Reduction in antipredator response detected between first and second generations of endangered juvenile Atlantic salmon Salmo salar in a captive breeding and rearing programme

Behaviour trials determining antipredator response were conducted on first and second generation juveniles from a captive breeding and rearing programme for endangered Inner Bay of Fundy Atlantic salmon Salmo salar. Second generation captive fry displayed significantly higher levels of risk‐taking behaviour before and after exposure to a simulated avian predator. Because the first and second generation fry were reared under the same environmental conditions and differed only in the number of generations spent in captivity, these results suggest that rapid genetic changes, possibly due to domestication selection, may have occurred. Antipredator response was also assessed in fully wild and highly domesticated experimental groups: wild fry displayed the greatest antipredator response and domesticated fry displayed the highest levels of risk‐taking behaviour. These results add to the growing evidence documenting rapid genetic change in response to rearing in a captive environment.     

Awareness reactions and avoidance responses to sound in juvenile Atlantic salmon, Salmo salar L.

The possibility of using intense sound as a deterrent for juvenile Atlantic salmon ( Sulmo salar L. ) was studied by recording both physiological awareness reactions in an acoustic tube and behavioural avoidance responses in a pool. The measured awareness reactions consisted of decreased heart rate and breathing movements. Three criteria for the awareness reaction were used to compare the effect of different frequencies between 5 and 150 Hz: (i) threshold for spontaneous awareness reactions relative to the hearing thresholds, (ii) magnitude of the change in heart rate, (iii) degree of habituation to sound. After these criteria the lowest frequencies (5–10 Hz) were most effective in eliciting an awareness reaction from the fish. The responses of freely swimming fish to 10 and 150 Hz sounds were studied in an artificial pool. Juvenile salmon showed avoidance responses to 10 Hz stimulation at intensities 10–15 dB above the threshold for spontaneous awareness reactions measured in the acoustic tube. The 150 Hz sound failed to evoke avoidance responses, even at a level 30 dB above the threshold for spontaneous awareness reactions.     

Migratory behaviour and growth of hatchery-reared post-smolt Atlantic salmon Salmo salar

Individually lagged, 1+ and 2+ hatchery-reared smolts of Atlantic salmon were released in spring and early summer at the mouth of the R. Imsa, south-western Norway. The post-smolts moved mainly northwards in the sea with the coastal current. The estimated mean migratory speed (± s.d. ) of those captured in the sea along the Norwegian coast was 7.45 (± 6.26) km day ⁻¹; in the fjords it was 1.63 (± 2.33) km day⁻². Many of the post-smohs ascended rivers the same year as released; 37.3% of the total number recaptured were caught in R. Imsa, upstream from the site of release, and 5.8% were caught in other rivers throughout middle and southern parts of Norway. The fish recaptured in rivers was probably sexually mature and entered rivers to spawn. Mean specific growth rate for post-smolts caught in the sea was higher than for those caught in R. Imsa (P <0.001) but not for those caught in other rivers (P> 0.05). Post-smolts ascending R. Imsa were smaller at release than those ascending other rivers. However, there was no size difference at release between post-smolts captured in the sea and those recaptured in rivers other than the R. Imsa.     

Behavioural influences on life-history variation in juvenile Atlantic salmon,Salmo salar

Synopsis Juvenile Atlantic salmon emigrate from the river in a given year as a consequence of a physiological decision influencing appetite and growth during the previous summer. The direction of the decision depends on developmental performance exceeding a genetically determined threshold at that time, and that performance is governed by environmental opportunity. The animal's foraging efficiency (ability to avoid predators, and to compete) determines how well that opportunity is used. Those fish which maintained relatively high growth after July preferred higher stream flows, and were more likely to hide than to flee from a predator. Predator vigilance reduced intake, and ability to discriminate edible particles. Early competitive ability depended on fierceness rather than size, and ultimate large size was a consequence of dominant status. Initial status among high ranking individuals (but not among low ones) predicted the likelihood of maintaining growth in late summer. Size by July was the better predictor for low ranked fish. The influence of high status on life-history variation depends on how much it suppresses the growth of those lower in the hierarchy. Invited review     

Social context, competitive interactions and the dynamic nature of antipredator responses of juvenile rainbow trout Oncorhynchus mykiss

