Large Parr Research Articles

THE BEHAVIOR OF YOUNG SALMON (SALMO SALAR L.) IN THE RIVER LIZHMA (LAKE ONEGO) IN THE SUMMER SEASON

It was found that each age group of young salmon has its own daily foraging activity pattern, mainly regulated by illumination. At the latitude of the Lizhma River (62°22ʹ40ʺ N, 34°29ʹ57ʺ E), which drains to Lake Onego, the foraging activity duration in June and July is 16 h ± 30 min. In twilight hours and in the dark (below 200 lx) it was absent in all age groups. Young-of-the-year (0+) maintained a constant level of foraging activity during the day, making about 900 darts at food. Parr aged 1+ and 2+ foraged the most actively in the morning (18,000 lx), after which the activity declined until 15 h (70,000 lx)and remained low until 19 h (21,000 lx). Then it increased slightly until dusk. The number of darts at food was about 350 per day. For 3+ parr, the activity was the lowest in the morning hours, gradually growing afterwards to reach a peak at around 15 hours, after which a gradual decline was observed. During the day they make about 300 darts at food. The foraging intensity for 0+ fish averages 63 darts per hour. Fish aged 1+ make less than 30 darts/h; 2+ make about 40 darts/h; 3+ salmon make about 25 darts/h. Foraging activity can be reduced by dense clouds and competition. Young fish aged 0+ and 1+ cannot compete with larger parr and other predators for fodder-rich sites. 2+ and 3+ parr occupy the most advantageous feeding microsites, where they perform up to 88 % of all daily darts for food in less than 50 % active time, and thus satisfy their daily nutritive demand. As a result, 2+ and 3+ parr would be more often seen inactive in “shelter” microsites compared to 0+ and 1+ individuals.

Effects of habitat on individual reproductive success of mature male parr of Atlantic salmon Salmo salar

The effect of the presence of stone blocks in the spawning habitat on the reproductive success of mature male parr of Atlantic salmon Salmo salar of various sizes and ages was tested in an artificial channel. Shelters allowed smaller individuals to contribute to egg fertilization as much as large parr, suggesting that the size-based dominance observed in a shelterless habitat was not maintained in a more complex habitat.

Delayed smolt migration of stocked Atlantic salmon parr

Abstract The timing of the smolt run in the Dale River in western Norway was monitored from 2002 to 2007 after annual stocking in late autumn 2000 to 2005 with 5000–10800, 11–16 g, Atlantic salmon, Salmo salar L., parr. The releases yielded an annual smolt production of 1000–2000 individuals, mainly 1+ smolts. Almost 5700 stocked smolts were trapped during smolt migration and 60% of these were genotyped for family identification. The date for 50% descent varied by 14 days from year to year. For the most part, however, the 2+ stocked smolts and the majority of the wild smolts left the river in May, while the 1+ stocked smolts migrated 23–26 days later in June. It was concluded that the strategy of stocking large parr in late autumn may conflict with the natural timing of smolt migration the following spring.

Habitat suitability indices development in Denmark: are international indices applicable under small lowland stream conditions?

The transferability of habitat suitability indices (HSIs) remains a controversial issue within physical habitat-based modelling. This issue is often exacerbated when the indices are obtained from international sources without adequate transferability tests being conducted. The aim of this paper was to assess the applicability of seven sets of HSIs (three local and four international) to small lowland Danish streams applied to large parr brown trout (Salmo trutta), an important ecological indicator in these systems. Using a simple hierarchical literature review, the applied indices were ranked firstly for their biological and physical similarities to the local Danish small lowland stream conditions, secondly on the methods used to devise the HSIs and collect the field data, and thirdly if they were locally or internationally sourced. The review ranked background information hierarchically (from most important to least) provided with the HSIs literature: (1) size class of species, (2) season, (3) river type, (4) discharge level, (5) HSIs type, (6) HSIs category, (7) data processing methods, (8) sampling methods, and (9) HSIs country of origin (local or international). To test the effectiveness of the hierarchical review-based system to rank the applicability of the HSIs, the impact of using the different HSIs for physical habitat-based modelling was tested using the hydraulic-habitat model RHYHABSIM. A set of locally derived indices were used as the baseline and compared to the other HSIs. There were large differences in the hydraulic-habitat model predictions of the maximum weighted usable habitat area (WUAmax, ranging from 0.459 to 1.023 m2m−1) and the corresponding optimum discharge (Q opt, ranging from 0.170 to 0.315 m3s−1). This emphasizes that model output is very dependent on the set of HSIs chosen; so careful consideration in the selection process is needed. The review ranking system compared favourably to the physical habitat model results, indicating that it is possible to transfer HSIs from international sources if the biological and physical conditions from their source study and stream(s) were similar to the target stream, irrespective of the country of origin. The study shows promising results for water managers wanting to use already developed HSIs by transferring international HSIs even when using simple transferability tests such as a hierarchical literature review.

