The Effect of Carlin Tags on Survival and Growth of Anadromous Arctic Charr, Salvelinus Alpinus

Fish tagging methods are important tools in the research and management of salmonids; the Carlin tag is widely used, especially in anadromous salmonids. However, this tagging method may interfere with fish behaviour and increase post-smolt mortality. To estimate Carlin-tag-inflicted mortality in Arctic charr, we used jet injection of alcian blue (colour tags) as a control. Recapture rates were higher for the colour-tagged fish than for the Carlin-tagged fish for both one- and two-year-old smolts. For one-year-old smolts in 1992, the recapture rate was 18.9% for colour-tagged fish and 10.0% for Carlin-tagged ones. For two-year-old smolts in the same year, 34.0% of colour- and 28.6% of Carlin-tagged fish were recaptured; in 1993, recapture rates were 17.2% and 6.3% for colour- and Carlin-tagged fish, respectively. Colour-tagged one-year-old Arctic charr also grew faster than their Carlin-tagged counterparts. No differences in growth rates were found between tagging methods in two-year-olds. These results imply that for hatchery-reared Arctic charr, survival rates using Carlin tagging may be half to one third that of colour tagging. Growth was also higher among colour-tagged fish, indicating that Carlin tags alter the behaviour of fish in the sea.     

The Relevance of Individual Size to Management of Arctic Charr, Salvelinus Alpinus, Populations

Arctic charr, Salvelinus alpinus, tend to form stunted populations presumably due to competition for limited resources. In this context a long-term intensive fishery programme aiming at reducing charr density, and thereby increasing growth and harvestable sizes, was initiated in the early 1980s in a Norwegian alpine lake. Here we present long-term data on catch statistics and changes in mean weights of charr caught with gill nets on spawning grounds, as well as changes in mean weight of juvenile charr caught with funnel traps during the 1990s. Furthermore, we present results from shorter-term studies on growth, size- and age-distribution, and size-related habitat and resource utilisation of Arctic charr and brown trout, Salmo trutta, in this lake. Mean weight (± SD) of charr caught on the spawning grounds increased significantly from 129.8g (±11.9) in the years 1982–1990 to 213.1g (±37.8) in the years 1996–1999, whereas catch per unit of effort decreased significantly. Mean weight of juveniles caught in funnel traps increased significantly from 21.2g (±6.9) in 1993 to 41.9g (±14.8) in 1999. Apparently the increase in weight of spawning charr coincided with the onset of trap fishing for juvenile charr. Compared to generally shallow dwelling trout, charr grew rapidly and were generally found in deeper areas of the lake. Charr went through a distinct size-related niche shift from mainly consuming small zooplankton in the pelagic to consuming large benthic prey in shallower waters. Resource and habitat utilisation in different size-groups of charr and trout are discussed with respect to possible competitive and predatory intra- and interspecific interactions, and with regard to management of charr populations.     

The Relationship Between Spatial Distribution and Diet of Arctic Charr, Salvelinus Alpinus, In Loch Ness, U.K.

The pelagic fish community of Loch Ness, U.K., is dominated by Arctic charr, Salvelinus alpinus. Previous studies have shown that the distribution of zooplankton along the south-west to north-east axis of this elongate loch is very dynamic and determined largely by prevailing winds, but Arctic charr are consistently more abundant in the southern half of the loch. In July 1993, the diet compositions of 161 Arctic charr from 53 to 330mm in length were determined and related to their spatial distribution and those of microcrustacean zooplankton and pelagic chironomid larvae and pupae. Diets were dominated by chironomid larvae, with chironomid pupae, Bythotrephes longimanus, Bosmina coregoni and Daphnia hyalina also frequently taken. Over the whole study period, B. longimanus were more important in the diet of fish from the northern half of the loch, while chironomid larvae were more important for fish from the southern half. As a result, per capita prey weight of fish from the south was greater than that of fish from the north. However, wind-induced changes in the distribution of zooplankton along the loch were accompanied by a change in the diet composition of Arctic charr from the south.     

