DOI: 10.5061/dryad.612jm643t
title: Data from: High summer macrophyte cover increases abundance, growth and feeding of juvenile Atlantic salmon

description: Aquatic habitats are severely threatened by human activities. For
 anadromous species, managing freshwater habitats to maximise production of
 more, larger juveniles could improve resilience to threats in marine
 habitats and enhance population viability. In some juvenile salmonid
 habitats, complexity created by large substrates provides resources and
 reduces competitive interactions, thereby promoting juvenile production.
 In lowland rivers, which lack large substrates, aquatic plants might
 provide similar complexity and enhance fish productivity. To test the
 influence of aquatic plants on juvenile Atlantic salmon and sympatric
 brown trout in a lowland river, we directly manipulated cover of the
 dominant macrophyte, Ranunculus, in nine sites during summer and autumn
 for two years. We quantified the abundance, site retention and growth of
 salmon and trout under high, medium and low Ranunculus cover. To
 investigate the effects of Ranunculus cover on feeding opportunities and
 interspecific competition, we quantified available prey biomass and body
 size, fish diet composition, and compared dietary niche overlap.
 Experimentally increased Ranunculus cover supported higher salmon
 abundance in summer and autumn, and higher site retention and growth of
 salmon in summer. Trout abundance and growth were not influenced by
 Ranunculus cover, but trout site retention doubled in high relative to low
 cover sites. Despite weak effects of Ranunculus cover on prey
 availability, salmon and trout inhabiting high cover sites consumed larger
 prey and a higher biomass of prey. Furthermore, dietary niche overlap was
 lower in high relative to low cover sites, suggesting that abundant
 Ranunculus reduced interspecific competition. This field experiment shows
 that high Ranunculus cover can support more and better growing juvenile
 salmon, and facilitate foraging and co-existence of sympatric salmonid
 species. Maintaining or enhancing natural macrophyte cover can be achieved
 through sympathetic in-river and riparian vegetation management and
 mitigating pressures on them, such as sediment inputs and low flows, or
 through planting. Further research should test whether macrophyte cover
 benefits propagate to subsequent life-stages, particularly juvenile
 overwintering associated with high mortality. This knowledge, in
 combination with our findings, would further clarify whether beneficial
 juvenile habitat can improve the viability of at-risk salmonid
 populations. Overall, our findings suggest that the aims of river
 restoration might be achieved through promotion of instream aquatic
 vegetation.
description: Fish abundance dataset Data corresponding to
 the analyses of juvenile (0+) salmon and trout abundance as a function
 of <em>Ranunculus </em>cover (%), explanatory variables
 describing the experimental design (Year, Month, Block), and explanatory
 variables representing site- and time-specific habitat characteristics of
 study sites (Water depth [cm], Proportion of Fast Velocities, Velocity
 Heterogeneity, Macroinvertebrate biomass [mg]).
 <strong>Fish site retention rate
 dataset</strong> Data corresponding to the
 analyses of juvenile (0+) salmon and trout site rentention rate
 (Recaptured fish caught in time <em>t, </em>Total fish tagged
 in time <em>t-1</em>) as a function
 of <em>Ranunculus </em>cover (%), explanatory variables
 describing the experimental design (Year, Period, Block), and explanatory
 variables representing site- and time-specific habitat characteristics of
 study sites, averaged across time period (Water depth [cm], Proportion of
 Fast Velocities, Velocity Heterogeneity, Macroinvertebrate biomass
 [mg]). <strong>Fish growth
 dataset</strong> Data corresponding to the
 analyses of change in weight (g) of individual juvenile (0+) salmon and
 trout as a function of <em>Ranunculus </em>cover (%), initial
 weight (g), and explanatory variables describing the experimental design
 (Year, Period, Block, Site).
 <strong>Macroinvertebrate biomass surber
 dataset</strong> Data corresponding to the
 analyses of macroinvertebrate biomass (sum) and average macroinvertebrate
 size (mean) in Surber samples as a function
 of <em>Ranunculus </em>cover (%) and explanatory variables
 describing the experimental design (Year, Month, Block, Site).
 <strong>Fish prey biomass dataset</strong>
 Data corresponding to the analyses of fish prey biomass (sum) and
 average fish prey size (mean) in individual fish diet contents as a
 function of <em>Ranunculus </em>cover (%), fish species
 (Salmon, Trout), individual fork length (cm), and explanatory variables
 describing the experimental design (Year, Month, Block, Site).
 <strong>Fish diet niche dataset</strong>
 Data corrresponding to the analysis of dietary niche overlap
 between salmon and trout in
 different <em>Ranunculus </em>cover levels using proportional
 abundance and proportional biomass of prey taxa in individual fish diet
 contents.