The influence of hydrology and hydraulics on salmonids between spawning and emergence: implications for the management of flows in regulated rivers

Abstract Flow regulation is a major constraint on fish populations in many river systems. Current scientific understanding of the direct and indirect influence of hydrology on salmonids between spawning and emergence is reviewed and used to identify key knowledge gaps. The review emphasises difficulties in linking ecological response to physical process understanding and, conversely, the difficulties in applying detailed process understanding to large‐scale management. It is suggested that the lack of process understanding in the development of current environmental standards reflects differences in perspective, language and scale consideration between researchers and river managers. This presents considerable difficulties for the development of new and more defensible environmental standards. Although upscaling of process understanding should remain a focus for researchers, it is also necessary to acknowledge the ‘uniqueness of place’ and consequently that local data collection may frequently be required.     

Behaviour and thermal experience of adult sockeye salmon migrating through stratified lakes near spawning grounds: the roles of reproductive and energetic states

Roscoe DW, Hinch SG, Cooke SJ, Patterson DA. Behaviour and thermal experience of adult sockeye salmon migrating through stratified lakes near spawning grounds: the roles of reproductive and energetic states. Ecology of Freshwater Fish 2010: 19: 51–62. © 2009 John Wiley & Sons A/S
Abstract –  Little is known about physiological factors underlying thermal behaviour in Pacific salmon ( Oncorhynchus spp.). We implanted acoustic transmitters and temperature loggers into migrating adult sockeye salmon ( Oncorhynchus nerka ) and nonlethally assessed their reproductive hormone levels and energetic states immediately prior to their passing through natal lakes en route to spawning grounds. We tested the hypothesis that energetic and reproductive status influence thermoregulatory and other in-lake behaviours. More reproductively advanced females with lower levels of energy transited through cooler temperatures compared to less mature females with high levels of energy, possibly to reduce metabolic energy expenditure and delay final maturation. Transit temperatures of males were not related to physiological variables. Salmon travelled on average 13.6 km·day⁻¹ through two lakes, and often circled or held for more than 1 day before moving upstream, but these behaviours were generally not related to physiological variables.     

A review of the biophysical properties of salmonid faeces: implications for aquaculture waste dispersal models and integrated multi-trophic aquaculture

Knowledge of the quantitative and qualitative properties of salmonid faeces is necessary for aquaculture waste dispersal models, and the design of integrated multi-trophic aquaculture (IMTA) systems. The amount and proximate composition of salmonid faeces can be estimated using a mass-balance, nutritional approach. Indigestible components of salmonid diets have the potential to affect faecal 'cohesiveness' or 'stability'. Nutrient content and density of faeces can vary depending on diet and submersion time. Faecal density has a greater influence on settling velocity than faecal size. Published settling velocity data on salmonid faeces are highly variable due to differences in fish size, rearing systems, collection time, water density, methodology, the mass fraction tested and diet. Most faecal settling data used in published salmonid waste dispersal models are rudimentary and recent information suggests that such models are highly sensitive to this input. The design of open-water IMTA systems and estimation of nutrient capture and recovery from co-cultured filter feeders is difficult due to limited information on particle size, digestibility, settleable and non-settleable mass fractions of salmonid faeces at cage environments. Implications of faecal properties on the accountability for the effects of aquaculture nutrient loading are discussed.     

Challenges in the conservation,rehabilitation and recovery of native stream salmonid populations: beyond the 2010 Luarca symposium

Abstract – In May 2010, I chaired a session on challenges to salmonid conservation at the international symposium ‘Advances in the population ecology of stream salmonids’ in Luarca, Spain. I suggested that in addition to scientific challenges, a major challenge will be improving the links between ecologists, conservationists and policy makers. Because the Luarca symposium focused mainly on ecological research, little time was explicitly devoted to conservation. My objective in this paper is to further discuss the role of ecological research in informing salmonid conservation. I begin with a brief overview of research highlights from the symposium. I then use selected examples to show that ecological research has already contributed much towards informing salmonid conservation, but that ecologists will always be faced with limitations in their predictive ability. I suggest that conservation will need to move forward regardless of these limitations, and I call attention to some recent efforts wherein ecological research has played a crucial role. I conclude that ecologists should take urgent action to ensure that their results are available to inform resource managers, conservation organisations and policy makers regarding past losses and present threats to native, locally‐adapted salmonid stocks.     

