Marine trophic niche use and life history diversity among Arctic charr Salvelinus alpinus in southwestern Greenland

Life history strategies and potential marine niche use of Arctic charr Salvelinus alpinus (n = 237, 84-652 mm, total body length, L_T ) were determined during the ice-free season (2012) at three different watercourses in south-western Greenland. All Arctic charr were collected from freshwater habitats. Based on stable isotopes of δ³⁴ S, the Arctic charr were categorized as either marine- or freshwater-dependent feeders. The use of time-integrated trophic tracers (stable isotopes of δ¹³ C, δ¹⁵ N, δ³⁴ S) suggested that several trophic groups of Arctic charr operate alongside within each fjord system. The groups suggested were one group that specialized in the marine habitat, in addition to two freshwater resident morphs (small-sized resident and/or large-growing cannibalistic individuals). Stomach contents consisted entirely of freshwater and terrestrial prey (i.e., insects), indicating that marine-dependent feeders also fed in freshwater habitats after return from their marine migration. Growth and maturity patterns further supported variable life history strategies within each watercourse. The life history strategy patterns and marine trophic niche use were consistent across the watercourses along several hundred kilometres of coastline. This study represents the first ecological baseline for partially anadromous populations of Greenland Arctic charr.

Demographic and genetic description of Greenland's only indigenous Atlantic salmon Salmo salar population

A survey of the Kapisillit River system was conducted in 2005 and 2012 to study the only indigenous Atlantic salmon Salmo salar population in Greenland. Little is known about its characteristics or its relationship with other S. salar populations across the species range. Juvenile S. salar were captured in all stations surveyed within the lower river with the highest densities lower in the river and decreasing densities with increasing distance from the river mouth. Captured juveniles ranged from 0+ to 7+ years old and the predominant smolt age was between 4 and 6 years. Median length of 0+ and 1+ juveniles in August-September was 38.8 and 70.4 mm, respectively. The proportion of mature male parr increased from 4% for 1+ year old fish to 95% for fish greater than 2 years old. Genetic analysis using 96 single nucleotide polymorphisms (SNP) revealed a high degree of genetic similarity between collections, extremely low genetic diversity and low estimates of effective population size (N_e = 28.7; 95% CI = 19.7-42.4). Genetic comparison to range-wide S. salar populations demonstrated that the Kapisillit River S. salar is an outgroup of the eastern Atlantic stock complex, which is consistent with the hypothesised colonisation from the east. River morphology and the absence of glacier runoff are hypothesised to be the main reasons for the relatively high river temperatures supporting this self-sustaining population of S. salar. Given its uniqueness and persistence, this population represents an important part of range-wide biodiversity of S. salar.

Effects of sound exposure from a seismic airgun on heart rate, acceleration and depth use in free-swimming Atlantic cod and saithe

Airguns used for offshore seismic exploration by the oil and gas industry contribute to globally increasing anthropogenic noise levels in the marine environment. There is concern that the omnidirectional, high intensity sound pulses created by airguns may alter fish physiology and behaviour. A controlled short-term field experiment was performed to investigate the effects of sound exposure from a seismic airgun on the physiology and behaviour of two socioeconomically and ecologically important marine fishes: the Atlantic cod (Gadus morhua) and saithe (Pollachius virens). Biologgers recording heart rate and body temperature and acoustic transmitters recording locomotory activity (i.e. acceleration) and depth were used to monitor free-swimming individuals during experimental sound exposures (18-60 dB above ambient). Fish were held in a large sea cage (50 m diameter; 25 m depth) and exposed to sound exposure trials over a 3-day period. Concurrently, the behaviour of untagged cod and saithe was monitored using video recording. The cod exhibited reduced heart rate (bradycardia) in response to the particle motion component of the sound from the airgun, indicative of an initial flight response. No behavioural startle response to the airgun was observed; both cod and saithe changed both swimming depth and horizontal position more frequently during sound production. The saithe became more dispersed in response to the elevated sound levels. The fish seemed to habituate both physiologically and behaviourally with repeated exposure. In conclusion, the sound exposures induced over the time frames used in this study appear unlikely to be associated with long-term alterations in physiology or behaviour. However, additional research is needed to fully understand the ecological consequences of airgun use in marine ecosystems.