Diversification, Sympatric Speciation, and Trophic Polymorphism of Arctic Charr, Salvelinus Alpinus Complex, in Transbaikalia

In northern Transbaikalia, independently evolving landlocked populations of Arctic charr are found in mountain lakes. To assess the diversity of charr in this region, speciation modes involved in the evolution of charr forms, and the role of trophic polymorphism in their divergence, we studied the morphology and feeding of dwarf, small, and large forms of Arctic charr from a number of Transbaikalian lakes. Meristic data on charr from five lakes support the earlier conclusion that the three forms do not represent separate lineages but have independently diverged in sympatry in each of the lakes. In 10 lakes, the dwarf form showed varying degrees of differentiation from normal (small and large) charr in meristic characters (up to morphologically distinct and presumably reproductively isolated groupings), which is viewed as various levels of sympatric divergence. Indexes of gill raker length in fish from 20 lakes vary among populations of both dwarf and normal charr, with forms having short and long rakers being sympatric in some of these lakes. However, the index can be used only for comparing charr of different forms up to about 32cm fork length (FL) because it is strongly negatively correlated with size in larger fish. The study of charr diets in 21 lakes indicates that large charr are piscivorous whereas dwarf and small charr feed on a wide range of invertebrates, partitioning these resources in different ways. Planktivores, including very specialized ones, and non-planktivores (benthic feeders, insectivores) can be identified within the small and dwarf forms. The proportion of plankton in the diets of dwarf and small charr is positively correlated with the number and length of gill rakers while the proportion of benthos is negatively correlated. Allopatric planktivorous and non-planktivorous small charr differ in body proportions; parallel emergence of such morphotypes in different parts of the range is a characteristic feature of the Salvelinus alpinus complex.     

Seasonal Changes in Osmotic and Ionic Regulation in Arctic Charr, Salvelinus Alpinus, From a High- and a Sub-arctic Anadromous Population

Seasonal changes in hypoosmoregulatory capacity were studied in hatchery-reared offspring of a high-Arctic strain of anadromous Arctic charr, Salvelinus alpinus, from Svalbard (79°N) and a sub-Arctic strain from Hammerfest, north Norway (70°N). The fish were held in freshwater under simulated, natural light conditions (Tromsø, 69°N) and natural water temperatures, and hypoosmoregulatory capacity was determined by seawater challenge tests between February and November. An improved hypoosmoregulatory capacity was seen in both strains at the time when their wild conspecifics migrate to the sea. The time when maximum hypoosmoregulatory capacity was achieved differed significantly between the two strains, suggesting that there may be genetic differences between the two populations in how environmental cues (e.g. temperature, photoperiod) entrain the development of seawater tolerance. The development and loss of hypoosmoregulatory capacity seemed to be more rapid and abrupt in the Svalbard charr than in the Hammerfest charr. This is hypothesised to be an adaptation to the stochastic and unpredictable variations in the time when the fish are allowed to migrate in the high-Arctic, and the need to prevent migration in years when the ice break occurs very late.     

Genetic Variability and Structuring of Arctic Charr (Salvelinus alpinus) Populations in Northern Fennoscandia

Variation in presumably neutral genetic markers can inform us about evolvability, historical effective population sizes and phylogeographic history of contemporary populations. We studied genetic variability in 15 microsatellite loci in six native landlocked Arctic charr (Salvelinus alpinus) populations in northern Fennoscandia, where this species is considered near threatened. We discovered that all populations were genetically highly (mean F _ST ≈ 0.26) differentiated and isolated from each other. Evidence was found for historical, but not for recent population size bottlenecks. Estimates of contemporary effective population size (N _e) ranged from seven to 228 and were significantly correlated with those of historical N _e but not with lake size. A census size (N _C) was estimated to be approximately 300 individuals in a pond (0.14 ha), which exhibited the smallest N _e (i.e. N _e/N _C = 0.02). Genetic variability in this pond and a connected lake is severely reduced, and both genetic and empirical estimates of migration rates indicate a lack of gene flow between them. Hence, albeit currently thriving, some northern Fennoscandian populations appear to be vulnerable to further loss of genetic variability and are likely to have limited capacity to adapt if selection pressures change.     

