Food of Trout and Salmon in Lake Ontario

Stomachs of trout and salmon (n = 1,904) were collected from fish registered at fishing tournaments held in New York State waters of Lake Ontario between April and September 1983 and 1984. Numbers of adult-sized fish containing identifiable food items were 323 lake trout (Salvelinus namaycush), 289 brown trout (Salmo trutta), 24 rainbow trout (S. gairdneri), 164 coho salmon (Oncorhynchus kisutch), and 63 chinook salmon (O. tschawytscha) Proportional similarity in diet between pairs of species was high and normally exceeded 0.70; diet composition of individual species was similar between years. Alewives (Alosa pseudoharengus) were the main prey of all species during all months and were normally 110–149 mm in standard length. Rainbow smelt (Osmerus mordax) was the second most common prey eaten but was generally found in fewer than 20% of the stomachs examined during any month. Diet diversity was generally higher during April-May than during July-September for coho salmon, lake trout, and brown trout. Larger brown trout ate larger alewife in 1983 but not in 1984. Results suggest that the five trout and salmon species in Lake Ontario are potential competitors.     

Seasonal Bathythermal Distribution of Juvenile Lake Trout in Lake Ontario

Bathythermal distributions of hatchery-reared lake trout (Salvelinus namaycush) of three genetic strains (Lake Superior; Clearwater Lake, Manitoba; and Seneca Lake, New York) were described from catches with bottom trawls in Lake Ontario during April-May, June, July-August, and October, 1978–1984. This work was part of a program to evaluate post-stocking performance of hatchery-reared fish and identify strains for continued use in rehabilitation of lake trout in Lake Ontario. All age groups of Lake Superior fish were in deeper water in April-May than in June each year; mean depth of capture was greatest at age II and became progressively shallower at ages III and IV. Mean depth of capture in April-May was positively correlated with severity of the preceding winter as judged by heating degree days and average wind speed. During July-August, the fish were concentrated between the epilimnion and 50 m, with no consistent trend in depth by age; however, 92% were captured at water temperatures of 12°C or lower. Mean temperatures of capture for Lake Superior fish during the four respective sampling periods were 3.9, 7.5, 6.9, and 9.5° C for fish of age II and 3.9, 8.4, 6.9, and 8.7° C for fish of age III. The age-II Clearwater Lake fish were consistently at shallower depths than age-II Lake Superior fish. Mean temperatures of capture were 4.2, 9.7, 9.6, and 10.7° C during the four respective sampling periods; during July-August, 91% were taken in water of 12° C or lower. The distribution of Seneca Lake fish was similar to that of the Lake Superior strain. Mean temperatures at which the three strains were captured were well below published preferred temperatures of yearlings in the laboratory. Annual variations in depth distributions during a given season were probably due to differing thermal regimes resulting from annual variations in the weather.     

Sculpins and Crayfish in Lake Trout Spawning Areas in Lake Ontario: Estimates of Abundance and Egg Predation on Lake Trout Eggs

Crayfish (Orconectes spp.) and sculpins (Cottus spp.) were collected at eight lake trout spawning reefs in Lake Ontario to assess abundance and potential to consume lake trout eggs. Abundance of crayfish ranged from a high of 9.5/m² in eastern Lake Ontario to 0/m² in western Lake Ontario where the absence or near absence at four reefs sampled was attributed to cold water upwelling. Sculpin abundance ranged from 4.2 to 50.1/m². Mean daily egg consumption (eggs/stomach) for sculpins 50 to 75 mm in length, ranged from 0 to 0.9 but differences among reefs were not significant. At one reef, significantly more eggs (2.5 eggs/stomach) were consumed by large sculpins (> 75 mm) than by small (44–49 mm) sculpins (0.2 eggs/stomach). Estimated egg consumption (eggs/stomach/m²) for sculpins > 43 mm for the eight reefs for the period between estimated date of peak lake trout spawning and a standardized 30-d period post spawning, ranged from 0 to 496 eggs/m² consumed or from 0 to 54% of estimated egg abundance. No lake trout eggs were found in crayfish stomachs, because of their mode of feeding. Estimated egg consumption by crayfish was indirectly estimated from a relationship developed between carapace length and egg consumption using published literature and experimental work. Using this procedure, estimated egg consumption by crayfish for a standardized 30-d period after the date of peak spawning ranged from 0 to 65 eggs/m² consumed, or from 0 to 82% of potential egg abundance for the eight reefs. At low egg abundance (< 100/m²), the density of crayfish and sculpin observed in Lake Ontario could result in sufficient egg consumption to cause almost 100% mortality of lake trout eggs. At higher egg abundance, however, mortality due to crayfish and sculpins appears to be relatively low. Deposition was sufficiently low at 5 of 8 sites to suggest the possible importance of sculpin and crayfish predation on lake trout recruitment failure in Lake Ontario.     

