Use of a simulation model to reconstruct PCB concentrations in prey of Lake Ontario lake trout
No abstract available.
New York, Quebec↗
Geology topics
Joseph H. Elrod
Publications and source records attributed to Joseph H. Elrod.
Shifts in depth distributions of alewives, rainbow smelt, and age-2 lake trout in southern Lake Ontario following establishment of Dreissenids
In the mid-1990s, biologists conducting assessments of fish stocks in Lake Ontario reported finding alewives Alosa pseudoharengus , rainbow smelt Osmerus mordax , and juvenile lake trout Salvelinus namaycush at greater depths than in the mid-1980s. To determine if depth distributions shifted coincident with the early 1990s colonization of Lake Ontario by exotic Dreissena mussels, we calculated mean depth of capture for each of the three species during trawl surveys conducted annually during 1978–1997 and examined the means for significant deviations from established patterns. We found that mean capture depth of alewives, rainbow smelt, and age-2 lake trout shifted deeper during the build up of the dreissenid population in Lake Ontario but that timing of the shift varied among seasons and species. Depth shifts occurred first for rainbow smelt and age-2 lake trout in June 1991. In 1992, alewives shifted deeper in June followed by age-2 lake trout in July–August. Finally, in 1993 and 1994, the distribution of lake trout and alewives shifted in April–May. Reasons why the three fishes moved to deeper water are not clear, but changes in distribution were not linked to temperature. Mean temperature of capture after the depth shift was significantly lower than before the depth shift except for alewives in April–May. Movement of alewives, rainbow smelt, and age-2 lake trout to colder, deeper water has the potential to alter growth and reproduction schedules by exposing the fish to different temperature regimes and to alter the food chain, increasing predation on Mysis relicta in deep water and decreasing alewife predation on lake trout fry over nearshore spawning grounds in spring.
Transactions of the American Fisheries Society↗
Reproductive potential and fecundity of lake trout strains in southern and eastern waters of Lake Ontario, 1977-1994
We assessed the reproductive potential of various genetic strains of hatchery lake trout ( Salvelinus namaycush ) in southern and eastern Lake Ontario from indices of fecundity and indices of male abundance. Indices were constructed from catches of mature lake trout in gill nets during September 1980 to 1994 after correcting for mortality from sea lampreys ( Petromyzon marinus ) which occurred between September sampling and late fall spawning. Strain and age were assigned to individual lake trout based on clipped fins and maxillary bones or coded wire tags. Fecundity-length relationships for fish of the same age, determined from mature females collected in 1977 to 1981 and 1994, were not different (P > 0.05) among genetic strains. For all strains combined, fecundity-length relationships in 1977 to 1981 were not different among fish of various ages but in 1994, age-5 and -6 fish had fewer eggs (P < 0.003) than age-7 fish, and age-7 fish had fewer eggs (P < 0.003) than fish of age 8, 9, or 10. Annual indices of fecundity varied 19 fold and indices of mature males varied 11 fold; both indices were low in the early 1980s, increased sharply in the mid 1980s, and peaked in 1993. The strain which dominated fecundity and mature male indices shifted during the study from Seneca Lake strain to Lake Superior strain and then back to Seneca Lake strain. However, changes in either reproductive potential or genotypes do not appear responsible for the abrupt appearance of naturally-produced yearling lake trout throughout southern and eastern Lake Ontario in 1994–1995, the first widespread occurrence of juveniles produced by hatchery lake trout in Lake Ontario.
Journal of Great Lakes Research↗
Survival of hatchery-reared lake trout stocked near shore and off shore in Lake Ontario
Establishing a stock of mature, hatchery-reared fish is necessary to restore a self-sustaining population of lake trout Salvelinus namaycush in Lake Ontario. Stocking fish off shore rather than near shore to reduce predation on these fish by large lake trout or piscivorous birds may enhance survival of hatchery-reared fish and accelerate establishment of a population of adults. Results of an earlier study did not support routinely stocking fish off shore by helicopter in Lake Ontario, but stresses associated with helicopter stocking suggested another method of transporting fish off shore might enhance survival. I conducted this study to determine whether stocking lake trout off shore by barge would enhance first-year survival. Two lots of yearling lake trout were stocked at each of four locations in Lake Ontario in May 1992. One lot was stocked from shore, and an identical lot was transported by barge 3.4–10.4 km off shore of nearshore locations and stocked in water 46–52 m deep. Fish were recovered during trawl, gillnet, and creel surveys in 1992–1996. First-year survival of lake trout stocked off shore tended to be better than that of fish stocked near shore. Predation by double-crested cormorants Phalacrocorax auritus likely affected survival of fish stocked near shore at two locations, 7 and 37 km, respectively, from a nesting colony of 5,443 pairs of double-crested cormorants. Predation by large lake trout remains a viable hypothesis, which explains, at least partially, lower survival of lake trout stocked near shore at two other locations. Stocking lake trout off shore of traditional nearshore stocking sites likely will enhance first-year survival of hatchery-reared fish and promote accumulation of an adult population, especially for those occassions where nearshore stocking locations are near nesting colonies of double-crested cormorants.
