Piscine reovirus (PRV) in wild Atlantic salmon,Salmo salar L., and sea‐trout,Salmo trutta L., in Norway

This is the first comprehensive study on the occurrence and distribution of piscine reovirus (PRV) in Atlantic salmon, Salmo salar L., caught in Norwegian rivers. PRV is a newly discovered reovirus associated with heart and skeletal muscle inflammation (HSMI), a serious and commercially important disease affecting farmed Atlantic salmon in Norway. A cross‐sectional survey based on real‐time RT‐PCR screening of head kidney samples from wild, cultivated and escaped farmed Atlantic salmon caught from 2007 to 2009 in Norwegian rivers has been conducted. In addition, anadromous trout (sea‐trout), Salmo trutta L., caught from 2007 to 2010, and anadromous Arctic char, Salvelinus alpinus (L.), caught from 2007 to 2009, were tested. PRV was detected in Atlantic salmon from all counties included in the study and in 31 of 36 examined rivers. PRV was also detected in sea‐trout but not in anadromous Arctic char. In this study, the mean proportion of PRV positives was 13.4% in wild Atlantic salmon, 24.0% in salmon released for stock enhancement purposes and 55.2% in escaped farmed salmon. Histopathological examination of hearts from 21 PRV‐positive wild and one cultivated salmon (Ct values ranging from 17.0 to 39.8) revealed no HSMI‐related lesions. Thus, it seems that PRV is widespread in Atlantic salmon returning to Norwegian rivers, and that the virus can be present in high titres without causing lesions traditionally associated with HSMI.     

Piscine orthoreovirus‐3 is prevalent in wild seatrout (Salmo trutta L.) in Norway

In 2017, a PCR‐based survey for Piscine orthoreovirus‐3 (PRV‐3) was conducted in wild anadromous and non‐anadromous salmonids in Norway. In seatrout (anadromous Salmo trutta L.), the virus was present in 16.6% of the fish and in 15 of 21 investigated rivers. Four of 221 (1.8%) Atlantic salmon (Salmo salar L.) from three of 15 rivers were also PCR‐positive, with Ct‐values indicating low amounts of viral RNA. All anadromous Arctic char (Salvelinus alpinus L.) were PCR‐negative. Neither non‐anadromous trout (brown trout) nor landlocked salmon were PRV‐3 positive. Altogether, these findings suggest that in Norway PRV‐3 is more prevalent in the marine environment. In contrast, PRV‐3 is present in areas with intensive inland farming in continental Europe. PRV‐3 genome sequences from Norwegian seatrout grouped together with sequences from rainbow trout (Oncorhynchus mykiss Walbaum) in Norway and Coho salmon (Oncorhynchus kisutch Walbaum) in Chile. At present, the origin of the virus remains unknown. Nevertheless, the study highlights the value of safeguarding native fish by upholding natural and artificial barriers that hinder introduction and spread, on a local or national scale, of alien fish species and their pathogens. Accordingly, further investigations of freshwater reservoirs and interactions with farmed salmonids are warranted.     

Recovery and re-establishment of Atlantic salmon, Salmo salar, in limed Norwegian rivers

A total of 21 acidified Norwegian rivers are now being limed to re‐establish or restore Atlantic salmon, Salmo salar L., stocks. Natural reproduction of Atlantic salmon was evident 1 year after the first year of liming in all rivers that had lost their native stocks (n = 9) except for one river. The density of fry (age 0+) developed significantly more rapidly in rivers that supported remnant stocks than in rivers that had lost their stocks, based on data 5 years after treatment. Nine of the study rivers were supplied with hatchery‐reared salmon, mainly unfed fry. Of the rivers with lost stocks, those which were supplied with fish had significantly higher densities than those that were not enhanced. On the other hand, rivers with remnant stocks that were supplied with fish had significantly lower densities of salmon fry than those that did not undergo such mitigation measures. In 2001, all limed rivers yielded 41.9 t of salmon.     

