Salar L. (salar + l)

Distribution by Scientific Domains

Kinds of Salar L.

  • atlantic salmon salmo salar l.
  • salmo salar l.
  • salmon salmo salar l.

  • Selected Abstracts

    Migration of landlocked brown trout in two Scandinavian streams as revealed from trap data

    J. Carlsson
    Abstract,,, Anthropogenic barriers that may interfere or prevent fish migration are commonly found in streams throughout the distribution of salmonids. Construction of fish passages in streams is a common solution to this problem. However, the goal with fish passages is often, at least in Scandinavia, to allow Atlantic salmon (Salmo salar L.) and migratory brown trout (S. trutta L.) to get access to spawning areas above these barriers. Hence, the fish passages may often only be open during the spawning migration of salmonids (late summer to autumn). We present data, on wild brown trout migration, from two trapping systems in two Scandinavian streams showing that intra- and interstream migrations are common throughout the summer and autumn. Moreover, differences in size were found between trap-caught trout and electrofished trout where trapped trout were generally larger than electrofished trout. We suggest that the current regime with fish passages only open parts of the year can have negative effects on populations by depriving trout from the possibility to perform migrations throughout the year. Resumen 1. Barreras de origin antrópico que pueden interferer o prevenir las migraciones de los peces son frecuentes a lo largo de las áreas de distribución de los salmónidos. Una solución común a este problema es la construcción de pasos. Si embargo, el fin general de estos pasos es, por lo menos en Escandinavia, permitir el acceso a las áreas de reproducción por encima de las barreras tanto a salmones (Salmo salar L.) como a truchas migratorias (S. trutta L.). Frecuentemente, estos pasos están solamente abiertos durante el período de migración reproductiva (final del verano y otoño) porque se piensa que este régimen no tiene consecuencias negativas ya que estas especies muestran movimientos muy limitados en otros periodos del año. 2. Presentamos datos sobre migraciones de truchas colectados en dos sistemas de trampas de dos ríos escandinavos. Un río localizado por encima de una catarata inaccesible. El segundo, con una población migratoria de truchas. Los datos indicaron claramente migraciones intensivas a lo largo de todo el período en el que las trampas estuvieron operativas. Ambos ríos mostraron un pico de migración aguas arriba a mediados de Julio. Migraciones aguas abajo fueron raramente observadas en la población por encima de la catarata aunque migraciones aguas abajo en la población del río fueron intensivas al final del otoño. 3. Sugerimos que el régimen actual de pasos de peces que abren solamente partes del año puede tener efectos negativos sobre las poblaciones, al privar a las truchas de la posibilidad de migrar a lo largo del año. Esto puede extenderse a otros sistemas con barreras ya que observamos también migraciones intensivas en la población localizada por encima de la catarata. [source]

    Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories

    A. Klemetsen
    Abstract ,,,Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life-history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life-history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3,5 sea-winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life-history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life-history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world-wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in streams, while littoral epibenthos in lakes and fish are most important for large trout. The sexes differ in resource use and size. Females are more inclined than males to become migratory and feed in pelagic waters. Males exploit running water, near-shore and surface waters more than females. Therefore, females feed more on zooplankton and exhibit a more uniform phenotype than males. The Arctic charr is the northernmost freshwater fish on earth, with a circumpolar distribution in the Holarctic that matches the last glaciation. Recent mtDNA studies indicate that there are five phylogeographic lineages (Atlantic, Arctic, Bering, Siberian and Acadian) that may be of Pleistocene origin. Phenotypic expression and ecology are more variable in charr than in most fish. Weights at maturation range from 3 g to 12 kg. Population differences in morphology and coloration are large and can have some genetic basis. Charr live in streams, at sea and in all habitats of oligotrophic lakes, including very deep areas. Ontogenetic habitat shifts between lacustrine habitats are common. The charr feed on all major prey types of streams, lakes and near-shore marine habitats, but has high niche flexibility in competition. Cannibalism is expressed in several cases, and can be important for developing and maintaining bimodal size distributions. Anadromy is found in the northern part of its range and involves about 40, but sometimes more days in the sea. All charr overwinter in freshwater. Partial migration is common, but the degree of anadromy varies greatly among populations. The food at sea includes zooplankton and pelagic fish, but also epibenthos. Polymorphism and sympatric morphs are much studied. As a prominent fish of glaciated lakes, charr is an important species for studying ecological speciation by the combination of field studies and experiments, particularly in the fields of morphometric heterochrony and comparative behaviour. [source]

