Predation on Atlantic salmon and sea trout during their first days as postsmolts

Radio-tagged smolts of Atlantic salmon Salmo salar and sea trout Salmo trutta were predated heavily by sea birds after crossing the saline limit in the estuary of the River Skjern, Denmark. Most predation took place within the first 9 h after estuarine entry. The field data do not contradict the hypothesis of maladaptive anti-predatory behaviour.     

Amino acid cues emanating from Pacific salmon eggs and ovarian fluid

The eggs of salmonid fishes are an important food source for many aquatic predators that detect eggs using olfaction. Moreover, chemicals from eggs and ovarian fluid aid sperm cells in detecting and locating eggs for fertilization, and ovarian fluid is attractive to conspecific males. Thus chemicals from eggs and ovarian fluid may facilitate reproduction but may also attract egg predators. The authors sampled mature females of three Pacific salmon species – Chinook (Oncorhynchus tshawytscha), coho (Oncorhynchus kisutch) and sockeye (Oncorhynchus nerka) – and determined the proportional representation of amino acids, potent fish odorants, from their eggs and ovarian fluid (Chinook and coho salmon only). They then tested juvenile coho salmon, an egg predator, for responses to ovarian fluid and egg odours using the electro-olfactogram (EOG) recording technique. The amino acid compositions of the salmon species were significantly and positively correlated with each other, and the interspecific differences were comparable to those between individuals of the same species. The egg water samples were, on average, dominated by lysine, alanine and glutamine (12.6%, 12.4% and 10.9%, respectively). The ovarian fluid samples were dominated by lysine (20.5%), followed by threonine (9.7%), glycine (9.2%) and arginine (8.8%). EOG recordings demonstrated the ability of juvenile coho salmon to detect the chemical traces of eggs and ovarian fluid. It is concluded that salmon eggs are a potent source of odours for potential predators but likely not highly differentiated among salmon species.     

Use of sequence data from rainbow trout and Atlantic salmon for SNP detection in Pacific salmon

Single nucleotide polymorphisms (SNPs) are a class of genetic markers that are well suited to a broad range of research and management applications. Although advances in genotyping chemistries and analysis methods continue to increase the potential advantages of using SNPs to address molecular ecological questions, the scarcity of available DNA sequence data for most species has limited marker development. As the number and diversity of species being targeted for large-scale sequencing has increased, so has the potential for using sequence from sister taxa for marker development in species of interest. We evaluated the use of Oncorhynchus mykiss and Salmo salar sequence data to identify SNPs in three other species (Oncorhynchus tshawytscha, Oncorhynchus nerka and Oncorhynchus keta). Primers designed based on O. mykiss and S. salar alignments were more successful than primers designed based on Oncorhynchus-only alignments for sequencing target species, presumably due to the much larger number of potential targets available from the former alignments and possibly greater sequence conservation in those targets. In sequencing approximately 89 kb we observed a frequency of 4.30 x 10(-3) SNPs per base pair. Approximately half (53/101) of the subsequently designed validation assays resulted in high-throughput SNP genotyping markers. We speculate that this relatively low conversion rate may reflect the duplicated nature of the salmon genome. Our results suggest that a large number of SNPs could be developed for Pacific salmon using sequence data from other species. While the costs of DNA sequencing are still significant, these must be compared to the costs of using other marker classes for a given application.     

中黑盲蝽对小地老虎和甜菜夜蛾的捕食作用

中黑盲蝽Adelphocoris suturalis(Jakovlev)具有植食性和肉食性,但对其肉食性缺乏研究。作者在室内环境下研究了中黑盲蝽对小地老虎Agrotis ipsilon(Hufnagel)、甜菜夜蛾Spodoptera exigua(Hübner)卵和初孵幼虫的捕食作用。研究显示:(1)中黑盲蝽的捕食量随猎物密度的增加而上升,捕食功能反应符合HollingⅡ型方程;(2)捕食量随着若虫龄期的增加而增加,高龄若虫、雌性成虫与雄性成虫之间的捕食量没有明显差异,但均显著高于2龄若虫。雌成虫对小地老虎卵及初孵幼虫、甜菜夜蛾卵及初孵幼虫的最大日捕食量分别为38.60粒和6.80头、56.62粒和5.80头,表明中黑盲蝽对小地老虎和甜菜夜蛾卵和初孵幼虫具有较强的捕食能力。     

