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

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.     

Life‐history differences of juvenile Chinook salmon Oncorhynchus tshawytscha across rearing locations in the Shasta River,California

Salmon from different locations in a watershed can have different life histories. It is often unclear to what extent this variation is a response to the current environmental conditions an individual experiences as opposed to local‐scale genetic adaptation or the environment experienced early in development. We used a mark–recapture transplant experiment in the Shasta River, CA, to test whether life‐history traits of juvenile Chinook salmon Oncorhynchus tshawytscha varied among locations, and whether individuals could adopt a new life history upon encountering new habitat type. The Shasta River, a Klamath River tributary, has two Chinook salmon spawning and juvenile rearing areas, a lower basin canyon (river km 0–12) and upper basin spring complex (river km 40–56), characterised by dramatically different in‐stream habitats. In 2012 and 2013, we created three experimental groups: (i) fish caught, tagged and released in the upper basin; (ii) fish caught at the river mouth (confluence with the Klamath River, river km 0), tagged and released in the upper basin; and (iii) fish caught at the river mouth, tagged and released in the lower basin. Fish released in the upper basin outmigrated later and at a larger size than those released in the lower basin. The traits of fish transplanted to the upper basin were similar to fish originating in the upper basin. Chinook salmon juvenile life‐history traits reflected habitat conditions fish experienced rather than those where they originated, indicating that habitat modification or transportation to new habitats can rapidly alter the life‐history composition of populations.     

Inter-stage survival of wild juvenile Atlantic salmon, Salmo salar L.

A biological model was developed to calculate annual survival between life stages of juvenile Atlantic salmon, Salmo salar L., in Catamaran Brook, a small stream basin (52 km²) in the Miramichi River catchment in New Brunswick, Canada. Seven years’ data (1990–1996) were used in the model. Input variables included: daily fish counts and measurements of parr (3–4 age classes), smolts, and adult salmon at a fish-counting fence near the stream mouth; biennial quantification of all habitat types along the watercourse; fish density estimated by electric fishing at 30 sites; and estimates of young-of-the-year emigration via stream drift. Continuous recording of stream discharge provided data to assist in interpretation of survival estimates. Annual survival for juvenile salmon in their first 3 years of life in the stream averaged between 31% and 34%. The greatest annual variation (CV = 0.699) occurred at the egg to 0+ (summer) stage with a low of 9.2% survival recorded for a winter with an atypical midwinter flood event; parr and pre-smolt survival were similarly affected. Survival from egg deposition (after correction for losses caused by predation and retention/non-fertilization) to smolt emigration was between 0.16% and 0.52%, which is low relative to estimates from many other studies. Survival of smolts to returning 1-sea-winter adults (grilse) averaged 8.5%. Potential errors in the computation of the model are discussed, e.g. inaccurate counts of spawning adults during high autumn stream flow. A possible explanation for the low egg to smolt survival was the environmental conditions experienced during various winters. Mean egg survival was 1.3 times higher (39.3%) and egg to smolt survival increased to 1.03% when the two winters characterized by extremely low discharge or midwinter freshets were excluded from the calculation. Density-dependent factors related to a beaver dam, which limited spawning distribution, may also have contributed to poor survival and increased fry emigration in one year. Environmental factors, particularly winter conditions, in streams such as Catamaran Brook may act as bottlenecks to natural production of Atlantic salmon.     

Deep habitats are important for juvenile Atlantic salmon Salmo salar L. in large rivers

Linnansaari T, Keskinen A, Romakkaniemi A, Erkinaro J, Orell P. Deep habitats are important for juvenile Atlantic salmon Salmo salar L. in large rivers. Ecology of Freshwater Fish 2010: 19: 618–626. © 2010 John Wiley & Sons A/S Abstract – Juvenile Atlantic salmon were studied by underwater video surveillance and self contained underwater breathing apparatus‐diving in deep (i.e. >1.0 m), fast flowing areas of two large river systems (River Teno, River Tornionjoki) in northern Finland. Both video and diving data indicated that young‐of‐the‐year (YOY) salmon (0+) and salmon parr (>0+) readily utilised habitats deeper than 1 m. Young‐of‐the‐year salmon and parr were observed through a range of 0.5–1.9 m and 0.4–2.2 m, respectively. A negative linear relationship between the mean abundance of YOY salmon and mean depth was noted from the diving transects. Salmon parr were similarly abundant throughout the range of depths studied. Video data showed that deep habitats were used throughout the summer (June–August). It was concluded that deep, fast‐flowing areas in large rivers may constitute a significant habitat resource for juvenile salmon that has not been traditionally accounted for when estimating salmon production.     

