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1.
Oxygen stable isotope temperature reconstruction methods were used to estimate mean experienced summer temperatures from growth zones within individual Arctic charr otoliths sampled from lakes with contrasting morphologies but proximate locations. For either lake, otolith‐estimated temperatures were not significantly related to back‐calculated growth. Fish in the smaller lake evidenced an increase in growth with age related to increasing use of cooler thermal habitats, with the use of thermal habitat possibly governed by predation risks. No relationships between age, growth or temperature were observed in the larger lake. Significant negative effects on back‐calculated growth were observed due to increasing air temperatures in the smaller and shallower lake, possibly owing to warmer surface and littoral waters and a limited amount of preferred cool‐water habitat. A similar relationship was not observed in the larger and deeper lake and indicated that resident Arctic charr were not as vulnerable to the impacts of temperature warming, possibly because of better behavioural thermoregulation opportunities in the cooler, deeper lake. Results provide evidence for differing climate‐influenced growth outcomes among proximately located populations, with outcomes likely to depend on the differences among habitats, including lake size and morphometry which may act to influence fish densities in available preferred thermal habitats.  相似文献   

2.
Anadromous Arctic charr, Salvelinus alpinus (L.), was introduced to a sub‐Arctic river–lake system near the village of Kujjuuaq, Nunavik, and the stable isotope values and diets of key resident fish species were used to assess changes in feeding patterns. Stable isotope values for most species did not differ significantly between the pre‐ and post‐introduction periods, with observed shifts being within the bounds of expected natural variation. Lake chub, Couesius plumbeus (Agassiz), were the single species to show a difference between study periods, with a small but significant increase in δ15N. No significant post‐introduction changes were seen in lake trout, Salvelinus namaycush (Walbaum), omnivory or in any of the assessed quantitative food web metrics. Gut contents of major fish species similarly showed significant temporal overlap between the pre‐ and post‐introduction periods, and there was no significant change in species' weight–length relationships. The minor ecological impact was interpreted in relation to the availability of open niches exploitable by ecological generalists such as Arctic charr. The explanation accords with the known habitat and feeding flexibility of Arctic charr and the ecological immaturity of sub‐Arctic lakes known to have driven adaptive variation among Arctic charr. Findings suggest that anadromous Arctic charr may be introduced at moderate densities to other sub‐Arctic watersheds without major negative food web consequences for other resident fish species.  相似文献   

3.
Abstract –  This study examined the degree and pattern of variability in trophic morphology in Arctic charr ( Salvelinus alpinus L. ) at three spatial scales: across 22 populations from Scotland and between and within two adjacent catchments (Laxford and Shin) in northern Scotland. In addition, the variability at six microsatellite loci between and within the Laxford and Shin systems was determined. Habitat use by charr differed significantly between populations. The pattern of variability in trophic morphology, known to influence foraging ability in charr, showed a very high degree of between-population variation with at least 52% of population pairs showing significant differences in head shape. Trophic morphology and genetic variation was also high over small geographical scales; variation being as high between charr from lakes within the same catchment, as between adjacent catchments. The pattern of both phenotypic and genotypic variation suggests a mosaic of variation across populations with geographically close populations often as distinct from each other as populations with much greater separation. Very low levels of effective migrants between populations, even within the same catchment, suggest that this variation is being maintained by very low straying rates between phenotypically and genetically distinct populations, even when there is no apparent barrier to movement. We conclude that the genetic and phenotypic integrity of charr populations across Scotland is high and that this adaptive radiation constitutes a 'hidden' element of diversity in northern freshwater systems. Two consequences of this are that the population (rather than the species) makes a more rational unit for the consideration of conservation strategies and that the habitat requirements and therefore management needs may differ significantly between populations.  相似文献   

4.
Individual measurements of annual, or within‐season growth were determined from tag‐recaptured Arctic charr and examined in relation to summer sea surface temperatures and within‐season capture timing in the Ungava and Labrador regions of Eastern Canada. Differences between two years of growth (2010–2011) were significant for Ungava Bay Arctic charr, with growth being higher in the warmer year. Growth of Labrador Arctic charr did not vary significantly among years (1982–1985). Regional comparisons demonstrated that Ungava Arctic charr had significantly higher annual growth rates and experienced warmer temperatures than Labrador Arctic charr. The higher annual growth of Ungava Bay Arctic charr was attributed to the high sea surface temperatures experienced in 2010–2011 and the localised differences in nearshore productivity as compared to Labrador. Within‐season growth rates of Labrador Arctic charr peaked in June, declined towards August and were negatively correlated with the length of time spent at sea and mean experienced sea surface temperatures. A quadratic model relating growth rate to temperature best explained the pattern of within‐season growth. Collectively, results suggest that increases in water temperature may have profound consequences for Arctic charr growth in the Canadian sub‐Arctic, depending on the responses of local marine productivity to those same temperature increases.  相似文献   

