Relationships among environment, spawning and settlement of Queen scallop in the Ría de Arosa (Galicia, NW Spain)

This study examines the relationship of the reproductive and reserve storage cycles and spat settlement of the Queen scallop (Aequipecten opercularis) to environmental factors. The possibility of farming this species from spat settled on collectors is considered. The gonad condition index shows maximum values between mid-May and early August. Another peak occurs in mid-November. In spring and summer, the energy needed for gametogenesis is derived from food, although it is possible that direct transfer may occur from the digestive gland to the gonad. The glycogen and lipid content of the reserve organs reaches maximum values between late summer and early autumn. The energy requirements related to gametogenesis, which begins in autumn, involve the consumption of accumulated reserves with the resulting reduction in the condition indices. There is a positive correlation between temperature and the condition indices of the digestive gland, the adductor muscle and their lipid and glycogen content, respectively. Two settlement periods were recorded, one in winter, which could not be associated with the spawning of the experimental animals, and another in summer, which coincided with the spawning that took place in spring. The reduced gonad indices recorded at the end of the summer and in winter did not lead to settlement.     

Differing body size between the autumn and the winter–spring cohorts of neon flying squid (Ommastrephes bartramii) related to the oceanographic regime in the North Pacific: a hypothesis

The neon flying squid (Ommastrephes bartramii), which is the target of an important North Pacific fishery, is comprised of an autumn and winter–spring cohort. During summer, there is a clear separation of mantle length (ML) between the autumn (ML range: 38–46 cm) and the winter–spring cohorts (ML range: 16–28 cm) despite their apparently contiguous hatching periods. We examined oceanic conditions associated with spawning/nursery and northward migration habitats of the two different‐sized cohorts. The seasonal meridional movement of the sea surface temperature (SST) range at which spawning is thought to occur (21–25°C) indicates that the spawning ground occurs farther north during autumn (28–34°N) than winter–spring (20–28°N). The autumn spawning ground coincides with the Subtropical Frontal Zone (STFZ), characterized by enhanced productivity in winter because of its close proximity to the Transition Zone Chlorophyll Front (TZCF), which move south to the STFZ from the Subarctic Boundary. Hence this area is thought to become a food‐rich nursery ground in winter. The winter–spring spawning ground, on the other hand, coincides with the Subtropical Domain, which is less productive throughout the year. Furthermore, as the TZCF and SST front migrate northward in spring and summer, the autumn cohort has the advantage of being in the SST front and productive area north of the chlorophyll front, whereas the winter–spring cohort remains to the south in a less productive area. Thus, the autumn cohort can utilize a food‐rich habitat from winter through summer, which, we hypothesize, causes its members to grow larger than those in the winter–spring cohort in summer.     

Reproduction and recruitment of the brown shrimp Crangon crangon in the inner German Bight (North Sea): An interannual study and critical reappraisal

The brown shrimp, Crangon crangon, is the most important target of the coastal crustacean fisheries in the German Bight. In order to evaluate the relation between the abundance of ovigerous females and larvae in spring and the recruitment success in autumn, we first analysed the seasonal appearance of ovigerous females and larvae from weekly samples throughout 2012. The spawning season in the German Bight extends over several months comprising multiple unsynchronized spawning events. The minimum shares of ovigerous females appeared in early autumn, and the highest shares in late winter bearing mostly early egg stages. We defined the putative start of the reproductive cycle for November when the frequency of ovigerous females started to increase. There was no distinct separation between winter and summer eggs, but a continuous transition between large eggs spawned in winter (the early spawning season) and batches of smaller eggs in spring and summer. Larval densities peaked in April/May. Consequently, regular annual larval surveys from 2013 to 2016 were scheduled for April/May and extended to six transects covering the inner German Bight. Ovigerous females were most abundant in shallow waters above the 20‐m isobaths, which also explained regional differences in abundance between the regions off North Frisia and East Frisia. No relation was obvious between the number of larvae in spring and recruited stock in autumn. Due to the short lifespan of C. crangon, the combination of various abiotic factors and predator presence seems to be the principal parameters controlling stock size.     

