The response of burbot (Lota lota) to change in lake trout (Salvelinus namaycush) abundance in Lake Opeongo,Ontario

The purpose of this study was to test the hypothesis that the burbot and lake trout compete with or prey on each other, and that a change in the abundance of lake trout has triggered a response in the burbot population. Burbot growth, length-weight relationship and population size did not change, and it appears that at these population levels, the changes in lake trout abundance had no detectable effect on burbot. It is suggested that the burbot population in Lake Opeongo is limited at the larval stage by competition with, or predation by, a planktivore, the lake herring.     

Molecular characterization of myxozoan parasites from Lake Sasajewun, Algonquin Park, Ontario, by riboprinting

The small subunit-rRNA genes of 18 myxozoans from Lake Sasajewun, Algonquin Park were amplified and digested with restriction endonucleases for riboprinting analysis. Identical riboprints were not found between the myxosporeans and the actinosporeans. The distinct riboprinting patterns observed among these myxozoans indicate considerable genetic diversity within this group. Identical riboprints were found between Myxobolus pendula and Myxobolus pellicides, and between triactinomyxon 'C' and Triactinomyxon ignotum. Parsimony analysis of the riboprints demonstrated that neither the myxosporeans nor the actinosporeans formed a monophyletic group. Some species of Myxobolus are more closely related to forms of triactinomyxon, echinactinomyxon or raabeia than to other Myxobolus species. These results are consistent with the two-host life cycle hypothesis of myxozoans that myxosporeans and actinosporeans are alternating stages of the same organisms.     

The longevity of actinosporean spores from oligochaetes of Lake Sasajewun, Algonquin Park, Ontario, and their reaction to fish mucus

The longevity of 7 forms of actinosporean spores and the reaction of 6 forms of actinosporeans to fish mucus were investigated. The maximum longevity of actinosporean spores kept at ambient laboratory temperatures was 14 days. Spore longevity ranged from 11 to 14 days among actinosporeans. The reaction of spores to fish mucus varied among the actinosporeans. Triactinomyxon F of Xiao and Desser, 1998 reacted only to the mucus of the common shiner Luxilus cornutus, and golden shiner Notemigonus crysoleucas, whereas the aurantiactinomyxon form of Xiao and Desser, 1998, and raabeia B of Xiao and Desser, 1998 reacted readily to mucus of all fish species tested. The differences in reaction to fish mucus among actinosporeans may indicate their different host range. These results indicate that actinosporean spores are short-lived and that actinosporeans respond to their hosts by chemodetection.     

Implications of testicular constrictions on spermatogenesis in Lake Ontario lake trout, Salvelinus namaycush

This study examines the histological significance of a testicular anomaly among hatcheryraised lake trout, Salvelinus namaycush , introduced into Lake Ontario as yearlings and subsequently recaptured at ages ranging from 4 to 7 years. The anomaly has been termed a constriction. Histological examination revealed that lake trout with constricted testes demonstrated delayed cycles of spermatogenesis throughout the testes at spawning time compared with normal testes. Constrictions were formed when spermatogonia within an adjacent group of lobules failed to undergo mitosis, hypertrophied and were subsequently resorbed. The walls of these lobules subsequently collapsed and were resorbed and replaced by dense fibrous connective tissue. The significance of these observations in relation to hormonal mechanisms and its potential effect upon reproduction in these fish is discussed.     

Descriptions and phylogenetic systematics of Myxobolus spp. from cyprinids in Algonquin Park, Ontario

Eight species of Myxobolus were collected from four species of cyprinids in Algonquin Park, Ontario. On the basis of spore morphology, five of these species are described as new and two are redescribed. The evolutionary relationships among these eight species were studied using partial small subunit ribosomal DNA (ssu-rDNA) sequence data. The resulting cladograms, which were highly resolved and with strongly supported relationships, allowed for the evaluation of spore morphology, host specificity, and tissue tropism, criteria traditionally used in species identification. These criteria, recently criticized for creating artificial rather than natural taxonomic groupings, were evaluated for their reliability in the systematics of the species examined. The data showed that distantly related species often infect the same host and tissue, and that closely related species often occur in different hosts. Morphologically similar species are more closely related to each other and the taxonomy based on spore morphology is consistent with the relationships depicted in the phylogenies. These results suggest that spore morphology is better than host specificity and tissue tropism as a species character, as well as for determining evolutionary relationships among the species of Myxobolus examined.     

