A. Gimpel et al. 
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Science of the Total Environment 878 (2023) 162902 
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Fig. 3. Diet composition of cod individuals at different size classes with prey samples standardized through conversion to proportional data. Results are shown from the 
sampling of cod individuals inside the Offshore Wind Farm during summer (OWF summer), during winter (OWF winter) and at stations outside the OWF in the German 
Zight during summer (GB summer). 
summer with 19.36 %o (+ 0.10; p < 0.05) and with 18.64 %o (+ 0.78; 
> < 0.05) during winter (Appendix D). Mean 8!°C also differed signifi- 
cantly. Cod samples from the GB had with — 18.67 %o (+ 0.59) a signifi- 
cantly lower mean 8'°C ratio than cod with —17.27 %o (+ 1.02; 
? < 0.05) from the OWF area during summer or with —17.18 %o (+ 
0.65; p < 0.05) during winter (Appendix D). These differences indicate 
‘hat these fish had persistently distinct diets for a longer period of time 
prior to sampling and suggest that cod caught in the OWF inhabits a differ- 
ent trophic niche than in the GB. Only one individual caught in the OWF in 
winter showed considerably different stable isotope values, which might 
indicate that it had only recently moved into the OWF (Fig. 5, Table 1 
and Appendix D). 
3.2. Reproduction potential 
Both male and female individuals in spawning condition (maturity 
stage 3) were caught inside the OWF in winter (Fig. 6). Fish in spawning 
condition were also observed outside the OWF (Table 1), which appears 
to match with the observations of a considerably higher amount of large 
fish (> 45 cm) in the GB in winter than in summer. 
Out of 214 cod-like eggs, which were subject to genetic barcoding for 
species identification, 78 cod eggs were identified. Backtracking simula- 
tions of these 78 eggs revealed that 10.3 % may have originated from 
areas inside the OWF (Appendix C, Table C.2). The mean age of the cod 
eggs that originated from the OWF was 90.25 h and the average water tem- 
zerature was 6.06 °C (+ 0.62). The reconstruction of individual drift trajec- 
:ories revealed that individual eggs had covered a distance of up to 40 km 
>rior to sampling. In 2019, this transport primarily occurred from a north- 
easterly, in 2020 from a westerly and southeasterly direction. Under these 
conditions, potential spawning events inside the OWF had their largest 
:ootprint north and east of the source region (Fig. 7). The second model 
set up revealed that simulated eggs had left the OWF area after 168 to 
336 h driven by tidal forcing and residual current flow. 
4. Discussion and conclusion 
4.1. Attraction and reproduction potential 
Adult cod prefer rocky habitats (Bergström et al., 2013; Kraufvelin et al., 
2023) and Reubens et al. (2014b) have already shown that cod aggregate at 
wind turbines with scour protection. The latter finding was confirmed by 
our results, as we caught adult cod only directly above the scour protection 
.n the immediate vicinity of the wind turbines. Angling only a few meters 
away from the scour protection did not result in any catches. Furthermore, 
catches from trawl surveys in the southern North Sea indicate that cod 
abundance over sandy bottom habitats is currently low (ICES, 2022).