North American Journal of Fisheries Management↗
Bathythermal distribution, maturity, and growth of lake trout strains stocked in U.S. waters of Lake Ontario, 1978-1993
Bathythermal distributions, sexual maturity, and growth of lake trout ( Salvelinus namaycush ) strains stocked in Lake Ontario were determined for fish collected with trawls and gill nets in 1978-93. The purpose was to augment the basis for deciding which strains to continue stocking in an effort to reestablish a self-sustaining population. The Clearwater Lake (CWL) strain was found in shallower, warmer water than all other strains; the Seneca Lake (SEN) strain was usually shallower than the Jenny Lake (JEN) and Lake Superior (SUP) strains at ages 1 and 2 but was usually deeper at age 3 and older. Depth distribution of the 'Ontario strain'--from gametes of several strains that survived to maturity in Lake Ontario-- was similar to that of the SEN and SUP strains. About half the males matured at age 4 and half the females at age 5; males < 500 mm and females < 600 mm long were rarely mature. Least-sqaures mean lengths and weights of the CWL strain were greater than those of all other strains through age 4. At age 7 and older, CWL and JEN fish were generally smaller than all other strains. Means lengths and weights of males and females of the same age and strain frequently differed at age 4 and older. Growth in weight at age 4 and older was not associated with biomass indices of prey fishes. Differences in growth rates among strains were associated with bathythermal distribution which is a heritable trait. Weight-length regressions differed by year, sex, and stage of maturity but were rarely different among strains. Competition for space appeared to affect condition of large lake trout. Growth rates and maturity schedules provide little basis for recommending stocking one strain in preference to another. Depth ranges of strains overlapped widely, but lake trout occupied only about one-fourth of available bottom habitat. Stocking several strains should be continued to maximize use of sustainable habitat.
Journal of Great Lakes Research↗
Geographical distributions of lake trout strains stocked in Lake Ontario
Geographical distributions of lake trout ( Salvelinus namaycush ) stocked at seven locations in U.S. waters and at four locations in Canadian waters of Lake Ontario were determined from fish caught with gill nets in September in 17 areas of U.S. waters and at 10 fixed locations in Canadian waters in 1986–95. For fish of a given strain stocked at a given location, geographical distributions were not different for immature males and immature females or for mature males and mature females. The proportion of total catch at the three locations nearest the stocking location was higher for mature fish than for immature fish in all 24 available comparisons (sexes combined) and was greater for fish stocked as yearlings than for those stocked as fingerlings in all eight comparisons. Mature fish were relatively widely dispersed from stocking locations indicating that their tendency to return to stocking locations for spawning was weak, and there was no appreciable difference in this tendency among strains. Mature lake trout were uniformly distributed among sampling locations, and the strain composition at stocking locations generally reflected the stocking history 5 to 6 years earlier. Few lake trout moved across Lake Ontario between the north and south shores or between the eastern outlet basin and the main lake basin. Limited dispersal from stocking sites supports the concept of stocking different genetic strains in various parts of the lake with the attributes of each strain selected to match environmental conditions in the portion of the lake where it is stocked.
