Native Whitefish Research Articles

Small but voracious: invasive generalist consumes more zooplankton in winter than native planktivore

In recent years, Lake Constance has experienced an invasion and domination of three-spined stickleback (Gasterosteus aculeatus) in the pelagic zone, which has coincided with a decline in the native whitefish (Coregonus wartmanni) population. Similar massive invasions of sticklebacks into pelagic zones have been recognized also in marine areas or small lakes worldwide. However, their diet overlaps with native species is rarely evaluated, especially in the winter season, which often presents a bottleneck for fish survival. In this study, we compared the diet of pelagic sticklebacks with the diet of the substantially larger native whitefish in different seasons, to evaluate the threat of the recent stickleback invasion on whitefish populations. By monthly sampling of zooplankton and both fish species diets, we could demonstrate that sticklebacks select similar prey throughout most of the year and consume more prey than whitefish during the winter. With relations between prey availability and prey selection, interspecific and intraspecific seasonal diet variability and indices like a prey-specific index of relative importance, we discuss the importance of zooplankton species traits and abundance for whitefish and stickleback predation. This study shows that sticklebacks, despite their small size, represent a serious potential diet competitor to native planktivorous fish. Sticklebacks quickly adapt to new environments, and thus we advocate precautions regarding their introduction into similar lakes as Lake Constance, as this could cause irreversible ecological changes.

Trophic niche segregation among native whitefish and invasive vendace in a north Norwegian lake system

AbstractIntroductions and invasions of non‐native species alter nutrient cycling and trophic dynamics resulting in significant ecological disturbance. Stable isotope data were used to test for evidence of invader‐induced trophic niche differences in a north Norwegian lake system differentially dominated by native European whitefish (Coregonus lavaretus) morphotypes and invasive vendace (Coregonus albula). Aspects of both realised trophic niche position and trophic niche width were affected by the invader, with the effects varying by whitefish morphotype. Densely rakered pelagic whitefish demonstrated a relatively lower reliance on pelagic resources in the presence of the invader and the isotopic niche size was relatively larger in conjunction with the broadening of the prey base. Within the benthic‐dwelling sparsely rakered whitefish morphotype, the trophic impacts of invading vendace were size‐dependent, with larger individuals experiencing niche compression. Smaller sparsely rakered whitefish increased, contrary to our hypothesis, reliance on pelagic‐based energy in the face of invasion. Our findings demonstrate that the trophic ecology of invaded systems can differ in multiple and subtle ways that have consequences for community‐ and ecosystem‐level energy flows, which if persisting over time are likely to have implications for the recruitment, growth and reproductive rate of the native fishes.

Anti‐predator mechanisms in evolutionarily predator‐naïve vs. adapted fish larvae

AbstractIt is a fundamental feature of evolution that natural selection acts on individuals to adapt to predation pressure via the development of anti‐predator mechanisms. As such mechanisms are costly in terms of energy and time, species living in habitats where predators are rare or absent were expected to show reduced predator responses. Such a reduction was expected for larvae of the native whitefish (Coregonus wartmanni) in Upper Lake Constance, as these pass their initial stage in a historically predator‐free pelagic habitat and only start to encounter predators in a later ontogenetic stage during which they shift to littoral habitat. However, a recent invader of the pelagic waters of the lake, the three‐spined stickleback (Gasterosteus aculeatus), is implicated in a severe decline in whitefish recruitment through larval predation. The predator‐naivety effect and its consequences on predation were experimentally tested by comparing predator defenses of different age classes of whitefish with those of roach (Rutilus rutilus) and perch (Perca fluviatilis), two species whose larvae grow up in a predator‐holding habitat. As predator, the three‐spined stickleback (Gasterosteus aculeatus) was selected. Sticklebacks actively hunted all prey species but predation was high on whitefish only. The addition of zooplankton (Daphnia) as alternative prey for sticklebacks in the experimental setup did not reduce predation on the whitefish larvae, indicating a clear preference for whitefish in this invasive predator. The escape responses of roach and perch were found to be clearly more complex and diverse to those of the predator‐naïve whitefish larvae. Particularly striking was that whitefish often did not show any apparent behavioral response to the approaching predator. Only large whitefish larvae (Table 1: length = 40.8 ± 0.6 mm) appeared capable of escaping predation, and this was correlated with a change in complexity of predator escape responses. Thus, differences in predation pressure for the different larvae species were highly related to the observed interspecific differences in predator defenses, and with the ontogenetic intraspecific change in whitefish from poor and inefficient predator escape responses to complex and more efficient predator escape responses. The evolutionary consequences of stickleback as an invasive predator on whitefish larvae behavior are discussed.

