Competitive exclusion of brown trout Salmo trutta L., by rainbow trout Oncorhynchus mykiss Walbaum, in lake tributaries, New Zealand

Spawning runs of brown trout Salmo trutta L., and rainbow trout, Oncorhynchus mykiss Walbaum, were compared in three tributaries of two lakes for timing, numbers and redd characteristics. Redd characteristics for the two species in four other streams were examined. No significant differences in redd characteristics between the two species were observed, but in all lake tributaries the possibilities of superimposition of spring spawning rainbow trout on redds of brown trout were examined. A common feature was the high ratio of numbers of spawners to the area of preferred spawning gravel, and it was concluded that in the lake tributaries, superimposition resulted in increased mortality of brown trout eggs, and in one case elimination of the brown trout population. Management possibilities for control of the species proportions in comparable situations are discussed.     

Timing of brown trout spawning in Alpine rivers with special consideration of egg burial depth

Timing of spawning, habitat use and egg burial depths of brown trout were studied in seven Swiss (alpine and prealpine) rivers, which differed in size, altitude and flow regime. In general, we observed brown trout spawning activity between the end of October and the beginning of January. The spawning duration differed significantly, however, between rivers, ranging from 28 to 72 days. Analysis of environmental parameters for their influence on spawning activity revealed mean water temperature and altitude as the most explanatory variables. Detailed investigation of redd characteristics based on water velocity, water depth and substrate size clearly showed differences between positions on the redd. Brown trout in Alpine rivers preferred to use velocities of 30–40 cm·s^?1, water depths of 10–20 cm and substrates of 16–32 mm for spawning. It has to be noted, however, that recorded values cover almost the whole range of data on spawning habitats that has been reported in literature so far. A special focus of this study was on egg burial depths, which were surprisingly not found to differ significantly between the rivers despite their different flow regimes. Recorded egg burial depths were, however, found to be distinctly lower (mean burial depth: 3.8 cm) than reported by almost any study so far. We see this observation of low burial depths in Alpine rivers as useful in the context of scouring effects, especially when evaluating the influence of scouring on fish populations.     

Factors affecting habitat selection by a small spawning charr population, bull trout, Salvelinus confluentus: implications for recovery of an endangered species

Bull trout, Salvelinus confluentus (Suckley), populations are declining in many streams of North America and are listed under the Endangered Species Act in the United States. Many small populations are isolated in fragmented habitats where spawning conditions and success are not well understood. Factors affecting habitats selected for redds by spawning bull trout and redd habitat characteristics within Gold Creek, a headwater stream in the Yakima River within the Columbia River basin, Washington State, USA, were evaluated. Most spawning (>80% of the redds) occurred in upstream habitats after dewatering of downstream channels isolated fish. Habitats were selected or avoided in proportions different to their availability. For example, most bull trout selected pools and glides and avoided riffles despite the latter being more readily available. Although preferences suggest influences of prolonged fish entrapment, site fidelity could be important. A habitat with redds commonly contained abundant cover, gravel substratum and higher stream flows. The major factors influencing habitat selection by spawning fish and their persistence in streams of the Yakima and Columbia River regions include entrapment of fish by dewatering of channels and geographical isolation by dams. The goal of the US Government's recovery plan is ‘to ensure the long‐term persistence of self‐sustaining bull trout populations’. Recovery plans linked to provisions for protecting and conserving bull trout populations and their habitats were recommended. Landscape approaches are needed that provide networks of refuge habitats and greater connectivity between populations. Concurrent recovery efforts are encouraged to focus on protecting small populations and minimizing dangers of hybridization.     

