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Mysids (Mysis diluviana) and dreissenids (Dreissena polymorpha and mostly D. bugensis) are important invertebrate taxa in the food webs of the Laurentian Great Lakes but there are uncertainties about the seasonal and spatial variability in their stable isotope signatures. We quantified δ13C and δ15N in 304 mysid and 366 dreissenid samples across five spatial ecoregions, varying site depth, and three seasons (spring, summer, and fall) in Lake Ontario in 2012 and 2013. Particulate organic matter (POM) was also collected across site depth and season from the Deep Hole ecoregion for use as an isotopic baseline. Lipid normalization models for δ13C were generated for both taxa to reduce lipid bias in our statistical analysis. Season was a significant predictor of POM stable isotopes, with δ13C lower in the summer and δ15N decreasing from spring to summer before increasing into fall. Mysid lipid normalized δ13C varied by site depth and ecoregion while δ15N decreased across season and did not vary by site depth or ecoregion. Dreissenid stable isotopes varied significantly across season, depth, and ecoregion, with site depth having positive relationship with δ15N. Mysids and dreissenids were two trophic positions higher than POM based on δ15N; this comparison was restricted to the one region where POM was collected. Isotopic variability suggested selective feeding within POM and differing trophic pathways between mysids and dreissenids. Collecting an appropriate taxon across all observed variables to serve as an isotopic baseline, particularly in spatial and temporal studies, is critical to the correct interpretation of trophic relationships. [ABSTRACT FROM AUTHOR]

Understanding the spatial use of reintroduced fish is useful for fisheries management and evaluating restoration success. Atlantic salmon (Salmo salar) were reintroduced into Lake Ontario in the 1990s; however, the movement ecology of these land-locked fish is unknown. Using acoustic telemetry and Floy tag mark-recaptures, we examined seasonal home range and space use of Atlantic salmon in Lake Ontario. Hatchery-raised adult Atlantic salmon were tagged with acoustic transmitters (n = 14; 8 with depth sensors) or Floy tags (n = 1915) and released. Both acoustic telemetry and Floy tag recaptures (n = 90) indicated cross lake movements, and home ranges encompassed nearly the entire lake in summer but was smaller in winter. Movements were nearshore (<2 km from shore) from spring to summer at ∼20 m bathymetric depths, with movements closer to shore in the fall, and further offshore (∼5.5 km from shore and 45 m bathymetric depths) in winter. Depth use was relatively shallow (<4 m) with occasional deeper dives (max = 28.5 m), and small diel vertical movements (1–5 m), moving deeper during daytime, consistent with ocean movements of Atlantic salmon. There appears to be spatial segregation among Atlantic salmon and other Lake Ontario salmonids, however, overlap likely occurs in nearshore waters during the spring. Wide-ranging movements of Atlantic salmon in binational (Canada/USA) waters reflects the importance of government agencies collaborating to ensure sustainable fisheries and the coordination of species restoration activities. This is the first study to provide detailed spatial use of Lake Ontario Atlantic salmon to assist in the management of this reintroduced species. [ABSTRACT FROM AUTHOR]

Invasive species are a key threat to biodiversity in freshwater ecosystems; and, as such, their management can be an important part of ecosystem restoration and conservation. In Hamilton Harbour, an impaired Lake Ontario embayment, invasive species are an important threat. In the early 2000s, an increase in invasive goldfish (Carassius auratus) was identified during monitoring surveys. This population of goldfish was studied via acoustic telemetry to gain knowledge about its biology to support management control options. Hamilton Harbour goldfish exhibited seasonal patterns in site and depth use, and clear preferences for over-wintering and spawning areas. Goldfish were largely resident to Hamilton Harbour with the exception of one individual. To predict when goldfish would move into spawning areas, we examined goldfish presence, abundance, and temperature at a fish-barrier connected to the harbour and developed models to predict goldfish presence based on Cumulative Growing Degree Days (CGDD) and Day of Year (DOY). Goldfish were captured in large numbers (>100 day−1) at the fishway when CGDD > 25.0 and DOY > 100; therefore, we predicted that our tagged fish would move to spawning areas when these thresholds were reached. Both models accurately predicted when tagged fish moved to spawning areas which largely occurred when water temperatures were lower (≥ 9.7 °C) than thresholds previously identified in the literature (i.e., 15.0 °C − 22.0 °C). This suggested that pre-spawn/staging behaviour was detected using telemetry driven by factors including water temperature. Results from this work will inform control strategies for goldfish, including active removal during aggregation prior to spawning. [ABSTRACT FROM AUTHOR]

Abstract Lake Ontario supports a diversity of native and non-native salmonids which are managed largely through stocking practices. Ecological changes (e.g., invasive species) altering the food web structure accompanied with shifts in prey abundance, necessitate understanding the trophic niches of Lake Ontario salmonids to aid in management. The objectives of this study were to quantify salmonid (5 species) trophic niches and dietary proportions using stable isotope ratios (δ13C and δ15N) of a large sample set (adult fish (>300 mm; n = 672) and key offshore prey (5 species, n = 2037)) collected across Lake Ontario in 2013. Estimates of prey based on stable isotope ratios were similar to stomach contents. Based on stable isotope ratios, non-native prey dominated salmonid diet; in particular alewife (Alosa pseudoharengus) constituted the majority (0.31 to 0.93) of all salmonid diets, and round goby (Neogobius melanostomus) contributed 0.26 and 0.19 of brown trout (Salmo trutta) and lake trout (Salvelinus namaycush) diets, respectively. Trophic niche overlap was high between all salmonids, except lake trout. The largest trophic niche overlap occurred between Chinook (Oncorhynchus tshawytscha), coho (Oncorhynchus kisutch), and Atlantic salmon (Salmo salar), and their reliance on alewife infers a strong pelagic foraging strategy. Lake, brown and rainbow (Oncorhynchus mykiss) trout had larger and/or more distinct trophic niches indicative of a more variable diet across individuals and utilizing different foraging strategies and/or habitats. Overall, Lake Ontario salmonids maintained a high reliance on alewife, and their potential for plasticity in diet provides important information to management regarding population sustainability. [ABSTRACT FROM AUTHOR]

Catch and release is a common practice among recreational anglers. In instances when fish are deeply hooked, the proper techniques for promoting survival are poorly understood, although evidence suggests that the fishing line should be cut rather than attempting to remove the hook. BluegillsLepomis macrochiruswere used as a model to identify the role of hook size (sizes 8 and 12), style (Aberdeen, baitholder, single egg), and the presence of barbs (only for baitholder hooks in size 10) on survival and hook retention for fish deeply hooked and the line cut. Eight hook style and size variants were manually embedded in the dorsal esophagus of fish, monitored over 10 d, and compared with unhooked controls. There was some evidence that Aberdeen style and larger hooks (size 8) incurred greater mortality over the 10-d monitoring period, while barbless hooks did not improve survival. Hook retention was high (>90%) for all deeply hooked fish. “J” style hooks, such as Aberdeen, and larger hooks may not be warranted for bluegills; however, we suggest that anglers use an adaptive approach when they select for a gear type appropriate to their target catch and simply adjust for alternate gear and techniques if deep hooking persists. Received May 25, 2012; accepted June 5, 2012 [ABSTRACT FROM PUBLISHER]