Julian Dodson - Academia.edu (original) (raw)
Papers by Julian Dodson
We develop the view, based on life cycle differences and recently published sister group relation... more We develop the view, based on life cycle differences and recently published sister group relationships, that the freshwater life cycle was the ancestral character state leading to anadromy among salmoniforms, whereas the marine life cycle was the ancestral character state leading to anadromy among osmeriforms. In contrast to most salmonid fishes, the reproductive migrations of smelts are generally characterized by brief excursions to spawn in freshwater, and larvae may spend no more than 24 h in freshwater before being transported to coastal marine or estuarine environments. We reconstructed the phylogeny of the suborder Osmeroidei to establish the phylogenetic relationships among anadromous, marine, and freshwater species of this taxon. We mapped these life cycles onto phylogenetic trees of osmeriforms and salmoniforms and applied character-reconstruction methodology based on simple parsimony and likelihood methodologies. A freshwater origin of salmonids was supported by our analyses, whereas either marine or anadromous life cycles characterized the evolution of osmeroids. The possibility that the evolution of anadromy in salmonids and osmeroids followed separate paths requires a reconsideration of some generalizations concerning anadromy. We hypothesize that anadromy in osmeroids may be first and foremost an adaptation to place embryos and the early larval stages in reproductive safe sites to maximize their survival. The evolution of exclusive freshwater species of osmeriforms has occurred via anadromy through the various processes associated with landlocking. Freshwater amphidromy in osmeroids is most likely a consequence of anadromy rather than a precursor and may be contingent upon the availability of food resources in freshwater. Finally, marine osmeroids have been derived from anadromous ancestors and are "safe-site" specialists, exploiting principally the upper intertidal zone for reproduction. We also suggest that such contrasting evolutionary pathways to anadromy may provide insight into the evolution of partial migration, observed uniquely in salmonids, and the nature and extent of population genetic structure found in the two groups of fishes.
Journal of Fish Biology, Oct 1, 2007
The hypothesis that a part of the yellow American eel Anguilla rostrata sub-population of the St ... more The hypothesis that a part of the yellow American eel Anguilla rostrata sub-population of the St Jean River in eastern Quebec feeds in the brackish environment during summer and returns to the river to overwinter was tested. Three years of microtagging and the acoustic tagging and tracking of 40 American eels demonstrated that a part of the downstream migrants exploited the estuary as a summer feeding area. Upstream movement of some microtagged American eels provided support for the hypothesis that a part of those American eels returned to the river to overwinter. In addition to the demonstration of amphidromous behaviour of yellow eels, the study revealed that American eels in the estuary were active at night but homed to specific daytime resting sites.
Environmental Biology of Fishes, Dec 1, 1989
Recent sampling programs conducted in the estuaries of the Eastmain and La Grande rivers (James B... more Recent sampling programs conducted in the estuaries of the Eastmain and La Grande rivers (James Bay) and the Great Whale, Little Whale, Innuksuac and Povungnituk rivers (Hudson Bay) revealed patterns of coregonine fish distribution that differ from previous observations. The relative abundance of cisco, Coregonus artedii, and lake whitefish, C. clupeaformis, varied among rivers but did not reveal a latitudinal
disruption of dominance hierarchies by a non-native species:
PLOS ONE, 2015
<p>Each individual is represented by a thin vertical line, which is partitioned into <i&... more <p>Each individual is represented by a thin vertical line, which is partitioned into <i>K</i> colored segments that represent the individual's estimated ancestry within each <i>K</i> cluster. Two values of <i>K</i> are presented; upper panel: <i>K</i> = 2 (optimal <i>K</i> using Evanno’s criterion) and lower panel: <i>K</i> = 7 (optimal K using Pritchard’s criterion. Black lines separate individuals of different sampling sites. Population clusters are labeled above the Fig., individual sampling sites and sample category, below the Fig.</p
Transactions of the American Fisheries Society, 2021
Allowing reproductive individuals to colonize novel habitat or recolonize previously occupied hab... more Allowing reproductive individuals to colonize novel habitat or recolonize previously occupied habitat is increasingly being considered as a tool for recovery of depleted populations of anadromous salmon. Successful application of these techniques requires thorough understanding of how adults use the riverscape during colonization to ensure that programs achieve desired outcomes. We examined movements and habitat use of adult Atlantic Salmon Salmo salar, during colonization of novel habitat in an eastern Canadian river using a novel combination of acoustic telemetry, remote sensing, ground surveys, and continuous records of river temperature and discharge. Females moved less than males regardless of river temperature or discharge, whereas males engaged in more extensive movements except at elevated temperature and discharge. Probability of movement was lower during the summer, coincident with individuals holding in pools during high heat/low discharge events. River temperature, discharge, and day of year were influential in predicting whether salmon held in pools, and size was the most important physical characteristic identifying "suitable" holding pools. Observed movement patterns may reflect different evolutionary strategies employed by each sex to maximize reproductive fitness. Because spawning behavior is highly conserved within salmonids, these findings may 1) provide a generalized picture of how Atlantic Salmon use space during colonization of unoccupied habitat and 2) be used to optimize future reintroduction and assisted migration programs.