Brown trout redd superimposition in relation to spawning habitat availability

Abstract – The relationship between redd superimposition and spawning habitat availability was investigated in the brown trout (Salmo trutta L.) population inhabiting the river Castril (Granada, Spain). Redd surveys were conducted in 24 river sections to estimate the rate of redd superimposition. Used and available microhabitat was evaluated to compute the suitable spawning habitat (SSH) for brown trout. After analysing the microhabitat characteristics positively selected by females, SSH was defined as an area that met all the following five requirements: water depth between 10 and 50 cm, mean water velocity between 30 and 60 cm s^?1, bottom water velocity between 15 and 60 cm s^?1, substrate size between 4 and 30 mm and no embeddedness. Simple regression analyses showed that redd superimposition was not correlated with redd numbers, SSH or redd density. A simulation‐based analysis was performed to estimate the superimposition rate if redds were randomly placed inside the SSH. This analysis revealed that the observed superimposition rate was higher than expected in 23 of 24 instances, this difference being significant (P < 0.05) in eight instances and right at the limit of statistical significance (P = 0.05) in another eight instances. Redd superimposition was high in sections with high redd density. High superimposition however was not exclusive to sections with high redd density and was found in moderate‐ and low‐redd‐density sections. This suggests that factors other than habitat availability are also responsible for redd superimposition. We argue that female preference for spawning over previously excavated redds may be the most likely explanation for high superimposition at lower densities.     

Brook trout spawning areas in lakes

Abstract— Nine lakes containing self-sustaining populations of brook trout ( Salvelinus fontinalis ) were surveyed to provide quantitative information on the abundance and distribution of redd sites. We measured rates of groundwater flow at redds in four of these lakes, and in one of these lakes we also compared the frequency of site use over four years from spawning observations. The number of redd sites in each lake ranged from 1 to 53 (mean=30) with most found relatively close to shore (∼ 1 m deep). Spawning areas per lake (16.9–829.4 m²) were not related to lake size and were often not continuous areas of littoral zone habitat. Rates of groundwater flow in lakes, averaged across redd sites in each lake, ranged from 20.0 to 107.9 ml. m.⁻² min^−1. The intensive survey of redd site use in one lake demonstrated that only 11% of sites (10 of 92) were used in all four years of observation. The mean rates of groundwater flow at sites used in all four years were significantly greater than at sites used intermittently. Data from this and other studies point to the conservation of subcatchments associated with groundwater discharge areas used by spawning brook trout as a means of maintaining self-sustaining populations.     

The effects of flow on Atlantic salmon (Salmo salar) redd distribution in a UK chalk stream between 1980 and 2015

Atlantic salmon are an ecologically and economically important migratory fish in the UK, whose stocks have been declining over the past 30 years. Future climate and water use changes have the potential to alter the reproductive behaviour and distribution of salmon within a river, by restricting times and ability to access suitable spawning areas. As the survival of emergent salmon juveniles is density dependent, understanding how climate‐driven changes in flow affect the location of salmon redds is important for future conservation efforts. This study examined how flow conditions affect the distribution of redds within a UK chalk stream, the river Frome in Dorset. Sixteen years of redd distribution and flow data between 1980 and 2015 were analysed using linear mixed‐effects modelling. Generally, highest redd densities occurred within middle reaches of the main river. Mean flow during the river Frome critical migration period (October–December) did not affect the density of redds directly but affected the relationship between redd density and distance from tidal limit: redd densities were spread more uniformly throughout the river under high flow conditions, whereas redds were more aggregated in the middle river reaches under low flow conditions. Together, these findings suggest that access to upstream spawning grounds was limited under low flow conditions, which could have negative repercussions on juvenile survival. This study has revealed the distribution of redds along the river Frome for the first time and provided a basis for further study into the effects of redd distribution on subsequent juvenile life stages.     

Competitive interactions between native and exotic salmonids: a combined field and laboratory demonstration

Abstract –  We studied the impact of two exotic salmonid species (brook trout, Salvelinus fontinalis and rainbow trout, Oncorhynchus mykiss ) on native brown trout ( Salmo trutta fario ) habitat, growth and survival. Habitat selection and vertical distribution between young-of-the-year of the three species were examined in a stream aquarium under different sympatric and allopatric combinations. In addition, similar species combinations were introduced in a Pyrenean mountain stream (southwest France) in order to extend laboratory results to growth and apparent survival. Both laboratory and field results indicated that rainbow trout significantly affected native brown trout habitat selection and apparent survival. On the contrary, brown trout habitat, growth and apparent survival were hardly affected by brook trout. These results support the idea that rainbow trout negatively influence native brown trout, and that competition could influence the outcome of fish biological invasions in freshwater ecosystems.     

