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1.
Abstract –  Lake Höytiäinen in eastern Finland has suffered from a prolonged vendace Coregonus albula (L.) recession during the last two decades. The present study examined the capacity of smelt Osmerus eperlanus (L.) to prey on vendace larvae as well as the diet of smelt in Lake Höytiäinen to reveal its possible predation on vendace larvae. The larvae were observed to be most vulnerable to smelt >100 mm (TL) predation at a total length of 13 mm. In Lake Höytiäinen, the diet of smelt was clearly dominated by zooplankton and no vendace larvae were found in the stomachs, probably due to small size of the smelt and low abundance of the larvae. Spawning time of smelt and larval period of coregonids overlap in spring and an observed decrease in feeding activity of smelt during spawning time may provide a temporal refuge against predation. Although smelt has been found to intensively predate on coregonid larvae in other lakes, it does not play an important role in maintaining the present low-density state of vendace in Lake Höytiäinen.  相似文献   

2.
Mating in nature is rarely random, and most fish species have refined mating systems. The vendace (Coregonus albula) is a short‐lived, small‐sized, cold‐water‐adapted pelagic schooling species that is known to spawn in groups, but the actual mating system of this species, like many other group‐spawning fishes, has not been described in detail. Vendace typically spawn in the littoral or sublittoral zones of lakes in late autumn, and the hatching of larvae occurs close to icebreak in the following spring. In our large study lake, vendace larvae were caught in 93% of 1,149 random sampling locations lake‐wide. We examined the courtship and mating of vendace under experimental conditions by nonintrusive observation of the natural behaviour, to clarify whether spawning activity is associated with illumination and to assess the postspawning mortality of vendace. Here, we describe and document in detail for the first time the spawning behaviour of vendace: they spawn in the dark, and females release a small portion of their eggs (on average 1% of mean total individual fecundity) when the female and male, side by side, dart from near the bottom up towards the surface, that is perform a spawning rise. Males and females had several spawning rises (on average 1,200). Our results showed high postspawning mortality (56%). The spawning stress seems to be a potential component of mortality regulating the lifespan duration of vendace.  相似文献   

3.
Low survival of vendace (Coregonus albula) eggs incubating on natural spawning grounds (due to silting, oxygen deficits and action of predators) is discussed as one of the reasons for the great fluctuation in numbers of commercial fish. Incubation of eggs in hatcheries where the survival rate averages 60% could compensate for the great numerical disparity between the eggs spawned naturally and those taken for hatcheries. In the absence of the effects of mass stocking of lakes with vendace larvae, one can conclude that apparent mortality during the larval stage also determines the strength of the successive year-class.Vendace larvae are usually stocked immediately after the ice cover recedes from lakes. At this time they often face a period of cold weather when water temperature is low and food organisms are scarce. Poor environmental conditions cause slow growth of larvae. This increases the period of highest vulnerability of the larvae to predation.It is possible to accelerate the growth of larvae by synchronizing the time of stocking with the development of favourable thermal conditions and food availability in lakes. In Polish climatic conditions the first 10 days of May seem to be a suitable time for stocking lakes.A technique for delaying vendace egg hatching by cooling the hatchery water has been developed. It enables hatching of vendace to be delayed from the beginning of April until the beginning of May, thereby inducing mass hatching of larvae when lake conditions are optimal for stocking.  相似文献   

4.
Enhancement stocking is a widespread but rarely evaluated practice in German vendace, Coregonus albula L. fisheries, which is precautionarily carried out to buffer yield fluctuations. However, it is assumed that stocking of larval vendace can elevate year‐class strength only in the presence of substantial reproductive deficits, which so far cannot be detected prior to the spring time period when stocking is conducted by fisheries managers. Simple measures for the early quantification of natural reproduction were tested, and the efficiency of larval enhancement stocking in a lake with strong reproduction deficits was analysed. Analysis in four lakes over 3 years revealed a significant positive correlation between standardised catches of vendace larvae caught with pump‐driven illuminated traps in spring and the abundance of young‐of‐year (YoY) vendace in the following autumn, whereas standardised catches of spawners were insufficient to forecast YoY recruitment. In a lake with low natural vendace reproduction, stocked vendace contributed 73–100% of year‐class strength and fisheries yield. Accordingly, enhancement stocking can efficiently compensate for reproduction deficits, and the simple larvae sampling method may facilitate early detection of these deficits, which would allow fisheries managers to respond accordingly through larvae stocking.  相似文献   