Marine Ecology Progress Series, 2017
Marine and Freshwater Research, 2018
Advances in telemetry technologies have provided new opportunities to reveal the often-cryptic sp... more Advances in telemetry technologies have provided new opportunities to reveal the often-cryptic spatial ecology of anguillid eels. Herein we review 105 studies published between 1972 and 2016 that used a variety of telemetry technologies to study the movements of eels in a variety of habitats. Eight anguillid species have been tracked in three main geographical locations: Western Europe, the north-eastern part of North America and Australasia. Telemetry has proven to be an effective method for determining patterns of yellow eel movements in continental waters. It has also been used extensively to investigate the migratory behaviour of maturing eels as they leave fresh water to reach the sea. Among recent findings is the observation that downstream migration in continental waters is quite discontinuous, characterised by extended stopovers. Reconstructed migration routes in the open ocean obtained from satellite tags have provided indications of spawning areas, extensive vertical migra...
The Bulletin of zoological nomenclature, 1999
Case 3061 Hemibagrus Bleeker, 1862 (Osteichthyes, Siluriformes): proposed stability of nomenclatu... more Case 3061 Hemibagrus Bleeker, 1862 (Osteichthyes, Siluriformes): proposed stability of nomenclature by the designation of a single neotype for both Bagnis nemurus Valenciennes, 1840 and B. sieholdii Bleeker, 1846, and the designation of the lectotype of B. planiceps
ICES Journal of Marine Science, 2015
Both the American eel (Anguilla rostrata) and European eel (Anguilla anguilla) undertake long-dis... more Both the American eel (Anguilla rostrata) and European eel (Anguilla anguilla) undertake long-distance migrations from continental waters to their spawning sites in the Sargasso Sea. Their migration routes and orientation mechanisms remain a mystery. A biophysical particle tracking model was used in this study to simulate their oceanic migration from two release areas: off the Scotian Shelf (Canada) and off the Irish continental shelf. Two plausible swimming-directed behaviours were considered for simulating two different migratory paths: true navigation to specific spawning sites and innate compass orientation towards the vast spawning area. Several combinations of swimming speeds and depths were tested to assess the effect of ocean circulation on resulting migratory pathways of virtual eels (v-eels), environmental conditions experienced along their oceanic migration, and energy consumption. Simulations show that the spawning area can be reached in time by constantly swimming and f...
Environmental Pollution (1970), 1979
The rheotaxis and swimming speeds of rainbow trout in response to a water current simulated by mo... more The rheotaxis and swimming speeds of rainbow trout in response to a water current simulated by moving a striped background past the fish were observed following 24-h exposures to field application concentrations of the herbicides diquat, simazine and their eommereialjbrmulations. Fish tissues were subsequently analysed to assess the extent of uptake of the herbicides. Toxicological modification of rheotaxis and swimming speeds was observed in fish exposed to diquat and its formulation Reglone A ® resulting in an increased incidence of downstream drift. Simazine residues infish increased in proportion to treatment let'els whereas diquat residues in fish levelled off with increasing treatment lerels. The toxicological modification of rheotropism is presented as a sensitit'e bioassay to assess sublethal effects of biocides.