Behavioural ecology at sea of Atlantic salmon (Salmo salar L.) kelts from a Newfoundland (Canada) river

For migratory fishes such as Atlantic salmon, temporal variation in the utilization of thermal and depth habitats in the marine environment is likely to occur at both broad and fine scales, reflecting both ecological and metabolic factors. To test this, we implanted 26 Atlantic salmon kelts (i.e., post‐spawners) descending Campbellton River, Newfoundland, with data storage tags that recorded date/time, internal and external temperatures, pressure, and light. The salmon that returned to Campbellton River after an average of 62 days at sea were consecutive spawning kelt. Detailed data were recovered from eight of these fish and revealed distinct patterns in their utilization of thermal and depth habitats. Water temperatures experienced over the period at sea showed a wide range for all fish (from <0 to nearly 20°C); however, there were two clear frequency modes; one at 6–7°C and the other at 11–12°C. The cooler mode was indicative of daytime profiles and the warmer mode of night‐time profiles. This corresponded with the depth profiles, which indicated that salmon dove more frequently below 5 m (mean ± SD = 23 ± 0.9 dives per day) and spent less time (approximately 18%) near the sea surface (<1 m) during the day than during the night (4 ± 0.4 dives per night; approximately 45% time <1 m). The diurnal pattern may be indicative of a reliance on vision for feeding at depth and the short duration of dives (<10 min) may be a strategy that allows salmon a metabolic advantage (e.g., swimming capacity) over their prey living constantly at depth in cool waters.     

Effects of hook and release on Atlantic salmon in the River Alta, northern Norway

The purpose of the study was to collect information on angling procedures and the effects of hook and release on Atlantic salmon in the River Alta, northern Norway, covering both grilse and multi-sea-winter salmon in a non-artificial setting with real anglers. Information on the angling procedure, handling of the fish and the condition of the fish at release was collected for individual salmon in catch logs (n=543, mean body length 82 cm), whereas physiological stress was studied in a sub-sample (n=15, mean body length 77 cm). To study post-release behaviour, survival and recapture rates, salmon were tagged with radio transmitters (n=30, mean body length 83 cm) and anchor T-tags (n=353, mean body length 79 cm). To evaluate the effects of the hook and release programme on the salmon population, number of spawning redds were recorded from a helicopter in 6 years during 1989–2000.

The results showed that at water temperatures 10.0–14.5 °C, a high proportion of the radio tagged salmon (97%) survived hook and release and stayed in known spawning areas during the spawning period. However, the behaviour after release seemed to be affected by hook and release. Only a small proportion (4%) of the anchor T-tagged salmon was caught more than once within the same season. Increased playing time, increased number of runs during the angling event, hooking in the throat, bleeding at the hook wound, increased handling time, air exposure and water temperature were factors that affected hooked and released Atlantic salmon negatively, either indicated by a poor condition at release, increased stress levels or unnatural behaviour after release. Number of spawning redds were more than doubled after the introduction of compulsory release of all angled salmon in Sautso (the upper 16% of the watershed inhabited by salmon) in 1998, which indicates that hook and release can be an effective management tool to enhance declining Atlantic salmon populations.     

Evaluation of a portable electrode array for a resistivity fish counter

Abstract This study aimed to develop and test an electrode array for a resistivity fish counter that could be easily installed in a small river without a weir. An electrode array consisting of three steel cables laid in parallel across the stream channel and connected to a microprocessor-based counter was tested in an Atlantic salmon, Salmo salar L., spawning tributary. The accuracy of the counter was assessed by observing fish movements with closed-circuit television. Most salmon moving upstream were registered correctly (90% overall). Detection of downstream movement was less reliable (60% overall), as a consequence of downstream swimming behaviour. The accuracy of the downstream count was improved by tensioning the cable electrodes, but remained lower than that of the upstream count. Since salmon swam repeatedly up- and downstream, this discrepancy resulted in an overestimate of the net upstream count. The accuracy of the downstream count needs to be improved before a bed-mounted electrode array could be used for routine salmon counting.     

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

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.     

