Polymorphic mountain whitefish (Prosopium williamsoni) in a coastal riverscape: size class assemblages,distribution, and habitat associations

We compared the assemblage structure, spatial distributions, and habitat associations of mountain whitefish (Prosopium williamsoni) morphotypes and size classes. We hypothesised that morphotypes would have different spatial distributions and would be associated with different habitat features based on feeding behaviour and diet. Spatially continuous sampling was conducted over a broad extent (29 km) in the Calawah River, WA (USA). Whitefish were enumerated via snorkelling in three size classes: small (10–29 cm), medium (30–49 cm), and large (≥50 cm). We identified morphotypes based on head and snout morphology: a pinocchio form that had an elongated snout and a normal form with a blunted snout. Large size classes of both morphotypes were distributed downstream of small and medium size classes, and normal whitefish were distributed downstream of pinocchio whitefish. Ordination of whitefish assemblages with nonmetric multidimensional scaling revealed that normal whitefish size classes were associated with higher gradient and depth, whereas pinocchio whitefish size classes were positively associated with pool area, distance upstream, and depth. Reach‐scale generalised additive models indicated that normal whitefish relative density was associated with larger substrate size in downstream reaches (R² = 0.64), and pinocchio whitefish were associated with greater stream depth in the reaches farther upstream (R² = 0.87). These results suggest broad‐scale spatial segregation (1–10 km), particularly between larger and more phenotypically extreme individuals. These results provide the first perspective on spatial distributions and habitat relationships of polymorphic mountain whitefish.     

Behaviour and physiology of mountain whitefish ( Prosopium williamsoni) relative to short‐term changes in river flow

Despite the growing recognition that river flow can have an effect on the growth, distribution and survival of fishes, little is known about the underlying mechanisms to explain this effect. Furthermore, there are few examples of integrated measures of behaviour and physiology to study the responses of fish to river hydrology. Here, axial swimming muscle electromyograms were logged as a sensitive indicator of activity from 19 mountain whitefish ( Prosopium williamsoni) across a large range of hourly discharge magnitudes (mean = 621 m³·s^?1, range = 0–1770 m³·s^?1) in a hydropeaking reach of the Columbia River, Canada. Hourly mean discharge had a significant positive effect on swimming muscle activity. However, a large amount of the variance was unexplained, possibly due to social interactions, feeding and/or flow‐refuging behaviours. Fluctuating flows were no more energetically costly than stable flows. Discharge magnitude had a significant positive effect on blood cortisol concentrations. Yet, cortisol concentrations were low overall (mean ± SD = 1.60 ± 0.09 ng·ml^?1), suggesting that the small observed response could be the result of routine physiological processes rather than a stress response per se. Based on low blood lactate concentrations, mountain whitefish were not swimming exhaustively (i.e., anaerobic burst‐type swimming) at high flows.     

Movement patterns of seaward migrating European eel (Anguilla anguilla) at a complex of riverine barriers: implications for conservation

River infrastructure such as weirs and hydropower stations commonly present migrating fish with multiple potential passage routes. Knowledge of the cues fish use to navigate such environments is required to protect migrants from hazardous areas and guide them towards safe passage; however, this is currently lacking for many species. Employing high‐resolution positioning telemetry, this study examined movements of downstream migrating adult European eel, Anguilla anguilla, as they encountered a complex of water control structures in one location on the River Stour, southern England. The distribution of eels across five potential routes of passage differed from that predicted based on proportion of discharge alone. Certain routes were consistently avoided, even when the majority of flow passed through them. Passage distribution was partially explained by avoidance in the vicinity of a floating debris boom. Movement paths were nonrandomly distributed across the forebay and eels moved predominantly within a zone 2–4 m from the channel walls. Understanding of avoidance and structure oriented movementation exhibited by eels will help advance effective guidance and downstream passage solutions for adults.     

