Abundance Of Atlantic Salmon Research Articles

Spatial variation in transcript and protein abundance of Atlantic salmon during feeding migration in the Baltic Sea.

The fitness and reproductive output of fishes can be affected by environmental disturbances. In this study, transcriptomics and label-free proteomics were combined to investigate Atlantic salmon (Salmo salar) sampled from three different field locations within the Baltic Sea (Baltic Main Basin (BMB), Gulf of Finland (GoF), and Bothnian Sea (BS)) during marine migration. The expression of several stress related mRNAs and proteins of xenobiotic metabolism, oxidative stress, DNA damage, and cell death were increased in salmon from GoF compared to salmon from BMB or BS. Respiratory electron chain and ATP synthesis related gene ontology-categories were upregulated in GoF salmon, whereas those associated with RNA processing and synthesis, translation, and protein folding decreased. Differences were seen also in metabolism and immune function related gene expression. Comparisons of the transcriptomic and proteomic profiles between salmon from GoF and salmon from BMB or BS suggest environmental stressors, especially exposure to contaminants, as a main explanation for differences. Salmon feeding in GoF are thus “disturbed by hazardous substances”. The results may also be applied in evaluating the conditions of pelagic ecosystems in the different parts of Baltic Sea.

The use (and misuse) of archaeological salmon data to infer historical abundance in North America with a focus on New England

Information about historical animal or plant abundance often either explicitly or implicitly informs current conservation practice. If it can be shown that an organism was not historically abundant in a region, its conservation importance may be downgraded. In contrast to abundant archaeological support for historic importance of salmon in the Pacific Northwest, historic abundance of Atlantic salmon in New England has been called into question based on the rarity of salmon bones in archaeological sites. These data have been used to argue that the importance of salmon to the region has been exaggerated and that expensive restoration efforts in some rivers should be reconsidered. Here, we argue that lack of archaeological bone fragment abundance does not make a convincing case against historical Atlantic salmon abundance in New England for three primary reasons. First, salmon bones were rare or absent at sites that still have large salmon runs. Second, the lack of salmonid bones in general at archaeological sites suggests poor preservation and/or recovery of bone for these species relative to bones of other fishes. Third, given the presence of large numbers of non-salmonid anadromous fish in the site areas where people fished and deposited fish bones, power to detect salmon bones in studies to date may have been generally low. We present reliable historical accounts that help build a convincing case that salmon were historically abundant in New England rivers. We suggest that rarity of salmon bones in the existing archaeological data should not have unwarranted influence on present-day conservation decision-making in New England.

Evaluation of a river classification system as a conservation measure in the management of Atlantic salmon in Insular Newfoundland

AbstractIn an effort to address the decline in abundance of Atlantic salmon, Salmo salar L., in insular Newfoundland rivers, resource managers introduced a River Classification System (RCS) in 1999 to assist in the management and conservation of the resource. The RCS set daily and seasonal bag limits in the recreational fishery on a river by river basis. An analysis of the catch and effort data before and after the implementation of the RCS showed an overall decline in the number of retained salmon after the implementation of the RCS, but no change in overall effort. Upon closer examination, it was found that retention increased on Class I rivers, which had the highest allowed retention, but declined on the other class rivers. On one particular river (Harry's River), which alternated classifications from 2007 to 2010, it was found that exploitation rates increased as allowed retention increased. Newfoundland salmon anglers appear to be retention anglers and therefore the RCS was an effective tool for diverting catch and effort to specific rivers by changing retention limits.

Street lighting delays and disrupts the dispersal of Atlantic salmon (Salmo salar) fry

There has been a decline in the abundance of Atlantic salmon (Salmo salar) despite significant conservation measures designed to reduce fishing mortality. Populations at the southern edge of their historical distribution, where anthropogenic impacts on the freshwater environment may be greater, have suffered the largest decline. In this investigation, we compared the timing of Atlantic salmon fry dispersal from incubators in an aquarium under control and ecologically relevant broad spectrum street-lit conditions (median night light intensity=12lx). Fry dispersal occurred 2.8days later (F=82.9, df=1,8, p<0.001), and on average the fry were smaller at dispersal (0.017g, se=0.0012, p<0.001, n=730), in the incubators exposed to street lighting. Significant disruption to the diel pattern of fry dispersal was also observed. Dispersal under control conditions was significantly directed around a mean time of 4:17h after dusk (p<0.001, r=0.76, n=1990) with very few fry (<2%) dispersing during daylight hours. Under street lighting, the dispersal of fry was significantly delayed (mean time 6:38h after dusk; p<0.001, r=0.39, n=2413) with a significant proportion (32%) dispersing during daylight hours. Survival to dispersal in the controlled aquarium conditions was not lower under street-lit conditions (p=0.21, n=5000eggs across 10incubators). However, in the wild, the period between fry emergence and the establishment of feeding territories is considered to be of critical importance in the dynamics of salmonid populations and any disruption may reduce fitness.

