Different longitudinal distribution patterns of native white-spotted charr and non-native brown trout in Monbetsu stream, Hokkaido, northern Japan

Abstract  This study focused on longitudinal distribution patterns of native white-spotted charr and non-native brown trout in a mountainous stream in Hokkaido, Japan. Brown trout ratio, which is the proportion of brown trout in the catch of salmonids, was decreasing from downstream to upstream. Brown trout ratio correlated negatively with water temperature. Thus, our results suggested that temperature may influence the possible competition between native white-spotted charr and non-native brown trout.     

A spatial linkage between dams and non-native fish species in Hokkaido, Japan

Abstract –  The native and non-native freshwater fish species richness as well as the proportion of native fish species to overall fish species were examined to test a hypothesis of a spatial linkage between the distributions of dams and non-native fishes based on survey data collected in rivers and streams in Hokkaido, Japan. Non-native fish species have steadily increased in Hokkaido since the mid 1970s, as indicated by the decreasing proportion of native fish species per fish survey. Non-native species richness was significantly higher in areas above dams (i.e., reservoirs and their inlet streams) compared to areas without dams. As a result, the proportion of native fish species was lower above dams. This proportion was lower in developed and agricultural areas compared with forest areas, although both native and non-native species richness were higher in areas with development and agriculture. Non-native cyprinids, catfish and snakehead occurred primarily in a particular river basin with the largest drainage area, the longest history of reclamation and highest human population in the island. Non-native salmonids on the other hand, occurred in forest areas at higher elevations and their occurrence was associated with the existence of dams. There was a spatial linkage between the distribution of dams and non-native species, although it was applicable only to salmonids. The management of dams and reservoirs needs a strategy to prevent further expansion of exotic salmonids such as rainbow and brown trout. These species can be a significant threat to native Japanese salmonids as a result of various biological mechanisms.     

Differences in longitudinal distribution patterns along a Honshu stream of brown trout <Emphasis Type="Italic">Salmo trutta</Emphasis>, white-spotted charr <Emphasis Type="Italic">Salvelinus leucomaenis</Emphasis> and masu salmon <Emphasis Type="Italic">Oncorhynchus masou</Emphasis>

Brown trout Salmo trutta were first introduced into Japan in 1892, and they currently naturally reproduce in several rivers in Honshu and Hokkaido, Japan. Although negative impacts of brown trout introductions on native salmonid fishes have been documented in some Hokkaido rivers, studies of ecological interactions between brown trout and native salmonid fishes on Honshu are limited. In this study, we describe the longitudinal distribution patterns of introduced brown trout, white-spotted charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou in a 4 km stretch of a stream in central Honshu. Underwater observations were conducted in all pools within upstream, middle and downstream sections (190–400 m in length) of this stretch in order to estimate the densities of these species. Only white-spotted charr was observed in the upstream section, while brown trout and masu salmon were observed in the middle and downstream sections. Masu salmon densities, however, were much lower than brown trout densities. In the downstream section, white-spotted charr was absent. These results are consistent with results from previous studies of Hokkaido rivers, where it was found that white-spotted charr in low-gradient areas tend to be displaced by brown trout.     

Passive immunization of rainbow trout,Oncorhynchus mykiss (Walbaum), against Flavobacterium psychrophilum,the causative agent of bacterial coldwater disease and rainbow trout fry syndrome

Flavobacterium psychrophilum, the causative agent of bacterial coldwater disease (CWD) and rainbow trout fry syndrome (RTFS), causes high mortality in cultured salmonids. The present study was designed to determine the role antibody plays in conferring protection to rainbow trout fry, Oncorhynchus mykiss (Walbaum), by passive immunization with convalescent serum or serum from adult rainbow trout immunized with F. psychrophilum, and goat anti-F. psychrophilum serum. In each experiment, rainbow trout fry were injected intraperitoneally with antiserum and challenged by subcutaneous injection with a virulent strain (CSF-259-93) of F. psychrophilum 24-h post-immunization. Relative percentage survival (RPS) ranged from 9-42% when rainbow trout fry (mean weight 1.3 g) were injected with a 1:2 dilution of 25 microL of convalescent serum ranging in enzyme-linked immunosorbent assay antibody titres from 1600-102400. Rainbow trout fry (mean weight 1.0 g) passively immunized with 25 microL of serum from immunized adult fish exhibited RPS values of up to 57%. In each of these experiments, RPS increased with increasing antibody titres against F. psychrophilum. Passive immunization with 25 or 50 microL goat anti-F. psychrophilum serum, however, did not confer protection to fry (mean weight 1.3 g). These results suggest that trout antibody plays a role in conferring protection to F. psychrophilum, but antibody alone is unable to provide complete protection.     