Dynamics of Reproduction by Hatchery Lake Trout on a Man - Made Spawning Reef

Reproduction by hatchery lake trout, critical for rehabilitation of lake trout stocks in the Great Lakes, had not been previously described and measured. Reproduction by hatchery lake trout on a man-made spawning reef in Presque Isle Harbor, Lake Superior, in 1977-80 was qualitatively and quantitatively described using gill nets, egg traps, and fry traps. Scuba divers measured physical parameters of the reef. Lake trout spawned during a 15- to 28-day period between 12 October and 14 November mainly during 1800–2000 hours. The Petersen single census was a better method of estimating adults than either multiple-census or fecundity-egg deposition methods. The Petersen estimate of adults was nearly 4,000 males and 1,900 females in 1979. Egg deposition and swim-up fry production ranged from 122 to 518/m² and 20 to 46/m², respectively. Substrate on the man-made reef was a 27- to 42-cm thick layer of granite and limestone cobbles 6 to 20 cm in diameter. Spawning behavior and quantitative aspects of reproduction by hatchery lake trout were similar to that previously reported for native lake trout in the Great lakes and elsewhere. Man-made reefs may be a valuable lake trout management tool.     

Seasonal Food of Juvenile Lake Trout in U.S. Waters of Lake Ontario

Stomach contents of 3,554 lake trout (Salvelinus namaycush), 100 to 449 mm in total length, captured with bottom trawls during April through October 1978–81 along the south shore of Lake Ontario were examined. Invertebrates appeared to be an important food of lake trout less than 200 mm long but were only occasionally eaten by larger fish. For all seasons and size groups of juvenile lake trout combined, the slimy sculpin (Cottus cognatus) was the principal forage fish, making up 42% (by weight) of identifiable fish remains. Young-of-the-year slimy sculpins were a major food of recently stocked yearling lake trout during July through October. Alewives (Alosa pseudoharengus) were the principal forage during April and May, and made up 28% (by weight) of the identifiable fish remains. They were rarely eaten during July and August, however, when lake trout remained in the hypolimnion and alewives were above it. Over 99% of the alewives eaten from April through August were yearlings and over 99% eaten during October were young-of-the-year. Rainbow smelt (Osmerus mordax) were the primary forage during July and August, but contributed only a small part of the diet during other seasons; overall, they made up 25% of identifiable fish remains. Johnny darters (Etheostoma nigrum) made up 4% of identifiable fish remains and were most common in stomachs of small lake trout during October.     

Diet Composition and Feeding Periodicity of Wild and Hatchery Subyearling Chinook Salmon in Lake Ontario

Diel feeding periodicity, daily ration, and diet composition of wild and hatchery subyearling Chinook salmon Oncorhynchus tshawytscha were examined in Lake Ontario and the Salmon River, New York. The diet of wild riverine salmon was composed mainly of aquatic invertebrates (63.4%), mostly ephemeropterans (25.8%), chiromomids (15.8%), and trichopterans (8.3%). The diet of riverine Chinook was more closely associated with the composition of drift samples rather than bottom samples, suggesting mid-water feeding. In Lake Ontario terrestrial invertebrates were more important in the diet of hatchery Chinook (49.0%) than wild salmon (30.5%) and diet overlap between hatchery and wild salmon was low (0.46%). The diet of both hatchery and wild Chinook salmon was more closely associated with the composition of mid-water invertebrate samples rather than benthic core samples, indicating mid-water and surface feeding. Hatchery Chinook salmon consumed significantly less food (P < 0.05) than wild Chinook salmon in the lake and in the river, and wild salmon from Lake Ontario consumed more food than wild salmon in the Salmon River. Peak feeding of wild Chinook salmon occurred between 1200–1600 hours in Lake Ontario and between 1600–2000 hours in the Salmon River; there was no discernable feeding peak for the hatchery Chinook in Lake Ontario. Hatchery Chinook salmon also had the least diverse diet over the 24-hour sample period. These results suggest that at 7 days post-stocking hatchery Chinook salmon had not yet fully adapted to their new environment.     