    The effects of fluvial processes and habitat heterogeneity on distribution, growth and densities of juvenile Atlantic salmon (Salmo salar L.), with consequences on abundance of the adult fish

    R. J. Gibson
    Abstract,,,The required freshwater habitats of juvenile Atlantic salmon (Salmo salar) are, in general, well known, but vary in quality, related to interacting effects of several variables, which may depend on different parts of a river system. Examples are given of ranges of densities and growth that can be found at various sites in eastern Canada, illustrating the biological and physico-chemical factors affecting production of juvenile salmon. Relative growth rates can indicate habitat quality and population densities. Salmon parr have negative effects on brook trout in riffle habitats. The effects of migrations within the river and of changes with stream succession on juvenile salmon production are illustrated with examples from a Newfoundland river. Migration of age-classes can be quantified from ,self-thinning' curves. Lakes have enhancing effects on downstream fluvial habitats, and, at least in Newfoundland, and probably in many boreal areas, the lacustrine proportion of the basin can be used as an index for deriving estimates of required spawning escapement. The factors described should be taken into account for more refined estimates of river production and management of the salmon resource. [source]

    Resource partitioning between lake-dwelling Atlantic salmon (Salmo salar L.) parr, brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus (L.))

    L. Jørgensen
    Abstract , Resource partitioning between Atlantic salmon parr, brown trout and Arctic charr was studied throughout the ice-free season in a north Norwegian lake. Juvenile salmon and trout (,160 mm) utilized the littoral zone and juvenile charr the profundal, while adult trout and charr (>160 mm) were found in both. Juvenile salmon and trout had a similar diet, although trichopteran larvae were more important for the trout and chironomid pupae and three-spined sticklebacks for the salmon parr. Small salmon and trout parr (,120 mm) had a higher diet overlap than larger parr (121,160 mm). The feeding habits of adult trout were similar to that of juvenile trout, but the former took larger prey items. At the population level, both salmon and trout were generalistic feeders with a broad diet, but at the individual level, both species had specialized on a single or a few prey categories. Juvenile charr were segregated from salmon and trout in both habitat and food utilization; they had a narrow diet consisting of chironomids and zooplankton, possibly reflecting their confinement to the profundal habitat which have a low diversity of potential prey. Larger charr also took zoobenthos and sticklebacks in the littoral zone., [source]

    An evolutionary view on tooth development and replacement in wild Atlantic salmon (Salmo salar L.)

    A. Huysseune
    SUMMARY To gain an insight into the evolution of tooth replacement mechanisms, we studied the development of first-generation and replacement teeth on the dentary of wild Atlantic salmon (Salmo salar L.), a protacanthopterygian teleost, using serially sectioned heads of early posthatching stages as well as adults. First-generation teeth develop within the oral epithelium. The anlage of the replacement tooth is first seen as a placode-like thickening of the outer dental epithelium of the predecessor, at its lingual and caudal side. Ongoing development of the replacement tooth germ is characterized by the elaboration of a population of epithelial cells, termed here the middle dental epithelium, apposed to the inner dental epithelium on the lingual side of the tooth germ. Before the formation of the new successor, a single-layered outer dental epithelium segregates from the middle dental epithelium. The dental organs of the predecessor and the successor remain broadly interconnected. The absence of a discrete successional dental lamina in salmon stands in sharp contrast to what is observed in other teleosts, even those that share with salmon the extraosseous formation of replacement teeth. The mode of tooth replacement in Atlantic salmon displays several characters similar to those observed in the shark Squalus acanthias. To interpret similarities in tooth replacement between Atlantic salmon and chondrichthyans as a case of convergence, or to see them as a result of a heterochronic shift, requires knowledge on the replacement process in more basal actinopterygian lineages. The possibility that the middle dental epithelium functionally substitutes for a successional lamina, and could be a source of stem cells, whose descendants subsequently contribute to the placode of the new replacement tooth, needs to be explored. [source]