5.
ABSTRACT:   Ontogenetic changes of tolerance to, and avoidance of, ultraviolet-B radiation (UV-B) were examined in red sea bream Pagrus major and black sea bream Acanthopagrus schlegeli . In the tolerance experiment, larvae and juveniles (age 13–46 days) were put in beakers, and were exposed to one of five different levels of UV-B radiation (1.8, 1.1, 0.2, 0.1, and 0 W/m2) for one hour. Their survival rates were calculated either 12 or 24 h later. In the avoidance experiment, fish (age 3–49 days) were put in a long experimental tank, half of which was covered with UV-blocking film and placed under two levels of UV-B radiation (1.1 and 0.2 W/m2), and their avoidance indices were calculated. Black sea bream had significantly better survival compared to red sea bream for most ages. Only black sea bream of ages 37 and 49 days showed significant avoidance of UV radiation under the higher level of UV-B, whereas both species did not show avoidance on any days at the lower level. The present results suggest that black sea bream are significantly better adapted to habitats with high UV-B radiation, than red sea bream, reflecting that back sea bream live in shallower waters through their early life stages.  相似文献   

6.
To improve the efficiency of stocking lakes with vendace (Coregonus albula) larvae, a technique for delaying egg hatching was developed. This synchronizes mass hatching with the development of suitable thermal conditions and food availability in the lake.Water temperatures were measured in Polish hatcheries and a mathematical model of the dependence of C. albula embryogenesis on incubation temperature was utilized to predict the possibilities of delaying egg hatching. Vendace hatching can be delayed by cooling the circulation water (to 1 or 2°C) during March and April. At the beginning of May, when lake conditions are optimal for stocking, the incubation temperature should be raised (at a rate of 1.5°C h?1) to that of the water supply. This ensures mass hatching of strong, normally developed larvae within 2–3 days. This technique facilitates both the delay of vendace hatching at minimal cost and the production of larvae on demand for lake stocking.  相似文献   

7.
Abstract. At different temperatures (4.5, 6.0, 8.6, 10.4, 13.5, 15.9 and 19.0°C), time from hatching to exogenous feeding (DEP50) in vendace, Coregonus albula (L.), larvae decreased from 8 to 2 days when the temperature increased from 4-5 to 19 0°C. Starved larvae at 10.4°C, when offered food at successive days after acclimation to different temperatures, started external feeding on the same day, irrespective of the acclimation temperature.
Larvae started exogenous feeding after attaining a particular larval development stage (LDS 1-2), while their age (days after hatching) was of secondary significance. In the vendace population the larvae start exogenous (mixed) feeding at a total length of 9.5 mm, irrespective of their age and rearing temperature. As total length of larvae is closely related to their development stage, the length of fish can be used in a hatchery practice as a parameter indicative of the time of the first feeding of larvae or of their release into the stocked lakes.  相似文献   

8.
Abstract  The in situ avoidance reaction of vendace, Coregonus albula L., in relation to continuous artificial light in terms of a scaring device was tested by split-beam echosounding. The tests were carried out in the mesotrophic Bigge Reservoir (Germany) in November 2007 and 2008 using a Simrad EK 60 echosounder (120 kHz). An underwater lamp with light turned on and off was lowered to 30 m water depth at four sampling sites. No reaction of vendace was observed for the sampled references (light off), but strong avoidance behaviour by swimming mainly downwards was observed when the light was turned on. The light avoidance reaction was confirmed by the volume backscattering strength ( S v) and calculated fish densities (fish ha−1). The mean fish densities for the samples carried out with light turned on were lower (268 fish ha−1, ±409 SD, n  =   32) than for the references with light turned off (5028 fish ha−1, ±2317 SD, n  =   56). The related median values (33 and 3726 fish ha−1, respectively, n  =   88) differed significantly (Mann–Whitney test, P  = <0.001). In conclusion, artificial light has great potential to scare pelagic vendace from areas near the bottom outlets of reservoirs to prevent entrainment losses.  相似文献   

9.
Abstract  Interlocked use of multiple inland vendace, Coregonus albula (L.), stocks is a relatively new strategy to exploit asynchronous fluctuations in abundance of natural fish stocks between waterbodies. It combines vendace stocks from different lakes or parts of lakes into one interlocked stock to be managed across waterbody ownership boundaries. Management of interlocked stocks can be regarded as one form of portfolio management. Exploitation of interlocked stocks should reduce the interannual variation in yield, and thus ensuring fishers more constant income and the market more constant material flow. The strategy requires fishers to increase their mobility, to benefit from asynchronous fluctuations in abundance of vendace stocks between exploitable waters. A postal inquire addressed to Finnish commercial inland fishers examined whether existing property rights institutions' and fishers' harvesting policies were appropriate to establish interlocked use of multiple vendace stocks. Almost half of fishers had, to some extent, reaped benefit from a fishing strategy that included small-scale mobility, which is consistent with the proposed strategy. By harvesting three or four lakes and stocks, fishers increased their yield compared with exploiting one fishing ground and one vendace stock. Public ownership provided fishers access to stocks nearer their place of residence than other ownership types.  相似文献   