Journal of Great Lakes Research↗
Lake trout rehabilitation in Lake Ontario
Attempts to maintain the native lake trout ( Salvelinus namaycush ) population in Lake Ontario by stocking fry failed and the species was extirpated by the 1950s. Hatchery fish stocked in the 1960s did not live to maturity because of sea lamprey ( Petromyzon marinus ) predation and incidental commercial harvest. Suppression of sea lampreys began with larvicide treatments of Lake Ontario tributaries in 1971 and was enhanced when the tributaries of Oneida Lake and Lake Erie were treated in the 1980s. Annual stocking of hatchery fish was resumed with the 1972 year class and peaked at about 1.8 million yearlings and 0.3 million fingerlings from the 1985–1990 year classes. Survival of stocked yearlings declined over 50% in the 1980 s and was negatively correlated with the abundance of lake trout > 550 mm long (r = −0.91, P < 0.01, n = 12). A slot length limit imposed by the State of New York for the 1988 fishing season reduced angler harvest. Angler harvest in Canadian waters was 3 times higher in eastern Lake Ontario than in western Lake Ontario. For the 1977–1984 year classes, mean annual survival rate of lake trout age 6 and older was 0.45 (range: 0.35–0.56). In U.S. waters during 1985–1992, the total number of lake trout harvested by anglers was about 2.4 times greater than that killed by sea lampreys. The number of unmarked lake trout < 250 mm long in trawl catches in 1978–1992 was not different from that expected due to loss of marks and failure to apply marks at the hatchery, and suggested that recruitment of naturally-produced fish was nil. However, many of the obstacles which may have impeded lake trout rehabilitation in Lake Ontario during the 1980s are slowly being removed, and there are signs of a general ecosystem recovery. Significant recruitment of naturally produced lake trout by the year 2000, one interim objective of the rehabilitation plan for the Lake, may be achieved.
Journal of Great Lakes Research↗
Survival of lake trout stocked in U.S. Waters of Lake Ontario
Lake trout Salvelinus namaycush of the 1979–1990 year-classes (Lake Superior strain) were marked and stocked as fingerlings or yearlings in U.S. waters of Lake Ontario and recaptured during annual surveys with trawls and gill nets. Catches (as proportions of fish stocked) of age-2 fish by trawls and age-3 fish by gill nets were used as indices of survival. Mean survival indices of stocked fish declined over 50% from the 1980 to the 1990 year-class for fish stocked as yearlings and declined more than 90% for those stocked as fingerlings. Survival indices for fish stocked as yearlings were negatively and significantly correlated with abundance indices of large (≥550 mm total length) lake trout caught in gill nets in the year of stocking. This relation was not significant for fish stocked as fingerlings. Mean weight at stocking more than doubled for yearlings and increased by about one-third for fingerlings during this study. The increase in size at stocking may have offset what would otherwise have been a more drastic increase in mortality due to predation.
North American Journal of Fisheries Management↗
Effect of stocking season and technique on survival of lake trout in Lake Ontario
To identify the stocking season and technique that resulted in maximum contribution of hatchery‐reared lake trout Salvelinus namaycush to the population in Lake Ontario, paired lots of yearlings were stocked near shore in March, near shore in May, and offshore by helicopter in May. All mortality associated with stocking season and technique apparently had occurred by age 2. Therefore, survival comparisons were based on combined recoveries of age‐2 and older fish. We found statistically significant differences in survival ratios for 19 of 30 comparisons among individual paired lots, but results were not consistent. For example, among 17 comparisons of lake trout stocked near shore in May and offshore in May, survival was significantly better for fish stocked near shore in four cases and for fish stocked offshore in six cases. With fish stocked near shore in May used as the control group, mean survival ratios (near shore March : near shore May : offshore May) were 0.86:1.00:1.12. However, the 95% confidence interval indicated that the survival ratios were not significantly different from 1:1:1. Variables other than stocking date and technique apparently had a major influence on survival of lake trout following stocking in Lake Ontario. Predation by large salmonids may have been the dominant mechanism affecting survival.
Lake Ontario↗
Diet of juvenile lake trout in southern Lake Ontario in relation to abundance and size of prey fishes, 1979-1987
We examined the diet of juvenile lake trout Salvelinus namaycush (<450 mm, total length) in Lake Ontario during four sampling periods (April–May, June, July–August, and October 1979–1987) in relation to changes in prey fish abundance in the depth zone where we caught the lake trout. Over all years combined, slimy sculpins Cottus cognatus contributed the most (39–52%) by wet weight to the diet, followed by alewives Alosa pseudoharengus (3–38%), rainbow smelt Osmerus mordax (17–43%), and johnny darters Etheostoma nigrum (2–10%). Over 90% of alewives eaten during April–May and June were age 1, and 98% of those eaten during October were age 0 (few alewives were eaten in July–August). Mean lengths of rainbow smelt and slimy sculpins in stomachs increased with size of lake trout. Juvenile lake trout generally fed opportunistically—seasonal and annual changes in diet usually reflected seasonal and annual changes in abundance of prey fishes near bottom where we captured the lake trout. Furthermore, diet within a given season varied with depth of capture of lake trout, and changes with depth in proportions of prey species in lake trout stomachs mirrored changes in proportions of the prey species in trawl catches at the same depth. Alewives (ages 0 and 1) were the only prey fish eaten in substantial quantities by both juvenile lake trout and other salmonines, and thus are a potential focus of competition between these predators.
