Microhabitat use of landlocked juvenile Atlantic salmon (Salmo salar)

Large-scale reintroduction programs for landlocked Atlantic salmon Salmo salar are ongoing in Lakes Ontario and Champlain. Commonly, these programs involve stocking hatchery reared juveniles into streams and thus, quantifying the in situ habitat use of stocked fish can help support these efforts. To examine habitat use, we stocked young-of-the-year (YOY) Atlantic salmon into 14 reaches of the Boquet River in the Lake Champlain Basin. The habitat used by YOY Atlantic salmon, measured from microhabitats that were used versus not used, differed between early and late summer for water depth. In early summer, YOY Atlantic salmon used a more narrow range of habitats compared to late summer. However, in both early and late summer, YOY most often used intermediate values in habitat variables except for water velocity in early summer. In early summer, YOY Atlantic salmon had the highest probability of using a water depth of 26 cm, a water velocity of 1 cm/sec, and a pebble substrate. In late summer, the probability of use was highest at a water depth of 61 cm, a water velocity of 11 cm/sec, and a pebble substrate. Our results show that stocked landlocked YOY Atlantic salmon use similar habitats to anadromous populations and may help managers when determining stocking locations or habitat alterations.     

Importance of environmental flow on feeding and distribution of juvenile Labeobarbus species in the Gumara River,Lake Tana Sub-basin,Ethiopia

The tributary rivers of Lake Tana are important nursery grounds for larvae and juveniles of the migratory endemic Labeobarbus species, but very little is known about their functional habitat and feeding preferences. This study investigated nursery grounds, habitat shifts, and potential energy sources for juvenile Labeobarbus species. Electrofishing point abundance sampling for juvenile sampling and stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were applied to trace potential energy sources. Habitat use shifting was observed among labeobarbus size classes from weak or no flow pool to fast-flowing riffle mesohabitats. The young-of-the-year (YOY) were mainly found in microhabitats with a weak to moderate water velocity (i.e., < 0.3 m s^?1), while 1⁺ juveniles (>7 cm FL) adapted to velocities of > 0.3 m s^?1. Juveniles suffered from limited access to run and riffle habitats during the peak dry season (March-April). They were subsequently exposed to resource competition and predation risk which led to lower catches. Juveniles of different size classes used different food sources. C1 (<3 cm) and C3 (5.1–7 cm) size classes mainly relied on algal sources, while C2 (3 – 5 cm) and C4 (>7 cm) on zooplankton. Insect larvae were a relatively important source for larger juveniles. Maintaining appropriate flow that permits juveniles to access preferred foraging and nursery habitat in the Gumara River is crucial for the sustainable management and conservation of the Labeobarbus population in Lake Tana.     

Differences in seasonal distribution of wild and stocked juvenile lake trout by depth and temperature in Lake Champlain

Lake trout (Salvelinus namaycush) reared in hatcheries are exposed to an environment and feeding regime that is different from wild lake trout, and are stocked at substantially larger sizes with higher lipid reserves. In addition to differences in diet and growth, this early experience may alter habitat use compared to the wild cohort. We used seasonal data on the depth and temperature distribution of wild and stocked juvenile lake trout to test for differences in habitat use and inform sampling strategies to evaluate annual recruitment. Bottom trawling was conducted from 2015 to 2019 in the central basin of Lake Champlain every two to four weeks during the ice-free season. Differences in distribution of wild and stocked lake trout were most pronounced during thermal stratification, when wild juveniles were more abundant than stocked juveniles at shallower depths and warmer temperatures and stocked juveniles were more abundant at deeper depths and colder temperatures. Temperature preferences may be a consequence of different early rearing environments; wild lake trout are acclimated to lake temperatures and forage, whereas stocked fish entered the lake with high lipid content and little foraging experience. Unbiased assessment of the proportion of wild lake trout and growth and survival of the entire juvenile lake trout population using bottom trawl sampling should either take place in the pre- and post-stratification seasons when wild and stocked fish are at the same depths, or include the full range of depths and temperatures that wild and stocked fish occupy during the stratified period.     