The use of angler diary surveys to evaluate long-term changes in muskellunge populations on Lake of the Woods, Ontario

Reported improvements in the muskellunge angling fishery on Lake of the Woods, Ontario over the last two decades have paralleled an increase in the practice of catch and release angling, and an increase in minimum size regulations for this species. The overall status of muskellunge populations in this large, complex lake has proven difficult to monitor using standard assessment methods. A volunteer muskellunge angler diary program, established in 1988, has provided a cost effective method of gathering a large amount of information with which to track this fishery and associated populations. Results from angling diaries indicated increased angling effort, catch and success rates for muskellunge on Lake of the Woods since the early 1990s. Although the month of July accounted for the majority of angling effort and catch, angling success rates and sizes of fish reported in diaries improved monthly into the late fall. Angling success rates were consistently higher in angling diaries than from creel surveys, but both survey types showed similar long-term trends in the fishery. Angler diary data, incorporating both the numbers of fish caught and/or seen by anglers, were used to calculate catch equality indices which proved to be sensitive to changes in population abundance. Increased minimum length regulations for muskellunge during 1987–2001 have been largely responsible for a decline in harvest rates from an estimated 36% in 1986 to 0% since 1999. Although higher size limits have yet to produce more quality-sized fish in angler catches, diary survey data, supported by recent improvements in catch rates from assessment gill nets, would indicate that muskellunge recruitment has increased. This article concludes with a brief review of how muskellunge angler diary data has been used in the past, including recommendations to minimize biases associated with this survey method.     

Lower fitness of hatchery and hybrid rainbow trout compared to naturalized populations in Lake Superior tributaries

We have documented an early life survival advantage by naturalized populations of anadromous rainbow trout Oncorhynchus mykiss over a more recently introduced hatchery population and outbreeding depression resulting from interbreeding between the two strains. We tested the hypothesis that offspring of naturalized and hatchery trout, and reciprocal hybrid crosses, survive equally from fry to age 1+ in isolated reaches of Lake Superior tributary streams in Minnesota. Over the first summer, offspring of naturalized females had significantly greater survival than offspring of hatchery females in three of four comparisons (two streams and 2 years of stocking). Having an entire naturalized genome, not just a naturalized mother, was important for survival over the first winter. Naturalized offspring outperformed all others in survival to age 1+ and hybrids had reduced, but intermediate, survival relative to the two pure crosses. Averaging over years and streams, survival relative to naturalized offspring was 0.59 for hybrids with naturalized females, 0.37 for the reciprocal hybrids, and 0.21 for hatchery offspring. Our results indicate that naturalized rainbow trout are better adapted to the conditions of Minnesota's tributaries to Lake Superior so that they outperform the hatchery-propagated strain in the same manner that many native populations of salmonids outperform hatchery or transplanted fish. Continued stocking of the hatchery fish may conflict with a management goal of sustaining the naturalized populations.     

Distribution and onshore migration behaviour of burbot larvae in Lake Constance, Germany

Larval abundance of burbot Lota lota in the pelagic zone of Lake Constance, Germany, peaked during April and remained at a constant but lower level until mid‐June. From the end of May onwards a significant diel vertical migration pattern was observed: while burbot larvae were distributed above as well as below the thermocline in the daytime with the highest percentages of abundance at water depths of 30 and 50 m (below the thermocline) on 5 and 25 June, they were concentrated from 2 to 15 m (above the thermocline) during the night. This migration pattern coincided with a significant decline in the food items preferred by burbot at this life stage, cyclopoid copepods. This phase of diel vertical migration lasted for c . 4 weeks until the burbot larvae suddenly disappeared from the pelagic zone. This indicated a short phase, lasting only a few days, of larval settlement into profundal benthic habitats. This was supported by a significant, abrupt decrease in the absolute growth rates of the larvae at day 56 after hatching. The day–night pattern of vertical migration observed could be assumed to be a transition phase from a pelagic to a benthic lifestyle, as reported for juveniles of several other, marine gadoid species.     

