The littoral zone of lakes is used as spawning, shelter, or feeding habitat for many fish species and hence is of key importance for overall lake functioning. Despite this, hardly any studies exist examining the long-term dynamics and response of the littoral fish community, composed mostly of juvenile fish, to environmental change. Here, we study the response of total catch per unit effort (CPUE) and individual species CPUE of such a community to 17 years of oligotrophication and examine whether the species responses can be characterised as synchronous or asynchronous. We analyse a data set of beach seine catches carried out during morning and twilight, late spring and late summer at three sites in large and deep Lake Constance from 1997 to 2014. Generalised additive mixed models were used to explore changes in CPUE of the overall community and of the most frequently occurring species, and Kendall's W test was applied to examine whether the dynamics of fish species were synchronous or asynchronous. Species-specific and total CPUE strongly differed between morning and twilight and between spring and summer indicating an important role of behavioural and life cycle adaptations of species for CPUE. In addition, also the CPUE of some species seeking shelter behind larger stones was lower at sites without these. Total CPUE did not decline suggesting the overall abundance of littoral fish was resilient to declining nutrients. In contrast, fish community composition changed strongly during the study period due to increases in some species (dace, loach, perch) and decreases in others (bream, burbot, chub, ruffe), indicating response diversity of fish to oligotrophication. The type of community dynamics was scale-dependent, whereby significantly synchronous dynamics according to Kendall's W were observed when taking seasonal variability into account. In contrast, significantly asynchronous species dynamics were observed when only the low-frequency variability of species dynamics was considered separately for spring and summer time series. Resilience of littoral fish total CPUE to oligotrophication might have important consequences for ecosystem dynamics and ecosystem services beyond the littoral zone. As small fish often impose strong predation pressure on zooplankton, their resilience might sustain a high top-down control on zooplankton resulting in a further reduction of zooplankton biomass. This could contribute to delayed food web responses and reduced growth of fish with oligotrophication.

A lake wide fishing survey of Upper Lake Constance revealed that in September 2014 three-spined sticklebacks (Gasterostetts aculeatus) made up 96% of the pelagic fish community in terms of number. To narrow down the point in time when sticklebacks started to colonize the pelagic zone and to reconstruct the build-up of this unprecedented population size, we analysed 18 hydroacoustic surveys from March 2009 to March 2018. As current analysis techniques do not allow discriminating echoes from different fish species of similar size, we considered as sticklebacks all fish smaller than a certain single-target threshold minus the average abundance of small fish well before the sticklebacks invaded the pelagic zone. Our data suggest that sticklebacks colonized the pelagic zone in 2012, one year before they appeared as by-catch in test fisheries. Population density fluctuated between 1280 and 7990 individuals/ha from November 2012 to March 2018 but never fell below 2900 individuals/ha in recent years. These estimates do not include shallow waters where densities might be even higher because the nearshore zone was excluded from our surveys.

It is well recognized that environmental degradation caused by human activities can result in dramatic losses of species and diversity. However, comparatively little is known about the ability of biodiversity to re-emerge following ecosystem recovery. Here, we show that a European whitefish subspecies, the gangfisch Coregonus lavaretus macrophthalmus, rapidly increased its ecologically functional diversity following the restoration of Lake Constance after anthropogenic eutrophication. In fewer than ten generations, gangfisch evolved a greater range of gill raker numbers (GRNs) to utilize a broader ecological niche. A sparse genetic architecture underlies this variation in GRN. Several co-expressed gene modules and genes showing signals of positive selection were associated with GRN and body shape. These were enriched for biological pathways related to trophic niche expansion in fishes. Our findings demonstrate the potential of functional diversity to expand following habitat restoration, given a fortuitous combination of genetic architecture, genetic diversity and selection.

Climate change, land-use change, pollution and exploitation are among the main drivers of species' population trends; however, their relative importance is much debated. We used a unique collection of over 1,000 local population time series in 22 communities across terrestrial, freshwater and marine realms within central Europe to compare the impacts of long-term temperature change and other environmental drivers from 1980 onwards. To disentangle different drivers, we related species' population trends to species-and driver-specific attributes, such as temperature and habitat preference or pollution tolerance. We found a consistent impact of temperature change on the local abundances of terrestrial species. Populations of warm-dwelling species increased more than those of cold-dwelling species. In contrast, impacts of temperature change on aquatic species' abundances were variable. Effects of temperature preference were more consistent in terrestrial communities than effects of habitat preference, suggesting that the impacts of temperature change have become widespread for recent changes in abundance within many terrestrial communities of central Europe.

