Optimization of the technique of horizontally glued oysters
Final report

Brantville Aquaculture Ltd.
AIMAP-2009-G03

1. Introduction

The goal of this project is to increase the productivity and profitability of a unique technique in which oysters are glued to ropes and suspended horizontally. The feasibility of vertically glued oysters has been demonstrated in New Brunswick and elsewhere in the world, but that technique is limited to deep water areas. However, new flotation structures for horizontally glued oysters have been developed in New Brunswick by Brantville Aquaculture and the Department of Fisheries and Aquaculture. In a recent study sponsored by the New Brunswick Department of Agriculture and Aquaculture, the average performance in terms of weight and size of glued oysters was 50% better than it was for oysters in floating bags (Mallet and Doiron 2009).

This technique also improves the quality of the oyster's shape over time. At the end of the 2008 monitoring period, quality indicators for shape were better in the glued oyster group than in the floating bag group. In terms of biological and commercial productivity, the rope method (glued oysters) produced significantly better results than the floating bag method. However, the commercial feasibility of this approach has yet to be seen.

2. Task 1: Improve the oyster gluing process

Objective No. 1 – Improve the glue distribution process
In June 2009, InNOVAcorp engineer Tim Edmonds assessed the properties of PL Premium glue and how it was being applied to the oysters. His analysis concluded that certain constraints related to PL Premium would prevent the glue distribution system from being highly automated. Specifically speaking, PL Premium cannot be obtained in bulk and it has a very high viscosity. In July and August 2009, Norbert and Eric Thibodeau nevertheless tried to improve the glue distribution system with Darryl Pitre from the Loctite company. The first trials were conclusive in that a fairly precise quantity of glue could be transferred to the oysters repeatedly, and the vacuum created by the compressed air pressure controller helped reduce the glue streak, which was problematic with the 30–40 mm oysters.

Mr. Edmonds had thought of a design for a system in which the glue cartridge would be set up on a fixed point and activated by a pneumatic cylinder, and a tube equipped with a dispenser would be used to transfer the glue to the oysters. However, the probable hardening of the glue in the tube could have become problematic with that approach. The system now under consideration operates with compressed air. The glue cartridge is placed in a hermetically sealed dispenser, and the dispenser's plunger, which pushes the glue to the tip of the cartridge, is activated by compressed air controlled by a pedal mechanism. The quantity of glue that comes out of the cartridge depends on how long the pedal is pressed. One button controls the air pressure that pushes the glue down, and another button controls the vacuum that draws the plunger backwards to prevent long streaks of glue from coming out.

The way this system is designed, the air pressure controller can be set up away from the work area, and a small air tube connects the system to the glue cartridge. The potential problem of glue blocking the distribution tube is completely eliminated, and the glue cartridge can be replaced very quickly.

Typically, the unit should be installed on the floor so that it is foot-activated. In December 2009 and January 2010, the compressed air controller was modified to make it easier to use. The pedal mechanism was removed from the control system and replaced by a cylinder that is activated by an air intake, which pushes down a piston, which triggers the compressed air valve, which controls the glue cartridge plunger. This cylinder simply replaces the pedal mechanism.

To activate the compressed air cylinder and activate the system, the glue cartridge dispenser was equipped with a handle and trigger. When the trigger is pulled, compressed air is injected into the cylinder, which pushes out a piston, which drives the dispenser plunger and pushes the glue to the tip. When the trigger is released, the piston retracts into the cylinder, and the system creates a vacuum that draws the plunger backwards, preventing any more glue from coming out.

Conclusions: Despite the pessimistic prognosis at the beginning of the project, where it was asserted that constraints related to PL Premium glue would not allow for the development of an improved glue distribution system, a significant development was nevertheless made. The glue is still applied manually, but the process of transferring glue from cartridge to oyster shell is now done using compressed air, which should allow for faster and more controlled glue application.