Condition and recruitment of Aristeus antennatus at great depths (to 2,300 m) in the Mediterranean: Relationship with environmental factors

Depth and seasonal trends in the biological condition and recruitment of the red shrimp (Aristeus antennatus) have been analyzed over the slope to 2,233 m in the western Mediterranean. The best biological condition of A. antennatus (gonadosomatic index [GSI]) for mating and spawning occurred at 800–1,300 m in summer, in areas deeper than the fishing grounds distributed between 500 and 800 m. Females moved shallower to feed on the upper slope during periods of water‐mass homogeneity (autumn–winter), increasing their hepatic gland weight (hepatosomatic index [HSI]). Females moved downslope (800–1,100 m) to spawn (high GSI) during periods of water mass stratification (late spring–summer). The HSI of females decreased with depth down the slope in autumn, after the reproductive period. Small juveniles were distributed deeper than 1,000 m, associated with high near‐bottom O₂ levels, low turbidity and high C:N in sediments, implying favorable trophic conditions. This confirms the importance in studying the biology of deep‐sea species over their entire depth range. The progressive warming and increasing salinity of deep Mediterranean waters could provoke a decrease of dissolved O₂ that would affect the life cycle of A. antennatus.     

Accumulation of a bitter amino acid,pulcherrimine, in sea urchin ovaries and its relevance to the annual reproductive cycle

Hemicentrotus pulcherrimus in the Tohoku area is not utilized as a fishery product because the ovaries have a bitter taste almost all year. To discover the cause, we compared the annual reproductive cycles and ovarian accumulation of a bitter amino acid, pulcherrimine, in H. pulcherrimus collected at Mikuni (Fukui Prefecture), where it is fished in summer, and Iwaki (Fukushima Prefecture), where it is not utilized. At both sites, pulcherrimine increased in maturing ovaries as oogenesis proceeded from autumn to winter, decreased after spawning in spring, but remained in spent and immature ovaries for a few months. In Mikuni, pulcherrimine was scarcely detected in the ovaries for several months in summer. However, in Iwaki, late spawning delayed the disappearance of pulcherrimine in summer, and early initiation of oogenesis advanced the restart of pulcherrimine accumulation in autumn compared to Mikuni. Consequently, the period when the ovaries were palatable because of the absence of pulcherrimine during summer was short in Iwaki. The major cause of such short-term palatability could be the lower seawater temperature in the Tohoku area. Furthermore, pulcherrimine was never detected in other sea urchins, although a bitter taste was found in the mature ovaries of some species.

     

Reproductive cycle of the venerid clam <Emphasis Type="Italic">Meretrix lusoria</Emphasis> in Ariake Sound and Tokyo Bay,Japan

We assessed the reproductive cycle of the venerid clam Meretrix lusoria by histological analysis of the gonads. Individuals for study were collected from natural populations on the Shirakawa tidal flat, Ariake Sound, and from populations that had been transplanted from the Shirakawa flat to the Oi flat in Tokyo Bay. In both study areas, the reproductive cycle was synchronized between sexes. Gonads of the clam started to develop in early spring and matured during the summer. Mass spawning occurred in the late summer/early fall. The clam matured at a shell length of 17–20 mm, which is much smaller than previously considered. While trophic conditions and salinity differed considerably in the two study areas, water temperatures showed similar seasonal changes (12°C during the winter and around 30°C during the summer). Thus, temperature probably controlled gonadal development. The coincidence of the period of spawning with the period of frequent intrusion of hypoxic waters into the tidal flats in Tokyo Bay suggests that such hypoxic events interfere with clam recruitment and are at least partly responsible for the disappearance of the natural population at this location.     

Reproduction, condition and mortality of the Pacific oyster Crassostrea gigas (Thunberg) in Sonora, México

Starting in 1997, mortality outbreaks in cultured oysters Crassostrea gigas have been reported in northwestern México. Previous studies have shown that massive die‐offs result from multi‐factor processes related to reproduction of the species. We studied the reproductive cycle and the condition index of cultured oysters in the coastal lagoon of El Soldado, Sonora, as well as the relationship of the life cycle with environmental parameters. We used oocyte diameter to determine reproductive stages and the condition index to describe the physiological state of oysters. Additionally, the temperature, salinity, seston and chlorophyll a were recorded at the study site. The results showed that C. gigas began accelerated reproductive activity in March under the influence of high temperature and increased concentrations of food. No spawning events were recorded and gametes were reabsorbed within the gonad in September and October. The results showed a period of nutrient storage during autumn–winter and another period of gamete production in spring–summer. A mortality event occurred at the end of winter, tied to significant increases in temperature and availability of food and in accelerated reproductive activity and high condition index. These conditions were very similar to those reported in other countries during summer die‐offs of C. gigas.     