Transactions of the American Fisheries Society↗
Growth and survival of stocked lake trout with nuclear cataracts in Lake Ontario
Four strains of yearling lake trout Salvelinus namaycush from the 1985 and 1986 year-classes at the Allegheny National Fish Hatchery were evaluated for nuclear cataracts prior to stocking in Lake Ontario in June 1986 and 1987. Lake trout recaptured by bottom trawling from April to August 1987 and 1988 were examined for cataracts. Cataract frequencies in three strains of yearling lake trout at stocking in 1986 and after 14 and 26 months in the lake were: Seneca Lake–35, 24, and 29%; Lake Ontario–32,24, and 42%; and Lake Superior–7,4, and 6%. Cataract frequencies for yearlings at stocking in 1987 and after 2 and 14 months were: Seneca Lake–51, 37, and 51 %; Lake Superior–7,12, and 12%; and Jenny Lake–46,13, and 36%. Cataract frequency was lower ( P < 0.05) at capture in three of the six groups recaptured in 1987 and in two of the six groups in 1988. Fish with cataracts in the 1987 recovery had survival ratios of 17–186% after 2 months in the lake and 48–67% after 14 months, compared with normal-eyed fish of the same strain. Nuclear cataract frequency was relatively stable after the first year of lake residency, when equilibrium was achieved between the increased mortality of cataract phenotypes and the rate of cataract development in normal-eyed phenotypes. Within groups, weight and length were not different between healthy fish and fish with cataracts. The absence of growth depression in fish with cataracts and the reduced survival rate suggested that faster growing fish were more susceptible to cataract formation.
North American Journal of Fisheries Management↗
Sample size requirements and analysis of tag recoveries for paired releases of lake trout
A simple chi-square test can be used to analyze recoveries from a paired-release experiment to determine whether differential survival occurs between two groups of fish. The sample size required for analysis is a function of (1) the proportion of fish stocked, (2) the expected proportion at recovery, (3) the level of significance (∝) at which the null hypothesis is tested, and (4) the power (1 – β) of the statistical test. Detection of a 20% change from a stocking ratio of 50: 50 requires a sample of 172 (∝ = 0.10; 1 – β = 0.80) to 459 (∝ = 0.01; 1 – β = 0.95) fish. Pooling samples from replicate pairs is sometimes an appropriate way to increase statistical precision without increasing numbers stocked or sampling intensity. Summing over time is appropriate if catchability or survival of the two groups of fish does not change relative to each other through time. Twelve pairs of identical groups of yearling lake trout Salvelinus namaycush were marked with coded wire tags and stocked into Lake Ontario. Recoveries of fish at ages 2–8 showed differences of 1–14% from the initial stocking ratios. Mean tag recovery rates were 0.217%, 0.156%, 0.128%, 0.121%, 0.093%, 0.042%, and 0.016% for ages 2–8, respectively. At these rates, stocking 12,100–29,700 fish per group would yield samples of 172–459 fish at ages 2-8 combined.
North American Journal of Fisheries Management↗
Effect of rearing density on poststocking survival of lake trout in Lake Ontario
Six paired lots of yearling lake trout ( Salvelinus namaycush ) reared at densities of 41,000 and 51,000 fish per raceway during their last 9 months in the hatchery were stocked in Lake Ontario. Poststocking survival of the high-density (HD) and low-density (LD) fish was not different for the 1982 year-class. However, for the 1983 year-class, mean survival was significantly different between HD and LD fish ( P < 0.01). Mean survival of HD fish was only 76% that of LD fish ( P < 0.01), and most of the mortality attributable to rearing conditions had apparently occurred within 2 months after stocking. Mean size at stocking was not different for HD and LD fish of the 1982 year-class, but for the 1983 year-class, the LD fish were 6% longer and 22% heavier than the HD fish. Mean lengths and weights of LD and HD fish were not different in samples collected in Lake Ontario at age 2 and older. Size at stocking was not likely the factor that caused the difference in survival. Rather, the rearing conditions (probably water exchange rate in relation to number of fish in the raceway) that resulted in slower growth of the HD fish of the 1983 year-class also caused them to be poorer physiologically than the LD fish. The number of yearling lake trout per rearing unit that will result in maximum contribution to populations in the Great Lakes after stocking may be lower than the rearing densities customarily used at some hatcheries.
