Wild Salmon Smolts Research Articles

Salmon lice biology, environmental factors, and smolt behaviour with implications for the Norwegian salmon farming management system: A critical review

AbstractIn 2017, a new regulatory management system, the traffic light system (TLS), was implemented to estimate the effects of salmon lice from Norwegian salmon aquaculture on marine survival of wild Atlantic salmon and forms the basis of aquaculture capacity regulation. The TLS relies on observational data and a set of models to estimate the risk for negative impact on wild salmon populations. This review of the literature that forms the basis for the TLS as well as other relevant studies is presented in the context of the currently practiced TLS and suggestions are made for immediate and long‐term improvements. The main findings of this review are that: (1) assumed timing and duration of smolt migration contribute to unreliable observational and modelled data and overestimates of infection pressure; (2) production of lice larvae from farmed salmon is overestimated; (3) TLS model systems rely on or are calibrated by the same potentially flawed data; (4) lice‐associated mortality in wild salmon smolts may be overestimated; and (5) lice infection levels on farms are not associated with measurable effects on wild salmon. Recommendations to improve the accuracy and reliability of the TLS, and hence its environmental efficiency include the more complete use of available biological and physical environmental variables, adjusting the time period that observational data are registered and modelled data are integrated, adjusting the interpretation of data including recognition of uncertainty in model outcomes, and use of more realistic assumptions concerning lice‐induced mortality thresholds.

Considering elements of natural strategies to control salmon lice infestation in marine cage culture

Salmon lice are a severe problem in salmonid aquaculture and also affect wild salmon smolts migrating through fjord systems in spring. To keep the lice burden within acceptable limits, frequent use of chemical delousing has resulted in the parasite becoming resistant to these treatments. Alternative thermal and mechanical delousing practices induce welfare problems and loss of farmed fish. To avoid losing the constant arms race with the parasite, we need a new approach to the problem. Inspired by the natural host-parasite balance, we propose a change in salmonid aquaculture practices by combining and improving existing management strategies for a more holistic and sustainable vision of the industry. Before salmonids were farmed in open cages, few hosts were available for salmon lice during winter, which reduced the salmon lice populations to a minimum when the wild smolts were migrating to sea. Thus, the natural strategy is to decrease host availability for a sufficient period of time to allow salmon lice nauplii to die of starvation. Due to the long survival and drift of the nauplii, it is important to significantly increase the distance between open farming units, either by organising and aggregating farms in extensive fallowing areas with significant distance to other corresponding areas or by controlling water flow through active production units during extensive fallowing. Here we primarily address environmental interactions. Economic and juridical implications of the proposed strategy are not discussed in detail. However, we do briefly suggest relevant current regulations and possible costs and benefits of reducing delousing treatment intensity.

Activities for Prevention of Gyrodactylus Salaris Distribution in the Kola Peninsula Rivers

Monitoring of distribution of monogenean ectoparasite Gyrodactylus salaris, dangerous for wild populations of the Atlantic salmon in northwest Europe, is carried out by Veterinary Services and the profile scientific organizations in different European countries. In Murmansk area, Gyrodactylus lavareti was first found in a trout farm in Tuloma River in 1996. From now on, representatives of genus Gyrodactylus are annually identified in farmed fish in Tuloma River, according to ichthyopatholocic observations of salmonid farms in Murmansk area. Species G. salaris was indicated in 2016 in farmed trout in Tuloma River and in wild salmon smolts in Pak River of the Nizhnetulomsky water basin. Throughout a number of years, the experts of Regional Veterinary Service and the scientific organizations of Murmansk area discuss necessity of working out of measures to prevent Gyrodactylus salaris introduction in the rivers of the Kola Peninsula with wild populations of the Atlantic salmon. Any transport of smolt and live fish from the freshwater objects of Baltic Sea basin to the water objects of the Barents Sea basin sea would become the most significant threat by parasite Gyrodactylus salaris distribution and might cause a damage of natural populations of the Atlantic salmon of Kola Peninsula.

Immune response genes and pathogen presence predict migration survival in wild salmon smolts.

We present the first data to link physiological responses and pathogen presence with subsequent fate during migration of wild salmonid smolts. We tagged and non-lethally sampled gill tissue from sockeye salmon (Oncorhynchus nerka) smolts as they left their nursery lake (Chilko Lake, BC, Canada) to compare gene expression profiles and freshwater pathogen loads with migration success over the first ~1150 km of their migration to the North Pacific Ocean using acoustic telemetry. Fifteen per cent of smolts were never detected again after release, and these fish had gene expression profiles consistent with an immune response to one or more viral pathogens compared with fish that survived their freshwater migration. Among the significantly upregulated genes of the fish that were never detected postrelease were MX (interferon-induced GTP-binding protein Mx) and STAT1 (signal transducer and activator of transcription 1-alpha/beta), which are characteristic of a type I interferon response to viral pathogens. The most commonly detected pathogen in the smolts leaving the nursery lake was infectious haematopoietic necrosis virus (IHNV). Collectively, these data show that some of the fish assumed to have died after leaving the nursery lake appeared to be responding to one or more viral pathogens and had elevated stress levels that could have contributed to some of the mortality shortly after release. We present the first evidence that changes in gene expression may be predictive of some of the freshwater migration mortality in wild salmonid smolts.

