Brown trout growth in Minnesota streams as related to landscape and local factors

Brown trout (Salmo trutta) are ecologically and socioeconomically important throughout the world. As such, understanding population dynamics is critical for brown trout management. Brown trout support a valuable recreational fishery in the Driftless Ecoregion of southeast Minnesota, where growth (i.e. mean back-calculated length-at-age) varies among streams but the relative effects of landscape (i.e. watershed level) and local (i.e. reach-level) factors on growth are unclear. Thus, the objective of this study was to evaluate effects of drainage area on individual brown trout growth relative to the effects of local factors (i.e. thermal regime, riparian land cover, relative abundance) to provide managers with strategies for increasing growth and the abundance of large individuals in southeast Minnesota streams. Linear mixed-effects models with combinations of these factors were compared using information-theoretic model selection and multimodel inference. Age, which explained 63% of variation in growth, differed among streams for age-1 and age-2, but not age-3 brown trout. Model averaging indicated growth of age-1 and age-2 individuals increased primarily with drainage area and secondarily with forested riparian area. Brown trout relative abundance did not affect growth, so it is realistic for managers to sustain high-quality, high-quantity brown trout populations. Overall, this synthetic landscape and local study advances brown trout management by illustrating that systems with large watersheds and forested riparian zones are suitable for management strategies (e.g. harvest regulations, habitat restoration) to increase growth and the abundance of large brown trout in socioeconomically valuable southeast Minnesota streams.