Introduced European smelt (Osmerus eperlanus) affects food web and fish community in a large Norwegian lake

Invasive and introduced fishes can affect recipient ecosystems and native species via altered competitive and predatory interactions, potentially leading to top-down and bottom-up cascading impacts. Here, we describe a case from a large lake in southern Norway, Storsjoen, where the illegal introduction of a small, predominantly planktivorous fish species, European smelt (Osmerus eperlanus), has led to changes in the native fish community and lake food web. Survey fishing data collected before (2007) and after (2016) the introduction indicates that smelt has become the numerically dominant fish species both in benthic and pelagic habitats, with concurrent reductions in the relative abundance of native European whitefish (Coregonus lavaretus) and Arctic charr (Salvelinus alpinus) populations. Stable isotope (δ13C and δ15N) data indicate minor changes in the trophic niches of native whitefish and Arctic charr despite partly overlapping niches with the introduced smelt. In contrast, brown trout (Salmo trutta) showed an earlier shift to piscivory, a more pelagic niche and increased growth rate, likely because of the smelt induced increase in pelagic prey fish abundance. The main trophic pathway supporting top predators (i.e., large brown trout) in Storsjoen has, therefore, shifted from a littoral to a more pelagic base. Our study demonstrates that small-sized introduced fishes can alter lake food-web dynamics, with contrasting impacts on native fishes. This knowledge is vital for future evaluation and mitigation of potential impacts of smelt introductions on lake ecosystems.

Synchronous decline of three morphologically distinct whitefish (Coregonus lavaretus) stocks in Lake Oulujärvi with concurrent changes in the fish community

Identification of ecologically mediated mechanisms that drive population dynamical changes in fish communities and polymorphic fish stocks such as those of whitefish, Coregonus lavaretus, requires data that are seldom available in freshwater systems. We assessed the stock of each morphologically distinguishable whitefish form (native lesser sparsely-rakered whitefish, native blue whitefish and stocked northern densely-rakered whitefish) in the Lake Oulujärvi during 1973–2014, and related temporal variations in population dynamics to environmental data and catch per unit of effort (CPUE) data on other species having fisheries significance. The results demonstrated a synchronous major decline in the abundance of the native whitefish forms and a decline in the length-at-age of all forms. During the study period, summer time water temperature increased and surface water phosphorous concentration decreased. Recruitment in all whitefish forms showed Ricker-type dependence on spawning stock biomass but little residual correlation with the environmental parameters. Cross-correlation analyses suggested that the re-establishment of pikeperch Sander lucioperca population affected negatively both the recruitment and biomass of whitefish but the exact effect mechanisms require further assessment. Our results exemplify that ecosystem-based fisheries management in inland waters must take into account both natural and human-induced environmental changes as well as stockings, and that knowledge-based inland fisheries management is inherently data-intensive.

Thermal habitat segregation among morphotypes of whitefish (Coregonus lavaretus: Salmonidae) and invasive vendace (C. albula): a mechanism for co‐existence?

Summary Aquatic invasive species can have a variety of negative impacts on the ecosystems they invade. Carbon and nitrogen stable isotopes in the muscle tissue of aquatic organisms have proved useful for evaluating post‐invasion dietary shifts among species. However, oxygen and carbon stable isotopes in fish otoliths have the potential to provide additional data on thermal habitat, diet and metabolism, when investigating interactions among sympatric native and invasive fishes. We conducted oxygen and carbon stable isotope analysis on the otoliths of three morphotypes of native whitefish (Coregonus lavaretus) and invasive vendace (Coregonus albula) at two sites within the sub‐Arctic Pasvik watercourse in northern Norway. Mean temperature use among morphotypes and species over the course of the growing season ranged from 7.5 °C to 11.2 °C. Otolith δ13C was significantly positively correlated to fish muscle tissue δ13C (P < 0.05, r2 = 0.53). Significant differences in temperature use and δ13C among morphotypes and between species were found in the downstream site but not the upstream site. Complementary partitioning of thermal and dietary resource use in the downstream site coincides with a higher abundance of whitefish, enabling the coexistence of both species. In contrast, vendace were dominant in the upstream site where no differentiation in resource use among morphotypes and between species was evident. This study demonstrates the usefulness of stable oxygen and carbon otolith isotopes for characterising resource use and highlights the importance of investigating thermal habitat use as a factor influencing the success of invasive fishes.