Egg Thiamine Status of Lake Ontario Salmonines 1995–2004 with Emphasis on Lake Trout

Alewives (Alosa pseudoharengus), the major prey fish for Lake Ontario, contain thiaminase. They are associated with development of a thiamine deficiency in salmonines which greatly increases the potential for developing an early mortality syndrome (EMS). To assess the possible effects of thiamine deficiency on salmonine reproduction we measured egg thiamine concentrations for five species of Lake Ontario salmonines. From this we estimated the proportion of families susceptible to EMS based on whether they were below the ED20, the egg thiamine concentration associated with 20% mortality due to EMS. The ED20s were 1.52, 2.63, and 2.99 nmol/g egg for Chinook salmon (Oncorhynchus tshawytscha), lake trout (Salvelinus namaycush), and coho salmon (Oncorhynchus kisutch), respectively. Based on the proportion of fish having egg thiamine concentrations falling below the ED20, the risk of developing EMS in Lake Ontario was highest for lake trout, followed by coho (O. kisutch), and Chinook salmon, with the least risk for rainbow trout (O. mykiss). For lake trout from western Lake Ontario, mean egg thiamine concentration showed significant annual variability during 1994 to 2003, when the proportion of lake trout at risk of developing EMS based on ED20 ranged between 77 and 100%. Variation in the annual mean egg thiamine concentration for western Lake Ontario lake trout was positively related (p < 0.001, r² = 0.94) with indices of annual adult alewife biomass. While suggesting the possible involvement of density-dependent changes in alewives, the changes are small relative to egg thiamine concentrations when alewife are not part of the diet and are of insufficient magnitude to allow for natural reproduction by lake trout.     

Content and Chemical Form of Mercury and Selenium in Lake Ontario Salmon and Trout

The content and chemical form of mercury and selenium were determined in the edible tissue of salmon (coho, chinook) and trout (lake, brown) taken offshore from Lake Ontario near Rochester, New York. For all fish species, total mercury content ranged from 0.3 to 0.8 μg/g (fresh-weight), which is similar to concentrations commonly found in canned tuna. Most of the total mercury (63 to 79 percent) was present as methylmercury, the remainder being divalent inorganic mercury. For all species, 6 to 45 percent of the total selenium content was present as selenate (SeVI), the remainder being selenite (SeIV) and selenide (Se-11). On a molar basis, total selenium content usually exceeded that of total mercury. Samples of smoked and unsmoked brown trout fillets were also examined. Based on the results of this study there is no immediate human health hazard from mercury and selenium. However, there is a need to report specific chemical forms of these metals in Lake Ontario salmonid fishes so that elevated concentrations can be better evaluated.     

Alternative Ecological Pathways in the Eastern Lake Ontario Food Web—Round Goby in the Diet of Lake Trout

Round goby (Neogobius melanostomus) range expansion and their possible inclusion in the diet of lake trout (Salvelinus namaycush) were investigated. Fish community index bottom trawls in eastern Lake Ontario (Kingston basin) during summer 2003 and 2004 indicated the presence of the round goby at relatively low densities (3.72 × 10^–2 ± 5.24 × 10^–3 fish/m²) in depths up to 30 m. Lake trout (mean fork length = 585 ± 78 mm and mean weight = 2,770 ± 1,134 g) stomach contents showed round goby to be the second most abundant diet item at almost 20% by number (36% by mass). Round goby ingested by lake trout ranged in total length from 50 to 110 mm. The most important prey species in terms of abundance (68%) and mass (56%) was alewife (Alosa pseudoharengus). Alewives were the most important diet item for all sizes of lake trout sampled, except those in the 550 - 650 mm size class, which ingested more round goby by mass than alewife. Round goby range expansion to deep water and prominence in the diet of lake trout signal significant change in the eastern Lake Ontario food web.     