Spawning period of a southern brown trout population in a highly unpredictable stream

Abstract –  The spawning period of brown trout ( Salmo trutta L.) was studied in the river Castril, southern Spain, by means of redd counts. This mountain stream is located near to the southern limit of the species' natural distribution range and it shows a highly unpredictable flow regime. The spawning period extended from December to mid-April and the maximum reproductive activity was in February. These results represent the latest reproduction date and the longest spawning period reported in the literature along the natural distribution range of the species. However, belated spawning in the Castril is congruent with the known latitudinal cline: the lower the latitude, the later the spawning period. Our results, along with a review of the literature on natural populations, also showed that the duration of reproduction is the longer, the lower the latitude. Spawning lasted twice as long in the main stem of the river, which is connected with a reservoir, than in the isolated reaches. These differences may be linked to the influence of the reservoir and to habitat fragmentation. We discuss and support the hypothesis that a long spawning period is an advantage for survival in unpredictable habitats. The belated and protracted spawning period found in river Castril has important implications in fisheries management. A strong research effort is needed in order to fill the critical lack of data on southern brown trout populations.     

Composition and location of simulated lake-shore redds influence incubation success in kokanee, Oncorhynchus nerka

Abstract  Methods for improving spawning habitat for lakeshore spawning kokanee, Oncorhynchus nerka (Walbaum), were explored by quantifying incubation success of embryos exposed to three substrate treatments in Lake Pend Oreille, Idaho, USA. Substrate treatments included no modification that used existing gravels in the lake (EXISTING), a cleaned substrate treatment where existing gravels were sifted in the water column to remove silt (CLEANED) and the addition of new, silt-free gravel (ADDED). Incubation success was evaluated using Whitlock–Vibert incubation boxes buried within each substrate treatment that contained recently fertilised embryos. Upon retrieval, live and dead sac fry and eyed eggs were enumerated to determine incubation success (sac fry and eyed eggs × 100/number of fertilised embryos). Incubation success varied significantly among locations and redd treatments. In general, incubation success among ADDED redds (0.0–13.0%) was significantly lower than that for EXISTING (1.4–61.0%) and CLEANED (0.4–62.5%) redds. Adding new gravel to spawning areas changed the morphometry of the gravel-water interface and probably exposed embryos to disturbance from wave action and reduced embryo survival. Moreover, efforts to improve spawning habitat for lakeshore spawning kokanee should consider water depth and location (e.g. protected shorelines) as important variables. Adding clean gravel to existing spawning areas may provide little benefit if water depth or lake-bottom morphometry are altered.     

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.     

Relationship between stream temperature, thermal refugia and rainbow trout Oncorhynchus mykiss abundance in arid-land streams in the northwestern United States

Abstract – Warm stream temperatures may effectively limit the distribution and abundance of Pacific salmon Oncorhynchus spp. in streams. The role of cold thermal refugia created by upwelling groundwater in mediating this effect has been hypothesized but not quantitatively described. Between June 21 and September 15, 1994, rainbow trout O. mykiss abundance within 12 northeast Oregon (USA) stream reaches was inversely correlated with mean ambient maximum stream temperatures ( r =−0.7, P <0.05). Some rainbow trout used thermal refugia (1–10 m² surface area) that were on average 3–8°C colder than ambient stream temperatures. Within the warmest reaches, high ambient stream temperatures (>22°C) persisted from mid-June through August, and on average 10–40% of rainbow trout were observed within thermal refugia during periods of midday maximum stream temperatures. Frequency of cold-water patches within reaches was not significantly associated with rainbow trout density after accounting for the influence of ambient stream temperature ( P =0.06; extra sum of squares F -test). Given prolonged high ambient stream temperatures in some reaches, the thermal refugia available in the streams we examined may be too small and too infrequent to sustain high densities of rainbow trout. However, these refugia could allow some rainbow trout to persist, although at low densities, in warm stream reaches.     

