DEVELOPING A RESEARCH PROGRAM TO ADDRESS SHELLFISH GROWERS NEEDS: NINGRET POND - A CASE STUDY

Transcription

1 DEVELOPING A RESEARCH PROGRAM TO ADDRESS SHELLFISH GROWERS NEEDS: NINGRET POND - A CASE STUDY Dale Leavitt, Robert Rheault, & Heather Kinney Center for Economic and Environmental Development Roger Williams University & East Coast Shellfish Grower s Association

2 The situation: In recent years, there has been a rapid and substantial increase in oyster plantings on farms in a concentrated portion of Ninigret Pond (Charleston, RI). Ninigret Pond is a shallow coastal pond bounded by a barrier beach with a single narrow breachway to Rhode Island Sound.

3 The technology: Oysters held in polyethylene mesh bags. The mesh bags are kept in a wire cage with multiple shelves.

4 The problem: Since the initial development of oyster farms on the pond, starting in 1999, farmers have noted Increasing numbers of oysters being planted, Decreasing oyster growth rates and increasing mortality on their farm sites.

5 Soliciting help: In 2015, a group of six oyster farms on the pond, in collaboration with an academic researcher, submitted a proposal to the RI Department of Environmental Management s Local Agriculture and Seafood Act (LASA) Grants Program.

6 Proposed Collaborative Study: Question: had the increase in oyster plantings exceeded the carrying capacity of the pond?* Academic Researcher(s) Study seasonal and tidal variation in food levels across planting area. Measure chlorophyll and POM in water as it flows across the farms. Farmers Observe growth, survival and condition index in oysters being cultivated at varying densities on existing farms in Ninigret Pond. *NOTE: Previous research had suggested that there was enough primary productivity in RI coastal ponds to allow for significant increases in oyster densities within existing farms.

7 Yay they were awarded the grant funding! But.the Shellfish Biologist informed the farmers that he was not available to conduct the research as he was out of the country for the summer! WTF? Resulted in a panicked phone call to the local aquaculture extension agent (me) to assist the farmers in designing and implementing a research program to answer their question as to whether the increased oyster plantings had exceeded the carrying capacity of the pond. This happened approximately 2 weeks before the first set of experiments should have been started.

8 Now what? After numerous phone calls, discussions, meetings, and site visits over a very short time interval, we Cursed the original researcher for not carrying through with his commitment, Developed a reasonable study plan based on the funds available, Cleared our work schedule to allow for the study to take place, Assembled a team to conduct the study, Collected the required equipment and tested the proposed protocols to complete the study.

9 Study Objectives: 1. Monitor seasonal variation in food levels along a transect cutting through the existing farms in Ninigret Pond. 2. Measure oyster survival and growth at various stocking densities within the six participating farms. 3. Evaluate the condition of oysters growing at those various stocking densities.

10 Objective 1: Monitor seasonal variation in food levels along a transect cutting through the existing farms in Ninigret Pond. Completed a series of sampling transects at three time intervals across the oyster growing season. Followed a drifter that was positioned to move through the sequence of farms with the current over a tidal cycle.

11 Transect Objective 1: Monitor seasonal variation in food levels along a transect cutting through the existing farms in Ninigret Pond. Completed a series of sampling transects at three time intervals representing the oyster growing season. Summary of conditions in Ninigret Pond during sampling intervals. Date Time Interval Avg Drifter Speed (m/s) Avg Water Temp ( o C) Avg do (% sat) Avg Salinity (ppt) Avg Chlorophyll-a (µg/l) Avg Phycocyanin (µg/l) Avg POM (mg/l) 1a 29-Jul-15 7:30-9: % b 9:56-15: % a 20-Aug-15 7:30-10: % b 10:35-14: % a 16-Oct-15 9:25-11: % b 11:40-16: %

12 Objective 1: Monitor seasonal variation in food levels along a transect cutting through the existing farms in Ninigret Pond. During Transects 1 and 3, the POM available was in the range of 4.5 to 9.0 mg/l With little noticeable impact from the farms along the path of the transect. During Transect 2, there is a noticeable decline in the POM as one moves through the field of oyster farms. The level of POM was noticeably higher (range of 20 to 25 mg/l) such that the POM level at the downstream end was higher than the levels observed during the other sampling intervals.

13 Objective 2: Measure oyster survival and growth at various stocking densities within the six participating farms. Each farmer stocked two oyster bags at their regular stocking volume at one-half their normal stocking volume at twice their normal stocking volume The six bags were stocked into a conventional oyster cage The treatments were repeated for a second site on each of the farms. After a minimum of one month the bags were retrieved the total volume of oysters in each of the bags was measured as a proxy for overall oyster growth. This experiment was repeated twice on each of the farm.

14 Objective 2: Measure oyster survival and growth at various stocking densities within the six participating farms. Average Stocking Density % Survival 1/2x 96.7% 1x 97.0% 2x 97.2% All data 97.0% Average Initial Stocking Density (liters) % increase in volume stdev N % 14.4% % 14.9% % 17.5% % 25.8% % 3.7% 2 Oyster survival was similar across all stocking densities at all times on all farms and was very high. There was a direct and consistent relationship between stocking density and oyster growth Where the lower the stocking density (range of 1-2 liters per bag) supported better growth than higher densities (>3.5 liters per bag).

15 Objective 3: Evaluate the condition of oysters growing at those various stocking densities. As the farmer s growth experiment was initiated and retrieved, 10 oysters from each treatment were returned to RWU The oysters were measured for shell morphometry then shucked The shell and soft tissue dried at 60 o C for 48 hours A Condition Index (CI) was calculated for each oyster using the formula: CI = soft tissue dry weight/(live weight dry shell weight) x 1000

16 Objective 3: Evaluate the condition of oysters growing at those various stocking densities. 401 Oyster Farm Ninigret Oyster Farm East Beach Blondes I East Beach Blondes II Walrus & Carpenter Behan Family Farm In all but one farm, the condition of the oysters decreased, although there was a great deal of variability in the data. Because the oysters were immature, the decline could not be attributable to changes in reproductive status.

17 Objective 3: Evaluate the condition of oysters growing at those various stocking densities. Initial Stocking Density (liters) Average % change in CI stdev N % 27.3% % 17.1% % 33.5% % 29.4% % 58.7% 3 Overall, the reduced condition index did not correlate well with stocking density.

18 Study conclusion: While food resources in the pond were consistently adequate, a localized effect of oyster growth depression was noted in bags as the stocking density increased. Growth depression with increasing stocking density is likely the result of a very low rate of food flux through the oyster bags Due to a very low flow of water moving through the farms (in the range of 0.06 to 0.17 m/s) As they increased their farm production, they increasingly overstocked their oyster bags to conserve on equipment and handling time. Farmers need to adjust their stocking density to accommodate this observation.

19 Situation conclusions: (From the perspective of an Aquaculture Extension Agent) Trust It is important that farmers are aware that you are available and have the expertise to assist them with their problems. Time You need to have the flexibility to respond to last minute requests for time, effort and expertise. Support Having access to assistance, equipment and lab space is critical for you to provide services for the farmers that need it. Collaboration Working with farmers can be frustrating and time consuming as their business needs come first and research comes second.

20 Questions?