La truite arc-en-ciel est un poisson exotique qui a été introduit au Québec (Canada) en 1893-1894... more La truite arc-en-ciel est un poisson exotique qui a été introduit au Québec (Canada) en 1893-1894. Malgré un zonage piscicole restreignant spatialement son ensemencement à des fins de pêche sportive, l'espèce s'est dispersée le long du fleuve Saint-Laurent. Dans cette étude, la relation entre l'occurrence de la truite arc-en-ciel (présence ou absence) et des variables abiotiques (géomorphologie fluviale et climat) a été examinée pour 91 rivières côtières situées dans l'Est du Québec, afin de déterminer
Transactions of the American Fisheries Society, 1979
The rheotropic response of rainbow trout (Salmo gairdneri) to a water current, simulated by a str... more The rheotropic response of rainbow trout (Salmo gairdneri) to a water current, simulated by a striped background moving past the fish, was observed following 24-hour exposures to field application concentrations of the aquatic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) but-oxyethanol ester and its commercial formulation Aqua-Kleen. Toxicological modification of rheotropism occurred that would in nature lead to an increased incidence of downstream
Science, 1985
Molecular Ecology, 1994
Episodes of trans‐Arctic faunal exchange and isolation between the north Pacific and Atlantic oce... more Episodes of trans‐Arctic faunal exchange and isolation between the north Pacific and Atlantic ocean basins have been implicated as important historic geological events contributing to extant patterns of genetic diversity and structure in Holarctic faunas. We made a further test of the significance of such biogeographic events by examining mitochondrial DNA (mtDNA) restriction fragment length and cytochrome b sequence polymorphism among north Pacific and Arctic, north‐western Atlantic (north‐eastern North American), and north‐eastern Atlantic (European) regional forms of the boreal smelt, genus Osmerus. Our analyses also assessed whether the regional forms within this ‘species complex’: (i) represent a single widely distributed and polytypic species, or is composed of three geographically distinct species, and (ii) resulted from a single split from north Pacific ancestral Osmerus or two independent Pacific‐Atlantic divergences. MtDNA sequence divergence estimates among forms ranged f...
Marine Ecology Progress Series, 2002
The lower St. Lawrence estuary (LSLE) is a narrow and deep basin under the influence of both estu... more The lower St. Lawrence estuary (LSLE) is a narrow and deep basin under the influence of both estuarine and marine processes. As a result, the LSLE is characterized by strong spatiotemporal heterogeneity in biological and physical environmental conditions. Previous studies have indicated a bias in the summer composition of the copepod population for predominance of late-development stages of Calanus spp., in comparison with adjacent waters of the Gulf of St. Lawrence (GSL) and northwest Atlantic. In this study, we use a 22 mo spatial survey of the LSLE to determine spatial and temporal variations in the copepod community and the relative contribution of Calanus spp. (C. finmarchicus and C. hyperboreus). Multivariate analysis revealed 4 copepod assemblages associated with seasonal patterns in temperature and chlorophyll a. Calanus spp. dominated the early summer community whereas the seasonal increase in abundance of the more surface-dwelling species (Acartia spp., Oithona spp. and Pseudocalanus spp.) explained the mixed Calanus spp./surface species community observed in late summer-autumn and winter. Three recurrent geographic zones can be discriminated in the LSLE on the basis of specific composition and abundance. The copepod community in the upper-central Laurentian Channel was dominated by Calanus spp. Downstream, in late summer-autumn and winter, a mixed Calanus/surface species assemblage was observed. In the shallow region, a very low abundance of Calanus spp. resulted in dominance of surface species after the early summer period. The genus Calanus spp. was the dominant component of the copepod community in LSLE as a whole because of its consistently high abundance along the Laurentian Channel during different seasons. A change in environmental conditions in the 1990s associated with a decadal climate variation in the GSL-LSLE region appears to be related to a dramatic increase in abundance of midwater copepod species (mainly Metridia longa) and, subsequent decline in the relative abundance of Calanus spp. We develop the hypothesis that the observed patterns in copepod species composition in the LSLE are primarily a consequence of the combined effect of the export in the residual surface outflow of early life stages of Calanus spp. and small surface-dwelling species and the upstream advection of late-development stages of Calanus spp. and midwater species in the inflowing deep water of the Laurentian Channel.