    Real options for precautionary fisheries management

    FISH AND FISHERIES, Issue 2 2008
    Eli P Fenichel
    Abstract The 1996 Food and Agriculture Organization's (FAO) ,Guidelines on the Precautionary Approach to Fisheries and Species Introduction' raise important issues for fisheries managers, but fail to prescribe an approach for risk management. The distinguishing characteristics of the ,precautionary approach' are the inclusion of uncertainty and ,an elaboration on the burden of proof'. The FAO precautionary approach emphasizes that managers should be risk-averse, but does not provide tools for determining the appropriate degree of risk aversion. Consequently, application of the precautionary approach often leads to decision-making based on ad hoc safety margins. These safety margins are seldom chosen with explicit consideration of trade-offs. If the emphasis was shifted to choosing between competing uncertainties, then managers could manage risk. By attempting to avoid risk, managers may gain exposure to other risks and perhaps miss valuable opportunities. We place fishery management problems within the rubric of ,real investment' problems, and compare and contrast the consideration of risk by alternative investment frameworks. We show that traditional investment frameworks are inappropriate for fishery management, and furthermore, that traditional precautionary approaches are arbitrary and without basis in decision theory. Quantitative decision-making techniques, such as formal decision analysis (FDA), enable integration of competing hypotheses that help alleviate burden-of-proof issues. These techniques help analysts consider sources of uncertainty. FDA, however, can still be subject to arbitrary safety margins because such analyses often focus on determining which strategies best achieve, or avoid, targets that have been established without complete consideration of trade-offs. A managerial finance approach, real options analysis (ROA), is an alternative and complementary decision-making technique that enables managers to compute precautionary adjustments that couple the size of the ,safety margin' with the amount of uncertainty, thereby optimizing risk exposure and avoiding the need for arbitrary safety margins. We illustrate the advantages of an approach that combines FDA and ROA, using a heuristic example about a decision to re-introduce Atlantic salmon (Salmo salar L.) into Lake Ontario. Finally, we provide guidance on applying ROA to other fishery problems. The precautionary approach requires that managers consider risk, but considering risk is not the same as managing it. Here ROA is useful. [source]

    Run timing and migration routes of returning Atlantic salmon in the Northern Baltic Sea: implications for fisheries management

    A. SIIRA
    Abstract, Return migration of Atlantic salmon, Salmo salar L., was studied in the Gulf of Bothnia, northern Baltic Sea, by a mark-recapture experiment and catch records from commercial trap-nets. Coastal salmon fishing is regulated by delayed opening of the fishery in consecutive regions based on the assumption that the wild fish migrate before reared ones and the migration is unidirectional and continuous from south to north. Neural network modelling suggested that the migration does not progress linearly from one regulation region to another, but shows variation between origin and sea age among and within regions. Further evidence of the non-linear migration included a noticeable part of salmon on their way to two major estuaries first visiting the northern-most Bothnian Bay before turning back south. Salmon returning to the different homing sites in the north showed no differences in run timing in the southern Gulf whereas the same individual fish showed differences in catch accumulation further north. Run timing estimates indicated only a slight tendency towards earlier migration for wild salmon compared with reared fish. [source]

    The effects of stream canopy management on macroinvertebrate communities and juvenile salmonid production in a chalk stream

    W. D. RILEY
    Abstract, The effects of changes in shading (through riparian canopy removal and re-growth) on juvenile salmon, Salmo salar L., trout, Salmo trutta L., and grayling, Thymallus thymallus (L.) populations, and macroinvertebrate biomass and species composition in a chalk stream in southern England were examined. Low levels of in-stream weed growth, because of shading by closed tree canopy, diminished macroinvertebrate production and diversity. 0+ salmon and trout had lower densities under closed canopy, relative to adjacent open sites with substantial weed cover, where fish were also found to be larger. Canopy removal positively affected the growth of aquatic macrophytes and the availability of potential prey for juvenile salmonids. The findings have implications for the management of chalk streams, in particular, that riparian tree canopy should be managed to prevent complete closure, and excessive cutting of weed should be avoided where salmon production is below sustainable levels. [source]

    Night stocking facilitates nocturnal migration of hatchery-reared Atlantic salmon, Salmo salar, smolts

    Abstract, Hatchery-reared salmon, Salmo salar L., smolts are generally stocked during daylight hours, but the natural migration of smolts tends to occur at night. Recapture rates and timing of migration were compared between Atlantic salmon smolts stocked during the day and during the evening. Timing of release had no significant effect on the number of smolts recaptured, but had a strong effect on nocturnal behaviour. When stocked in the evening (but not during the day) hatchery-reared smolts moved almost exclusively during the night. This study suggests that timing the release to coincide with the natural time of smolt migration may provide valuable acclimatisation and facilitate nocturnal smolt passage. [source]

    Seasonal variation in rod recapture rates indicates differential exploitation of Atlantic salmon, Salmo salar, stock components