Marine depth use of sea trout Salmo trutta in fjord areas of central Norway

The vertical behaviour of 44 veteran sea trout Salmo trutta (275-580 mm) in different marine fjord habitats (estuary, pelagic, near shore with and without steep cliffs) was documented during May-February by acoustic telemetry. The swimming depth of S. trutta was influenced by habitat, time of day (day v. night), season, seawater temperature and the body length at the time of tagging. Mean swimming depth during May-September was 1·7 m (individual means ranged from 0·4 to 6·4 m). Hence, S. trutta were generally surface oriented, but performed dives down to 24 m. Mean swimming depth in May-September was deeper in the near-shore habitats with or without steep cliffs (2·0 m and 2·5 m, respectively) than in the pelagic areas (1·2 m). May-September mean swimming depth in all habitats was slightly deeper during day (1·9 m) than at night (1·2 m), confirming that S. trutta conducted small-scale diel vertical movements. During summer, S. trutta residing in near-shore habitat progressively moved deeper over the period May (mean 1·1 m) to August (mean 4·0 m) and then reoccupied shallower areas (mean 2·3 m) during September. In winter (November and February), individuals residing in the innermost part of the fjords were found at similar average depths as they occupied during the summer (mean 1·3 m). The swimming depths of S. trutta coincide with the previously known surface orientation of salmon lice Lepeophtheirus salmonis. Combined with previous studies on horizontal use of S. trutta, this study illustrates how S. trutta utilize marine water bodies commonly influenced by anthropogenic factors such as aquaculture, harbours and marine constructions, marine renewable energy production or other human activity. This suggests that the marine behaviour of S. trutta and its susceptibility to coastal anthropogenic factors should be considered in marine planning processes.

The first months at sea: marine migration and habitat use of sea trout Salmo trutta post-smolts

The early migration and habitat use of brown trout Salmo trutta post-smolts tagged with acoustic transmitters (n = 50) were investigated in a fjord system in central Norway from 30 April to 26 November 2014. The main aims were to investigate return rate, marine residence time and spatial use of the fjord system. Median seaward migration and return to fresh water dates were 22 May and 4 July, respectively. Of the 40 seaward migrating smolts, 26 returned to fresh water, giving a minimum return rate to fresh water of 65%. Entrance to the fjord from the river occurred mainly at night (80% of the S. trutta), however, no such diurnal pattern was observed during the return migration. Mean marine residence time was 38 days, but with large individual variation (22-99 days). The innermost parts of the study area were more utilized than the outer part of the fjord system during the sea residency, and with more use of the near shore habitat than the open, pelagic areas. Many post-smolts also utilized the outer part of the fjord system, however, and 94% of the post-smolts were recorded at least 14 km from the home river mouth. Marine survival and distribution in the fjord were size dependent with the largest individuals utilizing outer fjord areas and having higher return rates to fresh water. As far as is known, this is the first published study on temporal and spatial behaviour in the marine environment of first-time S. trutta migrants during the full course of their first trip to sea.

Does reduced feeding prior to release improve the marine migration of hatchery brown trout Salmo trutta smolts?

The aim of this study was to test the hypothesis that hatchery brown trout Salmo trutta smolts, with 50% reduced or no feeding over the last 5 months before release, were more likely to migrate to the sea than individuals with standard feeding ratios. The juvenile fish were divided into three groups 176 days before release: (A) with no feeding, (B) with 50% and (C) with 100% feeding. To study their seaward migration, 40 fish from each feeding group were tagged with acoustic transmitters and tracked by automatic listening stations in the River Nidelva, Trondheim, Norway, its estuary and in the nearest marine environment. At the time of release, mean condition factor was significantly lower in group A and the fish from groups A and B had higher levels of Na+, K+-ATPase. Significantly more fish from group A migrated to the sea, but the rate of downstream progression from release to the estuary did not differ between the three groups. In conclusion, the S. trutta smolts with no access to food in the last 176 day before release were more likely to migrate to the sea. Fish from all three feeding groups, however, appeared to smoltify and had the same rate of downstream progression to the estuary. This indicates that differences in migratory behaviour between individuals from the three feeding groups begin from the time when the fish reach saline waters. It is suggested that feeding in hatcheries has to be greatly reduced (by 50% or more) over several months to have a pronounced effect on the migratory behaviour in S. trutta.