Journal of Fish Biology, 1988
The time elvers of the American eel, Anguilla rostrata, spend in an estuary prior to their migrat... more The time elvers of the American eel, Anguilla rostrata, spend in an estuary prior to their migration into fresh water was assessed. A distinct mark was formed on elvers' otoliths during their first 2 to 3 weeks in the river estuary. This mark was used to distinguish between growth in fresh water and in salt water. Migrating eels collected at a falls 4 km from the estuary exhibited bimodal length and weight distributions. Frequency distributions showed that eels collected in the estuary were smaller and had smaller otoliths than eels collected at the falls, indicating that elvers do not reach the falls in the same year as they enter the estuary. The three modal groups most probably represent three age–classes. However, the otoliths of elvers collected in the estuary had only the mark of transition whereas eels in the first and second mode at the falls usually had two rings (1–4) and four rings (3–6) per otolith, respectively, in addition to the mark of transition, as viewed under...
Journal of Evolutionary Biology, 2010
Environmental Toxicology and Chemistry, 1995
Induction of hepatic ethoxyresorufin-0-deethylase (EROD) activity and accumulation of chloropheno... more Induction of hepatic ethoxyresorufin-0-deethylase (EROD) activity and accumulation of chlorophenolic compounds typical of bleached-kraft mill effluent (BKME) in fish sampled downstream of a pulp mill on the St. Maurice River, Quebec, Canada, provided evidence of chemical exposure to BKME. In comparison, fish sampled over the same distances and in similar habitats in a noncontaminated reference river, the Gatineau River, demonstrated low EROD activity and contamination levels. Accelerated growth of white suckers occurred between 2 and 10 years of age in both rivers at downstream stations relative to upstream stations, suggesting the existence of gradients of nutrient enrichment independent of BKME contamination. The impact of BKME exposure was expressed as reduced investment in reproduction, as revealed by greater length at maturity, reduced gonad size, and more variable fecundity. These effects were not obvious in simple upstream-downstream comparisons, but became evident when fish from the uncontaminated Gatineau River showed increased gonadal development and reduced age and size at maturity in response to enhanced growth rates. Keywords-Bleached-kraft mill effluent EROD MFO 0.176" over 136 km site 1: 76"Ol'; 46"46' site 2: 75"58'; 46"23' site 3: 75"55'; 45"53' Precipitation (mm), monthly average' 937 k 92 1,022 t 150 Log-floating Yesd Yes Water flow, monthly average (~n~/ s)~ Water temperature, "C, monthly averagee 295 t 84 (n = 21 months) 8.3 k 7.5 465 t 165 (n = 18 months) 8.8 + 8.7 Water PH Water conductivity (pS/cm)e Air temperature, "C, monthly average' No. days over 5°C per year' 6.7 k 0.3 35.6 k 6.3 5.3 k 10.5 190 f 6 6.5 f 0.1 4.6 t 11.2 27.3 f 3.9 186 & 4 Unless otherwise indicated, monthly averages are given for 1990. aFrom the head of the river to the St. Lawrence River (St. Maurice R.), and to the Ottawa River (Gatineau R.). bSt. Maurice: measured at La Tuque and Grand-Mtre dams; Gatineau: measured at Mercier and Paugan Falls 'Measured at 5 stations on each river. Data are from Quebec Ministry of Environment, Meteorological Services. dLog-floating stopped in 1992. eMeasured at 6 stations on the St. Maurice River, and at 7 stations on the Gatineau River. Data are from Quebec dams. Data are from Quebec Ministry of Environment, Hydrological Services. Ministry of Environment, Water Quality Services.