Predicting population responses to restoration of breeding habitat in Atlantic salmon

SummaryHabitat degradation is seriously threatening stream biodiversity and productivity world‐wide. For salmonid fish, restoration projects in disturbed systems commonly aim at increasing the availability of suitable breeding habitats, but expectations of effects on population abundance based on explicit models are lacking.We used a spatial population model to predict how breeder dispersion may influence population dynamics of salmonids. Simulations involved changing the relative abundance of habitat suitable for two juvenile size classes (small fry and larger parr), the type of density‐dependent regulation (effects on survival only vs. effects on survival and growth) and intercohort competitive mechanisms.Increased breeding dispersion could alter patterns of density‐dependent mortality and increase equilibrium adult abundance and maximum sustainable yield (MSY). However, there was a strong interaction between stage‐specific habitat abundance and breeding dispersion. The most pronounced effects of breeding dispersion were observed under intermediate levels of fry habitat abundance.When fry habitat was abundant, density‐dependent mortality was most intense during the parr stage, and increased breeding dispersion did not increase adult abundance or MSY. In fact, when populations were regulated in the parr stage, increased breeding dispersion could cause decreased adult abundance because of the effects of intercohort competition. This negative effect only occurred, however, when competition among juveniles was symmetric (no age or size advantage).Synthesis and applications.The population effects of restoring breeding habitat can differ among environments, and we have demonstrated how these differences can be understood in the light of stage‐specific density dependence. Increasing spatial dispersion of breeders may often be an efficient measure for conserving threatened populations and increasing yields in fished populations. However, if direct evidence or habitat considerations suggest that fish populations experience density‐dependent mortality during the parr stage, attempts to increase abundance through increased breeding distribution or artificial stocking should be avoided, as these are likely to be ineffective or even detrimental. The difference between fishing rates providing maximum sustainable yield and extinction is particularly small for such populations, suggesting that fish managers should adopt a conservative and flexible regulation regime.

Movements of wild atlantic salmon parr in relation to peaking flows below a hydropower station

AbstractMovements of 20 radio‐tagged wild Atlantic salmon (Salmo salar) parr were studied 1.3 km downstream of a hydropower station. Ten parr were free‐ranging and ten were restricted to an area near the river bank by a 75 m2 rectangular containment pen that was flooded at high flow, but dry at low flow except for a small refuge at the low end. The positions of contained parr were continuously recorded within a four‐cell uniform grid by continuous data logging, while free‐ranging fish were positioned by manual tracking four times per day. River discharge was manipulated to run five pseudo‐replicated series of three step changes from 30 to 70 to 110 m3 s−1, with slow (2 h) and rapid (0 h) increase and decrease in discharge, as well as during day and night. No differences in movements or home ranges (mean 2770 m2 ± 1759 SD) were detected related to manipulated discharge variations or time of day or night for the free‐ranging parr. No free‐ranging parr were stranded during rapid flow reductions. In the containment pen, the parr distributed themselves relatively evenly among the cells. They moved significantly more at changing than at stable flows. In the containment pen, most of the fish that were stranded were observed during rapid flow reductions at night. Rapid reductions in water flow may cause increased mortality in large parr in shallow habitats if movements are restricted; however, rapid fluctuations did not appear to influence movements or cause stranding by free‐ranging Atlantic salmon parr, which moved considerable distances regardless of discharge. Copyright © 2004 John Wiley & Sons, Ltd.

Is Atlantic salmon production limited by number of territories?

Thirty Atlantic salmon Salmo salar parr (mean 135 mm total length, LT) in the River Alta, Norway, were radio‐tagged and tracked during a 11–13 day period. The parr stayed within defined home ranges with a 95% probability of localization within an average area of 1286 m2(241–3484 m2). On average, each parr had overlapping home ranges with 7·7 other parr, and the overlap between pairs of fish covered on average 24% of their home range areas. Mean length of the river stretch used was 90 m (22–383 m). On average, during 38%(16–77%) of the tracking surveys, the fish had moved >10 m since the previous survey. Mean total distance moved during the whole study was 402 m (208–862 m). The Atlantic salmon were most often recorded in riffles, but 27% of the parr alternated between riffles and pools. The extensive movements, flexible habitat utilization and relatively large home ranges, together with the fact that all the parr had home ranges partly overlapping with other radio‐tagged parr, indicate a flexible and variable behaviour and, thereby, a more complex social structure than a rigid defence of a fixed territory. Thus, Atlantic salmon production seems not to be limited by the highest potential number of territories for large parr in a given area.

