Importance of marinas and off-channel water bodies as refuges for young fishes in a regulated lowland river

Using graphical and statistical methods, I demonstrate that significantly higher numbers of 0+ fish were observed in off-channel water bodies than in the regulated, channelized River Great Ouse (ANOVA, d.f.=2399, F=3·01, p<0·03); this study emphasizes the importance of marinas and other off-channel areas as refuges and nurseries for small and young fishes. Also, a near significant decrease (Mann–Whitney U-test, p=0·0533) was observed in the frequency of samples containing fish in the main river following macrophyte cutting operations in the main channel, with a significant rise in an adjacent commercial marina (Mann–Whitney U-test p<0·03). Although not conclusive, the results corroborate previous results that macrophyte cutting operations can be detrimental to the recruitment of 0+ fish, which rely upon the submerged macrophytes for both feeding and refuge.