Improving abundance estimates from electrofishing removal sampling

Estimates of fish abundance from electrofishing surveys depend on accurate estimation of capture probability. We examine in this paper how estimates of capture probability and abundance of Atlantic salmon from multi-pass removal sampling can be improved by comparing the results of an experimental programme of closed electrofishing sites within selected rivers in west-central Norway, and those obtained from open electrofishing sites established for monitoring long-term juvenile Atlantic salmon population abundance within the Burrishoole catchment, western Ireland. We first establish that the Carle & Strub method provides a more robust estimate of population abundance than the Zippin and Seber methods. We then show how prior information on capture probability may be used to improve the accuracy of the abundance estimate in open sites. We also show that the use of prior information with single-pass electrofishing may improve the accuracy of the abundance estimate so that it is comparable with that of multi-pass electrofishing in terms of stock prediction while requiring less sampling effort.

Weir removal in salmonid streams: implications, challenges and practicalities

Low-head dams and weirs can greatly limit the distribution and abundance of Atlantic salmon and other migratory salmonids in streams. Weirs can significantly increase the vulnerability of migratory fish to anglers, alter natural migration patterns, and exacerbate the effects of opportunistic predators. Overcrowding of fish at downstream pools can also facilitate the spread of parasites and infectious diseases, magnify the impact of pollution incidents, and increase the risk of mass mortalities, particularly at low flows. Not surprisingly, augmenting the accessible stream area constitutes one of the best ways to restore depleted salmonid populations. In this context, the removal of unused or illegal weirs can be an efficient, cheap solution to increase stream accessibility. Here, I examine some impacts of weirs on Atlantic salmon populations, and document with case studies the removal and breaching of weirs in several Iberian streams.

Twenty years of hydropower regulation in the River Alta: long-term changes in abundance of juvenile and adult Atlantic salmon

The River Alta, northern Norway (70°N), was regulated for hydropower in 1987. Densities of juveniles and catches of adult Atlantic salmon have been studied since 1980–1981 to examine the effects of regulation. The need to control environmental variables during electrofishing was emphasized, as flow variables explained up to 42% of the variation in estimated juvenile densities. The number of spawning redds was counted along the river from 1996 to 2005. The annual number of spawning redds was correlated with the catch of multi-sea-winter salmon (predominantly females). In the upper 7 km section, just downstream of the power station outlet, juvenile densities were reduced by 80% from pre-regulation levels to minimum levels in 1992–1996. This was followed by partial recovery during 1997–2005, although not entirely back to pre-regulation levels. In contrast, the general trend in the middle part of the river was a linear increase in juvenile densities during 1981–2005. Decreased juvenile densities in the upper section was subsequently followed by reduced catches of adult salmon in this part of the river. The relative catches of smolt year classes migrating to sea in the upper section was reduced by up to 75% from 1991 onwards. Spawning and recruitment in the upper section have increased in recent years, probably back to the introduction of catch-and-release angling and an increase in salmon runs. However, present day smolt production in the upper section is still reduced compared to the middle part of the river, 18 years after regulation. The decreased densities of juvenile salmon in the upper section were probably caused by several factors, of which stranding mortality due to sudden drops in the water level and increased winter mortality due to changed environmental conditions, especially reduced ice-cover, may be the most important. In conclusion, the regulation caused a considerable reduction of the salmon production in the upper 16% of salmon reaches, but did not affect the salmon population negatively further downstream. This study illustrates that apparently small environmental disturbances can cause large changes in Atlantic salmon abundance in high latitude populations.