The Biology of Arctic Charr, Salvelinus Alpinus, of Gander Lake, A Large, Deep, Oligotrophic Lake in Newfoundland, Canada

Resident Arctic charr, Salvelinus alpinus, are widespread throughout the island of Newfoundland. This study examines aspects of the biology and spatial and temporal distributions of the charr of Gander Lake, the third largest in Newfoundland (surface area = 11320ha, maximum depth = 288m, mean depth = 105.4m). The deepest part of the lake is approximately 258m below sea level. The lake is well oxygenated from the surface to the bottom during all seasons. Sampling was conducted with Lundgren multiple-mesh experimental gillnets and baited hooks. There appears to be two morphs present, based on colour (dark and pale) and certain meristic characteristics. Dark charr were caught mainly in benthic nets (at depths from 1 to 100m inclusive) with only a few pelagic captures. Pale charr were caught only in benthic nets at depths between 20 and 100m inclusive. The maximum depth sampled was 196m, but there was no catch. There was a tendency for dark charr to be found in deeper, cooler water as the upper water column and inshore areas warmed during summer. There was no apparent trend in size of charr with depth sampled. Dark and pale charr both fed on benthic macroinvertebrates; sticklebacks were consumed only by dark charr and the importance of this prey item increased with size of predator. Zooplankton and surface food were not utilised by Gander Lake charr. Results of the study are compared with findings reported for other water bodies in Newfoundland and Labrador, North America, and Europe, particularly Loch Ness which has similarities in morphometry and trophic status to Gander Lake.     

Temporal and Spatial Habitats of Anadromous Brook Charr in the Laval River and its Estuary

Anadromy in brook charr occurs across the species’ range, but few studies have examined contiguous seasonal movements and habitat utilization of freshwater and estuarine environments. We used acoustic telemetry to track movements of anadromous brook charr for 1 year in the Laval River, Quebec. Fish entered the marine environment in May and June, inhabited shallow (<1.7 m), near-shore areas (<500 m from shore), and rarely ventured beyond the headlands of the bay. They were found where salinities were 1–34 ppt and temperatures 5–18°C. There was a strong tidal periodicity to observed movements with fish running up into bays as they became inundated at high tide and then returning to deep river channels in the bays at low tide. Between late July and early September, the charr returned to freshwater and spawned in the middle and upper sections of the river in October and November. Winter habitats were dispersed over 22 km of the river including two lakes. These detailed observations are an important contribution to our understanding of the evolutionary significance of anadromy in this species. The salinity and temperature co-tolerance provides insights into the species’ post-glacial dispersal, present-day distribution, and potential habitat maps for conservation, restoration, and enhancement programmes.     

Growth and Dietary Niche in Salvelinus Alpinus and Salvelinus Fontinalis as Revealed by Stable Isotope Analysis

Arctic charr, Salvelinus alpinus, and brook charr, Salvelinus fontinalis, inhabiting three lakes in the de la Trinité River and adjacent watershed, north shore, Gulf of St. Lawrence, were sampled in 1998. Arctic charr growth differed among lakes with the smallest fish coming from the largest lake. Arctic charr weight–length equation exponents were almost identical at all sample sites. Brook charr growth was also similar in all lakes. July stomach samples from Arctic charr consisted almost entirely of cladocerans in the largest lake, less so in the intermediate sized lake and were mostly aquatic insects in the smallest lake. Brook charr stomach contents were more varied and included fish. Carbon, nitrogen and sulphur stable isotope analyses (SIA) were used to provide a spatially and temporally integrated image of charr diets. SIA corroborated observed among-lake differences and similarities in species diets and suggested lake morphometry may influence measured results. The ¹⁵N signature in brook charr muscle increased with fork-length, as a result of a shift towards piscivory with size. The ¹⁵N signature in Arctic charr muscle tissue showed a significant negative correlation with fork-length in two of the studied lakes that appears related to dietary niche shifts. Results demonstrate the ability of SIA to detect dietary shifts otherwise unobservable from standard gut content analysis.     