5.
Abstract – Stable oxygen isotopes (δ18O) derived from otoliths were used to estimate mean annual water temperatures experienced by individual Svalbard Arctic charr, Salvelinus alpinus (L.), during their first four growth seasons. The analysed Arctic charr experienced a high variety of temperatures, indicating the use of different thermal habitats. A higher proportion of the juveniles experienced warmer temperatures during their first summer compared with later summers, suggesting the selective use of the shallowest littoral areas of the lake. Although the estimated temperatures were consistent with water temperatures found in High Arctic rivers and lakes during summer, they did not represent the annual variation in air temperature registered over the 20 years of otolith measurement. Furthermore, summer otolith increment width did not correlate with the experienced temperature. However, after the second year, otolith increment width was highly dependent on increment width during the previous summer. This study estimated mean summer water temperatures experienced by individual Arctic charr during the first four growth seasons providing additional evidence that stable oxygen isotope analysis can be used to provide insight into the thermal habitat use by juvenile Arctic charr.  相似文献   

6.
Understanding the relationship between intraspecific phenotypic variation and habitat is fundamentally important to ecology and evolution. However, it is largely unknown whether the environment drives the morphological variation in riverine fish otoliths, which are potential phenotypic markers. In this study, we investigated morphological variations in the otoliths of an endemic Chinese fish (Schizothorax nukiangensis Tsao) collected from seven sites with varying environmental gradients along the Nu‐Salween River. We compared morphological characters of S. nukiangensis otoliths among sampling sites and identified environmental sources of otolith morphological variation using multivariate regression trees and multiple factor analysis. Results showed that S. nukiangensis otoliths collected from different habitats were significantly different in morphology, mainly at the rostrum, excisura and posterior rim. Variations in otolith morphology (specifically the increase in otolith length) were predominantly governed by average river gradient; this might be a functional response to hydrogeomorphic conditions. Other environmental gradients (i.e., altitude, latitude and average annual temperature) played a minor role in otolith shape. This study highlighted the role of environmental factors in determining the otolith shape in riverine fish; thus, species and population discriminations based on otolith morphology should consider intraspecific variability.  相似文献   

7.
For circumpolar species, little is known on how somatic growth rates can vary at large, transcontinental spatial scales. In this study, a meta‐analysis of growth rates was conducted for northern pike ( Esox lucius) across North America and Eurasia. Growth rates of northern pike did not differ between North American and ‘coastal Eurasian’ pike (e.g., UK, Ireland, Sweden), while growth rates for both of these groups were significantly higher compared to ‘inland Eurasian’ pike (mainly in Russia). There was no difference in growth between lentic and lotic habitats on either continent. In North America, pike growth was positively correlated with temperature, but in Eurasia, pike growth correlated poorly with most climatic variables. Similarly, maximum longevity in pike populations was significantly predicted by latitude in North America, but not in Eurasia. After standardising annual pike growth by the thermal opportunity for growth, a highly significant countergradient growth relationship was found for North American pike, while a significant, but considerably less predictive countergradient growth relationship was found for Eurasian pike. This study provides novel insights into the ecology of a circumpolar species and how populations function at extraordinarily large spatial scales. First, pike appear to be cosmopolitan across hydrologic habitats having fast or slow growth in either lentic or lotic environments. Secondly, continental‐scale differences in pike growth rates are suggestive of major genetic and life‐history differences. Finally, variable climate–growth relationships and countergradient growth patterns indicate that global climate change is likely to affect circumpolar fishes like pike in complex, nonlinear ways.  相似文献   

8.
Abstract Two methods of otolith increment analysis were used to describe spatial, temporal and gender variation in growth of sand whiting, Sillago ciliata (Cuvier), in four south‐east Australian estuaries. Mean annual standardised otolith increment widths were used as indices of individual lifetime growth rates, while raw otolith increment widths were used to describe variation in growth throughout the life of S. ciliata. Temporal variation in growth was observed at an annual scale, while spatial variation in growth was observed between estuaries. Growth rates increased significantly with decreasing latitude and greater mean sea surface temperatures. A divergence in growth rates between sexes was detected, with females growing faster than males after sexual maturity. This study highlights how otolith increment analyses can: (1) be used to analyse temporal trends in growth from a single sample and (2) provide insight into juvenile growth when samples have an absence of undersized fish.  相似文献   

