PRODUCTION OF OYSTER SPAT IN A NATURAL ENVIRONMENT PHASE I - TESTING OF COLLECTOR CUPS

Table of contents

• SUMMARY
• INTRODUCTION
• METHODOLOGY
• Economic analysis and operational monitoring
• RESULTS AND DISCUSSION
• Characteristics of experimental structures
• Collection rates
• Seed size on collectors
• Oyster size after sorting
• Operational aspects
• Seed-stripping of cups
• Cups operation
• Cost analysis
• Cups purchase price
• Longlines
• Nursery stage longline
• Collector operating labour costs
• CONCLUSIONS
• BIBLIOGRAPHY

SUMMARY

Oyster spat collection tests were conducted at Bouctouche and Caraquet to assess the performance of a new type of collector cup. The idea was to potentially adapt the technique to current cultivation activities. Specifically, the project sought to adapt the French technique of capturing and producing oyster spat to the peculiarities of shellfish culture in eastern Canada in order to mechanize the operation and reduce production costs. The project also sought an alternative to Chinese hat collectors, which present constraints for setting up a sorting strategy to select the best performing individuals in terms of growth. The results were convincing in terms of capture rates and mechanization of operations, but highlighted deficiencies in terms of the nursery stage, both for the collector cups and Chinese hats.

INTRODUCTION

The oyster industry is booming in New Brunswick as a result of the floating bag culture technique, developed at the beginning of the new millennium (SEnPAq; 2000, 2001). Since then, several research projects have been conducted with a view to master the various aspects of this production technique (SEnPAq 2000, 2001; Lanteigne, 2005, 2006; Mallet et al 2008; Mallet and Doiron, 2009). They have primarily focused on nursery technologies; people in the industry estimate that the Chinese hat collectors were adequately mastered and well suited to the particularities of NB ostreaculture. Little effort has been made to improve collection, production and spat sorting techniques. Although the literature is overflowing with work on genetic selection of hatchery larvae (Boudry, 2006, Franklin & Downing, 1989; Taris et al, 2006a; 2006b; 2007), and work is currently underway at the Coastal Zone Research Institute (CZRI), it is quite limited in terms of selection (culling) from spat and oyster seeds produced in a natural environment. Raising oysters from hatchery spat does not justify this type of scientific process since sorting takes place in the hatchery at the larva stage. The only listed articles on culling oyster spat were written by Alexander and Newkirk (1988) and Rosique et al (1993). According to Alexander and Newkirk (1988), oyster growth seems to be more influenced by competition factors than genetic traits. Therefore, it becomes rather difficult to select individuals with traits of interest to oyster farmers as a result of environmental factors. Despite these operational constraints, Rosique et al (1993) emphasized the advantages of culling based on growth performances of flat oysters, captured and nursed on Chinese hat collectors.

Based on these studies and the confidence the company has in implementing this approach, Aquaculture Acadienne Ltée, in 1995, in partnership with Maison BeauSoleil Inc. and Ferme Marine Lanteigne Inc., embarked on their research project to develop a technique for sorting oyster spat produced on Chinese hat collectors to select the best performing individuals. Lanteigne's work (2007, 2008, and 2009) confirmed the culling approach and shortened the oyster production run, while decreasing the proportion of low growth individuals in end-of-production inventory. The final report concluded that it would be possible to reduce the number of bags needed to produce one million oysters by 34%, resulting in a significant reduction in production costs (Lanteigne, 2009).

Although the results were conclusive, the technique does not allow for an optimal degree of precision; a relatively large proportion of small-sized individuals, theoretically less successful, were still present in culture inventories following sorting. Sorting could be made more precise by improving spat quality (shape) through better capture techniques and an efficient nursery stage system, reducing abrasion to the oyster frill during sorting and a more efficient sorting system to improve the accuracy of population division, by reducing the range of size frequency distribution. The research activities exposed two important constraints on sorting efficiency associated with the collector, namely, the shape and size of the Chinese hats as well as the mixture (lime-cement-sand) used as a collection substrate. The shape and size of the Chinese hat collectors would tend to emphasize the influence of environmental factors (the effect of shade between individuals, the circulation of water on food supply and the elimination of feces and pseudofeces) on growth performance, thereby masking the effect of genetic variability on growth rates. Small oysters on residual pieces of cement during seed stripping would tend to introduce small specimens into large-seed groups. It became worthwhile to assess a new collector that might be better suited to our collection, sorting and nursing stage activities.