Resource partitioning and spatial segregation in native and stocked brown trout, Salmo trutta L., and Arctic charr, Salvelinus alpinus (L.), in a hydroelectric reservoir

Abstract. Habitat use, food and spatial segregation in native and stocked brown trout, Salmo trutta L., and Arctic charr, Salvelinus alpinus (L.), were studied during summer 1989 and 1990 in the hydroelectric reservoir Lake Tunhovdfjorden. There was no difference in habitat use and feeding habits between wild and stocked brown trout. In epibenthic areas brown trout lived chiefly down to 2 Secchi disc units, whereas Arctic charr were most abundant between 1 and 4 Secchi disc units. In pelagic areas the catches were low for both species, and they were chiefly confined to surface waters down to 1 Secchi disc unit. The food segregation between brown trout and Arctic charr was almost complete. Both pelagic and epibenthic Arctic charr fed mainly on cladocerans ( Bosmina longispina and Daphnia galeata ), whereas surface insects of terrestrial origin and Arctic charr were the dominant food items for brown trout. Pelagic Arctic charr were significantly older, larger and more homogeneous in size than epibenthic charr. During calm weather schools of Arctic charr were observed cruising with the dorsal fin above the surface.     

Threats to at-risk salmonids of the Canadian Rocky Mountain region

Trout and charr, members of the salmonid family, have high conservation value but are also susceptible to anthropogenic threats in part due to the specificity of their habitat requirements. Understanding historical and future threats facing these species is necessary to promote their recovery. Of freshwater trout and charr in the Canadian Rocky Mountain region, westslope cutthroat trout (Oncorhynchus clarkii lewisi), bull trout (Salvelinus confluentus; a charr species) and Athabasca rainbow trout (Oncorhynchus mykiss) are of conservation concern. And indeed, range contractions and declining populations are evident throughout much of their ranges. Range contraction was most evident in the southern Alberta designatable unit (DU) of westslope cutthroat trout. Diminished populations were also evident in the downstream watersheds of the Alberta bull trout range, and throughout the Athabasca rainbow trout range. We assessed historical and future threats to evaluate the relative importance of individual threats to each DU and compare their impact among species. Individual threats fall into the broad categories of angling, non-native species and genes, habitat loss and alteration, and climate change. Severity of each threat varies by DU and reflects the interaction between species’ biology and the location of the DU. Severity of threats facing each DU has changed over time, reflecting extirpation of native populations, changes in management and industry best practices, expansion of non-native species and progressing climate change. The overall threat impact for each DU indicates a high probability of substantial and continuing declines and calls for immediate action.     

Habitat niche separation of the nonnative rainbow trout and native masu salmon in the Atsuta River,Hokkaido, Japan

The mechanisms by which nonnative species establish populations can be classified into two broad categories: they usurp the niches of native species through interspecific competition, or they avoid this intense interspecific competition by making use of minimal niche overlap with the native species. In this study, we considered how a nonnative salmonid species, the rainbow trout Oncorhynchus mykiss, established a population in the presence of the native salmonid species, the masu salmon O. masou, in Hokkaido, Japan. Circumstantial field evidence shows that the masu salmon exceeds the rainbow trout in abundance and suggests that these species use different types of cover habitat (rainbow trout abundance increases with increasing abundance of large woody debris aggregates, whereas masu salmon abundance increases with increasing abundance of undercut banks). These results imply that the rainbow trout established a population due to minimal niche overlap with the masu salmon, and not by competitive exclusion of the native species.     

Trophic interactions between introduced lake trout (Salvelinus namaycush) and native Arctic charr (S. alpinus) in a large Fennoscandian subarctic lake

Introduced fishes may have major impacts on community structure and ecosystem function due to competitive and predatory interactions with native species. For example, introduced lake trout (Salvelinus namaycush) has been shown to replace native salmonids and induce major trophic cascades in some North American lakes, but few studies have investigated trophic interactions between lake trout and closely related native Arctic charr (S. alpinus) outside the natural distribution of the former species. We used stomach content and stable isotope analyses to investigate trophic interactions between introduced lake trout and native Arctic charr in large subarctic Lake Inarijärvi in northern Finland. Both salmonids had predominantly piscivorous diets at >280 mm total length and were mainly caught from the deep profundal zone. However, lake trout had a more generalist diet and showed higher reliance on littoral prey fish than Arctic charr, whose diet consisted mainly of pelagic planktivorous coregonids. According to length at age and condition data, lake trout showed slightly faster growth but lower condition than Arctic charr. The results indicate that introduced lake trout may to some extent compete with and prey upon native Arctic charr, but currently have only a minor if any impact on native fishes and food web structure in Inarijärvi. Future monitoring is essential to observe potential changes in trophic interactions between lake trout and Arctic charr in Inarijärvi, as well as in other European lakes where the two salmonids currently coexist.     

