Abstract:We use fish and environmental data from 40 wetlands of the Laurentian Great Lakes to develop the Wetland Fish Index (WFI), a tool that can be used to assess the quality of coastal marshes. A partial canonical correspondence analysis was used to ordinate fish species along multidimensional environmental axes that accounted for anthropogenic disturbance based on temperature, conductivity, and the presence of pollutants (e.g., suspended solids and primary nutrients). Compared with other measures of fish habitat quality (e.g., Shannon-Wiener diversity index and species richness), the WFI was the only index that was significantly related to the degree of water quality degradation and wetlands condition, as indicated by an independent index of wetland quality, the Water Quality Index (WQI). WQI ranks sites according to deterioration in water quality and is statistically related to the degree of land-use alteration in wetland watersheds. We demonstrate the usefulness of the WFI for detecting intrawetland variation between two sites in a degraded urban wetland, Frenchman's Bay, Lake Ontario, and to distinguish the heavily impacted wetlands in lower Green Bay from the less-impacted marshes in middle and upper Green Bay, Lake Michigan. This was accomplished by using only published fish data without corresponding environmental variables.Résumé : Nous avons utilisé des données sur les poissons et sur le milieu provenant de 40 terres humides des Grands Lacs laurentiens afin de mettre au point un indice ichtyologique des terres humides (WFI, Wetland Fish Index), un outil qui peut permettre d'évaluer la qualité des marais côtiers. Une analyse partielle des correspondances canoniques a servi à ordonner les espèces de poissons le long d'axes environnementaux multidimensionnels qui expliquent les perturbations anthropiques d'après la température, la conductivité et la présence de polluants (par exemple, de solides en suspension et de nutriments primaires). Par comparaison à d'autres mesures de la qualité de l'habitat des poissons (par exemple, l'indice de diversité de Shannon-Wiener et la richesse spécifique), le WFI est le seul qui soit relié significativement à l'importance de la dégradation de la qualité de l'eau et à l'état des terres humides, tel qu'indiqué par un indice indépendant de la qualité des terres humides, l'indice de qualité de l'eau (WQI, Water Quality Index). Le WQI ordonne les sites d'après la détérioration de la qualité de leur eau et montre une corrélation significative avec les modifications associées à l'utilisation des terres dans le bassin versant des terres humides. Nous montrons l'utilité de WFI pour détecter la variation dans un même système entre deux sites dans Frenchman's Bay, lac Ontario, une terre humide urbaine et dégradée; il peut aussi distinguer les terres humides fortement modifiées de la partie inférieure de Green Bay. lac Michigan, des régions moins affectées des parties moyennes et supérieures de la baie. Cela a pu être réalisé à partir seulement des données publiées sur les poiss...

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Frenchman's Bay is a barrier beach wetland with a highly urbanized watershed located east of Toronto, along the north shore of Lake Ontario. Degradation of water quality has reduced the historically large stand of emergent vegetation to fringe emergent beds to the north and south of the Bay. Altered hydrology and runoff from the urban watershed and a nearby major highway have resulted in poor water quality, and warmer waters at the northern site. By contrast, the southern site has considerably cleaner and cooler water, as it is influenced by exchange of good-quality water with Lake Ontario. These differences in water quality were reflected in the composition of the fish assemblages that were sampled at the two sites over a 2-year period. Comparisons with past studies indicate that the dominant fish community of Frenchman's Bay has been relatively stable for the last 20 years. Scores for the Wetland Fish Index, an indicator of wetland condition, were significantly higher in the south site than in the north site, which corresponded to significant differences in Water Quality Index scores. Although the northern portion of Frenchman's Bay shows clear signs of degradation, the southern portion contains important fish habitat for western Lake Ontario.

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