2008 Lake Ontario Lakewide Fishery Assessment

Lake trout abundance in Lake Ontario is now at a low level that has not been observed since modern restoration efforts began in the 1970s. However, the continued observations of small numbers of naturally spawned age-2 lake trout in assessment surveys and the appearance of mature lake trout of suspected natural origin, despite low abundance of the stocked population, is encouraging. Changes in stocking policy for Canadian waters in the early 1990s has produced a situation where lake trout along the north shore are concentrated in the west and east and suggests that the lakewide indicators of restoration progress used in the past for this part of the lake are in need of re-evaluation. In addition, this absence of lake trout along the central northern shore may be decreasing ecosystem stability and resistance to invasive species affects. Low lake trout abundance also seems to have positive implications for native preyfish recovery. Concurrent with lake trout declines, native deepwater sculpin (Myoxocephalus thompansonii) have reappeared (Lantry et al. 2007) and their recovery may indicate an enhanced opportunity exists for restoration of extirpated native deepwater coregonines. The results from this study thus far indicate that it would be beneficial to periodically repeat the whole lake survey and the five year interval of the EPA/EC Great Lakes cooperative monitoring cycle seems adequate and presents an ideal opportunity for researchers from this and other programs to share data and sampling infrastructure. Periodic lakewide lake trout assessments will extend annual monitoring of the condition of the lake trout population for the southern and north eastern areas of the lake to the whole lake and provide opportunity for assessment along the north shore. The whole lake surveys will also provide opportunities to calibrate between the annual USGS/NYSDEC standard lake trout assessments along the south shore and the OMNR community index netting occurring in the northeast portion of the lake; and an opportunity for collection of tissue samples for periodic examination of dietary trends and reproductive health

2010 Status of the Lake Ontario Lower Trophic Levels

This report presents data on the status of lower trophic level components of the Lake Ontario ecosystem (zooplankton, phytoplankton, nutrients) in 2010 and compares the 2010 data with available time series. Lower trophic levels are indicators of ecosystem health [as identified by the Lake Ontario Pelagic Community Health Indicator Committee (EPA 1993) and presented in the biennial State of the Lake Ecosystem Conference (SOLEC) reports] and determine the lake’s ability to support the prey fish upon which both wild and stocked salmonids depend. Understanding the production potential of lower trophic levels is also integral to ecosystem-based management. Continued evaluation of lower trophic levels is particularly important for fisheries management, as the observed declines in alewife and Chinook salmon in Lake Huron in 2003 may have been partly the result of changes in lower trophic levels (Barbiero et al. 2009)

Long-term impacts of invasive species on a native top predator in a large lake system

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

Gastrin-releasing peptide receptor-based targeting using bombesin analogues is superior to metabolism-based targeting using choline for in vivo imaging of human prostate cancer xenografts

Purpose: Prostate cancer (PC) is a major health problem. Overexpression of the gastrin-releasing peptide receptor (GRPR) in PC, but not in the hyperplastic prostate, provides a promising target for staging and monitoring of PC. Based on the assumption that cancer cells have increased metabolic activity, metabolism-based tracers are also being used for PC imaging. We compared GRPR-based targeting using the68Ga-labelled bombesin analogue AMBA with metabolism-based tar

Comparisons among three diet analyses demonstrate multiple patterns in the estimated adult diet of a freshwater piscivore, Salvelinus namaycush

Understanding trophic interactions is critical for successful resource management. However, studying diet patterns (e.g., spatial and seasonal changes) can require extensive effort. Using individual analyses to interpret patterns may be further complicated by assumptions and limitations of the analytical approach. We investigated and compared predicted adult lake trout (Salvelinus namaycush) diet composition and patterns using stomach content analysis (SCA), fatty acid analysis (FAS), and stable isotope analysis (SIA) individually and simultaneously. The three analyses were conducted for fall-captured fish in Lake Ontario and provided different diet composition estimates; SCA suggested alewife (Alosa pseudoharengus) was dominant by frequency and mass, while FAA and SIA suggested rainbow smelt (Osmerus mordax) contributed the most based on similarity among fatty acid signatures and two-stable isotope (carbon and nitrogen) mixing models, respectively. We hypothesize the disagreement among diet estimates is a result of a seasonal shift in diet variably expressed due to differing extent of time reflected by the diet metric: hours to days for SCA, weeks to months for FAA and several months for SIA. Despite variability in diet composition estimates among methods, similar patterns in lake trout diet were observed among the three diet analyses; the contribution of alewife in lake trout diet was greater for larger individuals and for males compared to females, particularly in the east and northeast regions of the lake where alewife density was relatively low. Thus, the complementary results from the three analyses suggest that length, location, sex, and season all influence lake trout diet. Individually, analyses often failed to identify these patterns in lake trout diet with significance, and some of the patterns have not been observed in previous studies of lake trout diet in Lake Ontario. The thorough description of lake trout diet obtained from a single sampling season demonstrates how simultaneous use of multiple diet analyses may allow investigation of spatial and seasonal diet composition and with reduced sampling effort