The effects of food ration and social context, as well as possible interactions, on the antipredator behaviour of juvenile rainbow trout Onchorhynchus mykiss were investigated in a pair of laboratory studies. In experiment 1, pairs of dominant and subordinate O. mykiss were exposed to conspecific alarm cues when maintained under high or low food rations. Under high food rations, dominant individuals responded to predation risk, whereas subordinates used the opportunity to feed. Under low food ration, however, the opposite pattern was observed, where subordinates responded to predation cues and dominants did not. Experiment 2 consisted of performing the same experiment, however separating the dominant and subordinate O. mykiss 3 h before testing. When tested separately, dominant and subordinate individuals did not differ in their responses to alarm cues, regardless of food ration. These results demonstrate that there is a complex interaction between current energy status and social context on decision making by prey animals.     

Age-specific aggregation of wild juvenile Atlantic salmon Salmo salar at cool water sources during high temperature events

This study quantified the use of cool water sources by wild 0+, 1+ and 2+ year Atlantic salmon Salmo salar during high water temperatures ( i.e. >23° C) in summer 1995 and 2004. During these events, 0+ year Atlantic salmon did not aggregate or increase in abundance in cool water sites. Interestingly, 1+ and 2+ year Atlantic salmon numbers increased in cool water sites. In addition, these older juveniles formed numerous, discrete aggregations along the plume created by a tributary with aggregation locations being similar between years. Aged 2+ year fish aggregations were at the coolest sources whereas 1+ year aggregations were in locations cooler than the main river. Fish in aggregations on average used deeper sections (average depth: 380 mm) compared with the coolest available habitat in the thermal plume (average depth: 230 mm). Hence, during high temperature events, older juvenile Atlantic salmon moved to cooler water sites and then aggregated in deeper microhabitats.     

Estuarine survival and migratory behaviour of Atlantic salmon Salmo salar smolts

To estimate mortality rates, assess the spatio‐temporal dynamics of natural mortality and examine migratory behaviour during the fresh to saltwater transition, 185 wild Atlantic salmon Salmo salar smolts were implanted with coded acoustic transmitters. Seaward migration of tagged S. salar from four river systems in an area of Nova Scotia, Canada known as the Southern Upland was monitored using fixed receivers and active telemetry over 3 years. Cumulative survival through the river, inner estuary, outer estuary and bay habitats averaged 59·6% (range = 39·4–73·5%). When standardized to distance travelled, survival rates followed two patterns: (1) constant rates of survival independent of habitat or (2) low survival most frequently associated with inner estuary habitats. In rivers where survival was independent of habitat, residency periods were also independent of habitat, post‐smolts exhibited few upstream movements, took a more direct route to the ocean and reached the ocean rapidly. Alternatively, in rivers where survival was habitat specific, residency was also habitat specific with overall increased residency, more frequent upstream movements and delayed arrival to the open ocean. The sudden disappearance of most (75–100%) smolts and post‐smolts assumed dead during the course of this study warrants further examination into the role of avian predators as a mortality vector.     

Migration and survival of Atlantic salmon Salmo salar smolts in a large natural lake

An investigation with acoustic telemetry of the passage of Salmo salar smolts through a large natural lake found heavy mortality occurred at the river‐to‐lake confluences (mean 31.2% km^?1), but was lower in the main body of the lake (mean 2.4% km^?1). Predation was a significant pressure on emigrating smolts as tagged pike Esox lucius aggregated at river‐to‐lake confluences during the peak of the smolt run. Tagged smolts mainly emmigrated into the lake in the late evening after dusk, possibly as a predator‐avoidance behaviour.     

The effects of intraperitoneally implanted dummy acoustic transmitters on the behaviour and physiology of juvenile Atlantic salmon, Salmo salar L

The behavioural and physiological effects of surgical implantation of dummy miniature acoustic transmitters into the peritonealcavities ofjuvenile Atlantic salmon, Salmo salar L., were assessed. lntraperitoneal implantations had no significant effect on growth, feeding or swimming behaviour in either parr or smolts. Recovery from the surgical implantation was both rapid and total; infection was absent; and physiological processes such as smoltification and maturation of testes in precocious parr were unaffected. Expulsion of the transmitter through the body wall, not through the implantation wound, occurred in a number of fish but without adversely affecting the animals. The intraperitoneal implantation technique is discussed in relation to its use during biotelemetry studies.     