Environmental Biology of Fishes, 1990
Synopsis We tested the hypothesis that the mechanism of retention of tomcod, Microgadus tomcod, l... more Synopsis We tested the hypothesis that the mechanism of retention of tomcod, Microgadus tomcod, larvae and juveniles in the well-mixed part of the St. Lawrence Estuary is similar to that of sympatric smelt, Osmerus mordax, larvae who actively migrate to the surface during flood tides and to the bottom during ebb tides so as to minimize net downstream displacement. The
We develop the view, based on life cycle differences and recently published sister group relation... more We develop the view, based on life cycle differences and recently published sister group relationships, that the freshwater life cycle was the ancestral character state leading to anadromy among salmoniforms, whereas the marine life cycle was the ancestral character state leading to anadromy among osmeriforms. In contrast to most salmonid fishes, the reproductive migrations of smelts are generally characterized by brief excursions to spawn in freshwater, and larvae may spend no more than 24 h in freshwater before being transported to coastal marine or estuarine environments. We reconstructed the phylogeny of the suborder Osmeroidei to establish the phylogenetic relationships among anadromous, marine, and freshwater species of this taxon. We mapped these life cycles onto phylogenetic trees of osmeriforms and salmoniforms and applied character-reconstruction methodology based on simple parsimony and likelihood methodologies. A freshwater origin of salmonids was supported by our analyses, whereas either marine or anadromous life cycles characterized the evolution of osmeroids. The possibility that the evolution of anadromy in salmonids and osmeroids followed separate paths requires a reconsideration of some generalizations concerning anadromy. We hypothesize that anadromy in osmeroids may be first and foremost an adaptation to place embryos and the early larval stages in reproductive safe sites to maximize their survival. The evolution of exclusive freshwater species of osmeriforms has occurred via anadromy through the various processes associated with landlocking. Freshwater amphidromy in osmeroids is most likely a consequence of anadromy rather than a precursor and may be contingent upon the availability of food resources in freshwater. Finally, marine osmeroids have been derived from anadromous ancestors and are "safe-site" specialists, exploiting principally the upper intertidal zone for reproduction. We also suggest that such contrasting evolutionary pathways to anadromy may provide insight into the evolution of partial migration, observed uniquely in salmonids, and the nature and extent of population genetic structure found in the two groups of fishes.
Journal of Fish Biology, Oct 1, 2007
The hypothesis that a part of the yellow American eel Anguilla rostrata sub-population of the St ... more The hypothesis that a part of the yellow American eel Anguilla rostrata sub-population of the St Jean River in eastern Quebec feeds in the brackish environment during summer and returns to the river to overwinter was tested. Three years of microtagging and the acoustic tagging and tracking of 40 American eels demonstrated that a part of the downstream migrants exploited the estuary as a summer feeding area. Upstream movement of some microtagged American eels provided support for the hypothesis that a part of those American eels returned to the river to overwinter. In addition to the demonstration of amphidromous behaviour of yellow eels, the study revealed that American eels in the estuary were active at night but homed to specific daytime resting sites.
Environmental Biology of Fishes, Dec 1, 1989
Recent sampling programs conducted in the estuaries of the Eastmain and La Grande rivers (James B... more Recent sampling programs conducted in the estuaries of the Eastmain and La Grande rivers (James Bay) and the Great Whale, Little Whale, Innuksuac and Povungnituk rivers (Hudson Bay) revealed patterns of coregonine fish distribution that differ from previous observations. The relative abundance of cisco, Coregonus artedii, and lake whitefish, C. clupeaformis, varied among rivers but did not reveal a latitudinal
disruption of dominance hierarchies by a non-native species:
PLOS ONE, 2015
<p>Each individual is represented by a thin vertical line, which is partitioned into <i&... more <p>Each individual is represented by a thin vertical line, which is partitioned into <i>K</i> colored segments that represent the individual's estimated ancestry within each <i>K</i> cluster. Two values of <i>K</i> are presented; upper panel: <i>K</i> = 2 (optimal <i>K</i> using Evanno’s criterion) and lower panel: <i>K</i> = 7 (optimal K using Pritchard’s criterion. Black lines separate individuals of different sampling sites. Population clusters are labeled above the Fig., individual sampling sites and sample category, below the Fig.</p
Transactions of the American Fisheries Society, 2021
Allowing reproductive individuals to colonize novel habitat or recolonize previously occupied hab... more Allowing reproductive individuals to colonize novel habitat or recolonize previously occupied habitat is increasingly being considered as a tool for recovery of depleted populations of anadromous salmon. Successful application of these techniques requires thorough understanding of how adults use the riverscape during colonization to ensure that programs achieve desired outcomes. We examined movements and habitat use of adult Atlantic Salmon Salmo salar, during colonization of novel habitat in an eastern Canadian river using a novel combination of acoustic telemetry, remote sensing, ground surveys, and continuous records of river temperature and discharge. Females moved less than males regardless of river temperature or discharge, whereas males engaged in more extensive movements except at elevated temperature and discharge. Probability of movement was lower during the summer, coincident with individuals holding in pools during high heat/low discharge events. River temperature, discharge, and day of year were influential in predicting whether salmon held in pools, and size was the most important physical characteristic identifying "suitable" holding pools. Observed movement patterns may reflect different evolutionary strategies employed by each sex to maximize reproductive fitness. Because spawning behavior is highly conserved within salmonids, these findings may 1) provide a generalized picture of how Atlantic Salmon use space during colonization of unoccupied habitat and 2) be used to optimize future reintroduction and assisted migration programs.