Evaluation of a new management scheme for Norwegian Atlantic salmon Salmo salar

Atlantic salmon, Salmo salar L., stocks are decreasing worldwide, and major efforts are underway to conserve populations that are threatened. In a recent effort to conserve the Norwegian salmon, the Norwegian government implemented in 2007 a scheme called National Atlantic Salmon Watercourses and Fjords (NASW), where 52 rivers were given special protection. Here, the scheme is described and it is evaluated if and to what extent the scheme has led to changes in management practice. After the implementation of the NASW scheme, fewer plans for development (e.g. hydropower plants, water abstraction, flood and erosion control) at the within‐river level were accepted for NASW‐rivers than for rivers not in the scheme. However, at the same time, there was a tendency for fewer plans overall being sanctioned in all types of rivers probably due to overall changes in management practices not related to the NASW scheme. In total, these changes could lead to increased protection of Norwegian Atlantic salmon populations.     

Effects of the Faroese long-line fishery, other oceanic fisheries and oceanic variations on age at maturity of Icelandic north-coast stocks of Atlantic salmon (Salmo salar)

Investigations were conducted on the effects of oceanic variations (as indicated by sea temperatures) and catches of the Faroese, Norwegian Sea and West Greenland salmon fisheries on the sea-age composition of Atlantic salmon (Salmo salar L.) from 22 Icelandic north-coast rivers. Catches of grilse in rivers were strongly correlated among the 22 rivers, as were the ratios of grilse caught to two-sea winter (2SW) salmon caught the next year. Four of the 22 rivers showed increasing ratios over time and three of these rivers, all in the northeast, had significantly higher mean ratios after the expansion of the Faroese fishery than before (P < 0.05). No evidence was found from ratios for the other 18 rivers to suggest that Faroese fishing was significantly depleting those stocks, even though 13 micro-tagged north-coast salmon had been recovered in the fishery in the 1988–1989 season. No evidence was found that Norwegian Sea or West Greenland fisheries affected stock composition. The mean April–May sea temperature prior to when the smolts enter the sea was significantly and positively related to ratios in eight of the 22 rivers. This result, along with frequent significant correlations in ratios among rivers, indicated that more rapid growth of smolts in their first summer may have increased grilse to 2SW salmon ratios on several rivers.     

Prediction of potential freshwater pearl mussel habitat aids in discovery of a large population of Margaritifera laevis in Iturup Island,Russia

1. Freshwater pearl mussels (family Margaritiferidae) are sensitive to human impact and environmental changes. Large declines in their abundance have prompted studies of distribution and estimations of population densities.
2. Iturup Island, a part of Kuril Islands, Russia, is considered to be within the distribution area of freshwater pearl mussels, but this information is based on only two specimens collected several decades ago. Detailed survey of the island is challenging as most of its territory is nearly impassable.
3. A preliminary analysis of island rivers was carried out prior to the surveys to discover potential freshwater pearl mussel habitats. Based on previous experience from European Russia, freshwater pearl mussel habitat was expected to occur in rivers flowing out of lowland lakes.
4. Live individuals of Margaritifera laevis were found during surveys in one river together with the unionid Beringiana beringiana, which were also found in two other rivers where the predicted habitat occurred. Based on prediction and surveys, the occurrence of freshwater pearl mussels in other rivers of Iturup Island is unlikely.
5. Pearl mussels were concentrated in a small section of the Zmeika River with a population of about 100,000 mussels. Present threats to the population include overharvest of host fish masou salmon (Oncorhynchus masou).
6. Surveys using similar methods can help to reveal unknown freshwater mussel populations on other Kuril Islands and on the mainland.