Following a period of eutrophication in the 1960s and 1970s, the productivity of many European lakes was restored to near-pristine levels at the end of the 20(th) century, a process termed re-oligotrophication. Lower phosphorus concentrations, however, lead to slower growth of fish due to a reduced food base, and eventually to smaller harvests. This problem is particularly serious in perialpine lakes whose fish communities are dominated by whitefish. In these lakes fishermen benefitted from enhanced lake productivity under eutrophic conditions but are now confronted with smaller whitefish yields under oligotrophic conditions. As growth of lake whitefish is density-dependent, manipulation of standing stock biomass has the potential of increasing growth rate and eventually harvests. This possibility is evaluated through bioenergetics modelling, simulating growth and yield of whitefish under various population densities and zooplankton food concentrations. These simulations clearly indicate that not only individual growth but total biomass production increase with decreasing population size, and the increase in total biomass production is even more pronounced at low ration levels. Decreasing whitefish population density therefore has the potential of increasing fishery yields. The unresolved problem however persists, how whitefish population density can be manipulated in the desired way.

The colour of the ventral, anal and caudal fins of Eurasian perch can range from pale yellow to intense red. Within spatially separated populations, however, individuals are usually very uniform in colour. We fed astaxanthin- and canthaxanthin-enriched dry feed to juvenile perch from a yellow-finned and a red-finned population to compare the influence of dietary carotenoids on fin colour between these two populations. In this way we wanted to test whether fin colour in perch is predominantly a phenotypically plastic trait or whether differently coloured individuals represent colour morphs. The ventral fins of perch from the red-finned population always exhibited significantly more intense redness when their feed was supplemented with either one or both carotenoid additives. Perch from both populations deposited more canthaxanthin in their ventral fins than astaxanthin, red-finned perch in particular. Yellow-finned perch probably converted canthaxanthin into beta-carotene, which was the dominant carotenoid in their ventral fins, whereas the fins of red-finned perch contained only trace amounts of beta-carotene. We conclude that these two populations represent colour morphs that differ fundamentally in their ability to metabolise and deposit dietary carotenoids into their ventral fins. Considering the multiple physiological functions of carotenoids, these fundamental differences in carotenoid metabolism between perch colour morphs may have far-reaching consequences for the performance of different populations, for example in their response to parasite infections. (C) 2016 Elsevier GmbH. All rights reserved.

Upper Lake Constance (ULC) is a large pre-alpine lake situated between Austria, Germany and Switzerland (9°18'E, 47°39'N). Along with the smaller, conjoined expanse of Lower Lake Constance, it forms the third largest lake in Europe. Its waters underwent pronounced eutrophication during the 20th century. Commercial fisheries benefitted strongly from the increased productivity during an initial mesotrophic phase, but these advantages were effectively neutralized when eutrophication became severe. By the turn of the 21 century, internationally coordinated measures to reduce nutrient input to the lake had returned ULC to its historic reference state as an oligotrophic ecosystem. However, the remarkable success of the nutrient management program has been to the detriment of commercial fishers. Yields of most commercially important fish species have decreased, along with lake productivity. As a consequence, the high market demand for local fish products is nowadays met mainly by imports, the ecological footprint of which offsets the local benefits of environmental restoration. Responsibility for fisheries and environmental aspects of ULC managing is shared by the national and federal state administrations and in all cases, tourism, drinking water and environmental interests now take priority over fisheries. As a result, the number of fishers operating viably on Germany’s largest inland water body continues to decline and the longterm viability of commercial capture operations is in doubt. Aquaculture of locally desired fish species may become an important factor in the future of the Lake Constance fisheries. 1. Lake Constance’s Fish Community Lake Constance has a total surface area of 536 km2 and is divided into a large (472 km2), deep (zmax = 254 m, zmean = 101 m) Upper Lake (Photo 1) and a small (63 km2), shallow (zmean = 16 m) Lower Lake (Figure 1). This paper deals solely with the better documented warmmonomictic pre-alpine expanse of Upper Lake Constance (ULC) which has supported a regionally important fishery for many centuries. In: A.M. Song, S.D. Bower, P. Onyango, S.J. Cooke, R. Chuenpagdee (Eds.), Inter-Sectoral Governance of Inland Fisheries (pp. xx-xx). TBTI Publication Series, St John's, NL, Canada. 2 Figure 1. Location of Lake Constance in Europe and between Germany, Switzerland and Austria. Photo 1. Scenery of Upper Lake Constance More than 30 species of fish currently occur in ULC (Rösch 2014). The pelagic fish fauna is dominated by whitefish Coregonus spp. Four species of this highly important commercial genus were originally found in the lake: the pelagic spawning Blaufelchen (Coregonus wartmanni [Bloch 1784]), the nearshore spawning Gangfisch (Coregonus macrophthalmus [Nüsslin 1882]), the larger Sandfelchen (Coregonus arenicolus [Kottelat 1997]), and a deepwater dwarf species known as Kilch (Coregonus gutturosus [Gmelin 1818]). The latter disappeared from ULC between 1970 and 1980 as a result of oxygen depletion of the

