Water levels in a highland lake control the quantity and quality of spawning habitat for a littoral‐spawning galaxiid fish

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Fine‐scale acoustic telemetry reveals unexpected lake trout,Salvelinus namaycush,spawning habitats in northern Lake Huron,North America

Previous studies of lake trout, Salvelinus namaycush, spawning habitat in the Laurentian Great Lakes have used time‐ and labour‐intensive survey methods and have focused on areas with historic observations of spawning aggregations and on habitats prejudged by researchers to be suitable for spawning. As an alternative, we used fine‐scale acoustic telemetry to locate, describe and compare lake trout spawning habitats. Adult lake trout were implanted with acoustic transmitters and tracked during five consecutive spawning seasons in a 19–27 km² region of the Drummond Island Refuge, Lake Huron, using the VEMCO Positioning System. Acoustic telemetry revealed discrete areas of aggregation on at least five reefs in the study area, subsequently confirmed by divers to contain deposited eggs. Notably, several identified spawning sites would likely not have been discovered using traditional methods because either they were too small and obscure to stand out on a bathymetric map or because they did not conform to the conceptual model of spawning habitat held by many biologists. Our most unique observation was egg deposition in gravel and rubble substrates located at the base of and beneath overhanging edges of large boulders. Spawning sites typically comprised <10% of the reef area and were used consistently over the 5‐year study. Evaluation of habitat selection from the perspective of fish behaviour through use of acoustic transmitters offers potential to expand current conceptual models of critical spawning habitat.     

Genetic persistence of an initially introduced brown trout (Salmo trutta L.) population despite restocking of foreign conspecifics

The persistence of the initial genetic structure despite later stocking with foreign conspecifics is influenced by several factors, leading to different levels of introgression. Stream spawning has been assumed to be the prevailing recruitment strategy of brown trout (Salmo trutta L.). However, in lakes with limited stream spawning habitat, but still with high natural recruitment, lake spawning has been proposed. Using fourteen microsatellites, we assessed the genetic structure in a small allopatric brown trout population in the Lake Skavatn, located on the Hardangervidda mountain plateau, Norway. A total of 265 brown trout were obtained from the lake itself, the outlet stream, two tributaries, a littoral sample from a presumed lake spawning site, a suggested stocking source, and a lake sample from 1967, representing the initial lake population. The six Skavatn samples were best represented by three genetic components, showing a shift from the initial population, but with no genetic signal from the suggested stocking source. The littoral sample had the largest similarity to the initial lake population, possibly indicating the importance of lake spawning in a system where streams offer unpredictable spawning and rearing conditions. Due to large annual variations in recruitment contributions from the different spawning and rearing locations, the genetic structure of the lake population probably vary over time.     

物理栖息地模型在中华鲟自然繁殖生态流量决策中的应用

以国家一级保护物种中华鲟(Acipenser sinensis)为研究对象,探讨三峡大坝和葛洲坝水利工程在不同流量调度措施下对中华鲟产卵栖息地的影响。通过考虑中华鲟生境需求特性建立了中华鲟产卵场的物理栖息地模型,根据模型得出的适宜栖息地面积变化来量化不同的流量调度措施对其产卵场质量的影响,然后利用实测的中华鲟产卵量和资源量数据来验证和评价物理栖息地模型的可靠性和实用性,从而进行合理的生态流量决策。结果发现,年平均适宜栖息地面积的变化曲线与中华鲟的产卵量和资源量变化曲线有着相同的变化趋势,从而推断适宜栖息地面积可以反映中华鲟产卵栖息地的质量;并通过不同流量工况的计算,进行最佳生态流量决策。利用该物理栖息地模型可以有效地量化流量改变对目标物种栖息地质量的影响,为中华鲟产卵栖息地的生态水利调度提供评估和决策的方法。     

2023年三峡水库生态调度对四大家鱼生境面积影响研究

2023年5月27日至6月3日，三峡水库开展了针对葛洲坝下游四大家鱼自然繁殖的生态调度试验，为量化此次生态调度对四大家鱼生境面积影响，以葛洲坝至枝江江段为研究区域，选择水位变幅、水深、流速、水温4个主要生境因子，建立了耦合平面二维水动力学模型和产卵栖息地适宜度曲线的四大家鱼产卵生境质量评估模型，实现了产卵综合适宜度指数的时空分布的精细化模拟。结果表明：生态调度期间，研究区域四大家鱼产卵综合适宜度指数呈现稳定增加趋势，四大家鱼产卵加权可利用面积占研究区域总面积比例由30.45%增加至约55%；适宜四大家鱼产卵区域（产卵综合适宜度指数在0.6～1.0范围）明显增加，占研究区域总面积比例由4.67%增加至约60%。2023年三峡水库生态调度显著改善了葛洲坝至枝江江段四大家鱼产卵生境质量。     

