Ecology and distribution of the Arctic Tadpole Shrimp Lepidurus arcticus (Branchiopoda, Notostraca) in the Fennoscandian Mountain Range and on the Svalbard Archipelago

Little research has been conducted on effects of iteroparous anadromous fishes on Arctic lakes. We investigated trophic ecology, fish growth, and food web structure in six lakes located in Nunavut, Canada; three lakes contained anadromous Arctic charr (Salvelinus alpinus) whereas three lakes did not contain Arctic charr. All lakes contained forage fishes and lake trout (Salvelinus namaycush; top predator). Isotope ratios (δ13C, δ15N) of fishes and invertebrates did not differ between lakes with and without anadromous Arctic charr; if anadromous Arctic charr deliver marine-derived nutrients and/or organic matter to freshwater lakes, these inputs could not be detected with δ13C and/or δ15N. Lake trout carbon (C):nitrogen (N) and condition were significantly higher in lakes with Arctic charr (C:N = 3.42, K = 1.1) than in lakes without Arctic charr (C:N = 3.17, K = 0.99), however, and ninespine stickleback (Pungitius pungitius) condition was significantly lower in lakes with Arctic charr (K = 0.58) than in lakes without Arctic charr (K = 0.64). Isotope data indicated that pre-smolt and resident Arctic charr may be prey for lake trout and compete with ninespine stickleback. Linear distance metrics applied to isotope data showed that food webs were more compact and isotopically redundant in lakes where Arctic charr were present. Despite this, lake trout populations in lakes with Arctic charr occupied a larger isotope space and showed greater inter-individual isotope differences. Anadromous Arctic charr appear to affect ecology and feeding of sympatric freshwater species, but effects are more subtle than those seen for semelparous anadromous species.

We studied the trophic structure in the pelagial and crustacean remains in the surface 1 cm of the sediment of 13 shallow, high arctic lakes in northeast Greenland (74° N). Seven lakes were fishless, while the remaining six hosted a dwarf form of Arctic charr (Salvelinus alpinus). In fishless lakes, Daphnia pulex was abundant, while no daphnids were found in the pelagial of lakes with fish. In fish lakes, the zooplankton community was dominated numerically by cyclopoid copepods and rotifers. Both lake sampling and analysis of remains in the top 1 cm of the sediment indicated that the phyllopod, Lepidurus arcticus, occurred in all fishless lakes, but was either absent or present in low densities from lakes with fish. Adult Lepidurus are mainly predators and forage in the top layer of the sediment. An analysis of surface sediment revealed low abundance of the benthic chydorids Alona sp. and Macrothrix sp. in lakes with Lepidurus, while they were abundant in lakes with fish. The low abundance in fishless lakes could not be explained by damage of crustacean remains caused by Lepidurus feeding in the sediment, because remains of the more soft-shelled, pelagic-living Daphnia were abundant in the sediment of these lakes. No significant differences between lakes with and without fish were found in chlorophyll a, total phosphorus, total nitrogen, conductivity or temperature, suggesting that the observed link between Lepidurus arcticus and the benthic crustacean community is causal. Consequently, remains of crustaceans in high arctic lake sediments may be useful for detecting the impact of past climate change on top-down control by fish. Not only remains of pelagic species, but also of Lepidurus and some benthic chydorids, may be used to detect changes in fish abundance and predation pressure in the past.

Leptin and ghrelin in anadromous Arctic charr: Cloning and change in expressions during a seasonal feeding cycle

Salmonid fishes exhibit marked intra-specific variation in muscle pigmentation, primarily due to individual differences in the accumulation and assimilation of dietary carotenoids. Carotenoids are synthesized by primary producers and microorganisms, and present in the tissues of crustaceans that can serve as important prey for salmonids. Despite anadromous Arctic char ( Salvelinus alpinus ) being a key subsistence and economic resource across Inuit Nunangat, their muscle pigmentation in relation to diet and environmental variability (e.g., sea ice dynamics) has not been investigated. Using carotenoid spectrophotometry analysis and a muscle colour scale, we examined the influence of Arctic char diet, inferred from stomach contents, stable isotopes (δ 15 N), and highly branched isoprenoids on their muscle pigmentation, as well as muscle pigmentation of their prey near the communities of Rankin Inlet and Naujaat, Nunavut in two years (2021, 2022) with contrasting sea ice cover. Among prey types, invertebrates had higher carotenoid concentrations than fishes. Arctic char in Naujaat contained higher muscle carotenoid concentrations and redder muscle than in Rankin Inlet in 2021, associated with a higher invertebrate-based diet and more prevalent sea ice cover. In 2022, muscle carotenoid concentrations of Naujaat and Rankin Inlet Arctic char were similar, associated with a largely fish-based diet and similar sea ice cover, although muscle still remained redder in Naujaat Arctic char. Inter-annual variation in carotenoid concentration and muscle pigmentation associated with diet variability observed in this species may affect local resource users over the long-term due to unpredictable climate-driven environmental changes, resulting in socioeconomic impacts across the Arctic.