     

ON THE WILLINGNESS-TO-PAY FOR RECREATIONAL FISHING—ESCAPED FARMED VERSUS WILD ATLANTIC SALMON

This article explores to what extent escaped farmed salmon from fish farms affect the willingness-to-pay for recreational fishing of Atlantic salmon in Norwegian rivers. This is a first attempt to explore the economic consequences of escaped farmed species in terms of the anglers’ willingness-to-pay for fishing permits working through the relationship between the price of fishing permits and the share of escaped farmed salmon. The empirical analysis is based on the results from a contingent valuation survey conducted in Norway. It is found that the presence of escaped farmed salmon in Norwegian rivers may have severe economic consequences on the willingness-to-pay for recreational fishing with a reduction of up to 85% compared to a situation with a ‘pure’ wild salmon stock.     

Marine temperatures experienced by postsmolts and the survival of Atlantic salmon, Salmo salar L., in the North Sea area

The survival of two Atlantic salmon stocks that inhabit rivers confluent with the North Sea was examined in respect to historical distributions of sea surface water temperatures. The rivers Figgjo and North Esk are relatively small salmon rivers in southern Norway and eastern Scotland, respectively. Wild salmon smolts have been tagged in these rivers since 1965. Tag returns were used to evaluate the survival of salmon in the North Sea. Survival rates of one-sea-winter (1SW) and 2SW fish were correlated within stocks, as well as between stocks. Survival rates were compared with the areal extent of thermal habitat in the north-eastern Atlantic Ocean. A positive correlation was found between the area of 8–10°C water in May and the survival of salmon. A reciprocal negative correlation was also found between survival and 5–7°C water in the same month. An analysis of sea surface temperature distributions for periods of good vs. poor salmon survival showed that when cool surface waters dominate the Norwegian coast and North Sea during May, salmon survival has been poor. Conversely, when the 8°C isotherm has extended northward along the Norwegian coast during May, survival has been good. The effect of water temperature distributions on the growth of postsmolts and other survival factors are discussed.     

Prospects for the future of pink salmon in three oceans: From the native Pacific to the novel Arctic and Atlantic

While populations of other migratory salmonids suffer in the Anthropocene, pink salmon (Oncorhynchus gorbusca Salmonidae) are thriving, and their distribution is expanding both within their natural range and in the Atlantic and Arctic following introduction of the species to the White Sea in the 1950s. Pink salmon are now rapidly spreading in Europe and even across the ocean to North America. Large numbers of pink salmon breed in Norwegian rivers and small numbers of individuals have been captured throughout the North Atlantic since 2017. Although little is known about the biology and ecology of the pink salmon in its novel distribution, the impacts of the species' introduction are potentially highly significant for native species and watershed productivity. Contrasts between pink salmon in the native and extended ranges will be key to navigating management strategies for Atlantic nations where the pink salmon is entrenching itself among the fish fauna, posing potential threats to native fish communities. One key conclusion of this paper is that the species' heritable traits are rapidly selected and drive local adaptation and evolution. Within the Atlantic region, this may facilitate further establishment and spread. The invasion of pink salmon in the Atlantic basin is ultimately a massive ecological experiment and one of the first examples of a major faunal change in the North Atlantic Ocean that is already undergoing rapid changes due to other anthropogenic stressors. New research is urgently needed to understand the role and potential future impacts of pink salmon in Atlantic ecosystems.     

Lake-use by juvenile Atlantic salmon (Salmo salar L.) and other salmonids in northern Norway

Abstract– The utilization of lakes, and inlet and outlet streams by juvenile Atlantic salmon ( Salmo salar L.), brown trout ( Salmo trutta L.) and Arctic charr ( Salvelinus alpinus (L.), were investigated in 16 watercourses northern Norway, all known to inhabit salmon stocks. In lakes, fish were caught by small mesh size gill nets, while in rivers fish were caught electrofishing. In the shallow littoral (0-3 m depth) there were juvenile salmon in 15 of 19 investigated lakes, juvenile trout in 17 and juvenile charr in seven. Trout dominated significantly in numbers in the shallow littoral of seven lakes, while salmon and charr dominated in three lakes each. When trout and salmon were frequent in the shallow littoral, charr was usually not present in this habitat, but were found in the profundal zone in most of the lakes. Atlantic salmon parr utilized both shallow and deep lakes, and used both stones and macrophytic vegetation as shelter. The utilization of lakes by salmon parr seemed to be closely related to utilization of small inlet streams for spawning. In most inlet and outlet streams salmon dominated over trout in numbers, while charr were absent. This is the first documentation of lake-use by naturally occurring salmon parr in Scandinavia.     