Lake sturgeon population characteristics in Rainy Lake, Minnesota and Ontario

Rainy Lake contains a native population of lake sturgeon Acipenser fulvescens that has been largely unstudied. The aims of this study were to document the population characteristics of lake sturgeon in Rainy Lake and to relate environmental factors to year‐class strength for this population. Gill‐netting efforts throughout the study resulted in the capture of 322 lake sturgeon, including 50 recaptures. Lake sturgeon in Rainy Lake was relatively plump and fast growing compared with a 32‐population summary. Population samples were dominated by lake sturgeon between 110 and 150 cm total length. Age–structure analysis of the samples indicated few younger (<10 years) lake sturgeon, but the smallest gill net mesh size used for sampling was 102 mm (bar measure) and would not retain small sturgeon. Few lake sturgeon older than age 50 years were captured, and maximum age of sampled fish was 59 years. Few correlations existed between lake sturgeon year‐class indices and both annual and monthly climate variables, except that mean June air temperature was positively correlated with year‐class strength. Analysis of Rainy Lake water elevation and resulting lake sturgeon year‐class strength indices across years yielded consistent but weak negative correlations between late April and early June, when spawning of lake sturgeon occurs. The baseline data collected in this study should allow Rainy Lake biologists to establish more specific research questions in the future.     

Eutrophication of Lake Hayq in the Ethiopian Highlands

Lake Hayq was previously described as having exceptionally clearwater and very low phytoplankton biomass. It is now very different,with a shallow euphotic depth and abundant phytoplankton. Zooplanktonpopulations have changed as well; Daphnia and Diaphanosoma wererecorded before, whereas we found no Cladocera. Among the possiblecauses for this change in trophic status is the introductionof the planktivorous fish Oreochromis niloticus.     

Quantification of virus genes provides evidence for seed-bank populations of phycodnaviruses in Lake Ontario,Canada

Using quantitative PCR, the abundances of six phytoplankton viruses DNA polymerase (polB) gene fragments were estimated in water samples collected from Lake Ontario, Canada over 26 months. Four of the polB fragments were most related to marine prasinoviruses, while the other two were most closely related to cultivated chloroviruses. Two Prasinovirus-related genes reached peak abundances of >1000 copies ml⁻¹ and were considered ‘high abundance'', whereas the other two Prasinovirus-related genes peaked at abundances <1000 copies ml⁻¹ and were considered ‘low abundance''. Of the genes related to chloroviruses, one peaked at ca 1600 copies ml⁻¹, whereas the other reached only ca 300 copies ml⁻¹. Despite these differences in peak abundance, the abundances of all genes monitored were lowest during the late fall, winter and early spring; during these months the high abundance genes persisted at 100–1000 copies ml⁻¹ while the low abundance Prasinovirus- and Chlorovirus-related genes persisted at fewer than ca 100 copies ml⁻¹. Clone libraries of psbA genes from Lake Ontario revealed numerous Chlorella-like algae and two prasinophytes demonstrating the presence of candidate hosts for all types of viruses monitored. Our results corroborate recent metagenomic analyses that suggest that aquatic virus communities are composed of only a few abundant populations and many low abundance populations. Thus, we speculate that an ecologically important characteristic of phycodnavirus communities is seed-bank populations with members that can become numerically dominant when their host abundances reach appropriate levels.     

