Stomach contents, parasite assemblages and morphometrics were compared in brook charr Salvelinus fontinalis from the littoral and pelagic zone of two adjacent lakes on the Canadian Shield. In lac Baie des OnzeÎles, fish from the littoral zone had greater abundance of benthic prey in their stomach and were more heavily infected by parasites that use intermediate hosts associated with the littoral zone than fish captured in the pelagic zone. Littoral and pelagic brook charr from this lake also differed in regard to body shape and fin length, with each group being anatomically adapted to exploit their respective habitats. The highly significant correlation between morphometric and parasite canonical scores supports the hypothesis of functional diversification of individuals within lac Baie des OnzeÎles. While fish from littoral and pelagic zones of lac Caribou did not differ in terms of diet, parasite assemblages or morphometrics, they were different to fish from lac Baie des OnzeÎles in that they were less frequently infected with parasites that use gastropods as intermediate hosts, and had shorter pectoral fins. The inter-lake comparisons suggested that parasite assemblages and morphometrics of brook charr reflected the dominance of the limnetic and littoral habitats in lacs Caribou and lac Baie des OnzeÎles, respectively. # 2008 Her Majesty the Queen (Environment Canada)

Summary 1. The feeding range of an individual is central to food web dynamics as it determines the spatial scale of predator–prey interactions. However, despite recognition of its importance as a driving force in population dynamics, establishing feeding range is seldom done as detailed information on trophic interactions is difficult to obtain. 2. Biological markers are useful to answer this challenge as long as spatial heterogeneity in signal is present within the area investigated. A spatially complex ecosystem, Lake St. Pierre (LSP), a fluvial lake of the St Lawrence River (Québec, Canada), offered a unique opportunity to determine the feeding range of a secondary consumer, yellow perch (Perca flavescens) using isotopic ratios of carbon (δ13C). However, because food chains based on phytoplankton have generally more negative δ13C than those depending on periphyton, it was essential to determine the contribution of zooplankton in fish diet to correctly interpret spatial patterns of δ13C. We used parasites in perch to examine whether their δ13C was reflecting local δ13C baseline conditions rather than a feeding specialization on zooplankton. 3. δ13C of primary consumers was highly variable and exhibited a striking gradient along the shore–channel axis, suggesting that δ13C should reflect an individual consumer’s spatial position in LSP. 4. This strong isotopic gradient allowed us to estimate the spatial scale of the resources used by individual perch following an approach presented by Rasmussen, Trudeau & Morinville (Journal of Animal Ecology, 78, 2009, 674). By comparing the δ13C variability in perch to that of primary consumers, we estimated that the adults feeding range was around 2 km along the shore–channel axis. 5. The combined use of isotopic ratios and parasites allowed us to determine that the adult population uses a wide range of habitats between the flood plain and the main channel. However, individually, each perch depended on a limited foodshed.

Impoundments and dams are frequently used in wetlands to stabilize water levels and maintain breeding habitat for waterfowl. The objective of the study was to examine the effect of reduced water level fluctuations and connectivity on fish parasitism in wetlands caused by the installation of such structures. We compared parasites of juvenile yellow perch (Perca flavescens) from two enhanced wetlands where water level is regulated and where connection with the main channel occurs only during spring flood (enhanced wetlands) to parasites of juvenile perch living in seasonally flooded wetlands where connection with the main channel is continuous (natural wetlands). Parasite species richness and Shannon diversity index were higher in natural than in enhanced wetlands. Jaccard similarity index revealed a higher similarity in parasite assemblages within than between each type of wetlands. Glochidia and parasites that include clams in their life cycle were absent from the two enhanced wetlands. Our study suggested that local factors such as water level fluctuation and connectivity in enhanced wetlands may limit the establishment of bivalves and that the use of impoundments and dams in wetlands areas may have an impact on some components of the food web.