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Baseline Testing of Tray Rack Inserts for a Floating Upweller Nursery System

Final Report
Mac's Oyster Ltd
AIMAP 2012-P16

Executive Summary

Early commercialization and baseline testing of a new rack and tray insert system for a Floating Upweller Nursery System (FLUPSY) bins (silos) has been completed up to the first week of January 2013. This system, based on a prototype tested in 2005, was brought to commercial scale and tested for biological, environmental and economic performance. This project took place at Mac's Oysters Ltd FLUPSY site located at Sykes Island in Jervis Inlet, British Columbia using Pacific oyster (Crassostrea gigas) seed. Comprised of aluminum racks, the system holds layers of seed within trays and is suspended within the FLUPSY bins. The stacked trays increase the culture surface area, and allow for a greater volume of seed with less grading than previously possible. Two rack configurations were demonstrated: 1) a stacked raceway system and 2) a stacked full upwelling system.

Biological performance was positive with rack treatments outperforming traditional methods (controls) with respect to growth. Raceway racks had slightly better growth than upwell type racks (0.07mm/day and 0.05 mm/day respectively) from September to November. There were no significant growth differences among the layers (bottom to top) in either configuration. The upwell versus raceway rack type did not significantly differ in survival (both at 86%, 60,000 seed per rack) but stocking densities above 300,000/bin (with rack or control) had significant decreases in survival. Both controls and racks became heavily fouled with colonial hydroids but with the racks, fouling was restricted to the bottom layer which could easily be replaced.

Environmental performance - water quality and carbon footprint - results were also positive. Oxygen and ammonia concentrations, were not influenced by any treatment (rack or control) with no measureable differences of either parameter from the inflow to the outflow. The lack of detectable differences may be the result of declining autumn water temperatures which increase oxygen solubility and reduce metabolic rates of oysters. The rack inserts did significantly reduce flow rates compared to control bins, especially when fouled, but this was easily remedied by cleaning (or replacing) the bottom rack screens and adjusting the baffle openings into the raceway. The carbon foot-print was lowest in the rack treatments with 300,000 and 575,000 oysters (0.46 and 0.31 Mt CO2/million surviving oysters/month), significantly lower than all other treatments.

Economic performance was also improved by the rack system with control bins requiring 65LH/bin and rack bins requiring 25LH/bin (over 3-4 months). The difference is because oysters in control bins had to be graded every 3-4 weeks and the size categories split into different bins, each bin requiring the same amount of labour after the grade. Rack system bins did not require grading or splitting due to the ample room for growth within each tray. Cleaning was needed every two weeks (all treatments). The 10 year Net Present Value (NPV) was positive for all rack system treatments and highest at 150,000 oysters per rack ($808,000), over 7x higher than the same stocking density in bins without the rack system due to improved survival and reduced labour.

Introduction & Overview

Mac's Oysters Ltd has adopted and baseline tested a new rack and tray insert system for our floating upweller shellfish nursery (FLUPSY). The objective of this project was to improve our shellfish nursery production system by increasing the culture surface area (3-D space) available in each bin (also known as silos). This system was based on a prototype tested in 2005 which indicated that both growth and survival could be significantly improved with layered bin inserts. 

Located in Jervis Inlet, BC, our FLUPSY has been operating since the late 1990's and has periodic episodes of high mortality. These episodes generally follow a period of rapid growth. These periods (associated with plankton blooms) are typically 1 to 2 weeks in duration and cause seed volumes to increase by 2-5×. The result of this is a stratification of seed within the bin with oysters at the surface growing larger and surviving better than those beneath that layer. Increasing the flow rates can alleviate stratification in a limited way but excessive flow can fluidize the seed to the point where they become agitated and fail to filter. Grading the larger seed out can also relieve the crowding, but this is very labour intensive and the rate of grading becomes a bottleneck when growth is rapid. To address these issues we have taken the concept of a stacked upweller system to commercial scale. 