    Abstract, Differential exploitation of the various components of a fish stock can adversely affect the diversity, abundance and long-term survival of the entire stock. Many anadromous salmonid stocks exhibit a seasonal structuring of their run-timing that allows fisheries managers to map monthly rod catches onto stock components. To estimate the rod exploitation levels of the various run-timing groups, fishing guides on the River Spey, Scotland, floy-tagged 786 rod-caught and released Atlantic salmon, Salmo salar L., between 2000 and 2002 and recorded recaptures. Whereas 25% of the fish tagged early in March were recaptured, only 2% of those tagged early in June were caught a second time. Exploitation is biased towards the early-running stock components which current assessments show to be least abundant. Management of Atlantic salmon based on an average exploitation rate is inappropriate. [source]

    Snorkelling as a method for assessing spawning stock of Atlantic salmon, Salmo salar

    P. ORELL
    Abstract, Reliability of underwater snorkel counts of adult Atlantic salmon, Salmo salar L., was analysed in the tributaries of the River Teno, close to the spawning period. In small (width 5,20 m) rivers, the replicated total counts of salmon were reasonably precise (CV = 5.4,8.5%), while in the medium-sized river (width 20,40 m) the precision of the counting method was considerably lower (CV = 15.3%). Low precision in a medium sized river was also observed in an experiment using marked live fish where the observation efficiency varied between 36.4% and 70.0%. In a small river, the detection efficiency of artificial fish silhouettes (test salmon) was almost perfect in pools (98%), but decreased in rapids (84%). Separate counts of males, females, grilse and large salmon were usually more variable than total counts, indicating that divers were more capable of locating a fish than properly identifying its sex and sea-age. The behaviour of adult salmon was favourable to conduct snorkel counts, as fish normally stayed still, or after hesitating, moved upstream (>95%of the cases) when encountering a diver. The high observation efficiency (>90%) and precision, favourable behaviour of salmon and congruence between snorkel counts and catch statistics in small rivers suggest that reliable data on Atlantic salmon spawning stock can be collected by snorkeling provided that the environmental conditions are suitable and the divers are experienced. [source]

    Assessment of salmon stocks and the use of management targets; a case study of the River Tamar, England

    Abstract, Over recent years the rod and net catch of Atlantic salmon, Salmo salar L., on the River Tamar in south-west England has decreased markedly, resulting in a consistent failure to meet the minimum egg deposition target (conservation limit). Compliance with the target is by annual assessment using rod catch as the major input variable. Further analysis suggested a disproportionate deterioration in the rod fishery performance of the Tamar compared with rivers locally, regionally and nationally. A concomitant decrease in rod licence sales and fishing effort, above both national and regional trends was also evident. However, examination of juvenile electric fishing and adult fish counter data revealed a different trend for the past 10 years, indicating a stable fish population, albeit at a lower level of abundance than previously. The analyses suggested that without consideration of changes in effort and rod exploitation rate, rod catch alone is not a reliable indicator of stock abundance and hence should not be used as such in stock assessment. [source]

    Straying of Atlantic salmon, Salmo salar, from delayed and coastal releases in the Baltic Sea, with special focus on the Swedish west coast

    Abstract, Atlantic salmon, Salmo salar L., reared from two Baltic strains were released around the islands Bornholm and Møn in the Baltic Sea between 1995 and 1999. A total 600 000 reared salmon were released from net pens using the delayed release technique, keeping the salmon in net pens for approximately 3 months after smolting, and 208 000 were released directly from the hatchery. Of these, 15 958 were tagged with Carlin tags. Additionally, 65 300 coded wire tagged salmon were released as delayed release salmon close to Bornholm in 2000. Recaptures from the five years of Carlin tagged releases varied between 2.8% and 21.2% (average 13.1%). Most recaptures were from within the Baltic Sea (average 98%), but some were recaptured outside the Baltic Sea, either in the sea (1%) or in fresh water (1%). Recaptures outside the Baltic Sea and in fresh water were higher for releases at Møn in the western part of the Baltic, than releases at Bornholm. Straying rates from the releases into six rivers on the Swedish west coast were estimated using information from capture in traps and sport and broodstock fisheries. The proportion of straying salmon in rivers on the Swedish west coast was about 3.8% of the salmon run, but with large variations between rivers. Releases were discontinued because of possible deleterious effect on the local wild salmon populations. [source]

    Modelling the impacts of removing seal predation from Atlantic salmon, Salmo salar, rivers in Scotland: a tool for targeting conflict resolution

