Michael D. Chambers

Open Ocean Aquaculture engineering II

The University of New Hampshire, Center for Ocean Engineering (UNH/COE) Open Ocean Aquaculture (OOA) engineering efforts continue to be focused on developing engineering design and analysis tools for assessing, evaluating and optimizing engineering systems required for successful open ocean aquaculture. During 2002, this effort was focused on four tasks to continue the understanding of OOA: (1) investigation of commercial size cages, (2) expansion of the mooring system at the experimental location, (3) feed buoy development, and (4) net panel drag studies to enhance the understanding of this issue. Commercial size cage investigations included numerical and physical modeling of the SADCO-Shelf fish cage, and an initial study of a Sea Station 3000 cage with a tension leg mooring. Analysis of the expansion of the existing mooring was begun to study the effects of having many cages and larger cages at the site. Feed buoy development moved forward with the deployment of a separate independently moored system. The drag studies on net panels provided insight to the increased drag due to biofouling of experimental panels deployed at the offshore site. This paper presents selected results from these four tasks.

Comparative Growth and Survival of Juvenile Atlantic Cod (Gadus morhua)Cultured in Copper and Nylon Net Pens

Bio-fouling on net pens has been a major concern for the marine aquaculture industry. As cage systems increase in size, so does the surface area for the attachment of colonial organisms that create drag on the net, reduce water flow important to fish health, and increase operational expenses due to net cleaning. To solve this problem, the International Copper Association (ICA) has been developing copper alloy netting for sea cages. Copper netting has unique properties that minimize bio-fouling, reduce the risk of fish escapement, prevent predators from entering the net pen, and is recyclable. To test the alloy netting, an experiment was conducted to compare juvenile cod cultured in traditional nylon nets with cod grown in Seawire copper netting (Seawire@Luvata.com). Six, 0.78 m3 cages were each stocked with 200 Atlantic cod (Gadus morhua) averaging 29 ± 2.2 g and grown for 4 months in coastal waters of New Hampshire, USA. Results of the study indicated no significant differences in cod growth, survival, feed conversion ratio (FCR), specific growth rate (SGR), or Fulton’s condition factor (K) between the fish grown in the copper alloy and nylon nets. A chemical analysis was conducted on the cod and indicated no differences in copper levels in muscle, liver and gill tissues taken from the net treatments. Nylon nets with antifouling paint accumulated significantly more bio-fouling than the copper nets. Materials that were in direct contact with the copper netting (plastic cable ties) fouled heavily with hydroids indicating minimal leaching to the environment. This study describes some of the beneficial attributes of copper netting, however future studies need to be conducted over a longer period of time, on a larger scale, and in a more energetic environment to definitively test the utility of this new product.

Engineering Overview of the University of New Hampshire's Open Ocean Aquaculture Project

Aquaculture products are projected to play an important role infilling the global demand for seafood in the world marketplace. In the US, stiff resistance to near shore aquaculture sites (where most farms are located) will drive the industry to more exposed locations. In an effort to better understand open ocean aquaculture challenges, the University of New Hampshire (UNH) has been investigating the biological, engineering, environmental and economical issues. This overview focuses on the engineering approach utilized by UNH to determine aquaculture system loads, motions and operational logistics by utilizing a variety of tools including numerical and physical models and field experimentation. Numerical modeling is performed with Aqua-FE, a finite element analysis (FEA) program developed to study aquaculture type systems, MSC.MARC/Mentat, a FEA structural modeling program, and FLUENT, a computational dynamics program. Scaled physical model tests are performed in the UNH wave/tow tank. In addition, an extensive field program experiments with the use of biofouled net panels, telemetry and control systems, feed buoys, scaled cages and various environmental monitoring equipment. Biofouled net panels were tested to determine the blockage effect due to the biological growth. Feed buoys, with telemetry and control options, have been deployed and tested. A new 20 ton capacity feed buoy has been designed and is currently under construction. A scale, experimental, submersible net pen has been designed, built and deployed to determine the feasibility of various components. Environmental measurements are collected with a surface buoy and the data is transmitted to shore. The resulting information from these experiments can help move the near shore aquaculture industry to more exposed locations