While New Brunswick producers use a lime-cement-sand mixture as a collection substrate on Chinese hat collectors, French oyster farmers use only lime on the collector cups, which allows them to eliminate substrate residue caused by friable lime, and by doing so, minimize the occurence of small individuals in the larger seed batches. Another working hypothesis was that the size of the cups (17 cm diameter) compared to the Chinese hats (14" diameter) also allowed for better water circulation in the centre of the cups, which should support uniform food supply and minimize the effect of environmental factors on oysters in the centre of the collectors versus those in the periphery. Columns of collector cups are installed on stands that fit 18.5 columns of 12 Chinese hats per operation. In addition, the cups are ready to be limed and reused immediately after seed stripping, while the Chinese hat collectors must first be assembled, dismantled for seed stripping annually and then re-assembled before they can be reused. Using collector cups should therefore, in theory, reduce seed production costs. In addition, equipment has already been developed to mechanize the seed-stripping process. A demonstration by Yvon Madec de Prat-ar-Coom (oyster producer in the Brittany Region) suggests that it would be possible to process (seed stripping, sorting and bagging) 50 collector cups every two hours (Lanteigne, 2008), while it would take an entire workday to process the same amount using Chinese hat collectors.

Adapting the French technique for collection and production of oyster spat to our cultivation activities and the anticipated benefits of sorting precision should greatly increase the profitability and competitiveness of NB oyster production operations. Perfecting a new collection and nursery stage technique could lead to reduced oyster seed production costs and should reduce the production cycle by one year, which represents a significant improvement, considering that it spans a 4-5 year period in NB (Lanteigne, 2001). Although fiscal agencies consider a production run for 15-25 mm spat as lasting 3 years, oyster farmers say that it would take at least 5 years in northeastern NB. Several factors can explain this situation, including spat quality. Therefore, the expected shortening of production runs is a major objective in the improvement of oyster business profitability.

It is becoming increasingly difficult to procure Chinese hat collectors given the poor quality of the latest deliveries, which suggests that the mold used to manufacture them is worn. Given the limited market, the oyster industry being the only consumer of this type of collector, the supplier would not be interested in investing in a new mold. Nevertheless, the cost of acquiring Chinese hat collectors has significantly increased in the past few years. A column of 12 Chinese hats currently costs $45, which would equate to less than $20 for collector cups (commercial volume order). This new technique would also lead to saving in terms of lime, cement and sand. Liming 300 Chinese hat collectors requires an annual investment of $2,500 for material, in addition to equipment rental and staffing costs. The manufacturing and operating costs for 300 collectors would total $15,000 annually. Using collectors could lead to considerable savings given that liming, set up and removal would be greatly simplified and liming would cost less.

METHODOLOGY

The project was run on lease MS-0100 in Lamèque Bay in northeastern NB and in Aquaculture Acadienne Ltée facilities in the Richibouctou Region in southeastern NB. The collectors were spread out in Caraquet Bay in northern NB and Bouctouche Bay in southeastern NB. Trial runs for the various collection approaches were tested in the Lamèque Region, while Richibouctou acted as a control site.

Three experimental structures were compared, specifically: 45-column cups on stands for use on the bottom (45 cups), three columns of 25 cups on stands for use in suspension (75 cups), while 12 columns of Chinese hats were used as a control group.

The bottom stand allows for the use of 24 columns and 45 cups. Shaped like a long pyramid, it is made with 3/4" iron rods, given the weight and volume oysters can be at the time of harvesting. Two, 2.1 x 1.2 metre sides are installed on an angle on a 2.1 x 1.8 metre base to form a triangle. Two iron bars are installed lengthwise on the sides where the cups are arranged. The cups are simply set up on the bars after being limed. French oyster farmers submerge the entire collection structure into a liming tank. A third rod with a hook on one end and a U-bolt on the other secures the columns on the metal structure. Legs were installed on three bases to attempt to document colonization of the structures by bottom-dwelling organisms that might prey on the oyster spat. Seven structures were placed directly on the bottom. A third group of two stacked structures was placed on the bottom.

The proposed structural design for the trial runs in suspension was modified as a result of Maurice Daigle's comments about the anticipated weight of the collectors at harvest. The stands used in the experiment held 3 columns of 25 cups, while the system initially proposed was 4 columns of 25 cups.

Given the weight at harvest time, his process likely would have required two technicians rather than one as Mr. Daigle pointed out. It would have also required two technicians to install the structures on a longline because there are ropes at each end to ensure they remain stable on the longlines. Only one rope is needed for the three-column units. The three and four column structures amount to 1.3 and 1.7, 12-column Chinese hats, respectively.

Five collection substrates were tested for each type of structure; an equal proportion lime-cement-sand mixture used by the NB oyster industry, lime-cement-sand mixtures
in 4-1-1, 3-1-1 and 2-1-1 proportions and a hydrated lime solution similar to what the majority of French producers use (Yvon Madec, pers. comm.).

