Improvement and demonstration of subtidal cage culture methods to cultivate oysters in Delaware Bay, New Jersey

Improvement and demonstration of subtidal cage culture methods to cultivate oysters in Delaware Bay, New Jersey

Summary

The purpose of this project was to improve cage-oyster culture technologies and methodologies to minimize handling costs and enhance profitability of subtidal oyster aquaculture on leased bottoms of the Delaware Bay. Specifically objectives were to: (1) evaluate the production of oysters grown in two types of cage systems, tiered rack and bag and stacked flip top; (2) examine fouling and ease of handling of the two types of cage systems; (3) optimize husbandry practices to maximize production and minimize labor costs; and (4) modify vessel gear to improve handling of cage culture systems.

Two types of oyster cages were evaluated. The first type, which was used in prior trials was a three tiered-cage system that accommodated 3 standard 7/8th inch mesh ADPI bags. The second cage type was a 3’ x 4’ interlocking vinyl covered steel mesh tray, purchased as a kit from Ketchum Traps (www.lobstering.com). The cages were assembled in May 2012. The finished cages consisted of a top unit with a flip top lid, affixed to a bottom legged cage. Both cage types were deployed on the bottom as independent units. A line with a buoy served for marking and hoisting the cages.

Four production regimes, or treatments were evaluated—2 cage types (flip top and 3-tiered cage and bag) and 2 husbandry routines (cleaning every 2 or 4 weeks). An initial investigation was initiated in May 2012. Four replicates were established for each treatment. However, due to limited availability the preferred size class of 1” seed was not available and the study was initiated with 2” submarket oysters. On the first 4-week sample date, a large number of market oysters were removed from the trays and as a result of a misunderstanding of the experimental design the remaining submarket oysters were pooled and redeployed. Due to the small number of remaining oysters and loss of replication, the investigation was terminated in favor of a new start.

The second trial began in early July 2012. Submarket hatchery reared oysters were obtained from a farm located in the lower Delaware Bay and placed in the cages at a volume of 30L (10 L per bag) for the 3-tier cage, and 60 L (30 L per tray) for the flip top system. Duplicate cages were established for each treatment. Oysters at the start of the experiment averaged 57 mm shell height. The cages were deployed on a lease located at Maurice River Cove. Oysters were removed from the cages monthly to maintain similar densities in the bags and cages. Duplicate cages were sampled monthly through October 2012 and the following parameters were assessed: oyster mortality, growth, and market yield; Dermo disease and fouling. Statistical analyses included ANOVA. Where appropriate data was arcsine transformed prior to analysis. Labor invested in the husbandry of the cages was also documented.

Oyster production (number marketed in respect to number planted) was also recorded during the course of the grow-out season. Analysis of production data is currently underway.

The data has been compiled and preliminary analyses of the results have begun. Outreach efforts have included a poster presentation at the Aquaculture and Restoration: A Partnership Conference of the Northeast Aquaculture Conference & Exposition, the Milford Aquaculture Seminar, and the International Conference on Shellfish Restoration held on 12-15 December 2012 ?at the Mystic Marriott Hotel and Spa?in Groton Connecticut. Informal discussions of the project have been conducted with several new oyster farmers who are working subtidal areas in the lower Delaware Bay.

Objectives/Performance Targets

Accomplishments/Milestones

Oysters maintained in the flip top cages exhibited lower levels of Dermo disease, better survival when a 2-week cleaning regime was employed, and slightly faster growth than those held in the 3-tier systems (Figure 1, attached). Crew preferred the flip top cages to the 3-tier cages as they were easier to clean and work over.

Biofouling during the study period varied temporally, both in terms of the fouling organism and the intensity of fouling. Fouling was significantly lower in the cages cleaned every 2 weeks than in cages cleaned monthly. Polydora sp. was the most significant and damaging pest. During heavy fouling periods a two-week cleaning regime was preferred due to ease of cleaning and better survival. However, the less intensive 4-week cleaning regime did not significantly negatively impact oyster growth.

Though this study captured only a single season of a four to ten-season grow out cycle, the results suggest that subtidal cage culture of oysters is a viable option for growing oysters on the traditional planting grounds of the Delaware Bay.

The flip top cage systems offered some advantages to the three tier systems; however, differences in oyster growth and mortality between the two systems were not significant and do not warrant a complete replacement of 3-tier systems that farmers already have in operation.

Future efforts by the farmers will employ the 3-tier system for smaller seed with a transfer to the flip top cages as the oysters grow to 1.5” size. Previously at the end of the grow out season we have moved submarket oysters to lower bay intertidal waters for overwintering; however, this year we will use the flip-top cage systems for overwintering submarket oysters on our Maurice River Cove grounds. In regards to cleaning of fouling organisms, we will continue to check the cages at two week intervals during the period May through September when fouling peaks.

No significant changes have occurred on our farm; however, we are presently working with a group of other oyster farmers to develop the Delaware Bay Oyster Growers Cooperative, which would serve as a marketing and production coop.

This project has been conducted through a collaboration of farmers Barney Hollinger and Bill Riggin and Lisa Calvo, Rutgers University extension staff. A crew of four part-time laborers have assisted with farm operations.

• Figure 1

Impacts and Contributions/Outcomes

Collaborators: