Planktivory and diet-overlap of densely rakered whitefish (Coregonus lavaretus (L.)) in a subarctic lake

Abstract –  Three sympatric whitefish ( Coregonus lavaretus (L.)) forms, one being pelagic and two benthic, segregate available habitat and food resources in subarctic Lake Muddusjärvi, northern Finland. Zooplankton availability in the lake, food composition, diet-overlap and growth of densely rakered (DR) whitefish were examined during June to September to explore the reasons for the small individual size of the pelagic form. DR whitefish used zooplankton as main food item and prey selection followed zooplankton species density proportions in the lake. Zooplankton density and water temperature was highest in July–August. The average lengths of Bosmina spp., Daphnia spp., Calanoida and Cyclopoida in DR whitefish stomach were higher than in zooplankton sample during June–September, except Calanoida in June. Diet-overlap between DR whitefish age groups was high at all months indicating intercohort resource competition. DR whitefish reached sexual maturity at 3 years of age and at the length of 12 cm, after which somatic growth almost ceased. Reason for the small average size and slow growth of DR whitefish were connected to high diet-overlap between age groups and early sexual maturation.     

The effects of winter ice cover on the trophic ecology of whitefish (Coregonus lavaretus L.) in subarctic lakes

Lakes in Arctic and subarctic regions display extreme levels of seasonal variation in light, temperature and ice cover. Comparatively little is known regarding the effects of such seasonal variation on the diet and resource use of fish species inhabiting these systems. Variation in the diet of European whitefish Coregonus lavaretus (L.) during periods of ice cover in this region is often regarded as ‘common knowledge’; however, this aspect of the species' ecology has not been examined empirically. Here, we outline the differences in invertebrate community structure, fish activity, and resource use of monomorphic whitefish populations between summer (August–September) and winter (February–March) in three subarctic lakes in Finnish Lapland. Benthic macroinvertebrate densities did not exhibit measurable differences between summer and winter. Zooplankton diversity and abundance, and activity levels of all fish species (measured as catch per unit effort) were lower in winter. The summer diet of C. lavaretus was typical of a generalist utilising a variety of prey sources. In winter, its dietary niche was significantly reduced, and the diet was dominated by chironomid larvae in all study sites. Pelagic productivity decreases during winter, and fish species inhabiting these systems are therefore restricted to feeding on benthic prey. Sampling time has strong effect on our understanding of resource utilisation by whitefish in subarctic lakes and should be taken into account in future studies of these systems.     

Impact of electric fishing on egg survival of whitefish,Coregonus lavaretus

Previous studies on the effects of electrofishing on fish eggs have reported widely varying results, ranging from gentle to adverse impacts on egg survival rates, and this may be attributable to inadequately standardised assessment methods. The impact of electrofishing on the survival of European whitefish, Coregonus lavaretus L., eggs was analysed in laboratory experiments and in a comparative field study. Different anode distances and time points post‐treatment were evaluated after artificial fertilisation with milt of untreated males, and survival rates were determined in the morula stage. In the laboratory, no significant difference in survival rates was found between various time points of stripping the gametes post‐electric shock. In the treatment group, significantly lower survival rates were detected in eggs (98.6%; SE = 0.20%) compared to the control group (99.6%; SE = 0.11%). Analysis of the egg survival rates in relation to effective voltage, rather than anode distance, revealed a significant trend of declining survival with increasing effective voltage. In field studies, eggs of electroshocked fish showed significantly lower survival (94.8%; SE = 1.03%) than untreated controls (98.7%; SE = 0.38%). Although electrofishing enhanced egg mortality, overall survival was noticeably high (>90%), indicating a relatively small impact.     

Influence of dietary fat level on feed intake, growth and fat deposition in the whitefish Coregonus lavaretus

Whitefish, Coregonus lavaretus, of initial mean weight 260–265 g were fed either a high-fat or a low-fat diet (dietary fat: 27.5% vs. 12.6%) to examine the influence of dietary fat level on feed intake, growth and patterns of fat deposition. The fish were held at 14.5 °C under a 24L:0D photoperiod, and were fed for 4 h each day. The experiment was run for 11 weeks during which feed intake (three times by X-radiography) and growth were monitored. Samples of fish were taken for body composition analysis at the start and end of the experiment. There were only small differences between dietary treatment groups in feed intake and final body weights, but the body composition of the fish was significantly influenced by the fat content of the diet. The whitefish fed the high-fat diet tended to have higher relative fat contents in the viscera [% fat as mean (SD): 29.6 (9.4)% vs. 22.1 (10.0)%] and carcass [% fat: 12.7 (1.9)% vs. 10.5 (1.3)%] than their counterparts fed the low-fat diet. This resulted in a higher whole-body fat concentration [% fat: 14.0 (1.9)% vs. 11.5 (1.5)%] amongst the fish fed the high-fat diet, and these fish had a higher energy gain than the whitefish fed the low-fat diet. The results confirm that it is possible to manipulate the chemical composition of whitefish by changing dietary composition. © Rapid Science Ltd. 1998     

Investigation of wild caught whitefish, Coregonus lavaretus (L.), for infection with viral haemorrhagic septicaemia virus (VHSV) and experimental challenge of whitefish with VHSV

Abstract One hundred and forty-eight wild whitefish, Coregonus lavaretus (L.), were caught by electrofishing and sampled for virological examination in December 1999 and 2000, during migration from the brackish water feeding grounds to the freshwater spawning grounds, where the whitefish may come into contact with farmed rainbow trout. All samples were examined on cell cultures. No viruses were isolated. Three viral haemorrhagic septicaemia virus (VHSV) isolates of different origin were tested in infection trials by immersion and intraperitoneal (IP) injection, using 1.5 g farmed whitefish: an isolate from wild caught marine fish, a farmed rainbow trout isolate with a suspected marine origin and a classical freshwater isolate. The isolates were highly pathogenic by IP injection where 99-100% of the whitefish died. Using an immersion challenge the rainbow trout isolates were moderately pathogenic with approximately 20% mortality, whereas the marine isolate was virtually non-pathogenic. At the end of the experiment it was possible to isolate VHSV from survivors infected with the marine and suspected marine isolates. Because of the low infection rate in wild whitefish in Denmark, the role of whitefish in the spread of VHSV in Denmark is probably not significant. The experimental studies, however, showed that whitefish are potential carriers of VHSV as they suffer only low mortality after infection but continue to carry virus.     

Genetic structure of the whitefish (Coregonus lavaretus) population inhabiting the Miedwie Lake, Poland, based on partial ND-1 and ITS-1 gene sequences

The aim of this study was to characterize whitefish and peled populations in Miedwie Lake by means of the genetic analysis of ND-1 (NADH dehydrogenase 1) gene and the ITS-1 (internal transcribed spacer 1) region in order to distinguish native forms from whitefish/peled hybrids. In the analysis, archival specimens of Coregonus lavaretus maraena from the Berlin Museum für Naturkunde were used. Genetic analysis performed with the aid of MEGA 4.0 software explicitly indicated that samples from Miedwie Lake belonged entirely to a native (rapidly growing) form of whitefish. Furthermore, the conducted research has also provided crucial information for a C. lavaretus management program for Miedwie Lake.     

Tagging juvenile European whitefish (Coregonus lavaretus (L.)) with passive integrated transponders—Impact of fish size on growth performance and tag retention

The study examined the effect of PIT tagging and size on the growth, survival, food conversion, tag retention and wound healing in juvenile European whitefish. Three size classes of juvenile whitefish (class S—body weight (b.w.) approx. 4.0 g; class M—b.w. approx. 8.0 g; class L—b.w. approx. 13.6 g) were tagged with PIT implanted intraperitoneally (TROVAN^®, United Kingdom). These groups formed S‐P, M‐P and L‐P respectively. Fish from the control groups (groups S‐C, M‐C and L‐C) were not tagged. Whitefish from the tagged and control groups were reared for 28 days in recirculating aquaculture systems. Only in the fish from the smallest group (group S‐P) was tagging confirmed to have a negative impact on growth rate and survival, which, after 28 days, was 70% in comparison with 94.4% in group S‐C. The rate of wound healing in all whitefish groups was similar. After 28 days following PIT implantation, all wounds were healed. Short‐term PIT retention (28 days) for all the groups was > 90%, and no differences were noted among groups. In summary, it is recommended that whitefish be PIT‐tagged using the intraperitoneal method after they have attained a body weight > 8 g. Tagging smaller specimens of this species leads to higher mortality.     

Influences of population density,temperature and latitude on the growth of invasive topmouth gudgeon Pseudorasbora parva

Plasticity in life‐history traits provides advantages for introduced fish in overcoming demographic bottlenecks that would otherwise inhibit establishment. Here, the influence of population density, temperature and latitude was tested on the growth increments and growth rates of invasive populations of topmouth gudgeon Pseudorasbora parva, a small Asian cyprinid fish that is invasive across Europe. Aquaria experiments tested the roles of fish number and temperature on growth increments under a fixed food supply, pond experiments tested the role of density on growth increments, and a field study completed in England and Wales tested the influence of density and latitude on growth rates. In aquaria experiments, whilst growth increments were higher at 21 and 23 °C than at 19 and 25 °C, fish number had a greater influence on growth than temperature. Higher growth increments were produced at lower densities. In experimental ponds, growth increments were significantly higher in ponds with low densities of P. parva compared with those at elevated densities. In the field study comprising 10 wild populations across a latitudinal gradient of 4.0°N, a difference in mean air temperatures of approximately 3 °C, and estimated densities between 0.5 and 65.0 m^?2, population density was the only significant predictor of growth rates. Whilst populations at very low densities comprised of significantly faster growing individuals, there were no significant differences when densities were between 15 and 65 m^?2. Thus, invasive P. parva populations have considerable growth plasticity, especially at low densities, with this likely to be important in their ability to colonise new environments.     

程海浮游动物种群特征与数量的周年变化

为深入了解程海湖泊生态系统的状况,2009年10月至2010年7月对程海浮游动物进行了季节性调查。结果表明,程海有浮游动物34科、59属、86种;其中,原生动物13科、18属、28种,轮虫10科、23属、34种,枝角类5科、7属、11种,桡足类2科、7属、9种,其他浮游动物4科、4属、4种。原生动物纤毛虫类(Ciliophora)四季均为优势类群,溞钟虫(Vorticella kahli)春季数量较多,而急游虫(Strombidium sp.)和湖累枝虫(Epistylis lacustris)在秋季数量达到高峰。轮虫优势种为暗小异尾轮虫(Trichocerca pusilla)、奇异巨腕轮虫(Pedalia mira)、裂痕龟纹轮虫(Anuraeopsis flasa)和萼花臂尾轮虫(Brachionus calyciflorus)。枝角类种类少、数量多,主要是棘爪网纹溞(Ceri-odaphnia reticulata)、短尾秀体溞(Diaphanosoma brachyurum)、透明溞(Daphnia hyaline)、园形盘肠溞(Chydorus sphaericus)和长肢秀体溞(D.leuchtenbergianum);桡足类种类少、数量低,近剑水蚤(Tropocyclops sp.)、锯齿真剑水蚤(Eucyclops macruroides deticulatus)、透明温剑水蚤(Thermocyclops hyalinus)常见并有一定优势。浮游动物数量为3316.9个/L;其中,春季2635.6个/L,夏季3010.7个/L,秋季3998.0个/L,冬季3623.5个/L;水平分布南部明显偏高,东部数量高于西部,湖心明显偏少。相关分析表明,影响浮游动物数量变动的主要因子是温度、食物和鱼类摄食。在水体富营养化和太湖新银鱼(Neosalanx taihuensis)的强大摄食压力下,程海浮游动物小型化趋势明显。     