Seasonal differences in effect of broodstock diet on spawning success in the great scallop

Great scallop (Pecten maximus L.) broodstock collected at two different seasons, spring (May) and winter (December), were given four different diets during conditioning. The spring group was spawned in late June, and the winter group in February.The highest number of veligers in the summer spawning (30 millions per 10broodstock), was produced using a diet consisting of 80% Tahitian Isochrysis galbana. In the winter spawning, broodstock given a dietconsisting of 80% diatoms (Skeletonema costatum/Chaetocerosgracilis) produced the highest number of veligers (29 millions per 10broodstock). Fecundity and the number of egg-releasing individuals were higher in the early summer spawning (June) than in the winter spawning (February), however, the total number of three days old veligers produced was nearly the same in the two seasons.     

Seasonal spawning and wind‐regulated retention‐dispersal of early life stage Atlantic cod (Gadus morhua) in a Newfoundland fjord

Sequential ichthyoplankton surveys were used to determine the spatial and temporal distribution of eggs and larvae over coastal spawning grounds of Atlantic cod (Gadus morhua) in Smith Sound, Trinity Bay, Newfoundland, during the spring and summer of 2006 and 2007. Egg densities showed similar patterns for both years with two peaks in abundance in spring (March–April) and late summer (late July). A clear progression of development stages (1–4) was observed in spring and summer in 2006 and summer in 2007, suggesting retention of eggs within the Sound during these periods. Modelled predictions of vertical egg distributions indicated eggs were broadly distributed near the surface during spring (March–April), but were concentrated below the pycnocline (>10 m) within the inner portions of the Sound during the summer months (July–August). Back‐calculated peaks in spawning based on water temperatures were estimated at 11 and 4 April for 2006 and 2007, respectfully, with late season peaks centred on 21–24 July for both years. Environmental data indicated cooler water temperatures and periods of high wind stress in spring, and warmer, calmer periods late summer, consistent with higher retention and faster development times on the spawning grounds later in the season. We conclude that spring and summer spawning events result in different distributions of early life stages and may lead to different distributions of juvenile and adult fish.     

Variability of the reproductive cycle in estuarine and coastal populations of the mussel Mytilus galloprovincialis Lmk. from the SE Bay of Biscay (Basque Country)

Mussel commercial production depends on wild populations to obtain the seed. Therefore, any new farming initiative needs deep knowledge on reproductive cycle of native mussel populations. The reproductive cycle of Mytilus galloprovincialis Lmk. from five sites, three estuarine and two coastal, along the coast of the Basque Country were assessed using gonad index and stereology over 2 consecutive years (2010 and 2011). Sex ratios, developmental stages of gonads , as well as reserve tissue cycle were analyzed. The onset of gametogenesis was observed from winter to spring, with spawning occurring from spring till summer. A resting phase followed with an increase in reserve tissues (adipogranular cells) was observed in fall. Mussels stayed ripe during winter until favorable environmental conditions were met in spring. Differences in reproductive cycles were found among populations, and also, year-to-year variability was observed within each population. In two of the studied sites asynchrony in the timing of spawning was observed between genders. These timing differences, however, did not prevent mussels at those sites from reproducing successfully. The Bidasoa estuary points to the potential of such studied sites for becoming the main source of wild mussel spats for future expected commercial mussel farming in the Basque Country. To ensure year-to-year maximum reproductive output, however, wild mussels harvest should be avoided from spring to the end of summer in this region.

     

Environmentally conditioned,year‐round volitional spawning of cobia (Rachycentron canadum) in broodstock maturation systems

Year‐round control of the spawning cycle of cobia (Rachycentron canadum) has been established by using water temperature manipulation. To compare the effectiveness of using this method to induce volitional spawning in cobia, two 80 m³ recirculating aquaculture systems (RAS) were used. Temperatures in one of the maturation tanks (‘Mat 1’) were maintained between 27 and 29°C for 12 months of the 15.5‐month study period. Temperatures in the second maturation tank (‘Mat 2’) were allowed to fluctuate naturally throughout the year and ranged from 20 to 32°C. A total of 101 spawning events occurred in the tanks between the spring of 2008 and the summer of 2009 (3 April 2008 to 17 June 2009). Of the 38 total spawning events in Mat 1, 17 of them (44.7% of all Mat 1 spawning events) occurred during the off‐season (fall and winter). The egg viability rates did not differ significantly (P > 0.05) between on‐ and off‐season spawns in Mat 1. Conversely, cobia broodstock exposed to natural water temperatures (no environmental manipulation) in Mat 2 followed the natural pattern of warm water (>26°C) dependence, limiting egg production to spring and summer seasons. This method of water temperature manipulation allows for effective control of the cobia reproductive cycle without compromising egg viability.     