Temporal spawning migration patterns of landlocked Atlantic salmon (Salmo salar) in a constructed stream

Landlocked Atlantic salmon (ouananiche, Salmo salar) spawning migration timing varies throughout its range and is influenced by a variety of environmental variables. This study examined the spawning migration time of landlocked Atlantic salmon in a small (4 ha) constructed stream linked to a large reservoir (32,600 ha) in Newfoundland, Canada. Salmon use of the stream was passively monitored using Passive Integrated Transponder (PIT) Tags from 2006 to 2012. Of the salmon tagged throughout the reservoir, 48% entered the stream during the spawning season and remained there for 18–36 days from late September to November before they returned to the reservoir. Most fish entered the stream at dusk (32%). The lunar cycle influenced the timing of migration each year. Mean stream discharge (cubic metres per second) influenced migration timing in some years, and water temperature appeared to have minimal impact on migration timing. Twenty per cent of fish migrated to the stream in multiple years and 51% of these individuals appeared to use the stream on a biennial or alternate year cycle. These results demonstrate that small constructed streams can attract salmon from throughout a large reservoir and can provide valuable habitat in areas where spawning habitat is limited.     

Impact of stocked Atlantic salmon (Salmo salar L.) on habitat use by the wild population

Laffaille P. Impact of stocked Atlantic salmon (Salmo salar L.) on habitat use by the wild population.
Ecology of Freshwater Fish 2011: 20: 67–73. © 2010 John Wiley & Sons A/S Abstract – We investigated the summer habitat occupied by populations of young‐of‐the‐year wild and stocked (farmed populations released into the native range) Atlantic salmon under allopatric and sympatric conditions. Under allopatric conditions, farmed and wild salmon occupied habitats with the same characteristics. The salmon preferentially occupied the riffle areas. However, under sympatric conditions, the fish occupied meso‐ and micro‐habitats with different characteristics. Wild salmon avoided habitats used by farmed salmon and preferred glide areas with considerable vegetation cover. This study suggests that differences in the pattern of habitats used by young Atlantic salmon were both size‐ and origin‐dependent and may result from intra‐species competition between farmed and wild populations. Given that stocking with farmed Atlantic salmon is carried out intensively to enhance recreational angling or to conserve salmon populations, this study warns that this can have a negative impact on the extant wild Atlantic salmon population.     

Factors influencing fallback by adult Atlantic salmon following transport into a novel river reach

Transport of salmonids allows upstream migrating adults to bypass barriers to migration, for example hydroelectric dams or adverse habitats. Downstream movement (“fallback”) after transport is common and removes individuals from spawning populations, with possible detrimental consequences for population productivity. Time‐to‐event analysis was used to determine effects of fish characteristics, transport conditions and environmental variables on fallback by adult Atlantic salmon transported to an inaccessible river reach as a population enhancement strategy on the Rivière Sainte‐Marguerite Nord‐Est (Québec, Canada). Of 68 salmon transported, 19 exhibited post‐transport fallback within seven days of transport. Fork length (FL) was the only factor that increased risk of post‐transport fallback; there was a 5% increase in the proportion of large salmon (≥780 mm FL) exhibiting post‐transport fallback relative to individuals of median size (750 mm FL). Although the present study was limited by small sample size, the findings will help inform design of transport programmes in freshwater systems.     

Comparison of population dynamics of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in a small tributary of the River Scorff (Brittany, France)

The population dynamics of Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) were compared in a small tributary of the River Scorff (Brittany, France) from spawning time to the beginning of the third growing season. The spawning and fry emergence of the two species took place at approximately the same time. In the first autumn, the densityof 0+ juveniles and settling rate from the egg stage were much higher in trout than in salmon. The emigration rate from 0+ population was much higher in trout than in salmon. The size of resident and migrating fish was always smaller in salmon than in trout, whatever the age. The low level of salmon production in the brook, compared with trout, was the result of low survival from egg to 0+ stage in autumn, combined with the small proportion of juveniles migrating after the first growing season. This was not compensated by a high number of migrants the next year. The role of physical habitat, inter-and intraspecific competition, predation and migration dependence on size and early sexual maturity is discussed. Indications are that small tributaries of the type studied are of great value for recruitment in trout but not very productive for juvenile salmon.     

