We modeled recruitment variation of age‐0 walleyes Stizostedion vitreum in Escanaba Lake, Vilas County, Wisconsin, to determine factors regulating their abundance. Abundance of age‐5 and older walleyes (spawning population), variation in May water temperatures, and abundance of 152.4‐mm total length and longer yellow perch Perca flavescens explained 89% of annual variation of age‐0 walleye abundance from 1958 through 1995. Abundance of age‐5 and older spawners accounted for 32% of the recruitment variation and indicated that maximum numbers of age‐0 recruits were produced at low numbers of spawners (fewer than 1,000 individuals). The coefficient of variation of May water temperatures improved the model fit to 56% of recruitment variation and indicated that increased variation of May water temperatures greatly reduced recruitment. The abundance of yellow perch 152.4 mm and longer further improved the model fit to 78% of recruitment variation and also reduced recruitment, though not as much as variation in May water temperatures. The interaction between May temperature variation and yellow perch abundance improved the model to explain 89% of walleye recruitment variation. We interpret the results of the model to mean that walleye recruitment in Escanaba Lake is regulated by competition with or cannibalism by walleyes, variation in May water temperatures, and competition with or predation by adult yellow perch.

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We evaluated the effects of dam removal on fish assemblage structure and spatial distributions after four low-head dam removals in the Baraboo River, Wisconsin, using data collected at 35 study sites over 7 years. After dam removal, biotic integrity scores (possible range ¼ 0-100) increased by 35-50 points at three of the four former impoundments as a result of decreases in percent tolerant species, increases in the number of intolerant species, and in some cases, increases in species richness. Fish assemblage shifts were muted at a fourth, lower-gradient impoundment site, indicating that responses differ among dam sites within a river system. In tailwater areas, postremoval assemblage shifts were transient; biotic integrity and species richness declined initially but then recovered at two of the three sites within 2 years after dam removal. An analysis of spatial distributions before dam removal revealed 11 fish species that were found below, but rarely or never above, the downstream-most dam. After dam removal, 10 of the 11 species were collected at new sites upstream from the dam, indicating that recolonization of reconnected upstream sites had occurred. Some species recolonized rapidly and in large numbers. For example, emerald shiners Notropis atherinoides recolonized 16 upstream sites and were collected 123 km upstream from the dam within the first year after removal. One of the nine recolonizing species, the spotted sucker Minytrema melanops, was only detected during spring, suggesting that these fish recolonized seasonally, perhaps for spawning. Recolonizing species were generally lacustrine or large-river fishes known to undergo overwintering and spawning migrations. Our study suggests that dam removal is a viable option for restoring lotic fish communities, but further study is needed on recovery patterns as they relate to channel morphology, hydrologic characteristics, impoundment sediment storage capacity, and the distance to source populations of recolonizing taxa.

The objective of this study was to quantify the physical characteristics of coarse woody structure (CWS) as fish habitat in a north temperate lake. Sixteen species of fish were observed in submerged CWS habitat. Branching complexity, distance above the bole, area below the bole, distance to other CWS, and water depth around CWS were significantly related to abundance of schooling cyprinids (Cyprinidae), rock bass (Ambloplites rupestris), smallmouth bass (Micropterus dolomieu), bluegill (Lepomis macrochirus), yellow perch (Perca flavescens), and walleye (Sander vitreus). Branching complexity was the most common characteristic of CWS related to richness, diversity, and total adult abundance of fish taxa, but was not correlated with the total lengths of fish found in submerged trees. Branchingcomplexity values ranged from 1 (simple) to 500 (moderately complex) in the littoral zone; for comparison, a living riparian conifer had a branching-complexity value of over 1000. Most CWS in the littoral zone was composed of simple trees without branching, but fish tended to inhabit CWS with branching-complexity values greater than 45. This study shows the importance of CWS with fine branching as littoral-zone fish habitat.Résumé : L'objectif de notre travail est de décrire quantitativement les caractéristiques physiques des structures ligneuses grossières (CWS) qui servent d'habitat aux poissons dans un lac tempéré nordique. Seize espèces de poissons s'observent dans l'habitat CWS. La complexité des branchements, la distance au-dessus du tronc, la surface sous le tronc, la distance des autres CWS et la profondeur de l'eau autour du CWS sont toutes reliées à l'abondance des bancs de cyprinidés (Cyprinidae), de crapets de roche (Ambloplites rupestris), d'achigans à petite bouche (Micropterus dolomieu), de crapets arlequins (Lepomis macrochirus), de perchaudes (Perca flavescens) et de dorés jaunes (Sander vitreus). La complexité des branchements est la caractéristique des CWS qui est le plus souvent associée à la richesse en taxons des poissons, à leur diversité et à l'abondance totale des adultes, mais elle n'est pas reliée aux longueurs totales des poissons trouvés parmi les arbres submergés. Les valeurs de complexité des branchements varient de simple (1) à modérément complexe (500) dans la zone littorale; pour fins de comparaison, un conifère vivant sur la berge possède une valeur de complexité des branchements de plus de 1000. La plupart des CWS dans la zone littorale consistent en arbres simples sans branches, alors que les poissons tendent à s'abriter dans des CWS avec des valeurs de complexité des branchements supérieures à 45. Notre étude démontre l'importance des CWS avec un branchement élaboré comme un habitat pour les poissons dans la zone littorale.[Traduit par la Rédaction] Newbrey et al. 2123