Behavioural approaches to demonstrate the ecological significance of exposure of juvenile Pacific salmon (genus Oncorhynchus) to the antisapstain fungicide TCMTB

Simulated stream conditions were used to expose underyearling Pacific salmon (genus Oncorhynchus) to sublethal doses of TCMTB (2-thiocyanomethylthio) benzothiazole; a fungicide used by the lumber industry to protect against discolouration by sapstain fungi. Observed changes in schooling, swimming, and respiration were studied in more detail utilizing progressively more complex and ecologically relevant experimental designs. Laboratory troughs (600 litre) were used to quantify innate shelter-seeking behaviour and susceptibility to predation during salinity stress. Swimming speed, schooling behaviour and responses to salinity and hypoxia were studied in a 4500-litre Water Column Simulator under vertically stratified conditions (fresh water overlying sea water). Finally a similarly stratified 15,500-litre outdoor tank was designed to compare susceptibility to predation during a volitional salinity challenge. Relative to controls, TCMTB-exposed underyearling salmon exhibited a reduction in cover response, were slower to seek shelter from bright light, were more erratic in their swimming behaviour and more likely to be eaten by marine predators. Videotape analyses confirmed that TCMTB reduced exploratory behaviour and swimming speed under both normoxic and hypoxic conditions in the WCS. The ecological consequences of these overt behavioural changes were experimentally linked to a clear increase in risk from predation by yellowtail rockfish (Sebastes flavidus) inhabiting the marine zone below the halocline of the 15,500-litre tank. These techniques illustrate our most recent efforts to correlate cumulative sublethal physiological stress with ecologically meaningful behavioural dysfunction.     

Fine structure of the adenohypophysis in immature sockeye salmon,Oncorhynchus nerka

Summary The ultrastructure of the secretory cells of the adenohypophysis of juvenile sockeye salmon was investigated. Pituitary glands were collected from immature fish transferred experimentally to sea water and subsequently returned to fresh water. The rostral pars distalis contained three cell types: ACTH cells, prolactin cells, and non-secretory cells. The prolactin and non-secretory cells were joined together in the form of follicles by desmosomes and they both had cilia and microvilli projecting into the follicle lumen. Various follicular structures such as lumen, multivesicular structures, and peripheral basement membrane are discussed as possible sites of prolactin cell granule release. The columnar ACTH cells were found at the junction of the rostral pars distalis and the neurohypophysis. The cytoplasmic granules in these cells were characteristically separated from their limiting membrane by a clear space. Multivesicular structures were also found in association with this cell type. The caudal pars distalis also contained three cell types: one acidophil (putative somatotrop) and two basophils (putative thyrotrops and gonadotrops), all of which were similar to those described in adult fish. The pars intermedia contained only one cell type. They appeared to be active cells and were characterized by containing membrane-bounded granules similar to those found in the ACTH cells. Changes in ambient salinity had no apparent effect on any cell type described.The work was supported by a grant in aid of research from the National Research Council of Canada. We wish to thank Mr. R. Lindsay, Mr. C. Cooper, and Mr. G. Longworth for their technical assistance. We would also like to thank Mr. S. Killick of the International Pacific Salmon Fisheries Commission for his assistance in the collection of fish and Dr. H. Cook for his helpful discussion of the project. This paper is No. 058 in the University of Guelph Migration Series.     

Territory size and distribution of newly-emerged Atlantic salmon (Salmo salar)

Newly emerged Atlantic salmon (Salmo salar) were observed from May to August 1981 at six isolated redds in Washington County, Maine, USA. Territorial size and distribution were measured. At the end of the emergence period (12 to 28 May), fish maintained positions (stations) at redds where water velocity did not exceed 52 cm s^–1 By 12 June, most salmon (80–96%) had moved off the redds of origin and had established territories 1 to 5 m from the redd. The area defended increased substantially after mid-June, but territorial aggression diminished by 15 July, and the fry dispersed downstream. All fish observed were territorial, and the percentage of time during which stations were held decreased from 89 in mid-May to as low as 40% in mid-June.Cooperators are the Maine Department of Inland Fisheries and Wildlife, University of Maine, U.S. Fish and Wildlife Service, and the Wildlife Management Institute     

Interaction between hatchery and wild Pacific salmon in the Far East of Russia: A review

We review studies of interactions between hatchery and wild Pacific salmon in the Russian Far East. This includes the role of hatchery practices that result in premature migration to the sea and increased mortality, and data on feeding and territorial competition between juveniles of hatchery and wild origin. In the course of downstream migration many juvenile hatchery salmon are eliminated by wild salmon predation. During the marine period, Japanese hatchery chum salmon (Oncorhynchus keta) distribution overlaps the distribution of Russian wild salmon. Consequently, replacement of wild populations by hatchery fishes, as a result of abundant juvenile hatchery releases combined with extensive poaching in spawning grounds, is apparent in some Russian rivers. Interactions between the populations occur in all habitats. The importance of conservation of wild salmon populations requires a more detailed study of the consequences of interactions between natural and artificially reared fishes.     