The Effect of Acute Stress and Temperature on Plasma Cortisol and ion Concentrations and Growth of Lake Inari Arctic Charr, Salvelinus Alpinus

One year old, individually tagged Lake Inari Arctic charr, Salvelinus alpinus, were reared at three constant temperatures, 10.3°C, 14.1°C and 18.1°C, over four weeks. Blood samples were collected from a group of unstressed fish after the cultivation period at the same time as another group of fish were subjected to acute handling stress treatment (2min netting in air and 40min (± 20min) recovery period in water). Plasma cortisol, calcium, sodium, potassium and chloride concentrations were measured on both groups. To study the effect of minor daily temperature fluctuations on the stress response of Arctic charr, two additional daily fluctuating temperature (14 ± 1°C, 18 ± 1°C) treatments were established. The samples were taken in the same manner as those in the constant temperature treatments. Growth was fastest at 10.3–14.1°C and clearly lower at 18.1°C. Pre-stress plasma cortisol levels were low but increased slightly with increasing temperature. After stressor treatment, the cortisol concentrations of Arctic charr were clearly higher in all temperature treatments but there were no significant differences in plasma cortisol concentrations among temperatures. Plasma calcium levels increased during the stress treatment but temperature did not modulate this effect. The plasma potassium concentrations declined at 14.1–18.1°C after acute stress but the response was not affected by temperature within this range. The concentrations of sodium and chloride were unaffected by acute stress. Temperatures of 10.3–18.1°C and fluctuating temperature treatments had no influence on any plasma ion concentrations. Arctic charr were able to maintain the plasma ion concentrations in fresh water at 10.3–18.1°C and after acute stress treatment. Results indicate that the optimum temperature for growth of Arctic charr has little to do with the plasma ion concentrations or the ability to maintain those concentrations after short-term stress. The plasma cortisol responses further indicate that the optimum temperature for growth of Arctic charr is not related to the suppressed ability to react to an acute handling stressor. Temperature fluctuations did not cause significant differences in cortisol levels when compared with constant temperatures.     

Takvatn Through 20 Years: Long-term Effects of an Experimental Mass Removal of Arctic Charr, Salvelinus Alpinus, From a Subarctic Lake

Between 1984 and 1989, the experimental removal of 31 tons (666000 fish) of stunted Arctic charr, Salvelinus alpinus, from Takvatn in northern Norway, had strong effects on the populations of Arctic charr, brown trout, Salmo trutta, and three-spined sticklebacks, Gasterosteus aculeatus. The littoral catch per unit effort (CPUE) of charr had decreased by 90% in 1990 and then increased to about 50% of the initial level by 1994 while the pelagic CPUE had decreased to zero. Growth in both charr and trout greatly improved when the charr density had decreased, and large fish of both species appeared in the catches. These large fish became predators on small charr in the littoral zone. The incidence of trout increased from below 1% to 15% from 1988 to 1999 after a brief peak at 30% in 1992 and 1993. The charr population attained a bimodal size distribution and did not return to the stunted state during the 10 years following the intensive fishing period. The mass removal experiment showed that it is possible to change the structure of a charr population by intensive fishing. Predation on small charr from cannibals and large trout was probably essential for maintaining the new population structure. An increase in the growth of young charr from 1995 to 1997 was related to a high consumption of Daphnia and Eurycercus. Rapid changes in the growth of charr followed the density fluctuations in sticklebacks, which show large annual variations in this system; the rapid changes in charr growth were probably caused by variations in the competition intensity for cladoceran prey between young charr and sticklebacks. Twenty years of data has provided important information, but even more time is needed to follow the long-term trends in northern lakes such as Takvatn.     

Temporal Persistence of Resource Polymorphism in Brook Charr, Salvelinus Fontinalis

Resource polymorphisms are believed to be an important intermediate step in competitive sympatric speciation. Reports of resource polymorphisms in fishes are becoming more common, but tests of the temporal persistence of resource polymorphisms remain scarce. We examined the temporal persistence of a body shape dimorphism reported previously for stream dwelling young-of-the-year brook charr, Salvelinus fontinalis, inhabiting slow vs. fast running water. In the year of our study, we found no difference in body shape between individuals in slow vs. fast flowing water, although fish in fast flowing water were of greater standard length than those in slower flowing water. We conclude that the resource polymorphism reported earlier for brook charr in streams is not stable temporally.     

The Relationship between Egg Size and the Rate of Early Development in Arctic charr, Salvelinus alpinus

Previous studies have found no consistent relationship between egg size and the rate of development in fish. This is surprising since there are several hypothesis as to why such a relationship should exist. By using eggs from Arctic charr, Salvelinus alpinus, we examined several developmental features repeatedly on live individuals. In all measured parameters except date of hatching, embryos from smaller eggs were found to develop faster. Time of hatching has often been used as a principal measurement for rate of development in fish, but our results suggest that this should be discontinued, since it is poorly correlated with the rates of development of other early life history features.     