Temporal variation in Lake Balaton and its fish populations

Abstract— Dramatic changes have occurred in Lake Balaton in the last 40–45 years. Variations in water quality have resulted in a decrease in fish and invertebrate diversity. Fish assemblages have changed in response to human-induced eutrophication, environmental perturbations, introduction of exotic fish species, over-fishing and species-habitat interactions. Fish biomass and productivity first increased during the early 1970s with enhanced primary production, then decreased with the reduction of exploitation since the late 1970s and induced intra- and interspecific competition. Previous stable populations began to oscillate, and the majority of stocks became fragile by the mid-1980s. Extinction of native fish and invasion of new alien species alternate. Alien species have transformed the food webs, causing long-lasting ecological changes. Reduced and non-selective exploitation has resulted in higher fish density and lower production rates. Recent studies have revealed differences in the carrying capacity of fish between the littoral zone and the open water areas.     

The effect of stocking size on the first winter survival of whitefish, Coregonus lavaretus (L.), in the Gulf of Bothnia, Baltic Sea

The anadromous whitefish, Coregonus lavaretus (L.), is the most numerous fish species stocked in the Gulf of Bothnia, Baltic Sea. One-summer-old-whitefish fingerlings are mostly 8–10 cm long when released annually in September–October, whereas the wild whitefish are 10–12 cm at that time. About 6 million, one-summer-old, spray-marked, whitefish were released in the northern and central parts of the Gulf in 1995–1998. To study the effect of the stocking length on the survival of the marked fish, the length of the recaptured whitefish as 1-year-olds was back-calculated. Altogether 1106 whitefish recaptured in the Gulf of Bothnia were analysed. The back-calculated length was slightly greater than the stocking length but not as large as the length of the wild fish. In the central part of the Gulf of Bothnia, where the mean stocking length was more than 10 cm, the back-calculated length was 10.5–11.1 cm. In the northern part of the Gulf the mean stocking length varied between 8.8 and 10.0 cm annually, and the corresponding back-calculated mean lengths were 9.3–9.7 cm. It also seemed that bigger fingerlings started their feeding migration earlier or they migrated faster than the smaller ones to the southern parts of the Gulf of Bothnia.     

Morphological and ecological responses to a conservation translocation of powan (Coregonus lavaretus) in Scotland

• 1. The establishment of refuge populations has become a common management tool for threatened fish species in recent years, yet the effects of translocation are not fully understood in a conservation context.
• 2. This paper examines the hypothesis that phenotypic changes have occurred during the formation of two refuge populations of the nationally rare powan (a freshwater fish species) which were established in Loch Sloy and Carron Valley Reservoir in Scotland.
• 3. Significant differences in head morphology, size and growth between the founder and refuge populations and between the two refuge populations were demonstrated. These changes are probably due to a combination of founder effects, intense selection and phenotypic plasticity. These changes can undermine the rationale behind the establishment of refuge populations.
• 4. The results call into question the usefulness of translocation as a conservation measure; however, there are times when this is the only viable management option available. The future of translocation and the validity of establishing refuge populations for powan conservation are discussed. Copyright © 2010 John Wiley & Sons, Ltd.

     

Review of climate change impacts on marine fish and shellfish around the UK and Ireland

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Vulnerability of Cape Fold Ecoregion freshwater fishes to climate change and other human impacts

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Effects of current and future climates on the growth dynamics and distributions of two riverine fishes