Assessment of a submerged grid mooring in the Gulf of Maine

The University of New Hampshire (UNH) developed and maintained an offshore aquaculture test site in the Western Gulf of Maine, south of the Isles of Shoals in approximately 50 m of water. This site was designed to have a permanent moored grid to which prototype fish cages or surface buoys could be attached for testing new designs and the viability of the structure in the exposed Gulf of Maine. In 1999, the first moorings deployed consisted of twin single bay grids each capable of each securing one fish cage. These systems were maintained until 2003. To expand the biomass capacity of the site, the single bay moorings were recovered and a new four bay submerged grid mooring was deployed within the same foot print of the previous twin systems. This unique system operated as a working platform to test various structures, including surface and submersible fish cages, feeding buoys and other supporting equipment. In addition, the expanded capability allowed aquaculture fish studies to be conducted along with engineering and new cage/feeder testing. The 4 bays of the mooring system were located 15 meters below the surface. These bays were supported by nine flotation elements. The system was secured to the seafloor on the sides with twelve catenary mooring legs, consisting of Polysteel® line, 27.5 m of 52 mm chain and a 1 ton embedment anchor, and in the center, with a single vertical line to a 2 ton weight. To size the mooring gear, the UNH software package Aqua-FE was employed. This program can apply waves and currents to oceanic structures, predicting system motions and mooring component tensions. The submerged grid was designed to withstand 9 meter, 8.8 second waves with a 1 m/s collinear current, when securing four fish cages. During its seven year deployment, the site regularly experienced extreme weather events, most notably a storm with a 9 m significant wave height, 10 second dominate period in April 2007. The maximum currents at the site were observed during internal solitary wave events when 0.75 m/s currents with 25 minute periods and 8 m duration were observed. The mooring was recovered in 2010 after 7 years of continuous deployment without problems. The dominate maintenance requirement of the mooring was the cleaning once a year of excessive mussel growth on the flotation elements and grid lines. No problems of anchor dragging or failure of mooring components were documented during the deployment. Upon recovery, critical mooring components were inspected and documented, focusing on items with wear or other areas of interest. The mooring proved to be a reliable, stable working platform for a variety of prototype ocean projects, highlighting the importance of a sound engineering approach taken in the design process.

Design of a 20-Ton Capacity Finfish Aquaculture Feeding Buoy

A design for a 20-ton capacity buoy was developed to feed fish in four submerged cages at an exposed site south of the Isles of Shoals, New Hampshire, USA. The buoy was designed to contain all the equipment necessary to accomplish the feed dispensing tasks as well as have the strength and stability to remain on location in a variety of sea states. New feed handling and distribution systems were developed and tested. To evaluate seakeeping response a Froude scaled physical model was constructed and tested at the Ocean Engineering wave/tow tank at the University of New Hampshire (UNH). The mooring system was designed using the UNH developed finite element analysis program called Aqua-FE. The prototype buoy is now under construction, and is scheduled for deployment in late summer 2006

Offshore and Multi-Use Aquaculture with Extractive Species: Seaweeds and Bivalves

Aquaculture of extractive species, such as bivalves and macroalgae, already supplies a large amount of the production consumed worldwide, and further production is steadily increasing. Moving aquaculture operations off the coast as well as combining various uses at one site, commonly called multi-use aquaculture, is still in its infancy. Various projects worldwide, pioneered in Germany and later accompanied by other European projects, such as in Belgium, The Netherlands, Norway, as well as other international projects in the Republic of Korea and the USA, to name a few, started to invest in robust technologies and to investigate in system design needed that species can be farmed to market size in high energy environments. There are a few running enterprises with extractive species offshore, however, multi-use scenarios as well as offshore IMTA concepts are still on project scale. This will change soon as the demand is dramatically increasing and space is limited.