Reproductive Investment and Energy Allocation in an Alpine Arctic Charr, Salvelinus alpinus, Population

Reproductive investment was determined in a population of stunted Arctic charr, Salvelinus alpinus, living in an ultra-oligotrophic alpine lake (altitude 1100m) in central Norway (62°51W). No reductions in somatic energy content (carcass and intestines) were detected during the spawning period. Post-spawning somatic lipid, protein and total energy content did not differ between male spawners, female spawners and immatures. The recorded reproductive output consisted of gonad tissue equivalent to 13% of total pre-spawning energy in females and 4% in males, respectively. Mean stored somatic lipid reserves were as low as 2.8% and did not change significantly from pre- (30 June) to post-spawning (1% October) samples. Female fecundity varied between 41 and 84 (mean 60) eggs, with a corresponding body length varying between 110 to 160mm (mean 13%). Mean yearly survival rate after maturation was 70% for females and 64% for males, respectively. This particularly low reproductive investment is discussed in relation to environmental conditions and low resource availability.     

A comparison of Lateral Line Morphology of Blue Cod and Torrentfish: Two Sandperches of the Family Pinguipedidae

Parapercis colias (blue cod) and Cheimarrichthys fosteri (torrentfish) are two members of the family Pinguipedidae. They reside in habitats with different background levels of hydrodynamic activity and differ in their feeding ecology. The peripheral morphology of the mechanosensory lateral line system was investigated in each species. The torrentfish is the only freshwater member of this otherwise exclusively marine family. It resides in turbulent fast flowing habitats and feeds nocturnally on stream drift. Torrentfish have many superficial neuromasts and a simple unbranched canal system. In comparison the blue cod resides in sub-tidal slow flowing habitats, is a diurnal predator and has relatively few superficial neuromasts and a well-developed branching canal system. For these two species the background level of hydrodynamic activity does not appear to be the dominant selection pressure on lateral line morphology, in the case of the torrentfish in particular it is more compelling to view lateral line morphology in the light of environmental pressures that have favoured the evolution of nocturnal feeding.     

Dietary preference and feeding selectivity of common dragonet Callionymus lyra in U.K

The gut contents of 90 individuals of common dragonet Callionymus lyra were analysed, of which 76 contained prey, along with 100 corresponding benthic grab samples in order to assess the diet of C. lyra in relation to the availability of its prey in the environment. Forty-five prey taxa were identified in the diet from 350 potential prey taxa identified in the environment. Calculation of the index of relative importance (I(RI) ) found the main food components were crustaceans (%I(RI) = 86·3), mostly the porcelain crab Pisidia longicornis (%I(RI) = 43) and other decapods (%I(RI) = 18). Polychaetes played only a supplementary role in the overall diet (%I(RI) = 12·5). This study demonstrated that C. lyra is predominantly an opportunistic feeder that can modify its feeding behaviour to exploit alternative, more abundant prey.     

Extensive feeding on sockeye salmon Oncorhynchus nerka smolts by bull trout Salvelinus confluentus during initial outmigration into a small,unregulated and inland British Columbia river

Stomach contents were collected and analysed from 22 bull trout Salvelinus confluentus at the edge of the Chilko Lake and Chilko River in British Columbia, Canada, during spring outmigration of sockeye salmon Oncorhynchus nerka smolts. Twenty of the 22 (>90%) stomachs contained prey items, virtually all identifiable prey items were outmigrant O. nerka smolts and stomach contents represented a large portion (0·0–12·6%) of estimated S. confluentus mass. The results demonstrate nearly exclusive and intense feeding by S. confluentus on outmigrant smolts, and support recent telemetry observations of high disappearance rates of O. nerka smolts leaving large natural lake systems prior to entering high‐order unregulated river systems.     

