METHOD FOR THE POLYCULTURE OF CLAMS WITH OYSTERS

Abstract

A method for polycultivating clams with oysters in subtidal zones in an oyster growing-out bag at a low density, then placing the bags in the upper layer of the water by floating system including floating cage or floats. The clam could be Mya arenaria, and all other economic bivalve species that require burrowing in sand to ensure their growth.

Claims

1. A method for cultivating clams comprising: placing clam seed in a mesh bag with live juvenile oysters, placing the mesh bag containing clam seed and live juvenile oysters in a floating system so that the mesh bag is held under the surface of the water.

2. The method of claim 1, wherein the clam seed are selected from the group consisting of Mya arenaria, razor clam, hard clam, and Atlantic surf clam.

3. The method of claim 1, wherein the clam seed is Mya.

4. The method of claim 1, wherein the mesh bag is maintained at 1 inch to 48 inches under the surface of the water.

5. The method of claim 1, wherein the mesh bag is maintained at 2 inches to 36 inches under the surface of the water.

6. The method of claim 1, wherein the mesh bag is maintained at 6 inches to 24 inches under the surface of the water.

7. The method according to claim 1, wherein the mesh bag is an oyster grow-out bag.

8. The method according to claim 1, wherein the ratio of clam seed to oysters is 74:100 to 100:300.

9. The method according to claim 1, wherein the ratio of clam seed to oysters is 100:75 to 100:300.

10. The method according to claim 1, wherein the ratio of clam seed to oysters is 1:1

11. The method according to claim 1, taking place in a subtidal zone.

12. The method according to claim 1, wherein the mesh bag is contained in a floating oyster cage or is directly held by floats.

13. The method according to claim 1, wherein the juvenile oysters are less than one year old at an initial culture time.

14. The method according to claim 1, taking place in a subtidal zone in a Maryland portion of the Chesapeake Bay.

15. The method according to claim 1, wherein water salinity is in the range of 2 ppt to 30 ppt.

16. The method according to claim 1, wherein water salinity is in the range of 4 ppt to 20 ppt.

17. The method according to claim 1, wherein water salinity is in the range of 6 ppt to 15 ppt.

18. The method according to claim 1, taking place in brackish water of an estuary.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG. 1 is an illustration of Mya seed placed in an oyster grow-out bag.

[0023] FIG. 2 shows a 32 cell bottom cage used to hold the grow-out bags according to embodiments of the invention.

[0024] FIG. 3 shows an oyster cage with a float attached.

[0025] FIG. 4 shows floating cages and floating bags according to an embodiment of the invention.

[0026] FIG. 5 shows an example of a soft bag loaded with clam seeds.

[0027] FIG. 6 is a chart showing clam shell length at the end of a growth period using different culture methods.

[0028] FIG. 7 is a chart showing oyster and clam grown in monoculture and polyculture.

[0029] FIG. 8 is a chart showing survival rate of clams at the end of a growth period using different culture methods.

DETAILED DESCRIPTION OF THE INVENTION

[0030] Experiment 1: To test if the sand-free off-bottom polyculture method of the invention can facilitate Mya growth and ensure a high survival rate, a field test was performed between the polyculture method of the invention and two other methods, a. the soft-bag on-bottom culture, and b. the sand-tray on-bottom culture.

[0031] The soft-bag on-bottom culture is a common method that is often used in hard clam aquaculture. The clam seed are put in a large soft mesh bag (FIG. 5) then the bags are fixed on the water bottom. The bags protect clams from predators and prevent clams from moving to other places. Sediment in the water gradually gathers and covers the top of the bags to create a simulated burying-into-sediment environment. Given that both hard clam and soft-shell clam require burrowing themselves into sand to ensure growth, it seemed likely that this hard clam culture method might also be suitable for the soft-shell clam culture. The advantages are that this method is easy to deploy and harvest, and the bags are in an acceptable price range. For this experiment, the soft bag on bottom was used with clams only (monoculture).

