SUMMARY1. In this review, we first summarize how hydrologic connectivity has been studied for riverine fish capable of moving long distances, and then identify research opportunities that have clear conservation significance. Migratory species, such as anadromous salmonids, are good model organisms for understanding ecological connectivity in rivers because the spatial scale over which movements occur among freshwater habitats is large enough to be easily observed with available techniques; they are often economically or culturally valuable with habitats that can be easily fragmented by human activities; and they integrate landscape conditions from multiple surrounding catchment(s) with in-river conditions. Studies have focussed on three themes: (i) relatively stable connections (connections controlled by processes that act over broad spatio-temporal scales >1000 km 2 and >100 years); (ii) dynamic connections (connections controlled by processes acting over fine to moderate spatio-temporal scales 1-1000 km 2 and <1-100 years); and (iii) anthropogenic influences on hydrologic connectivity, including actions that disrupt or enhance natural connections experienced by fish. 2. We outline eight challenges to understanding the role of connectivity in riverine fish ecology, organized under three foci: (i) addressing the constraints of river structure; (ii) embracing temporal complexity in hydrologic connectivity; and (iii) managing connectivity for riverine fishes. Challenges include the spatial structure of stream networks, the force and direction of flow, scale-dependence of connectivity, shifting boundaries, complexity of behaviour and life histories and quantifying anthropogenic influence on connectivity and aligning management goals. As we discuss each challenge, we summarize relevant approaches in the literature and provide additional suggestions for improving research and management of connectivity for riverine fishes. 3. Specifically, we suggest that rapid advances are possible in the following arenas: (i) incorporating network structure and river discharge into analyses; (ii) increasing explicit consideration of temporal complexity and fish behaviour in the scope of analyses; and (iii) parsing degrees of human and natural influences on connectivity and defining acceptable alterations. Multiscale analyses are most likely to identify dominant patterns of connections and disconnections, and the appropriate scale at which to focus conservation activities.

Accurate estimates of abundance are imperative for successful conservation and management. Classical, stratified abundance estimators provide unbiased estimates of abundance, but such estimators may be imprecise and impede assessment of population status and trend when the distribution of individuals is highly variable in space. Model-based procedures that account for important environmental covariates can improve overall precision, but frequently there is uncertainty about the contribution of particular environmental variables and a lack of information about variables that are important determinants of abundance. We develop a general semiparametric mixture model that incorporates measured habitat variables and a nonparametric smoothing term to account for unmeasured variables. We contrast this spatial habitat approach with two stratified abundance estimators and compare the three models using an intensively managed marine fish, darkblotched rockfish (Sebastes crameri). We show that the spatial habitat model yields more precise, biologically reasonable, and interpretable estimates of abundance than the classical methods. Our results suggest that while design-based estimators are unbiased, they may exaggerate temporal variability of populations and strongly influence inference about population trend. Furthermore, when such estimates are used in broader meta-analyses, such imprecision may affect the broader biological inference (e.g., the causes and consequences of the variability of populations).Résumé : Des estimations exactes de l'abondance sont essentielles au succès de la conservation et de la gestion. Si les estimateurs d'abondance stratifiés classiques fournissent des estimations non biaisées de l'abondance, ces estimateurs peuvent être imprécis ou entraver l'évaluation de l'état et de la tendance de la population si la répartition des individus est très variable dans l'espace. Si des procédures basées sur des modèles qui tiennent compte d'importantes covariables environnementales peuvent améliorer la précision globale, il y a souvent une incertitude associée à la contribution de différentes variables environnementales et un manque d'information sur les variables qui sont d'importants déterminants de l'abondance. Nous avons développé un modèle de mélange semi-paramétrique général qui incorpore des variables mesurées de l'habitat et un terme de lissage non paramé-trique pour tenir compte des variables non mesurées. Nous comparons cette approche d'habitat spatial à deux estimateurs d'abondance stratifiés à la lumière d'observations sur un poisson marin faisant l'objet d'une gestion intensive, le sébaste tacheté (Sebastes crameri). Nous démontrons que le modèle d'habitat spatial produit des estimations de l'abondance plus précises, interprétables et raisonnables du point de vue biologique que les méthodes classiques. Nos résultats donnent à penser que, si les estimateurs basés sur la conception de l'échantillonnage sont non biaisés, ils peuvent exagérer la variabilité temporelle des populations et influencer fo...

We used temporally consistent patterns in the spatial distribution of returning adult coho salmon (Oncorhynchus kisutch) to explore relationships between salmon abundance, landscape characteristics, and land use patterns in the Snohomish River watershed, Wash. The proportion of total adult coho salmon abundance supported by a specific stream reach was consistent among years, even though interannual adult coho salmon abundance varied substantially. Wetland occurrence, local geology, stream gradient, and land use were significantly correlated with adult coho salmon abundance. Median adult coho salmon densities in forest-dominated areas were 1.5–3.5 times the densities in rural, urban, and agricultural areas. Relationships between these habitat characteristics and adult coho salmon abundance were consistent over time. Spatially explicit statistical models that included these habitat variables explained almost half of the variation in the annual distribution of adult coho salmon. Our analysis indicates that such models can be used to identify and prioritize freshwater areas for protection and restoration.

Multiple stressors in estuaries can cause declines in native species and impairment of ecosystem goods and services. In contrast, one stressor -the introduction of non-native speciesactually leads to higher local richness. We examined the changes in ecosystem function associated with introductions into Willapa Bay, Washington, USA, a relatively undeveloped estuary with 45 documented exotic marine species. The replacement of native oysters by 2 new bivalve species has increased secondary production of harvested suspension feeders by 250% over peak historic values (3.3 × 10 5 vs. 0.9 × 10 5 kg dry wt yr -1), based on >150 yr of records of harvested biomass. Key aspects of aquaculture -particularly planted area -have remained constant over time, so we attribute much of the altered secondary production to higher growth rates of non-native species. The addition of 2 tracheophytes has increased primary production on the tideflats by > 50% (5.3 × 10 7 vs. 3.5 × 10 7 kg dry wt yr -1 ), which we calculated by scaling up local measurements of plant growth to the total area occupied by each species. These changes in production are also associated with altered detritus, water filtration, and biogenic habitat. Because other stressors are largely absent from Willapa Bay, the addition of particular exotic species has dramatically enhanced system production, while fundamentally reshaping the ecological character of the estuary. These strong ecological impacts of introduced species have rarely been measured at whole-ecosystem scales, and they occur in part because new species occupy habitats where similar native species were not present.