All of the collectors were placed during seed collection peaks. The collectors in Caraquet Bay were transferred to the Lamèque Bay culture site two weeks after harvesting, while the collectors in Bouctouche Bay were not transferred until the fall for seed stripping. Seed stripping took place starting in the first week of October in Lamèque Bay and in mid-October in the Richibouctou Region. A seed stripping and sorting line was installed on the Lamèque dock and included a collector cup seed stripper, a vibrating screen and a bagger. The seed stripper was replaced by a food conveyor for the Chinese hat collectors seed stripping. For the purposes of the project, a new collector cup seed stripper, based on the systems used in France, was built to strip individual columns. Aquaculture Acadienne Ltée opted for a seed stripping system that it had initially developed for drainage piping collectors. That system seems better suited to the 75-cup collectors used in suspension; they can be broken down into three-column structures without needing dismantling. Seed stripping trial runs were conducted at Lamèque with the various columns (25-45 cups) and collection substrates.

The collection rates and spat sizes were assessed for each collector type and collection substrate. Three collector columns were stripped and the volume of oysters was determined. Three samples of 500 ml were taken for each column and all of the oysters were counted. The capture rates by collector were extrapolated according to the volume of oysters in the 500 ml samples. Subsamples of 200 oysters were then taken from the seed stripped column samples and all of the oysters were measured for length.

In the Richibouctou Region, a different approach was used to determine collection rates as a result of lower collection rates and the abundance of barnacles collected. Five plates were sampled on three collector columns (Chinese hats and cups). All the oysters were counted on every side of the plate. Five subsamples of 200 oysters were then taken from all of the seed stripped column samples and all of the oysters were measured for length.

Three oyster samples were taken for each collector and collection substrate after the sorting process, during seed stripping to assess efficiency (precision of sorting) according to the various collector types and the effect of sorting on the seed. Densities (number of individuals per volume sampled) were estimated for each sample. A subsample of 200 oysters was then taken from each sample and each oyster was measured for length.

Variance analyses were conducted to determine the effect of the collection technique on the collection rates and quality of spat produced in terms of intensity, size distribution and sorting effectiveness.

Economic analysis and operational monitoring

The collectors were monitored in an operational context and the production parameters (staff, material and equipment needs, processing steps and duration) were recorded for each collector group for every step of the process to grasp the advantages/disadvantages of the new collector and to prepare a cost analysis of the various collection approaches. The analysis also includes the oyster spat production component after sorting to determine the effectiveness of sorting and spat quality after sorting.

RESULTS AND DISCUSSION

Characteristics of experimental structures

The 75-cup collector has a 27,481 cm² collection surface compared to a 21,643 cm² surface for a column of 12 Chinese hats and 16,481 cm² for the 45-cup collector. Therefore, a 75-cup collector would be equal to 1.3 Chinese hats in terms of collection surface, while it would take 1.3, 45-cup collectors to equal a column of 12 Chinese hats. Respectively, the circumference of a 75-cup collector and a 45-cup collector would be 2.7 and 1.6 times that of a Chinese hat collector, which implies that a greater proportion of oysters in the collector cups would be on the periphery.

Several oyster farmers use 10-column Chinese hat collectors because of the weight at the time of harvesting or the condition of the collectors. In that context, a 75-cup collector would correspond to 1.5 columns of 10 Chinese hats while it would take 1.1, 45-cup collectors to amount to one Chinese hat collector in terms of collection surface.

Collection rates

Collection rates of just over 100,000 spats were obtained in Caraquet Bay for the Chinese hats. These results compare favourably to collection rates obtained in the region since the spatfall prediction service began there and, more specifically, to the best rates ever obtained in 2000 and 2005 (Doiron, 2000 to 2008). The collection rates were much lower in the Bouctouche Region with rates of 26,745 ± 5,046 spats per 75-cup (1.0 ± 0.2 spat/cm²). The degree of success capturing spat in that region seems to be greatly influenced by a significant collection of barnacles - one of the factors that can influence the successful capture of oysters. For Maurice Daigle, that is the main limitation on oyster spat capture in the southeast part of the province. The Miramichi Estuary region is also experiencing barnacle infestations during their oyster spat capture period.

The 75-cup collectors had the best absolute yields. However, when we convert the collection rates to the equivalent in Chinese hat collectors, the 45-cups have an average yield of 135,000 spats per Chinese hat (6.2 spat/cm²), which were the best collection rates, while the Chinese hats (4.9 spat/ cm²) had the lowest yields. These differences would signify P 0.000. The significant difference between the 75 and 45-cups was surprising. However, a difference like that can be explained by the fact that the 45-cups were placed on the bottom and the 75-cups were kept suspended close to the water's surface. It is possible that a more stable structure on the bottom could facilitate oyster spat collection, while movement of structures close to the surface due to waves could have adverse effects on successful collection.