Objective No. 2: Develop a technology to dry the oyster shells
Preparing the oyster shell surface is essential for good adhesion of the PL Premium glue. In 2009, oysters were washed in a washer and dried under ambient conditions. The oyster gluing work was therefore dependent on weather conditions: if the humidity was too high and the temperature too cold, the shell surface did not dry and it was impossible to apply the glue. In the rainy conditions of June 2009, it was impossible to glue oysters for several weeks. It had therefore become essential to develop an effective oyster-drying system.

In July 2009, talks were initiated with Atlantic System Manufacturing in Prince Edward Island for the construction of an oyster dryer. The system was designed to dry 5000 oysters in two hours. To estimate the necessary capacity of the dehumidifier, dry oysters were weighed, wetted and re-weighed. Based on those figures, it was calculated that each oyster had approximately 1 mL of water on its surface, so the dehumidifier had to be designed to remove 5 L of water in two hours.

The dryer had been designed with 10 levels and stainless steel mesh at the bottom. The system was to initially recover heat through air exchangers, but Mike Caudle (Tank Doctor) suggested to us that that option was not worth the expense.        

A second design was made, but with the option of air recirculation that could be controlled by closing the intake and outlet. In very dry weather conditions, the system could operate as an open circuit, but in humid conditions the system would have to operate as a closed circuit. Since the dehumidifier's fan had a capacity of 450 cfm, it was decided to build the prototype with that level of ventilation.

The dehumidifier's control system had to be modified to keep the fan operating continuously, and the heating unit's airflow sensor had to be correctly positioned. Initial trials showed that half of the oysters near the air intake were well dried but the ones farther away were still very wet after 75 minutes in the cabinet. An additional fan was installed in the pipe between the heating unit and the cabinet. We found that the additional fan decreased the oysters' drying time, and after 60 minutes, approximately 70% of the oysters were dry, but approximately 30% of the oysters in the middle of each level were still wet. After 60 minutes, the temperature inside the system was 32°C and the relative humidity was 27%. At that point, we concluded that a greater supply of air into the cabinet could speed things up greatly and that a large ventilation system needed to be installed to increase air circulation in the cabinet. Atlantic System Manufacturing offered to modify the system at no charge. Trials conducted after those modifications suggest that it is possible to obtain a drying time of approximately 60 minutes for 5000 oysters and that the unit is ready to be put into commercial operation.

Conclusions: In this project, a new technology for drying oysters was designed and built. We believe that we can increase drying times even further by making a few minor adjustments to this initial prototype. Also, the layout of the components could be improved to reduce the floor space that this technology occupies. This technology is ready for commercial use and should produce the desired results.

3. Task 2: Assess a hot glue

In the 1990s, Fisheries Resource Development Limited (FRDL), a subsidiary of National Sea Products, invested considerable resources to find a glue and to develop an automatic system for gluing 20–30 mm sea scallops onto strips. The adhesive selected for that process was a hot glue, which sets quickly, thereby allowing the scallops to be placed back in the water approximately 20 minutes after the glue is applied. As for the process of gluing oysters with PL Premium glue, two oysters are placed on a tray, a sufficient quantity of glue is applied between the two oysters so that it touches them both, a rope is extended over a row of 26 oysters, and a third oyster is then pressed against the rope onto the lump of glue. Hot glue cannot be used in this process because it hardens too quickly and does not have the high viscosity of PL Premium. We tested various scenarios to first determine whether this glue had any potential. In duplicate, we prepared the following experimental batches for two sizes of oyster:

1. A lump of hot glue, then the rope, then an additional dab of glue, then the third oyster (size 30–40)
2. A lump of hot glue, then the rope, then the third oyster (size 30–40)
3. With the larger oysters (size 40–50), a lump of hot glue, then the rope, then a large dab of additional glue, then the third oyster
4. BullGrip control group

Conclusions: Preliminary trials with hot glue suggest that PL Premium glue is considerably more effective at holding the oysters on the rope. Hot glue, however, does not cause mortality in the oyster batches but its high fluidity could cause the oysters to close permanently.