Marking of fish otoliths with oxytetracycline and tetracycline is a widely used method to evaluate the effectiveness of stocking operations. Available protocols for the labeling of fish specify a number of factors influencing mark quality and potential risk for fish during marking. This study investigates the influence of water hardness on mortality of freshwater fish during marking with OTC. In order to pursue this question complexation of OTC with Mg2+ and Ca2+ cations was measured spectrophotometrically. Furthermore, zebrafish (Danio rerio) were immersed in OTC solutions (1200 mg/L; 48 h immersion) combined with varying levels of water hardness (5.5, 15.5, 25.5, 32.5°dH). The amount of OTC-Mg–Ca-complexes was positively correlated to water hardness. Moreover, it could be demonstrated that mortality of zebrafish during marking varied as a factor of water hardness. Highest mortalities occurred at the lowest (5.5°dH) and the highest (32.5°dH) tested levels during marking with OTC.

Fish species diversity can be lost through interacting stressors including habitat loss, stocking and overfishing. Although a multitude of stressors have played a role in the global decline of coregonid (Coregonus spp.) diversity, a number of contemporary studies have identified habitat loss stemming from eutrophication as the primary cause. Unfortunately, reconstructing the role of fishing and stocking practices can be difficult, because these records are incomplete or appear only in hard-to-access historic grey literature. Based on an illustrative set of historic and contemporary studies, we describe how fisheries management practices may have contributed to coregonid diversity loss in European and North American lakes. We provide case studies examining how fishing and stocking may reduce coregonid diversity through demographic decline and introgressive hybridization. In some lakes, fisheries management practices may have led to a loss of coregonid diversity well before issues with habitat degradation manifested. Our review suggests that fish conservation policies could beneficially consider the relative importance of all stressors, including management practices, as potential drivers of diversity loss.

In this study we show that the number, position and shape of stripes were sufficiently unique to demonstrate that juvenile Eurasian perch Perca fluviatilis can be individually identified based on their stripe patterns. The stripe patterns in perch and also other species may thus be used in experiments as an alternative to conventional marking techniques that frequently cause stress to the fish.

A full factorial crossing experiment with five females and five males of each of two coregonid species from upper Lake Constance was used to test for intrinsic post-zygotic incompatibilities during early ontogeny. Up until shortly before hatching, there was no difference in embryo mortality between homo and heterologous crosses. A maternal effect on mortality was found in both species, but paternal effects and female-male interactions were absent. Thus, genetic incompatibility during early ontogeny does not appear to prevent introgressive hybridization, suggesting that genetic divergence between these species is maintained primarily by pre-zygotic barriers. The recent genetic homogenizations of coregonid species flocks in European alpine lakes may have been caused by a flattening of adaptive landscapes through eutrophication, but intensive stocking with larvae obtained in hatcheries from artificially fertilized eggs is also likely to be a contributing factor. To safeguard diversity among sympatric coregonids, it is important to re-establish ecological conditions conducive to species divergence and to revise traditional management strategies.

Human-induced nutrient input can change the selection regime and lead to the loss of biodiversity. For example, eutrophication caused speciation reversal in polymorphic whitefish populations through a flattening of littoral-pelagic selection gradients. We investigated the current state of phenotypic and genetic diversity in whitefish (Coregonus macrophthalmus) in a newly restored lake whose nutrient load has returned to pre-eutrophication levels and found that whitefish spawning at different depths varied phenotypically and genetically: individuals spawning at shallower depth had fewer gill rakers, faster growth, and a morphology adapted to benthic feeding, and they showed higher degrees of diet specialization than deeper spawning individuals. Microsatellite analyses complemented the phenotype analyses by demonstrating reproductive isolation along different spawning depths. Our results indicate that whitefish still retain or currently regain phenotypic and genetic diversity, which was lost during eutrophication. Hence, the population documented here has a potential for future divergence because natural selection can target phenotypes specialized along re-established littoral-pelagic selection gradients. The biodiversity, however, will have better chances to return if managers acknowledge the evolutionary potential within the local whitefish and adapt fishing and stocking measures.