There were no significant differences in terms of collection success between the various collection substrates, with the exception of the 75-cups, which had been immersed in a lime solution and had much lower capture rates. These results can be explained by the loss of collection substrate on the upper portion of the 75-cups. Collectors often bump against one another when they are handled during transportation to collection sites, when they are immersed and again when transferred to nursery stage sites. The lime substrate, as the most friable of all the substrates tested, would be the most likely to come off the collector. The upper part of the 75-cups covered in lime substrate would most likely be affected because of the fragility of the collection substrate and the chances of collision, which would explain why there was less collection substrate on the top of the collectors and therefore less collection. Losses were minimal for the Chinese hats covered in lime substrate because of the care taken when handling the control group collectors. Collisions between Chinese hat collectors are likely to occur more frequently in an operational context and should lead to the same results as the 75-cups. The base structures make it possible to handle the 45-cups without risking collision. No substrate loss, other than minimal, was observed for those collectors. French oyster farmers primarily use lime in the 45-cups and have not reported any substrate loss issues.

Seed size on collectors

There seem to be no growth differences between the various collection substrates and column positions tested except for the spat on top of the 75-cups covered with a lime substrate. That difference may be explained by the lower densities in the upper part of the columns. Since the loss of collection substrate reportedly led to a decrease in density on the top of the 75-cups, that situation could have facilitated the growth of oyster spat.

A significant difference (P=0.000) was observed between the various collectors tested.  The 75-cups presented the best results with spat measuring 11.43 ± 4.05 mm compared to 9.9 ± 4.42 mm for the 45-cups and 10.61 ± 4.25 mm for the Chinese hats. These differences could be explained by the shading phenomenon (Lanteigne, 2006) between the collection structures and on a given structure (45-cups) or even, by the higher collection rates and therefore increased competition for space and food that is particularly obvious on the Chinese hats and 45-cups.

The columns of 45-cups are very closely arranged on the bottom structures, which could negatively affect water circulation and increase shading between columns. It might have resulted in decreased food supply and consequently, decreased growth rates. The slope of cup columns on the base structures that seems to have encouraged brown macrophytic algae growth on the sun-exposed sides could also affect oyster growth. The sizes of the oysters on that side of the collector appear smaller than those on the shady side. However, no samples were taken to confirm that observation.

Differences in oyster size were observed on the same plate, whether on Chinese hat or collector cups. These variations in size on a given collector could explain the size variations between 75-cups and Chinese hats. For a comparable capture surface, 75-cup collectors have a 2.7% larger circumference than the columns of 12 Chinese hats, which assumes that the 75-cups have a larger proportion of oysters in the periphery than the Chinese hats. Therefore, a larger proportion of oysters would have optimal conditions for growth on the cups as compared to the Chinese hats. Size differences have been observed between oysters in the centre of the plates for the Chinese hats and the collector cups. In light of the observations about growth differences between the Chinese hats and 75-cups, the size of the oysters in the centre and periphery of the 75-cups and Chinese hats was estimated through image analysis using UTHSCSA Image Tool software. Although the software does not offer absolute precision due to the varying angles of the oysters and tends to tone down the size variations, it does provide a good estimate of the growth differences observed between the centre and periphery of the plates. There was a significant difference (P=0.000) between the size of the oysters in the centre and on the periphery of the collectors. Although the same phenomenon was observed on both collectors, there were more oysters on the periphery of the 75-cups, which consequently increased the average size of the oyster population size growing there when compared to the Chinese hats.

It is difficult to distinguish the space between the cups because of the growth of oysters on the periphery, which should impede water circulation between the cups and food supply for oysters in the centre of the collector. There was a low level of capture compared to the collectors in Caraquet Bay and the barnacle infestations. It is important to remember the uniformity of sizes and the effect of growth rates on the entire plate, which supports the hypothesis on the lack of food for oysters in the centre of overloaded collectors.

This can be corrected by spacing out the cups but an overly large space would lead to a decrease in the number of cups per column and, subsequently, less collection surface and volume. However, that is not a major factor. Maurice Daigle is considering reducing the size of the 75-cups (60-cups) to reduce the weight of the collectors. Increasing the space between the collector cups by 5 mm would mean that a 75-cup collector would correspond to 1.1 rather than 1.2 Chinese hats. Another potential consequence of spreading out the cups would be a decrease in oyster larvae retention between cups, which could lead to lower collection rates. However, there is no scientific or technical information to support the last hypothesis, which was based on personal observations of the arrangement of oyster spat on the collectors. The best collection rates were observed inside the parts of collectors capable of providing better larvae retention. When asked about this, the supplier indicated that spacing between collector cups was solely based on practical cnsiderations, in order to maximize the number of cups per column. A greater distance between cups could lead to better growth rate uniformity on the entire collection surface, which would then allow for improved sorting precision by reducing the effect of environmental factors on spat growing on collectors. Although this approach might involve a decrease in the number of cups on the suspended structures, that could be substantially offset by an increase in growth rates as a result of size uniformity which could be obtained on the entire collector surface.
 