    J. R. A. BUTLER
    Abstract, Bioenergetics were used to model the potential impacts on adult Atlantic salmon, Salmo salar L., stocks and rod fisheries of removing harbour seals, Phoca vitulina L., from three rivers of different scales in the Moray Firth, Scotland, viz: the Spey (large), Conon (medium) and Moriston (small). Overall, seals had the greatest impact on the Moriston, where removal of a single animal could increase cumulative catch by 17% during the fishing season. On the Conon and Spey the impacts were negligible, and resulted in increased catches of <1% annually. On all rivers eliminating seal predation had the greatest impact during the spring due to the smaller size of spring salmon sub-stocks. A generalised model of seal removal illustrated that stocks and catches increased by >33% in rivers with monthly rod catches ,10 fish, but declined to <10% for rivers with catches >34 fish. The outputs of the models are qualitative, but provide a management tool for targeting action to resolve seal-salmon fishery conflict. Smaller salmon population units, and spring salmon sub-stocks and fisheries in particular, are most vulnerable to predation. The merit of this approach is discussed regarding the management of Special Areas of Conservation for salmon and seals. [source]

    Seasonal variation in habitat use by salmon, Salmo salar, trout, Salmo trutta and grayling, Thymallus thymallus, in a chalk stream

    W. D. RILEY
    Abstract, A portable multi-point decoder system deployed in a tributary of the River Itchen, a southern English chalk stream, recorded the habitats used by PIT-tagged juvenile salmon, Salmo salar L., trout, Salmo trutta L. and grayling, Thymallus thymallus L., with a high degree of spatial and temporal resolution. The fishes' use of habitat was monitored at 350 locations throughout the stream during September/October 2001 (feeding period) and January/February 2002 (over-wintering period). Salmon parr tended to occupy water 25,55 cm deep with a velocity between 0.4 and 1.0 m s,1. During both autumn and winter, first year salmon (0+ group) were associated with gravel substrate during the daytime and aquatic weed at night. In autumn, 1+ salmon were strongly associated with hard mud substrates during the day and with marginal tree roots at night. In winter, they were located on gravel substrate by day and gravel and mud at night. Trout were associated with a greater range of habitats than salmon, generally occupying deeper and faster water with increasing age. During the autumn, 0+ trout were located along shallow (5,10 cm) and slow (,0.1,0.4 m s,1) margins of the stream, amongst tree roots by day and on silty substrates at night. During winter the 0+ trout occupied silty substrates at all times. As age increased, trout increasingly used coarse substrates; hard mud, gravel and chalk, and weed at night. All age groups of grayling (0+, 1+ and 2+) tended to occupy hard gravel substrate at all times and used deeper and faster water with increasing age. The 1+ and 2+ groups were generally found in water 40,70 cm deep with a velocity between 0.3 and 0.5 ms,1, whilst the 0+ groups showed a preference for shallower water with reduced velocity at night, particularly in the winter. There were greater differences in the habitats used between species and age groups than between the autumn and winter periods, and the distribution of fish was more strongly influenced by substrate type than water depth or velocity. The results are discussed in relation to the habitat requirements of mixed salmonid populations and habitat management. [source]

    Use of biological reference points for the conservation of Atlantic salmon, Salmo salar, in the River Lune, North West England

    Abstract, The development and use of biological reference points (BRPs) for salmon, Salmo salar L., conservation on the River Lune, England were examined. The Lune supports recreational and net fisheries with annual catches averaging 1332 and 2146 salmon, respectively. Using models transported from other river systems, BRPs were developed that were exclusive to the Lune; specifically the number of eggs deposited and carrying capacity estimates for age 0+ and 1+ parr. The conservation limit was estimated at 11.9 million eggs, and to ensure that the conservation limit was exceeded 80% of the time, the management target was set at 14.4 million eggs (equivalent to ,5000 adults). Between 1989 and 1998 the management target was exceeded in only 2 years. Comparison of juvenile salmon densities in 1991 and 1997 with estimates of carrying capacity indicated that 0+ and 1+ parr densities were at around 60% of carrying capacity and may relate to the number of eggs deposited in 1990 and 1996 being approximately 70% of the target value. From, and including, the 2000 fishing season, regulations to ensure that the conservation limit is met 4 years out of 5 were introduced. These consisted of a reduction from 26 to 12 haaf nets, from 10 to seven drift nets and a four-fish bag limit for the rod fishery. In the period between 2000 and 2004 there was a marked increase in the estimated number of salmon spawning and the management target value of ,5000 spawning adults was exceeded in all years. There was also an increase in the juvenile salmon population. The estimated level of exploitation in the net and rod fisheries reduced from 29.9% to 13.8% and from 26.4% to 14.8% respectively, after the introduction of the regulations. [source]