Growth in Arctic charr and rainbow trout fed temporally concentrated or spaced daily meals

The effect on growth of distributing feed over a few hours compared tomore frequent meals was tested on 1+ Arctic charr (Salvelinus alpinus L.) and 1+ rainbow trout (Oncorhynchus mykiss Walbaum). Triplicate hatchery groups for each treatment were fed at a ration level of 1%/dayeither with few meals (8 times per day divided into morning and evening)or with frequent meals (32 meals equally distributed during the day). Wefound an opposite effect of meal frequency on growth in the two species.Low feeding intensity (8 meals per day) had a significantly positive effecton growth in rainbow trout but a significantly negative effect on growth inArctic charr when compared to feeding the fish frequent meals. Theopposite response to meal frequency is likely to be an effect of thedifferences in activity during feeding. Rainbow trout feed much moreaggressively than charr which can result in feeding being a more stressfulevent. In this experiment, the specific growth rate was lower and the feedconversion ratio higher for Arctic charr compared to rainbow trout.     

Maternal variation in juvenile survival and growth of triploid hybrids between female rainbow trout and male brown trout and brook charr

Related sib‐groups of rainbow trout × brown trout and rainbow trout × brook charr triploid hybrids and monospecific diploid and triploid rainbow trout controls were obtained from a common set of rainbow trout dams. On the basis of hybrid juvenile performances, 10 sib‐groups were selected and the corresponding diploid rainbow trouts were raised up to adult stage. Females from each group of rainbow trout were used to produce a second generation of hybrid progeny, the performances of which were analysed for grandmaternal variation and relation with first‐generation relatives. Results showed that hybrid traits (alevin yield and weight, survival and growth of fingerlings) were strongly influenced by maternal origin, and could be correlated to those of rainbow trout controls, but that maternal abilities had a low rate of inheritance. It was concluded that little improvement can be expected through selective breeding within parental populations.     

The effect of competition among three salmonids on dominance and growth during the juvenile life stage

Although non‐native species can sometimes threaten the value of ecosystem services, their presence can contribute to the benefits derived from the environment. In the Great Lakes, non‐native brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) support substantial recreational fisheries. With current efforts underway to restore once‐native Atlantic salmon (Salmo salar) to Lake Ontario, there is some concern that Atlantic salmon will impede non‐native contributions to the recreational fishery because Atlantic salmon exhibit niche overlap with brown trout and rainbow trout, particularly during the juvenile life stage. We therefore examined competition and growth of juvenile Atlantic salmon, brown trout and rainbow trout in semi‐natural streams. We found that brown trout were the most dominant and had the greatest growth rate regardless of what other species were present. Rainbow trout were more dominant than Atlantic salmon and consumed the most food of the three species. However, in the presence of brown trout, rainbow trout fed less frequently and exhibited negative growth as compared to when the rainbow trout were present with only Atlantic salmon. These data suggest that, outside of density‐dependent effects, Atlantic salmon will not impact stream production of brown trout and rainbow trout.     

Foraging mode variation in three stream‐dwelling salmonid fishes

Despite long‐standing interest in foraging modes as an important element of animal space use, few studies document and compare individual foraging mode differences among species and ecological conditions in the wild. We observed and compared foraging modes of 61 wild Arctic charr, Salvelinus alpinus, 42 brown trout, Salmo trutta, and 50 Atlantic salmon, Salmo salar, in their first growing season over a range of habitats in 10 Icelandic streams. We found that although stream salmonids typically sit‐and‐wait to ambush prey from short distances, Arctic charr were more mobile during prey search and prior to prey attack than Atlantic salmon, whereas brown trout were intermediate. In all three species, individuals that were mobile during search were more likely to be moving when initiating attacks on prey, although the strength and the slope of this relationship differed among species. Arctic charr also differed from salmon and trout as more mobile individuals travelled longer distances during prey pursuits. Finally, coupled with published data from the literature, salmonid foraging mobility (both during search and prior to attack) clearly decreased from still water habitats (e.g., brook charr), to slow‐running waters (e.g., Arctic charr) to fast‐running waters (e.g., Atlantic salmon). Hence, our study suggests that foraging mode of young salmonids can vary distinctly among related species and furthers our understanding of the behavioural mechanisms shaping the geographical distribution of wild salmonids.     