Marine Ecology Progress Series, 2017
Marine and Freshwater Research, 2018
Advances in telemetry technologies have provided new opportunities to reveal the often-cryptic sp... more Advances in telemetry technologies have provided new opportunities to reveal the often-cryptic spatial ecology of anguillid eels. Herein we review 105 studies published between 1972 and 2016 that used a variety of telemetry technologies to study the movements of eels in a variety of habitats. Eight anguillid species have been tracked in three main geographical locations: Western Europe, the north-eastern part of North America and Australasia. Telemetry has proven to be an effective method for determining patterns of yellow eel movements in continental waters. It has also been used extensively to investigate the migratory behaviour of maturing eels as they leave fresh water to reach the sea. Among recent findings is the observation that downstream migration in continental waters is quite discontinuous, characterised by extended stopovers. Reconstructed migration routes in the open ocean obtained from satellite tags have provided indications of spawning areas, extensive vertical migra...
The Bulletin of zoological nomenclature, 1999
Case 3061 Hemibagrus Bleeker, 1862 (Osteichthyes, Siluriformes): proposed stability of nomenclatu... more Case 3061 Hemibagrus Bleeker, 1862 (Osteichthyes, Siluriformes): proposed stability of nomenclature by the designation of a single neotype for both Bagnis nemurus Valenciennes, 1840 and B. sieholdii Bleeker, 1846, and the designation of the lectotype of B. planiceps
ICES Journal of Marine Science, 2015
Both the American eel (Anguilla rostrata) and European eel (Anguilla anguilla) undertake long-dis... more Both the American eel (Anguilla rostrata) and European eel (Anguilla anguilla) undertake long-distance migrations from continental waters to their spawning sites in the Sargasso Sea. Their migration routes and orientation mechanisms remain a mystery. A biophysical particle tracking model was used in this study to simulate their oceanic migration from two release areas: off the Scotian Shelf (Canada) and off the Irish continental shelf. Two plausible swimming-directed behaviours were considered for simulating two different migratory paths: true navigation to specific spawning sites and innate compass orientation towards the vast spawning area. Several combinations of swimming speeds and depths were tested to assess the effect of ocean circulation on resulting migratory pathways of virtual eels (v-eels), environmental conditions experienced along their oceanic migration, and energy consumption. Simulations show that the spawning area can be reached in time by constantly swimming and f...
Environmental Pollution (1970), 1979
The rheotaxis and swimming speeds of rainbow trout in response to a water current simulated by mo... more The rheotaxis and swimming speeds of rainbow trout in response to a water current simulated by moving a striped background past the fish were observed following 24-h exposures to field application concentrations of the herbicides diquat, simazine and their eommereialjbrmulations. Fish tissues were subsequently analysed to assess the extent of uptake of the herbicides. Toxicological modification of rheotaxis and swimming speeds was observed in fish exposed to diquat and its formulation Reglone A ® resulting in an increased incidence of downstream drift. Simazine residues infish increased in proportion to treatment let'els whereas diquat residues in fish levelled off with increasing treatment lerels. The toxicological modification of rheotropism is presented as a sensitit'e bioassay to assess sublethal effects of biocides.