9.
Spatial and temporal variation in copepod community structure, abundance, distribution and biodiversity were examined in the western subarctic North Pacific (40–53°N, 144–173°E) during 2001–2013. Continuous Plankton Recorder (CPR) observational data during the summer season (June and July) were analyzed. The latitudinal distribution of warm‐water species in June shifted northward after 2011 while no apparent latitudinal shift of cold‐water and other species was observed. Species number and the Shannon–Wiener biodiversity index (H′) in June tended to increase in the northern area after 2011. The warm‐water species abundance and center latitude of warm‐water distribution were positively correlated with sea surface temperature (SST) across sampling locations, whereas no significant correlations with SST were observed for cold‐water species or other species. Warm SSTs in June after 2011 appeared to cause the northward shift of warm‐water species distribution, which in turn contributed to the higher biodiversity in the northern area. This study demonstrated the rapid response of warm‐water species to warm SST variation, whereas cold‐water and other species did not exhibit such clear responses. These findings indicate that the response of copepods to environmental changes differs among copepod species, highlighting the importance of investigating lower trophic levels to the species level to evaluate individual species’ responses to climate change.  相似文献   

10.
Anadromous Arctic charr, Salvelinus alpinus, feed in the marine environment for several months during the summer and migrate back to fresh water in late summer to spawn and/or overwinter. While overwintering, anadromous Arctic charr are generally believed to reduce or cease feeding, and they are poorly described in their winter movement activity. This study used telemetry data collected from two locations to describe overwintering movement activity, including interindividual variation. Movement activity declined markedly during the ice‐covered period, suggesting opportunistic maintenance feeding was used as an energy conservation strategy. Fall and spring movement was correlated with daylight hours, and ice break‐up had a significant effect on the timing of outmigration. Movement activity was negatively correlated with body length, with smaller individuals being more active than larger fish. Although general activity patterns were evident, there were significant differences among individuals, particularly during spring immediately prior to lake departure. Lake size and individual differences in metabolic rate may account for some of this variation.  相似文献   

11.
Abstract – The piscivorous behaviour in a brown trout ( Salmo trutta L.) population was studied in four discrete periods over seven decades (1917–94) in the hydroelectric reservoir Tunhovdfjord in Norway established in 1919. Piscivorous brown trout were extremely scarce prior to the introduction of two fish species Arctic charr ( Salvelinus alpinus L.) and European minnow ( Phoxinus phoxinus L.) in the 1920s. Brown trout started eating minnow at 17 cm and Arctic charr at 22 cm of length. In the 1950s, the brown trout predated extensively (60% of analysed trout) on Arctic charr and minnow. During the next four decades, the incidence of piscivorous brown trout declined to 15%, whereas the frequency of brown trout eating Arctic charr remained constant at 10%. The growth pattern, expressed as back-calculated length, demonstrated similarity in three periods (1920s, 1960s and 1990s) and improved growth in the 1950s. The improvement was addressed the impoundment of a reservoir upstream. We did not find any marked change in growth rate due to piscivority, but coefficient of variance of back-calculated lengths indicated significant variation in individual growth in age group ≥6 years from 1950 onwards. We accredit this variation to the rise of piscivorous brown trout.  相似文献   

12.
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13.
In order to understand better the recruitment variability in European anchovy in the Bay of Biscay, it is important to investigate the processes that affect survival during the early life stages. Anchovy juvenile growth trajectories and hatch‐date distributions were inferred over a 3‐year period based on otolith microstructure analysis. Otolith growth trajectories showed a characteristic shape depending on their hatch‐date timing. Earlier‐born juveniles had notably broader maximum increments than later born conspecifics, resulting in higher growth rates. This observation suggests that early hatching would be beneficial for larval and juvenile growth, and, therefore, survival. The estimated juvenile hatch‐date distributions were relatively narrow compared with the extended anchovy spawning season (March–August) in the Bay of Biscay and indicated that only individuals originated mainly from the summer months (June–August) survived until autumn. Hatch‐date distributions were markedly different among years and seemed to influence the interannual recruitment strength of anchovy. We conclude that years characterized by juvenile survivors originating from the peak spawning period (May and June) would lead to considerable recruitment success. Downwelling events during the peak spawning period seem to affect larval survival. Furthermore, size‐dependent overwinter mortality would be an additional process that regulates recruitment strength in the anchovy population in the Bay of Biscay.  相似文献   