Cost–benefit analysis of Atlantic salmon smolt releases in relation to life-history variation

Cost–benefit analysis was applied to estimate the net present value (NPV) of Atlantic salmon (Salmo salar, Carl Linnaeus) hatchery smolt releases and the spatial distribution of the present value of benefit [PV(B)] in the Baltic Sea. The benefit was assessed for the commercial fishery and separately from hatchery-reared and wild smolts. Data on Carlin tagging and on the proportions of individual salmon stocks in the commercial catches were used. The NPV of hatchery smolt releases appeared to be negative with current rearing costs and the range of applied discount rates (2–4%), and especially with the currently low overall survival of salmon smolts in the sea (<2%). A 5% recapture rate had been needed for a positive outcome. The PV(B) of wild salmon smolts was higher than that of reared salmon smolts due to their larger catch size and higher recapture rate. Both wild and reared salmon mostly benefited the fishermen operating in the Baltic Main Basin, while few fish and minor revenues were left for the coastal and river fisheries in the Bothnian Bay. Six salmon stocks, three wild and three reared, originating from the Bothnian Bay accounted for 60% of the total Atlantic salmon catch in the Baltic Sea. The current economical benefits from hatchery smolt releases to professional fishermen barely overcome the costs they cause to rearing and releasing counterparties.

Some observations on the impact of temperature and low flow on the onset of downstream movement of wild Atlantic salmon, Salmo salar L., smolts

A variety of proximate environmental triggers including water temperature and river flow have been correlated with the intensity and timing of salmon smolt migrations. In this study, the migratory timing and behaviour of wild salmon smolts leaving their natal stream were determined using a passive integrated transponder (PIT) antenna system at a study site on a tributary of the River Itchen, England. To examine the role of cumulative temperature, the onset of downstream movement of smolts was observed under natural control conditions (2000–2006). These control observations were then compared with a year when a managed severe low-flow event was imposed (2007). Under natural control conditions the onset of downstream movement was later when cumulative temperature was higher. The effect was stronger using the 30days prior to 15 March (slope=0.083, t4=3.0, p=0.04) than when using the cumulative temperature since 21 December (slope=0.037, t4=1.3, p=0.26). Analysing the effects for each age group separately retained some evidence for a later migration for smolts aged 1+ (30days prior to 15 March: slope=0.069, t4=1.5, p=0.20; since 21 December: slope=0.033, t4=0.92, p=0.41), while for 0+ smolts there was very little effect (30days prior to 15 March: slope=0.031, t4=0.2, p=0.88; since 21 December: slope=−0.010, t4=−0.5, p=0.66). Taken as a whole, the results show no evidence of a negative relationship between cumulative temperature and the initiation of downstream movement of salmon smolts, and therefore appear contrary to previous studies. Migration of smolts under both control conditions and low flow was significantly correlated with sunset (p<0.01, r=0.47, n=170; p<0.01, r=0.48, n=36, respectively). The mean date of migration for 0+ smolts under low flow conditions was estimated to be 5.8days earlier than in the control years (95% CI 0.8 to 10.9days earlier). This difference was statistically significant (t5=−3.0, p=0.031). By contrast, 1+ smolts did not migrate earlier under low flow (estimated 1.1days earlier, t5=−0.27, p=0.80, 95% CI 11.6days earlier to 9.5days later) and the migratory behaviour of both age groups appeared to be unaffected by the drought conditions.