Consequences of connectivity alteration on riverine fish assemblages: potential opportunities to overcome constraints in applying conventional monitoring designs

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Spatial distribution patterns of fish egg and larval assemblages in the lower reach of the Yangtze River: Potential implications for conservation and management

1. River fish diversity is threatened by anthropogenic environmental alteration to landscapes. The early life-history stages of fish play an important role in maintaining diversity and population recruitment and can be heavily influenced by landscape patterns. Information on temporal and spatial distribution patterns of fish eggs and larvae is also important for biodiversity conservation and management of fish resources.
2. The Yangtze River possesses a high diversity of fishes, including many commercially important species. The economy along the lower reach of the river is well developed, and most of the area is experiencing high pressure from human impacts. This section of the Yangtze River connects with the largest freshwater lake in China at the upstream end and flows into the estuary at the downstream end. These two landscape features are likely to have a significant impact upon the spatial distributions of fish egg and larval assemblages.
3. Environmental variables, fish eggs, and larval assemblages were sampled in three locations, at Hukou, Anqing, and Jingjiang, in the lower reach of the Yangtze River. The results suggest that the higher number of species and greater abundance in upstream sites reflect the critical function of connectivity of Poyang Lake with the river for fish recruitment in the lower Yangtze. The delayed bloom of larval fish, occurrence of estuarine species, and a lower species number and abundance of freshwater fish downstream reflect the influence of tidal intrusion from the estuary.
4. This study highlights the value of maintaining natural river–lakes connectivity in the Yangtze River as a conservation measure. The connected river–lake system should be designated as a priority area for fish resource protection in the lower reach of the Yangtze River. We recommend further measures to break down barriers between the river and other lakes and to restore the natural lateral connectivity of the floodplain ecosystem.

     

Assemblage patterns of fish functional groups relative to habitat connectivity and conditions in floodplain lakes

Miyazono S, Aycock JN, Miranda LE, Tietjen TE. Assemblage patterns of fish functional groups relative to habitat connectivity and conditions in floodplain lakes.
Ecology of Freshwater Fish 2010: 19: 578–585. © 2010 John Wiley & Sons A/S Abstract – We evaluated the influences of habitat connectivity and local environmental factors on the distribution and abundance patterns of fish functional groups in 17 floodplain lakes in the Yazoo River Basin, USA. The results of univariate and multivariate analyses showed that species–environmental relationships varied with the functional groups. Species richness and assemblage structure of periodic strategists showed strong and positive correlations with habitat connectivity. Densities of most equilibrium and opportunistic strategists decreased with habitat connectivity. Densities of certain equilibrium and opportunistic strategists increased with turbidity. Forested wetlands around the lakes were positively related to the densities of periodic and equilibrium strategists. These results suggest that decreases in habitat connectivity, forested wetland buffers and water quality resulting from environmental manipulations may cause local extinction of certain fish taxa and accelerate the dominance of tolerant fishes in floodplain lakes.     

Consequence of habitat segregation to growth rate of two sparsely rakered whitefish (Coregonus lavaretus (L.)) forms in a subarctic lake

Abstract  – The aim of this study was to explain the growth differences of the two sympatric sparsely rakered whitefish ( Coregonus lavaretus (L.)) forms in the subarctic Lake Muddusjärvi by comparing their habitat and food selection to available benthic food resources. The average number of gillrakers was 22.9 for large sparsely rakered whitefish (LSR) and 16.8 for small sparsely rakered whitefish (SSR). LSR dwelled primarily in the littoral zone at depths < 10 m, whereas SSR used mostly profundal habitats in depths > 10 m. LSR and SSR consumed mainly benthic macroinvertebrates, their abundance, biomass and diversity was highest in the littoral, decreasing towards the profundal. As the individual size of fish increased, LSR was able to shift to larger food items, which were available in the littoral. Possibility of SSR to ontogenetic food shift was scarce in the profundal, where availability of larger benthic macroinvertebrates was low. Because of abundant food resources in the littoral, growth rate of LSR was faster than that of SSR.     