Deployment of the northern fish cage and mooring, University of New Hampshire — Open Ocean Aquaculture Program summer 2000

Fudning was provided by the National Oceanic and Atmospheric Adminstration for the Open Ocean Aquaculture Project under Contract No. NA86RG0016 to the Univesity of New Hampshire and under Subcontracts 00-394 and 01-442 to the Woods Hole Oceanographic Institution.

Offshore Platforms and Mariculture in the US

Global demand for seafood is increasing. Supply from wild caught sources has been essentially flat for twenty years and, depending on the specific fishery, in decline for many species that are considered fully exploited or over-exploited. As the fastest growing sector of world food production, aquaculture is increasingly playing a major role and currently accounts for nearly half of the total aquatic production worldwide. Marine cage culture in particular provides an opportunity to utilize vast amounts of the world’s surface area to produce fish, shellfish, and plants, while avoiding land-use conflicts in crowded coastal regions. Currently in the US, very small volumes of marine fish are produced and very large volumes are imported. This trend shows no signs of slowing down with an ever increasing annual seafood trade deficit. In an effort to initiate more domestic production, private companies, research institutions, and government agencies have all been involved in various types of aquaculture production. Aquaculture can be generally categorized as land-based, near shore, or offshore. Offshore marine fish culture utilizing cages has been conducted on both the east and west coast of the US as well as in the Gulf of Mexico (GoM). Specifics on the projects in the GoM are described in the following sections.

Technological Approaches to Longline- and Cage-Based Aquaculture in Open Ocean Environments

As the worldwide exploitation rate of capture fisheries continues, the development of sustainable aquaculture practices is increasing to meet the seafood needs of the growing world population. The demand for aquatic products was historically satisfied firstly by an effort to expand wild catch and secondly by increasing land-based and near-shore aquaculture. However, stagnation in wild catch as well as environmental and societal challenges of land-based and near-shore aquaculture have greatly promoted efforts to development farming offshore technologies for harsh, high energetic environments. This contribution thus highlights recent technological approaches based on three sample sites which reach out from sheltered near-shore aquaculture sites to sites with harsh wave/current conditions. It compares and evaluates existing technological approaches based on a broad literature review; on this basis, we then strongly advocate for presently available aquaculture technologies to merge with future offshore structures and platforms and to unveil its added value through synergetic multi-use concepts. The first example describes the recent development of longline farming in offshore waters of New Zealand. New Zealand has designated over 10,000 ha of permitted open ocean water space for shellfish farming. The farms range from 8 to 20 km out to sea and a depth of 35–80 m of water. Research has been ongoing for the last 10 years and the first commercial efforts are now developing in the Bay of Plenty. New methods are being developed which should increase efficiency and reduce maintenance with a particular focus on Greenshell mussel (Perna canaliculus) and the Pacific Oyster (Crassostrea gigas), Flat Oyster (Tiostrea chilensis) and various seaweeds. The second case study involves a long-term, open ocean aquaculture (OOA) research project conducted by the University of New Hampshire. During the course of approximately 10 years, the technological aspects of OOA farming were conducted with submersible cages and longlines, surface feeding systems and real time environmental telemetry. The grow-out potential of multiple marine species such as cod (Gadus morhua), haddock (Melanogrammus aeglefinus), halibut (Hippoglossus hippoglossus), blue mussel (Mytilus edulis), sea scallop (Placopecten magellanicus) and steelhead trout (Oncorhynchus mykiss) were investigated at a site 12 km from shore. The last study presents a multi-use aspect of aquaculture for an open ocean site with fish cages attached to existing offshore wind energy foundations. Technological components such as mounting forces and scour tendencies of two different cage structures (cylindrical and spherical) were investigated by means of hydraulic scale modeling. The cages were pre-designed on the basis of linear theory and existing standards and subsequently exposed to some realistic offshore wave conditions. The wind farm “Veja Mate” in German waters with 80 planned 5 MW turbines anchored to the ground by tripiles is taken as the basis for the tested wave conditions. Based on findings stemming from the three example approaches conclusions are drawn and future research demand is reported.