Commercial Justification

Technology Background

The negative correlation between stocking density and growth rates of nursery reared bivalve seed is well established. There are upper limits to the capacity of an upweller unit beyond which growth is stunted; Mercenaria mercenaria seed (up to 7 mm shell length), for example, have a maximum upweller carrying capacity of 62kg/m2 when fed natural seawater in ideal conditions. This translates to approximately 6 to 10 cm deep in our current system. When experiencing high growth periods, the depth of our seed can quickly increase from 4 cm to 20 cm, poor growth and survival typically follow. One option to alleviate this problem is to initially stock less seed in the system but that strategy is contrary to our production needs in the face of ever growing demand. Another solution is to purchase additional FLUPSY units but the high capital and operational costs, as well as the significant increase in the footprint of our nursery area, make this an unattractive option. Frequent grading can alleviate many of the issues with overcrowding but labour availability and the efficiency of grading equipment can be a bottleneck in this process. Plus, the seed at the time of grading is often too small to be transferred to growout equipment and must remain in the FLUPSY meaning that it must be returned to the system at higher than desired densities. Frequent grading can also stress or damage juvenile bivalves, causing reduced growth and survival. Therefore, we believe the most practical solution to the problem is to increase the culture surface area within the bins via the rack and tray insert system. Our initial 2005 experiments with using this concept showed reduced mortalities (a 60% improvement over existing treatments) and overall better growth (15 to 40% higher growth rates). 

To our knowledge a system like the one demonstrated in this project has not been reported in the scientific literature or in industry reports. We therefore believe that this is a new innovation with vast potential to improve FLUPSY productivity (better growth, better survival and potentially higher carrying capacity). The closest comparable systems are traditional raceways where seed growth is determined by distance from the water source (a phenomenon that we anticipated may happen within the racks due to layering) and traditional upwellers which as have very limited space available for growth; performance of both systems are functions of flow rate, food availability, oxygen levels and stocking density. Based on this knowledge, we anticipated that stocking density, rack configuration and tray position would be key factors determining performance of the demonstrated system. The basic biological performance measures were growth (shell length) and survival (by %). We also quantified water quality responses (e.g. oxygen depletion, ammonia accumulation and plankton depletion) and assessed flow dynamics within the bins. Productivity was also be assessed by comparing labour requirements for the new system to the old systems. 

Demonstration (materials and methods)

All demonstrations were conducted at Mac's Oysters FLUPSY site in Jervis Inlet, BC. AquaPacific constructed the trays and ArounTuit Services constructed the frames. Construction began in June 2012. Prototype evaluation was completed by mid August 2012 for fit of the trays to the racks, fit of the rack to the bins and water flow characteristics using dye.

The proposed evaluation of biological, economic and environmental performance could not be completed as originally designed due to delays in gear and seed deliveries. Instead, a series of smaller demonstrations were conducted. This report is completed up to the first week of January 2013, a time frame long enough to produce valuable information, but monitoring of parameters will continue up to June 2013 to obtain a full 10 months as indicated in the terms of the Agreement. The demonstrations were:

Demonstration 1- Effects of rack type (raceway versus upweller) and tray layer on growth and survival compared to traditional FLUPSY methods (controls and historic records)

Effects of rack type (upwell versus raceway) and tray level (position within rack) on growth and survival were examined. Differences among the rack configurations were determined using an un-replicated 2 factor ANOVA, all compared to controls (Dunnet's test) and historical data (single factor T-test)]. Stocking density was 12,000/tray (5 tray rack, total of 60,000/rack) and 60,000 oysters in the control bin. Initial SL was 4-6 mm and ran from mid August to the end of October. Comparisons to historic records were isolated to the relevant time period of the demonstration. 

Demonstration 2 – Effects of stocking density on growth and survival in racks compared to control bins and historic records

Seed was tested for effects of stocking density on growth and survival from early September to late November 2012 in racks and control bins at various stocking densities. Initial shell lengths ranged from 1.8 to 5.5 mm and were standardized to daily growth (mm/day). Original design was to have control bins of 150,000, 250,000 and 350,000/bin with paired rack treatments (5 trays per rack) with double the stocking density of each control. Volume measures of the small seed, however, had very high error so the final densities were: controls= 112,000, 160,000 and 496,000 oysters/bin; racks = 300,000, 575,000 and 765,000/bin. Results were analyzed with One-way ANOVA and Tukey's test. One-sample t-tests were used to compare results with historic records.

Demonstration 3 – Grade and separate seed into tray partitions

The effects of partitioning seed size groups into the different quarters of the trays was proposed, but were not necessary due to the uniformity of growth and the ample room for volume expansion with growth. Partitioning will be tested if the seed require grading at a later date (to be included in a Final Report Update).

Evaluation of the prototype

Biological Performance

Biological performance was assessed to determine the general response of the animals to the prototype racks and provide information on the general health of the animals. Animals that are in generally good health are less likely to contract diseases that can have negative impacts on other species or con-specifics in the area. Biological parameters (monitored monthly) were shell length, survival and condition index over time. For condition index (dry weight soft tissue/dry shell weight*1000) sample animals (at least 30 per treatment) from each rack demonstration and control bin have been collected and frozen (-30ºC). Monitoring will continue until June 2013 to obtain 10 months of monitoring. Preserved animals have yet to be analyzed. Anticipated completion time is December 31, 2013.