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

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.Note

Spatial niche variability for young Atlantic salmon (Salmo salar) and brown trout (S. trutta) in heterogeneous streams

Abstract–Habitat is important in determining stream carrying capacity and population density in young Atlantic salmon and brown trout. We review stream habitat selection studies and relate results to variable and interacting abiotic and biotic factors. The importance of spatial and temporal scales are often overlooked. Different physical variables may influence fish position choice at different spatial scales. Temporally variable water flows and temperatures are pervasive environmental factors in streams that affect behavior and habitat selection. The more frequently measured abiotic variables are water depth, water velocity (or stream gradient), substrate particle size, and cover. Summer daytime, feeding habitats of Atlantic salmon are size structured. Larger parr (>7 cm) have a wider spatial niche than small parr. Selected snout water velocities are consistently low (3–25 cm. s−1). Mean (or surface) water velocities are in the preferred range of 30–50 cm. s−1, and usually in combination with coarse substratum (16–256 mm). However, salmon parr demonstrate flexibility with respect to preferred water velocity, depending on fish size, intra‐ and interspecific competition, and predation risk. Water depth is less important, except in small streams. In large rivers and lakes a variety of water depths are used by salmon parr. Summer daytime, feeding habitat of brown trout is also characterized by a narrow selection of low snout water velocities. Habitat use is size‐structured, which appears to be mainly a result of intraspecific competition. The small trout parr (<7 cm) are abundant in the shallow swift stream areas (<20–30 cm depths, 10–50 cm. s−1water velocities) with cobble substrates. The larger trout have increasingly strong preferences for deep‐slow stream areas, in particular pools. Water depth is considered the most important habitat variable for brown trout. Spatial niche overlap is considerable where the two species are sympatric, although young Atlantic salmon tend to be distributed more in the faster flowing and shallow habitats compared with trout. Habitat use by salmon is restricted through interspecific competition with the more aggressive brown trout (interactive segregation). However, subtle innate differences in behavior at an early stage also indicate selective segregation. Seasonal changes in habitat use related to water temperatures occur in both species. In winter, they have a stronger preference for cover and shelter, and may seek shelter in the streambed and/or deeper water. At low temperatures (higher latitudes), there are also marked shifts in habitat use during day and night as the fish become nocturnal. Passive sheltering in the substrate or aggregating in deep‐slow stream areas is the typical daytime behavior. While active at night, the fish move to more exposed holding positions primarily on but also above the substrate. Diurnal changes in habitat use take place also in summer; brown trout may utilize a wider spatial niche at night with more fish occupying the shallow‐slow stream areas. Brown trout and young Atlantic salmon also exhibit a flexible response to variability in streamflows, wherein habitat selection may change considerably. Important topics in need of further research include: influence of spatial measurement scale, effects of temporal and spatial variability in habitat conditions on habitat selection, effects of interactive competition and trophic interactions (predation risk) on habitat selection, influence of extreme natural events on habitat selection use or suitability (floods, ice formation and jams, droughts), and individual variation in habitat use or behavior.