10.
Density and biomass estimates of pelagic fish are essential to understand food web interactions and ecosystem functioning. We conducted surveys of six subarctic lakes for assessing both mono‐ and polymorphic whitefish Coregonus lavaretus (L.) populations. Monomorphic whitefish lakes were inhabited by a habitat and diet generalist, large sparsely rakered (LSR) morph, whereas polymorphic whitefish lakes had a littoral benthivorous LSR morph, a pelagic planktivorous densely rakered (DR) morph and in two cases a benthivorous small sparsely rakered (SSR) morph inhabiting the profundal zone. In addition, an introduced specialist zooplanktivore, vendace Coregonus albula (L.), inhabited one of the monomorphic lakes. Hydroacoustics was found to be an appropriate method for estimating coregonid densities and biomasses in large and deep polymorphic lakes occupied by the planktivorous DR morph or vendace, but only during dark nights in autumn. The suitability of hydroacoustic assessment for benthivorous LSR and SSR morphs was low, especially in polymorphic whitefish lakes due to their preference for near‐bottom habitat or shallow areas not sampled with hydroacoustics. The pelagic density of DR morph varied from 330 to 1780 fish·ha?1 and biomass from 1.4 to 13.3 kg·ha?1 in polymorphic whitefish lakes, whereas corresponding estimates for LSR morph were 10–320 fish·ha?1 and 0.5–8.4 kg·ha?1 in monomorphic whitefish lakes. In general, polymorphism tended to increase the density and biomass of whitefish in the pelagic area compared with monomorphic systems.  相似文献   

11.
Abstract Lake-to-lake variation in brown trout, Salmo trutta m. lacustris L., yield from stocking was examined in 34 lakes in northern Finland. The trout were mainly stocked as 2–3-year-old fish. Catch statistics were compiled with information on water quality, water level fluctuations, fishing effort and lake geomorphology. Absolute brown trout yields (kgha-1) increased with increasing stocking rate, but there was an indication of non-linearity at higher stocking densities. Relative yields (kg per thousand trout released) were highest at low stocking rates. Stepwise multiple regression analysis was used to determine the best predictive model for lake-to-lake variability in brown trout yields. Seventeen measured regressands were used initially, and then replaced with scores obtained in a principal component analysis of highly correlated water quality variables and species-specific fish yields. Three major determinants of brown trout yields in these lakes were found in both analyses: fish community, stocking rate and fishing effort. Brown trout yields from stocking were higher in lakes with proportionally high yields of vendace or vendace and whitefish and proportionally low yields of pike.  相似文献   

12.
The perch population in Lake Höytiäinen was intensively fished to reduce the density of the population and hence also the predation pressure by perch on vendace larvae. A hypothesis suggests that this predation can prevent recovery of commercially important vendace stock from a state of low-density. In the 1990s the density of the perch population in Lake Höytiäinen has increased, while the vendace stock has been sparse. Intensive fishing was conducted by professional fishermen with a paired bottom trawl, seine net, hoop net and small fish traps and by recreational fishermen with small fish traps. The size of perch population during the intensive fishing period was studied by test fishing with multi-mesh gillnets and the Leslie method in which trawl YPUE was regressed on the cumulative yield. The results suggest that the population size clearly diminished in the area where the fishing pressure was strongest. YPUE of test fishing decreased ca. 30% whereas the Leslie method gave almost a decrease twice as large as that of the former. Mean weight of perch increased in the trawl and test fishing catches during the intensive fishing period. The most effective fishing gear was trawl (62% of the total yield), but importance of trap net fishing by recreational fishermen was also high as they caught 22% of the total yield.  相似文献   