La truite arc-en-ciel est un poisson exotique qui a été introduit au Québec (Canada) en 1893-1894... more La truite arc-en-ciel est un poisson exotique qui a été introduit au Québec (Canada) en 1893-1894. Malgré un zonage piscicole restreignant spatialement son ensemencement à des fins de pêche sportive, l'espèce s'est dispersée le long du fleuve Saint-Laurent. Dans cette étude, la relation entre l'occurrence de la truite arc-en-ciel (présence ou absence) et des variables abiotiques (géomorphologie fluviale et climat) a été examinée pour 91 rivières côtières situées dans l'Est du Québec, afin de déterminer
Transactions of the American Fisheries Society, 1979
The rheotropic response of rainbow trout (Salmo gairdneri) to a water current, simulated by a str... more The rheotropic response of rainbow trout (Salmo gairdneri) to a water current, simulated by a striped background moving past the fish, was observed following 24-hour exposures to field application concentrations of the aquatic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) but-oxyethanol ester and its commercial formulation Aqua-Kleen. Toxicological modification of rheotropism occurred that would in nature lead to an increased incidence of downstream
Science, 1985
Molecular Ecology, 1994
Episodes of trans‐Arctic faunal exchange and isolation between the north Pacific and Atlantic oce... more Episodes of trans‐Arctic faunal exchange and isolation between the north Pacific and Atlantic ocean basins have been implicated as important historic geological events contributing to extant patterns of genetic diversity and structure in Holarctic faunas. We made a further test of the significance of such biogeographic events by examining mitochondrial DNA (mtDNA) restriction fragment length and cytochrome b sequence polymorphism among north Pacific and Arctic, north‐western Atlantic (north‐eastern North American), and north‐eastern Atlantic (European) regional forms of the boreal smelt, genus Osmerus. Our analyses also assessed whether the regional forms within this ‘species complex’: (i) represent a single widely distributed and polytypic species, or is composed of three geographically distinct species, and (ii) resulted from a single split from north Pacific ancestral Osmerus or two independent Pacific‐Atlantic divergences. MtDNA sequence divergence estimates among forms ranged f...
Marine Ecology Progress Series, 2002
The lower St. Lawrence estuary (LSLE) is a narrow and deep basin under the influence of both estu... more The lower St. Lawrence estuary (LSLE) is a narrow and deep basin under the influence of both estuarine and marine processes. As a result, the LSLE is characterized by strong spatiotemporal heterogeneity in biological and physical environmental conditions. Previous studies have indicated a bias in the summer composition of the copepod population for predominance of late-development stages of Calanus spp., in comparison with adjacent waters of the Gulf of St. Lawrence (GSL) and northwest Atlantic. In this study, we use a 22 mo spatial survey of the LSLE to determine spatial and temporal variations in the copepod community and the relative contribution of Calanus spp. (C. finmarchicus and C. hyperboreus). Multivariate analysis revealed 4 copepod assemblages associated with seasonal patterns in temperature and chlorophyll a. Calanus spp. dominated the early summer community whereas the seasonal increase in abundance of the more surface-dwelling species (Acartia spp., Oithona spp. and Pseudocalanus spp.) explained the mixed Calanus spp./surface species community observed in late summer-autumn and winter. Three recurrent geographic zones can be discriminated in the LSLE on the basis of specific composition and abundance. The copepod community in the upper-central Laurentian Channel was dominated by Calanus spp. Downstream, in late summer-autumn and winter, a mixed Calanus/surface species assemblage was observed. In the shallow region, a very low abundance of Calanus spp. resulted in dominance of surface species after the early summer period. The genus Calanus spp. was the dominant component of the copepod community in LSLE as a whole because of its consistently high abundance along the Laurentian Channel during different seasons. A change in environmental conditions in the 1990s associated with a decadal climate variation in the GSL-LSLE region appears to be related to a dramatic increase in abundance of midwater copepod species (mainly Metridia longa) and, subsequent decline in the relative abundance of Calanus spp. We develop the hypothesis that the observed patterns in copepod species composition in the LSLE are primarily a consequence of the combined effect of the export in the residual surface outflow of early life stages of Calanus spp. and small surface-dwelling species and the upstream advection of late-development stages of Calanus spp. and midwater species in the inflowing deep water of the Laurentian Channel.