Diel habitat selection of largemouth bass following woody structure installation in Table Rock Lake,Missouri

Largemouth bass Micropterus salmoides (Lacepède) use of installed habitat structure was evaluated in a large Midwestern USA reservoir to determine whether or not these structures were used in similar proportion to natural habitats. Seventy largemouth bass (>380 mm total length) were surgically implanted with radio transmitters and a subset was relocated monthly during day and night for one year. The top habitat selection models (based on Akaike's information criterion) suggest largemouth bass select 2–4 m depths during night and 4–7 m during day, whereas littoral structure selection was similar across diel periods. Largemouth bass selected boat docks at twice the rate of other structures. Installed woody structure was selected at similar rates to naturally occurring complex woody structure, whereas both were selected at a higher rate than simple woody structure. The results suggest the addition of woody structure may concentrate largemouth bass and mitigate the loss of woody habitat in a large reservoir.     

Potential for reintroduction of lake sturgeon in five northern Lake Michigan tributaries: a habitat suitability perspective

• 1. Conservation and rehabilitation efforts for lake sturgeon Acipenser fulvescens throughout the Great Lakes include the re‐establishment of self‐sustaining stocks in systems where they have been extirpated.
• 2. Information on the suitability of potential lake sturgeon habitat in tributaries is important for determining their capacity to support lake sturgeon stocking and to develop system‐specific rehabilitation strategies.
• 3. Geo‐referenced habitat information characterizing substrate composition, water depth, and stream gradient were applied to a life‐stage specific lake sturgeon habitat suitability index in a geographic information system to produce spatially explicit models of life‐stage specific habitat characteristics in five northern Lake Michigan tributaries from which lake sturgeon have been extirpated.
• 4. Habitat models indicated that high quality lake sturgeon spawning and staging habitat comprised 0 to 23% and 0 to 9% of the available habitat, respectively, whereas high quality juvenile lake sturgeon habitat was relatively ubiquitous throughout each river and comprised 39 to 99%.
• 5. Comparison of these data to lake sturgeon habitat availability in Lake Michigan tributaries currently supporting populations indicated that spawning and staging habitats may limit the ability of these systems to support spawning. Efforts to re‐establish lake sturgeon populations in these systems should consider the creation of spawning and staging habitat to increase reproductive and recruitment potential prior to the initiation of stocking efforts.

Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

Islands in the ice stream: were spawning habitats for native salmonids in the Great Lakes created by paleo‐ice streams?

Lake trout Salvelinus namaycush, lake whitefish Coregonus clupeaformis and cisco Coregonus artedi are salmonid fishes native to the Laurentian Great Lakes that spawn on rocky substrates in the fall and early winter. After comparing the locations of spawning habitat for these species in the main basin of Lake Huron with surficial substrates and the hypothesized locations of fast‐flowing Late Wisconsinan paleo‐ice streams, we hypothesize that much of the spawning habitat for these species in Lake Huron is the result of deposition and erosion by paleo‐ice streams. This hypothesis may represent a new framework for the identification and protection of spawning habitat for these native species, some of which are currently rare or extirpated in some of the Great Lakes. We further suggest that paleo‐ice streams may have been responsible for the creation of native salmonid spawning habitat elsewhere in the Great Lakes and in other glaciated landscapes.     

The Spawning of Perch (Perca fluviatilis L.) in Loch Leven, Kinross, Scotland

Investigations were carried out in 1979 and 1980 into the location of spawning grounds of perch in Loch Leven, the comparative intensity of their use and the duration of the spawning period. Spawning was found to take place in depths of 1–5 m and there was an indication that depths around 3 m are preferred. Silt and mud apparently inhibit spawning on exposed shores down to 2.5 m although natural shelter probably ameliorates this. Macrophytic vegetation is rarely present at the preferred depths, therefore, artefacts and artificial substrates must be most frequently used. Spawning started about 25 April in a ‘mild’ spring and about 9 May in a ‘cold’ spring. The duration of the spawning period was 4–5 weeks. A double peak in spawning intensity was found in 1979 and, if valid, could indicate a division of spawning fish into two groups, possibly by age as the peaks were not associated with the location of spawning sites. Although spawning tended to be more intense on the southern shore and around one of the islands almost any part of the loch down to 5 m may be used.     

Egg drift and hatching success in European river lamprey Lampetra fluviatilis: is egg deposition in gravel vital to spawning success?