    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

    J. B. Dempson
    Abstract Closure 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. [source]

    Survival of stocked Atlantic salmon and coarse fish and an evaluation of costs

    M. W. Aprahamian
    Abstract The stocking of fish represents a major activity in current fisheries management practice. To maximise benefit to the environment in general and to fisheries in particular, optimal stocking strategies need to be developed. Examples from two studies, one involving Atlantic salmon, Salmo salar L., and the other involving three coarse fish species, are used to illustrate how such strategies might be developed. Atlantic salmon fed fry (age 0+) were stocked into eight streams in the North West of England at densities ranging from 1 to 4 m,2 over a period of up to 3 years to evaluate survival to the end of the first and second growing periods. Survival to the end of the first growing period (mean duration 108 days) varied between 1.2 and 41.3% with a mean of 20.45% and CV of 0.53. Survival from the end of the first growing period to the end of the second growing period (mean duration 384 days) ranged from 19.9 to 34.1% with a mean of 26.3% and a CV of 0.21. Hatchery-reared roach, Rutilus rutilus (L.), chub, Leuciscus cephalus (L.) and dace, Leuciscus leuciscus (L.), were stocked into four rivers to determine the optimal age and season which would maximise survival over a 6-month post-stocking period. Post-stocking persistence within the stocked reaches was generally low; the highest level of persistence was estimated at only 33.8%. However, most of the estimates of persistence were considerably lower and (in practical terms) approached zero in several instances. The analysis indicated that river-specific factors are important in determining the success of stocking exercises. The survival estimates derived from these two studies were compared with other published estimates. [source]

    Upstream migration of Atlantic salmon at a power station on the River Nidelva, Southern Norway

    E. B. Thorstad
    Abstract The upstream migration of 17 radio-tagged adult Atlantic salmon, Salmo salar L., past hydroelectric developments on the River Nidelva, Southern Norway, was examined. Salmon migrated quickly from the site of release in the lower part of the river up to the tunnel outlet of Rygene power station, but were substantially delayed at the outlet. The salmon stayed in the outlet area for 0,71 days (median = 20), and mainly took up a position inside the dark power station tunnel. Water discharge in the tunnel was 57,176 m3 s,1, while residual flow in the river between the outlet and the dam 2.5 km further upstream was 3 m3 s,1. Ten salmon passed the outlet and entered the residual flow stretch, but none passed the dam. Six of the 10 salmon returned to the tunnel outlet. No major migration barriers were identified in the residual flow stretch, suggesting lack of motivation among the salmon to migrate due to either low water discharge compared with the main river, or several minor migration barriers along the river stretch. [source]

    Return migration of adult Atlantic salmon, Salmo salar, in relation to water diverted through a power station

    E. B. Thorstad
    Abstract ,The migration of Atlantic salmon, Salmo salar L., returning to the River Suldalslågen, Norway, was studied in relation to redirection of freshwater flow through a power station. The outlet of the power station is situated in the Hylsfjord, a fjord adjacent to the river mouth. Seventy-two salmon were tagged with acoustic transmitters, released in the outer part of the fjord system and automatically recorded when entering the Hylsfjord or the river. Data were collected during one period when the power station was running and two periods when the power station was closed. The release of water from the power station did not greatly attract the salmon during their return migration. Proportions of salmon entering the river or time from release to entering the river did not differ among salmon tagged in the different periods. The salmon were recorded in the Hylsfjord both when the power station was running and closed and there were no differences in number of times, number of days or hours recorded in the Hylsfjord among salmon tagged in the three periods. The only significant difference found among periods was duration of continuous stays in the inner part of the Hylsfjord. This may indicate a slight attraction to the freshwater release, but the difference seems small (1.8 vs. 0.7 h) compared with the time the fish stayed in the fjord system before entering the river (16,85 days). [source]

    Uncertainty about estimating total returns of Atlantic salmon, Salmo salar to the Gander River, Newfoundland, Canada, evaluated using a fish counting fence

    M. F. O'Connell
    Abstract ,For a number of rivers in Newfoundland, Atlantic salmon, Salmo salar L., is managed in relation to river-specific conservation spawning requirements. One such river is the Gander River, where between 1989 and 1999, the escapement of Atlantic salmon, a major factor in assessing the status of stock, was determined using a fish counting fence. In 2000, the counting fence was discontinued and alternative means of calculating total returns were explored. Regression and simulation methods, using relationships between total returns and salmon counts at an upstream tributary during 1989,99, formed the basis for estimates of returns for 2000, and the uncertainty around estimates. The accuracy of methods is evaluated by retrospective comparisons with actual total returns between 1989 and 1999. Estimates of total returns deviated from the actual by as much as 50,60%, depending on the method. Management implications of the approach are discussed. [source]