Sonic tracking of wild cod, Gadus morhua, in an inshore region of the Bay of Fundy: a contribution to understanding the impact of cod farming for wild cod and endangered salmon populations

Abstract Sea cage trials of Atlantic cod farming have begun in the Bay of Fundy region. We fitted inshore wild cod (n = 10) captured in the Quoddy region with sonic tags during the late summer of 2004 to provide data on their temporal and spatial residency and habitat usage, with a view to understanding the potential for impact between escaped farmed cod and wild cod and other fish species, particularly Atlantic salmon. Most of the tagged cod remained within a restricted corridor in the inshore zone, occupied deep water (75–130 m) within several kilometres of the release point, and undertook local movements. Three cod undertook more extensive movements; one fish emigrated offshore immediately, and two fish moved as far as 14 km from the release point before returning, 52–54 h later, to the area in which the other cod were located. The mean residence time in the inshore zone was 55 days. In the late autumn, there was a staggered pattern of departure from the coastal zone, although one fish over-wintered in Passamaquoddy Bay. Three of the nine cod that migrated offshore in autumn 2004 returned within a three-week period in May 2005, after a mean absence of 172 days, and reoccupied the inshore region inhabited the previous year. These cod left the region again after a mean residence of 120 days during the spring and summer. The presence of some of the tagged cod in the principal migration corridor for wild salmon smolts during the period of their migration suggests that escapes from cod farms could result in increased predation on salmon smolts from endangered populations.

Size of wild and hatchery-reared Atlantic salmon populations in the northern Baltic Sea estimated by a stratified mark-recapture method

Abstract We estimated the total size of the Atlantic salmon (Salmo salar) population complex (wild and cultured) in the Gulf of Bothnia, northern Baltic Sea, using a stratified mark-recapture method. In 2001 and 2002, 1970 salmon were captured by the commercial trapnet fishery and tagged with external arrow tags. A total of 349 tagged fish was later recaptured among 65 180 salmon screened for tags. Recoveries were gathered by the commercial trapnets and by screening fish entering counting facilities in rivers and broodstock fisheries at the river mouths. In addition, tags were recovered from recreational river catches. Our estimates suggest that the total size of the migrating population in both years was about 230 000 fish. Proportions of wild and cultured salmon differed between the two years. In 2001, the proportion of wild salmon was 37%; the corresponding figure for 2002 was 62%. Based on estimates of wild salmon smolt production and the number of released smolts, the estimated proportion of cultured smolts that survived the feeding migration and returned to the Gulf of Bothnia (2–4%) was approximately 2.5–4.5 times lower than that of wild smolts (9–10%).

Effects of water-borne 4-nonylphenol and 17β-estradiol exposures during parr-smolt transformation on growth and plasma IGF-I of Atlantic salmon ( Salmo salar L.)

4-Nonylphenol (4-NP) is an endocrine disrupting substance (EDS) capable of mimicking the action of 17β-estradiol (E 2). It has been hypothesized that 4-NP in a pesticide formulation is linked to historical declines in Canadian Atlantic salmon ( Salmo salar L.) populations, with effects being related to exposure during parr-smolt transformation (PST). To test this hypothesis, Atlantic salmon smolts were exposed to pulse-doses of water-borne 4-NP (20 ug/l), sustained doses of water-borne E 2 (100 ng/l) (positive control), or ethanol vehicle (negative control) in mid-May during the final stages of PST. Individually tagged smolts were then sampled at three times (June, July and October) to monitor subsequent growth in sea water and plasma insulin-like growth factor I (IGF-I) concentrations. Smolt weights and plasma IGF-I concentrations were both affected by E 2 and 4-NP. The effects of E 2 and 4-NP on mean smolt weights were most prominent in July and October {E 2 ( ∗98.1±2.8, ∗242.3±10.6 g), 4-NP ( ∗102.1±3.1, 255.7±9.5 g), controls (112.5±2.8, 282.3±8.8 g)} ( P<0.05), while their effects on mean plasma IGF-I concentrations were most prominent in June and October {E 2 (15.0±1.9, 28.4±1.8 ng/ml), 4-NP ( ∗14.8±1.9, ∗21.6±1.7 ng/ml), controls (20.0±1.1, 31.1±2.0 ng/ml)} ( P<0.05). Additionally, results suggest that the mechanisms of action of E 2 and 4-NP involve disruption in the GH/IGF-I axis, and that they may be different from each other. The effects of E 2 and 4-NP on growth and plasma IGF-I concentrations observed in this study are ecologically significant because they evoke concerns for successful growth and survival of wild salmon smolts exposed to low levels of estrogenic substances that may occur from current discharges into rivers supporting sea-run salmon stocks.

The Present State of Salmon (Salmo Salar L.) in Lithuania

According to historical data, salmon used to spawn in 16 rivers in Lithuania. At present wild salmon smolt production has been recorded in two rivers only, the Žeimena and Neris, both of them belonging to the Nemunas River basin. During the last decade the abundance of salmon migrating to the Nemunas River basin varied in the range of 3,400 to 7,800 individuals (on average – 4,818). The potential smolt production in Lithuanian rivers amounts to 180,000 ind. However, the actual annual wild salmon smolt production ranges from 4,500 to 20,200 ind, that makes only 2.5–11% of that potential. The average density of salmon parr in these rivers is low – 1.4 ind/100 m2. The maximum density of salmon parr in the Žeimena River amounts to 5.6–9.7 ind/100 m2 and the average density – to 4.56 ind/100 m2, 0+ age group predominating. Investigations of salmon smolt migration in the Mera River revealed, that migration usually starts in the beginning of April, and lasts till the beginning of May. Migration is the most inten...