Effect of smolt age on migratory behaviour of Baltic salmon, Salmo salar L., transplanted to the east Atlantic

Abstract. This paper describes tests which were made to determine if smolt age at release influences the migratory pattern of three different stocks of salmon, Salmo salar L. The fish were hatchery-reared and released in two different rivers, the River Imsa and the River Akerselv. Based on the tag returns we found that Baltic salmon from the River Neva, USSR differed in migratory pattern from two Norwegian stocks from the River Lone and the River Imsa. A large proportion of the 2+ River Neva smolts stayed in the fjord during the summer and autumn after release. On the other hand, 2+ smolts of the Norwegian stocks left the fjord and migrated to the feeding areas in the Norwegian Sea within a short time after release. The 1+ smolts of all stocks showed the same migratory pattern as the 2+ smolts of Norwegian origin. We propose that the observed differences in migratory pattern are influenced by the developmental rate of the smolts. The effect of developmental rate on the migration may differ among stocks. Our results show that it is possible to develop a fjord fishery by releases of 2+ smolts of Neva salmon. However, such releases must be carried out with the utmost caution, preferably in fjords with no salmon rivers, so that the possibility of gene flow between populations is minimized.     

A survey of the distribution of the PKD‐parasite Tetracapsuloides bryosalmonae (Cnidaria: Myxozoa: Malacosporea) in salmonids in Norwegian rivers – additional information gleaned from formerly collected fish

The malacosporean Tetracapsuloides bryosalmonae was detected in kidneys from Atlantic salmon parr in 64 of 91 sampled Norwegian rivers. Using real‐time PCR, this parasite was found to be present in Atlantic salmon parr in rivers along the whole coast, from the northernmost and southernmost areas of the country. In addition, T. bryosalmonae was found in kidneys from brown trout parr in 17 of 19 sampled rivers in south‐east Norway, and in Arctic charr sampled in the River Risfjordelva, located at the northernmost edge of the European mainland. In conclusion, T. bryosalmonae has a widespread distribution in salmonids in Norwegian watercourses. Proliferative kidney disease (PKD) caused by T. bryosalmonae and PKD‐induced mortality has been observed in salmonids in several Norwegian rivers and it can be speculated that more PKD outbreaks will occur as a result of climate change.     

Eggs of Atlantic Salmon (Salmo salar L) and Trout (S. trutta L); Identification by Phosphoglucoisomerase Zymograms*

Salmonid eggs were collected from spawning redds in the Norwegian rivers Alta, Gaula, and Driva in 1982. Their phosphoglucoisomerase (PGI; E.C. No. 5.3.1.9) patterns, as revealed by isoelectric focusing and histochemical staining, were compared to standard zymograms produced by Atlantic salmon (Salmo salar L.) and trout (S. trutta L.) white skeletal muscle extracts, and to the zymogram in salmon eggs of known origin. In salmon, the egg zymogram was identical with that of muscle. Two types of zymograms, identical with either salmon or trout muscle zymograms and thus regarded as species-determinants, were observed among the eggs from wild fish. Their proportions in the three rivers were as expected from current knowledge of species composition. The present findings are related to previous reports on PGI expression in salmonids. The PGI zymograms are probably diagnostic keys to species for eggs from Norwegian stream-dwelling salmonids, including Arctic char (Salvelinus alpinus L.). Some managemental implications of the present results are briefly discussed.     