A Global Assessment of Salmon Aquaculture Impacts on Wild Salmonids

Since the late 1980s, wild salmon catch and abundance have declined dramatically in the North Atlantic and in much of the northeastern Pacific south of Alaska. In these areas, there has been a concomitant increase in the production of farmed salmon. Previous studies have shown negative impacts on wild salmonids, but these results have been difficult to translate into predictions of change in wild population survival and abundance. We compared marine survival of salmonids in areas with salmon farming to adjacent areas without farms in Scotland, Ireland, Atlantic Canada, and Pacific Canada to estimate changes in marine survival concurrent with the growth of salmon aquaculture. Through a meta-analysis of existing data, we show a reduction in survival or abundance of Atlantic salmon; sea trout; and pink, chum, and coho salmon in association with increased production of farmed salmon. In many cases, these reductions in survival or abundance are greater than 50%. Meta-analytic estimates of the mean effect are significant and negative, suggesting that salmon farming has reduced survival of wild salmon and trout in many populations and countries.

Multidecadal North Atlantic climate variability and its effect on North American salmon abundance

Climate variability is now known to play a key role in the abundance of marine fisheries, and must be accounted for to implement sustainable management strategies. We show that North American Atlantic salmon abundance has fluctuated in parallel with the Atlantic Multidecadal Oscillation (AMO); a basin‐wide, low frequency climate mode producing cold‐warm‐cold sea surface temperatures over the last century. During the AMO warm (cool) phase salmon abundance is lower (higher). Changes in sea surface temperature associated with the AMO are most pronounced in the winter season near the Grand Banks of Newfoundland, a known overwintering area for salmon and an important time for determining survival. A moratorium on salmon fishing was established in 1992, but has so far contributed few signs of improvement in stock size. This may be explained by a shift in the AMO to a positive phase, producing persistently warm temperatures in the marine environment. Our findings show that a continued warming near the Grand Banks of Newfoundland will have a detrimental impact on this already depleted stock despite the reduction in commercial fishing.

Congruence between automatic fish counter data and rod catches of Atlantic salmon (Salmo salar) in Scottish rivers

Abstract The potential utility of rod catch and automatic fish counter data as measures of Atlantic salmon (Salmo salar) abundance in Scottish rivers was assessed. The trend (long-term) and residual (short-term) variation in the net annual count for 12 counters were compared with the trend and residual variation in either the annual or spring (February–May) rod catch, as appropriate, for the fisheries district in which the counter is located. Trends were fitted using a cubic smoothing spline and compared using reference bands. In eight of the 12 short-term comparisons, the residuals were significantly correlated. The four incongruent short-term comparisons involved the shortest time-series (≤12 years) or lowest rod catches. In eight of the 12 long-term comparisons, the trends fell within the reference bands in 50% or more of the years. Rod catch and counter data both contain useful information about Atlantic salmon abundance, albeit on different temporal and spatial scales, which should be integrated into assessment schemes.

Temporal synchrony and variation in abundance of Atlantic salmon (Salmo salar) in two subarctic Barents Sea rivers: influence of oceanic conditions

Long-term variation in Atlantic salmon (Salmo salar) stocks was analyzed in two Barents Sea rivers, the Teno and Näätämöjoki, that represent the northernmost distribution area of the species. In contrast to most of the North Atlantic area, these rivers are among a group of northern salmon rivers that, despite wide annual variation in catches, demonstrate no consistent trend for declining abundance. Variations in abundance were generally synchronous for the total catch and numbers of 1-sea-winter (1SW) and 2SW salmon during period of 1972–2003. Part of the variation observed in catches could be related to ocean climate conditions as the mean seawater temperature in July during the year of smoltification for the Kola section of the Barents Sea was significantly related to numbers of 1SW, 2SW, and 3SW salmon in the large River Teno. In contrast, NAO (North Atlantic Oscillation) indices were not related to salmon catches. The latest increase (1999–2001) in salmon catches in these rivers reflects both temporarily improved oceanic conditions and past management measures affecting offshore, coastal, and river fisheries.

Spatial and temporal trends in abundance of Atlantic salmon, Salmo salar, in Newfoundland with emphasis on impacts of the 1992 closure of the commercial fishery

AbstractClosure of the Newfoundland commercial Atlantic salmon, Salmo salar L., fishery in 1992 was the most restrictive measure introduced to help rebuild depressed local stocks of salmon. Here, the effects of the closure are evaluated by analysing trends in abundance since 1984, and estimates of survival in both freshwater and marine environments derived from enumeration of salmon at fish counting facilities. While freshwater production of smolts generally has been maintained, marine survival rates remain low (2–10%), and highly variable. Overall, total stock size differs little from that prior to the closure of the commercial salmon fishery. Spawning escapements have increased by a factor of 2 or 3 in some rivers, but in other areas total returns are lower on average than those prior to the fishery closure. Factors other than exploitation are contributing to lack of stock recovery, resulting in continued conservation concerns.