Interactions between invading benthivorous fish and native whitefish in subarctic lakes

Summary Many species are expanding their distribution towards higher latitudes and altitudes in response to climate change. These range shifts are expected to change fish community structure and alter food‐web dynamics in subarctic lakes. However, the impacts of invading species on native fish and invertebrate prey communities remain understudied. The trophic ecology of invasive species determines the likelihood of direct resource competition with native taxa. In Northern Europe, perch (Perca fluviatilis), a trophic generalist, and ruffe (Gymnocephalus cernuus), a benthic specialist, are expanding their distribution ranges northwards, colonising lakes inhabited by a native generalist, whitefish (Coregonus lavaretus). We predicted that increased fish diversity and density would deplete the invertebrate community and increase resource competition between native and invasive species. To assess the degree of resource competition between native and invasive species, we compared (i) fish and invertebrate community structure; (ii) diet and stable carbon and nitrogen ratios of whitefish, ruffe and perch and (iii) growth, condition and relative population size of whitefish in two non‐invaded lakes with two lakes containing one and two lakes containing both invasive species. Each lake was sampled on a single occasion between August and September. Benthic macroinvertebrate density and community structure were unaffected by increased consumer diversity, while top‐down control of pelagic zooplankton density and size was evident in lakes with increased fish diversity. Differences in diet and stable isotope ratios were evident between all whitefish populations, although these were not directly related to the presence of invasive species. Specialised adaptations of invasive species may confer a competitive advantage in invaded lakes; ruffe dominated the profundal niche, while perch displayed an ontogenetic shift to piscivory, reducing niche overlap with native whitefish. Growth rate and population density of whitefish were largely independent of fish community structure and were governed by local variations in lake productivity. However, there was a sign of lowered condition of whitefish in invaded systems. Shallow and more productive lakes with higher food availability supported populations of native and invasive species. Our findings indicate that trophic specialisations of invasive species play a key role in determining their impacts on the systems they invade. This study focussed on early stages of invasion, and the outcome of species interactions may change following the establishment of new species. In addition, these impacts will not be uniform across the invaded landscape as lake‐specific variations in morphometry and resource availability will alter the competitive balance between native and invasive species.

Species introduction promotes hybridization and introgression in Coregonus: is there sign of selection against hybrids?

Species introductions are considered one of the major drivers of biodiversity loss via ecological interactions and genetic admixture with local fauna. We examined two well-recognized fish species, native whitefish (Coregonus lavaretus) and introduced vendace (Coregonus albula), as well as their morphological hybrids in a single lake to test for selection against hybrids and backcrosses in the wild. A representative random subsample of 693 individuals (27.8%) was taken from the total catch of coregonids. This subsample was examined with the aim to select c. 50 individuals of pure whitefish (n = 52), pure vendace (n = 55) and putative hybrid (n = 19) for genetic analyses. The subsequent microsatellites and mitochondrial (mt) DNA analyses provided compelling evidence of hybridization and introgression. Of the 126 fish examined, four were found to be F(1) , 14 backcrosses to whitefish and seven backcrosses to vendace. The estimates of historical gene flow suggested higher rates from introduced vendace into native whitefish than vice versa, whereas estimates of contemporary gene flow were equal. Mitochondrial introgression was skewed, with 18 backcrosses having vendace mtDNA and only three with whitefish mtDNA. Hybrids and backcrosses had intermediate morphology and niche utilization compared with parental species. No evidence of selection against hybrids or backcrosses was apparent, as both hybrid and backcross growth rates and fecundities were high. Hybrids (F(1) ) were only detected in 2 year-classes, suggesting temporal variability in mating between vendace and whitefish. However, our data show that hybrids reached sexual maturity and reproduced actively, with backcrosses recorded from six consecutive year-classes, whereas no F(2) individuals were found. The results indicate widespread introgression, as 10.8% of coregonids were estimated to be backcrosses.