Impact of tagging with coded wire tags on marine survival of wild Atlantic salmon ( Salmo salar L.) migrating from the R. Bush, Northern Ireland

Migrating wild salmon smolts on the R. Bush, Northern Ireland, are tagged with coded wire tags (CWTs), as part of a study of salmon marine survival. We report the results of a comprehensive comparison of the effects of tagging on wild smolt survival, made possible by the total trapping facilities on the river, which allows simultaneous assessment of returns to the river of untagged wild fish. Analysis of one sea winter (grilse) returns to fresh water of tagged and untagged wild salmon over a 13-year period indicated that the tagged groups displayed significantly poorer return rates in each year of the study and overall ( P<0.001). The difference between tagged and untagged fish varied from year to year, ranging from 0.33:1 to 0.84:1, tagged fish on average surviving at a rate of 43.6%, relative to untagged fish. While procedures were kept constant as far as possible during the study, evidence of avian predation of tagged fish released during daylight prompted a change to night-time release. This significantly improved survival of the tagged fish, but did not explain the source of the mortality differential, which remained significant throughout. Other factors possibly contributing to mortality in the tagged fish are outlined and discussed with reference to literature examples. The importance of being able to correct for mortality when using data from tagged groups of wild salmon smolts in studies of marine survival is emphasised.

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.

Potential for dispersal of Gyrodactylus salaris (Platyhelminthes, Monogenea) by sea-running stages of the Atlantic salmon (Salmo salar): field and laboratory studies

Population growth of Gyrodactylus salaris increased exponentially on Atlantic salmon (Salmo salar) smolts in laboratory experiments conducted at 12.0°C. Furthermore, G. salaris was transmitted successfully from salmon smolt to parr at 0.0, 7.5, 10.0, and 20.0%° salinity and reproduced in fresh water after direct transfer from 7.5%° (16 days), 20.0%° (4 and 8 h), and 33.0%° (5, 15, and 30 min). No G. salaris were observed on salmon parr exposed to 33.0%° for 60 min. The prevalence of G. salaris on wild salmon smolts caught approximately 25 km from the river mouth in the Drammensfjord (surface salinity 2.0-3.5%°) was 71.2% compared with 88.0% on those from the neighbouring River Lierelva. Adult wild salmon caught as prespawners, spawners, and postspawners (kelts) in the River Drammenselva were infected with G. salaris. The prevalence and abundance increased from autumn to spring, in contrast with earlier studies on salmon parr, demonstrating the possible importance of adult salmon as reservoirs for G. salaris during winter. The results support the hypothesis of brackish water dispersal of G. salaris by infected salmonids migrating in estuaries and fjords. The use of salt as a disinfectant against G. salaris in hatcheries, and the stocking of possibly infected fish into brackish and seawater, should also be reexamined.

What is the value of a wild salmon smolt, Salmo salar L.?

Information on marine and freshwater survival and exploitation of River Bush salmon was developed into a model illustrating the potential ranges of grilse production per 1000 smolts. Values were attributed to the grilse ‘crop’ at each of three potential production stages – commercial landings, angler catches and fertilized egg production – using both published and derived valuations. Using the model, a range of values per wild smolt was calculated for grilse production on the River Bush.

Strontium levels in scales and vertebrae of wild and hatchery-reared Atlantic salmon, Salmo solar L., smolts

. Analyses of the Sr-contenl in scales of Atlantic salmon, Salmo saiar L., smolts from two hatcheries revealed significant (P < 0·001) differences. These differences were reflected in the Sr-conients of their respective diets. Sr-values in scale samples taken from wild salmon smolts from 10 Norwegian rivers showed a considerable variation. Analysis of variance showed that sampling site was the major source of variation. In general the Sr-content in scales cannot be used to distinguish between hatchery-reared and wild salmon smolls, although the present results nevertheless suggest that such a distinction is possible in some localities. The Sr-contenl of the vertebrae was somewhat lower than that of the scales in both hatchery-reared and wild smolls. The Sr-conient of the scales of sea trout, Salmo trutta L., smolts from one of the sampling sites was significantly (P < 0·001) higher than that of scales of Atlantic salmon smolts from the same site. The Sr-content of the scales of all the salmon smolts sampled from a lake was higher than the values recorded for sea trout and salmon after their stay in the sea. Use of the Sr-contenl of the scales todistinguish between migratory and resident individuals should therefore be done with care.