Trade‐offs between salinity preference and antipredator behaviour in the euryhaline sailfin molly Poecilia latipinna

Salinity preference and responses to predatory chemical cues were examined both separately and simultaneously in freshwater (FW) and saltwater (SW)‐acclimated sailfin mollies Poecilia latipinna, a euryhaline species. It was hypothesized that P. latipinna would prefer FW over SW, move away from chemical cues from a crayfish predator, and favour predator avoidance over osmoregulation when presented with both demands. Both FW and SW‐acclimated P. latipinna preferred FW and actively avoided predator cues. When presented with FW plus predator cues v. SW with no cues, P. latipinna were more often found in FW plus predator cues. These results raise questions pertaining to the potential osmoregulatory stress of salinity transitions in euryhaline fishes relative to the potential fitness benefits and whether euryhalinity is utilized for predator avoidance. This study sheds light on the potential benefits and consequences of being salt tolerant or intolerant and complicates the understanding of the selection pressures that have favoured the different osmoregulatory mechanisms among fishes.     

The effects of prior residence on behavior and growth rates in juvenile Atlantic salmon (Salmo salar)

It is well documented that prior residence confers advantagesin territorial disputes, but its impact on other aspects ofbehavior and fitness is less understood. We tested how priorresidence influences the subsequent feeding behavior and growthperformance of dispersing Atlantic salmon fry (Salmo salar)using experimental manipulations of residence in a seminaturalstream tank. In replicated trials, groups of seven "primary"fish were released into the stream tank 3 days ahead of seven"secondary" fish. Standardized behavioral observations were madeon each fish over the following 14 days, after which all fishwere removed and measured. Primaries and secondaries were initiallythe same size and body condition and exhibited the same degreeof site fidelity. However, primaries darted higher into thewater column to intercept prey items, fed at a higher rate,and subsequently grew faster. Larger fish (in terms of body length)tended to be more dominant, and dominants grew faster than subordinates.However, there was no difference in dominance between primaries andsecondaries. These results suggest that the well-documentedadvantage of early-emerging salmon fry over late-emerging frycannot be completely attributed to intrinsic differences andthat the advantage is partly mediated via a prior residenceeffect. Furthermore, prior residents gain foraging advantageswithout necessarily becoming more dominant.     

Seasonal variation in the thermal performance of juvenile Atlantic salmon (Salmo salar)

1. Experimental data on the maximum growth and food consumption of winter‐acclimatised Atlantic salmon (Salmo salar) juveniles from three Norwegian rivers situated at 59 and 70°N were compared with predictions from published models of growth and food consumption of summer‐acclimatised fish from the same populations. 2. All winter‐acclimatised fish maintained positive growth and a substantial energy intake over the whole range of experimental temperature (1–6 °C). This contrasted with predictions from growth models based on summer acclimatised Atlantic salmon, where growth and energy intake ceased at approximately 5 °C. 3. Growth and food consumption varied significantly among populations. Winter‐acclimatised fish from a Northern population had a higher mass‐specific growth rate, higher energy intake and higher growth efficiency than southern populations, which is contrary to predictions from models developed using summer‐acclimatised salmon, where fish from the Northern population had the lowest growth efficiency. 4. The experiment provides evidence that thermal performance varies seasonally and suggests adaptation to the annual thermal regime.     

Interaction between migration behaviour and estuarine mortality in cultivated Atlantic salmon Salmo salar smolts