Seasonal Movements and Habitats of Brown Trout (Salmo Trutta) in Southcentral Lake Ontario

During 1980–82 the movements, seasonal locations, and habitat preferences of brown trout in southcentral Lake Ontario were examined using radio telemetry and vertical gill nets. In fall and spring 85% of the 28 brown trout tracked by radio moved east from tagging sites. Movements frequently centered around original stocking sites, streams, and power plant outflows. Fish moved farther in spring (4.4 ± 2.5 km/d) than in fall (2.4 ± 1.7 km/d) seasons, but short-term movement rates did not differ between seasons (0.4 ±0.1 km/h in spring vs. 0.4 ± 0.3 km/h in fall). Females moved farther and faster than males in the fall. Brown trout generally occupied shallow waters < 1 km from shore; 81% of temperatures occupied by trout were between 8–18°C in spring (10.6 ± 2.3°C) and fall (10.1 ± 3.9°C), but turbidity appeared to influence presence or absence of trout near shore on a daily basis. In summer 78% of the 75 brown trout netted were in 8–18° C water (12.6 ± 4.0°C); 88% were caught in or within ±3 m of the thermocline region. Brown trout occupied regions near the thermocline despite widely varying bottom depths and thermocline temperatures. All brown trout were netted within 3.2 km of shore in summer, most in water ≤ 30 m deep; 70% were caught more than 3 m off bottom. The strong association of brown trout with nearshore and thermocline regions may distinguish their distributions from other salmonid species in Lake Ontario.     

The Significance of Seasonal Changes on a Modern Cobble-Gravel Beach used by Spawning Lake Trout,Lake Ontario

In 1979, lake trout (Salvelinus namaycush) spawning was observed and confirmed by divers over a modern cobble-gravel beach in eastern Lake Ontario. Seasonal beach surveys determined that areas where egg deposition took place coincided closely with areas of coarse cobble-gravel where sediment accumulation rates were highest. Egg deposition occurred at depths below subsequent winter ice contact. The seasonal transport of cobble-gravel seems to have largely preceded the spawning episode but addition of some finer gravels, in the area of egg deposition, did occur before freeze-over. There was no survival to hatch.     

The Impacts of Atlantic Salmon Stocking on Rainbow Trout in Barnum House Creek,Lake Ontario

We compared the impacts of stocking age-0 Atlantic salmon (Salmo salar) at high and low densities, and no stocking on abundance and growth of age-0 rainbow trout (Oncorhyncus mykiss) in Barnum House Creek, Ontario during 1993 to 2005. A similar stream, Shelter Valley Creek, was chosen as an appropriate reference stream where age-0 Atlantic salmon were not stocked. The catches of age-0 rainbow trout in Barnum House and the reference stream were highly correlated (r = 0.96) during years when no stocking occurred; however, this relationship did not persist in years when Atlantic salmon were stocked. The catch of age-0 rainbow trout in Barnum House Creek was significantly lower under both high (P = 0.00026) and low (P = 0.011) density Atlantic salmon stocking treatments compared with the no stocking treatment. The catches of age-0 rainbow trout and age-0 Atlantic salmon were negatively correlated in Barnum House Creek (r = −0.63). The length of age-0 rainbow trout in Barnum House Creek was depressed significantly (P = 0.004), under the high intensity Atlantic salmon stocking treatment, but not under the low intensity treatment (P = 0.20). In contrast, the length of age-0 rainbow trout in Shelter Valley Creek was unchanged over the same period. Restoration stocking of Atlantic salmon in Lake Ontario tributaries may impact rainbow trout abundance and growth.     

Maturity Schedules of Lake Trout in Lake Michigan

We determined maturity schedules of male and female lake trout (Salvelinus namaycush) in Lake Michigan from nearshore populations and from an offshore population on Sheboygan Reef, which is located in midlake. Gill nets and bottom trawls were used to catch lake trout in fall 1994 and 1995 from two nearshore sites and Sheboygan Reef. Each lake trout was judged immature or mature, based on visual examination of gonads. Probit analysis, coupled with relative potency testing, revealed that age-at-maturity and length-at-maturity were similar at the two nearshore sites, but that lake trout from the nearshore sites matured at a significantly earlier age than lake trout from Sheboygan Reef. However, length at maturity for the nearshore populations was nearly identical to that for the offshore population, suggesting that rate of lake trout maturation in Lake Michigan was governed by growth rather than age. Half of the lake trout males reached maturity at a total length of 580 mm, whereas half of the females were mature at a length of about 640 mm. Over half of nearshore males were mature by age 5, and over half the nearshore females matured by age 6. Due to a slower growth rate, maturity was delayed by 2 years on Sheboygan Reef compared with the nearshore populations. Documentation of this delay in maturation may be useful in deciding stocking allocations for lake trout rehabilitation in Lake Michigan.     