Are native brook charr and introduced rainbow trout differentially adapted to upstream and downstream reaches?

Abstract— Due to species introductions, brook charr (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) occur together in many North American streams and typically exhibit a pattern of distribution in which brook charr numerically dominate headwaters and rainbow trout dominate downstream reaches. It has been suggested that 1) the two species compete or 2) the two species do not compete because they are differentially adapted to environmental conditions found in upstream and downstream zones. We assessed whether there were differences in growth and macrohabitat (pool, run and riffle) selection of brook charr and rainbow trout in upper, middle and lower stream zones of a small Pennsylvania stream. Brook charr and rainbow trout placed in replicate paired enclosures set in upstream and downstream reaches showed no significant differences in growth and survival rates upstream, but brook charr had significantly greater growth rates than rainbow trout downstream. Enclosed fish and free-ranging fish both had negative growth rates during the summer. Enclosed fish lost significantly less weight than free-ranging fish. Instantaneous growth rates of free-ranging adult brook charr and rainbow trout from May to August were negative for both species in all stream zones. Underwater observations of adult brook charr and rainbow trout showed both species occurred significantly more often in pool macrohabitats than expected on the basis of macrohabitat availability, except for rainbow trout in the upstream zone. The proportion of pool macrohabitat was not significantly different among stream zones. Brook charr do not appear to be better adapted to upstream environments in Powdermill Run based on growth, survival and macrohabitat selection during summer. Negative biotic interactions acting along with differential environmental adaptations may explain the pattern of distribution of brook charr and rainbow trout in streams, but long-term transplant experiments with additional life stages will be necessary to examine this hypothesis.     

Habitat use, size and age structure in sympatric brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) stocks: resistance of populations to change following harvest

Abstract– Habitat use and population dynamics in brown trout Salmo trutta and Arctic charr Salvelinus alpinus were studied in an oligotrophic lake over a period of 10 years. Previous studies showed that the species segregated by habitat during summer. While brown trout occupied the surface water down to a depth of 10 m, Arctic charr were found deeper with a maximum occurrence at depth 10–15 m. Following the removal of a large number of intermediate sized fish in 1988–89, habitat segregation between the species broke down and Arctic charr were found in upper waters, while brown trout descended to deeper waters. The following year, both species were most frequently found in surface waters at depths of 0–5 m. During the last four years, the species reestablished their original habitat segregation despite another removal experiment of intermediate-sized fish in 1992–1994. The removal of fish resulted in an increased proportion of large (≥ 25 cm) fish in both species. Furthermore, the charr stock responded by reduced abundance and increased size-at-age. The results revealed plasticity and strong resistance to harvest populations of brown trout and Arctic charr. This is probably due to internal mechanisms of intraspecific competition within each population, which result in differential mortality among size classes.     

东北地区虹鳟IHN和IPN流行病学的初步研究

本文报道了虹鳟鱼病毒性疾病IHN和IPN的流行与危害情况，对这二种病毒性疾病的症状和病理变化作了初步的研究，并进行了病原学鉴定。文中建议严格地把住进口鱼卵或鱼苗的检疫工作，采取更严格的防疫措施，多层次地防止疫病的传播和蔓延。     

Diurnal stream habitat use of juvenile Atlantic salmon, brown trout and rainbow trout in winter

Abstract  The diurnal winter habitat of three species of juvenile salmonids was examined in a tributary of Skaneateles Lake, NY to compare habitat differences among species and to determine if species/age classes were selecting specific habitats. A total of 792 observations were made on the depth, velocity, substrate and cover (amount and type) used by sympatric subyearling Atlantic salmon, subyearling brown trout and subyearling and yearling rainbow trout. Subyearling Atlantic salmon occurred in shallower areas with faster velocities and less cover than the other salmonid groups. Subyearling salmon was also the only group associated with substrate of a size larger than the average size substrate in the study reach during both winters. Subyearling brown trout exhibited a preference for vegetative cover. Compared with available habitat, yearling rainbow trout were the most selective in their habitat use. All salmonid groups were associated with more substrate cover in 2002 under high flow conditions. Differences in the winter habitat use of these salmonid groups have important management implications in terms of both habitat protection and habitat enhancement.     