The population dynamics of coregonids in European alpine lakes have been studied intensively during recent decades.Many of these studies have focussed on the impacts of anthropogenic eutrophication and subsequent re-oligotrophication.These changes in productivity represent the single most important perturbation of coregonid habitats since the mid-twentieth century.While the problem of eutrophication has been successfully addressed in many European alpine lakes, new forms of anthropogenic challenge such as climate change and the colonization of lakes by non-native aquatic species continue to impact on coregonid populations and demand research.The picture that emerges from a compilation of primary research papers suggests that abiotic and biotic factors are most influential on year-class strength during the larval phase, exerting more moderate effects during the embryonic and reproductive phases, and only a weak influence during the growth phase.In contrast, individual biomass is mainly determined during the growth phase, but moderate effects on growth may also occur during the larval and reproductive phases.Changes in lake productivity influence the various life-history phases of coregonids in both positive and negative ways, for example by improving feeding conditions and via deterioration of spawning habitat quality.Climate change, on the other hand, seems to influence mainly the embryonic and larval phases, with the available studies suggesting that higher temperatures and earlier onset of stratification in spring tend to boost year-class strength.These effects, however, appear insufficient to balance the marked effects of re-oligotrophication, which has caused and continues to cause a marked depression of growth in many European alpine lakes.The bumper fish harvests obtained during the peak of anthropogenic eutrophication are thus a thing of the past.

Fisheries-induced evolution (FIE) has been reported for several intensively exploited fish stocks worldwide. Most studies focused on marine populations of high commercial interest, but FIE may also occur in intensively harvested freshwater fish stocks. An example is the whitefish (Coregonus lavaretus) stock of Lake Constance. Previous evidence for FIE in this stock, through the analysis of long-term data sets, showed a long-term effect on growth and reproductive traits in addition to the effects of environmental factors. In this study, we tested whether growth rates of Lake Constance whitefish were partially hereditary, and whether the results of this experiment support the fisheries-induced evolution scenario for Lake Constance whitefish. In a laboratory experiment using whitefish larvae, we hypothesized that slow-growing females would produce slow-growing offspring. Our experimental setup allowed rearing of 24 different batches of larvae over 40 days. Growth of larvae was inversely correlated to their weight-at-hatch, and larvae with larger yolk sac volume grew slower. We attribute this result to the intensive size-selective harvest that has occurred in Lake Constance during the past several decades because fish that allocate more energy to reproduction at the expense of growth have an advantage under the present harvest regime over fish that follow the opposite allocation strategy. Our results are in line with FIE theory and suggest a genetic component to life-history traits of Lake Constance whitefish, whereby slow-growing females tend to produce larvae of a lower growth performance.

Fish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage structure may be expected owing to direct effects of temperature and indirect effects operating through eutrophication, water level changes, stratification and salinisation. We reviewed published and new long-term (10–100 years) fish data series from 24 European lakes (area: 0.04–5,648 km2; mean depth: 1–177 m; a north–south gradient from Sweden to Spain). Along with an annual temperature increase of about 0.15–0.3°C per decade profound changes have occurred in either fish assemblage composition, body size and/or age structure during recent decades and a shift towards higher dominance of eurythermal species. These shifts have occurred despite a reduction in nutrient loading in many of the lakes that should have benefited the larger-sized individuals and the fish species typically inhabiting cold-water, low-nutrient lakes. The cold-stenothermic Arctic charr has been particularly affected and its abundance has decreased in the majority of the lakes where its presence was recorded. The harvest of cool-stenothermal brown trout has decreased substantially in two southern lakes. Vendace, whitefish and smelt show a different response depending on lake depth and latitude. Perch has apparently been stimulated in the north, with stronger year classes in warm years, but its abundance has declined in the southern Lake Maggiore, Italy. Where introduced, roach seems to take advantage of the higher temperature after years of low population densities. Eurythermal species such as common bream, pike–perch and/or shad are apparently on the increase in several of the lakes. The response of fish to the warming has been surprisingly strong and fast in recent decades, making them ideal sentinels for detecting and documenting climate-induced modifications of freshwater ecosystems.

The stocking of hatchery-produced whitefish is a common practice in most countries of the species' natural range. Rigorous monitoring of the effects of stocking is less common, however, and possible negative impacts of stocking on the target population are rarely considered, even though supportive stocking might exert a series of negative effects. The present study discusses these potential impacts, taking Upper Lake Constance whitefish as an example. In 2003, a proportion of the larvae stocked into the lake were labelled with Alizarin Red S. The contribution made by stocking to virtual cohort size was estimated at 83%. Survival rates from egg or larval stages to adulthood for naturally produced fish and those incubated in hatcheries in 2003 were compared with those estimated from records pertaining to the cohorts of 1925-1939. Survival rates for lake-hatched larvae in 2003 fell between 1 and 10% of historic values. Several factors that may have contributed to this decline are discussed, of which the most potent seems to be the massive stocking of the lake with delayed hatchery larvae. Continued successful stocking will increase the contribution to the population of fish with partial or complete hatchery ancestry, and it may compromise the stock's ability to adapt to a changing environment through natural selection.