Size segregation and seasonal patterns in rusty crayfish Faxonius rusticus distribution and abundance on northern Lake Michigan spawning reefs

Non-native rusty crayfish are abundant egg predators on spawning reef habitats for lake trout and coregonines in northern Lake Michigan. To better understand rusty crayfish life-history on these unique habitats, we conducted monitoring in 2012 and 2013 at four locations previously identified as spawning areas for native fish. With the aid of a graphical causal model, we conducted an exploratory statistical analysis using a Bayesian multilevel modeling approach with model selection based on information criteria to identify important environmental variables for predicting rusty crayfish distribution and abundance on spawning reefs. We also compared seasonal trends in relative abundance, inferred from catch-per-unit-effort calculations from trapping, to previously reported accounts from a smaller inland lake. The results from our modeling provide evidence of size-class segregation across subtle changes in habitat characteristics of spawning reefs. Specifically, we found evidence that the distribution of >30 mm rusty crayfish was only weakly related to rock density (#/m²) relative to juveniles and smaller size classes. We also observed highest relative abundances from minnow trap monitoring in mid-October when water temperatures averaged 13.9 °C, which is later in the year and at cooler temperatures than similar monitoring from smaller inland lakes has reported. We hypothesize that unique environmental conditions elicit novel life-history responses from rusty crayfish on Lake Michigan spawning reefs and discuss our findings in the context of native fish restoration in the Laurentian Great Lakes.     

A Comparison of Total Phosphorus,Chlorophyll a,and Zooplankton in Embayment,Nearshore, and Offshore Habitats of Lake Ontario

Lower trophic levels were compared in embayment, nearshore, and offshore habitats of Lake Ontario, 1995 to 1997, in the context of oligotrophication and invasion of dreissenid mussels. Total phosphorus (TP), chlorophyll a (chl a), Secchi disk depth, temperature, and zooplankton were measured to spatially and temporally contrast these habitats and to test for recently hypothesized “decoupling” of chl a from TP (lower than predicted chl a per unit TP, consistent with dreissenid mussel grazing). The embayment habitat had higher concentrations of TP and chl a, greater volumetric zooplankton density and biomass, and higher springtime water temperatures than both nearshore and offshore habitats, while overall areal zooplankton biomass was highest in the offshore. Furthermore, concentrations of TP and volumetric zooplankton density in nearshore habitats are now more similar to the offshore pelagia than they were three decades ago. Finally, a lower yield of chl a per unit TP was found in nearshore habitat compared to offshore and embayment habitats. The current lower yield of chl a per unit TP in nearshore habitat can be attributed more to Dreissena than to erosion and/or resuspension of sediments.     

Habitat and Site Affinity of the Round Goby

A study was conducted in 1996 to compare densities of the round goby (Neogobius melanostomus) in rock and sand habitats in day and night at three sites (Sarnia, St. Clair River; town of Belle River, Lake St. Clair; Peche Island, Detroit River). The sites represent an expansion in round goby distribution from Sarnia where gobies were first reported in 1990 downstream to Peche Island where gobies appeared in 1993. Site affinity at Peche Island was estimated using mark-recapture and observations of individual fish. Mean density of round gobies differed among sites (p < 0.001), light regime (p < 0.001), habitat (p < 0.001), and the interaction of light regime and site (p = 0.007). Mean densities of the round goby were 0.3 to 3 fish/m² (Peche Island), 0.5 to 3 fish/m² (town of Belle River), and 5 to 9 fish/m² (Sarnia). Overall, highest densities of the round goby occurred in the day and on rocks. Small (≤5 cm) round gobies were most common at Peche Island, the most recently colonized site, indicating that juveniles may disperse more rapidly than adults. Of 200 fish that were marked, 58% were recaptured, indicating high site fidelity among round gobies. The estimated mean (± SE) home range of the round goby determined using SCUBA (5 ± 1.2 m²) was likely underestimated because few fish were observed. Larger round gobies may induce smaller fish to leave preferred rock habitats and move to sand habitats from which they disperse.     

Status and movement of adfluvial brook trout Salvelinus fontinalis at Isle Royale,Michigan, Lake Superior

Adfluvial brook trout Salvelinus fontinalis populations in the Lake Superior basin have suffered declines over the last century due to habitat degradation and exploitation. Natural resources agencies throughout the basin have restored habitat and implemented restrictive angling regulations as tools to protect remnant coaster brook trout populations, but the success of these practices is unknown in some locations. We used electrofishing and passive integrated transponder (PIT) tag movement data from 2008 to 2020 to describe population characteristics, temporal trends, and adfluvial life history of coaster brook trout in Washington Harbor, Isle Royale National Park, Lake Superior after implementation of catch-and-release regulations in 2004. Our results document the presence of an adfluvial coaster brook trout population in Washington Harbor, Isle Royale. Temporal trends indicate that brook trout abundance and distribution in Washington Harbor increased since earlier observations in the late 1990s and early 2000s likely due to enactment of protective regulations, and increased stream flows and water levels observed in recent years in both Washington Creek and Lake Superior, respectively. Annual tag detection of Washington Harbor brook trout in Washington Creek at the antenna arrays varied from 25% in 2009 to 100% in 2011 and 2013, and averaged 60.7% throughout the study. Peak in adfluvial brook trout use of Washington Creek was from August – October with few detections occurring outside of the presumed spawning period. This study provides valuable insight into the population characteristics, movement patterns, and temporal increase in abundance of an adfluvial brook trout population in Lake Superior.     