Oogenesis and lipids in gonad and liver of daubed shanny (Leptoclinus maculatus) females from Svalbard waters

Oocyte and liver histomorphology of the daubed shanny (Leptoclinus maculatus) from Isfjorden and Kongsfjorden in Svalbard were investigated during three Arctic seasons: summer (July), autumn (October) and winter (April). Three oocyte developmental phases were observed: primary growth phase, secondary growth phase and maturation phase. We observed four different developmental stages: (1) perinucleolus stage with cortical alveolus formation, (2) lipid droplets formation, (3) vitellogenesis stage and (4) maturation. Late maturation stage of oocytes in the ovaries was from the autumn season. Females accumulated lipids in liver (up to 35.2?% dw) and deposited large amounts of lipids into gonads (up to 52.2?% dw) during maturation. Lipid classes in female gonads changed seasonally, with relative increase in cholesterol during summer and depletion of storage lipids (triacylglycerols and wax esters/cholesterol esters) during the winter. Lipid composition in liver changed during oocyte development and spawning, as neutral lipids were transferred to developing oocytes during summer to autumn. During winter, storage lipids were depleted during starvation. Based on the increase in gonadosomatic index (GSI) with length and observed maturation stages, females seem to mature at a length of about 125-130?mm. The GSI and hepatosomatic index of large females sampled in autumn (September-October) were significantly higher than for females in late winter (April) and spring (May). These results indicate that spawning takes place during winter in Isfjorden and that energy reserves stored in the liver are utilized by females during gonadal development and reproduction.     

东海生态系统中鱼卵、仔稚鱼种类组成、数量分布及其与环境因素的关系

为了解当前东海生态系统中鱼卵、仔稚鱼种类组成和数量分布的现状及其变化与物理环境因素的关系,根据2006年11月—2008年6月5个航次的鱼卵、仔稚鱼和物理环境调查资料,对鱼卵、仔稚鱼种类组成、数量分布与产卵场物理环境进行分析,探讨不同季节、不同年份鱼卵、仔稚鱼种类组成和数量分布的变化及其与物理环境的关系。结果显示,5个航次采集到74 813粒鱼卵、16 826尾仔稚鱼,共有135个种类。其中,鉴定到种的有109种,隶属于15目67科99属,还有17个种类仅能鉴定到属、6个种类仅能鉴定到科和3个种类仅能鉴定到目。2006年—2007年秋季、冬季和春季鱼卵、仔稚鱼的种类和数量随着季节变化逐渐增多;2008年春季的种类和数量较2007年春季明显偏少;2008年初夏种类的数量与2008年春季基本相近,但鱼卵的数量明显增多,仔稚鱼的数量基本相近。42种优势种类、重要种类和主要种类构成当前东海生态系统中鱼卵、仔稚鱼种类组成的主要成分。东海表层水温和盐度分布有显著的季节变化。秋、冬季表层水温锋面强度最强,春季次之,初夏最弱;锋面的位置秋季离岸最近,冬季次之,春季和初夏离岸最远,冬季偏南,初夏季节北移。表层盐度锋面主要分布在近岸区域,与岸线大致平行,其强度冬季最强,春、秋季次之,初夏季节最弱。秋、冬季节陆架深水海域的水温较沿岸海域高,鱼类生殖群体在陆架深水高温区产卵;春季和初夏季节沿岸海域明显升温,鱼类生殖群体由深水区向近岸海域进行生殖洄游,产卵场分布由陆架中部向近岸海域扩展,并在近岸海域形成了中心产卵场。鱼卵和仔稚鱼的分布与温、盐锋面和种类的温、盐属性的关系密切,主要分布在温度锋面暖水一侧,并有各自最适宜的温度和盐度范围。水温、盐度与种类的繁殖生物学特性是导致鱼卵和仔稚鱼种类组成与数量发生变化的主要因素;适宜的温度和盐度范围、锋区的辐聚和卷夹作用以及种类的生物学属性是影响鱼卵和仔稚鱼数量分布以及密集分布区形成的主要因素。     