Temporal and Age-Related Trends in Levels of Polychlorinated Biphenyl Congeners and Organochlorine Contaminants in Lake Ontario Lake Trout (Salvelinus namaycush)

Concentrations of 21 organochlorine contaminants (OCs) and 61 polychlorinated biphenyl (PCB) congeners were determined in archived samples of whole lake trout (Salvelinus namaycush), age 4 years, collected yearly from eastern Lake Ontario between 1977 and 1993. Temporal trend data show decreases in all parameters analyzed in samples collected from 1977 to 1993. OC levels declined between 60 and 90% from 1977 to 1993. Trends of total PCB and PCB congeners concentrations were variable, but overall levels declined 80% between 1977 and 1993, from 9,060 ng/g in 1,977 to 1,720 ng/g in 1993. Reanalyzed total PCB levels vary randomly from the historical total PCB levels, but overall exhibit a much smoother trend. The means of the two sample sets were not significantly different at a probability of 0.05. Lake trout aged from 3 to 9 years old, collected in 1988, were analyzed to determine changes in contaminant concentrations with age. OC levels on average increased three-fold from 3-year-old lake trout up to 9-year-old lake trout. Total PCB levels increased from 2,760 ng/g in 3-year-old lake trout to 8,000 ng/g in 9-year-old lake trout, and PCB congener concentrations showed similar increases over the same age range. Lipid content declined 30% between 1977 and 1993, but lipid normalizing the data did not change the observed trends.     

Maternal Characteristics versus Egg Size and Energy Density: Do Stocked Lake Trout in Lake Ontario Experience Premature Reproductive Senescence?

Observations from September 1994 and 1997 collections of hatchery-origin, mature female lake trout (Salvelinus namaycush) from Lake Ontario indicated that egg mass decreased with age, fueling the notion that stocked fish experienced premature reproductive senescence. Supplemental collections during September 2002 and November 2002-2004 were combined with the 1994 and 1997 samples to examine whether sample date or maternal age, body mass, condition (K), egg count, or strain were related to egg mass or energy content (percentage dry mass [%DM]). Body mass was correlated with egg mass for age ≥ 8 lake trout sampled in September, and egg count was correlated with egg mass for September age-6 lake trout only. Within each month, egg mass was not related to K or egg %DM, however, egg %DM was 1.52% greater (P ≤ 0.0247) in November than in September which is equivalent to a 110 cal/g difference. Samples were grouped for the three most abundant strains (Seneca, Superior, and Ontario) after finding no strain or year effects from our 1994 and 1997 samples and based on life history data from the literature and our assessment sampling. Further analysis indicated that September egg masses were greater for fish ages ≤ 6 than for fish ages ≥ 8. The age effect disappeared in November when mean egg mass across all ages (0.078 g) was greater than September means (P < 0.0005) for ages-5 (0.054 g), -6 (0.057 g) and ≥ 8 (0.041 g). Our results indicate that the decrease in egg mass with female age in September was not due to senescence, but to oogenesis being closer to completion in young age-5 and -6 fish than in older individuals.     

Starvation Resistance in Lake Trout Fry

Newly hatched fry were acclimated to 7 or 12°C and either fed daily (controls) or denied food for varying lengths of time and then fed daily until the end of the study (day 91 at 7°C and day 43 at 12°C). Growth was reduced by delays in the onset of feeding of 27 or more days at 7°C and 7 or more days at 12°C. Mortality of fry unfed for more than 34 days at 7°C, or more than 21 days at 12°C, was higher than among controls. Daily mortality increased with the length of the food deprivation period and did not cease immediately when food was made available, but reached zero by the end of the study. Mortality among unfed fry reached 50% in about 59 days at 7°C and 32 days at 12°C. Study results permitted calculation of the “point-of-no-return” (PNR) mortality, which included the mortality that occurred during the period of food deprivation, and also the delayed component of mortality that was directly attributable to starvation and that occurred after food was made available. The PNR for 50% mortality for food-deprived fry occurred after 52 days at 7°C and 24 days at 12°C. Thus, both measures of mortality indicate that lake trout fry would be highly resistant to death by starvation in the thermal habitat they would be expected to occupy in the Great Lakes. We conclude that a more likely adverse effect of reduced food availability would result from a reduction in growth rate that extends the length of time fry remain small and vulnerable to predation by adult alewives and other non-native fishes with which they associate.     