Historical genetic connectivity of lake sturgeon in a dammed Great Lakes tributary

Lake sturgeon (Acipenser fulvescens) populations are the focus of rehabilitation efforts across the Great Lakes. Although historical fisheries were a major cause of population collapses, habitat fragmentation and/or loss and reduced access to spawning and juvenile habitat impose contemporary challenges for population recovery. The loss of connectivity between habitat types required by different life stages may particularly limit recruitment rates, inhibiting population increase towards recovery targets. We used microsatellite DNA genotyping to assess population structure, diversity, and historical connectivity of lake sturgeon in the Black Sturgeon River watershed, a major tributary of Black Bay, Lake Superior with both historical and contemporary dams. Genotype data from lake sturgeon sampled above and below an existing major barrier, as well as from lakes in the upper watershed, showed evidence of historical connectivity throughout the watershed. Despite the existing barrier fragmenting the river and preventing upstream migration, lake sturgeon from the Black Sturgeon watershed showed clear membership to a single ancestral gene pool. Estimates of genetic effective population size (N_e) for the above- and below-barrier population segments were reduced compared to the larger (watershed level) gene pool. Although the longevity of lake sturgeon has largely enabled the retention of historical genetic diversity for the population in the watershed, the reduced productive capacity of this significant tributary may have implications for recovery rates for the regional Lake Superior metapopulation. Restoring connectivity among habitats would benefit the long-term conservation and management of this species throughout this river system, and potentially the regional metapopulation.     

Assessment of landed and non-landed by-catch of walleye, yellow perch and white perch from the commercial gillnet fisheries of Lake Erie, 1994-2007

Theoretical by-catch (including landed and non-landed bycatch) of walleye (S. vitreus), yellow perch (Perca flavescens), and white perch (Morone americana) from the Lake Erie commercial gillnet fisheries during 1994-2007, was predicted by a delta model developed on the fishery-independent survey data (Lake Erie Partnership Index Fishing Survey). The delta model consisted of one generalized additive model and one AdaBoost model. The generalized additive model was used to predict non-zero catches of the by-catch species, and the AdaBoost model was used to predict the probability of obtaining non-zero catches. Non-landed by-catch was estimated as the difference between the theoretical by-catch predicted from the delta model and the landed by-catch recorded in the commercial fishery data. The theoretical by-catch of walleye was relatively higher in the west basin in October. A higher theoretical by-catch of yellow perch occurred in the west central basin in November, and a higher theoretical by-catch of white perch occurred in the west central basin in October. We observed higher levels of non-landed by-catch of walleye in the west basin during August to September, higher levels of non-landed by-catch of yellow perch in the west central and east central basins in November, and higher levels of non-landed by-catch of white perch in the west basin in August and November. The combination of the AdaBoost model with the delta model provided an alternative model in by-catch analyses when the percentage of zero observations was high.     

Habitat use by subyearling Chinook and coho salmon in Lake Ontario tributaries

The habitat use of subyearling Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) was examined in three tributaries of Lake Ontario. A total of 1781 habitat observations were made on Chinook salmon (698) and coho salmon (1083). During both spring and fall, subyearling coho salmon used pool habitat with abundant cover. During spring, principal component analysis revealed that water depth was the most important variable governing subyearling Chinook salmon habitat use. Substrate materials used by Chinook salmon in the spring and coho salmon in the fall were significantly smaller than were present on average within the study reaches. When the two species occurred sympatrically during spring they exhibited similar habitat selection. Although the habitat used by coho salmon in Lake Ontario tributaries was consistent with observations of habitat use in their native range, higher water velocities were less important to Chinook salmon than has previously been reported.     