The aetiology of spinal deformity in Atlantic salmon, Salmo salar L.: influence of different commercial diets on the incidence and severity of the preclinical condition in salmon parr under two contrasting husbandry regimes

A large-scale trial of the effect of different commercial diets on the incidence of preclinical spinal deformation, as assessed by radiography, and the influence of two contrasting rearing systems was carried out. Two sets of three populations of Atlantic salmon, each of 20 000 first feeding fry of identical hatchery origin, created from equal numbers of eggs from 15 different families, were reared under commercial conditions on two different farms. Three commercial (closed formula) extruded fish meal-based diets were used in this study (diets A, B & C). Each diet was fed to one population of 20 000 fish at each site. Fish were fed a percentage of their body weight per day, with feeding rates set at commercial levels, based on water temperature, day length and fish biomass. Additional hand feeding was used to ensure satiation in all tanks. Fish in each tank were bulk-weighed and counted at the beginning and at 2-week intervals throughout the study. The fish were grown for 30 weeks. In addition, phosphorus (P) digestibility was evaluated by in-feed absorption testing in rainbow trout. The morphology of the radiographic lesions conformed to those described previously. Statistical analysis using multivariate regression analysis showed that date of sampling, site and diet were all statistically significant (P < 0.001) on univariable analysis. Farm A had significantly more affected fish than farm B (P < 0.001), which may have been attributable to variation in dissolved oxygen levels. The available dietary P levels were low in each diet. The number of fish affected in the group of fish being fed diet B was significantly lower than in the groups being fed diets A or C (P < 0.001). It appears most likely that the occurrence of preclinical radiographically apparent defects in parr which are believed to lead to the condition known as 'spinal deformity' is predominantly caused by a deficiency of available dietary P in first-feeding fry. The availability of dietary P may also vary considerably between diets formulated using different ingredients. Phytate-P associated with plant ingredients may affect the availability of P as well as other essential dietary nutrients. Additionally, diets for the production of salmonids in fresh water are currently formulated to keep P effluent to a minimum compatible with healthy spinal development. These various factors combine to make it crucial that small Atlantic salmon, especially first-feeding fry, are provided with carefully formulated diets fortified to an adequate level with a high quality source of available P.     

Site fidelity of spawning sockeye salmon (Oncorhynchus nerka W.) in the presence and absence of olfactory cues

Abstract –  We examined the site fidelity of spawning adult sockeye salmon ( Oncorhynchus nerka ) by tagging and releasing fish in the same stream reach (controls) and displacing them among different but nearby sites ( c . 50 m away). Three sites – two above a stream junction ('upper' reach and 'pond') and one below ('lower' reach) – allowed us to compare the behavior of salmon in the presence and absence of olfactory cues and habitat similarity. Most controls of both sexes (90%) remained in the immediate vicinity of the tagging and release site. When displaced downstream, where the odors of both the upper reach and the pond were detectable, most salmon returned to their former site (65%). Displaced sockeye were more likely to return to the pond from the lower reach than from the upper one ( P  = 0.05), consistent with olfactory orientation and the hypothesis that salmon prefer certain habitats. Salmon displaced from the upper to the lower reach were much more likely to return than those displaced to the pond ( P  < 0.01), consistent with the role of odors in orientation and inconsistent with the habitat choice hypothesis.     

A matter of timing: the role of ocean conditions in the initiation of spawning migration by late‐run Fraser River sockeye salmon (Oncorhynchus nerka)

Year 1995 marked the start of a major shift to earlier river entry of late‐run Fraser River sockeye salmon (Oncorhynchus nerka) en route to the spawning grounds. Earlier entry has typically been accompanied by considerably greater in‐river mortality. We examine this behavioral change using correlation analyses between the entry timing of the Adams River and Weaver Creek stocks and the surface marine conditions encountered by the stocks during their homing migration from the northeast Pacific several months earlier. For Adams stocks, maximum correlation is between entry timing and offshore winds, such that the weaker the wind stress in the direction of the prevailing surface currents in early July, the earlier the river entry in late summer. For Weaver stocks, maximum correlation is with salinity, such that the lower the surface salinity along the coast in August, the earlier the river entry. We hypothesize that oceanic changes lead to changes in late‐run sockeye physiology which then leads to changes in behavior. Physiological changes are postulated to arise from two types of preconditioning: Type‐1 occurs in the offshore region, whereby the weaker the prevailing currents that normally hinder eastward migration, the more endogenous energy available for maturation and the earlier the river entry. Type‐2 occurs in coastal regions, whereby the lower the salinity, the more rapid the osmoregulatory adaptation to freshwater (and possible susceptibility to water‐borne pathogens) and the earlier the entry. Results suggest that the earlier entry that began in the mid‐1990s is linked to weaker ocean currents and lower coastal salinities.     

