Importance of windmill artificial reefs as feeding grounds for demersal fishes in the Belgian part of the North Sea
Heirman, E. (2011). Importance of windmill artificial reefs as feeding grounds for demersal fishes in the Belgian part of the North Sea. MSc Thesis. Ghent University: Gent. 32 pp.
A massive expansion of offshore wind power is expected in North-western Europe. The construction of the C-Power wind farm in the Belgian part of the North Sea (BPNS) created the opportunity to investigate the effects of windmill artificial reefs (WAR) on the ichthyofauna. This study investigated the importance of WAR as feeding grounds for demersal fishes in the BPNS. The following aims were set: (1) quantify energy content and proximate composition (proteins, carbohydrates and lipids) of cod and pouting and their main prey species (Jassa herdmani and Pisidia longicornis) using the cellular energy allocation (CEA) protocol, (2) identify the importance of the organic mats formed by J. herdmani in the diet of both fishes and (3) to calculate turnover rate from prey to fish. In this way, the population size of demersal fishes that could be sustained at the WAR by the epifauna present could be estimated.Since CEA protocols for fish were not available, adaptations were made to the original CEA protocol to obtain reliable and reproducible results. The net energy balance of the fish samples was calculated from the available and consumed energy (CEA = Ea/Ec). The results of this study indicated that the fish caught near the WAR had sufficient energy available for growth and reproduction. Energy contents of J. herdmani and P. longicornis were almost equal, indicating their similar nutritional value. The Jassa mats were found to be of no nutritional importance in the diet of the fishes.Fish cannot produce essential fatty acids (EFA) (such as EPA or DHA) themselves but have to acquire them from their prey. Therefore, fatty acid (FA) profiles can be used as a tool to establish the diet of predators. In this study, EPA and DHA were present in relatively high concentrations in the predominant prey species, but were very low in the Jassa mats. P. longicornis contained larger amounts of the FA C16:1?7 than any of the other prey species, indicating the importance of this particular prey in the fishes’ diet. Apart from this specific FA and the EFA, the FA profiles of fish species and prey species were similar, implying that they prey species (except for L. holsatus and the Jassa mats) were all important component of the diet of the fishes.Since there were no data available on the biomasses of prey present on the WAR, critical information needed to calculate the turnover rate from prey to fish was missing. Consequently, the population size of demersal fishes that can be sustained by the epifauna present at the WAR could not be estimated yet. In addition, more analyses are needed to determine the value of the adapted CEA assay. Continued research thus remains crucial.
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