Effectiveness of lake trout (Salvelinus namaycush) suppression in Lake Pend Oreille,Idaho: 2006–2016

The nonnative lake trout (Salvelinus namaycush Walbaum, 1792) population in Lake Pend Oreille, Idaho increased exponentially during 1999–2006. This led to an unsustainable level of predation mortality on kokanee (Oncorhynchus nerka Walbaum, 1792), increased the conservation threat to native bull trout (Salvelinus confluentus Suckley, 1859), and jeopardized the popular recreational fishery for kokanee and rainbow trout (Oncorhynchus mykiss Walbaum, 1792). In response, lake trout were suppressed since 2006 using incentivized angling, gill netting, and trap netting. From 2006 through 2016, 193,982 lake trout were removed (50% by gill netting; 44% by angling; 6% by trap netting). During this period, age-8 + (adult) lake trout abundance declined by 64%, age-3 (recruit) abundance declined by 56%, and mean total annual mortality (A) was 31.1%. Lake trout did not show evidence of a density-dependent response. Kokanee did not collapse and rebounded to abundances not observed since before lake trout expansion. Bull trout abundance declined during suppression, but the population was sustained. Lake trout suppression allowed a harvest fishery for kokanee and trophy fishery for rainbow trout to be restored. We conclude that suppression can be an effective management action for mitigating effects of nonnative lake trout in a large, deep lake.

     

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.     

Genetic signatures of historical bottlenecks in sympatric lake trout (Salvelinus namaycush) morphotypes in Lake Superior

Humans have played a significant role in reducing levels of genetic diversity and differentiation of many teleost fishes, leading to homogenization across biological entities. We compare patterns of historical and contemporary genetic structure for three sympatric Great Lake??s lake trout (Salvelinus namaycush) morphs (lean, siscowet, and humper) that differ in patterns of habitat occupancy, susceptibility to overfishing and predation by invasive sea lamprey (Petromyzon marinus). Differential susceptibilities to overfishing and predation were expected to result in different impacts to levels of genetic diversity loss for each morphotype. Genetic data was collected for samples at three points in time: 1948 (pre-collapse), 1959 (collapse) and 1990s (current), corresponding to periods of intensive fishing, mortality due to lamprey and recovery, respectively. The lean morph preferentially targeted by the fishery and recognized as highly preyed upon by sea lamprey was more highly impacted genetically than other morphs, as evidenced by greater loss of genetic diversity first during the period of overfishing, then during the period of high sea lamprey abundance once the fishery collapsed. The siscowet morph also experienced genetic bottlenecks during the period of overfishing (pre-collapse period). Results indicate significant levels of genetic differentiation among morphs historically prior to declines in abundance and also among contemporary populations, suggesting that periods of population decline and resurgence in abundance and distribution did not result in loss of genetic distinctiveness among morphs.     

Anadromy and marine habitat use of Lake trout (Salvelinus namaycush) from the central Canadian Arctic

Anadromy was documented in 16 lake trout, Salvelinus namaycush, from Canada's central Arctic using capture data and otolith microchemistry. For the first time, estuarine/marine habitat use was described for five individuals using acoustic telemetry. Age-at-first-migration to sea was variable (10–39 years) among individuals and most S. namaycush undertook multiple anadromous migrations within their lifetime. Telemetry data suggested that S. namaycush do not travel far into marine habitats and prefer surface waters (<2 m). These results further our collective understanding of the marine ecology of Arctic S. namaycush.     

Twelve microsatellite loci for lake trout (Salvelinus namaycush)

We describe 12 microsatellite loci isolated from lake trout (Salvelinus namaycush). The number of alleles at these loci ranged from two to 11 with an average of 5.3 alleles per locus. The expected heterozygosity ranged from 0.29 to 0.76, with an average of 0.68. Accidental (or illegal) introductions of lake trout into watersheds are decimating native trout populations in the northern Rocky Mountains, and these loci will be useful for identifying the source of these introductions and for estimating the number of founding individuals.     

The fine structure of the trout blastoderm, Salvelinus fontinalis (Mitchill)

The Speckled Trout blastoderm at the late high blastula stage is characterized by two different cell populations. The “light” blastomeres comprise one cell type while the “dark” and “medium” blastomeres appear to differ from one another only in degree and thus may be considered as the second type. “Dark” and “medium” blastomeres are irregular in shape, are located centrally and deep in the blastoderm, have an abundance of smooth endoplasmic reticulum with associated 520 Å glycogen particles and a single mitochondrial profile. The “light” blastomeres have randomly arranged glycogen particles in minimal quantities in contrast to the “medium” and “dark” blastomeres and in addition exhibit three mitochondrial profiles, which could however represent artifacts. It is postulated that in the Speckled Trout cellular differentiation has commenced by the third day of incubation at 10°C and that this is manifested visually by the appearance of two different cell populations; the more differentiated “dark” and “medium” blastomeres possibly destined to give rise to the hypoblast and the less differentiated “light” blastomeres.     

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.     

Helminths in an intensively stocked population of lake trout, Salvelinus namaycush, from Lake Huron

Eighty stocked lake trout Salvelinus namaycush (Salmonidae), collected from 2 locations in Lake Huron in May 1995, were examined for parasites. The parasite fauna of this top predator in Lake Huron was characterized by only 6 helminth species. Echinorhynchus salmonis infected all lake trout with a mean intensity of 163.9. The intensity of this acanthocephalan species significantly increased with host length and weight. Eubothrium salvelini infected 78 lake trout with a maximum number of 81 scoleces counted. Diplostomum sp., Cyathocephalus truncatus, Capillaria salvelini, and Neoechinorhynchus sp. infrequently infected lake trout. The low parasite species richness in these lake trout is believed to be due to their large size at stocking and to the loss of historical enzootic host-parasite relationships that followed the absence of this fish species in Lake Huron for 26 yr.     