Reducing the number of cups per column does not appear to pose any technical problems. According to the supplier, it would be possible to modify the size of the cup columns to meet industry needs. The length of the columns was established based on the size of the cargo pallets. Some oyster farmers use 1-metre rather than 1.2-metre columns. For suspended structures, it would be possible to either lengthen the cup columns or make groups of 4 cups. Maurice Daigle, of Aquaculture Acadienne Ltée, finds that the 75-cup collectors are too heavy at the time of seed stripping to be handled by one technician. He is considering, as previously noted, reducing the size of the cup columns to make them easier for one technician to manage. As previously mentioned, one 75-cup collector corresponds to 1.2 Chinese hat collectors. It would therefore be possible to eliminate 15 cups without changing the height of the columns. This approach would allow for a 5 mm increase in the space between cups. For the 45-cup collectors, that much distance would mean that it would require 1.6, 45-cup collectors to have the same collection surface as one column of 12 Chinese hats. The approach would reduce the effect of shading between the cup columns, which would compensate for the loss of collection surface. Trial runs should be conducted to determine optimal spacing between the cups in terms of collection and growth rates for the various approaches, namely, for 45-cup and 75-cup collectors.

Oyster size after sorting

The average size of the entire population for each collector type was obtained by weighting the averages of each size sub-group by the density of oysters in each sub-group.

The size of the oysters differed for each of the collectors tested. The 75-cup collectors had the best growth rates, followed by the Chinese hats and 45-cup collectors, which mirrors the situation before sorting. These are also significant differences. There do not seem to be any differences between the various collection substrates except for, as shown in the pre-seed stripping samples, the lime substrate on the 75-cup collectors.

Oyster spat size decreased by 2.62 mm for the 75-cups, by 2.20 mm for the 45-cups, and by 2.35 mm for the Chinese hats following sorting on the vibrating screen. All of those changes are significant. Size frequency distributions were compared in an attempt to understand which proportion of the population showed the most significant growth loss. A major increase in the proportions of oysters from groups 5 to 10 was noted for the three collector types. A uniform reduction should have led to an equally massive increase for the 0 to 5 mm group considering the proportions of the oysters in the 5 to 10 mm group. Frill (new growth) loss would therefore be more significant for the larger oysters. As a result, actual growth loss could be much greater given that smaller individuals are eliminated in any case during the selection process for fast-growing individuals. The loss of growth could approach that of the 5 mm group and have serious consequences on the production cycle.

The vibrating screen causes significant losses with respect to spat size. However, the effect of stress and the mortality that can be attributed to vibrating screen operation were not quantified.  It would be very worthwhile to develop a less restrictive sorting device. Moreover, the French industry recommends this approach. The French are currently adapting immersion screen technology to the oyster industry. According to the oyster gear suppliers we met at the Saint-Lô Conchy-pêche show in March 2008, oyster farmers think the vibrating screen would cause high oyster mortality rates while the immersion system would reduce oyster stress. At the 2007 AGM for the NBPSGA, André Mallet reported the high mortality rates of larger oysters, which he attributed to vibrating screen sorting during the spawning period.

Operational aspects

Seed-stripping of cups

A seed-stripper (based on French technology) was built for the collector cup column-stripping trials. Trials were initially conducted on the work platform next to the nursery stage longlines. However, due to engine operation constraints, the machine had to be moved to the dock. A seed stripping and sorting line was also installed, which included a cup seed stripper, a vibrating screen and a bagger.

The trial results were quite conclusive. The machine makes it possible to strip 45-cup collectors with a standard substrate (lime-cement-sand) in less than a minute. The seed-stripping yields were even better for the 45-cup collectors dipped only in lime substrate. Although the increase in production was not significant (40 seconds per column), the process was less taxing for the technicians, who did not need to hold back the columns to prevent them from passing through the system without being stripped. Some of the substrate remained on the cups limed with a lime-cement-sand mixture. Pieces of collection substrate were falling off the cups when they were taken down for sampling. It would have taken two minutes for three columns of 25 cups while it usually takes 17 minutes/technician to strip a column of 12 Chinese hats. However, seed-stripping by column is not recommended for 75-cups since the stands must be cut. That approach requires that the stands be rebuilt each year, which involves material and labour costs.

It would be easy to adapt the machine to strip a column of 75-cups without having to remove them from the stand. Mr. Daigle stripped his 75-cups without taking them down, using a system he initially developed for his drainage piping collectors. In light of what we observed at Aquaculture Acadienne Ltée, seed-stripping a 75-cup collector can be completed in under a minute by a technician.

Even though a machine was developed for seed-stripping Chinese hat columns (Doiron 2008), it is no longer used by the industry. Mr. Daigle used it for a few years but eventually stopped. The machine was breaking the Chinese hats and was too much trouble to use.

Cups operation

The cups have many advantages when compared to the Chinese hats. They do not need to be assembled for operation and disassembled for seed-stripping. It was therefore possible to mechanize this operation by building a cups seed-stripper. Structures must nonetheless be built in order to use them, which represents additional costs. However, the total cost would still be less than maintaining the Chinese hat collectors. These investments would also be recouped; from then on, it would no longer be necessary to set up the structures for liming and take them down for seed-stripping. We estimate that the size of the cups should make them last longer than the Chinese hats.