Arctic char (Salvelinus alpinus) are a fish species ubiquitous to the fresh waters of Arctic region and brook char (Salvelinus fontinalis) are similarly common across the sub-Arctic region of eastern Canada. Populations can be small in numbers, especially farther north thus it is important to develop non-lethal methods of sampling these fish to minimize the invasiveness and impact of scientific research. We examined the stable isotopes of nitrogen and carbon in white muscle, caudal fin, and adipose fin tissues of Arctic char and brook char (S. fontinalis) from northern Quebec and Labrador, Canada. Our results revealed several broad conclusions. First, differences among muscle, caudal fin, and adipose fin tissues were ~1 ‰ for freshwater Arctic and brook char. Second, the two species within the same drainage had similar stable isotope levels and tissue differences. Third, anadromous Arctic char show similar, non-significant differences among these tissues for δ15N, but muscle δ13C was highly enriched. Fourth, the stable isotope levels and tissue differences were the same for anadromous Arctic char from two watersheds where char use distinctly different ocean environments. Overall, it appears that caudal fin tissue in particular is a useful surrogate for white muscle δ13C and δ15N levels for Arctic and brook char in this region and thus, a non-lethal collection of a small sample of caudal fin tissue will provide an accurate measure of white muscle isotope levels.

– In 2000, the Atlantic salmon (Salmo salar L.) stock in the river Signaldalselva, North Norway was found to be infected with the monogenean Gyrodactylus salaris (Malmberg). This river system has a multispecies fish community of nine species in total. Low densities of Atlantic salmon parr were found during electrofishing in October (2003) with a prevalence of 94% and a mean abundance of 848 G. salaris. This watercourse also holds a riverine stock of anadromous Arctic charr (Salvelinus alpinus), which is not common in Norway. Among the parr of Arctic charr, 64% were infested with an abundance of 23 parasites per fish. The most heavily infected 0+ and 1+ juvenile Arctic charr had 469 and 534 parasites, respectively, indicating that the parasites are able to reproduce on Arctic charr in the wild. There was little variation in the rates of infestation of Arctic charr along the studied stretch of the river, even in areas with very low densities of Atlantic salmon parr. The parr of anadromous Arctic charr seem to be suitable as long‐term hosts for G. salaris. Moreover, a few (22%) infested adult sea‐running Arctic charr were captured after ascending the river in the autumn, which shows that large fish may also act as carriers of G. salaris. However, no parasites were recorded on potential anadromous Arctic charr before descending during early spring (April 2003 and April 2004). Thus, it is still not clear whether anadromous Arctic charr are able to disperse the parasite between watercourses. So far, it is uncertain whether G. salaris may increase the mortality rates of Arctic charr and thereby be a threat to these unusual occurring riverine anadromous Arctic charr stocks.

Gyrodactylus specimens infecting both anadromous Arctic charr (Salvelinus alpinus) from River Signaldalselva (northern Norway) and resident Arctic charr from Lake Pålsbufjorden (southern Norway) were identified as G. salaris using molecular markers and morphometrics. The infection in Pålsbufjorden represents the first record of a viable G. salaris population infecting a host in the wild in the absence of salmon (Salmo salar). G. salaris on charr from Signaldalselva and Pålsbufjorden bear different mitochondrial haplotypes. While parasites infecting charr in Signaldalselva carry the same mitochondrial haplotype as parasites from sympatric Atlantic salmon, G. salaris from charr in Pålsbufjorden bear a haplotype that has previously been found in parasites infecting rainbow trout (Oncorhynchus mykiss) and Atlantic salmon, and an IGS repeat arrangement that is very similar to those observed earlier in parasites infecting rainbow trout. Accordingly, the infection may result from 2 subsequent host-switches (from salmon via rainbow trout to charr). Morphometric analyses revealed significant differences between G. salaris infecting charr in the 2 localities, and between those on sympatric charr and salmon within Signaldalselva. These differences may reflect adaptations to a new host species, different environmental conditions, and/or inherited differences between the G. salaris strains. The discovery of G. salaris on populations of both anadromous and resident charr may have severe implications for Atlantic salmon stock-management as charr may represent a reservoir for infection of salmon.