The feeding strategy of dab Limanda limanda in the southern North Sea: linking stomach contents to prey availability in the environment

The feeding strategy of dab Limanda limanda was investigated within a predefined research area in the southern North Sea for 2 years. The aims were: 1) to establish the relationship between prey availability and dab abundance, distribution, body condition and prey selection, and 2) to determine the underlying functional processes of prey choice in dab. Temporal and spatial trends of prey availability in relation to dab abundances, distribution, condition and prey selection were analysed. Temporal trends in dab condition, percentage of empty stomachs and numbers of ingested prey were apparent. In particular in the winter period 2000–2001 dab were in poor condition and prey items were only rarely found in stomachs. Similarly prey availability decreased in the environment while the abundance of dab increased. Thus, temporal changes in the nutritive state were partly thought to be attributed to density‐dependent effects. The stomach composition of dab during the two consecutive summers was mainly dominated by Pariambus typicus and Ophiura albida while in the winter period only O. albida made a significant contribution to the stomach content. Analysis of prey characteristics indicated that only prey densities in the environment significantly influenced prey choice in dab, while other characteristics such as the position of the prey in the habitat, its palatability or mobility did not have significant effects. The feeding strategy of dab thus was highly opportunistic, although trends were apparent that suggested that buried living fauna was less likely to be ingested, which was also observed in previous studies.     

Effects of Fish-farm Activity on the Limnetic Community Structure of Brown Trout, Salmo trutta, and Arctic Charr, Salvelinus alpinus

Establishment of four fish-farms during the period 1971 to 1994 in the oligotrophic lake Skogseidvatnet affected Arctic charr, Salvelinus alpinus, but not brown trout, Salmo trutta. From 1971 to 1987, an increase in mean individual size of Arctic charr was recorded, while the mean individual size of brown trout remained stable. Arctic charr were found to use deeper benthic areas than brown trout. Approximately 8% of the Arctic charr population (>26cm), were found to switch to waste food from fish-farms, resulting in a novel feeding habitat for the species. They were, however, found in gillnets distant from the fish farm cages, indicating high mobility. The habitat segregation between the two species can most likely be explained by selective differences and asymmetric competition with brown trout as the dominant species. Based on the present results, changes in the Arctic charr population may be due to increased food availability and due to a new habitat use as a waste food feeder. The reason for the brown trout population to have remained stable with respect to mean size, growth pattern and habitat use, may be due to a different diet choice than Arctic charr in this lake. Brown trout were found to feed mainly on terrestrial insects, while Arctic charr fed mainly on zooplankton and on waste food.     

Addressing Temporal Variability in Bird Calling with Design and Estimation: A Northern Bobwhite Example

Imprecise or biased density estimates can lead to inadequate conservation action, overexploitation of game species, or lost recreational opportunities. Common approaches to estimating density of avian populations often either ignore the probability that an individual is present within the sampling area but is not available to be sampled (e.g., not vocalizing), or do not consider covariates that could influence availability. Additionally, management decisions made at the management unit scale are often informed by inadequate monitoring practices, such as limited sampling intensity. In such cases, management agencies calculate density by applying correction factors (e.g., detection probabilities estimated using empirical data from a different study system) to count data, rather than estimating a detection function directly using statistical models. We conducted a simulation study using northern bobwhite (Colinus virginianus; bobwhite) as a model species to quantify the consequences of mis-specifying avian point count models on bias and precision of density estimates. We compared bias and precision of estimates from a fully specified distance-sampling model that estimates availability and detection to 4 different mis-specified approaches, including 2 approaches to calculating density using correction factors. Using correction factors to calculate density produced estimates with low bias but relatively lower precision compared to the fully specified model (CV of density estimates at 35 sites over 5 years: fully specified = 10%, correction factors = 25% and 30%). Although the mean precision and bias of the fully specified model improved with more data (70 sites over 5 years, CV = 9%; 35 sites over 10 years, CV = 9%), precision of correction factors did not (70 sites over 5 years, CV = 22% and 27%; 35 sites over 10 years, CV = 24% and 29%). The fully specified model captured the underlying temporal variation in detection and availability. Increasing sampling duration from 5 to 10 years improved modeled estimates of growth rate, even for mis-specified models, but not derived growth rates using pre-determined detection functions. We demonstrated that conducting point counts 3 times/year at a feasible number of sites can produce relatively unbiased estimates of bobwhite density. Pre-determined detection functions can be fortuitously unbiased for certain years, but they are not a reliable method for determining density or identifying trends in density over time. © 2020 The Wildlife Society.