Parasites of juvenile brook trout (Salvelinus fontinalis) from Hunt Creek, Michigan

Four parasite species (Crepidostomum cooperi, Cystidicoloides ephemeridarum, Acanthocephalus dirus, Salmincola edwardsii) infected 215 juvenile brook trout (105 young-of-year; 110, 1-yr-old) from Hunt Creek, Michigan, in 2003, 2004, and 2005. Prevalences of these species in 2004 (main study year) varied from 29 to 37%. Crepidostomnum cooperi had the highest mean intensity and mean abundance, followed by C. ephemeridarum. The number of fish infected with each parasite species was significantly higher in 1-yr-old fish than in young-of-year fish. Also, the mean intensities and mean abundances of C. cooperi and C. ephemeridarum and the mean abundance of A. dirus were significantly higher in older fish. The mean intensity of C. cooperi and prevalence of A. dirus were significantly higher in fish between creek sections. Fish length had a significant positive effect on the abundances of C. cooperi and C. ephemeridarum; parasite species richness, on the abundances of A. dirus and S. edwardsii; and parasite species richness in the 2003 and 2004 trout cohorts, respectively. Crepidostomum cooperi, C. ephemeridarum, A. dirus, and S. edwardsii commonly infect Michigan brook trout. The small number of parasite species infecting Hunt Creek brook trout is similar to the number of parasite species of brook trout from other Michigan creeks.     

Identification of sex chromosomes in lake trout (Salvelinus namaycush)

In the male trout there is a difference in the quinacrine banding and C-banding patterns between the two homologs of the second largest chromosome pair. This chromosome is the only large submetacentric in the karyotype, making it easy to identify and suggesting that the sex chromosomes have become differentiated since the time of tetraploidization. In males one homolog has a medium-to-large quinacrine bright heterochromatic band on the end of the short arm, while the other lacks it completely. In females both homologs have medium-to-large quinacrine bright heterochromatic bands. Approximately half the progeny from every lake trout cross studied and half the eggs from every lake trout population examined were heteromorphic for a difference in this chromosome band. Results from sexed fish, reciprocal F1 hybrids between brook trout and lake trout, and gynogenetic haploids are all consistent with the interpretation that chromosome 2 is the sex chromosome. These results suggest that the addition of heterochromatin to the X can be the first step in the inhibition of crossing over between the X and Y chromosomes required for sex chromosome differentiation.     

Cells, proteins, and certain physical-chemical properties of brook trout (Salvelinus fontinalis) blood

Laboratory brook trout were used to evaluate, refine, or develop biochemical procedures for the analysis of fish blood. Analytical values were obtained for the following blood properties: total and differential leucocytes and erythrocytes; erythrocyte and plasma proteins (by electrophoresis); plasma refractive index; erythrocyte sedimentation rate; erythrocyte osmotic fragility; blood surface tension and density; haemoglobin; and packed cell volume. These blood factors are discussed with reference to fish health and disease and to changes caused by deleterious quantities of water pollutants.     

Long-term suppression of the Lake Trout (Salvelinus namaycush) population in Lake Pend Oreille,Idaho

Hydrobiologia - A simulation model of lake trout Salvelinus namaycush (Walbaum 1792) population dynamics in Lake Pend Oreille, Idaho, was used to estimate (1) the optimal allocation of effort among...     

Autosomal localization of interstitial telomeric sites (ITS) in brook trout, Salvelinus fontinalis (Pisces, Salmonidae)

Cytogenetic analysis of brook trout performed with molecular and conventional methods led to identification of interstitial telomeric sites on one or two subtelocentric chromosomes within the same pair. Morphology and specific patterns of these chromosomes using fluorochromes associated with A/T- or G/C-rich DNA proved that these chromosomes are not sex related. The chromomycin-positive region was located on the short arms of the ITS bearing chromosome pair and flanked by telomeric sequences, suggesting that this part of the chromosome had been translocated from another one. Our observations confirm that GC-rich regions are highly mobile genetic structures, and led to ITS formation on brook trout chromosomes.     

Breeding success of male brook trout (Salvelinus fontinalis) in the wild

Competition for females generally results in some males adopting alternative reproductive tactics to acquire matings. For fish, the ecological and evolutionary consequences of these tactics are not well understood because of an inability to link directly the interactions of individuals on the breeding grounds with genetic data. This study combines behavioural observations with genetic estimates of male reproductive success within an intensively studied wild population of lacustrine brook trout (Salvelinus fontinalis). Male brook trout exhibit a conditional reproductive strategy with small males adopting a peripheral position to that of larger dominant males in their proximity to spawning females. Parentage analysis of eggs collected from wild redds confirmed the reproductive success of individual males. Males relegated to peripheral positions during spawning participated frequently in spawning events, but in most cases the first male to spawn was the sole contributor, and no more than two males contributed successfully to a single brood. While behavioural observations of salmonines suggests that reproduction is partitioned among males in a manner dependent upon body size and proximity to spawning females, the genetic evidence from this study suggests a more limited distribution of reproductive success in the field. The genetic contributions of male brook trout are highly skewed towards larger males for this population. A review of the salmonine literature suggests little difference in individual reproductive success for males exhibiting size-related tactics within a conditional mating strategy vs. precocial maturation. Collectively, these genetic studies provide new insights on the evolution of alternative life histories among salmonines.