Research Papers

Field Studies of Corrosion Behaviour of Copper Alloys in Natural Seawater

research_corrosionEight copper alloys were tested in a one-year field deployment in the North Atlantic Ocean. The corrosion behaviour was characterized by weight loss, optical and electronic microscopy analyses. The biofouling performance was quantified in terms of the biomass accumulation. The testing program included specimens in tensioned and untensioned configurations, as well as a set for seasonal deployments. The seasonal corrosion rates were 140% higher, and the rates of tensioned specimens were 39% higher than those of the untensioned specimens after 12 months of deployment. Good biofouling resistance was observed for all but one alloy, which exhibited heavy fouling by barnacles.

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Andrew Drach (a), Igor Tsukrov (a), Judson DeCew (a), Jochen Aufrecht (b), Adolf Grohbauer (b), Uwe Hofmann (b)
(a) Mechanical Engineering Department, University of New Hampshire, Durham, NH 03824, USA
(b) Wieland-Werke AG, Ulm, Germany

Copper Alloy Mesh Pens Easily Meet Stringent Water Quality Standards for Copper in British Columbia

Researchers monitoring copper concentrations from two copper-alloy mesh (CAM) pens installed in the Fortune Channel in British Columbia (BC), found full compliance with strict BC environmental regulations. The International Copper Association worked with Mainstream Canada to install the copper alloy mesh pens in the Fortune Channel near Tofino, B.C. in November of 2012.

An aquatic chemistry team from Wilfrid Laurier University in Ontario monitored copper concentrations in the channel before, during, and after CAM pen installation, to identify any increases in copper concentrations above preexisting background levels associated with the installation. The team also monitored the potential corrosion of the CAM materials. The monitoring was required to ensure compliance with British Columbia’s marine water quality standards for copper – the most stringent in the world (2.0 ug/L total copper average and no single value higher than 3.0 ug/L).

The results of this monitoring study were presented by the Wilfrid Laurier Team at Aquaculture Canada 2013 in Guelph, Ontario in the “Innovative Technologies” session on June 3.

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The results were quite favorable. Pre-installation background copper concentrations averaged 0.3 ug/L, with a few excursions as high as 1.5 ug/l. Copper concentrations were monitored for 15 days once the installation started. Concentrations downcurrent of the pens averaged about 0.4 ug/l, with one set of samples, nine days after the installation was completed, with a maximum of 2.6 ug/L. The team concluded that all of the monitoring data demonstrated full compliance with the BC copper standards.

The Laurier team also showed that the BC copper standards were more protective than necessary. The marine Biotic Ligand Model (BLM) was used. This model estimates how much of the total copper is bioavailable (and thus potentially toxic) to aquatic organisms. The BLM was also used to predict an alternative standard based on the copper’s bioavailability to blue mussels (the most sensitive organism to copper). The BLM model’s predictions indicated that copper concentrations in these waters could be as high as 7 to 11 ug/L before being toxic to mussels and other aquatic biota (post-installation measured concentrations averaged 0.4 ug/L, up to one sample at 2.6 ug/L). Thus, the BLM predictions show that the BC standards for copper are 3-to 5-times more protective than needed for all aquatic biota in these waters.

The Copper Alliance advocates the adoption of copper bioavailability and the use of tools like the BLM to set science-based copper standards with regulatory agencies worldwide. Environment Canada is now reviewing both freshwater and marine versions of the BLM for updating its copper standards.

Prepared May 30, 2013
By: Bob Dwyer
Associate Director for Environment in the Health, Environment and Sustainable Development (HESD) Initiative
International Copper Association (ICA)

Van Diemen Aquaculture Study

There is a great deal of complexity associated with the analysis of performance of Atlantic salmon in brass nets at Van Diemen Aquaculture (VDA) and it is challenging to succinctly portray the advantages of brass nets based on VDA performance over the last six years – having said that VDA would no longer be a commercially viable Atlantic salmon farm if it were farming in netting technology other than brass nets. It is not possible to make direct comparisons with the performance of other Tasmanian salmon farming operations as there is no access to verifiable performance data from those companies, and the farming conditions at VDA differ greatly from southern Tasmania – research scientists from an international feed company have described VDA as the world’s only “hot water” salmon farm.