Increasing experimental approaches in stream trout research – 1987–2006

Abstract –  This review of stream trout research literature for the 1987–2006 period covered >1300 papers dealing with 22 relevant topics, when compared with <400 papers on 18 topics in the previous one (1967–1986). The percentage of experimental approaches here quantified for both research reviews was 18% in the 1967–1976 period, increased to 21% in 1977–1986, to 39% in 1987–1996, and up to 43% in 1997–2006. Particular journals in the recent two decadal period published high percentages of experimental papers ( The Journal of Animal Ecology and Canadian Journal of Fisheries and Aquatic Sciences ; 62.9% and 62.4%, respectively), others, intermediate percentages ( Nordic Journal of Fisheries Research , Transactions of the American Fisheries Society , North American Journal of Fisheries Management and Ecology of Freshwater Fish : 44.1%, 42.4%, 40.5%, and 35.6%, respectively); the remainder covered ≤33%. Research papers on stream 'trouts' published over the last two decades were classified into 22 subject areas for nine major journals separately and combined for 55 other journals. Subject areas dealing with the biology and ecology of trout redds, egg development, alevin emergence and onto fry and parr were the most heavily reported in nine major journals, as well as in all other journals combined. Habitat characteristics and cover use by trout were the next. Atlantic salmon and brown trout were the species with highest publication coverage in nearly all subject areas, with low coverage for all salvelinid (charr) species except brook charr. Research on Atlantic salmon in the UK used experimental approaches in nearly 60% of publications and in mid to high 30% for those on Atlantic salmon and brown trout in Scandinavian countries. Consideration is given to future research needs for stream trouts.     

Spawning salmon increase brook trout movements in a Lake Michigan tributary

Abstract – Salmon and trout have been introduced to many ecosystems worldwide, yet the ecological impacts of salmonid introductions remain poorly understood. We investigated the effects of introduced Pacific salmon on stream‐resident fish in the Great Lakes basin by monitoring the movements of passive integrative transponder (PIT)‐tagged brook trout in a Lake Michigan tributary receiving a salmon spawning run and in a nearby stream not receiving salmon. Coincident with the September arrival of salmon, an estimated 52% of resident brook trout moved >200 m, while no such movements were detected in the nonsalmon stream. After 3–4 days, however, brook trout movement patterns became similar in the two streams, suggesting that salmon effects on brook trout movements were short‐lived. Movements in the salmon stream were predominantly upstream in direction, with 50% of the tagged brook trout travelling from below to above the stationary PIT tag readers during the study. Declining water temperatures with the onset of fall coincided with low levels of brook trout movement at both sites, likely due to relocation for spawning. Increased brook trout movements coincident with the arrival of salmon spawners could be driven by a combination of interference competition and egg consumption. Using a bioenergetics model, we estimated that the energy lost to movement was likely compensated by the energy obtained from consuming salmon eggs. We conclude that salmon spawners can substantially increase brook trout movement, but in our study, these effects were short‐lived and likely negligible from a bioenergetics perspective.     