Zooplankton were collected from Lake Taal between January and December 2008 in order to test for differences in species composition and abundance between a lake basin with intensive fish cage (FC) aquaculture and an open water area without FCs. Most species showed similar patterns of occurrence in both basins while having differences in abundance. Several rotifer species were more abundant in FC sites most of the year, while for microcrustaceans higher abundances in FC sites only happened during the first 2 months. Their distribution is attributed to the presence of higher nutrient levels in FC sites as well as wind-induced basin-wide water movements during the different monsoon seasons which disperse plankton and nutrients from FC sites to other parts of the lake. Zooplanktonic indicators, such as the Brachionus–Trichocerca quotient (Q B/T) and the ratio of calanoids to cladocerans and cyclopoids, clearly demonstrate the eutrophic state of the lake. A comparison with previous studies suggests that the lake was already eutrophic prior to the introduction of aquaculture in the 1970s. The trophic conditions in Lake Taal may be attributed to the lakes’ tropical and volcanic nature, with productivity further enhanced by increased nutrient input from aquaculture.

P>The ecosystem of Lake Constance in central Europe has undergone profound modifications over the last six decades. Seasonal and inter-annual changes in the vertical distribution patterns of whitefish were examined and related to changes in biotic and abiotic gradients. Between 1958 and 2007, the average fishing depth in late summer and autumn was related to two factors influencing food supply of whitefish - lake productivity and standing stock biomass. In years with low food supply, whitefish were harvested from greater depths, where temperatures were up to 4 degrees C lower. The whitefish's distribution towards colder water might be a bioenergetic optimisation behaviour whereby fish reduce metabolic losses at lower temperatures, or it may result from a reassessment of habitat preference under conditions of limited food supply, according to the ideal free distribution theory.

P>1. Burbot larvae (Lota lota) perform a substantial diel vertical migration (DVM) of increasing amplitude in the pelagic zone during a 3-month period before migrating to the littoral zone as early-juveniles. We hypothesised that feeding in the warm surface layers at night and then spending the day in cold water below the thermocline reduces metabolic costs and earns burbot larvae an energetic advantage.2. To test our hypothesis, we mimicked the temperature conditions experienced by vertically migrating burbot in the pelagic zone. We also simulated three further scenarios, in which temperature remained constant.3. Burbot showed the best performance (defined as specific growth rate multiplied by the probability of survival) in the treatments simulating DVM. The high temperature treatment, simulating permanent residence in the warm epilimnion, resulted in high growth combined with high mortality. At a permanently low temperature, simulating life in the hypolimnion, growth was poor and activity reduced.4. In a deep, temperature-stratified lake, where the apparently beneficial overall medium temperature is found in a restricted layer within the thermocline, DVM optimises performance in young burbot. Various ultimate factors might act synergistically in selecting for DVM in larval and early-juvenile burbot.

Fisheries Management and EcologyVolume 17, Issue 3 p. 291-293 Re-establishment of the North Sea houting in the River Rhine J. BORCHERDING, J. BORCHERDINGSearch for more papers by this authorM. HEYNEN, M. HEYNENSearch for more papers by this authorT. JÄGER-KLEINICKE, T. JÄGER-KLEINICKESearch for more papers by this authorH. V. WINTER, H. V. WINTERSearch for more papers by this authorR. ECKMANN, R. ECKMANNSearch for more papers by this author J. BORCHERDING, J. BORCHERDINGSearch for more papers by this authorM. HEYNEN, M. HEYNENSearch for more papers by this authorT. JÄGER-KLEINICKE, T. JÄGER-KLEINICKESearch for more papers by this authorH. V. WINTER, H. V. WINTERSearch for more papers by this authorR. ECKMANN, R. ECKMANNSearch for more papers by this author First published: 07 May 2010 https://doi.org/10.1111/j.1365-2400.2009.00710.xCitations: 12 Jost Borcherding, University of Cologne Zoological Institute, General Ecology and Limnology, Research Station Grietherbusch, D-46459 Rees-Grietherbusch, Germany (e-mail: jost.borcherding@uni-koeln.de) Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume17, Issue3June 2010Pages 291-293 RelatedInformation