The Atlantic salmon in fresh water: spawning, rearing and production

Fluvial salmonids have evolved to use the diversity of habitats in natural streams for different life history stages and at different seasons. Required freshwater habitat of Atlantic salmon can be classified generally as that suitable (i) for spawning, (ii) for feeding during the major growing period, and (iii) for overwintering. Spawning habitat of salmon is usually in rapid water at the tail of pools on the upstream edge of a gravel bar, ideally with depths about 25 cm, in mean water velocities of about 30–45 cm s-1, with maximum velocities about 2 body lengths s-1, and with a substrate of irregularly shaped stones of cobble, pebble, and gravel. Underyearling salmon ( 7 cm TL) are usually in riffles deeper than 20 cm with a coarse substrate. Depth preference increases with size. Multiple linear regression models quantifying parr habitat have identified substrate as an important variable, with a positive relationship to an index of coarseness. Negative relationships were found with mean stream width, range of discharge, and overhanging cover. Water chemistry, especially alkalinity, nitrates, and phosphates, are important regulators of production. Although similar variables had importance, coefficients among rivers differed. Interactions occur among variables. Further studies are required to quantify productive capacity of habitat for parr. Results suggest that useful models can be derived and if a river system is mapped, and stratified by habitat, then smolt yield could be predicted and the required egg deposition could be estimated. In winter, young salmon shelter among coarse substrate or move to pools, but continue feeding, with larger parr being more active. Feeding is in general opportunistic. Food consists mainly of insects, taken primarily in the water column, but also from the surface and at the bottom. Young salmon in flowing water are highly territorial but are less so in slow or still waters. In fast water, parr use their large pectoral fins to apply themselves to the substrate, allowing them to occupy this type of habitat with little expenditure of energy. Height above the substrate decreases with water velocity, but increases with temperature and social status. Although riffles are preferred habitat, and are relatively more productive, lentic waters can be occupied where there are few predators or severe competitors and may provide significant smolt yield in some systems. Selective segregation minimizes competition between salmon and brook charr or brown trout, but brook charr and brown trout may have negative effects on underyearling salmon, and on parr in pools, whereas salmon have negative effects on small brook charr and brown trout in riffles and flats. Competition by both interference and exploitation results in interactive segregation when the resource, mainly food, becomes limiting. Limited downstream movement of underyearling salmon may occur during the summer. Older juveniles may make upstream movements, but generally migrate downstream, with most movements in the spring, and a lesser peak of activity in the autumn. Dispersal tends to be mainly downstream, indicating that for full distribution, spawning areas are best located upstream. High densities of yearling parr may have negative effects on growth and survival of underyearlings in some river systems, but apparently not in others, so that future research is required in this regard. Density-dependent growth is evident where food is limiting, and can provide an indicator of densities of cohorts so that if a quantitative relationship has been derived, mean size from a sample can give an estimate of the density at that station, with minimum size occurring at carrying capacity. Such regressions vary between habitats with differing productive capabilities, so that future research could provide useful models for assessing productive capacity of a habitat, and optimum densities. Life history strategies can change with changes in density-dependent growth rates. Present stock-recruitment functions do not take environmental variables into consideration, and have limited applicability. Further research is required to determine optimum spawning requirements for salmon in different types of river systems in different geographical areas.

Downstream Movements and Estuarine Residence by Atlantic Salmon Parr (Salmo salar)

Downstream migrations and estuarine residence by Atlantic salmon (Salmo salar) parr and smolts were studied in a small river on the northwest coast of Newfoundland in 1983 and in 1987. There were large downstream migrations in the spring and small downstream migrations in the fall. The major differences between the two types of migrant were that parr migrated about 1 wk before smolts and at a younger age compared with smolts and while parr remained in the estuary throughout the summer, smoits did not. Modal age and mean size were less for parr sampled in the estuary compared with those sampled at the counting-fence which suggested that the smallest parr were not captured by the fence. The estuarine population of parr represented a significant proportion of the river's total production of salmon. Parr were found throughout the estuary in salinities up to 24 parts per thousand but were most abundant near the river mouth. There was evidence that larger parr became smolts and eventually migrated to sea, but smaller parr probably returned to the river for overwintering. It is clear that estuaries should be included as habitat used for rearing Atlantic salmon.

Selection of Microhabitat in Summer by Juvenile Atlantic Salmon (Salmo salar)

This study was designed to define the microhabitats selected in summer by juvenile Atlantic salmon (Salmo salar). Curves were developed describing the preference of 880 young salmon for water velocity at the fish's position (nose velocity), mean water column velocity, total water depth, and stream substrate size. Study sites were chosen in six morphologically diverse streams in Nova Scotia and New Brunswick during 1982–84. Of the four variables measured, only nose velocity chosen by both fry and parr was not significantly different among years or rivers. Atlantic salmon fry (< 65 mm) most frequently selected nose velocities between 5 and 15 cm∙s−1, small parr (65–100 mm) between 5 and 25 cm∙s−1 and large parr (> 100 mm) between 5 and 35 cm∙s−1. Apparently, juvenile salmon utilized water depths and stream substrates which varied within tolerable limits according to their availability in conjunction with preferred water velocities. Significant differences in the body shape and size of the pectoral fin of Atlantic salmon parr in different rivers did not influence the selection of nose velocities within the range of flow conditions sampled.