13.
Abstract –  Behaviour and morphology were both shown to differ between 1+ perch from two lakes that in earlier studies showed differences in size-specific predation risk. As the level of nourishment is known to affect behaviour and morphology, we fed perch of the two lakes in tanks for 40 days with two food levels, to study whether observed differences remain stable with changes in food availability. The perch fed in excess grew significantly, while the perch at the low food conditions lost weight, clearly indicating undernourishment. In aquarium experiments, the starved perch from both lakes were much bolder in the trade-off between foraging and predator avoidance than their well-fed conspecifics. In addition, the shape of perch differed significantly between feeding treatments. At low food levels perch got a more slender body, while at high food levels they developed a deeper body and a relatively smaller head. Independent of feeding level, the comparison between the two lakes revealed a clearly deeper body and a larger head area for one population, a shape difference that remained stable after the feeding period. The results give evidence that the level of nourishment is an important factor that quickly alters risk-taking behaviour. In body morphology, however, more stable shape characteristics must be distinguished from more flexible ones. Consequently, the level of nourishment is a potential factor that may quickly hide other proximate cues and must be considered attentively in studies, in which shape changes and behaviour are related to environmental factors like diet, predation pressure or habitat diversity.  相似文献   

14.
Abstract –  Spawning biomass and recruitment data for vendace from a central Finnish lake were analysed by fitting various recruitment models and comparing the fits statistically. The compensatory models of Ricker, Cushing and Beverton & Holt fitted the data better than the H 0 hypothesis of constant proportionality, but model and parameter uncertainties were high. Additional variables were included in an attempt to reduce uncertainties. Heavy wind forcing during the first month after hatching of larvae reduced the recruitment success. For the Ricker and the Cushing models, recruitment seemed to be also negatively associated with the density of the previous year-class. The r 2 increased considerably with inclusion of these additional variables, but the precision of model parameters remained low. Monte Carlo simulation of a vendace stock was applied to evaluate the interference of biases from the measurement error (ME) and time series error (TSE) in the analysis. Especially in the case of the Cushing model, compensatory density dependence can be overestimated severely. Increasing the number of observations decreases the biases in some cases. In view of potential biases and uncertainties, a precautionary management policy is recommended.  相似文献   

15.
Abstract

The freshness of vendace (Coregonus albulaL.) caught in Finland either in August or in April was followed over the storage period of 7 days. Microbiological analyses, measurement of volatile compounds using ion mobility based gas detector and measurements of electrical properties (Torrymeter score values) of fish were used to estimate the freshness of vendace. In the low environmental temperatures, the number of fish-associated bacteria was lower than during the summer season. This could be seen in 1-2 days longer shelf life of the catch, the maximum shelf life of vendace being approximately 6-7 days for winter fish and 5-6 days for summer fish. The differences in the amount of proteolytic and lipolytic bacteria may affect the degradation process during the storage of fish.  相似文献   

16.
Mehner T, Busch S, Helland IP, Emmrich M, Freyhof J. Temperature‐related nocturnal vertical segregation of coexisting coregonids.
Ecology of Freshwater Fish 2010: 19: 408–419. © 2010 John Wiley & Sons A/S Abstract – Habitat choice of fish may be influenced by many different ecological factors, e.g., predation risk, feeding opportunity, or temperature and oxygen availability. However, because most of the fish prey and their predators rely on vision for feeding, the predator avoidance and feeding opportunity hypotheses may fail to predict distribution of fish at complete darkness. Here, we accumulated patterns of nocturnal vertical distribution of two coexisting coregonid populations in Lake Stechlin from 13 samplings over 4 years, conducted by hydroacoustics and simultaneous midwater trawling. We calculated population depths, dispersion, illumination strengths and vertical temperature gradients for all sampling dates. Illumination strengths at fish population depths were far below the critical levels for feeding by vision, suggesting that predator avoidance or feeding opportunity did not trigger the depth distribution at night. In contrast, nocturnal population depths and dispersion of vendace Coregonus albula were significantly associated with the seasonally changing vertical temperature gradient in Lake Stechlin, whereas night‐time distribution of the coexisting Fontane cisco Coregonus fontanae was almost unaffected by temperature. Vendace occurred just below the thermocline in isothermal water layers of about 6.5–9 °C during stratification of Lake Stechlin, whereas Fontane cisco preferred 4–6 °C cold layers. These experienced temperatures roughly correspond to species‐specific optimum metabolic temperatures determined in earlier experiments. We assume, therefore, that the temperature‐related vertical segregation during non‐feeding hours at darkness is linked with metabolic benefits, thus suggesting that bioenergetics efficiency contributes to ultimate causes of diel vertical migrations at least in vendace.  相似文献   

17.
Based on existing models of fish vision and turbulence-mediated ingestion rates, we develop a model of ingestion rates in larval fish that combines several physical properties of the environment (turbulence, irradiance, light attenuation) and visual characteristics of predators and prey. The model of visual range was calibrated with observed estimates in larval herring ( Clupea harengus ) and cod ( Gadus morhua ). The improved visual ability with length of larvae was predicted to be the most sensitive part of the model. Both turbulence and light had strong impacts on the ingestion rate of larval fish. The optimal level of turbulence increased with larval length. Also, due to the exponential decay of light with depth, it was predicted that larvae will have higher ingestion rates near the surface, even at high wind velocities. It is also proposed that larvae (particularly the smallest larvae) should concentrate on larger prey in turbulent environments. We suggest that biophysical models of larval growth and survival in field situations should include these factors to account for environmental effects on growth, survival and recruitment processes in the early life stages.  相似文献   

