Adaptation and integration of remote setting, selective breeding and triploid production technologies to revitalize oyster culture in Delaware Bay

Task 1. During July 2011, Harbor House scraped, cleaned and sampled Delaware Bay leased ground 138C. The ground was effectively void of oysters. The upper end of the lease was good clean bottom with a decent shell base, so it was decided not to plant shell on the lease. The portion with good clean bottom was divided into two plots: one that would receive spat on shell and one that was left alone to catch wild set for comparison.

Task 2. The Port Norris facility includes an acre of property along the Maurice River (150 ft of river footage) with a 3,000 square ft building and a commercial dock with 100 ft of frontage. The building had been used for storage and was not functional for this project. It was cleaned out, painted and 120 sq ft converted into laboratory space for this project (Figure 2). The laboratory portion was air conditioned and included a 10 ft lab bench. Laboratory equipment included a dissecting scope to count and assess larval viability and spat abundance, a refractometer to determine salinity, a refrigerator to hold ALGAL paste (concentrated phytoplankton) to feed oysters during setting, a water quality test kit, and an assortment of buckets, beakers and graduated cylinders for handling larvae.

Ground on the property was leveled to create a foundation to hold three 3,000 gallon fiberglass tanks (53” deep x 130” in diameter) for setting oyster larvae (Figure 3). Additional space was cleared to accommodate a total of 12 tanks for future expansion. The tanks were plumbed to receive salt water from the adjacent Maurice River as independent static or flow through systems. A 3 hp 3 phase seawater pump was installed inside the building and 2” pvc used to draw seawater from the Maurice River to supply the tanks (Figure 4). Tanks were fitted with 25-micron bag filters to remove zooplankton present in the river water that may act as predators or competitors during setting of oyster larvae (Figure 5). A 2.5 hp 3 phase regenerative blower (Figure 6) was installed in the building to provide aeration via 2” PVC pipe laid in a double ‘H’ configuration along the bottom of the tanks (Figure 7). Holes drilled into the top of the pipes were variously plugged with stainless steel screws until air flow was balanced across the tank when filled with water. A triple tube straight immersion heaters was coupled to a heat controller and mounted on the side of one tank to allow for early season production by increasing ambient water temperature to 25oC to promote setting of eyed larvae (Figure 8).

Oyster cultch (shucked oyster shells) were accumulated during the previous year’s shucking operation and stored in open air to cure for this project. Shells were pressure washed with fresh water to remove debris prior to use. To contain the shell in the setting tanks and facilitate moving shell from the shucking house to the tanks and from the tanks to the Martha Meerwald for planting, 30 pvc coated heavy wire metal cages were constructed to hold approximately 20 bushels of oyster shell each (Figure 9). Cages consisted of two rows of four columns separated by a 4” channel. This design follows that developed by the University of Maryland, except their design included a second channel bisecting the rows in half. By eliminating this cross channel we increased the capacity of shell that could be added to a setting tank by allowing us to place eight cages in a tank instead of six. We tested whether or not this decreased larval access to the shell (see results), as this was the primary reason for the channels.

Task 3. An Case frontend loader and an 80 x 2 ft loading conveyor belt were used to fill cages with oyster shell that had been retained for this project by the Harbor House shucking operation during the previous year. A 5 ton Grove cranes was used to move cages filled with oyster shell into and out of setting tanks and onto the deck of the Martha Meerwald for planting on our oyster lease (Figure 10a and b).

Disease resistant triploid eyed larvae (i.e., mature larvae ready to metamorphose and attach to oyster shell) were received on July 30th (10.9 million), August 5th (9.7 million), and August 16 (2.6 million). These dates were later than originally planned due to construction delays and subsequent hatchery delays but corresponded to the period of natural oyster recruitment in Delaware Bay enabling us to continue the project as planned. In total, 23 million eyed larvae were purchased from the NJ AIC for use in this project. Upon arrival, larvae were inspected with Dr. Bushek instructing our staff how to handle and evaluate them for viability and abundance, and then prepare them for adding to the setting tanks. Eight cages were added to a setting tank for each batch of larvae two to three days before delivery of eyed larvae to allow natural microbial films to develop that encourage setting of oyster larvae. Tanks were filled with 25 micron filtered river water during high tide (slack high plus up to one hour past slack) to obtain the highest salinity water with the least sediment. Crystal Sea Salt(registered trade mark) was added as needed to increase salinity to 20 ppt to minimize differences between hatchery conditions and setting conditions. Salinity was monitored regularly before and during setting. The eyed larvae were then resuspended in a five gallon bucket containing about four gallons of water from the setting tank (Figure 11). Larvae were continuously mixed with the bottom of a graduated cylinder and inspected for activity, then added to the setting tank by pouring about half a liter at a time into different portions of the tank to ensure larvae were well dispersed (Figure 12). Tanks were left static after larvae were added for a period of three days to ensure larvae time to set (i.e., attached to oyster cultch).