[0032] The sand-tray on-bottom culture uses a tray for holding sand. The clam seed is placed in the sand and a net is used to cover the top of the tray to protect the clams from predators. This method has been used in some sand-needed bivalve subtidal aquaculture trials, but has not been popularized because a tray made strong enough to hold the large amount of sand required for makes this method costly and difficult to operate. Additionally, the top cover can be easily destroyed by predators or strong water currents.

[0033] Experiment 2: To examine if both Mya and oyster grow normally in a floating polyculture method, the same polyculture equipment (FIGS. 1-4) were also used for Mya monoculture and oyster monoculture as controls in the field test.

[0034] Experiment 3: To determine what water layer (upper or bottom) that the polyculture generates the faster Mya and oyster growth, a comparison was also made between floating polyculture and on-bottom polyculture method. The on-bottom polyculture used the same bags and cage (FIGS. 1 and 2) that were used for the floating polyculture but without the floats, so they were placed on the water bottom.

[0035] All the experiments 1-3 were conducted synchronously, enabling comparisons with each other. The Mya seed used was produced by Morgan State University's Patuxent Environmental Area Research Laboratory (PEARL) aquaculture team using Maryland local wild broodstock. The initial Mya density for all methods was 100 per bag/tray. The initial oyster density in polyculture or monoculture was 100 per bag as well. The average Mya shell length was obtained by randomly measuring 100 Mya and oysters before deployment. All methods employed at least three replicates. The cultures were all deployed at the end of October 2022. The cultures were collected in early June 2023. The shell length and survival rate were examined to evaluate the performance of each culture method. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Clam Average Clam Shell Shell sur- Average Oyster Culture Repli- Length Length vival survival survival methods cate (mm) mm % % % Soft-bag 1 27.2216 65 on-bottom 2 28.3612 61 culture 3 26.9932 27.52533 66 64.00 Floating 1 30.7294 94 monoculture 2 29.0802 97 3 29.6678 29.8258 98 96.33 Floating 1 32.09327 96 97 polyculture 2 30.9369 100 95 3 30.87583 31.302 100 98.67 89 On-bottom 1 26.3434 99 monoculture 2 28.1538 94 3 26.3944 26.96387 100 97.67 On-bottom 1 24.9416 95 100 polyculture 2 25.0896 92 96 3 24.5378 24.85633 97 94.67 100 Sand-tray 1 31.9432 88 on-bottom 2 31.5858 92 culture 3 30.9866 31.5052 76 85.33

[0036] The results showed Mya grew faster in both sand-tray and floating polyculture methods, compared to other tested methods (Table 1 and FIG. 6). The average shell lengths in the sand-tray and floating polyculture methods were quite similar (31.05 mm and 31.03 mm) after an about 7.5 month field culture (Table 1). The floating polyculture had the highest survival rate, and all the polyculture methods, both floating and on-bottom, had high survival rates compared to other methods (Table 1 and FIG. 8).

[0037] While the Mya in sand-tray culture showed strong growth, this method requires the purchase or fabrication of heavy duty sand trays and the use of large amounts of sand that may lead to high costs. Additionally, the deployment and harvesting of the trays is difficult because the sand-laden trays are very heavy, especially after being immersed in the water for several months. And the protective net cover on the top of the sand tray is also easily destroyed by large predators or strong water currents that will cause a loss of the cultured Mya.

[0038] The Mya in floating polyculture grow a little bit faster than a Mya monoculture, and the oysters in polyculture have the equivalent growth with the oyster monoculture in the same equipment (Table 1 and FIG. 7). This indicates in a limited farm space, polyculture can output both oysters and clams that will double growers' profit without purchasing new equipment.

[0039] The floating polyculture showed faster growth rate compared to the on-bottom polyculture (Table 1 and FIG. 8). That suggest floating polyculture should be used to ensure the fastest growth.

[0040] Having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications of the embodiments herein shown and described will obviously occur to those skilled in the art upon becoming familiar with said underlying concept.