Diel differences in 0+ fish samples: Effect of river size and habitat

Abstract

Studies of diel patterns in 0+ fish assemblages in rivers are scarce and produce contradictory results. We compared day and night electrofishing samples at 29 sites on rivers of different sizes in the Czech Republic. Diel patterns of 0+ fish differed among sites, but were consistent within each river stretch. River size was negatively correlated with both the day:night ratio of abundance (day samples produced more 0+ fish in smaller streams, night samples produced more 0+ fish in larger rivers) and similarity between day and night assemblage. A higher day:night ratio of abundance and lower similarity between day and night samples were observed at shelter-lacking habitats (beach) compared with shelter-providing habitats (boulder bank and flooded terrestrial vegetation). Differences in 0+ fish size were not dependant on diel period, river size, habitat or species. Day-only or night-only samples provided only two-third of the information provided by a combination of day and night samples. The effect of habitat type and river size on diel differences in electrofishing catches should be considered when deciding on 0+ fish sampling protocol. © 2011 John Wiley & Sons, Ltd.