Spatial Patterns in PCB Concentrations of Lake Michigan Lake Trout

Most of the PCB body burden in lake trout (Salvelinus namaycush) of the Great Lakes is from their food. PCB concentrations were determined in lake trout from three different locations in Lake Michigan during 1994–1995, and lake trout diets were analyzed at all three locations. The PCB concentrations were also determined in alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax), bloater (Coregonus hoyi), slimy sculpin (Cottus cognatus), and deepwater sculpin (Myoxocephalus thompsoni), five species of prey fish eaten by lake trout in Lake Michigan, at three nearshore sites in the lake. Despite the lack of significant differences in the PCB concentrations of alewife, rainbow smelt, bloater, slimy sculpin, and deepwater sculpin from the southeastern nearshore site near Saugatuck (Michigan) compared with the corresponding PCB concentrations from the northwestern nearshore site near Sturgeon Bay (Wisconsin), PCB concentrations in lake trout at Saugatuck were significantly higher than those at Sturgeon Bay. The difference in the lake trout PCB concentrations between Saugatuck and Sturgeon Bay could be explained by diet differences. The diet of lake trout at Saugatuck was more concentrated in PCBs than the diet of Sturgeon Bay lake trout, and therefore lake trout at Saugatuck were more contaminated in PCBs than Sturgeon Bay lake trout. These findings were useful in interpreting the long-term monitoring series for contaminants in lake trout at both Saugatuck and the Wisconsin side of the lake.     

Effect of Fish Age on Predicted and Observed Chronic Toxicity of Lead to Rainbow Trout in Lake Ontario Water

Exposure of rainbow trout (Salmo gairdneri) starting at the egg stage to water-borne lead in Lake Ontario water (hardness of 135 mg CaCO₃/L) resulted in black tails (early symptoms of spinal deformities) at lead concentrations as low as 22 μg/L. No black tails were observed at 11 μg/L. Previous publications demonstrated that the lowest lead concentration causing black tails in trout exposed from the fingerling stage in Lake Ontario water was 120 μg/L, suggesting that fish exposed from the egg stage are 5 times as sensitive as those exposed from the fingerling stage. Compared to previously published data on fish exposed from the egg stage, blood lead of fish exposed from the egg stage was greater for a similar lead exposure. However, the relationship between blood lead and enzyme inhibition (erythrocyte δ-amino levulinic acid dehydratase) was unchanged. Therefore the increased sensitivity of trout exposed from the egg stage was probably due to enhanced lead accumulation rather than to an enhanced response to the lead taken up. The incidence of black tails at this hardness corresponded well to a prediction based on published lead toxicity at extremes of water hardness.     

Distribution,Fecundity, and Genetics of Cercopagis pengoi (Ostroumov) (Crustacea,Cladocera) in Lake Ontario

Two distinctive forms of cercopagids, first detected in 1998 and identified as Cercopagis pengoi and C. ossiani using taxonomic keys, were observed to co-occur in Lake Ontario. C. ossiani was the predominant form in western Lake Ontario in mid-June 1999 but was then replaced by C. pengoi-like animals over the rest of the season. Mitochondrial DNA analyses revealed that these forms were genetically identical at the ND5 gene and that they are morphologically distinctive forms of C. pengoi. In 1999, Cercopagis reached a maximum abundance of 1,759 individuals/m³ (average abundance = 281 individuals/ m³, average biomass = 5.2 mg/m³). In August, Cercopagis biomass was lowest at nearshore and embayment sites and highest at offshore sites. Body length of parthenogenetic females was lower at nearshore (1.16 mm) and embayment (1.19 mm) sites relative to offshore (1.32 mm) ones. Maximal clutch size of parthenogenetic females was 24 embryos per individual. Cercopagis has already spread to Lake Michigan and five Finger Lakes. Although waterfowl may disperse Cercopagis, these invasions likely resulted from human activities.     

Evidence of Natural Reproduction by Planted Lake Trout in Lake Michigan

Lake trout (Salvelinus namaycush) fry were captured in southeastern Lake Michigan for the first time since the species was reintroduced from hatchery stocks in 1965. Spawning apparently occurred in fall 1979 on newly placed limestone riprap covering recently constructed power plant intake and discharge pipelines. Eggs presumably hatched in late February–March, 1980, and 57 fry (22–43 mm total length) were collected April–June, 1980, and three fry (55–62 mm) were collected in August, 1980.