4. Task 3: Develop a float for the culture structure

The structure that supports the glued oyster lines is currently made of galvanized rebar. Until 2009, the structure was held afloat by Styrofoam floats attached to the galvanized rebar structure with bungee cord. In 2009, a float with PVC tubing was designed and put into use. This float is made of PVC tubing, 8 feet long and 4 inches in diameter, with a cap glued to one end and a threaded cap screwed onto the other end. The screwed-on cap is removed in fall, and the structure can be set on the bottom with the pipes. In spring, the structures will be taken out, the water drained and the caps put back on, allowing the line structures to float. An important aspect of cultivating glued oysters is having the ability to turn the structures over to expose the oysters to the sun and eliminate fouling such as mussels, oysters and barnacles.

In order to turn the structure over and expose the oysters to air, we first had to cover the centre rebar with plastic tubing to prevent the rope of glued oysters from wearing through. One person can turn over the structure from a boat, but it is preferable to have two people turn these structures over at sea.

The floats were attached to the galvanized iron structure with bungee cords. In a few cases, the bungee cord wore through, and the structure detached from the floats. One approach that we considered near the end of the project was completely eliminating the galvanized metal structure and using an aluminum bar that would be attached to the rigid float. Ultimately, it would be the floats that would give the culture structure its rigidity. One development that remains to be made with this structure is the ability to take the oysters out of the water when the structure is turned over. We can see two potential scenarios: (1) using tubing with a five-inch diameter, which would provide greater flotation; or (2) raising the float's crossbars. In this case, there would be a greater distance between the water surface and the lines of glued oysters.

5. Conclusions

In terms of biological productivity, growing horizontally glued oysters produces significantly higher yields than using floating bags. Scientific studies conducted in 2008 by the New Brunswick Department of Aquaculture and Agriculture and by Fisheries and Oceans Canada in 2009 (André Mallet, results not published) show the undeniable advantage of this culturing technique. However, the economic feasibility of this approach has yet to be established.

Several technological aspects of growing horizontally glued oysters were developed or improved through this project. These improvements should help reduce production costs and increase the profitability of this culturing technique. Despite an initially negative prognosis, Norbert Thibodeau (Brantville Aquaculture) successfully improved the glue distribution system by adapting existing components to meet his operational needs. Oysters can now be glued from multiple stations at once, which should increase the daily oyster gluing capacity. The development of an oyster dryer will standardize the drying process, which was previously done out in the sun. The problem of cold or rainy days is now resolved, and oysters can be dried at any time and on a predictable schedule. Lastly, the culture structure's flotation was greatly improved, and some good headway was made towards developing a better culture structure. In particular, the possible elimination of the galvanized-iron rope support structure and the use of floats with aluminum crossbars would create a lighter structure, which should be considered as a longer-term strategic investment. The structure still needs to be configured so that the ropes come fully out of the water when the structure is turned over in order to expose the oysters to the sun. Lastly, in the glue trials, hot glue showed a significantly poorer performance than PL Premium.

The elements for setting up a pilot project for horizontally glued oysters are now established and well known, such that a profitability analysis can now be conducted. The workers are well trained, the tools are either in place or have been developed to support further development, and the commercial yields are very promising. Oysters in floating bags could be deployed in parallel for a comparative study. The results could be used to determine the commercial feasibility of raising oysters in suspension in New Brunswick.

6. Acknowledgments

We would like to thank the organizations and individuals who made it possible for us to conduct this research. In particular, Rhonda Dillon from the Industrial Research Assistance Program of the National Research Council (IRAP-NRC), Florence Albert from the Aquaculture Innovation and Market Access Program of Fisheries and Oceans Canada (AIMAP-DFO), and Silvio Doiron from the New Brunswick Department of Agriculture and Aquaculture (NBDAA).

7. Literature cited

Mallet, A.L. et S. Doiron 2009. ÉVALUATION DE LA CROISSANCE DES HUÎTRES COLLÉES ET EN POCHES FLOTTANTES. Ministère d’Agriculture et Aquaculture du Nouveau-Brunswick. AFA9004