Immunoreactive somatolactin cells in the pituitary of young,migrating, spawning and spent chinook salmon,Oncorhynchus tshawytscha

Immunocytochemical techniques using an antiserum to cod somatolactin (SL) demonstrated the presence of SL cells in the intermediate lobe of the pituitary in Oncorhynchus tshawytscha. The cells were small in yearling fish. Two groups of maturing fish were studied. In the spring run salmon collected in April and May during the upstream migration, the SL cells appeared stimulated. In September, during spawning, SL cell stimulation was maximal with indices of hypertrophy and degranulation often more marked in females than in males. In the other group, salmon of the fall run collected in the Pacific Ocean in August had well developed gonads, large gonadotropes and abundant SL cells. In spawning salmon (September) the SL cells were stimulated, mainly in females. However, the final stimulation was less intense than in spring run spawning fish. The SL cells were smaller, without evident granule release, but still abundant in spent salmon of the fall run caught at the end of November. Various factors (time spent in rivers before spawning, starvation, decalcification, stress, hypothalamic influences) were considered which might explain differences between spring and fall run salmon. These observations suggest that SL may play a role in the control of gonadal maturation in chinook salmon as it may also do in sockeye and chum salmon previously studied, and that SL cells may be sensitive to the ambient salinity.     

Modelling the migratory behaviour of salmonids in relation to environmental and physiological parameters using telemetry data

Abstract Advances in the field of telemetry techniques during the last few decades have greatly expanded our knowledge on migratory behaviour and provided the opportunity to obtain practically useful data for the conservation and management of salmonid populations. However, applying this information to the development of much needed population‐based migration models has been limited. Furthermore, this research has generally been restricted to assessing the role of river flow on fish movement. Models derived from a 6‐year telemetry study on the movements of Atlantic salmon, Salmo salar L., and sea trout, Salmo trutta L., in the River Tyne are presented together with an assessment of counter data from the same river to highlight the importance of additional environmental and physiological parameters in regulating fish movement. The data are discussed in relation to the advantages of telemetry data, the need to develop predictive models, the statistical methods used and the potential direction of future work in this area.     

Health status of two salmonid aquaculture facilities in North Portugal: characterization of the bacterial and viral pathogens causing notifiable diseases

A comparative bacteriological and virological survey was conducted in two fish farms in the North of Portugal. The fish species examined included cultured rainbow trout, Oncorhynchus mykiss (Walbaum), and brown trout, Salmo trutta L., as well as wild fish captured near both facilities. The microbial load in the internal organs of apparently healthy fish was nonitored over a year, an all the disease problems occurring during this period were investigated. Although both farms presented intermediate levels of infection(30–40% infected fish), farm B showed the poorest microbiological quality since constant but low mortalities were observed throughout the year. Flavobacterium and Psedomonas-Xanthomonas were the predominant bacterial groups, comprising around 40–50% of the isolates from each farm. In farm B, members of the Enterobacteriaceae and mortile Aeromonas also showed significant prevalence (about 20%). The only outbreak of a notifiable disease was an occurrence of furunculosis, caused by Aeromonas salmonicida subsp. salmoncida, in farm A. However, Yersinia ruckeri was isolated not only from diseased fish, but also from asymptomatic fish, usually in mixed infections with motile Aeromonas or infections with motile Aeromonas or infectious pancreatic necrosis virus (IPNV). While Y. ruckeri isolates associated with mortalities belonged to the serotype O1 (subgroup a), those isolated from asymtomatic fish corresponded to serotype O3. Two strains of IPNV (serotype Ab) were isolated in farm B, which represents the first viral agent detected in Portuguese aquaculture. Qualitative and quantitative differences in microbial load were observed between cultured and wild fish. No notifiable bacterial or viral pathogens were detected in any of the feral species studied.     

The prevalence of escaped farmed salmon, Salmo salar L., in the River Ewe, western Scotland, with notes on their ages, weights and spawning distribution

Abstract  The prevalence of escaped farmed Atlantic salmon, Salmo salar L., in the River Ewe, western Scotland, was assessed. After the establishment of smolt cages in the catchment and marine cages near the river mouth during 1986–1987, approximately 425 000 parr and smolts, and 122 000 growers have escaped. Between 1987 and 2001, farmed salmon occurred in the rod fishery in 13 of the 15 years, contributing at least 5.8% of the total catch, with a maximum annual frequency of 27.1%. It was estimated that <1% of fish escaping from the marine cages entered the river, but contributed at least 27% of potential anadromous spawners in 1997. Radiotagged, farmed fish in 2001 probably spawned in three subcatchments also used by tagged wild fish. Despite the likelihood of hybridisation there was no change in the median weight or marine age of wild fish, but smolt age decreased significantly ( P  < 0.02). The Ewe has a depleted wild salmon population (≤900 anadromous adults), and further genetic introgression by escapees should be prevented.     