Annual Production of Burrowing Mayfly Nymphs (Hexagenia spp.) in U.S. Waters of Lake St. Clair

Burrowing mayfly nymphs (Hexagenia spp.) were sampled monthly, September through October 1995 and April through August 1996, with a standard Ponar grab (538 cm² jaw opening) at 16 stations in U.S. waters of Lake St. Clair. Annual production (production, P) was 0 to 477 mg dry weight/m² at three stations where pollution and sediment grain-size distribution limited the population, and was 738 to 5,255 mg dry weight/m² at the other 13 stations. The highest production value measured for Hexagenia in Lake St. Clair was about three times higher than the highest value reported for other areas in the northern United States and Canada (39° to 53° North latitude). The production-mean annual biomass (biomass, B) ratio (P/B) for Hexagenia in Lake St. Clair in 1995–96 was described by the straight line P = 2.4 B (R² = 0.94). Adding published P/B data for other North American populations changed the relation only slightly to P = 2.5B (R² = 0.96). A P/B ratio of 2.5 is consistent with the expected value for an aquatic insect with a 2-year life cycle and overlapping cohorts, and these data suggest this relation has general applicability for estimating production of Hexagenia in the northern United States and Canada. Size-class and seasonal partitioning of Hexagenia biomass and production were evident in the data. Both biomass and production were highest among nymphs 16.0 mm and larger, and biomass was highest in October and again in June, immediately before the annual emergence of subimagos. The large size of the mature nymphs and the concentration of biomass and production among the larger nymphs in the population is consistent with their importance in the diets of many fishes in the northern United States and Canada.     

Patterns of fish diversity in a mainstem Missouri River reservoir and associated delta in South Dakota and Nebraska,USA

There is an expansive and expanding delta at the confluence of the Niobrara and Missouri Rivers in the Lewis and Clark Reservoir. The delta provides diverse aquatic habitat that is somewhat similar to the historic Missouri River and to remnant river habitats. As such, the delta may have relatively high fish species diversity compared to lentic reservoir habitats. To compare patterns of fish diversity between the delta and reservoir habitats, we collected fish in several nursery habitats in both areas using four gear types (seine, gill net, electrofisher and fyke net) on three occasions (July, August and September) in 2005. Species richness was higher in the delta ( n = 34) than the reservoir ( n = 22). Thirteen species composed more than 1% of delta collections while only four species composed more than 1% of reservoir collections. Species diversity (Fisher's α) was also significantly higher in the delta. Higher species diversity in the delta may be explained by higher habitat diversity. These results suggest that newly forming deltas have the potential to protect and restore fish species diversity, because they retain natural river functions such as sediment transport and habitat formation. Copyright © 2007 John Wiley & Sons, Ltd.     

In Situ Determination of the Annual Thermal Habitat Use by Lake Trout (Salvelinus namaycush) in Lake Huron

Records of the temperatures occupied by 33 lake trout (Salvelinus namaycush) at large in Lake Huron were obtained for up to 14 months per fish, at 75-minute intervals, from surgically implanted archival temperature tags. The dataset covered nearly three years, from October 1998 to June 2001, and included 160,000 observations. The objectives of the tagging were to obtain temperature data to refine bioenergetics models of sea lamprey (Petromyzon marinus) predation on lake trout, and compare the temperatures occupied by strains of lake trout stocked in Lake Huron. The seasonal, thermal-use profiles of lake trout followed the general warming and cooling pattern of Lake Huron. During periods when the zone of surface water mixing extended below the depth range occupied by lake trout, variability among individual fish and strains was low and followed surface temperature. However, during the period of summer stratification, the average temperatures occupied varied substantially among individual fish and strains. Strains originating from the upper Great Lakes (Lake Superior and Lewis Lake, WY) occupied similar temperatures. Between June and mid August, upper Great Lakes lake trout typically occupied water several degrees warmer than that occupied by lake trout of Finger Lakes, New York origin. Most of the lake trout occupied summer temperatures lower than the preferred temperatures suggested by laboratory studies. In October, all strains occupied water as warm or warmer than that occupied in summer, which may partially explain the higher lethality of sea lamprey attacks during October.     