Ecology and movement of juvenile salmonids in beaver-influenced and beaver-free tributaries in the Trøndelag province of Norway

There is concern that expanding beaver (Castor fiber) populations will negatively impact the important economic, recreational and ecological resources of Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) populations in Europe. We studied how beaver dams influenced habitat, food resources, growth and movement of juvenile Atlantic salmon and trout on three paired beaver-dammed and beaver-free (control) tributaries of important salmon rivers in central Norway. Lotic reaches of beaver-dammed and control sites were similar in habitat and benthic prey abundance, and ponds were small (<3,000 m²). Though few juvenile salmonids were detected in ponds, trout and salmon were present in habitats below and above ponds (comprising 9%–31% and 0%–57% of the fish collected respectively). Trout dominated control sites (79%–99%), but the greatest proportion of Atlantic salmon were upstream of beaver ponds (0%–57%). Growth rates were highly variable, with no differences in growth between lotic reaches of beaver-dammed and control sites. The condition and densities of juvenile salmon and trout were similar in lotic reaches of beaver-dammed and control sites, though one beaver-dammed site with fine sediment had very few juvenile salmonids. Beaver dams did not block the movement of juvenile salmonids or their ability to use upstream habitats. However, the degree of repeated movements and the overall proportion of fish moving varied between beaver-dammed and control sites. The small scale of habitat alteration and the fact that fish were able to move past dams makes it unlikely that beaver dams negatively impact the juvenile stage of salmon or trout populations.     

Drift diving: A quick and accurate method for assessment of anadromous salmonid spawning populations

The accuracy of drift diving surveys of Atlantic salmon, Salmo salar L. and sea trout, Salmo trutta L., was evaluated by comparing the abundance and size distribution with catches in a fish trap over 6 years in the River Etneelva, western Norway. The population count from drift diving accounted for on average 96.3% of the salmon in the trap after accounting for the catches during fishing. Size structure registered during drift diving corresponded with trap catches of salmon, but the number of small salmon (<3 kg) appeared to be somewhat underestimated, while large salmon (>7 kg) were overestimated in drift diving. For sea trout, the match between drift diving counts and trap registrations was poorer (average 76.3%), but may have been affected by the surveys being performed too late with regards to sea trout spawning time. The study illustrates the utility of drift counting for estimating the entire population of anadromous salmonids in a river.     

Effects of intra‐ and interspecific competition and hydropeaking on growth of juvenile Atlantic salmon (Salmo salar)

The effects of hydropeaking and intra‐ and interspecific competition on the growth performance (growth in length, mass and lipid content) of juvenile Atlantic salmon Salmo salar and brown trout Salmo trutta were studied in six experimental channels (three experiencing hydropeaking and three controls with a stable discharge of water). Changes in the water‐covered area in the hydropeaking channels were small to avoid fish stranding. Each channel was divided into three similar‐sized sections and stocked with either low or high density of Atlantic salmon, or a mix of Atlantic salmon and brown trout, with the density of the latter equalling the high‐density treatment of Atlantic salmon. A marked effect of competition was visible as salmon in the low‐density treatment were significantly larger (27–33%) and had a higher mass (30–38%) than salmon in both the high‐density salmon treatment and the high‐density salmon and trout treatment. Hydropeaking had only minor and insignificant effects on the growth performance: overall final length, mass and body lipid content in the salmon experiencing hydropeaking differed by ?9%, ?7% and +2% compared with controls. Furthermore, there was no indication that the competitive regime influenced hydropeaking effects. The increase in both intra‐ and interspecific competition among the juvenile salmon had a pronounced and significant effect on growth. Our study adds to the growing evidence that energetic consequences of hydropeaking are likely to be small for Atlantic salmon and that stress and mortality associated with stranding represent the main source of population impact.     

Migratory behaviour of adult wild and escaped farmed Atlantic salmon, Salmo salar L., before, during and after spawning in a Norwegian river

The migratory behaviour of adult wild and escaped farmed Atlantic salmon, Salmo salar L., before, during after spawning in the River Namsen, Norway, was analysed using radio telemetry. The fish were caught, radio tagged and released into the fjord between 7 and 25 km from the river mouth. A significantly higher proportion of wild (74%) than farmed (43%) salmon was subsequently recorded in the river. Wild salmon (33%) were more frequently captured in the sea and in rivers than farmed salmon (14%). The migration speed from release to passing a data logger 11 km upstream from the river mouth was not significantly different between wild (20.6 km day^?1) and farmed (19.8 km day^?1) salmon. Wild salmon tagged when water flow in the river was increasing had a significantly higher migration speed than wild salmon tagged when water flow was decreasing. This was not true for farmed salmon. Farmed salmon were distributed significantly higher up the river than wild salmon during spawning, although both types of fish were found together in spawning areas. Thus, there was no geographical isolation to prevent spawning between wild and escaped farmed salmon. Farmed salmon had significantly more and longer up- and downstream movements than wild salmon during the spawning period. Unlike farmed salmon, the number of riverine movements by wild salmon increased significantly when variation in water flow increased. A smaller proportion of wild (9%) than farmed (77%) salmon survived through the winter after spawning.     