Invasive fish species in the largest lakes of Scotland, Northern Ireland, Wales and England: the collective UK experience

An invasive species is defined as an alien (or introduced or non-native) species whose establishment and spread threaten ecosystems, habitats or species with harm. Such threats to UK lake fish communities have long been appreciated and this review assembles case histories, including new data, from the largest lakes of Scotland, Northern Ireland, Wales and England to examine the hypothesis that at least some of these introductions have become invasive. Loch Lomond in Scotland has experienced six introductions [chub (Leuciscus cephalus), common bream (Abramis brama), crucian carp (Carassius carassius), dace (Leuciscus leuciscus), gudgeon (Gobio gobio) and ruffe (Gymnocephalus cernuus)], of which the most significant has been that of the percid ruffe, which has been implicated in a recent decline of the native coregonid whitefish (Coregonus lavaretus). In Northern Ireland, the introduction of the cyprinid roach (Rutilus rutilus) to Lough Neagh has apparently had a negative impact on some overwintering waterfowl, although the native coregonid pollan (Coregonus autumnalis) remains abundant. Llyn Tegid in Wales has received three introductions [rudd (Scardinius erythrophthalmus), ruffe and silver bream (Blicca bjoerkna)], although no impacts on the native whitefish or other fish populations have been observed. In England, individuals of at least 12 native and non-native fish species have been brought to Windermere for the purpose of live-baiting, although only those of the cyprinids roach and common bream have established abundant populations. At the same time, the native salmonid Arctic charr (Salvelinus alpinus) has declined markedly while the native esocid pike (Esox lucius) has shown changes in abundance, distribution and individual condition, although these developments have not been shown to be causally linked. None of these introductions were sanctioned by appropriate fisheries or other regulatory bodies and almost all of them probably arose from the release or escape of live-bait used by pike anglers. Of the 10 species introductions documented here, four (common bream, gudgeon, roach and ruffe) have established abundant populations and two of these (roach and ruffe) have apparently caused or currently threaten harm, supporting the hypothesis that at least some of these introductions have become invasive.

Is coexistence mediated by microhabitat segregation? An in‐depth exploration of a fish invasion

Vendace Coregonus albula has invaded the subarctic Pasvik hydrosystem, northern Norway and Russia, after being translocated from its native Finnish range into Lake Inari (Finland), upstream of Pasvik. The development of the invader and the effects on two native lake communities in the upstream and downstream part of the hydrosystem, respectively, have been monitored since 1991. In the upstream lake location, the invader relegated the native whitefish Coregonus lavaretus from the pelagic habitat within a few years. An expected similar development in the downstream location was, however, not observed. Data are presented on the diet and microhabitat use (vertical pelagic zone) for three types of replicated situation: (1) the invader v. the native species, (2) upstream v. downstream lakes and (3) early and late invasion stages, to explore the outcome of the competitive interactions. The use of different microhabitats available within the deeper pelagic zone in the downstream location was observed to have delayed the negative effects on native whitefish, possibly enabling a persistent coexistence between the two species in the pelagic zone of this lake.

THE COMPETITIVE EDGE OF AN INVADING SPECIALIST

Introduced species represent major threats to native and natural biodiversity. On the other hand, biologists may increase the understanding of ecological interactions by following communities during establishment of exotic species. Accordingly, feeding ecology and habitat use were studied in native whitefish (Coregonus lavaretus) and recently invading vendace (C. albula) in two lake localities situated 50 km apart within the subarctic Pasvik River system, northern Norway and Russia. Whitefish originally dominated the native fish communities of both lakes. The recent invasion and successive downstream expansion of vendace allowed comparisons between two sites: one in which the influence of the new potential competitor on the native fish species was weak, and one in which the influence was strong. In the downstream lake vendace was recorded for the first time at the time of the study, and only in small numbers, whereas in the upstream lake vendace had established a high population density and was the dominant fish species in the pelagic zone. No vertical segregation in pelagic habitat use was found between the two fish species in either lake. In the downstream lake both whitefish and vendace fed exclusively on zooplankton and had almost identical diets. In the upstream lake, in contrast, whitefish fed predominantly on zoobenthos and surface insects, while vendace fed mainly on zooplankton. Thus, the strong presence of vendace as a specialized planktivore reduced the availability of zooplankton as prey for the more generalist whitefish. The food segregation between the two fish species in the upstream lake was apparently interactive and caused by a strong asymmetrical competition for zooplankton, vendace being the superior species. The ecological consequences (including reduced zooplankton size and species diversity, alteration of the pelagic food web, and eutrofication as a possible cascading effect on the primary production) of the vendace invasion in the Pasvik watercourse are considerable, even after a few years, and are likely to proceed and intensify in the future.