There was concern about predation by benthic organisms when using traps on the bottom of collection sites. That is why legs were added to determine whether it would be possible to minimize the incidence of predators on bottom structures. In the end, that approach proved unnecessary as only 8 crabs were observed on the bottom structures during transfer to the nursery stage site.

Cost analysis

A cost analysis was done to assess the financial benefits of using cups as an alternative to Chinese hats. The cost analysis comprises the purchase price for the collectors and the structures required to run them, as well as labour costs for their operation. To compare the various collectors tested, costs were converted based on the equivalent cost of a column of 12 Chinese hats.

Cups purchase price

The price of a 45-cup would be $13.50/unit ($17.72/equivalent Chinese hats) for a full container delivered to the facility, while a 75-cup would be $28.50 ($22.45/equivalent Chinese hats). Transportation costs are a significant part of the purchase costs. Pre-assembled cups limit the number of units that can be shipped per container. The 25-cups would therefore cost more per collection surface because of the additional handling charges for assembly and increased transportation costs. It would cost $42/unit to deliver a column of 12 unassembled Chinese hats to Shippagan. Increasing the space between the cups would increase their price for material, handling charges and transportation. However, it would be possible to buy assembly kits; assembly would then become the reponsibility of the oyster farmer.

The cost estimates are for an operation of 300 Chinese hat collectors and an anticipated annual production of one million oysters. It would take 236, 75-cups and 395, 45-cups to equal 300 Chinese hat collectors. The purchase price for each type of collector would be: $12,600 for the Chinese hats, $6,732 for the 75-hats and $5,328 for the
45-hats.

Operating the 45-cups requires a bottom structure. The structure used for the trials can hold 24, 45-cups and costs $200. The cost per collector would be $8.33/$10.41. However, given the shading effect noted in 2008, especially for the 45-cups, we recommend using 20 columns per collection structure, bringing the price to $10.00/$13.10 per collector. Therefore, 20 support structures would be needed to operate 400, 45-cups.

Assembly costs for the three columns of 25 cups (75-cups) would be $4.00/$3.15 based on material and labour. If extra space is added between cups, costs for the suspended support system would increase to $4.00/$3.15 per collector per collection surface.

Support structures would cost $4,000 for the 45-cups and $944 for the 75-cups. In all, the purchase and set-up costs for 300 collectors would be $12,600 for the Chinese hats, $9,278 for the 45-cups and $7,676 for the 75-cups.

Longlines

Operating the 45-cups involves simply placing the support structures on the bottom; it therefore requires very little material. At most, it requires a 6-metre by 15-mm length of rope with a marker buoy, which is $3.00 per support ($0.12/collector). In addition, given that it is possible to operate double supports, the material costs would only be $0.06/collector. As with the Chinese hats, operating the 75-cups requires longlines. A longline to operate 40 suspended collection structures (Chinese hats or 75-cups) would cost $352.42, that is $10.68/25-cup ($8.42/equivalent Chinese hats) and $10.68/column of 12 Chinese hats. Fewer longlines would be needed to operate 75-cups collectors considering the requirements of a 75-cups collector for the same collection surface.

Nursery stage longline

Rather than leaving our collectors in Caraquet Bay until the fall, we transfer our collectors earlier in the season (2-3 weeks after collection) to take advantage of better growing conditions on our culture sites. We leave them suspended on nursery stage longlines until the fall. One hundred columns of Chinese hats and 75-cups can be operated on a 100-metre longline. Fifty structures of 20, 45-cups could be operated on a 100-metre longline with a theoretical support capacity of 1,000, 45-cups. The cost of manufacturing one longline is $308. One 8 x 20 buoy is used to float a 25-cups collector or a Chinese cups collector. It took 5 balls, 16" in diameter, to float a 24, 45-cup support structure. That number should be reduced to 4 for the 20-cup structure. An 8 x 20 buoy costs $6.50 compared to $11.75 for a ball. Flotation costs for the nursery stage longlines would be $7.75 for 75-cups and Chinese hats, and $2.53 for 45-cups. However, it would be possible to use the same collection longlines for intermediate spat growth on 75-cups and Chinese hats.

Collector operating labour costs

Collection and nursery stage steps include: 1. assembly of collectors, 2. liming, 3. transportation to collection sites, 4. immersion, 5. removal, and 6. transfer to nursery stage sites.

Following initial assembly, 75-cups and 45-cups do not require any set-up, while Chinese hats must be set up every season for collection and taken down for seed-stripping. It takes approximately 15 minutes/technician ($4.37) to set up a column of 12 Chinese hats, which is $1,311/300 collectors. This component includes managing the batches before and after set-up, installing the hats and dividers on the centre rod, positioning the dividers across the outline of the hats to prevent the sides from caving in, and installing the closure ring.