Movements of Murray cod (Maccullochella peelii peelii) in a large Australian lowland river

Abstract –  This study of Murray cod ( Maccullochella peelii peelii ) movements in a large lowland river in south-eastern Australia indicated that the species was not sedentary, but undertook complex movements that followed a seasonal pattern. While there were sedentary periods with limited home ranges and high site fidelity, Murray cod also under took larger movements for considerable portions of the year coinciding with its spawning schedule. This generally comprised movements (up to 130 km) from a home location in late winter and early spring to a new upstream position, followed by a rapid downstream migration typically back to the same river reach. Timing of movements was not synchronous amongst individuals and variation in the scale of movements was observed between individuals, fish size, original location and years.     

长江中游监利江段鱼卵及仔稚鱼时空分布

2010年5-7月对长江中游监利江段鱼卵和仔稚鱼的时空分布进行调查,共采集到鱼卵样品9494粒,仔稚鱼样品328422尾,分属8目15科43属51种.结果显示:5-7月鱼卵的平均密度为13.3 ind./100m3,最大密度值87.8 ind./100 m3,主要集中在5月;5-7月仔稚鱼平均密度为61.8 ind./...     

长江口日本鳗鲡苗的时空分布与捕捞生产现状

为掌握长江口日本鳗鲡的苗汛特征与捕捞生产现状,于2017—2020年在长江口开展了定点监测和走访调查,分析了长江口鳗苗的汛期规律、捕捞努力量及捕捞产量和产值。研究发现,长江口鳗苗旺发期为2-4月,主要捕捞区域分布在东旺沙、佘山岛和南汇嘴附近水域。长江口鳗苗捕捞努力量呈现下降趋势,有效网口面积从2017年的78.72万m²,下降到2020年的50.40万m²,下降了36%。长江口鳗苗汛期的单位捕捞努力量渔获量(CPUE)和总捕捞产量呈现波动变化趋势,2017和2020年较高,分别为(4 474±256)尾/100 m²和(5 220±1 063)尾/100 m²,2018和2019年较低,分别为(1 917±335)和(1 365±257)尾/100 m²。研究表明,长江口鳗苗生产值受到捕捞总产量影响,近4年来逐渐下降。建议进一步加强长江口鳗苗的资源监测和科学评估,指导规范鳗苗捕捞生产。     

Efficiency of a dual density studded fish pass designed to mitigate for impeded upstream passage of juvenile European eels (Anguilla anguilla) at a model Crump weir

This study demonstrated that juvenile (glass) eels used a specific substrate (eel tiles) to circumvent a model Crump weir under an experimental setting. Upstream passage efficiency was 0 and 67% for the unmodified (no studded eel tiles on the downstream face; control) and modified (with studded eel tiles on the downstream face; treatment) set‐ups, respectively, and was greater for a small (59%) compared to large (41%) stud configuration. Eels were active and motivated to ascend the weir during both control and treatment set‐ups. Approach and attempt rates were elevated during the first few minutes of the treatment compared to control trials. Eels were edge‐oriented under both set‐ups and ascended the weir through the tiles during single burst swimming events (reaching estimated speeds of 68.5 cm·s⁻¹). Eel tiles may provide a cost‐effective solution for mitigating impacts of anthropogenic barriers to juvenile eel migration. Further research is required to determine passage efficiencies under higher flows, for a greater size range of eel, and for other migratory anguilliform fish (e.g. lamprey, Lampretra spp. and Petromyzon marinus L.). The performance of eel tiles should be validated through robust field studies.     

Groundwater contribution to baseflow maintains habitat connectivity for Tandanus bostocki (Teleostei: Plotosidae) in a south‐western Australian river