Seasonal adjusted diets to Atlantic salmon (Salmo salar): Evaluations of a novel feed based on heat-coagulated fish mince, fed throughout 1 year in sea: Feed utilisation, retention of nutrients and health parameters

The present paper reports the results of a 1 year experiment using Atlantic salmon with a starting weight of 1.7 kg, and final weight of 7.4 to7.8 kg dependent of diet group. The experiment aimed to evaluate a direct production method of feed where landings from fishing vessels are used directly in feed processing. The dietary compositions followed the natural rhythm in lipid level of the catches of herring in the North Sea (Catch group) adjusted to be stable throughout one season only, and compared to a control diet (constant composition throughout the year) and a designed diet (opposite to the natural biorhythm of salmon lipid stores) (diet group Design). Four seasons were defined: spring (March, April, May), summer (June July August), autumn (September, October, November), winter (December, January, February). All diets varied in protein and lipid due to the adjustment according to season. The experiment was run in triplicate sea cages for each diet, using natural light and temperature regimes (21°N). All diet groups showed equal growth throughout each season, except for the Catch group during autumn showing lower SGR-values. SGR values varied significantly also between seasons for all diet groups, ranging from 0.29 during spring to 0.81 during autumn. Feed conversion ratio varied dependent on season and the dietary protein to energy ratio, at all seasons except winter. Quite a large variation between diet groups and seasons were registered in condition factor. Whole body lipid varied between seasons, as a consequence of dietary lipid levels, and increased as fish weight increased. After autumn growth only, whole body protein levels were significantly lower in the Catch group compared to the two other diet groups. Muscle lipid levels did not vary as a consequence of fish size alone, but varied substantially between seasons in both the Catch and Control groups, but not in the Design group. Muscle alpha-tocopherol and fatty acid profile varied due to diet in spring and autumn seasons, but with minor variations due to diet in summer and winter periods. Only minor influences from diet were registered in liver and heart compositions. Haematological parameters and plasma nutrient values ranged within normal values for salmon, and together with close to no mortality throughout the experiment, fish health was concluded to be good in all diet groups at all seasons. However, plasma asparagine aminotransferase (ASAT) values were quite high during summer and autumn, especially in the control group. These results point to the need of optimizing antioxidant composition of diets during the summer and early autumn season. Overall results show the possibility to obtain acceptable production results when feeding Atlantic salmon a diet adjusted to each season, as long as the fish protein to energy (P:E) requirements are met, further that total body lipid stores varied more than muscle lipid concentrations, and that the lipid levels were highly dependent on season, diet composition and fish size.     

Annual variations in hepatic antioxidant defenses and lipid peroxidation in a temperate fish,common bream Abramis brama (L.)

Alternation of physiological states during the annual cycle (pre-spawning mobilization, spawning energy loss, post-spawning accumulation of energy reserve, declined metabolic activity during the wintering) occurring in the wide temperature range requires high plasticity of fish defense systems. The article presents a 2-year study of hepatic antioxidant defenses and lipid peroxidation in the temperate cyprinid fish, common bream Abramis brama (L.), in relation to basic annual rhythms, such as photoperiodic and temperature cycling, reproduction and feeding activity. The objective of the study was to evaluate the plasticity of antioxidant defenses in bream under normal conditions throughout the annual cycle, by measuring hepatic antioxidants (superoxide dismutase, catalase, glutathione-S-transferase activities and reduced glutathione concentrations) and products of lipid peroxidation (thiobarbituric acid reactive substances concentrations). The results suggested that hepatic levels of antioxidants in bream varied dramatically during the annual cycle allowing bream to develop necessary adaptation and implement reproduction program. The lowest values of all studied antioxidants were witnessed in the middle of winter. In early spring, antioxidant enzyme activities increased rapidly reaching their maxima in late spring and summer. Toward the end of autumn, enzyme activities were declining toward the levels observed before the ice breakup. Spring–summer up-regulation of antioxidant defenses along with increased lipid peroxidation indicated bream to be experiencing mild oxidative stress.     

