The breakeven price for blue mussels was app. 1.5 ⬠kg¯¹ in a traditional long-line solution, and app. 2 ... However, present design of WF, O&M and rough.
ICES CM 2010/O:12
Offshore wind farms and their potential for shellfish aquaculture and restocking Claus Stenberg1, Mads Christoffersen1, Patrizio Mariani1, Carsten Krog2, Per Dolmer1, Marie Maar3 & Ditte Tørring4 Wind farms in European waters have become relatively common and are quickly expanding. In Denmark 11 offshore wind farms are in operation and an additional 23 new installations are being considered to be operational by 2025. This study aims to investigate whether shellfish production can be combined with the industry in Danish waters. Three of the worlds largest offshore wind farms (Horns Rev 1, Anholt & Nysted) are used as cases. Wind Farms
Species and production potential
Wind farms (WF) in Danish waters are among the largest in the world (80‐110 turbines, 25‐80 km² in area, figure 1). WF are placed in shallow waters, relatively close to harbors. To prevent sediment erosion large boulders are placed around the monopole turbines. The distances between the turbines are app. 500 meters. The increasing number of WF, their volume and spatial placement calls for multiple uses of the large areas. One promising co‐use is mari‐ culture. However, operation & maintenance (O&M) of the turbines have high priority and involves small boats, boats larger barges and ship cranes. (table 1). This challenges design, pos‐ sibilities and management of mari‐ culture in a WF.
Blue mussels (Mytilus edulis): Long‐line concept with pelagic production. Individual biomass was estimated using a Dynamic Energy Budget (DEB) model (Maar et al., 2009). The model estimated yearly biomass production, and total harvest pr meter of culture to be 25‐35 % higher at Horns Rev 1 compared to Anholt and Nysted (table 2). I order In d to allow ll O&M off turbines bi mussell production d i units i covering 25% of the total WF area. The production potential was estimated to be between 15‐25 % higher at Horns Rev 1 compared to the other two sites (table 2).
Figure 1. Map showing running, and proposal for future WF in Denmark
Table 1. O&M in a typical WF
European lobster (Homarus gammarus): Sea ranching concept with yearly release of 5‐6 cm juvenile lobsters. Nysted WF with salinities below 10 ‰ was below the tolerance limit for lobster. Catch size was set to 25 cm total size, The period estimated to reach this size 25 cm was app. 5½ years (table 2). The Th scour projection j ti att each h turbine t bi was considered id d the th only l suitable habitat for lobster in a WF. The total density was set to 25 individuals pr turbine. The production potential at a WF was estimated to be app. 300‐ 400 kg (table 2). Table 2. Production and harvest potential.
Horns Rev Anholt Nysted
Yearly production kg mˉ² yearˉ¹ 6,5 4,8 5,2
Blue mussels Total harvest kg mˉ¹ 15 11 12
Total harvest pr WF tons 2100 1925 1680
European lobster 25 cm TL Total harvest pr WF years tons 5,3 0,28 5,7 0,37 ‐ ‐
Economical profitability
Environment The three WF sites are located along a marked salinity gradient Horns Rev 1 (surface 32/bottom 33), Anholt (23/29) and Nysted (13/16). WF are generally placed in areas with strong winds. Strong winds which lead to high waves and hamper O&M. The maximum significant wave height for O&M is 1.2 m. Wind speeds >8 m sˉ¹ occur about 40‐50% of the time in WF (figure 2). Observations and high resolution models of the atmospheric boundary layer have shown strong effects of turbines in generating turbulent wakes where wind velocity is reduced and turbulence motion increases. This effect could have great importance for the suitability of WF as sites for aquaculture activities.
In order to evaluate the economical sustainability a ”back of the envelope” calculation was performed to estimate breakeven price. Initial investment, life span and yearly running expenses for blue mussels was provided by Møhlenberg et al (2008) while for lobsters it was estimated to be 16350€, 8 years and 4100€ respectively. The breakeven price for blue mussels was app. 1.5 € kgˉ¹ in a traditional long‐line solution, and app. 2 € kgˉ¹ in a Smart Farm solution. European lobster was app. 15.5 € kgˉ¹ in a sea ranching solution.
Conclusions & future perspectives Blue mussels: Mariculture is possible in WF. However, present design of WF, O&M and rough wind/wave conditions provide challenges. Production is feasible in Anholt, while environmental conditions are too rough on Horn Rev 1, and salinity too low at Nysted for production of high quality mussels for human consumption. 25% of the area in a WF is likely to be available. Bottom culture is an alternative that increases the production area and is in less conflict with O&M in the WF Large scale production would probably reduce operating costs which was not included in the evaluation of the economic sustainability. European lobster: The habitat in a WF covers a small proportion. An increase in suitable habitat could be combined with innovative cable protection or artificial lobster reefs within the WF. Production is feasible in Horns Rev 1 and Anholt, while salinity is too low at Nysted Sea ranching in WF will in present conditions only be small scale. However, the economical analysis indicates that it could be profitable. Acknowledgements Thanks to P.E. Amby, site coordinator Horns Rev 1, Vattenfall for detailed information on drift and logistic in a WF and wave data, K. S. Hansen, senior research scientist, DTU Mechanical Engineering, L. E. Jensen, Manager, Wind Power Analysis, DONG Energy for providing wind data. Dr. A. L. Agnalt, Inst of Marine Research, Norway , and Per Thomsen, manager, Norwegian Lobster Farm for providing useful information on lobster biology. This study was funded by The Danish Food Industry Agency, Ministry of Food, Agriculture and Fisheries.
References
Figure 2. Wind speeds from the three different sites.
Maar, M., Bolding, K., Petersen, J.K., Hansen, J.L.S., Timmermann, K. (2009) Local effect of blue mussels around turbine foundations in an ecosystem model of Nysted off‐shore wind farm, Denmark. Journal of Sea Research 62: 159‐174. Møhlenberg, F., Holtegård, L.E., Hansen, F.T. (2008) Miljøneutral udvidelse af havbrugsproduktion. Dansk Akvakultur Rapport. DSC and DHI. 1National
Institute of Aquatic Resources, Charlottenlund Castle, Jægersborg Alle 1, DK-2900 Charlottenlund, Denmark
2Krog
Consult ApS, Skæringvej 100, DK-8520 Lystrup, Denmark
3The
National Environmental Research Institute, Aarhus University, Frederiksborgvej
4Danish
Shellfish Centre, Øroddevej 80 7900 Nykøbing Mors