Suitable habitat model for walleye (Sander vitreus) in Lake Erie: Implications for inter-jurisdictional harvest quota allocations

Models predicting habitat distributions can give insight into species–habitat requirements and anticipate how populations respond to environmental change. Despite the economic and ecological importance of walleye (Sander vitreus) in Lake Erie, no preferred-habitat model exists and the spatial extent of suitable habitat is poorly understood. Empirical species-habitat models for three groups of walleye (juveniles, adults, and all walleye) was developed using records from a long term gill net data base (21 years). We examined the degree to which habitat suitability varies with vertical stratum for each group and whether the new model yields different estimates of available walleye habitat when compared to the current depth-based approach. Walleye occurrence in gill nets was positively related to water temperature, negatively related to water depth and water clarity, and unrelated to dissolved oxygen concentration. A model that incorporated interaction terms among the independent variables performed better than the linear, quadratic, and cubic generalized linear models (GLMs) for all three groups. Our results indicate that the extent of suitable habitat varies spatially in Lake Erie and is greatest in the West basin. Weighted Habitat Suitability Areas (WHSA), a combination of habitat quality and quantity, differed significantly among basins and vertical strata in Lake Erie. The current quota allocation strategy for Lake Erie walleye is based on the proportional amount of preferred habitat by jurisdiction. However, the current depth-based definition of preferred habitat may not be an adequate representation of walleye suitable habitat shared by each jurisdiction.     

Linking emergent midges to alewife (Alosa pseudoharengus) preference for rocky habitat in Lake Michigan littoral zones

Alewife (Alosa pseudoharengus) abundance and condition are in decline in Lake Michigan, where they not only exert negative effects on several native fish species but also support an economically valuable salmon sport fishery. We investigated feeding-related habitat selection for adult alewives occurring in Lake Michigan's littoral zone by comparing the relative abundance of alewives and non-biting midges (Chironomidae) on littoral rocky and sandy habitats. Both alewives and midges strongly favored hard over soft substrate, with approximately 22 and 23 times greater catch rates on rock than sand, respectively, from June through August 2005. Relative to sand, 92.2% of alewives and 94.8% of emergent midges were captured over rocky habitat. Gut content analysis suggested that the supplement of midge pupae created a benefit for alewives on rocky habitat and that midge emergence may be the basis for rocky habitat selection. Alewife consumption of midge pupae correlated with midge emergence events, frequency occurrence of midges in ale wife diets was significantly greater on rocky habitat, and alewives collected over sand were 1.5 times more likely to have empty stomachs than those collected over rocks. Our results indicate that alewives, the dominant pelagic forage fish in Lake Michigan, are seasonally encountered in littoral rocky communities, where midges are an important seasonal component of alewife diet.     

Spatial and temporal distribution of the cyanotoxin microcystin-LR in the Lake Ontario ecosystem: Coastal embayments,rivers, nearshore and offshore,and upland lakes

Cyanotoxins, a group of hepatotoxins and neurotoxins produced by cyanobacteria, pose a health risk to those who use surface waters as sources for drinking water and for recreation. Little is known about the spatial and seasonal occurrence of cyanotoxins in Lake Ontario and other lakes and ponds within its watershed. Within the embayments, ponds, rivers, creeks, shoreside, and nearshore and offshore sites of Lake Ontario, microcystin-LR concentrations were low in May, increased through the summer, and reached a peak in September before decreasing in October. Considerable variability in microcystin-LR concentrations existed between and within habitat types within the Lake Ontario ecosystem. In general, the average microcystin-LR concentration was two orders of magnitude lower in embayment (mean = 0.084 μg/L), river (mean = 0.020 μg/L), and shoreside (mean = 0.052 μg/L) sites compared to upland lakes and ponds (mean = 1.136 μg/L). Concentrations in the nearshore sites (30-m depth) and offshore sites (100-m depth) were another order of magnitude lower (mean = 0.006 μg/L) than in the creek/river, bay/pond, and shoreside habitats. Only 0.3% (2 of 581) of the samples taken in Lake Ontario coastal waters exceeded the World Health Organization (WHO) Drinking Water Guideline of 1 μg microcystin/L for humans. In contrast, 20.4% (20 of 98) of the samples taken at upland lakes and ponds within the watershed of Lake Ontario exceeded WHO Guidelines. No significant relationship between nitrate and microcystin-LR concentrations was observed in Lake Ontario even though a significant positive relationship existed between phosphorus and phycocyanin and microcystin-LR concentrations. At an upland lake site (Conesus Lake) in the Ontario watershed, the development of a littoral Microcystis population was not observed despite high nutrient loading (P and N) into the nearshore zone, well-developed nearshore populations of filamentous Spirogyra and Zygnema, the occurrence of Dreissena spp., and the known occurrence of Microcystis and microcystin production in the pelagic waters of Conesus Lake.     