Estimation of seasonal spawning ground locations and ambient sea surface temperatures for eggs and larvae of Pacific saury (Cololabis saira) in the western North Pacific

Since there have been practically no surveys of the eggs of Pacific saury (Cololabis saira) in the western North Pacific (WNP), its spawning ground (SG) distribution has been poorly resolved, based mainly on the larval distribution. This means of estimating SG distribution is imprecise because saury eggs drift for more than a week before they hatch, in a region with intense western boundary currents and their extensions. To improve our understanding of the immature saury, a large number of larvae (body length <25 mm) collected in the WNP during 1993–96 were numerically backtracked to take into account the advection by geostrophic and wind‐forced Ekman currents, and the SG locations and ambient sea surface temperatures (SSTs) for the eggs and larvae on the backtracking trajectories were estimated. The resulting seasonal distributions of SGs indicated that both the locations and the intensities of spawning change from season to season. Moreover, the ambient SSTs for eggs just after fertilization ranged from a high of around 21.5°C in early autumn (September to October) to a low of around 15.0°C in late spring (May to June) with an intermediate of around 20.0°C in winter (January to February). The ambient SSTs showed seasonally different gradients while the individuals developed from eggs to early larvae: the SSTs decreased throughout the autumn (September to December), stayed rather constant in winter (January to February), and increased throughout the spring (March to June). The ambient SSTs for the early larvae were at around 19.0°C in autumn and winter (September to February) and around 16.5°C throughout the spring (March to June).     

Reproductive periodicity of a Penaeus esculentus population near Low Islets,Queensland, Australia

Since a major expense in the aquaculture of prawns is the location of gravid females, an investigation into the spawning habits of a north Queensland population of P. esculentus was begun as part of a wider survey of the East coast penaeid populations. This 31-month survey revealed a period of high reproductive potential limited to the autumn for both the new season prawns just reaching sexual maturity and the remnants of the last season's prawn population. The autumn sexual maturation was followed by a quiescent period through early spring when maturation again proceeded to the spawning period in the following autumn. In fact, the new season prawns' rapid sexual and somatic growth in the autumn was repeated by both generations in the summer and early autumn during the 3-year study. The temporal coincidence of both sea temperature and rainfall patterns with both somatic and gonad growth was investigated.     

Impact of paralarvae and juveniles feeding environment on the neon flying squid (Ommastrephes bartramii) winter–spring cohort stock

In this study, we found that there were significant positive correlations between the catch per unit effort (CPUE, a squid abundance index) for the neon flying squid (Ommastrephes bartramii) winter–spring cohort and the satellite‐derived chlorophyll a concentrations in their spawning grounds located at 140–160°E where 21°C < sea surface temperature < 25°C from February to May. The spawning grounds of the winter–spring cohort are located in a quiet stream region, and a particle tracking experiment, based on the velocity field obtained from an ocean data assimilation system, showed that paralarvae and juveniles aged <90 days remained in their spawning grounds and the chlorophyll a concentration in their habitat had a significant positive correlation with the CPUE. A backward particle tracking experiment also showed that the chlorophyll a concentration in the spawning grounds had a significant positive correlation with the autumn–winter mixed layer depth. Based on these results, we hypothesize that the CPUE interannual variability is caused by variations in the feeding environment of the paralarvae and juveniles, which may be linked to autumn–winter mixed layer depth variations.     

Understanding the life histories of amphidromous fish by integrating otolith‐derived growth reconstructions,post‐larval migrations and reproductive traits

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Seasonal movements of non‐native lake trout in a connected lake and river system

Abstract Non‐native lake trout, Salvelinus namaycush (Walbaum), threaten native salmonid populations in the western United States. Effective management of lake trout requires understanding movements within connected lake and river systems. This study determined the seasonal movements of subadult lake trout in the Flathead River upstream of Flathead Lake, Montana, USA using radio telemetry. The spatiotemporal distribution of lake trout in the river was related to water temperature. Lake trout were detected in the river primarily during autumn, winter and spring, when water temperatures were cool. By contrast, fewer were detected when temperatures were warmest during summer and during high spring flows. Downriver movements to Flathead Lake occurred throughout autumn and winter when water temperature decreased below 5 °C, and in late spring as water temperature rose towards 15 °C and river discharge declined following spring runoff. Upriver movements occurred primarily in October, which coincided with migrations of prey fishes. These results suggest that lake trout are capable of moving throughout connected river and lake systems (up to 230 km) and that warm water temperatures function as an impediment to occupancy of the river during summer. Controlling source populations and maintaining natural water temperatures may be effective management strategies for reducing the spread of non‐native lake trout.