Interactions between naturalised exotic salmonids and reintroduced Atlantic salmon in a Lake Ontario tributary

Abstract – Atlantic salmon (Salmo salar) was once native to Lake Ontario, however, its numbers rapidly declined following colonisation by Europeans and the species was extirpated by 1896. Government agencies surrounding Lake Ontario are currently undertaking a variety of studies to assess the feasibility of reintroducing Atlantic salmon. We released hatchery‐reared adult Atlantic salmon into a Lake Ontario tributary to examine spawning interactions between this species and fall‐spawning exotic salmonids found in the same stream. Chinook salmon, coho salmon and brown trout were observed interacting with spawning Atlantic salmon in nearly one‐quarter of our observation bouts, with chinook salmon interacting most frequently. Whereas a previous investigation found that chinook salmon caused elevated agonistic behaviour and general activity by spawning Atlantic salmon, the present study found that interspecific courtship was the most common form of exotic interaction with spawning Atlantic salmon. In particular, we observed precocial male Chinook salmon courting female Atlantic salmon and defending the female against approach by male Atlantic salmon. We discuss the potential implications of these interactions on the Lake Ontario Atlantic salmon reintroduction programme.     

The age structure and distribution of Atlantic salmon parr, Salmo salar L., in small tributaries and main stems of the subarctic River Teno, northern Finland

Parr of the Atlantic salmon in subarctic River Teno, northern Finland (70°N, 28°E), are found to migrate to small tributaries that are not spawning areas for the adult salmon. The age distribution of the salmon differs significantly between these brooks and the natal rivers, the parr in the brooks being typically 2–4 years old, whereas those in the main rivers were mostly of age 0–2 years. The older fish were found in the uppermost regions of the brooks. The ratio of salmon to brown trout decreases towards the upper reaches of the brooks. At least some of the young salmon overwinter in the brooks. However, the number of fish and the area inhabited diminished towards the autumn in some occasions. It is suggested that this migratory behavior may be an adaptational phenomenon that could cause variation in survival among young salmon in the River Teno.     

Natural re‐establishment of Atlantic salmon reproduction and the fish community in the previously heavily polluted River Purtse,Baltic Sea

Abstract – The River Purtse was historically a significant Atlantic salmon spawning river in the Gulf of Finland (Baltic Sea). After the establishment of oil shale mining and processing in the catchment area in the late 1920s, the salmon population went extinct. By the 1970s, the river was heavily polluted and the lower reaches lacked any fish fauna. However, since the 1990s, pollution from oil shale mines was greatly reduced and water quality started to improve. The first fish species to repopulate the polluted area were gudgeon and nine‐spined stickleback. The first salmon parr from wild spawning were recorded in 2006. Up to 2009, a total of fifteen fish species have been recorded including trout and the sensitive bullhead. This study illustrates the natural recovery of the fish fauna following water quality improvement.     

Life stage‐specific,stochastic environmental effects overlay density dependence in an Atlantic salmon population

Atlantic salmon populations appear to fluctuate stochastically through time. It is suspected that both density‐dependent and density‐independent factors cause these fluctuations but the relative importance of each, and the life stages at which they operate, is not well known. In this study, a long‐term data set on Atlantic salmon migrants returning to the Foyle catchment, Ireland, was used to determine the role of density‐dependent and life stage‐specific environmental factors regulating population size. A Ricker density‐dependent model showed that spawning adult population size significantly predicted variation in the resultant filial generation; however, a large amount of variation (ca. 68%) remained unexplained. It was shown that environmental factors were significant in explaining some of the remaining variance and that these influences were linked to specific life stages. Three life stages—spawning and incubation, fry emergence and marine survival—were shown to have significant environmental effects that resulted in changes in the returning cohort strength. It is concluded that these life stage‐specific environmental effects are likely to contribute to the stochastic variation in population size resulting from the application of traditional stock–recruitment models. The identification and quantification of these effects should allow improved model accuracy.