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We determined how ice affects selection of habitats and distribution of post-young-of-the-year Atlantic salmon (Salmo salar) parr during winter. Night snorkeling surveys were completed between November and April to evaluate parr habitat use and movements. Systematic measurements of water depth and velocity were recorded during ice-free and [Formula: see text]55% iced conditions to quantify habitat availability. Ice formation altered the distribution and reduced the abundance of habitats commonly used by parr; differences between parr habitat use and habitat availability were greatest when ice was present. Edge ice formation resulted in the concentration of flows, and areas of high flow were formed in midchannel; few parr were observed in midchannel after ice had formed. Through the winter, most parr were found lateral to high flows on the ice edge boundary or in the post-ice period lateral to the stream midchannel. The correspondence of parr movements during winter to changes in the physical habitat associated with ice formation indicates that movements and redistributions may be important for survival in streams affected by ice.

La predation est souvent etudiee dans des systemes aquatiques qui abritent des saumons. Etant donne que ces systemes sont difficiles a manipuler et a reproduire, il est essentiel de pratiquer des comparaisons rigoureuses entre systemes. J'examine ici la litterature concernant les facteurs qui peuvent influer sur la predation dans les systemes. J'ai evalue plus precisement si la predation sur les salmonides etait importante par rapport aux taxons proies, au stade de developpement, a l'habitat, aux donnees sur les predateurs, a la methodologie et a l'echelle spatiale. J'ai de plus recherche quels facteurs avaient de l'influence dans les systemes ou la predation etait importante. Dans neuf revues, entre 1959 et 1996, 45 etudes de terrain verifiaient explicitement l'importance des effets directs de la predation sur les salmonides anadromes proies. Les auteurs de 36 (80 %) de ces etudes concluaient a l'importance de la predation. La majorite des etudes dans lesquelles la predation etait jugee importante portaient sur les smolts soumis a la predation par des poissons dans les habitats transitionnels des cours d'eau et des estuaires. En outre, les releves a grande echelle spatiale etaient les plus couramment employes. Enfin, la plupart des etudes donnaient peu d'information sur les facteurs qui compliquent l'etude de la predation. Si nous voulons tirer une lecon de ces systemes complexes, nous devons recueillir, analyser et rapporter des types d'information similaires qui sont recoltes dans plusieurs systemes et sur plusieurs annees, a l'aide de methodes rigoureuses et systematiques.

Incorporating human impacts into conservation plans is critical to protect natural resources. Using a model that examines how anthropogenic changes might be proactively influenced to promote conservation, we argue that a denser human population does not spell inevitable doom for Atlantic salmon (Salmo salar). Humans affect the Atlantic salmon ecosystem deleteriously through landscape alteration, exploitation, external inputs, and resource competition. An intact ecosystem provides positive feedback to society by providing food, ecosystem services, and improving the quality of life. As Atlantic salmon and associated ecosystem benefits are increasingly valued by society, policies, laws, and regulations that protect salmon populations and habitats are codified into a "control system" or institutional infrastructure. Via research that helps maintain wild salmon populations and in informing the public about the benefits of a healthy Atlantic salmon ecosystem, scientists can influence public attitudes and facilitate the implementation of environmental policies that moderate harmful anthropogenic changes. Because exchange among scientists is of paramount importance in increasing our understanding of important interrelationships between humans and fish, we recommend the establishment of an international salmon organization for research.

Atlantic salmon (Salmo salar) is an excellent species on which to focus synthetic, integrative investigations because it is an economically important species that captures the public imagination, is heavily impacted by humans, uses several ecosystems over its life, and is the subject of a large body of extant literature. The following 24 papers were solicited to provide the biological basis for effective and innovative approaches that biologists, managers, and social scientists can use to develop policies that sustain Atlantic salmon and related species. Together these papers highlight the need for and benefits of (a) synthesizing within populations, (b) choosing the appropriate scale, (c) comparing across populations using rigorous, focused, question-oriented methods, ( d) integrating across disciplines, (e) incorporating the human perspective, ( f ) linking multiple ecosystems, and (g) applied problem solving. To show how Atlantic salmon can guide research and conservation efforts for other species in other systems, we review the justification for the supplement and summarize the defining concepts that emerge from the volume. Resume : Le saumon de l'Atlantique (Salmo salar) est une excellente espece pour la realisation d'etudes synthetiques integrant diverses composantes parce qu'elle a une importance economique et qu'elle interesse le public, est fortement exposee aux impacts anthropiques, utilise plusieurs ecosystemes durant son cycle vital et fait l'objet d'une abondante litterature. Nous avons sollicite les 24 articles suivants pour presenter les bases biologiques qui peuvent s'averer utiles dans l'elaboration de methodes efficaces et novatrices que les biologistes, les gestionnaires et les specialistes des sciences sociales pourront utiliser pour etablir des politiques favorables au saumon atlantique et aux especes apparentees. Ensemble, ces articles font etat de la necessite et des avantages des actions suivantes : ( a) considerer les populations de facon synthetique, (b) choisir l'echelle appropriee, ( c) comparer les populations au moyen de methodes rigoureuses bien ciblees et fondees sur le questionnement, ( d) faire appel aux diverses disciplines concernees, (e) incorporer la dimension humaine, ( f ) etablir des liens entre les multiples ecosystemes, et ( g) appliquer des processus de resolution de problemes. Pour montrer comment le saumon atlantique peut guider les efforts de recherche et de conservation visant d'autres especes et d'autres systemes, nous revoyons la justification du present supplement au journal et resumons les concepts cles qui emergent des articles.