    Effects of catch and release angling on Atlantic salmon, Salmo salar L., of the Conne River, Newfoundland

    The effects of catch and release angling on survival of Atlantic salmon, Salmo salar L., at Conne River, Newfoundland, were investigated by retaining angled (n=49; experimental group) and trap-caught (n=20; control group) fish in holding cages for up to 40 days. Samples were obtained from 8 June to 4 July, 2000, and partitioned among four water temperature strata. Apart from not being angled, control fish were handled, tagged, and transferred to holding cages in a manner similar to angled salmon. Water temperatures and discharge were monitored throughout the duration of the study. Overall, 8.2% of salmon caught and released died, but 12% died among salmon angled in water temperatures , 17.9 °C. No control fish died. There were no significant differences in time associated with angling, exposure to air, tagging, transfer to holding cages, nor total handling time between salmon that survived vs. those that died. Results of the study should encourage managers to continue to use catch and release as a viable tool in the management of Atlantic salmon stocks. [source]

    The onset of downstream movement of juvenile Atlantic salmon, Salmo salar L., in a chalk stream

    W. D. RILEY
    The downstream movements of wild Atlantic salmon, Salmo salar L., from their established feeding territories in the River Itchen, Hampshire, UK, were logged continuously over an 11-month period using a passive integrated transponder (PIT) antenna system. The time of these movements was then related to a number of monitored and calculated environmental parameters. Initial downstream movement of smolts in April was correlated with the onset of darkness, at which time salmon moved from their established feeding territories alone. No relationship was found between the number of smolts migrating and river flow or maximum daily water temperature. The timing of downstream movement of parr between October and March was random with regard to sunset and time of maximum daily water temperature, suggesting the environmental cue that initiates movement may be different outside the spring smolt period. [source]

    The efficacy of air, sound and acoustic bubble screens in deflecting Atlantic salmon, Salmo salar L., smolts in the River Frome, UK

    J. S. WELTON
    Atlantic salmon, Salmo salar L., smolts are vulnerable to entrainment in a variety of man-made structures as they migrate downstream. The ability of acoustic bubble screens to deflect smolts from potential hazards was assessed. Screens were deployed, in turn, across one of the two identical channels through which the millstream of the River Frome flowed and the efficiency of these screen systems was tested by counting smolts by video recording in each channel. It was concluded that these screens deflected a significant number of smolts. Efficiencies were greater at night than in daylight because of smolt behaviour. [source]

    Chemical pollution as a factor affecting the sea survival of Atlantic salmon, Salmo salar L.

    D. Scott
    The catch of Atlantic salmon Salmo salar L., from ocean and coastal fisheries since 1960 is described and the decline starting in 1973 noted. This decline continued despite cessation of some fisheries, and evidence indicates a marine locus for the decline. Oceanic pollution has received little attention, and ozone loss has caused an increase in UV radiation reaching the surface of the North Atlantic. Direct effects of this increase include negative impacts on the food chain. Photo-induced toxicity of polycyclic aromatic hydrocarbons (PAH) is a possible effect, but concentrations of these compounds in oceanic waters are low. Chlorinated organic compounds are widely distributed in the North Atlantic, and their persistence, lipophilicity, bioaccumulation potential and toxicity represent a potential hazard to salmon. The suggested causes of decline are likely to be complementary rather than exclusive. [source]

    Predation by seals on salmonids in two Scottish estuaries

    T. J. Carter
    Detailed observations of the behaviour of harbour seals, Phoca vitulina L., at sites within the estuaries of the Rivers Dee and Don, in north-eastern Scotland, were made over two full years between 1993 and 1996. Small numbers of grey seals, Halichoerus grypus Fab., were also present. The presence of seals within the estuaries was strongly related to season, with maximum numbers observed in winter and early spring; seals were virtually absent in June and July. The River Don was used largely as a haul-out site, while the River Dee was used predominantly as a foraging site, although it was not possible to determine whether the same seals were using the two estuaries. More seals were hauled-out on the River Don during twilight and dark than in daylight. The seals were observed to eat mostly salmonids, Salmo salar L. and S. trutta L., unidentified roundfish and flounder, Pleuronectes flesus L. The otoliths identified in scats collected at the mouth of the River Don belonged to marine species indicating that the seals were also feeding outside the estuaries. A minimum estimate is given of the numbers of large salmonids eaten in each river during the course of the year. Although no information was available on the numbers of salmonids using the rivers or the reproductive status of the fish eaten by the seals, as a cause of mortality, seal predation on large salmonids in estuaries is apparently an order of magnitude less important than mortality caused by angling within the river. [source]