Habitat suitability of golden mahseer young ones (Tor putitora,Hamilton 1822) in Himalayan waters,India

Habitat suitability refers to the mechanism that enables organisms to choose suitable habitats to survive. In the present study, we studied the habitat suitability of young golden mahseer (fingerlings and juveniles) in the streams of the Ramganga River, one of the prominent rivers of the western Himalaya. Different habitat types and microhabitat features were documented. Habitat suitability was evaluated by generating habitat suitability criteria curves in response to varying habitat availability and use by young golden mahseer during different seasons. Generalised linear modelling (GLM) was used to analyse environmental characteristics responsible for selecting golden mahseer habitats. We studied mahseer based on body size into two main classes, that is, fingerlings (1.5–10 cm) and juveniles (10–30 cm). Golden mahseer fingerlings preferred mean depth (0.1–0.6 m) and mean stream velocity (0–0.2 m/s) at stream reach dominated by diverse substrate compositions such as sand, gravel, and small cobbles. Similarly, juveniles preferred mean depth (0.1–1.5 m) and mean water velocity (0.1–0.5 m/s), with cobbles, bedrock, and sand dominating their habitats. The GLM results indicated that dissolved oxygen, temperature, and water velocity were the significant factors influencing habitat suitability. High dissolved oxygen positively influenced fingerlings, whereas moderate to high water velocity affected juveniles the most. Therefore, to understand the flow requirement for threatened species like golden mahseer, it is essential to characterise critical habitats and develop criteria based on habitat suitability curves.     

Stomach contents and stable isotopes confirm ontogenetic diet shifts of Nile perch, Lates niloticus, in southern Lake Victoria

Nile perch (Lates niloticus), a main target for Lake Victoria's fisheries, shifts its diet from invertebrates to fish during its ontogeny. We combined stomach contents with stable isotopes to study these diet shifts in Mwanza Gulf, southern Lake Victoria. During four seasons between 2009 and 2011 we collected and analysed 6697 stomachs and 516 stable isotope samples of Nile perch. Caridina shrimp and haplochromine cichlids were the major food items in Nile perch of 5–40?cm. Based on stomach contents, the shift of dominance of Caridina towards haplochromines in the diet varied from 6.7?cm length in the southern part of the gulf, to >20?cm in the northern part, possibly related to the higher abundance of Caridina in the north. In general isotope-based and stomach-content-based estimates of Nile perch diets agreed. We observed only two discrepancies: in Nile perch >20?cm, the isotope-based estimates of the contribution of haplochromines to the diet were much lower than based on stomach contents and the contribution of juvenile Nile perch to the diet were much higher in the isotope-based estimates than in the stomach based-based estimates. This discrepancy may be explained by e.g. different timespan-coverages between isotopes and stomach contents, by movements of Nile perch between the Gulf and the rest of Lake Victoria, or by the overlapping isotopic profiles of haplochromines and juvenile Nile perch. With the recent recovery of haplochromines in Lake Victoria, Nile perch appears to rely more on this prey again, as it did in the 1980s.     

Does Lake Erie still have sufficient oxythermal habitat for cisco Coregonus artedi?

In Lake Erie, cisco (Coregonus artedi) once supported one of the most valuable freshwater fisheries on earth, yet overfishing caused their eventual extirpation from the lake. With warming lake temperatures, some have questioned whether Lake Erie still contains suitable oxythermal conditions for cisco. Using published oxythermal thresholds for adult cisco (which have more stringent requirements than juveniles) and oxythermal profiles from Lake Erie, we sought to answer two questions critical to cisco restoration science. First, is cisco habitat still available during the most restrictive periods? Second, what is the distribution of cisco habitat during these times? Beta regression was used to determine that cisco habitat was most limited during the month of August, and that August of 2010 was the most restrictive period in the time series. We then used Empirical Bayesian Kriging (EBK) to map the spatial extent of cisco habitat during these times. EBK maps revealed large areas of summer refugia for cisco in Lake Erie, even during the least favorable periods. Most of the Central and East Basins contain suitable habitat during the average August, yet during August of 2010, suitable conditions were limited to the eastern edge of the Central Basin and the deep waters of the East Basin. These findings aligned well with historical accounts of cisco landings. While suitable oxythermal habitat still exists for cisco in Lake Erie, future restoration efforts, if attempted, will partially depend on: 1) better management of nutrient inputs, 2) the realization of future climate scenarios, and 3) the ability of cisco to adapt to a changing lake.