Beatty SJ, Morgan DL, McAleer FJ, Ramsay AR. Groundwater contribution to baseflow maintains habitat connectivity for Tandanus bostocki (Teleostei: Plotosidae) in a south‐western Australian river.
Ecology of Freshwater Fish 2010: 19: 595–608. © 2010 John Wiley & Sons A/S Abstract – A global biodiversity hotspot, south‐western Australia is characterised by a highly endemic freshwater fish fauna that is severely impacted by habitat alterations. As is the case with many rivers in this region, the Blackwood River is secondarily salinised as a consequence of agricultural practices and this has caused population depletions of halo‐intolerant fishes. This study is the first to examine the role that groundwater intrusion has in maintaining habitat connectivity for an obligate freshwater fish in a secondarily salinised river. We determined the significance of nonsaline groundwater intrusion in maintaining habitat and migratory routes of the freshwater cobbler, Tandanus bostocki during prolonged annual dry periods; characteristic of Mediterranean climatic zones. Tandanus bostocki undertook large, yet spatially and temporally variable, localised movements through riffles. During baseflow, the period of major groundwater influence, movements were significantly associated with discharge. Analysis of gonadal development suggested that such movements were not strictly related to reproduction and were probably for foraging purposes. The study reveals groundwater is crucial in maintaining migratory routes through riffles and suggests T. bostocki may be reliably used as an indicator of aquatic habitat connectivity in light of groundwater extractions and also continued rainfall reductions in this region due to climate change.     

海州湾及邻近海域日本枪乌贼时空分布的异质性

根据海州湾及邻近海域2011、2013、2014和2015年春、秋两季渔业资源底拖网调查的资料,运用重心分布和空间变异函数等方法研究了日本枪乌贼(Loligo japonica)资源密度重心和个体大小分布的变化趋势及其时空分布的异质性。结果表明,日本枪乌贼在不同年份春季的平均胴长均比秋季大,且春季日本枪乌贼胴长的年间差异不显著(P0.05),而秋季除2011与2013年、2013与2015年胴长的年间差异不显著(P0.05)外,其他年间胴长存在显著性差异(P0.05);大、小个体日本枪乌贼空间分布的区域化差异不明显,春、秋季日本枪乌贼的优势胴长组均为20~50 mm;春、秋季日本枪乌贼的资源分布重心移动轨迹相反,在年际、季节间重心分布的差异不显著(P0.05);日本枪乌贼的资源密度在20~30 km的尺度范围内空间异质比小于75%,呈现中等或强烈的空间自相关,具有良好的空间结构性。对日本枪乌贼个体规格与资源密度时空异质性的研究,可为其渔业合理的开发管理提供科学依据。     

Migration and movement profiles of a potadromous fish (Brachymystax lenok Pallas 1773) in a highly connected river system (Mongolia)

Understanding a species’ spatial and temporal movements along with the way these shift under extreme environmental conditions is vital for developing scientifically sound conservation and management strategies. The aim of this research was to describe and quantify the seasonal migration patterns and fine‐scale movement profiles of Brachymystax lenok, a threatened, potadromous salmonid that inhabits the highly connected, boreal river basins of Siberia and northern Asia. During this study 21 mature individuals were monitored over a 15 month period in the upper Eroo River basin, Mongolia, using passive acoustic telemetry. Mean (±SD) B. lenok home ranges were 19.1 ± 15.1 km (median = 11.5 km), with maximum longitudinal movements detected > 45.3 km. Two periods of increased movements were identified; the first in late summer/early autumn when 10 B. lenok moved into deeper, overwintering pools, with the second period occurring in late spring and early summer when nine B. lenok were detected entering the surrounding tributaries. Diel activity and depth typically increased during daylight hours followed by decreased activity or resting periods in shallower river sections at night. These results highlight the need to maintain a high level of river connectivity and adequate fishing season closures by implementing and enforcing an expansive spatiotemporal management plan that can better protect and recover the Mongolian B. lenok populations. Such measures should be transferable to other threatened, potadromous fish species residing throughout the world's boreal river basins.     

Movement dynamics of smallmouth bass (Micropterus dolomieu) in a large river‐tributary system

Smallmouth bass, Micropterus dolomieu Lacepède, movement dynamics were investigated in a connected mainstem river‐tributary system. Smallmouth bass moved large distances annually (n = 84 fish, average = 24.6 ± 25.9 km, range = 0.03 to 118 km) and had three peak movement periods (pre‐spawn, post‐spawn and overwintering). Movement into and out of tributaries was common, but the movement between mainstem river and tributary habitats varied among tagging locations and season. In general, a large proportion of fish that were tagged in tributaries moved out of the tributaries after spawning (22/30 fish). Because of the importance of fish movement patterns on population dynamics, the observed individual variability in movement, quantified using a hierarchical model, and the potential for long‐distance movements are important considerations for smallmouth bass conservation and management. In addition, mainstem river‐tributary connectivity appears to play an important role for smallmouth bass during key life history events.     