    Variability in performance in wild Atlantic salmon, Salmo salar L., fry from a single redd

    C. García De Leániz
    Dispersal and growth were studied in Atlantic salmon, Salmo salar L., fry from a natural isolated redd. The distribution of fry leaving the redd was strongly peaked, 80% being caught within a 2-week period. Early in the dispersal period, all fry leaving the redd had remnants of yolk sac and had not fed; by half way through the dispersal period, no fry had any visible yolk, but 35% still had empty stomachs. Fry leaving the redd during the first half of the dispersal period tended to settle in different first feeding sites than those dispersing later. Predation on fry by larger salmonids was frequent, especially during dispersal. Coefficients of variation for length, weight and condition factor increased significantly over the study period and for individually recognised fry, growth rates varied markedly. Thus, individual salmon fry differ in physical status on emergence from the redd and these differences are amplified during the first few weeks after emergence. [source]

    Combining fishery prohibition with stocking of landlocked salmon, Salmo salar L.: an effort to gain bigger yield and individual size

    P. Hyvärinen
    After stocking landlocked salmon, Salmo salar L., in Lake Änättijärvi, all fishing was prohibited for 18 months to provide time for the fish to establish and reach a larger size prior to capture. The potential benefit of the fishery prohibition was severely diminished by emigration of the stocked fish down the watercourse to other lakes. Only 19% of the recaptures of Carlin-tagged individuals came from Lake Änättijärvi. Also, the CPUE of test fishing in Lake Änättijärvi indicated a steep decline in the density of stocked fish during the fishery prohibition period. The mean weight of landlocked salmon in the combined recaptures from Lake Änättijärvi and other lakes downstream was 660 g. When fishing was not prohibited, the corresponding mean weight at recapture was 442 g. It is recommended that landlocked salmon stocking should be carried out in lakes with relatively low fishing pressure. [source]

    Prespawning migratory behaviour and spawning success of sea-ranched Atlantic salmon, Salmo salar L., in the River Gudenaa, Denmark

    K. Aarestrup
    The migratory behaviour of sea-ranched Atlantic salmon, Salmo salar L., was analysed by radio-telemetry in the River Gudenaa, Denmark. The main objectives were to: (1) estimate mortality of returning adults through the fjord; (2) observe rate of progression and migratory pattern in the fjord and river; and (3) record whether spawning occurs in the river. Forty-two returning salmon (19 males and 23 females of total body length from 60,97 cm) reared and released as smolts, were caught and equipped with external radio transmitters in the outer estuary of the River Gudenaa in 1994 and 1995. Of the tagged salmon, 18 (43%) were caught in the estuary, four (10%) were not recorded after release and 20 (47%) entered the river. The mean rate of progression through the fjord was 7.6 km d,1 (range 1.4,18.2) in 1994 and 5.4 km d,1 (range 1.6,17.1) in 1995. Eleven salmon were alive at the onset of the spawning period. Eight were retrieved dead from the river during or after the spawning period; four with empty gonads assumed to be successful spawners, and four with intact gonads. In 1994, unsuccessful spawners (found dead with intact gonads) entered the river earlier and had a longer total migration distance in the river compared to successful spawners. This suggests that spawning success of sea-ranched salmon is associated with time of river entry and river migration length. [source]

    Unstable release strategies in reared Atlantic salmon, Salmo salar L.

    S. M. McKinnell
    The effects of year, size, sexual maturity and release date on the probability of recapture of tagged Atlantic salmon, Salmo salar L., released from a Swedish hatchery in the Baltic Sea were examined. The probability of recapture varied among years for individuals which were juvenile when released (1988, 13.5%; 1989, 4.4%; 1990, 1.2%) or previously mature males (1988, 1.9%; 1989, 0.5%; 1990, 0.4%). Body size was positively associated with the probability of recapture in each release year for both life-history types. Inter-annual changes in recapture rates were similar for both large and small smolts. There was a significant effect of life-history type on recapture rates in 1988 and 1989, but not in 1990. There was a significant effect of release date on recapture rates in 1988 and 1990, but not in 1989. The maximum recapture rates were associated with different release dates in each year, i.e. 27 May 1988, 6 June 1989 and 21 June 1990. [source]