Potential negative impacts of introduced rainbow trout on endangered Sakhalin taimen through redd disturbance in an agricultural stream, eastern Hokkaido

Nomoto K, Omiya H, Sugimoto T, Akiba K, Edo K, Higashi S. Potential negative impacts of introduced rainbow trout on endangered Sakhalin taimen through redd disturbance in an agricultural stream, eastern Hokkaido.
Ecology of Freshwater Fish 2010: 19: 116–126. © 2009 John Wiley & Sons A/S
Abstract –  Sakhalin taimen ( Hucho perryi ) populations have decreased in Hokkaido, northernmost Japan, primarily because of overexploitation and habitat degradation. Here we document another threat to this species, that of spawning redd superimposition by artificially introduced rainbow trout ( Oncorhynchus mykiss ). Sakhalin taimen and rainbow trout are the only spring-spawning salmonid species in Hokkaido. In 2006–2008, spawning activities of both these species were observed in a Hokkaido stream, and it was determined that their spawning periods overlapped during mid-late April. They also spawned at similar water velocities, depths and substrate compositions. Although female Sakhalin taimen were larger than female rainbow trout, their egg burial depths were nearly identical. During the observation period, rainbow trout redds were approximately five times more abundant than Sakhalin taimen redds, and about 30% of the observed Sakhalin taimen redds were superimposed by rainbow trout redds. The high degree of spatial and temporal overlap in spawning, the similar egg burial depths of both species, and the high proportion of superimposed redds suggest that the introduced rainbow trout impact the endangered Sakhalin taimen in Hokkaido, and possibly, in other areas where the two species occur together.     

The relationship between the snowmelt flood and the establishment of non‐native brown trout (Salmo trutta) in streams of the Chitose River,Hokkaido, northern Japan

Flow regime is one of the major determinants of establishment success for non‐native aquatic organisms. Here, we examine the influence of flow variability associated with snowmelt flood on the establishment success of non‐native brown trout in 10 streams in northern Japan. We regarded the presence of Age‐0 brown trout as the index of the successful establishment. The emergence of Age‐0 brown trout in our study region begins in May, a time that overlaps with the occurrence of snowmelt flood. The presence of Age‐0 brown trout was negatively associated with flow variability, and it was also negatively associated with summer water temperature. Our results indicate that the non‐native brown trout tends to establish in the streams with smaller snowmelt floods and lower summer water temperatures. Brown trout is an invasive, non‐native species that is problematic all over the world, and effective management strategies for preventing their further expansion are urgently needed. This study suggests that river managers should recognise that stable streams such as spring‐fed streams (i.e., low flow and summer water temperature) and flow‐regulated streams, have a higher potential risk of brown trout invasion.     

Competitive interactions among multiple non‐native salmonids and two populations of Atlantic salmon

Competitive interactions with non‐native species can have negative impacts on the conservation of native species, resulting in chronic stress and reduced survival. Here, juvenile Atlantic salmon (Salmo salar) from two allopatric populations (Sebago and LaHave) that are being used for reintroduction into Lake Ontario were placed into semi‐natural stream tanks with four non‐native salmonid competitors that are established in Ontario streams: brown trout (S. trutta), rainbow trout (Oncorhynchus mykiss), Chinook salmon (O. tshawytscha) and coho salmon (O. kisutch). Brown trout and rainbow trout reduced the survival and fitness‐related traits of Atlantic salmon, whereas Chinook salmon and coho salmon had no impact on these traits. These data support theories on ecological niche overlap and link differences in observed aggression levels with competitive outcomes. Measurements of circulating hormones indicated that the Atlantic salmon were not chronically stressed nor had a change in social status at the 10‐month time point in the semi‐natural stream tanks. Additionally, the Sebago population was better able to coexist with the non‐native salmonids than the LaHave population. Certain populations of Atlantic salmon may thus be more suitable for some environments of the juvenile stream phase for the reintroduction into Lake Ontario.     

Comparison of brown trout (Salmo trutta) reared in fresh water and sea water to freshwater rainbow trout (Oncorhynchus mykiss): II. Phosphorus balance

Brown trout and rainbow trout (average weight 100 g) were reared in fresh water at 12 °C under the same conditions before transferring brown trout to sea water, in order to compare phosphorus utilisation in both species. Apparent phosphorus availability, orthophosphate excretion and phosphorus accretion in the fish were directly determined. Thus, actual phosphorus mass balance was built. Rainbow trout raised in fresh water had a higher phosphorus retention coefficient (maximum 50 %) than brown trout reared in fresh water (maximum 45 %). Transferring brown trout to sea water induced a reduction in phosphorus retention (maximum 39 %). Orthophosphate excretion, ranging 7–20 mg phosphorus per kg wet weight per day, represented 10–20 % of ingested phosphorus. Phosphorus availability was lower in brown trout raised in sea water (65 %) than brown trout raised in fresh water (76 %). Phosphorus balance measurements showed that 90 to 98 % of phosphorus flow could be accounted for.