Brass nets were first introduced in February 2005 alongside both nylon and galvanized steel nets. They quickly demonstrated many advantages and the phase out of steel nets was completed in March 2007 with the installation of the first URX nets, however the company continues to use nylon nets inside brass nets for the initial stocking of small fish. The raw data on fish performance is available for all year classes stocked since 2002 and allows some limited fish performance analysis.

The transition to brass net technology has allowed VDA to significantly change farm management and production strategies, expand the farm in to a more physically challenging environment, and maintain adequate environmental conditions for the farming of Atlantic salmon despite external factors that on occasions are at the limits for successful culture of salmon.

Background to Van Diemen Aquaculture

Van Diemen Aquaculture P/L is a small privately owned company that farms Atlantic salmon, (Salmo salar), on a single farm site in northern Tasmania. It commenced operations in 1998 at a small trial site approximately one kilometre upstream from the existing site. Farming commenced at the current site in early 2000 with the installation of four steel cages. (See Figure 1) Since 2000 the operation has expanded from 4 to 28 cages (24*24m, volume of 6500 cubic metres per cage), increasing annual production to over 2600 tonnes. The farm is unique in the Tasmanian industry context – it utilizes a steel cage platform with a fixed link to the shoreline enabling vehicular and pedestrian access. The company does not need a fleet of boats to operate, smolt are delivered by pipe direct from shore to cage on arrival, feed is delivered from a shore based storage facility by pipeline to each cage and harvest fish are pumped ashore to a purpose built harvest facility.

Annual smolt intake of 750,000 occurs from April to August, and harvest is from June in the following year to January. Average harvest size over recent intakes has reached 4.3kg ITR (round weight). The site carries mixed year classes for 8-9 months of each year, with juvenile fish held in the relatively calmer conditions inshore, while larger production fish are held in outer farm positions in fast moving water. Van Diemen fish have a distinctive shape to help them cope with life in strong currents, characterized by a condition factor at harvest of 1.6 – 1.8; fish have strong shoulders, firm flesh and fillet recovery up to 2% greater than the Tasmanian industry average.

The annual production cycle is significantly influenced by water temperature and to a lesser degree by fluctuating salinity. Summer water temperatures generally exceed 20oC for at least some of the season, and this has a significant impact on growth potential.

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Report prepared by Michael Hortle, The Aquaculture Advisor

Effect of Netting Materials on Fouling and Parasite Egg Loading on Offshore Net Pens in Hawaii

Parasitic skin flukes, primarily Capsalid Monogeneans, Benedenia sp. and Neobenedenia sp. are a scourge to the marine aquaculture industry worldwide. These parasites infect a wide range of hosts in tropical and temperate waters, causing immediate irritation and stress to the animal and, if levels are left unchecked, can lead to bacterial infections and eventual death. The life cycle and physiology of these two genera lend themselves to exponential growth in fish tanks and seacages. A series of topical chemical treatments can often remedy the problem in land-based containment systems, but topical treatments are less effective in offshore net pens.

Neobenedenia, the parasite of concern in Hawaiian offshore mariculture, reproduces by releasing (up to) several hundred eggs daily (Whittington and Horton, 1996). These eggs are composed of a rugged shell and a long tendril. The tendrils allow the eggs to attach directly to netting or to fouling on the netting. Bathing of contained fish in a chemical compound such as Hydrogen peroxide only removes the infective stage of the parasite from the skin of the fish, leaving unhatched eggs attached to the netting unharmed. These eggs will tend to hatch and re-infect the fish within the net pen. Preventing reinfection requires a significant reduction in the ability of parasite eggs to efficiently colonize the netting material. The virulence of Neobenedenia infection can be greatly reduced by identifying netting materials which inhibit the efficacy of parasite egg colonization.

Several attributes make a netting material more or less resistant to parasite egg colonization. First, is the material porous or contain areas of overlap, such as in a braided rope? The small crevices formed by the strands of a braided rope give egg attachment mechanisms greater purchase. Second, is the material easy to clean? Smooth surface netting materials tend to facilitate easier removal of eggs and fouling with active cleaning methods such as pressure washing. Third, is there an antifoulant compound coated on the netting, or is it made of a compound that has antifoulant properties that will inhibit egg attachment or health?

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Prepared July 17, 2012
By: Jennica Lowell, M.S.
Blue Ocean Mariculture