Progressive Fish-Culturist↗
Comparison of hatchery-reared lake trout stocked as fall fingerlings and as spring yearlings in Lake Ontario
We made 16 paired releases of lake trout Salvelinus namaycush of four year classes (1979–1982) at five locations to compare survival and growth of hatchery-reared fish stocked as fall fingerlings (FF) and as spring yearlings (SY). Comparisons were based on fish at ages 2–8 recovered with bottom trawls, with gill nets, and from anglers' catches. Mean lengths and weights were greater for SY than for FF at all ages, and SY attained sexual maturity at an earlier age than FF. The survival of FF may have been affected by average size at stocking and by the severity of the weather during the first winter after stocking. Survival ratios of SY to FF lake trout from stocking to age 2 ranged from 1.32:1 to 6.80:1, and a ratio of 2.41:1 was considered to be typical. Stocking cost per 1,000 fish was US$21.76 for FF and $35.45 for SY. Under the most cost-effective hatchery regime for producing lake trout (the maximum number of SY plus some FF to fully utilize hatchery space and personnel year round), rearing cost per 1,000 fish was estimated to be $235.41 for SY and $38.75 for FF.
North American Journal of Fisheries Management↗
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.
Journal of Great Lakes Research↗
Dispersal of three strains of hatchery-reared lake trout in Lake Ontario
Rates of dispersal and resultant geographical distributions were determined for three strains of hatchery-reared lake trout ( Salvelinus namaycush ) stocked at six sites in U.S. waters of Lake Ontario. The strains were Lake Superior (SUP); Clearwater Lake, Manitoba (CWL); and Seneca Lake, New York (SEN). The fish were recovered with bottom trawls fished during July and August 1980–1985 at 16 locations, extending from Toronto southward and eastward along the south shore to Dablon Point at the east end of the lake. For SUP fish stocked as spring yearlings, the mean distances from stocking site to capture location 2, 14, and 26 months after stocking were 12, 57, and 62 km, respectively, for fish released at four south-shore sites and 5, 34, and 38 km for fish released at two eastern outlet basin sites. Rates of dispersal for the CWL fish were similar to those of the SUP strain for fish stocked at the four south-shore sites, but were considerably less for fish stocked in the eastern outlet basin. The SEN strain was stocked only in the eastern outlet basin; their dispersal was similar to that of the SUP strain. For fish of the same age, SUP fish stocked as fall fingerlings became more widely dispersed than those stocked as spring yearlings. Movement of lake trout between the eastern outlet basin and the lake proper was limited. Large numbers of fish were captured on the Niagara Bar, but few moved past there into the west end of the lake. Movements of lake trout from stocking sites were generally with the prevailing currents. Differences between geographical distributions of the SUP and CWL strains were probably due to the influence of different current regimes at the depths they occupied. These results will be useful in selecting the best genetic strains of lake trout for rehabilitating the species in Lake Ontario, as well as for identifying the best stocking sizes and maximizing post-stocking survival of hatchery-reared fish.
Journal of Great Lakes Research↗
Evaluation of coded wire tags for marking lake trout
Among hatchery-reared lake trout ( Salvelinus namaycush ) of the 1979-1982 year classes stocked in New York waters of Lake Ontario, more than 3 million fish were marked with a coded wire tag (CWT) plus an adipose fin clip, and 1.5 million with only conventional fin clips. Altogether, 7,640 tags were recovered from fish collected with bottom trawls and gill nets or caught by anglers during 1980-1983. One person was able to extract and decipher 200 or more CWTs per day with about a 1% error rate in reading and recording codes. Presence of the CWT did not affect growth. The adipose fin clip did not regenerate. The occurrence of fish with an adipose fin clip but no CWT resulted primarily from the regeneration of paired fins among fish marked with a combination of the adipose fin and a paired fin. Loss of CWTs between marking and stocking (generally 4-5 months for fish stocked in spring and 1-8 d for fish stocked in fall) declined from nearly 11% for the 1979 year class stocked as fall fingerlings to less than 3% for the 1981 and 1982 year classes - a difference that primarily reflected improvements in instrumentation and tagging technique. The rate of CWT loss after the marked fish were stocked was probably less than 1% per year. The CWT is a reliable method for marking hatchery-reared lake trout. A large number of experimental groups can be uniquely marked, and fish from each group can be accurately identified throughout their life. Use of this technique should greatly facilitate evaluations of genetic strain, hatchery experience, condition at time of stocking, season of stocking, size at stocking, method of stocking and other factors that affect poststocking survival and performance of lake trout stocked in the Great Lakes.
North American Journal of Fisheries Management↗
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.
Journal of Great Lakes Research↗