Offshore wind farms as productive sites or ecological traps for gadoid fishes?--impact on growth, condition index and diet composition.

With the construction of wind farms all across the North Sea, numerous artificial reefs are created. These windmill artificial reefs (WARs) harbour high abundances of fish species which can be attracted from elsewhere or can be the result of extra production induced by these wind farms. To resolve the attraction-production debate in suddenly altered ecosystems (cf. wind farms), the possible consequences of attraction should be assessed; thereby bearing in mind that ecological traps may arise. In this paper we investigated whether the wind farms in the Belgian part of the North Sea act as ecological traps for pouting and Atlantic cod. Length-at-age, condition and diet composition of fish present at the windmill artificial reefs was compared to local and regional sandy areas. Fish data from the period 2009-2012 were evaluated. Mainly I- and II-group Atlantic cod were present around the WARs; while the 0- and I-group dominated for pouting. For Atlantic cod, no differences in length were observed between sites, indicating that fitness was comparable at the WARs and in sandy areas. No significant differences in condition index were observed for pouting. At the WARs, they were slightly larger and stomach fullness was enhanced compared to the surrounding sandy areas. Also diet differed considerably among the sites. The outcome of the proxies indicate that fitness of pouting was slightly enhanced compared to the surrounding sandy areas. No evidence was obtained supporting the hypothesis that the WARs act as an ecological trap for Atlantic cod and pouting.

[1]  S. Degraer,et al.  Offshore wind farms in the Belgian part of the North Sea: Selected findings from the baseline and targeted monitoring , 2011 .

[2]  O. A. van Keeken,et al.  Residence time and behaviour of sole and cod in the Offshore Wind farm Egmond aan Zee (OWEZ) , 2010 .

[3]  Steven Degraer,et al.  Residency, site fidelity and habitat use of Atlantic cod (Gadus morhua) at an offshore wind farm using acoustic telemetry. , 2013, Marine environmental research.

[4]  P. Amundsen,et al.  A new approach to graphical analysis of feeding strategy from stomach contents data—modification of the Costello (1990) method , 1996 .

[5]  K. Hostens,et al.  Growth, feeding, production and consumption in 0-group bib (Trisopterus luscus L.) and whiting (Merlangius merlangus L.) in a shallow coastal area of the south-west Netherlands , 1993 .

[6]  Monitoring of the effects of offshore wind farms on the endobenthos of soft substrates: Year-0 Bligh Bank and Year-1 Thorntonbank , 2009 .

[7]  C. R. Merayo.  Seasonal changes in the biochemical composition of the muscle and liver of bib (Trisopterus luscus L.) (Pisces, Gadidae) from the Cantabrian Sea (N Spain) , 1996 .

[8]  A. Fernö,et al.  Diel activity pattern and food search behaviour in cod, Gadus morhua , 1999, Environmental Biology of Fishes.

[9]  Grete E. Dinesen,et al.  Effect of the Horns Rev 1 Offshore Wind Farm on Fish Communities. Follow-up Seven Years after Construction: Follow-up Seven Years after Construction , 2011 .

[10]  Age and growth of Trisopterus luscus (Linnaeus, 1758) (Pisces, Gadidae) off the coast of Asturias , 1994, Hydrobiologia.

[11]  A. Campos,et al.  Size selectivity for four fish species of the deep groundfish assemblage off the Portuguese southwest coast: evidence of mesh size, mesh configuration and cod end catch effects , 2003 .

[12]  Michael A. St. John,et al.  Fatty acid trophic markers in the pelagic marine environment. , 2003, Advances in marine biology.

[13]  N. Daan,et al.  Growth of North Sea cod, Gadus morhua , 1974 .

[14]  Raymond N. Gorley,et al.  PERMANOVA+ for PRIMER. Guide to software and statistical methods , 2008 .

[15]  D. Gaertner,et al.  Drifting fish aggregation devices could act as an ecological trap for tropical tuna species , 2008 .

[16]  T. Dempster,et al.  Proxy Measures of Fitness Suggest Coastal Fish Farms Can Act as Population Sources and Not Ecological Traps for Wild Gadoid Fish , 2011, PloS one.

[17]  P. Sherman,et al.  Ecological and evolutionary traps. , 2002 .

[18]  S. Degraer,et al.  Early development of the subtidal marine biofouling on a concrete offshore windmill foundation on the Thornton Bank (southern North Sea): first monitoring results , 2010 .

[19]  M. Vincx,et al.  Diel variation in feeding and movement patterns of juvenile Atlantic cod at offshore wind farms , 2014 .

[20]  T. Reubensa,et al.  Aggregation at windmill artificial reefs: CPUE of Atlantic cod (Gadus morhua) and pouting (Trisopterus luscus) at different habitats in the Belgian part of the North Sea , 2012 .

[21]  M. Öhman,et al.  Epibenthic colonization of concrete and steel pilings in a cold-temperate embayment: a field experiment , 2009, Helgoland Marine Research.

[22]  Marc Peeters,et al.  Biodiversity in Belgium , 2003 .

[23]  N. Daan.  A quantitative analysis of the food intake of North Sea cod, Gadus Morhua , 1973 .

[24]  K. R. Clarke,et al.  On resemblance measures for ecological studies, including taxonomic dissimilarities and a zero-adjusted Bray–Curtis coefficient for denuded assemblages , 2006 .

[25]  W. V. Berghe,et al.  The macrobenthos atlas of the Belgian part of the North Sea , 2006 .

[26]  L. Krag,et al.  Simulation-based study of the combined effect on cod-end size selection of turning meshes by 90 ◦ and reducing the number of meshes in the circumference for round fish , 2007 .

[27]  C. R. Merayo.  Reproduction and fecundity of the bib Trisopterus luscus (Linnaeus, 1758) (Pisces, Gadidae) in the central region of the Cantabrian Sea (northern Spain) , 1996 .

[28]  Y. Lambert,et al.  Condition and energy reserves of Atlantic cod (Gadus morhua) during the collapse of the northern Gulf of St. Lawrence stock , 1997 .

[29]  David Whitmarsh,et al.  Artificial reefs and fisheries exploitation: a review of the ‘attraction versus production’ debate, the influence of design and its significance for policy , 1997 .

[30]  M. Vincx,et al.  Energy profiling of demersal fish: a case-study in wind farm artificial reefs. , 2013, Marine environmental research.

[31]  S. Degraer,et al.  Offshore wind farms in the Belgian part of the North Sea: State of the art after two years of environmental monitoring , 2009 .

[32]  R. Connolly,et al.  Fishes associated with artificial reefs: attributing changes to attraction or production using novel approaches , 2005 .

[33]  Bruce A. Robertson,et al.  A framework for understanding ecological traps and an evaluation of existing evidence. , 2006, Ecology.

[34]  M. Vincx,et al.  Aggregation and feeding behaviour of pouting (Trisopterus luscus) at wind turbines in the Belgian part of the North Sea , 2011 .

[35]  G A Rose,et al.  Hyperaggregation of fish and fisheries: how catch-per-unit-effort increased as the northern cod (Gadus morhua) declined , 1999 .

[36]  Å. Bjordal,et al.  Species and size selectivity in longline fishing: a review , 1992 .