Migration behaviour and estuarine mortality of cultivated Atlantic salmon Salmo salar smolts in a 16 km long estuary were studied using two methods: (1) acoustic telemetry and (2) group tagging in combination with trap nets. Progression rates of surviving individuals through the estuary were relatively slow using both methods [0·38 L_T (total length) s^?1 v. 0·25 L_T s^?1]. In 2012, the progression rate was slow from the river to the estuary (0·55 L_T s^?1) and the first part of the estuary (0·31 L_T s^?1), but increased thereafter (1·45–2·21 L_T s^?1). In 2013, the progression rate was fast from the river to the estuary (4·31 L_T s^?1) but was slower thereafter (0·18–0·91 L_T s^?1). Survival to the fjord was higher in 2012 (47%) compared to 2013 (6%). Fast moving individuals were more likely to migrate successfully through the estuary compared to slower moving individuals. Adult recapture of coded‐wire‐tagged S. salar was generally low (0·00–0·04%). Mortality hot spots were related to topographically distinct areas such as the river outlet (in 2012) or the sill separating the estuary and the fjord (in 2013). At the sill, an aggregation of cod Gadus morhua predating on cultivated smolts was identified. The results indicate that slow progression rates through the estuary decreases the likelihood of smolts being detected outside the estuary. The highly stochastic and site‐specific mortality patterns observed in this study highlight the complexity in extrapolating mortality patterns of single release groups to the entire smolt run of wild S. salar.     

Effects of temperature and a piscivorous fish on diel winter behaviour of juvenile brown trout (Salmo trutta)

相似文献   

Effects of hydropeaking on the spawning behaviour of Atlantic salmon Salmo salar and brown trout Salmo trutta

An in situ camera set‐up was used to study the spawning activity of Atlantic salmon Salmo salar and brown trout Salmo trutta throughout two consecutive seasons in a spawning area affected by hydropower‐related pulse flows due to hydropeaking. The purpose was to test whether the flow variation discouraged spawning in shallow areas or motivated spawning into areas with elevated risk of incubation mortality. There were more S. salar observed on the spawning ground during days with high discharge. The presence of S. salar in the spawning grounds was not affected by the hydropeaking cycles of the preceding night. Female S. salar were observed preparing nests within the first hour after water discharge had increased to levels suitable for spawning. In contrast, the number of S. trutta was not correlated with flow and nest preparation was also observed at a discharge corresponding to the lowest discharge levels during a hydropeaking cycle. Survival was generally high in nests excavated the following winter, with only 5·4% suffering mortality due to dewatering. The results suggest that S. salar may respond rapidly to variable‐flow conditions and utilize short windows with suitable flows for spawning. Smaller S. trutta may utilize low‐flow conditions to spawn in areas that are not habitable by larger S. salar during low flow.     

Migratory behaviour of wild and farmed Atlantic salmon (Salmo salar) during spawning

Migratory behaviour at spawning of wild and newly-escaped farmed Atlantic salmon was analysed by radio telemetry in the River Alta, North Norway. Spawning areas were located by aerial surveys. Farmed females moved significantly more than wild females ( P <0.01). There was no such difference between the two groups of males. About 83% of the wild fish stayed within identified spawning areas for 1 day or longer. The corresponding figure for farmed salmon was only 43% ( P <0.05). Wild salmon stayed 8.1 days inside spawning areas and farmed salmon 5.2 days. The present results suggest that escaped farmed salmon had reduced spawning success compared with wild fish.     

Effects of discharge and local density on the growth of juvenile Atlantic salmon Salmo salar

The study explored the combined effects of density, physical habitat and different discharge levels on the growth of juvenile Atlantic salmon Salmo salar in artificial streams, by manipulating flow during both summer and winter conditions. Growth was high during all four summer trials and increased linearly with discharge and mean velocity. Differences in fish densities (fish m^?3) due to differences in stream volume explained a similar proportion of the variation in mean growth among discharge treatments. Within streams, the fish aggregated in areas of larger sediment size, where shelters were probably abundant, while growth decreased with increasing densities. Fish appeared to favour the availability of shelter over maximization of growth. Mean growth was negative during all winter trials and did not vary among discharge treatments. These results suggest that increased fish densities are a major cause of reduced summer growth at low discharge, and that habitat‐mediated density differences explain the majority of the growth variation across habitat conditions both during summer and winter.     

Diel activity pattern of juvenile Atlantic salmon (Salmo salar) in early and late winter

Radiotelemetry was used to investigate the diel activity pattern of juvenile Atlantic salmon (Salmo salar) in early and late winter. Fish were active throughout the diel cycle. However, there was significantly less daytime than nighttime movement and movement declined significantly with increasing fork length. Maximizing winter growth rate, through an overall increase in foraging activity, may reduce the risk of starvation in smaller fish. The results of the present study provide evidence that the activity patterns of juvenile salmonids are quite complex and support the suggestion that individual variation in activity patterns are, at least, partially driven by body size.