The liming process is the same for all of the structures tested and costs approximately $1.46/collector. The size and weight of the 45-cups would facilitate the liming process even though more units would need to be limed for the same collection surfaces compared to the other two collectors. There is no liming cost difference, since we can only use lime on its own as a collection substrate for the 45-cups. Handling needs for the 75-cups should be identical to the Chinese hats, although the 75-cups would be more ergonomical as they are only 17 cm wide and the Chinese hats are 35 cm wide, which means they must be worked with further away from the body. This task would be particularly difficult when the collectors must be moved for seed stripping, when they are loaded with a lime-cement-sand mixture, oyster spat and biofoulers. A collector may weigh 20 or even 30 kg at the time of seed stripping. The 75-cups would be the heaviest given their larger collection surface and better growth rates compared to Chinese hats.

The cost of transporting 300, 75-cup collectors and Chinese hats was calculated as follows: Three return trips must be made with 100 collectors per trip. One return trip takes a technician 2 hours. It takes 17 minutes for 2 technicians to load the trailer, or 50 minutes for the three trips. Transporting the collectors would cost $135 in labour. Gas for the truck and trailer fees would cost $150. Transfer and transhipment of the 45-cups from the liming site to the boat at the Lamèque dock might take a technician and truck driver 45 minutes ($13). A truck equipped with a hydraulic crane and driver costs $150.

Moving 300 suspended collectors could take 15 hours/technician ($262.00) including transhipment of the collectors from the trailer to the boats, transfer to the collection sites, set up and return to the loading dock. The gas for the boat must also be considered ($150). It takes 2 hours for a boat loaded with 45-cups to go from Lamèque dock to the Caraquet Bay collection site. This is completed by two technicians for safety reasons. The same amount of time must be allotted for transferring the boats and setting up the suspended collectors. It would take two employees and a hydraulic crane to set up 12, 45-cup structures. It would take 45 minutes for two employees ($26.25) to immerse 10, 45-cups (240 columns of 45-cups). This could be reduced to 25 minutes by using double structures given that no differences were noted in terms of collection rates.

The transfer to the nursery stage site might require 45 hours/technician ($787.50) for the 75-cups and Chinese hats considering that they must be transferred from the collection site to the transhipment site, to the Lamèque dock, onto a boat and installed on nursery stage longlines. The transfer of the 45-cups would only require 12 hours/technician ($210).

It seems clear that the collector cups would provide the most value for a new business or one looking to increase collection efforts. The cups are also more economical to operate. However, New Brunswick oyster farmers mostly use Chinese hats or drainage piping collectors. Converting to cups could be profitable over a 5.5 year period in the case of 75-cups, which are more likely to be used by oyster farmers based on the unique aspects of the industry. Few businesses own a boat equipped with a hydraulic system.  

CONCLUSIONS

Choosing the collector cups would be a wise option for the company. The cups provide oyster farmers with a viable alternative. Although investing in this type of technology is comparable given the additional cost sof buying a seed-stripping machine, the drop in operating costs and increase in growth rates are considerable. The drop in operating costs could be attributed to the fact that structures require no annual assembly or disassembly and that mechanization of the seed-stripping process is now possible. The bottom supports could be used with a boat with a hydraulic system while supports for suspended collectors would be appropriate for producers with only small crafts.

Collection rates compare favourably with those of Chinese hat collectors. Cups are only beneficial to the culling process if the space between them can be increased; this should help minimize environmental factors and provide better size uniformity on the collector as a whole. Increasing the periphery could also allow for better growth rates, since a larger proportion of the oysters would be in optimal growing conditions.

The Chinese hat collector is still a viable option for oyster farmers. However, although it could take 5.5 years before the costs of switching to cups are recouped, it might be worthwhile for oyster farmers to replace Chinese hats with cups, given the potential spat size increase. In any case, oyster farmers have no choice but to invest in new collectors if they want to implement a culling strategy in keeping with their business. According to Lanteigne (2009), oyster collection volumes would need to at least double to introduce an efficient selection approach for fast-growing oysters. The need for collectors could therefore increase over the next few years. Although building a seed-stripping machine is a considerable investment, it could easily be offset through equipment sharing. It takes less than a minute to strip a column of cups and two days at most to strip 100 cups.

BIBLIOGRAPHY

Alexander, L.B. and G.N. Newkirk. 1988. Growth and survival of Crassostrea rhizophorae of different spat size under natural subtital culture conditions. J. of Shellfish Res. 7 (1) : 146.
Boudry, 2006

Doiron, S. 2002. Prévision du captage du naissain d’huîtres américaines (Crassostrea virginica) dans la baie de Caraquet en 2008. Rapport technique. Agriculture et Aquaculture N.-B.

Doiron, S. 2003. Prévision du captage du naissain d’huîtres américaines (Crassostrea virginica) dans la baie de Caraquet en 2008. Rapport technique. Agriculture et Aquaculture N.-B.