Smolt of anadromous Arctic charrSahelinus alpinus(L.) migrating from Storvatn, northern Norway, had a similar feeding intensity as resident Arctic charr from the benthic‐ and pelagic zone in early summer in fresh water. While smolts fed mostly on surface insects, however, resident Arctic charr had a more broader diet consisting mostly of chironomids,Bosminasp., benthic prey and surface insects. This indicates that Arctic charr smolts have adopted a surface oriented feeding behaviour prior to their sea migration.

Arctic charr, Salvelinus alpinus (L.), occur as anadromous, resident, and landlocked populations within their circumpolar distribution. While resident Arctic charr reside in freshwater their entire life, anadromous Arctic charr migrate to sea in the summer due to the increased resource availability, but return to freshwater to overwinter and/or spawn. The migratory behaviour in Arctic charr is generally restricted to the northern range of their distribution area. The objective of this study was to estimate the amount of straying and contemporary gene flow among anadromous Arctic charr from eight river systems in northern Norway to illuminate the role of straying for the contemporary genetic stability of the populations. The results revealed that Arctic charr frequently stray among watercourses, especially among those in close geographical proximity, although strays were found nearly 500 km from their river of origin. While straying was revealed among six river systems, the results also revealed limited or no contemporary gene flow among the nine populations identified in the eight sampled river systems. The study also shows that Arctic charr may be a potential host for spreading diseases and parasites among watercourses.

Single-spawning (semelparous) anadromous fishes are known to transport contaminants from marine to freshwater habitats, but little research has been conducted on contaminant biotransport by multiple-spawning (iteroparous) anadromous fishes. We examined the effect of iteroparous, anadromous Arctic charr (Salvelinus alpinus) on mercury concentrations ([Hg]) in freshwater biota and compared [Hg] between species and life history types of Arctic charr and lake trout (Salvelinus namaycush). Data from six lakes and one coastal marine area in the Arctic territory of Nunavut, Canada, indicated that 1) lake trout had significantly lower [Hg] in lakes where anadromous Arctic charr were present; 2) [Hg] was significantly lower in recently discovered anadromous lake trout than in resident lake trout; and 3) regardless of life history, Arctic charr had significantly lower [Hg] than lake trout. These differences were explained by fish condition, age-at-size, and C:N. Biomagnification of Hg, measured as log(10)[Hg]-delta(15)N slopes, did not differ between lakes with and without anadromous Arctic charr but was significantly higher in freshwater food webs ( approximately 0.2) than in the marine food web (0.08). Some biomagnification estimates were affected by correction for fish age and size. In contrast to semelparous anadromous species, biotransport of Hg by anadromous Arctic charr appears to be offset by increased growth of freshwater fishes.

Glaciers in the Svalbard Archipelago are retreating rapidly in response to climate change. This retreat leads to the alteration of the hydrological and thermal regimes of freshwater ecosystems. In this delicate context, existing anadromous Arctic charr (Salvelinus alpinus) populations are at severe risk and might disappear from the archipelago. However, the retreat of glaciers also promotes the formation of new lake systems that might be suitable for colonization by anadromous Arctic charr. These systems may provide a substantial opportunity for the establishment of new populations of anadromous charr, potentially buffering the decline in existing systems. To date, there is a lack of information on the number of recently deglaciated lake systems that have emerged since the end of the Little Ice Age (ca. 1920) that might be suitable for charr colonization. Therefore, the goal of this paper is to provide an initial assessment of the number of these lakes. To this end, and in accordance with previously published research, this study assesses whether a recently deglaciated lake system is potentially open to colonization based on gradient, river length, and lake surface area. Depending on the applied threshold (four in total), up to 24 lake systems are classified as potentially open to colonization by anadromous Arctic charr, with Spitsbergen emerging as a potential hotspot for colonization. The findings of this paper might serve as basis for new studies and for implementing proactive management and conservation strategies to protect anadromous charr populations.