Journal of Fish Biology, 1988
The time elvers of the American eel, Anguilla rostrata, spend in an estuary prior to their migrat... more The time elvers of the American eel, Anguilla rostrata, spend in an estuary prior to their migration into fresh water was assessed. A distinct mark was formed on elvers' otoliths during their first 2 to 3 weeks in the river estuary. This mark was used to distinguish between growth in fresh water and in salt water. Migrating eels collected at a falls 4 km from the estuary exhibited bimodal length and weight distributions. Frequency distributions showed that eels collected in the estuary were smaller and had smaller otoliths than eels collected at the falls, indicating that elvers do not reach the falls in the same year as they enter the estuary. The three modal groups most probably represent three age–classes. However, the otoliths of elvers collected in the estuary had only the mark of transition whereas eels in the first and second mode at the falls usually had two rings (1–4) and four rings (3–6) per otolith, respectively, in addition to the mark of transition, as viewed under...
Journal of Evolutionary Biology, 2010
Environmental Toxicology and Chemistry, 1995
Induction of hepatic ethoxyresorufin-0-deethylase (EROD) activity and accumulation of chloropheno... more Induction of hepatic ethoxyresorufin-0-deethylase (EROD) activity and accumulation of chlorophenolic compounds typical of bleached-kraft mill effluent (BKME) in fish sampled downstream of a pulp mill on the St. Maurice River, Quebec, Canada, provided evidence of chemical exposure to BKME. In comparison, fish sampled over the same distances and in similar habitats in a noncontaminated reference river, the Gatineau River, demonstrated low EROD activity and contamination levels. Accelerated growth of white suckers occurred between 2 and 10 years of age in both rivers at downstream stations relative to upstream stations, suggesting the existence of gradients of nutrient enrichment independent of BKME contamination. The impact of BKME exposure was expressed as reduced investment in reproduction, as revealed by greater length at maturity, reduced gonad size, and more variable fecundity. These effects were not obvious in simple upstream-downstream comparisons, but became evident when fish from the uncontaminated Gatineau River showed increased gonadal development and reduced age and size at maturity in response to enhanced growth rates. Keywords-Bleached-kraft mill effluent EROD MFO 0.176" over 136 km site 1: 76"Ol'; 46"46' site 2: 75"58'; 46"23' site 3: 75"55'; 45"53' Precipitation (mm), monthly average' 937 k 92 1,022 t 150 Log-floating Yesd Yes Water flow, monthly average (~n~/ s)~ Water temperature, "C, monthly averagee 295 t 84 (n = 21 months) 8.3 k 7.5 465 t 165 (n = 18 months) 8.8 + 8.7 Water PH Water conductivity (pS/cm)e Air temperature, "C, monthly average' No. days over 5°C per year' 6.7 k 0.3 35.6 k 6.3 5.3 k 10.5 190 f 6 6.5 f 0.1 4.6 t 11.2 27.3 f 3.9 186 & 4 Unless otherwise indicated, monthly averages are given for 1990. aFrom the head of the river to the St. Lawrence River (St. Maurice R.), and to the Ottawa River (Gatineau R.). bSt. Maurice: measured at La Tuque and Grand-Mtre dams; Gatineau: measured at Mercier and Paugan Falls 'Measured at 5 stations on each river. Data are from Quebec Ministry of Environment, Meteorological Services. dLog-floating stopped in 1992. eMeasured at 6 stations on the St. Maurice River, and at 7 stations on the Gatineau River. Data are from Quebec dams. Data are from Quebec Ministry of Environment, Hydrological Services. Ministry of Environment, Water Quality Services.
Environmental Biology of Fishes, 1990
Synopsis We tested the hypothesis that the mechanism of retention of tomcod, Microgadus tomcod, l... more Synopsis We tested the hypothesis that the mechanism of retention of tomcod, Microgadus tomcod, larvae and juveniles in the well-mixed part of the St. Lawrence Estuary is similar to that of sympatric smelt, Osmerus mordax, larvae who actively migrate to the surface during flood tides and to the bottom during ebb tides so as to minimize net downstream displacement. The