Invasive, canopy‐forming macrophyte species such as Eurasian watermilfoil Myriophyllum spicatum and hydrilla Hydrilla verticillata are now widespread throughout North American lakes and reservoirs. However, their effects on economically and ecologically important species such as largemouth bass Micropterus salmoides are insufficiently understood. Canopy‐forming exotic macrophytes typically displace structurally diverse native macrophytes. In aquaria, we tested whether exotic macrophyte canopies negatively affect age‐0 largemouth bass foraging success compared with diverse macrophyte assemblages. In addition, we explored the relative effects of macrophyte density, and prey density of bluegills Lepomis macrochirus on largemouth bass foraging success. Bluegill prey density did not significantly affect largemouth bass foraging success. However, largemouth bass experienced shorter search times and greater attack and consumption rates in moderate plant density treatments (compared with dense) and diverse plant treatments (compared with canopy monocultures). Effects of macrophyte density and architecture (diverse versus canopy monoculture) on largemouth bass foraging success were similar in magnitude. Our results indicate that among lakes, the relative importance of macrophyte density and architecture to largemouth bass foraging will depend upon the extent to which each factor influences structural complexity.

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Article (refereed) -postprintWinfield, Ian J.; van Rijn, Joey; Valley, Ray D. 2015. Hydroacoustic quantification and assessment of spawning grounds of a lake salmonid in a eutrophicated water body.Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. AbstractAccurate information on the location and condition of spawning grounds of environmentallydemanding lithophilic fish species, which may use only a very small area of their habitat for spawning, is critical to their conservation and fisheries management but is frequently lacking. Here, the new hydroacoustic system BioBase, which enables the rapid characterisation of features including lake bottom hardness (with soft, medium hard and hard bottoms represented by values of 0 to 0.25, 0.25 to 0.40, and 0.40 to 0.50, respectively), was applied to known spawning grounds of Arctic charr (Salvelinus alpinus) in the north basin of the eutrophicated lake of Windermere, U.K. The output of BioBase was successfully ground-truthed using an independent video-based system (r 2 = 0.48, F = 17.705, p < 0.001) and depth and bottom hardness descriptive statistics were produced for six spawning grounds. Average depth ranged from 9.4 m (North Thompson Holme) to 38.5 m (Balla Wray), while average bottom hardness ranged from 0.254 (Low Wray Bay) to 0.303 (North Thompson Holme). Detailed visual outputs were also produced for contrasting shallow (North Thompson Holme) and deep (Holbeck Point) spawning grounds, both of which showed high withinsite spatial variation in bottom hardness and thus in suitability for spawning. Findings were consistent with earlier, less quantitative, interpretations of the possible effects of eutrophication and associated increased deposition of fine sediments on local Arctic charr reproduction.