacific geoduck clam industry.