2012). By now, only few studies focused on culture techniques, system design as
well as on the commercial potential and the management of fish cultivation in wind
farms (Buck et al. 2012). Existing studies on the biology of offshore fish cultivation,
however, did not directly deal with fish cultivation in co-use with wind farms.
Hundt et al. (2011) and Buck et al. (2012) provided a list of potential candidates for
the cultivation in wind farms in the EEZ of the German Bight, such as European sea
bass (Dicentrarchus labrax), cod (Gadus morhua), Atlantic halibut (Hippoglossus
hippoglossus), turbot (Scophthalmus maximus), haddock (Melanogrammus
aeglefinus), and Atlantic salmon (Salmo salar).
This selection of candidate species for offshore aquaculture in the German Bight
was based on mainly four criteria: (1) natural occurrence in the North Sea (absolutely no introduction of non-native species), (2) physical requirements of candidates match the conditions in the German Bight, (3) current status of farming
knowledge and available techniques, and (4) its economic feasibility (Buck et al.
2012). Generally, the harsh offshore conditions of the North Sea, namely strong
tidal currents and wave heights, and the wide temperature difference in the shallow
marginal sea limit the candidate list to few fish species. For the German Bight, the
strong temperature difference lies between <6 °C in winter and >21 °C in summer
and is probably the most limiting factor for cultivation of many fish species (Buck
et al. 2012). Furthermore, Buck et al. (2012) conducted studies on the welfare of
fish within net pens in RAS conditions that were similar to exposed conditions
offshore. These results demonstrated, that a clear understanding of the dependence
of fish fitness on strong hydrodynamic conditions is paramount.
11.3.4.1 Candidate: Dicentrarchus labrax
The European sea bass is a well-established species in aquaculture and with a
production of over 60,000 tons per year one of Europe’s most cultured marine fish
species (FAO 2005). The on-growing usually takes place in coastal surface cages
(FAO 2005), but the successful rearing under more exposed conditions was proven
in flexible surface cages in the Mediterranean (Sturrock et al. 2008), which is the
main site of production of European sea bass. Since sea bass is a physoclist species,
in which the swim bladder is closed and pressure compensation is only possible by
slow gas exchange, the ascent and decent of the cage has to include sufficient breaks
to prevent a barotrauma of the fish’s swim bladder (Korsøen 2011). However, the
eurythermal species is capable to tolerate temperatures below 5 °C (FAO 2005),
which would enable on-growing in the offshore regions of the German North Sea.
Nonetheless, the average temperature of 10 °C in the North Sea (Wiltshire and
Manly 2004) is below its optimum temperature range of 22–28 °C for growth
(Lanari et al. 2002), which will result in an extended on-growing phase. A rough
approximation of the actual length at the end of the on-growing can be based on the
growth models by Lanari et al. (2002) and the annual temperature of the water in
the German Bight (data BSH-German station bay, 10 m depth, daily mean values of
2009, www.bsh.de). The model suggests that an approximately 3 g fingerling
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B.H. Buck et al.
well as on the commercial potential and the management of fish cultivation in wind
farms (Buck et al. 2012). Existing studies on the biology of offshore fish cultivation,
however, did not directly deal with fish cultivation in co-use with wind farms.
Hundt et al. (2011) and Buck et al. (2012) provided a list of potential candidates for
the cultivation in wind farms in the EEZ of the German Bight, such as European sea
bass (Dicentrarchus labrax), cod (Gadus morhua), Atlantic halibut (Hippoglossus
hippoglossus), turbot (Scophthalmus maximus), haddock (Melanogrammus
aeglefinus), and Atlantic salmon (Salmo salar).
This selection of candidate species for offshore aquaculture in the German Bight
was based on mainly four criteria: (1) natural occurrence in the North Sea (absolutely no introduction of non-native species), (2) physical requirements of candidates match the conditions in the German Bight, (3) current status of farming
knowledge and available techniques, and (4) its economic feasibility (Buck et al.
2012). Generally, the harsh offshore conditions of the North Sea, namely strong
tidal currents and wave heights, and the wide temperature difference in the shallow
marginal sea limit the candidate list to few fish species. For the German Bight, the
strong temperature difference lies between <6 °C in winter and >21 °C in summer
and is probably the most limiting factor for cultivation of many fish species (Buck
et al. 2012). Furthermore, Buck et al. (2012) conducted studies on the welfare of
fish within net pens in RAS conditions that were similar to exposed conditions
offshore. These results demonstrated, that a clear understanding of the dependence
of fish fitness on strong hydrodynamic conditions is paramount.
11.3.4.1 Candidate: Dicentrarchus labrax
The European sea bass is a well-established species in aquaculture and with a
production of over 60,000 tons per year one of Europe’s most cultured marine fish
species (FAO 2005). The on-growing usually takes place in coastal surface cages
(FAO 2005), but the successful rearing under more exposed conditions was proven
in flexible surface cages in the Mediterranean (Sturrock et al. 2008), which is the
main site of production of European sea bass. Since sea bass is a physoclist species,
in which the swim bladder is closed and pressure compensation is only possible by
slow gas exchange, the ascent and decent of the cage has to include sufficient breaks
to prevent a barotrauma of the fish’s swim bladder (Korsøen 2011). However, the
eurythermal species is capable to tolerate temperatures below 5 °C (FAO 2005),
which would enable on-growing in the offshore regions of the German North Sea.
Nonetheless, the average temperature of 10 °C in the North Sea (Wiltshire and
Manly 2004) is below its optimum temperature range of 22–28 °C for growth
(Lanari et al. 2002), which will result in an extended on-growing phase. A rough
approximation of the actual length at the end of the on-growing can be based on the
growth models by Lanari et al. (2002) and the annual temperature of the water in
the German Bight (data BSH-German station bay, 10 m depth, daily mean values of
2009, www.bsh.de). The model suggests that an approximately 3 g fingerling
282
B.H. Buck et al.