Habitat suitability analysis for lacustrine brown trout (Salmo trutta) in Lake Walchensee,Germany: implications for the conservation of an endangered flagship species

• 1. The lacustrine brown trout (Salmo trutta) is endangered and of high conservation importance. In the only spawning habitat of the population in the Bavarian Lake Walchensee, the River Obernach, a substantial decrease in spawning runs has been reported. In this study, the present ecological state of the spawning stream was analysed with the objective of identifying life‐stage specific limitations to successful recruitment attributable to deficiencies in (i) spawning migration, (ii) spawning habitat quality, and (iii) habitat quality for juveniles.
• 2. Structural stream analysis showed that discharge and several migration barriers — particularly near the river outlet into the lake — prevent successful spawning migrations at normal water levels. Migration barriers are probably the main limiting factor for reproduction of lacustrine brown trout, whereas structural variability of the Obernach meets the habitat requirements of both spawners and juveniles.
• 3. Spawning site quality was suitable for trout, as indicated by stream substratum texture and high exchange rates between free‐flowing water and the interstitial zone in physico‐chemical parameters (redox potential, dissolved oxygen, pH, temperature and conductivity).
• 4. Analyses of fish community structure revealed dominance of lithophilic species, in particular of riverine brown trout (Salmo trutta). Its density and intact demographic population structure suggest that spawning and juvenile habitat quality for salmonids is not limiting. Recapture of stocked lacustrine trout juveniles also indicates habitat suitability for the juvenile stage.
• 5. In conclusion, the results show that the methodology used in this study is suitable for the identification of life‐stage specific habitat deficiencies in lacustrine brown trout and other fish species. Availability of habitat data throughout the species' distribution range is a first crucial step for the development of an effective recovery plan. Copyright © 2009 John Wiley & Sons, Ltd.

     

Temporal segregation in spawning between native Yellowstone cutthroat trout and introduced rainbow trout

Hybridisation with introduced taxa poses a threat to native fish populations. Mechanisms of reproductive isolation can limit or prevent hybridisation between closely related species. Understanding how these mechanisms interact between the same species across geographically distinct occurrences of secondary contact, and how regional factors influence them, can inform our understanding of hybridisation as a threat and management actions to mitigate this threat. We used data collected on adult fish migration timing and approximate emergence timing of subsequent juvenile fish paired with genomic data to assess whether temporal isolation in the timing of spawning exists between Yellowstone cutthroat trout, rainbow trout and hybrids in the North Fork Shoshone River drainage in northwest Wyoming. We found evidence that Yellowstone cutthroat trout spawn, on average, two to four weeks later than rainbow trout and hybrids and two environmental covariates related to water temperature and discharge were associated with differences in spawning migration timing. Despite statistical support for Yellowstone cutthroat trout spawning later, disproportionately high numbers of rainbow trout and hybrids, paired with extended spawning seasons, lead to substantial overlap between all genotypes. Our results provide further evidence of temporal segregation in the timing of spawning as a mechanism of reproductive isolation between closely related species, but substantial spawning overlap suggests temporal segregation alone will not be enough to curtail hybridisation in conservation populations.     

Thermal regime in the hyporheic zone of two contrasting salmonid spawning streams: ecological and hydrological implications

The temperatures of stream water and hyporheic water were monitored in spawning areas of an upland stream (Girnock Burn) and a degraded lowland stream (Newmills Burn). Both streams are located in North-east Scotland and are spawning streams for Atlantic salmon, Salmo salar L., and brown trout, S. trutta L. Monitoring between the spawning and hatching of ova revealed significant differences in the thermal regimes of the two sites. Whilst temperatures in stream and hyporheic water were similar in the Girnock, notable attenuation in the Newmills Burn resulted in increasing moderation of thermal regime with hyporheic depth. This probably reflects contrasting groundwater–surface water interactions in the two systems. In the Girnock an open gravel stream bed and lack of groundwater influence resulted in stream water downwelling through the gravel. In contrast, fine bed sediments and local groundwater inputs resulted in more complex stratification of temperatures in Newmills Burn. However, even in the conditions of the Newmills Burn, temperature based salmonid embryo development models predicted that egg burial depth has an insubstantial effect on ova development.     