Environmental Performance

Environmental performance was evaluated by measuring: a) water quality parameters and b) carbon footprint. Water quality indicates if the system is deteriorating water quality to a degree that could affect other species or con-specifics in the area. Environmental performance was evaluated with the following parameters:

Economic Performance

The various demonstration treatments were evaluated for production and productivity using the following metrics:

Total Production

Productivity – was measured in terms of labour and capital inputs:

DELIVERABLES - RESULTS & DISCUSSION

I- Finalized material selection and designs for all components

The aluminum grade selected for Prototype ά was too flexible for the full rack design and deformed with shear stress applied (June 2012). Prototype I (PI) a stand alone rack unit with the heavier gauge aluminum proved to be too heavy for practical use and did not fully solve the shear stress problems (July 2012). Prototype II (PII), a modular design (frames and lift bars separated) was settled upon (July 2012). Functionally identical to PI, PII allows for easier transport, more efficient storage and repairs or replacement.

In August the fit of the PII racks into the bins was tested using dye. Visual observations indicated that the flow rates in the full upwell stacks were steady and uniform across the surface areas of the bins. It could be seen in the stacked tray system that water flowed up through the screens as well as horizontally across the top as expected. Sealing around the edge of the trays was excellent and no dye was observed to flow around the trays edges. Initially, inserting the racks into the bins proved difficult. It was observed that the racks were catching on small screws on the interior of the bins; this was easily remedied by covering the screws.

II- Construction of the racks and trays

Fully production of the system began in August 2012. Due to unavoidable production delays with ArounTuit (the frame builder), the equipment was delivered in small batches between August and December. 

III - Evaluation of the system under different treatments – tests with Pacific oysters

Biological Performance

Demonstration 1- Raceway versus Upwell racks

The raceway type rack had the best growth of all treatments with 0.07mm/day, more than 3x better growth (shell length) than controls and historic growth rates. Survival rates were high (>85%) for raceway rack, upwell rack and control bins. The level within the racks was not a significant factor (for either type; p>0.45) with no influence on growth or survival.

Demonstration 2 – Stocking Density

The rack insert (raceway type only was tested) at 300,000 oystes/rack had the highest growth rates (0.07mm/day). Care must be taken to not stock at levels higher than this because both growth and survival are negatively affected by high stocking density (>300,000/rack or >160,000/control bin).

Demonstration 3 – Grade and separate seed into tray partitions

Partitioning size groups into the different quarters of the trays was proposed but not completed. This test proved to be unnecessary because the seed required no grading due to the uniformity of growth and space available for volume expansion. Partitioning will be tested if the seed require grading at a later date (to be included in a Final Report Update). In comparison, control bins required grading every 2-4 weeks over a three month period. 

Animal Health

Monthly Condition Index samples for treatments and controls have been collected and frozen
(-30ºC) for future analysis (preserved samples to be completed and reported in a Final Report Update). 

Biofouling

Biofouling was prevalent on both types of racks systems as well as the controls. Fouling accumulated quickly –within 2-3 weeks- and consisted almost entirely of colonial hydroids. Coverage of the mesh with biofouling was 84-86%. In control bins the hydroids attached to the bottom screen and oysters resting on top of the screen. It took considerable effort to remove the hydroids from the screen and oysters in control bins. In racks, the hydroids attached only to the lowest tray (attached to both screen and oysters) with virtually no fouling present in the higher levels. Switching the bottom layer of oysters to clean tray liners was all that was needed to control the problem. 

Environmental Performance

With respect to water quality, none of the treatments tested are likely to have any con-specific or inter-specific impacts in the area with no measurable changes from inflow to outflow (per bin or overall); both oxygen saturation and un-ionized ammonia showed no change from inflow to outflow. The lack of significant results may be related to the season when tested (Mid September to December) when water is cooling and metabolic and filtration rates are reduced; monitoring will be ongoing until June 2013. Initial cell counts of plankton (inflow versus outflow per bin) suggest that higher stocking densities remove more algae, independent of whether it's a rack or control treatment. These samples are yet to be fully analyzed so a full conclusion cannot be made (final results to be included in a Final Report Update). Plankton reductions are however minute in comparison to the surrounding water body and outflow water is quickly diluted and unlikely to have any environmental impact. 