Behavior, movements, and demographics of rabid raccoons in Ontario, Canada: management implications

During 1999-2003, 127 cases of raccoon variant rabies were reported in raccoons (Procyon lotor) and striped skunks (Mephitis mephitis) in Ontario, Canada. Raccoons accounted for 98% (125/127) of the reported cases with behaviors/conditions including aggression, fighting with dogs, ataxia, vocalizations, appearance of being sick, and the presence of porcupine (Erethizon dorsatum) quills. Seventy-eight percent of the rabid raccoons were adults. Juveniles were underrepresented (22%) compared with the adult/juvenile ratios found in nonrabid Ontario raccoon populations. Of the known aged raccoons, 83% were < or = 3 yr of age, and 22% of the rabid adult female raccoons had evidence of having had a litter during the year in which they were found to be rabid. The majority of rabid raccoons were reported during the fall, winter, and spring, suggesting a relationship between raccoon behavioral activities such as denning and breeding and the timing of rabies outbreaks. Multiple cases of raccoon rabies occurred at several barns, suggesting that those structures serve as focal points of rabies transmission as a result of denning activities. Movements of five rabid raccoons (range 1,564-4,143 m) were not different from movements of nonrabid raccoons in Ontario. Sixty-six percent of the rabid animals were submitted by government staff, stressing the importance of those agencies in rabies control and surveillance operations. Increased knowledge of the behaviors of rabid raccoons should assist in the development of management strategies for rabies.     

Distribution of Phoxinus eos,Phoxinus neogaeus,and Their Asexually-Reproducing Hybrids (Pisces: Cyprinidae) in Algonquin Provincial Park,Ontario

Hybrid Phoxinus are one of the few asexually reproducing vertebrates species. The distribution of hybrid Phoxinus among lakes in Algonquin Park, Ontario, was evaluated relative to the distribution of parental species and relative to physiochemical lake characteristics. No association between the distribution of hybrids and the distribution of parental species was found, suggesting that the hybrids can successfully coexist with either parental species. In addition, we found no association between hybrid distribution and the physiochemical characteristics of lakes, suggesting that the hybrids are generalists with respect to the ecological niches available in Algonquin Park. There was a difference between the physiochemical characteristics of lakes with and without the parental species P. neogaeus. The lakes containing P. neogaeus were lower elevation than the lakes containing the other parental species, P. eos. The difference in distribution between the parental species may therefore be due to different dispersal abilities, to later arrival following post-glacial dispersal, or to differences in ecology. These results suggest that asexual reproduction is a successful strategy for hybrid Phoxinus in Algonquin Park because these sperm-dependent asexual hybrids are able to survive and persist regardless of which parental species is present, and regardless of the physiochemical characteristics of their habitat.     

Evolution and diversity of two cisco forms in an outlet of glacial Lake Algonquin

The diversity of Laurentian Great Lakes ciscoes (Coregonus artedi, sensu lato) arose via repeated local adaptive divergence including deepwater ciscoes that are now extirpated or threatened. The nigripinnis form, or Blackfin Cisco, is extirpated from the Great Lakes and remains only in Lake Nipigon. Putative nigripinnis populations were recently discovered in sympatry with artedi in a historical drainage system of glacial Lake Algonquin, the precursor of lakes Michigan and Huron. Given the apparent convergence on Great Lakes form, we labeled this form blackfin. Here, we test the hypothesis that nigripinnis may have colonized this area from the Great Lakes as a distinct lineage. It would then represent a relict occurrence of the historical diversity of Great Lakes ciscoes. Alternatively, blackfin could have evolved in situ in several lakes. We captured more than 600 individuals in the benthic or pelagic habitat in 14 lakes in or near Algonquin Provincial Park (Ontario, Canada). Fish were compared based on habitat, morphology, and genetic variation at 6,676 SNPs. Contrary to our expectations, both cisco and blackfin belonged to an Atlantic lineage that colonized the area from the east, not from the Great Lakes. Sympatric cisco and blackfin were closely related while fish from different lakes were genetically differentiated, strongly suggesting the repeated in situ origin of each form. Across lakes, there was a continuum of ecological, morphological, and genetic differentiation that could be associated with alternative resources and lake characteristics. This study uncovers a new component of cisco diversity in inland lakes of Canada that evolved independently from ciscoes of the Laurentian Great lakes. The diversity of cisco revealed in this study and across their Canadian range presents a challenge for designating conservation units at the intraspecific level within the framework of the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).     