五种鱼类卵黄蛋白等电点特性分析

运用IFE-PAGE电泳技术,对施氏鲟(Acipenser schrencki Amur sturgeon)、小体鲟(Acipenser ruthenus Linnaeus)、西伯利亚鲟(Acipenser baeri Siberian sturgeon)、哲罗鲑(Huchotaimen Taimen)和虹鳟(Oncorhynchus mykissgo Lden rainbow trout)5种鱼类卵黄蛋白等电点的特性进行研究,建立了比较成熟的测定卵黄蛋白等电点的实验方法。5种鱼类卵黄蛋白等电聚焦电泳图谱都为3条带,表明5种鱼都是由3种卵黄蛋白组成,哲罗鲑和虹鳟卵黄蛋白都属于酸性类型,与鲟形目这3种鱼卵黄蛋白等电点差别较大。     

The effect of short-term starvation on ovarian development and egg viability in rainbow trout (Salmo gairdneri)

Adult female rainbow trout (Salmo gairdneri) were fed a commercial trout production diet until approximately 40 days prior to spawning at which time the fish were divided in two groups. One group continued to be fed while the other group was starved until spawning. Egg size, egg number, ovary weight, and egg proximate composition were examined periodically starting 5 months before spawning. Muscle tissues of the fish were sampled at spawning to measure somatic depletion of proximate consituents in the two groups. Egg hatchability was determined by incubating test lots from each spawning female. No significant differences (P > 0.05) were found in egg hatchability between the fed and starved groups. Changes in proximate composition were observed in the eggs during the months prior to spawning, but no differences were detected between the eggs of the starved and the fed groups. Short-term starvation did not significantly alter the proximate composition of muscle tissue of the spawned female trout.     

Seasonal stream habitat of adult Sakhalin taimen,Parahucho perryi,in the Bekanbeushi River system,eastern Hokkaido,Japan

Behavioural tracking of endangered adult Sakhalin taimen (Parahucho perryi) by acoustic telemetry was conducted in the Bekanbeushi River system that flows through eastern Hokkaido in 2008–2010. A total of 39 tracked P. perryi showed extensive use of the river system, both upstream and downstream, regardless of the month or year. No tracked adult P. perryi stayed in the ocean for more than 1 day. Some of the fish (20%) dwelled in upstream habitat consistently from spring to autumn, while 40% of individuals showed wide utilisation of the entire upstream and downstream systems. Although 39.4% of tracked fish utilised two or more primary tributaries to the main river, 6.1% used only the main river system. Distinct variability was observed between individuals based on the proportion of time spent in each stream reach (up‐, mid‐, and downstream). A trend was observed in 2008 and 2010 showing that tracked fish moved to the upper stream reaches when water temperatures downstream increased. This trend was not observed in 2009 when the summer water temperature downstream was more than 2 °C below average when compared to 2008 and 2010. Our results suggest that adult P. perryi in the Bekanbeushi River system exhibit high behavioural plasticity, that is, the fish can select habitats based on their own individual requirements. Our results also demonstrate the importance of physical continuity among river reaches both upstream and downstream such that P. perryi does not experience barriers in moving to optimal habitats.     

Influence of European sculpin, Cottus gobio, on Atlantic salmon Salmo salar, recruitment and the effect of gravel size on egg predation – implications for spawning habitat restoration

Abstract  The study examined if recruitment of juvenile Atlantic salmon, Salmo salar L., was influenced by the presence of European sculpin, Cottus gobio L., and if the spawning substrate size used by salmon influences sculpin predation on salmon eggs. A combination of information on spawning site selection by female salmon and associated densities of juvenile salmon indicated that recruitment of juvenile salmon was 10 times lower in areas where sculpin was present than areas without sculpin. Predation rate on salmon eggs was found to be dependent on substrate size in artificial redds created in stream aquaria using four different sizes of substrate (13, 23, 37 and 62 mm). Predation rate averaged 83% in the aquaria with the largest substrate size, whereas a rate of only 2–3% was observed using smaller substrate sizes. Sculpin may thus be an important factor influencing the recruitment of juvenile salmon. Selecting small enough gravel sizes during restoration of salmon spawning habitat could therefore be important to minimise egg predation.