This project continued testing the viability of growing clams in contained-culture in the sediments below a floating oyster farm. This iteration focused on obtaining a realistic view of the economic viability of the technique and aimed to reduce reduce nursery-stage loss seen in the 2017 experiment.
The project was designed to:
1) Test the efficiency of floating nursery equipment using two different clam-seed sizes (1mm and >1-4mm) measured in seed-loss and percent of seed-clams reaching plant-able size
2) Measure the growth rates of bottom-planted clams under different stocking densities
3) Note degree of mortality under different treatments
4) Record fouling and pest presence
5) Estimate projected value of crop (if best stocking densities were applied across the entire farm)
6) Perform a cost/benefit analysis to determine if this method could supply a viable supplemental farm income given equipment costs and labor
7) Determine actual value of crop if market-size within the study period.
Subtidal aquaculture offers the opportunity for farmers to expand their operations and diversify their crops by utilizing the vertical space of the water column. Most seafarms are monocultures that only use the portion of the water column that provides their specific crop optimal growth. Adding a species with different environmental needs would allow a farmer to expand in-place and reap the benefits of additional products and increased operational resilience to disease and pests (without needing to re-enter the arduous lease permitting process).
Eastern oysters and littleneck clams are a good pairing for both husbandry and market. Small, intensive oyster farms like my own (which make up a large proportion of aquaculture leases in the region) use floating equipment to grow oysters in the top few feet of the water column where strong currents deliver the most suspended plankton. Littleneck clams optimally grow in soft sediments and could be placed on longlines on the seafloor below an existing oyster farms. In this arrangement, the oysters and clams would not compete for food or space. The species are not closely related and could offer a backup income if disease or pests decimate one crop
Littleneck clams are an attractive secondary crop for oyster farmers. They are unique in that they are most valuable at a small size. Both species are sold in the per-piece half-shell (raw) market, which offers a considerably better price than the per-pound commodity market (where other northeastern clams and mussels are sold). Additionally, farm-grown shellfish often offers a premium over wild-harvested shellfish on the half-shell market.
The contained, subtidal (always submerged) method of growing littleneck clams proposed by this project offers considerable environmental and cultural benefits over the traditional intertidal methods used on the east coast. In intertidal culture, clams are planted in netted plots or bags on exposed mudflats. This practice can be disruptive to wildlife (including sensitive shorebirds) directly excluding them from critical feeding areas or driving them away with increased activity. In many places these farming practices are prohibited or limited by law.
The intertidal zone has traditionally been used as a commons for wild-harvest of clams and marine worms. There is strong resistance to removing any portion of the fishing commons for private use. Intertidal clam culture also finds conflict with shore-front property owners and those engaged in outdoor recreation for aesthetic reasons. Growing clams below an existing oyster farm would avoid these conflicts.
Where subtidal culture of littleneck clams is practiced, seed clams are sown loose on the ocean floor and are harvested by dredging or dragging (at great detriment to other bottom dwelling species and long-term habitat structure). This method is not compatible with floating oyster culture, as dragging is impractical in the footprint of the ropes and anchors that make up a floating farm. The contained subtidal method proposed in this project does not rely on any bottom dragging or dredging. Clams are contained in rigid-plastic shellfish bags and are brought to the surface with ropes.
2018 Field Work Summary
The farm was raised from its submerged overwintering wintering position to its floating growing-season position between April 7th and 30th.
Clam length, volume, mortality and pest presence were measured on 4/30, 6/1, 7/1, 8/4, 9/7, and 11/17.
Fine mesh screens and nursery bags were acquired/constructed in May and June.
New 1mm clam seed was planted on June 25th. The 2.5mm and 4mm seed originally ordered from the hatchery was not available. Small seed (<4mm) that remained from the 2017 planting was used to test new nursery equipment in the early part of the season, before the 2018 seed arrived.
Tests of the effects of density on clam growth began 9/7, when sufficient volume was achieved.
Preliminary Results (Annual Report). Data analysis for final report is ongoing.
Growth: Second year clams showed excellent growth throughout the 2018 season, with average shell lengths more than doubling in each treatment. Treatment volumes in sediment-grown clams increased by approximately 7 times, while surface-grown clams increased nearly 12 fold. (See preliminary chart below). The largest clams were approaching salable size at the end of the season.
Clams planted in July 2018 grew at a much slower rate than clams planted in 2017, with shell lengths growing just over 4 times in length (compared to 11 times in 2017). Seed retention was, however, much higher in the 2018 planting, with 87% retained (compared to 40% in 2017). Seed loss in 2018 can be attributed to handling. mechanical loss in the nursery was negligible.
Price: During the course of the growing season I negotiated prices for littleneck clams with my oyster current distributors. Wholesale distributors initially offered prices ranging from 30 cents to 40 cents per piece. All buyers said they would match the 40 cent price. This price range offers a 10 to 22 cent premium over clams that were wild-caught or cultured out-of-state.
Product Quality: Though still too small for sale during the 2018 growing season, the clams from both surface and sediment treatments had excellent meat quality, with an exceedingly high sugar content.
Education & Outreach Activities and Participation Summary
Our Farms, Our Future Conference
Portland Press Herald Are littleneck clams the next frontier in aquaculture? (Sunday circulation: ~55,000. Does not include online readers)
In-depth emails/phone calls with farmers inquiring about technique (3 individuals)
Northeast SARE Tour (~60 individuals)
Social media and website reach for research-specific posts (social media ~1862 views, website ~860 individuals)
How-to digital brochure in development.