14.
Brook charr inhabit a wide variety of habitats and exhibit considerable growth variation within and among populations. We used biannual mark–recapture electrofishing surveys and PIT tags at two streams in coastal Maine to examine spatial and temporal variability in brook charr growth. We documented considerable stream‐to‐stream and year‐to‐year variation in the growth of coastal brook charr. Based on 2892 recaptures between 2006 and 2010, we developed a suite of linear mixed models to examine variation in individual growth rates at Stanley Brook as a function of environmental variables. We distilled physical habitat data from surveys in 2010 into principle components for entry into the growth model. Growth was related primarily to an interaction between season and body length, mean water temperature, and instream location. Growth rates were highest in the summer, and smaller individuals grew more rapidly than larger conspecifics in the same stream. Individuals using habitats closer to the head of tide grew faster than those in upstream locations. Physical habitat variation was not an important control of individual growth variation within Stanley Brook. We suggest local variability in growth rates should be considered when developing management strategies for coastal populations.  相似文献   

15.
Pacific halibut (Hippoglossus stenolepis) are an ecologically, commercially, and culturally important Alaskan groundfish species. Commercial harvest of halibut dates back to the late 19th century and has been managed by the International Pacific Halibut Commission (IPHC) since 1921. IPHC surveys have revealed declining trends in survey biomass in multiple regions and region‐specific declines in mean size‐at‐age (size‐at‐age) over the past two decades (>50% in some areas). Changes in size‐at‐age can arise from a variety of physical, ecological, sampling, and fishery effects, including size‐dependent fishery or predation mortality, alteration in growth from variability in prey quality or quantity, and changes in temperature‐dependent metabolic demands. Here, we develop and apply a bioenergetics model for halibut using survey‐based diet and temperature data for Alaska to evaluate potential environmental drivers of size‐at‐age. In general, juvenile (<40 cm fork length) foraging rates were highest in the Gulf of Alaska concomitant with higher potential growth and elevated basal metabolic demands during warm summer conditions. In contrast, adult (40–120 cm FL) potential growth was highest in the Eastern Bering Sea, potentially reflecting lower metabolic costs and higher rates of prey consumption in that region. We additionally find evidence for interannual variation in potential growth, with a higher frequency of reduced growth potential in the last decade, particularly in the Eastern Bering Sea in 2015 and 2016 for both juvenile and adult halibut. These results suggest the potential for patterns in size‐at‐age to arise from trophic and environmental constraints that collectively limit growth in some regions and years.  相似文献   

16.
Resource polymorphism may play an important role in the process of speciation. The Arctic char (Salvelinus alpinus) exhibits great phenotypic and genetic diversity across its range, making it an ideal species for studies of resource polymorphism and divergence. Here, we investigated genetic variation at 11 microsatellite loci among 287 Arctic char from five isolated yet proximate postglacial lakes in south‐western Alaska that were previously examined for resource polymorphism. Significant differences in pairwise FST were detected among all lakes (range from 0.05 to 0.28, all P < 0.02). In one lake (Lower Tazimina Lake), we found evidence for two genetic groups of char and for significant differences in the distribution of microsatellite variability among at least two of the three previously described body size morphotypes (‘large’‐, ‘medium’‐, and ‘small’‐bodied char; maximum FST = 0.09; differences in admixture proportions). We also found a significant association between genetic admixture proportions and gill raker counts among body size morphs (r = ?0.73, P < 0.001). Our data represent the first record of genetically distinct sympatric morphs of Arctic char in Alaska and provide further evidence that differences in morphology associated with feeding (gill rakers) and growth trajectories reflect niche diversification and promote genetic divergence in Holarctic populations of Arctic char.  相似文献   

17.
The poleward flowing East Australian Current (EAC) drives sporadic upwelling, entrains coastal water and forms the western Tasman Front (wTF), creating a mosaic of water types and larval transport routes along south eastern Australia. The spatial distribution, otolith chemistry and growth rates of larval sardine (Sardinops sagax) were examined to infer spawning location and larval transport. A gradient of increasing larval size from north to south along the shelf was not detected but was evident between the shelf and offshore in the wTF. Here larvae were larger and older. Based on the occurrence of newly hatched larvae, spawning by S. sagax between southern Queensland and mid New South Wales (NSW) was more extensive than previously reported. The otolith chemistry from two wTF larval size classes differed, implying different origins. The otolith chemistry of wTF post‐flexion larvae was similar to larvae from northern NSW, whereas wTF flexion larvae were similar to larvae observed nearby from mid‐NSW. Two possible larval transport routes, direct and indirect, are inferred from otolith chemistry, current velocities and a previously published particle tracking study. Either larvae from northern NSW were advected south and entrained with younger larvae directly into the wTF, or larvae from a range of shelf regions were advected around the southern edge of an anticyclonic eddy, to join younger larvae directly entrained into the wTF. Based on the co‐occurrence of larval ages and sizes in the wTF and their advection routes, the wTF appears to be an important larval retention zone.  相似文献   