We combined laboratory and field studies to experimentally assess how the effects of feeding regime and time since feeding influence nitrogen (N), phosphorus (P), and the N:P ratio excreted by two common freshwater fish, bluegill (Lepomis macrochirus) and gizzard shad (Dorosoma cepedianum). In addition, for adult gizzard shad, we modelled excretion rates as a function of the nutrient content of ingested sediment detritus. For both bluegill and gizzard shad, feeding significantly increased nutrient excretion rates and altered excreted N:P ratios. For both species, excretion rates were highest immediately after feeding and declined thereafter. Because the phosphorus excretion rate decreased more rapidly after feeding than did the nitrogen excretion rate, the excreted N:P ratio increased with time since feeding. Young-of-year gizzard shad excreted more nitrogen than adults, resulting in a higher excreted N:P ratio for these small fish. For P, predictions from our model agreed well with our experiments with gizzard shad; for N, the agreement was not as strong yet was still reasonable. In summary, N:P ratios excreted by these fish differed across species, size, and time since feeding. Variation in these factors may explain discrepancies among studies that examine both trophic interactions and nutrient budgets.

In Ohio streams, the crayfish Orconectes rusticus is replacing O. sanborni, and herein we test how predators influence this replacement. In a field survey, crayfish were scarce when fish were abundant, suggesting that predators can adversely affect these prey. In laboratory experiments, we examined underlying mechanisms for this inverse relationship; specifically, we tested how crayfish species, adult aggression, and habitat heterogeneity influenced the predator–prey interaction. In a laboratory stream, smallmouth bass (Micropterus dolomieu) ate similar numbers of equal-sized O. rusticus and O. sanborni, but when sizes mimicked those in the field (i.e., O. rusticus 4 mm > O. sanborni), fewer O. rusticus were eaten. Fish also reduced juvenile activity and behaviors whereas adult aggression increased the frequency of these risky responses. More affected by adult crayfish, O. sanborni should suffer disproportional predation where adults and juveniles interact. Thus, fish predators should increase replacement rates and adult aggression should further accelerate this process. Manifested through crayfish size, both indirect and direct predator effects contribute to the replacement of O. sanborni by O. rusticus.

A crayfish species replacement is underway in Ohio streams. We explore how growth, mortality, habitat use, and size influence the replacement of Orconectes sanborni by O. rusticus. In field cages we assessed growth of crayfish. Both species grew faster when confined to riffles and O. rusticus grew faster than O. sanborni in this fast-water habitat. In another experiment, we tethered crayfish in riffles, shallow pools ( 40 cm) to assess mortality. After 8 d, more crayfish were eaten in deep pools than in riffles or shallow pools. Given this finding, we predicted that crayfish should preferentially occupy high-growth low-mortality riffles. To test this hypothesis, we quantified crayfish habitat use in sympatric streams, with and without fish predators. Crayfish did not prefer riffles. Apparently, juvenile crayfish do not assess specific benefits and costs using only food and fish predators. Other costs associated with riffles (e.g. passive drift, terrestrial predators, summer desiccation, physiological cost of position maintenance, etc.) must reduce riffle use. In addition, O. rusticus grows larger than O. sanborni. Because size confers advantages in biotic interactions, this critical finding may be the key to the replacement.

For stocked sportfish, stocking stress can cause substantial mortality. We evaluated mortality of three young-of-year esocids, northern pike (Esox lucius), muskellunge (E. masquinongy), and their F1 hybrid, the tiger muskellunge, in response to simulated handling, transport, and thermal stressors in the laboratory. In 15 °C acclimated esocids, a 10° rapid temperature increase caused little mortality. A 12° increase killed some fish in all taxa; however, mean mortality did not differ significantly among northern pike [Formula: see text], tiger muskellunge [Formula: see text], and muskellunge [Formula: see text]. Nearly all 15 °C acclimated fish (98%) died in response to a 15° increase. Tempering (0.15°∙min−1) did not reduce this near complete mortality. Handling (30 s dipnet) and transport confinement (60 g∙L−1 for 120 min) also did not alter mortality when compared with a 12° temperature increase alone. Field experiments, completed concurrently, confirmed our laboratory finding that healthy esocids, acclimated to 15 °C, stocked at lake temperatures corresponding to a temperature increase [Formula: see text], suffered little mortality. Because mortality did not differ among these two species and their hybrid, differential vulnerability to these stocking stressors need not be considered when deciding which esocid to stock.