Flow rates were significantly influenced by the rack inserts compared to controls, especially when fouled . These issues were easily remedied by altering baffle openings and ensuring that biofouling was removed. Due to the ease with which flow rates can be manipulated this parameter no longer needs to be monitored (ended November 2012). 

Since the amount of fuel consumed per bin is a constant, carbon footprint is a function of stocking density and survival. As a result, only the 300,000 and 575,000 oysters/rack treatments had a lower carbon footprint than the target level of 0.57 Mt CO2/surviving million seed/month . All others, with the exception of the 160,000 oysters/bin control exceeded the historic CO2 production (1.14 Mt CO2/surviving million seed/month). 

Economic Performance

Economic performance as measured by productivity of labour and 10 year net present value was very promising with rack treatments requiring less than one half of the labour of control treatments because the rack systems did not require grading (i.e., ample space for growth) or splitting into additional bins. Rack scenarios tended to have a higher 10 year NPV than scenarios without rack inserts due to higher survival, higher total FLUPSY stocking densities (racks do not need to be split into as many bins as the seed grows) and lower labour requirements. Also the rack scenarios were less sensitive to higher mortality rates. Due to late seed arrivals, no trayable seed could be produced making it impossible to properly evaluate total production and productivity of capital over the given time frame (monitoring is therefore ongoing). Despite this, it can be concluded that the rack system is an economic success based on productivity of labour and NPV analysis.

Social Impact Performance

To date, the results suggest that overall FLUPSY production can be increase from 2.5 to 3 million per year up to 4.5 million per year or more. This expected production increase will directly impact the labour and gear requirements at the grow-out level. If the system exceeds expectations we will sell produce surplus seed to other producers who in turn may need to hire more people or purchase more equipment. The expected employment and social impacts are outlined below:

Employment Impacts

Local Community Impacts

IV - Communication of project results

A PowerPoint presentation of the results will be given at the British Columbia Shellfish Growers Association's Annual General Meeting (October 2013). The presentation will include a summary of the biological, environmental and economic performance of the system as reported in this document and updates from future data collection.

V - Conclusions

Rack and tray floating upwell bin inserts significantly improved Pacific oyster seed performance. Growth rates were increased by up 2- 3x with rack inserts compared to traditional FLUPSY culture methods (raceway racks had better growth than full upwell racks). The rack inserts can also improve survival compared to controls and historic levels provided that stocking densities do not exceed 300,000/bin. Rack system bins did not require grading or splitting due to the ample room for growth within each tray. This translated into economic performance with rack bins requiring 25LH/bin (over 3-4 months) and control bins requiring 65LH/bin. The 10 year NPV was positive for all rack system treatments and highest at 150,000 oysters per rack ($808,000), over 7x higher than the same stocking density in bins without the rack system due to improved survival and reduced labour. The rack system also had no measurable deleterious effects on water quality (i.e. no oxygen depletion or ammonia accumulation) and the carbon foot-print can be considerably lowered compared to historic emission levels so long as there is a sufficiently high stocking density and survival rate per rack (300,000 and 575,000 oysters/rack emit 0.46 and 0.31 Mt CO2/million surviving oysters/month). 

Rack and tray systems, as demonstrated in this project, have the potential to help stabilize seed production for BC oyster farmers. Oyster seed, generally supplied from US hatcheries, has been in short supply since the mid 2000's. Typically, only about half the 2-3 mm sized seed ordered is delivered to BC farmers. The US hatcheries assert that they can meet BC's demands with 1mm screen seed (>1.2 mm SL) but most oyster producers do not have the traditional facilities (land based upwellers with cultured algae) required to rear 1mm seed. The stacked FLUPSY racks in this project successfully reared seed averaging 1.8mm without the need for a land based system. This simple modification to existing FLUPSY systems may help the BC industry to cope with the pressures of rearing smaller seed without the need for costly land based facilities. The rack system is particularly suited for small seed because it reduces the need for grading. Grading can fracture shells and induce lethal stress on oysters less than 5 mm. 

Future development for this system should include improvements to the tray liner system. The liner inserts tested were not rigid, making it difficult to remove seed from the liners. Also the sides of the liners can fold down into the tray, leading to potential seed loss or smothering. A clipping or framing system for the inserts would be beneficial. The use of artificial substrates in this tray system should also be investigated. Infaunal bivalve species (e.g., Manila clams, cockles and geoducks) are vulnerable to biofouling and develop shell deformities in deep water (as opposed to inter-tidal) culture environments. Studies have demonstrated that hydroponic clay balls can significantly reduce these problems. The rack and tray culture system, combined with the forced water flow of a FLUPSY, potentially make it ideal for artificial substrate applications. 

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