Estimating and forecasting pre-fishery abundance of Atlantic salmon (Salmo salar L.) in the Northeast Atlantic for the management of mixed-stock fisheries

Abstract Most exploitation of Atlantic salmon (Salmo salar) is restricted to “homewater fisheries”, which operate close to or within the rivers of origin of the stocks, but two “distant-water fisheries” are permitted to operate off the west coast of Greenland and in the Norwegian Sea, and take salmon from a large number of rivers over a wide geographical area. Providing robust quantitative catch advice for these mixed-stock fisheries depends upon the ability to forecast stock abundance for about 2000 salmon river-stocks around the North Atlantic, more than 1500 of which are in Europe. A “run-reconstruction” model is presented for estimating the historic pre-fishery abundance (PFA) of salmon for countries or regions around the Northeast Atlantic, based upon catch data and estimates of non-reporting rates and exploitation rates. These estimates are then used to develop predictive models of PFA on the basis of estimates of the egg deposition, derived from the run-reconstruction model and various environmental data. Although the selected environmental indices correlated with the PFA of both southern and northern European stock complexes, the main statistical significance in the forecast models was provided by temporal trends in the PFA. Clearly, such a model is only tenable in the short term, and will be poor at predicting a major change in stock status. Alternative approaches, based upon juvenile production indices and including Bayesian techniques, are therefore being considered.

Recent events concerning Atlantic salmon escapees in the Pacific

Atlantic salmon (Salmo salar L.) escapees from commercial salmon farms in Washington State, USA, and British Columbia, Canada, arecaught in fisheries from Washington State to Alaska. A large escape from a farm near Cypress Island, Washington, was likely to have been the cause of increased abundance of Atlantic salmon in Juan de Fuca Strait and higher than average catches on the west coast of Vancouver Island during the summer of 1996. The catch of Atlantic salmon in Alaska in 1996 exceeded the sum of catches in all previous years. The number of escapees recorded in fresh water has been increasing, with more than 210 adult fish observed in 29 rivers in British Columbia during 1996. During the winter of 1995/1996, 39 Atlantic salmon were reported caught in the Salmon River on Vancouver Island. Analysis of the stomach contents of these fish indicated that some were feeding in fresh water.

Fish species associations in riffle habitat of streams of varying size and acidity in New Brunswick and Nova Scotia

Factors related to stream size and alkalinity were most influential in determining fish species associations in three catchments of New Brunswick (NB) and Nova Scotia (NS) Canada, as determined by discriminant function analysis of TWINSPAN stream site classification.In the circumneutral Saint Croix (NB) catchment, the creek chub, Semotilus atromaculatus (Mitchill), brook trout, Salvelinus fontinalis (Mitchill), blacknose dace, Rhinichthys atratulus (Hermann), Atlantic salmon, Salmo salar Linnaeus, eel, Anguilla rostrata (Lesueur) and fallfish. Semotilus corporalis (Mitchill) dominated stream sites of progressively greater discharge and higher median mid‐summer temperature. In the acidic Gold (NS) system, the brook trout, Atlantic salmon, and eel exhibited a distribution pattern in relation to stream size and temperature similar to that for the Saint Croix, with the eel relatively more abundant in the Gold at large stream sites. The creek chub was excluded from the smallest tributaries by low pH. The ranges of blacknose dace and fallfish do not extend to southwestern Nova Scotia. In the Medway (NS) system (slightly more acidic than the Gold), the relative abundance of Atlantic salmon is reduced, and that of eel increased as compared with the Gold and Saint Croix systems. The lower limiting mid‐summer pH levels for creek chub, salmon, brook trout, and eel are 5.2, 5.0, 4.7 and &lt;4.5 respectively.

Juvenile Atlantic salmon Salmo salar abundance and angling success before and after river diversion

A hydroelectric development in Nova Scotia, Canada, diverted approximately 18% of the upper Cheticamp River drainage area for power generation. Comparisons of pre- and post-development Atlantic salmon Salmo salar juvenile populations and adult angling statistics indicate that the flow release strategy in the Cheticamp River was successful in protecting the valuable salmon resource. Predictions of how the fishery resource would respond to the altered hydrologic regime in the river were accurate. A lack of suitably precise pre-development baseline data on juvenile Atlantic salmon abundance, however, reduced the precision of the measurement of impact resulting from the altered flow regime. The inherent variability of population estimates based on the quantitative depletion method suggests that at least 10 samples are required to derive useful estimates of juvenile Atlantic salmon abundance under conditions found in the study river.