Economic valuation of inland recreational fisheries: empirical studies and their policy use in Norway

Cost-benefit analyses (CBAs) of liming programmes in selected acidified rivers and lakes in southern Norway, showed a benefit–cost ratio (B/C) varying from 1.2 for brown trout, Salmo trutta L., lakes to 4.4. for Atlantic salmon, S. salar L., rivers. Contingent valuation (CV) and travel cost (TC) methods were used to estimate recreational value (use value) and non-use value of increased fish stocks. These local studies, and two national CV surveys, were used by the environmental authorities to document the benefits of liming and other fish stock restoration and preservation programmes. They were also used to calculate social benefits from local reductions in air pollution and international agreements on reduced air emissions of acid compounds. The Norwegian Fishing and Hunting Association (NJFF) also successfully used the results to increase the governmental funds for liming by 300% between 1993 and 1995. The NJFF have since used these results to fight reductions in the liming budget, and has managed to keep it constant at about €13.5 million annually. However, €40 million are needed annually to neutralize the current acid depositions in Norway. Two national CV surveys found social benefits of increased fish stocks 2–4 times higher than these costs.     

African Freshwater Fisheries and their Management

The subsistence and commercial fisheries of African rivers, floodplains and lakes are described in general terms. The problems in the management of these fisheries are thought to be more similar to those of the marine than the freshwater fisheries of Europe. Some of the problems peculiar to fisheries management in developing countries are discussed, including the difficulty of collecting reliable statistics and the unsuitability of many stock assessment models. The self-regulatory mechanisms in traditional fisheries are described briefly. The possibilities of discovering new fish stocks in swamps and lakes are considered, and the problems of licensing systems to maintain optimum yields discussed. Traditional and introduced methods of processing catches are described, and the future for African freshwater fisheries considered.     

Incidence of hybridization between Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in Ireland

The substantial growth of the farmed salmon industry in Europe since the 1970s has highlighted concerns regarding the genetic impact of escaped farmed salmon on wild salmonid stocks. High incidences of salmon × trout hybrids have been recorded in rivers situated near intensive salmon farming in Norway and Scotland, which may be indicative of a breakdown in reproductive isolation between salmon, Salmo salar L., and brown trout, Salmo trutta L. In the present study, salmonid fry and 0+ parr were collected from rivers in western Ireland. Allozyme and minisatellite DNA analysis were carried out on fry to determine the frequency of F1 hybrids from 10 rivers located within 38 km of salmon farms and three rivers at least 80 km from salmon farms. A total of 49 hybrids were recorded from 4135 salmonid fry (frequency = 1.2%). Mitochondrial DNA analysis showed that all hybrids arose from Atlantic salmon female × brown trout male crosses. Hybrid parr were recorded from one of the low-risk rivers (1.0%), but were present in seven out of the 10 catchments located within 38 km of salmon farms, with frequencies ranging from 0.7% to 3.1%. The results of the present survey, which represents the first extensive record of the levels of salmon-trout hybridization in Ireland, are discussed in relation to the continued growth of salmon farming in this country.     

Selection experiments with salmon: IV. Growth of Atlantic salmon during two years in the sea

Brood stock of Atlantic salmon were sampled from 37 rivers or riversystems (strains) for three consecutive years. Each strain was represented by several full- and half-sib families. During the freshwater period each full-sib family was reared separately and each group was given as equal environmental conditions as possible. Fingerlings large enough to become 1-year-old smolt were freeze-branded and smolts from the different strains were sampled and transported to five salmon farms along the Norwegian coast. This paper deals with body weight and length of Atlantic salmon after a growth period of 2 years in the sea.Significant differences between strains were found for all three year classes. The interaction farm × strain was significant but accounted for only a small part of the total variation. It is concluded that genotype × environment interaction can be ignored when planning a selection programme for Altantic salmon for Norwegian farming conditions. A significant interaction sire × dam was found for the 1972 year-class, implying the presence of non-additive genetic variation. The heritabilities for body weight and length estimated from sire components (year-class 1973 and 1974) were quite high: 0.31 and 0.28, respectively. Genetic correlations between body weight and length were close to unity. The heritabilities for condition factor ($\text{K=}\text{weight in g}\text{(length in cm)}{}^3\text{·100}$ were small and none of the sire components were significant. It is concluded that the combination of weight and length used in calculating the K-factor has minor genetic basis.Genetic variation in body weight of Atlantic salmon is high, and about three times as high as for body length.     