Doiron, S. 2005. Prévision du captage du naissain d’huîtres américaines (Crassostrea virginica) dans la baie de Caraquet en 2008. Rapport technique. Agriculture et Aquaculture N.-B.

Doiron, S. 2005. Prévision du captage du naissain d’huîtres américaines (Crassostrea virginica) dans la baie de Caraquet en 2008. Rapport technique. Agriculture et Aquaculture N.-B.

Doiron, S. 2006. Prévision du captage du naissain d’huîtres américaines (Crassostrea virginica) dans la baie de Caraquet en 2008. Rapport technique. Agriculture et Aquaculture N.-B.

Doiron, S. 2007. Prévision du captage du naissain d’huîtres américaines (Crassostrea virginica) dans la baie de Caraquet en 2008. Rapport technique. Agriculture et Aquaculture N.-B.

Doiron, S. 2008. Prévision du captage du naissain d’huîtres américaines (Crassostrea virginica) dans la baie de Caraquet en 2008. Rapport technique. Agriculture et Aquaculture N.-B.

Franlkin, H.L. and S.L. Downing. 1989. Effects of culling and temperature on family contribution in hatchery reared Pacific oysters. J. of Shellfish Res. 8 (2) :447-448.

Lanteigne, L. 2003. Essais d’une poche de sub-surface et d’une filière simple pour l’élevage des huîtres en suspension. Rapport d’activité. La ferme marine Lanteigne.

Lanteigne L. 2005. Essais des casiers Dark Sea pour l’élevage des huîtres à la surface de l’eau. Rapport d’activité. Vienneau Aquacultures Inc.

Lanteigne L. 2006. Essais des casiers Dark Sea pour l’élevage des huîtres en eau profonde et performances de croissance selon la position dans la colonne d’eau. Vienneau Aquaculture Inc.

Lanteigne, L. 2007. Développement d’une technique de tri du naissain d’huîtres pour améliorer les performances de croissance dans les poches flottantes. Rapport des activités de recherche pour la saison 2006. La ferme marine Lanteigne/La maison BeauSoleil Inc./Aquaculture acadienne Ltée.

Lanteigne, L. 2008. Développement d’une technique de tri du naissain d’huîtres pour améliorer les performances de croissance dans les poches flottantes. Rapport des activités de recherche pour la saison 2007. La ferme marine Lanteigne/La maison BeauSoleil Inc./Aquaculture acadienne Ltée.

Lanteigne, L. 2008. Rapport de la mission technique menée en France du 28 mars au 04 avril 2008. La maison BeauSoleil Inc. Néguac, N.-B.

Lanteigne L. 2008. Rapport de mission technique en France.  La maison BeauSoleil Inc.

Lanteigne, L. 2009. Élaboration d’une stratégie de sélection des individus à croissance rapide dans la production d’huîtres. Rapport final (2005-2008). Aquaculture acadienne Ltée.

Mallet, A. et S. Doiron. 2009. Évaluation de la croissance des huîtres collées et en poches flottantes. Ministère de l’Agriculture et de l’Aquaculture du N.-B.

Mallet, A., C. Carver et T. Landry. 2008. Impact of suspended and off-bottom American oyster culture on the benthic environment in eastern Canada. Aquaculture 255 : 362-373.

Mallet, A., C. Carver et M. Hardy. 2008. A commercial strategy to minimize fouling and maximixe production in floating bag aquaculture. Aquaculture (Accepté pour publication).

Rosique, M.J., J. Moreno et B. Garcia Garcia. 1993. Croissance et survie des naissains de l’huître plate (Ostrea edulis L.) de la Mar Menor (SE Espagne). Spec. Publ. Eur. Aquacult. Soc.

SEnPAq 2000. Étude comparative des paramètres de production pour le développement de la technique d’élevage des huîtres en poches flottantes. Rapport d’activité pour 2000. Association des conchyliculteurs professionnels du Nouveau-Brunswick. Shippagan, N.-B.

SEnPAq 2001. Étude comparative des paramètres de production pour le développement de la technique d’élevage des huîtres en poches flottantes. Rapport final. Association des conchyliculteurs professionnels du Nouveau-Brunswick. Shippagan, N.-B.

Taris, N, F.M. Batista and P. Boudry. 2006a. Evidence of a response to unintentional selection for faster development associated with inbreeding depression in Crassostrea gigas. J. of Shellfish Res. 25 (2): 783.

Taris, N., B. Ermande, H. McCombrie and P. Boudry. 2006b. Phenotypic and genetic consequences of size selection at the larval stage in the Pacific oyster (Crassostrea gigas). J. Exp. Mar. Biol. Ecol. 333 (1): 147-158.

Taris, N, F.M. Batista and P. Boudry. 2007. Evidence of response to unintentional selection for faster development and inbreeding depression in Crassostrea gigas larvae. Aquaculture 227: S69-S79.