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Habitat distribution of fish in late summer: changes along a nutrient gradient in Danish lakes

Abstract – The horizontal distribution of fish in lakes varies with species, age, predation risk, vegetation coverage and water clarity. Although sporadic data are available for specific lakes, little is known about how habitat distribution generally changes along a gradient in nutrients and clarity. Here we analyse littoral and pelagic fish catch data for 34 Danish lakes (covering 94 lake years) with contrasting total phosphorus (TP) concentrations and mean depth levels (but mainly eutrophic and shallow). Electrofishing was conducted during day along the shore or along the edge of the reed belt if such existed. Gill nets were set overnight for 18 h in open water. We calculated a littoral proportion as: LITPRO = (100 × number caught by electrofishing in the near‐shore area)/(number caught by electrofishing in the near‐shore area and nets in the open water). At all summer TP concentrations LITPRO was high for several ‘littoral’ species such as gudgeon (Gobio gobio), rudd (Scardinius erythrophtalmus) and pike (Esox lucius) and low for more typical pelagic species like pikeperch (Sander lucioperca), ruffe (Gymnocephalus cernuus) and smelt (Osmerus eperlanus). However, for many of these species including the dominant roach (Rutilus rutilus) and perch (Perca fluviatilis) LITPRO increased with TP or lake water chlorophyll a (CHLA) for fish >10 cm, suggesting a more littoral distribution with increasing turbidity. Exceptions are pikeperch and bream (Abramis brama). For bream, LITPRO increased significantly with mean lake depth only. For fish ≤10 cm LITPRO showed only a weak relationship to TP, CHLA or depth. In accordance with the TP‐dependent distribution, major changes occurred in the fish community structure during the monitoring period following nutrient loading reduction. A comparison of LITPRO from the first part of the monitoring period (1989–1993) with a subsequent period (1997–2003) for four abundant species showed a significant decline in LITPRO over time for large‐ and small‐sized roach and perch and large rudd. This suggests a fast response in fish distribution to improved water quality. It further demonstrates that fish monitoring in lakes should cover both littoral and pelagic habitats to describe the recovery process.     

Habitats across the life cycle of hilsa shad (Tenualosa ilisha) in aquatic ecosystem of Bangladesh

Aquatic habitat connectivity is vital for the continued existence of migratory fish. Using GIS and outranking multicriteria analysis based on hydrometeorological data, this study describes habitat preference of egg, fry, juvenile and adult phases of hilsa shad, Tenualosa ilisha (Hamilton), as well as their spawning areas in the aquatic ecosystems of Bangladesh. The total area studied was 29 484 km², about 29% of which belonged to the Meghna, Shahbajpur, Tetulia and Ander Manik rivers, and the channels of Sandwip, Kutubdia and Moheshkhali islands, which provide the most suitable habitat for the species. An additional 27% of moderately suitable area was located in other deltaic rivers and inshore waters. The remaining 44% was offshore deeper water, which was least suitable for hilsa. The most suitable area for spawning, eggs, fry, adults and juveniles was 6, 11, 29, 38 and 56% of the area, respectively. The model outputs were validated against field measurements and fishers’ indigenous knowledge with an accuracy level of 92%. Thus, this study provides key information about the location of hilsa at different stages of its life cycle, information useful in understanding its occurrence over a relatively large geographical area. Information of this kind is useful in fishery conservation and management.     

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.     

Incubation success and habitat selection of shore‐spawning kokanee Oncorhynchus nerka: effects of water‐level regulation and habitat characteristics

Changes to water‐level regimes have been known to restructure fish assemblages and interfere with the population dynamics of both littoral and pelagic species. The effect of altered water‐level regimes on shore‐spawning kokanee Oncorhynchus nerka incubation success was evaluated using a comprehensive in situ study in Lake Pend Oreille, ID, USA. Survival was not related to substrate size composition or depth, indicating that shore‐spawning kokanee do not currently receive a substrate‐mediated survival benefit from higher winter water levels. Substrate composition also did not differ among isobaths in the nearshore area. On average, the odds of an egg surviving to the preemergent stage were more than three times greater for sites in downwelling areas than those lacking downwelling. This study revealed that shoreline spawning habitat is not as limited as previously thought. Downwelling areas appear to contribute substantially to shore‐spawning kokanee recruitment. This research illustrates the value of rigorous in situ studies both for testing potential mechanisms underlying population trends and providing insight into spawning habitat selection.     