18.
Spatial and seasonal variation in the abundance and composition of phytoplankton and other basal resources (bacteria, terrestrial detritus) influence the availability of essential polyunsaturated fatty acids (PUFA) for upper trophic levels in lake food webs. We studied accumulation, composition and content of fatty acids in planktivorous vendace (Coregonus albula) muscle tissue during the summer feeding period (May to late September) in six boreal lakes. Vendace muscle fatty acid content increased from ~17.7 mg/g DW to ~28.1 mg/g DW from spring to summer, corresponding to a ~59% increase in total fatty acids. PUFA accounted for 45%–65% of all fatty acids, and the most abundant fatty acid was docosahexaenoic acid (DHA, 22:6n‐3). The DHA content remained relatively constant throughout the sampling period (~7–8 mg/g DW), but the proportion of DHA decreased from ~40% in spring to ~30% in summer and autumn. The decrease in DHA proportion was due to accumulation of other fatty acids, primarily C18 PUFA (predominantly synthetised by algae) and monounsaturated fatty acids. A similar fatty acid accumulation pattern was observed in lipid storing copepods, an important prey for planktivorous vendace. The abundance of bacterial and terrestrial biomarker fatty acids in vendace muscle and prey items was low (<5% and <0.1% respectively). The increase in weight and the deposition of internal energy stores in vendace were achieved predominantly by algae‐based food chain. This has ecological implications, as vendace requires sufficient lipid stores for reproduction in autumn and survival over winter.  相似文献   

19.
Abstract The effects of eutrophication on fish and fisheries in Finnish lakes were determined by an extensive lake survey conducted in 1995 and 1996. The study lakes (873) were chosen by stratified random sampling from all Finnish lakes with a surface area ≥ 0.04km2 (29,515 lakes in all). The chemical parameters of the lake water were determined for water samples taken in autumn 1995. Information on the fish stocks of the study lakes was collected by means of a postal questionnaire sent to local fishing authorities and lake owners. The results show that the fish community structure is cyprinid dominated, reflecting eutrophication in 2100 lakes (7% of all the target lakes). Strong fouling of the fishing gear, as well as a great abundance of unwanted species in the catch of passive gears, were considered to be a continuous problem in more than 10% of the lakes. Roach, Rutilus rutilus (L.), and bream, Abramis brama (L.), were the most common species to have increased in abundance in the study lakes, whereas burbot, Lota lota (L.), and vendace, Coregonus albula (L.), decreased, especially in highly eutrophic lakes. High total phosphorus and cyprinid dominance in lakes were found mainly in the most intensive agricultural regions in the western and southern parts of Finland.  相似文献   

20.
Mobile hydroacoustic surveys are increasingly used to assess the distribution and abundance of freshwater fish; yet, fish may avoid moving vessels, potentially introducing bias in these assessments. In this study, avoidance in boreal lakes and reservoirs was quantified by developing a simple method based on paired drift:drift (D:D) and drift:motor (D:M) transects. Two systems in eastern Manitoba, Canada were studied: Lac du Bonnet reservoir and Nopiming. Acoustic data were collected using a digital DTX echosounder (BioSonics, Seattle, WA, USA), with a downward facing 200‐kHz split‐beam transducer, deployed from 5.5‐m vessels (Boston Whalers) modified for acoustic research. An avoidance coefficient (Ac) was developed based on comparisons of acoustic fish densities while the vessel moved over the same transects by drifting, and by motoring at survey speeds. Ac did not differ significantly from 1 (no avoidance) at Nopiming (median of 0.81, n = 13), but did at Lac du Bonnet (median of 0.51, n = 31, P < 0.05). Variability in Ac was as high in transect pairs and was unrelated to fish depth (mean 6.9 m at Lac du Bonnet; 13.1 m at Nopiming) or survey speed (up to 3.70 m·s?1, 7 knots). Results indicated that fishes did not dive in the presence of the motoring vessel, nor was avoidance size‐based. We did not detect any evidence of fish attraction to our drifting vessel. Our results suggest that boat avoidance during acoustic surveys of shallow boreal lakes may vary in relatively similar water bodies but can be quantified experimentally.  相似文献   

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