18.
Despite long‐standing interest in foraging modes as an important element of animal space use, few studies document and compare individual foraging mode differences among species and ecological conditions in the wild. We observed and compared foraging modes of 61 wild Arctic charr, Salvelinus alpinus, 42 brown trout, Salmo trutta, and 50 Atlantic salmon, Salmo salar, in their first growing season over a range of habitats in 10 Icelandic streams. We found that although stream salmonids typically sit‐and‐wait to ambush prey from short distances, Arctic charr were more mobile during prey search and prior to prey attack than Atlantic salmon, whereas brown trout were intermediate. In all three species, individuals that were mobile during search were more likely to be moving when initiating attacks on prey, although the strength and the slope of this relationship differed among species. Arctic charr also differed from salmon and trout as more mobile individuals travelled longer distances during prey pursuits. Finally, coupled with published data from the literature, salmonid foraging mobility (both during search and prior to attack) clearly decreased from still water habitats (e.g., brook charr), to slow‐running waters (e.g., Arctic charr) to fast‐running waters (e.g., Atlantic salmon). Hence, our study suggests that foraging mode of young salmonids can vary distinctly among related species and furthers our understanding of the behavioural mechanisms shaping the geographical distribution of wild salmonids.  相似文献   

19.
We studied the otolith microstructure and growth of sardine, Sardina pilchardus, in the North Aegean Sea (eastern Mediterranean Sea), using samples of larvae and juveniles that had hatched in winter (November–January) and winter–spring (February–May), respectively. The juveniles had developed during an extended period coinciding with marked pelagic ecosystem changes (from winter, mixed conditions to summer, stratified waters). To examine the relationship between environmental changes and the observed variability in their otolith increment–width trajectories (width‐at‐age), we summarized the shape of trajectories with a four‐parameter set estimated from a growth model fit to each width trajectory. The individual parameter sets were then related to the potential oceanographic conditions that fish experienced during their development, derived from a hydrodynamic–biogeochemical model (POM‐ERSEM), implemented in the sampling area. Substantial seasonal effects were demonstrated on the otolith microstructure (platykurtic versus leptokurtic trajectories in winter‐mixed versus summer‐stratified conditions), which were related to the progressive sea surface warming. In a subsequent step, in order to study the effect of oceanographic conditions on larval and juvenile daily growth rates, a GAM (Generalized Additive Model) analysis of otolith increment widths was carried out, using model‐derived oceanographic parameters and taking into account the ‘inherent otolith growth’, expressed by the explanatory variables ‘previous increment width’ and ‘Age’. Results showed a strong and positive, linear effect of temperature on the growth rate of winter‐caught larvae, whereas in juveniles, which had developed within a wide range of temperatures, an optimum temperature for growth was observed at around 24°C.  相似文献   

20.
Abstract – Owing to limited knowledge of the habitat use and diet of juvenile Arctic charr from the High Arctic, particularly young‐of‐the‐year (YOY), we assembled data obtained from samples taken in and around Lake Hazen, Nunavut, Canada, to assess juvenile habitat use and feeding. Juvenile charr demonstrated a preference for stream environments, particularly those fed by warm upstream ponds. Charr occupying both stream and nearshore lake habitats were found to feed similarly, with chironomids occurring most frequently in diets. Some older stream‐dwelling charr preyed on smaller, younger Arctic charr. Preferred stream occupancy is likely mediated by physical barriers created mainly by water velocity, and by distance from the lake, lake‐ice dynamics, low water depth, and turbidity. Water velocities resulted in stream habitat segregation by size, with YOY mainly found in low‐velocity pools and back eddies adjacent to stream banks, but not in water velocities >0.1 m·s?1. Greatest charr densities in streams were found in small, shallow, slow‐flowing side channels, which are highly susceptible to drought. Under predicted climate change scenarios, streams fed by small ponds will be susceptible to intermittent flow conditions, which could result in increased competition among juvenile charr for the remaining stream habitats. In addition, glacier‐fed streams are likely to experience increased flow conditions that will exacerbate physical barriers created by water velocity and further reduce the availability of preferred stream habitat.  相似文献   

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