To test the effect of removing the second cross channel in the shell cages, two central columns were left empty in four of the eight cages such that each column had at least three exposed sides (Figure 13). The four full cages contained four columns with only two exposed sides, possibly limiting access by larvae. Because differences were not detected during the first or second setting trial, all columns were filled for the third trial.

After adding larvae, 500 ml of concentrated phytoplankton (Instant Algae Shellfish Diet (registered trade mark), Reed Mariculture, Cambell, CA) was added to the tank and repeated twice daily while the tank was static and larvae were setting. Subsequently, feeding rations were increased to two liters per day as they larvae and spat were clearing the water column in the tank. On day three, the seawater pump was turned on to provided a continuous supply of food from the River. During this process, the salinity of the tanks equilibrated to that of the river water as the water in the tanks was replaced with river water. Shells were haphazardly collected on day two for the presence of spat (Figure 14). Spatted shells were planted on August 8th, August 15th, and on August 26, 2011 (Figure 15). The third planting was performed two days before hurricane Irene hit the coast of South Jersey. Before each planting shells were gathered from the top, middle and bottom of each cage to determine setting efficiency (that is, the percentage of the eyed larvae that had successfully attached to shells being planted).

Task 4. Because the bottom of the leased ground contained an adequate shell base following cleaning, no shell was planted.

Task 5. Our initial plan was to set larvae as soon as possible in May or June to extend the initial growing season so that oysters would get a head start on reaching predator size refuges and also reach market size earlier. Unfortunately, delays in construction and, more importantly, delays in hatchery production beyond our control that resulted from an unusual coast-wide larval mortality event, did not permit this early setting of oyster larvae. Nevertheless, we did successfully set larvae later in the year. The first planting was not conducted until August 8th and the third occurred on August 26, 2011. Two days after the third planting hurricane Irene hit the coast of South Jersey. Hurricane Irene was followed by Tropical Storm Lee and the combined effects of these storms caused unprecedented fresh water inflow (flooding) into the Delaware Bay. This dilemma led to many detrimental environmental conditions that threatened the survival of our newly planted spat on shell and detracted from our ability to completed monthly monitoring. Our science advisor from Rutgers, Dr. David Bushek, was able to deploy a salinity recorder directly over our shell plant within a week of the storms passing and determined that salinity levels recovered quickly although remained on the low side of average levels through September as freshwater worked its way down the bay. As a result, samples were only collected in November 2011.

Task 6. Results were analyzed by calculating setting rates (the percentage of eyed larvae that ended up on shell to be planted), estimating growth rate of oysters once planted and estimating survival through November 2011.

During the first and second remote setting we tested whether or not eliminating the cross channel in the shell container restricted access to shell by the setting oyster larvae. This was accomplished by leaving 2 center columns empty on 4 of the eight cages. At the time of the first planting, 25 shells were removed from each cage after it was dumped on board the Martha Meerwald (Figure 16). Spat were counted under a stereoscope in the laboratory and 25 measured to determine size at deployment. During the second planting, care was taken to remove shells separately from the top, middle and bottom of each cage (5 from each section) as the cage was emptied on the deck of the Martha Meerwald for transport to the leased ground and planting. For the third planting, 55 shells were collected from what was deposited on the deck of the Meewald to plant. Each group of shells was labeled and returned to the laboratory to be counted and measured (Figure 17). To evaluate on bottom survival and growth, a systematic sampling was accomplished in November 15, 2011 using Rutgers Haskin Shellfish Laboratory R/V Veliger and a small 0.81 m oyster dredge. Several tows were taken to obtain 45 shells with spat over the planted portion of the lease. No shells with spat were detected elsewhere on the leased ground used for this project.

• Figure 5: 25 micron filter bags
• Figure 8: Heater
• Figure 9: Cages of oyster shell loaded for setting
• Figure 10a: loading cages into setting tank
• Figure 10b: Loading cages onto Martha Meerwald
• Figure 14. Spat attached to shell
• Figure 11: Resuspending eyed larvae
• Figure 13: Cage with two columns of shell empty.
• Figure 2: Laboratory
• Figure 6: Regenerative air blower
• Figure 12: Adding larvae to setting tank
• Figure 15a: planting shell
• Figure 15b: washing spatted shell off deck of boat
• Figure 16: Sampling spatted shell on vessel
• Figure 17: Counting and measuring spat
• Figure 7: Airline in setting tanks
• Figure 3: setting tanks
• Figure 4: Seawater pump