Survival of reared Atlantic salmon and sea trout in relation to marine conditions of smolt year in the Baltic Sea

The marine survival of hatchery-reared Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) was examined in relation to marine conditions during post-smolt migration and in relation to stock traits. In 1970–2001, Carlin-tagged smolts were released in the Iijoki and Oulujoki rivers, the northern Baltic Sea. When both species were analysed together, the abundance of the three prey fish, herring (Clupea harengus), smelt (Osmerus eperlanus) and vendace (Coregonus albula) correlated positively with the survival of salmonids. In addition, the increase in smolt size appeared to improve the survival rate. Sea surface temperature (SST) may have affected indirectly through the abundance of prey fish during the post-smolt migration of salmon and sea trout. The smelt and vendace showed a statistical effect on survival only when the temperature effects were not included in the models. In sea trout, an increasing smolt length was not significantly correlated with the survival in good herring recruitment years, but in poor years survival increased very rapidly with increasing smolt size. The recapture rates of the salmonids tended to decrease between the years 1970 and 2001. During the same time period, the June SST slightly decreased. The positive correlation between the annual summer SST and recapture rate of salmon may partly explain the decreasing trend in recapture rates. An increase in smolt size did not compensate for the decline in the recapture rate of either species.     

The influence of environmental temperature on the apparent nutrient and fatty acid digestibility in Atlantic salmon (Salmo salar L.) fed finishing diets containing different blends of fish oil, rapeseed oil and palm oil

A 12‐week feeding trial was conducted to investigate the interactive effects between water temperature and diets supplemented with different blends of fish oil, rapeseed oil and crude palm oil (CPO) on the apparent nutrient and fatty acid digestibility in Atlantic salmon. Two isolipidic extruded diets with added fish oil fixed at 50% and CPO supplemented at 10% or 25% of total added oil, at the expense of rapeseed oil, were formulated and fed to groups of Atlantic salmon (about 3.4 kg) maintained in floating cages. There were no significant effects (P>0.05) of diet on growth, feed utilization efficiency, muscle total lipid or pigment concentrations. Fatty acid compositions of muscle and liver lipids were mostly not significantly different in salmon fed the two experimental diets but showed elevated concentrations of 18:1n‐9 and 18:2n‐6 compared with initial values. Decreasing water temperatures (11–6°C) did not significantly affect protein, lipid or energy apparent digestibilities of the diets with different oil blends. However, dry matter digestibility decreased significantly in fish fed the diet with CPO at 25% of added oil. Increasing dietary CPO levels and decreasing water temperature significantly reduced the apparent digestibility (AD) of saturated fatty acids. The AD of the saturates decreased with increasing chain length within each temperature regimen irrespective of CPO level fed to the fish. The AD of monoenes and polyunsaturated fatty acids was not affected by dietary CPO levels or water temperature. No significant interaction between diet and water temperature effects was detected on the AD of all nutrients and fatty acids. The results of this study showed that the inclusion of CPO up to about 10% (wt/wt) in Atlantic salmon feeds resulted in negligible differences in nutrient and fatty acid digestibility that did not affect growth performance of fish at the range of water temperatures generally encountered in the grow‐out phase.     

Sardine and anchovy regime fluctuations of abundance in four regions of the world oceans: a workshop report

Regimes of high abundance of sardine (Sardinops sagax and Sardina pilchardus) have alternated with regimes of high abundance of anchovy (Engraulis spp.) in each of the five regions of the world where these taxa co-occur and have been extensively fished. When one taxon has been plentiful, the other has usually been at a reduced level of abundance, and vice versa. Changes in the four heavily fished regions that support S. sagax–the Japanese, Californian, Humboldt, and Benguela systems–from a regime dominated by one taxon to a high level of abundance of the other have occurred more or less simultaneously. In the Pacific Ocean, sardines have tended to increase during periods of increasing global air and sea temperatures and anchovies to decrease. The Japanese system is dominated by sardines to a greater extent than the other systems, and sardines off Japan appear to increase as the Kuroshio Current cools. At the eastern edge of the Pacific Ocean, sardines colonize cooler areas during periods of warming. The Benguela system is out of phase with the three Pacific systems. The four systems all appeared to be in a state of flux in the 1980s. Increased abundance of the subdominant taxon is often one of the first signs of change. Sardines are relatively sedentary in refuge areas when scarce but change behavior to become highly migratory and colonize cooler areas when abundant. Anchovies, by contrast, expand around a fixed geographic center.     