Gene pool and connectivity patterns of Pinna nobilis in the Balearic Islands (Spain,Western Mediterranean Sea): Implications for its conservation through restocking

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2019年秋冬季南设得兰群岛南极磷虾集群时空分布特征

为了进一步研究南设得兰群岛附近海域南极磷虾集群时空分布特征,基于2019年秋冬季（4—7月）中国南极磷虾生产渔船声学调查及商业捕捞数据,从时空两个维度对南极磷虾集群中心深度、集群所处水深水温和集群形态进行了分析。结果显示,南设得兰群岛附近海域南极磷虾集群中心深度、集群所处水深水温和集群形态存在明显的时空差异。平均集群中心深度在4—7月总体呈递增趋势(变化范围为34.39～86.12 m),昼夜差异较小(P=0.325),峰值时段为日升阶段(sun rising, SRS)(64.06 m)和夜间(night, NIT)(65.32 m);平均集群中心深度低值区间为62.75°～63.75°S和58.25°～59.75°W,高值区间为61.75°～62.25°S和60.25°～61.75°W。平均集群所处水深水温在4—7月总体呈递减趋势(变化范围为-1.71～-1.50℃),昼夜集群水温差异明显,峰值时段为NIT(夜间)(-1.46℃)和暮光(evening twilight, ETW)(-1.4℃);平均集群所处水深水温低值区间为62.75°～63.75°S和61.25°～61.75°...     

Allometric and ontogenetic patterns related to feeding of a neotropical fish, Satanoperca pappaterra (Perciformes, Cichlidae)

Abstract –  This study aims to analyse whether Satanoperca pappaterra changes its feeding habit throughout ontogenetic development, and whether morphological ontogenetic patterns are related to its feeding habit and food capture. We collected 258 individuals in the Cuiabá river basin (Brazil) for analyses. There was a weak relationship between diet and body size, as evidenced by size class and multivariate analyses, and niche breadth did not vary strongly during ontogenetic development. Eight morphometric variables were measured in each individual. We found an isometric relationship for mouth height and width, and for head length. We found positive allometry for snout length and body height in relation to body length, whereas this relationship for intestine length and eye diameter showed negative allometry. These results suggest that morphology and consequently diet vary weakly during ontogenetic development of S. pappaterra .     

Invasive dynamics of the crayfish Procambarus clarkii (Girard, 1852) in the international section of the River Minho (NW of the Iberian Peninsula)

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A stochastic modelling approach to describing the dynamics of an experimental furunculosis epidemic in Chinook salmon, Oncorhynchus tshawytscha (Walbaum)

A susceptible-infected-removed (SIR) stochastic model was compared to a susceptible-latent-infectious-removed (SLIR) stochastic model in terms of describing and capturing the variation observed in replicated experimental furunculosis epidemics, caused by Aeromonas salmonicida. The epidemics had been created by releasing a single infectious fish into a group of susceptible fish (n = 43) and progress of the epidemic was observed for 10 days. This process was replicated in 70 independent groups. The two stochastic models were run 5000 times and after every run and every 100 runs, daily mean values of each compartment were compared to the observed data. Both models, the SIR model (R(2) = 0.91), and the SLIR model (R(2) = 0.90) were successful in predicting the number of fish in each category at each time point in the experimental data. Moreover, between-replicate variability in the stochastic model output was similar to between-replicate variability in the experimental data. Generally, there was little change in the goodness of fit (R(2)) after 200 runs in the SIR model whereas 500 runs were necessary to have stable predictions with the SLIR model. In the SIR model, on an individual replicate basis, approximately 80% of 5000 simulated replicates had R(2) = 0.7 and above, whereas this ratio was slightly higher (82%) with the SLIR model. In brief, both models were equally effective in predicting the observed data and its variance but the SLIR model was advantageous because it differentiated the latent, i.e. infected but not having the ability to discharge pathogen, from the infectious fish.