Analysis of Lake Ontario Lower Aquatic food web Assessment (LOLA 2003 and 2008) within the context of long-term ecological change

Lake Ontario is the 13th largest lake in the world with a surface area of 18,500 km² (Reynolds et al. 2000), has a population in the watershed of over 8 million, and provides a range of ecosystem services to the people in the watershed (freshwater for various uses, shipping, fisheries, and recreation). Currently, extensive surveys for each Great Lake occur on a rotating five-year schedule. This report presents the status of Lake Ontario’s lower trophic levels in 2008 and a detailed comparison with similarly collected in 2003 and with data collected by the collaborating agencies and Cornell University and discuss observed changes in relation to changes in nutrient concentration and food web configuration in Lake Ontario. There has been a spatial restructuring of the Lake Ontario offshore ecosystem through the increase in the deep chlorophyll layer and associated zooplankton. This has resulted in a Lake Ontario that in 2008 is more similar to Lakes Superior, Huron and Michigan than to the Lake Ontario of the 1990s. Major findings are Nutrients: Spring offshore total phosphorus and soluble reactive phosphorus increased from 2003 to 2008, but summer levels did not. Lake-wide average total phosphorus levels remained at or below the target level of 10 µg/L in all three seasons of 2008. Lake-wide nutrient concentrations have declined since the 1960s. However, phosphorus concentrations have been stable (~7-10 µg/L) since the mid-1990s. Spring silica was similar in 2003 and 2008 and was depleted by the summer in both years. This indicates continued spring diatom production in Lake Ontario. Phytoplankton: Summer epilimnetic chlorophyll-a increased by a factor of 2, the proportion of autotrophic algae increased, and summer water clarity declined from 2003 to 2008. Summer chlorophyll-a levels in 2008 were similar to the concentrations in the 1981-1995 time period. However, the trend towards mesotrophy in the summer of 2008 may be limited to that year as it was not followed by increased values in 2009 to 2011. Most of the chlorophyll in the water column was located in a deep chlorophyll layer in the thermocline. Zooplankton: Offshore epilimnetic zooplankton density and biomass declined from 2003 to 2008 by a factor of 5 to 12 in the summer and by a factor of 1.5 to 2.6 in the fall. This is consistent with long-term trends of declining epilimnetic zooplankton abundance including a larger decline in 2004-2005 coincident with an increase in the predatory Bythotrephes. Whole water column zooplankton density also declined from 2003 to 2008 in the summer and fall, but zooplankton biomass only declined in the fall. Large changes in whole water column zooplankton community composition occurred between 2003 and 2008 from a cyclopoid/bosminid dominated system in 2003 to a calanoid dominated system in 2008. Mysids, Diporeia and Mussels Mysid densities were similar in 2003 and 2008 indicating continued high biomass of mysids in Lake Ontario. In July of 2008, the biomass of Mysis diluviana was 17% of the crustacean zooplankton biomass in the offshore of Lake Ontario (depth >30m). Mysid densities appear stable in Lake Ontario. The native benthic amphipod Diporeia declined further in 2008 and is almost extirpated from Lake Ontario. Quagga mussels are very abundant as deep as 90 m, but populations in shallow water declined from 2003 to 2008. Few zebra mussels were present in either 2003 or 2008.Report for the GLRI funded project Improving Lake Ontario Environmental Management Decisions (Grant ID # 97220700-0

Feeding ecology and niche overlap of Lake Ontario offshore forage fish assessed with stable isotopes

The forage fish communities of the Laurentian Great Lakes continue to experience changes that have altered ecosystem structure, yet little is known about how they partition resources. Seasonal, spatial and body size variation in δ13C and δ15N was used to assess isotopic niche overlap and resource and habitat partitioning among the five common offshore Lake Ontario forage fish species (n = 2037) [Alewife (Alosa pseudoharengus), Rainbow Smelt (Osmerus mordax), Round Goby (Neogobius melanostomus), and Deepwater (Myoxocephalus thompsonii) and Slimy (Cottus cognatus) Sculpin]. Round Goby had the largest isotopic niche (6.1‰2, standard ellipse area (SEAC)), followed by Alewife (3.4‰2) while Rainbow Smelt, Slimy Sculpin and Deepwater Sculpin had the smallest and similar niche size (1.7-1.8‰2), with only the Sculpin species showing significant isotopic niche overlap (>63%). Stable isotopes in Alewife, Round Goby and Rainbow Smelt varied with location, season and size, but did not in the Sculpin spp. Lake Ontario forage fish species have partitioned food and habitat resources, and non-native Alewife and Round Goby have the largest isotopic niche, suggestive of a boarder ecological niche, and may contribute to their current high abundance.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Diet and trophic niche space and overlap of Lake Ontario salmonid species using stable isotopes and stomach contents

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 (\u3e300 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