The onset of spawning in the silver pomfret, Pampus argenteus (Euphrasen), in Kuwait waters and its implications for management

Abstract The spawning periodicity of silver pomfret, Pampus argenteus (Euphrasen), was investigated against a background of conflicting evidence on the onset of spawning in this species. Contrary to the existing view that silver pomfret in Kuwait waters begin to spawn in March–April, evidence is presented that indicates a delay in spawning until May. Only an insignificant level of spawning takes place in April which, from the management point of view, may be ignored. The species has a prolonged spawning period extending from May to August in females, although the males mature in April and ripe specimens are encountered in monthly samples until September. There are two spawning peaks, the first one in May and the second in August.     

多棘海盘车诱导排卵最佳KCl剂置以及水温和盐度对胚胎和幼虫发育的影响

海星的大量繁殖与入侵可对滩涂养殖贝类造成极大威胁.对海星繁殖生物学的研究可为有效控制海星过度增殖提供信息,同时也可为其胚胎和幼虫培育以及发育生物学的深入研究奠定基础.本研究以韩国和中国沿海常见的多棘海盘车(Asterias amurensis)为材料,研究KCl诱导海盘车排放生殖细胞的最佳剂量,以及水温和盐度对胚胎和幼虫发育的影响.采用不同剂量(1.0mL、3.0mL、5.0mL和7.0mL)0.5mol/L KCl注入性成熟海盘车体腔,皆可诱导生殖细胞的排放,3mL注射组的排放个体比例最高(80%),雌性个体排卵量最大(536.5×104个/ind),同时用诱导获得的精/卵进行人工授精后也获得了较高的受精率(92.7±2.9)%.水温和盐度对多棘海盘车胚胎和幼虫的存活率具有显著的影响.在盐度为35时,20℃时多棘海盘车羽腕幼虫的存活率最高(90.1±2.1)%,15℃时次之(84.4±5.2)%.在温度为15℃时,盐度为35时幼虫培养60 h后存活率最高(87.6±4.1)%,盐度为30时次之(85.4±4.0)%.多棘海盘车各期胚胎和幼虫的发育速度(1/t,h-1)随水温升高而加快,在一定温度范围内有明显的正相关性,其关系式为:至2-细胞:1/t=0.110 8Tw-0.599 7(r2=0.946 5);至8-细胞:1/t=0.045 4Tw-0.233 4(r2=0.947 7);至桑椹胚:1/t=0.017 9Tw-0.067 9(r2=0.868 7):至囊胚:1/t=0.004 2Tw(r2=0.89);至羽腕幼虫:1/t=0.000 6Tw-0.008 7(r2=0.878 4).盐度为35时,胚胎和幼虫的发育速度最快,发育至羽腕幼虫需55.4 h.根据不同水温和盐度条件下,胚胎和幼虫的存活率和发育速率,确定15～20℃是多棘海盘车发育的适宜温度,最适温度为20℃;适宜盐度为30～35,最适盐度为35.     

Status of the introduced cichlid Sarotherodon mossambicus (Peters) in the reservoir fishery of Sri Lanka: a management strategy and ecological implications

Abstract. The inland fishery in Sri Lanka (6–10°N; 79–82°E) is essentially a fishery confined to man-made lakes and is dominated by the introduced cichlid Sarotherodon mossambicus (Peters). Catch statistics of 20 such major reservoirs indicate that the yield of this species ranges from 64·0 to 918 kg per ha and accounts for between 56 and 99% of the total yield in individual reservoirs. The yield of S. mossambicus is closely related to the fishing pressure exerted. Catch/effort data from the individual reservoir fisheries when analysed collectively simulate changes in a single large fishery. In the fishery the relationship of yield to effort is described by the equation: Y = 4·OX – 53·8X ( r = 0·92; P < 0·001), where Y = yield in kg per ha per annum and X = number of craft-days per ha per annum, indicating that the reservoirs in Sri Lanka remain underfished. However, very high increases in fishing pressure in two reservoirs, for which data are available over a 5-year period, indicate that the increases have resulted in a significant decline in the catch per unit effort. The reasons for the success of the S. mossambicus fishery in individual reservoirs, and also simulation of features of a single large fishery in reservoirs, with widely different hydrological and limnological regimes, are discussed in qualitative terms. It is hypothesized that the abundance is determined by factors other than food availability. Fresh management strategies to optimize the fishery from the point of view of optimal fishing pressure permissible from the present analysis are suggested.