Ecotoxicological research detailing trace metal contamination and seasonal variation in the tissues of northern fishes such as Arctic charr (Salvelinus alpinus) has been poorly represented in the literature beyond examination of mercury. In an effort to address this, anadromous Arctic charr were collected from the Deception River watershed in the late summer and post-winter season, before quantifying seasonal and organotropic variations in dorsal muscle and liver concentrations of arsenic, cadmium, chromium, copper, nickel, lead, and zinc. Potential linkages with biological variables (fork length, age, and somatic condition) and indicators of feeding behavior (δ13C and δ15N) were also assessed. Trace metal organotropism favouring elevation in liver tissue concentrations was exhibited by cadmium, copper, nickel and zinc, while arsenic, chromium and lead exhibited no significant organotropic variation. Seasonal differences in concentrations were metal and tissue dependent, but generally increased in tissues collected from post-winter sampled Arctic charr. Significant correlations with biological and trophic descriptors were also determined to be element and tissue dependent. These parameters, in addition to season, were incorporated into multi-predictor variable models, where variations in trace metal concentration data were often best explained when season, somatic condition, and trophic descriptors were included. These variables were also of greatest relative importance across all considered trace metals and tissue types. These findings suggest that seasonally linked processes have the greatest influence on trace metal concentrations in anadromous Arctic charr. Future metal-related research on Arctic charr and other northern fish species should further consider these variables when evaluating elemental accumulation.

Anadromous Arctic char, Salvelinus alpinus, have been limited on the Norwegian coast to areas north of 65°N. In 1967 anadromous char invaded the river Granvinelv in the Hardangerfjord at 60°N, and have given rise to a dense population of stationary freshwater char in the lake Granvinvatn. During 1978–79 anadromous char spread to several rivers at the head of the fjord. Events assumed to have taken place during the melting-off phase of the last glacial period are recurring. The Hardangerfjord is colder than the outside coastal waters and will very probably function as a subarea of the char. The available data indicates that an average coastal water temperature of 14 °C at 4–5 m depth is limiting the anadromous char to the south on the Norwegian coast. Continuous water masses colder than 13.6 °C could have permitted the southward penetration of anadromous char to the Hardangerfjord in 1964, but the char may also have escaped from a hatchery in the vicinity of the fjord. Landlocked char of a river entering the head of the Hardangerfjord evidently do not possess the capacity to give rise to an anadromous population.Key words: Salvelinus alpinus, anadromous char, distribution area, southward penetration, temperature barrier

Plasma melatonin levels in the high-latitude teleost Arctic charr (Salvelinus alpinus) are constantly low during summer when feeding activity is high, and high during the dark winter when they eat little and loose weight. The question arises if melatonin is involved in the phase-setting of annual rhythms of feeding and growth and if low summer melatonin production is permissive for high summer growth in this species. The present study was therefore set out to compare the seasonal appetite and growth rhythms in Arctic charr with constantly high plasma melatonin levels from February throughout the Arctic summer (melatonin implanted, average mid-day plasma melatonin levels 1,106 ± 147 pg/ml) with those of fish with natural plasma melatonin levels (vehicle implanted and untreated fish with average mid-day plasma melatonin levels of 94 ± 13 and 58 ± 6 pg/ml, respectively). Feed intake, body mass or body length, as well as the timing of the seasonal growth rhythm, were not affected by the high summer plasma melatonin level. Further, Arctic charr fasted for 3 months had a 24 h plasma profile of melatonin which was consistently higher throughout the scotophase compared to fed charr. Although the daily melatonin production seems to be affected by the energy status of the fish, melatonin does not seem to be directly involved in regulation of the seasonal feeding and growth rhythm in the high-latitude, anadromous Arctic charr.

We examined whether brain glucocorticoid receptor (GR) modulation by polychlorinated biphenyls (PCBs) was involved in the abnormal cortisol response to stress seen in anadromous Arctic charr (Salvelinus alpinus). Fish treated with Aroclor 1254 (0, 1, 10, and 100 mg/kg body mass) were maintained for 5 mo without feeding in the winter to mimic their seasonal fasting cycle, whereas a fed group with 0 and 100 mg/kg Aroclor was maintained for comparison. Fasting elevated plasma cortisol levels and brain GR content but depressed heat shock protein 90 (hsp90) and interrenal cortisol production capacity. Exposure of fasted fish to Aroclor 1254 resulted in a dose-dependent increase in brain total PCB content. This accumulation in fish with high PCB dose was threefold higher in fasted fish compared with fed fish. PCBs depressed plasma cortisol levels but did not affect in vitro interrenal cortisol production capacity in fasted charr. At high PCB dose, the brain GR content was significantly lower in the fasted fish and this corresponded with a lower brain hsp70 and hsp90 content. The elevation of plasma cortisol levels and upregulation of brain GR content may be an important adaptation to extended fasting in anadromous Arctic charr, and this response was disrupted by PCBs. Taken together, the hypothalamus-pituitary-interrenal axis is a target for PCB impact during winter emaciation in anadromous Arctic charr.