Long-term hypo-osmoregulatory capacity in downstream migrating Atlantic salmon Salmo salar L. smolts

The duration of hypo-osmoregulatory capacity in downstream migrating Atlantic salmon Salmo salar L smolts previously stocked as startfed young-of-the year (YOY) parr was tested in the River Dalåa from mid-May to late-June 1999. Hypo-osmoregulatory capacity, measured as plasma osmolality and chloride, was assessed after seawater (SW) challenge tests (168 h, salinity = 35). All S. salar exhibited sufficient hypo-osmoregulatory capacity at the initiation of downstream migration in mid-May. Migrating S. salar smolts caught in mid-May and retained in fresh water displayed no signs of de-smoltification as they maintained hypo-osmoregulatory capacity through June. This indicates a physiological smolt window that lasts a minimum of 6 weeks (330 degree days; D°) for hatchery-produced S. salar smolts stocked as YOY parr. Based on the observed river migration speeds, it can be assumed that the S. salar smolts entered SW 2-4 weeks after initiation of migration in the upper parts of the River Dalåa. Hence, based on smolt migration and SW tolerance, it is suggested that stocking of YOY parr is a viable enhancement strategy in the River Dalåa.

Riverine and near coastal migration performance of hatchery brown trout Salmo trutta

To study migration performance and return rates of hatchery brown trout Salmo trutta smolts the first 5 months after release, 50 fish in each year (fork length, LF , 158-288 mm) were in two subsequent years tagged with acoustic transmitters and recorded by automatic listening stations in the River Nidelva (central Norway), its estuary and in the marine environment. More than half of the smolts became anadromous migrants (52% in 2011 and 70% in 2012). The fish spent longer time in the estuary than in the marine environment and the results suggest that migratory behaviour of S. trutta smolts is not only restricted to be resident or anadrome-lacustrine, but that there is also an intermediary strategy of estuarine feeding. There were no differences in LF or mass between groups of smolts with different migration patterns. Return rates from the sea within the first 5 months after release were in both years 16%. Median progression rate in the river was 0·090 LF s(-1) but decreased significantly as the smolts entered the estuary (0·015 LF s(-1) ). The long residential time in the estuary may increase the risk of negative effects of anthropogenic activities in estuaries, such as harbours and industrial development, and special attention should be given to evaluate effects of such activities.

Habitat use during the aquatic phase of the newts Triturus vulgaris (L.) and T. cristatus (Laurenti) in central Norway: proposition for a conservation and monitoring area

Abstract

Amphibian populations are declining at an alarming pace in many parts of the world. Consequently, as part of the strategy for establishing a 360 km2 conservation and reference area for amphibians in central Norway, 341 lentic water bodies were surveyed to investigate and briefly describe their hydrography and the occurrence of the newts Triturus vulgaris (L.) and T. cristatus (Laurenti) in the area. In particular we investigated the factors that could explain the presence of the respective newt species, including biotic and abiotic factors. The multiple logistic regression analyses suggested that the presence of T. cristatus was best explained by altitude and ion concentration, both in a nonlinear fashion, whereas fish had a negative effect on T. cristatus, which was never found coexisting with fish. The presence of T. vulgaris was best explained by altitude (linear relationship) and ion concentration (convex relationship), besides the occurrence of T. cristatus. Triturus vulgaris was occasionally found to occur at low densities in ponds having fish. For both species the probability of presence was higher when the opposite newt species was present. pH influenced both species in a convex nonlinear fashion with highest probability of presence around pH 6.5. This area is valuable for conservation, monitoring and reference for marginal amphibian populations. Any decline in their abundance would be discovered relatively quickly, and likely causes could be inferred. It can also serve as a reference area for future comparative studies of amphibians elsewhere.