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We measured stable isotopes of carbon (δ13C) and nitrogen (δ15N) and fatty acid profiles in Lake Ontario alewife ( Alosa pseudoharengus), rainbow smelt ( Osmerus mordax), slimy sculpin ( Cottus cognatus) and round goby ( Neogobius melanostomus) collected from 1982 to 2008 to investigate how temporal variability in these ecological tracers can relate to ecosystem-level changes associated with the establishment of highly invasive dreissenid mussels., Prey fish δ15N values remained relatively constant, with only slimy sculpin exhibiting a temporal increase in δ15N. In contrast, δ13C values for alewife, rainbow smelt and, especially, slimy sculpin became less negative over time and were consistent with the benthification of the Lake Ontario food web associated with dreissenids., Principal components analysis revealed higher contributions of 14:0 and 16:1n-7 fatty acids and increasingly negative δ13C values in older samples in agreement with the greater historical importance of pelagic production for alewife, rainbow smelt and slimy sculpin., Temporal declines in fatty acid unsaturation indices and Σn-3/Σn-6 ratios, and also increased 24:0/14:0 ratios for alewife, rainbow smelt and slimy sculpin, indicated the increasing importance of nearshore production pathways for more recently collected fish and resulted in values more similar to those for round goby., These results indicate a temporal convergence of the food niche, whereas food partitioning has historically supported the coexistence of prey fish species in Lake Ontario. This convergence is consistent with changes in food-web processes associated with the invasion of dreissenid mussels. [ABSTRACT FROM AUTHOR]

1. Declining abundances of forage fish and the introduction and establishment of non-indigenous species have the potential to substantially alter resource and habitat exploitation by top predators in large lakes. 2. We measured stable isotopes of carbon (δ13C) and nitrogen (δ15N) in field-collected and archived samples of Lake Ontario lake trout ( Salvelinus namaycush) and five species of prey fish and compared current trophic relationships of this top predator with historical samples. 3. Relationships between δ15N and lake trout age were temporally consistent throughout Lake Ontario and confirmed the role of lake trout as a top predator in this food web. However, δ13C values for age classes of lake trout collected in 2008 ranged from 1.0 to 3.9‰ higher than those reported for the population sampled in 1992. 4. Isotope mixing models predicted that these changes in resource assimilation were owing to the replacement of rainbow smelt ( Osmerus mordax) by round goby ( Neogobius melanostomus) in lake trout diet and increased reliance on carbon resources derived from nearshore production. This contrasts with the historical situation in Lake Ontario where δ13C values of the lake trout population were dominated by a reliance on offshore carbon production. 5. These results indicate a reduced capacity of the Lake Ontario offshore food web to support the energetic requirements of lake trout and that this top predator has become increasingly reliant on prey resources that are derived from nearshore carbon pathways. [ABSTRACT FROM AUTHOR]

Our results provide new information that diet, carbon source and trophic position of an invasive fish species, round goby (), varies seasonally, spatially and with body size in littoral habitats of Lake Ontario. Based on stomach contents and stable isotopes, round goby fed at a higher trophic position in the cooler, less productive Kingston Basin relative to the Bay of Quinte. Bay of Quinte round goby were more reliant on terrestrial carbon, whereas littoral carbon dominated in the Kingston Basin. Although stomach contents suggested dreissenids were the dominant prey item of round goby, stable isotope mixing models estimated that dreissenids were never >39% and 11% of the diet in Bay of Quinte and Kingston Basin, respectively. Stable isotopes indicated amphipods, chironomids and cladocerans were the most important prey, and were at times common items in stomach contents, but this varied with site, season and year. Given their high abundance, the impact of round gobies on the benthic biodiversity of the Great Lakes may be more significant than indicated by stomach content analysis alone. [ABSTRACT FROM AUTHOR]

A correction is offered to the article "Feeding ecology and niche overlap of Lake Ontario offshore forage fish assessed with stable isotopes," by James A. Mumby, Timothy B. Johnson, Thomas J. Stewart, Edmund A. Halfyard, Brian C. Weidel, Maureen G. Walsh, Jana R. Lantry and Aaron T. Fisk, which appeared in volume 75, number 5.