1. To facilitate conservation planning, there is a need for improved confidence in forecasts of climate change impacts on species distributions. Towards that end, there have been calls for the development of process-based models to test hypotheses concerning the mechanisms by which temperature shapes distribution and to corroborate forecasts of correlative models.
2. Models of temperature-dependent growth (TDG) were developed for two Australian riverine blackfishes with disjunct longitudinal distributions: Gadopsis marmoratus (occupies lower, warmer elevations) and Gadopsis bispinosus (occupies higher, cooler elevations). The models were used to (a) predict blackfish monthly and annual growth dynamics under current and future climate scenarios within different elevation bands of their current distribution, and (b) test the hypothesis that, under the current climate, the distributions of each species would be positively correlated with predicted TDG.
3. Increases in mean annual growth were forecast for both species under all warming scenarios, across all elevation bands. Both species currently occupy annual habitat temperatures below those optimal for growth. Under certain warming scenarios, the predicted increases in annual growth belie forecasts of within-year dynamics that may interact with the phenology of blackfish to impair recruitment.
4. There was not a significant positive linear relationship between predicted TDG and observed abundance among river segments for either species. Both species were strongly under-represented where annual growth rates were forecast to be optimal and over-represented where growth rates were forecast to be intermediate.
5. Confidence in forecasts of climate change impacts based on correlative models will increase when those forecasts are consistent with a mechanistic understanding of how specific drivers (e.g. water temperature) affect processes (e.g. growth). This process-based study revealed surprises concerning how future climates may affect fish growth dynamics, showing that although the blackfish distributions are correlated with temperature the temperature-dependent mechanisms underpinning that correlation require further investigation.

     

Review of climate change impacts on marine fisheries in the UK and Ireland

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Climate change in the southeastern Bering Sea: impacts on pollock stocks and implications for the oscillating control hypothesis

Concern about impacts of climate change in the Bering Sea prompted several research programs to elucidate mechanistic links between climate and ecosystem responses. Following a detailed literature review, Hunt et al. (2011) (Deep‐Sea Res. II, 49, 2002, 5821) developed a conceptual framework, the Oscillating Control Hypothesis (OCH), linking climate‐related changes in physical oceanographic conditions to stock recruitment using walleye pollock (Theragra chalcogramma) as a model. The OCH conceptual model treats zooplankton as a single box, with reduced zooplankton production during cold conditions, producing bottom‐up control of apex predators and elevated zooplankton production during warm periods leading to top‐down control by apex predators. A recent warming trend followed by rapid cooling on the Bering Sea shelf permitted testing of the OCH. During warm years (2003–06), euphausiid and Calanus marshallae populations declined, post‐larval pollock diets shifted from a mixture of large zooplankton and small copepods to almost exclusively small copepods, and juvenile pollock dominated the diets of large predators. With cooling from 2006–09, populations of large zooplankton increased, post‐larval pollock consumed greater proportions of C. marshallae and other large zooplankton, and juvenile pollock virtually disappeared from the diets of large pollock and salmon. These shifts in energy flow were accompanied by large declines in pollock stocks attributed to poor recruitment between 2001 and 2005. Observations presented here indicate the need for revision of the OCH to account for shifts in energy flow through differing food‐web pathways due to warming and cooling on the southeastern Bering Sea shelf.     

The large‐scale stocking of young anadromous whitefish (Coregonus lavaretus) and corresponding catches of returning spawners in the River Tornionjoki,northern Baltic Sea

Stocking and fishing effort are two important potentially conflicting factors in fish stock management that require appropriate assessment to ensure a sustainable fishery. In the River Tornionjoki, which discharges into the northern Baltic Sea, a summer‐ascending whitefish, Coregonus lavaretus L., stock has long been a target by traditional dipnet fishing. Enhancement stocking of young whitefish started in the River Tornionjoki in the 1970s after a collapse in catches, with millions of age‐0 whitefish stocked annually in the river, but after about three decades, the stocking rates were considerably reduced. As a result, dipnet catches of whitefish in the Kukkolankoski Rapids rose simultaneously, peaking in the 1980s and 1990s, and then subsequently decreased. There was a significant positive correlation between stocking intensity and catch, both in weight and in numbers, revealing a strong relationship between whitefish releases and dipnet catch. Changes in gillnet fishing effort in the sea affected dipnet catches in weight as well as in mean size of captured whitefish. When the combined effect of stocking and gillnet effort was evaluated, only stocking significantly affected dipnet catches.