Oceanographic influences on the distribution of Baltic cod, Gadus morhua, during spawning in the Bornholm Basin of the Baltic Sea

The Baltic Sea is a stratified, semienclosed sea typified by a low-salinity surface layer and a deep saline layer of varying volume, salinity, temperature and oxygen concentration. The relationships between these oceanographic factors and the distribution of Baltic cod are presented, utilizing results from a survey carried out during the 1995 spawning period in the Bornholm Basin, at present the main spawning area of this stock. Cod distribution, abundance and population structure were estimated from hydroacoustic and trawl data and related to hydrographic parameters as well as to bottom depth. In the central basin, cod were aggregated in an intermediate layer about 15 m thick. This area of peak abundance was defined at its upper limit by the halocline and at the lower limit by oxygen content. The majority of individuals caught in the basin centre were in spawning or pre-spawning condition with a high proportion of males to females. On the basin slopes, aggregations of cod were found near the bottom. These individuals were mainly immature and maturing stages with an increasing proportion of females to males with size. Salinity and oxygen conditions were found to be the major factors influencing the vertical and horizontal distribution of adult cod. Abundance of immature cod was also positively related to decreasing bottom depths. The effect of temperature was minor. The observed size- and sex-dependent spawning aggregation patterns, in association with habitat volume and stock size, may influence cod catchability and thereby the assessment and exploitation patterns of this stock.     

Detection efficiency and habitat use to inform inventory and monitoring efforts: juvenile coho salmon in the Knik River basin,Alaska

Imperfect detection associated with sampling gear presents challenges for wildlife inventory and monitoring efforts. We examined occupancy dynamics and habitat use of juvenile coho salmon, Oncorhynchus kisutch, in shallow lake environments over a summer and early fall season in the Knik River area of south central Alaska using models which control for and estimate sampling gear detection efficiency. In addition, we present statements for the probability that observed absences at a survey site or from a survey area (a collection of sites) are true absences given some amount of sampling effort and analysts' beliefs about site occupancy and sampling gear detection efficiency which can be used to guide inventory and monitoring efforts for juvenile salmon or other wildlife and plant species. Occupancy modelling results demonstrate that minnow traps were effective at sampling juvenile coho in shallow lake environments, with a mean probability of detection across the study period of 0.68 (i.e., probability of detecting the presence of juvenile coho given that they are present at a trap site; SE = 0.03). Juvenile coho salmon migrated into shallow water lakes in late summer and early fall, presumably to seek out overwinter habitat. N‐mixture modelling examination of habitat use demonstrated that once in shallow lake environments, juvenile coho were widely distributed across a range of microhabitats, with some evidence for preference for shallower depths and warmer water temperatures.     

Resource partitioning between lake-dwelling Atlantic salmon (Salmo salar L.) parr, brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus (L.))

Abstract – Resource partitioning between Atlantic salmon parr, brown trout and Arctic charr was studied throughout the ice-free season in a north Norwegian lake. Juvenile salmon and trout (≤160 mm) utilized the littoral zone and juvenile charr the profundal, while adult trout and charr (>160 mm) were found in both. Juvenile salmon and trout had a similar diet, although trichopteran larvae were more important for the trout and chironomid pupae and three-spined sticklebacks for the salmon parr. Small salmon and trout parr (≤120 mm) had a higher diet overlap than larger parr (121–160 mm). The feeding habits of adult trout were similar to that of juvenile trout, but the former took larger prey items. At the population level, both salmon and trout were generalistic feeders with a broad diet, but at the individual level, both species had specialized on a single or a few prey categories. Juvenile charr were segregated from salmon and trout in both habitat and food utilization; they had a narrow diet consisting of chironomids and zooplankton, possibly reflecting their confinement to the profundal habitat which have a low diversity of potential prey. Larger charr also took zoobenthos and sticklebacks in the littoral zone. ^Note     

Habitat use of lake trout (Salvelinus namaycush) following species introduction

Abstract – Although introductions of prey species have the potential to significantly alter habitat use by top predatory fish, this aspect has rarely been directly quantified. Introduction of yellow perch (Perca flavescens), a littoral–pelagic prey species, to a small boreal lake previously dominated by littoral cyprinids provided a unique opportunity to examine how a change in forage base influenced habitat use by the sole top predator, lake trout (Salvelinus namaycush). We monitored lake trout pelagic and spatial distribution using acoustic telemetry before (2001) and after (2008) the introduction of perch to determine whether habitat use reflected a deeper, offshore prey community. After accounting for differences in water temperature and dissolved oxygen concentrations between years and the inclusion of a control lake, our data suggest that lake trout habitat use changed after the introduction of yellow perch. Lake trout, on average, were 1.4 m deeper (P < 0.01), reduced their use of littoral habitat by 55% (P = 0.03) and experienced a 71% decrease in home range size (P < 0.01), consistent with a greater offshore habitat overlap between predator and prey after the introduction of yellow perch. This study illustrates how introduced prey species may have a significant influence on habitat use by top predatory fish, while also showing the importance of using direct measurements to quantify behavioural changes.