The natural regulation of numbers and growth in contrasting populations of brown trout, Salmo trutta, in two Lake District streams

SUMMARY. 1. This short review summarizes a long-term investigation of brown trout in two populations that probably represent opposite extremes of life histories in this polymorphic species; Bhick Brows Beck serves as a nursery for the progeny of migratory trout (mixture of sea and estuarine trout) and Wilfin Beck is populated by resident trout. 2. Population density in Black Brows Beck was always much higher than that in Wilfin Beck, and was regulated by density-dependent survival in the early stages of the life cycle. There was no evidence for similar density-dependent regulation in Wilfin Beck; simple proportionate survival occurred with fairly constant loss-rates. Survival was reduced in both populations by summer droughts and also by spates in Wilfin Beck. 3. Black Brows trout were always larger than Wilfin Beck trout of similar age; fry size at the start of the growth period was chiefly responsible for these differences. Variations in water temperature were chiefly responsible for differences in growth rates between year-classes within each population. Food intake was not a limiting factor, except in the first winter of the life cycle and for adults over 3 years old in Wilfin Beck. Variation in individual size was inversely density-dependent in Black Brows Beck and decreased with age in Wilfin Beck, these changes being due to natural (stabilizing) selection. 4. There is strong evidence for genotypic differences between the populations. The implications of this are discussed, especially the need to conserve different populations that may contain unique genetic material, and the importance of restocking with fish reared from the indigenous population that should always contain the optimum genotypes for a particular habitat. Restocking with juveniles should be done with caution because it could lead to a decrease in both numbers and size variation when the population is regulated by density-dependent mechanisms. 5. One major objective of future work should be the development and improvement of mathematical models that can be used to predict the optimum density for trout in different populations, the maximum attainable growth rate in different habitats, and the effects on trout populations of environmental changes due to natural causes (e.g. droughts and spates) or human activities.     

Environmental factors affecting the distribution and abundance of cyst-forming Myxobolus spp. and their cyprinid hosts in 3 lakes in Algonquin Park,Ontario

In 1999, 4 species of cyprinid were surveyed for myxozoan parasites in a watershed in Algonquin Park, Canada, Kathlyn Lake. Broadwing Lake, and Lake Sasajewun were included. Eight species of Myxobolus were found that differed in their prevalence and distribution among the 3 lakes. The oligochaetes and environmental parameters, including sediment types and aquatic plants, of these 3 lakes were surveyed the following year. Oligochaetes belonging to 17 species were collected from the 3 lakes. The distribution patterns of the oligochaete fauna, with respect to the environmental variables, were examined using canonical correspondence analysis. Naidids were predominant in all 3 lakes, particularly in the pebbly and sandy sediment of Lake Sasajewun. The highest percentage of tubificids occurred in the detritus and muddy substrate of Broadwing Lake. These findings indicate that the prevalence of certain oligochaetes is congruent with the absence or presence of particular myxozoan species and that substrates and aquatic plants influence the distribution of certain oligochaete species.     

Brown trout spawning habitat selection preferences and redd characteristics in the Credit River, Ontario

Brown trout Salmo trutta redds in the Credit River, Ontario, were enumerated and assessed for physical, location and cover feature characteristics during the 2002 spawning season. Hydraulic habitats were classified on the basis of channel morphology and availability recorded. Combined use and availability data were used to assess habitat selection preferences and test for significant differences. Significant preferences for upstream pool and riffle habitat were found, but all available habitat types were used to some degree. Non‐preferred habitat redds were significantly larger than those located in preferred habitats and more likely to be found in association with woody debris cover. Larger redds were interpreted as indicative of larger fish. The use of non‐preferred downstream habitats by larger fish was further interpreted in the context of overwinter habitat requirements to reflect possible trade‐offs between reproductive and adult over‐winter survival requirements resulting in the selection of habitat for multiple life‐history functions. Results suggest that redd density alone should not be used to infer critical autumn habitat requirements for brown trout.