Atlantic Salmon (Salmo salar L.) in Brittany and Lower-Normandy: Preliminary Observations on the General Characteristics of Adults

This paper presents some characteristics (length, weight and age) of adult Atlantic salmon in rivers of Brittany. The data were derived from 1,578 fish caught mainly by rod and line; the remainder being from net catches in estuaries and small samples taken outside the fishing season. The bulk of the fish spent 1 or 2 years in freshwater before smoltifying. Those fish becoming smolts at the end of 1 year were the most numerous (54%). The majority of the fish sampled were spring fish (82.4%). Very few summer fish were identified and those found were mainly grilse. The high proportion of spring fish in the sample is due to the high proportion of rod-caught fish. Probably a complete census over the year would show a larger proportion of grilse and summer fish as these are not subject to heavy rod-fishing the season being closed at the beginning of June. The relationship between sea age and river age and the influence of freshwater life upon the sea life were tested in four rivers. It seems probable that sea life depends chiefly on the river and the year of smoltification rather than on the freshwater stage. The biometric characteristics of Brittany salmon were compared with data from some foreign rivers. The angling exploitation of the spring Atlantic salmon in Brittany and the lack of data about summer migrations are discussed in regard to the future of this stock.     

Patterns of Tetracapsuloides bryosalmonae infection of three salmonid species in large,deep Norwegian lakes

Proliferative kidney disease (PKD), caused by the myxozoan endoparasite Tetracapsuloides bryosalmonae, is of serious ecological and economical concern to wild and farmed salmonids. Wild salmonid populations have declined due to PKD, primarily in rivers, in Europe and North America. Deep lakes are also important habitats for salmonids, and this work aimed to investigate parasite presence in five deep Norwegian lakes. Kidney samples from three salmonid species from deep lakes were collected and tested using real-time PCR to detect PKD parasite presence. We present the first detection of T. bryosalmonae in European whitefish in Norway for the first time, as well as the first published documentation of the parasite in kidneys of Arctic charr, brown trout and whitefish in four lakes. The observed prevalence of the parasite was higher in populations of brown trout than of Arctic charr and whitefish. The parasite was detected in farmed, but not in wild, charr in one lake. This suggests a possible link with a depth of fish habitat and fewer T. bryosalmonae-infected and PKD-affected fish. Towards a warmer climate, cold hypolimnion in deep lakes may act as a refuge for wild salmonids, while cold deep water may be used to control PKD in farmed salmonids.     

Effects of low pH on the reproductive behavior of salmonid fishes

In northern Europe and America, the acidification of lakes and rivers induced by acid precipitation has damaged fish populations. At present, rapidly expanding industrial activities in East Asia have led to continuous increases in the quantity of emission of acidic pollutants, and rain of acidic levels of pH4 has precipitated throughout Japan. In this way, the effects of acid rain on fish populations have also been manifested in Japan. In order to examine the effects of low pH on the reproductive behavior of salmonids which are known to be acid-sensitive species, changes in the frequency of upstream behavior and spawning-related female nest-digging behavior in response to changes in pH were observed in mature hime salmon (land-locked sockeye salmon) Oncorhynchus nerka, brown trout Salmo trutta and Japanese char Salvelinus leucomaenis. Digging and upstream behavior were significantly inhibited in weakly acidic water of pH 5.8–6.4 formulated using sulfuric acid. Land-locked sockeye salmon was the most sensitive to changes in pH among the three species.