Effects of Low Environmental pH on Smolting of Atlantic Salmon (Salmo salar)

We reared Atlantic salmon (Salmo salar) in soft water (hardness 13 mg/L as CaCO3) at two pH levels, 6.4–6.7 and 4.2–4.7, from February to June, to assess the effect of low pH on survival, growth, and the smolting process under rising (4–8.5 °C) or relatively constant (9.5–10.5 °C) temperature. Survival was lower as a result of low pH (4.2–4.7) under both temperature regimes. Neither group exposed to low pH gained weight whereas both control groups gained weight during the experiment. Parr–smolt transformation, as indicated by salinity tolerance and gill Na+, K+ ATPase activity, was impaired as a result of low pH. The large (17–19 cm) parr used in this study were initially salinity tolerant and those at control pH (6.4–6.7) increased tolerance to 35‰ salinity between March and May; those in low pH became intolerant of high salinity. ATPase levels in salmon reared at low pH were significantly lower than those at normal pH levels under both temperature regimes. ATPase activity was significantly greater in fish reared at pH 6.4–6.7 with rising than with constant temperature. Plasma chloride and sodium levels were low in response to low pH, indicating impaired ionic regulation in freshwater. Plasma calcium levels were higher at low pH in both temperature regimes; higher levels were reached under constant temperature. Moisture content rose less sharply under low than under control pH in both temperature regimes. In the rising temperature regime, lipid levels reached similar, low levels under low and control pH conditions. Thyroid hormone (T3 and T4) levels gave no clear indication of effects of low pH on smolting. Smoltification did not proceed normally in our Atlantic salmon subjected to low pH levels.

Effects on Wild Young Salmon of Spraying DDT over New Brunswick Forests

When DDT-in-oil was sprayed over large tracts of New Brunswick forest some of the spray got into drainage systems lying in the spray zones. As a result, many young salmon were killed and stocks were endangered.Most New Brunswick salmon spend 3 years in rivers before migrating to sea as smolts. The young fish can conveniently be divided into three size-groups, which are roughly comparable to each year of age. The groups are: underyearlings, small parr (over 1 year old but 10 cm and under from tip of snout to tip of extended tail fin), and large parr.Wild young salmon in unsprayed and sprayed streams were assessed for numbers in each size-group, abundance being expressed as population index = average number per 100 yards2 of stream bottom.DDT at[Formula: see text]. After such spraying young salmon of all size-groups were found in noticeably low numbers as compared with unsprayed situations. Underyearlings were only 2–10% as abundant (index reduced from 24 in places not affected by spray to less than 1 in most sprayed places), small parr only 30% (index reduced from 20 to 6), and large parr only 50% (index reduced from 12 to 6) as abundant.DDT at[Formula: see text]. After spraying at this dosage underyearlings were only about 50% as abundant as with no spraying; small parr were about 80% as abundant and large parr were affected hardly at all.DDT at[Formula: see text]applied twice. This was followed by low numbers of underyearlings, similar to those observed with a single application at [Formula: see text]. No equivalent data for parr are available but other information indicates effects similar to a single spraying with [Formula: see text].Downstream transport of the DDT-in-oil mixture was an important factor in extending the, harmful effects 30 or more miles below spray zones.Delayed mortality followed 4 to 6 months after the early mortality described above. It was associated with the onset of winter cold. It may have removed a large proportion of parr which survived early mortality but quantitative measurements of this factor were not made on wild populations.Reductions in numbers of young salmon were followed by declines in numbers of adults taken in fisheries and returning as spawners.With no spraying in subsequent years, promptness of recovery of young salmon populations depended primarily on abundance of parent stock.

Body Fluid Regulation in Smolting Atlantic Salmon

Parr–smolt metamorphosis in yearling Atlantic salmon was accompanied by variations in plasma and tissue electrolyte levels, and in tissue water distribution. Plasma chloride declined sharply with the onset of smoltification, but recovered to values somewhat higher than those seen in parr with the attainment of the silvery parr stage. Some decrease, with no evidence of a secondary increase, was observed in tissue chloride concentrations. Changes in chloride space values suggested that parr–smolt metamorphosis is also characterized by a shift of tissue fluids from the extracellular to the cellular phase. These variations in water–electrolyte balance are thought to reflect a premigratory activation and secondary suppression of the extrarenal salt excretion systems employed for osmotic and ionic regulation in sea water. Their occurrence in fish estimated upon the basis of morphological characters to be large parr suggests that the metamorphic process may occur earlier in the life cycle of this species than is generally recognized.

Cyclical Abundance and Birds versus Salmon

American mergansers and belted kingfishers that eat large parr, particularly during the low water of dry summers, fulfilled the prediction (based upon statistics) that the periodic scarcity of Atlantic salmon is due to a factor operating on the salmon when near the smolt stage. One year's bird control more than doubled the number of descending smolts and correspondingly increased the sea catch of salmon related to the experimental river, as demonstrated by the occurrence of fish marked as smolts in the river. Bird control may thus remedy periodical scarcity. This serves to explain the favourable influence on numbers of fish that man's presence has been observed to have.