Light-mediated predation by northern squawfish on juvenile chinook salmon

Northern squawfish Ptychocheilus oregonensis cause significant mortality of juvenile salmon in the lower Columbia River Basin (U.S.A.). The effects of light intensity on this predator-prey interaction were examined with laboratory experiments and modelling studies. In laboratory experiments, the rate of capture of subyearling chinook salmon Oncorhynchus tshawytscha by northern squawfish was inversely related to light intensity. In a large raceway, about five times more salmon were captured during 4 h periods of relative darkness (0–03 Ix) than during periods with high light intensity (160 Ix). The rate of predation could be manipulated by increasing or decreasing light intensity.
A simulation model was developed for visual predators that encounter, attack, and capture juvenile salmon, whose schooling behaviour was light-sensitive. The model was fitted to laboratory results using a Monte Carlo filtering procedure. Model-predicted predation rate was especially sensitive to the visual range of predators at low light intensity and to predator search speed at high light. Modelling results also suggested that predation by northern squawfish on juvenile salmon may be highest across a narrow window of fight intensity.     

Burying beetle Nicrophorus investigator reproduction on Pacific salmon carcasses

Abstract.  1. In many undisturbed watersheds along the Pacific Rim, anadromous salmon ( Oncorhynchus spp.) provide a predictable source of carrion to the riparian zone, largely due to horizontal transfer of salmon carcasses by bears ( Ursus spp.) and other vertebrates.
2. Burying beetles are important members of the north-temperate carrion fauna, and may utilise salmon carcasses and remnants for breeding. In this study, isotopic and observational data are reported that demonstrate previously unrecognised Nicrophorus investigator (Zetterstedt) reproduction on large salmon carcasses from five watersheds in coastal British Columbia.
3. Stable isotope signatures (δ¹⁵N and δ¹³C) of adult beetles collected in autumn indicate a diet of salmon origin in all but one individual from all watersheds, suggesting that this beetle–salmon association is widespread. Comparison of autumn isotope signatures to individuals collected randomly in summer suggests that isotope signatures represent the larval carrion source from the previous autumn rather than immediate adult diet.
4. In a survey of N. investigator use of salmon carcasses from two watersheds, 35 broods were observed on chum and pink salmon carcasses, including 16 natural brood complexes containing over 100 larvae, and five ranging from 250 to 750 larvae.
5. Overall, north-coastal populations of N. investigator breed on the rich and reliable salmon resource and may exhibit a system of communal breeding on these carcasses. This is most relevant when the dramatic reduction in salmon spawning biomass over the last century is considered.     

Effects of body size and predators on intracohort competition in wild and domesticated juvenile salmon in a stream

Competition between masu salmon (Oncorhynchus masou) of wild and aquaculture origin was investigated. Fry were individually marked and released in stream enclosures with and without a piscivorous predator. The aim was to assess the effects of predators and salmon body size on survival and growth of the two types of fish under natural conditions. The presence of predaceous Japanese huchen (Hucho perryi) resulted in lower mean growth rates of surviving fry. Relatively large fish survived and grew better than relatively small fish in the absence of predators, but not in their presence. This probably indicates an indirect effect of predation risk on within-cohort competitive behavior among salmon juveniles, with larger fish forced to give up their position as superior competitors. Domesticated fish survived in larger numbers and grew much faster than wild fish, irrespective of predator presence. Comparison with similar field studies revealed a pattern that the pre-experimental environment influenced the outcome of competition between wild and domesticated juvenile salmon. Domesticated fish were superior competitors even in the absence of an initial size advantage, which commonly gives a further advantage to hatchery-raised fish in natural streams. Therefore, caution dictates to avoid the release or escape of such fish into the wild.     

Genetic mapping of Y-chromosomal DNA markers in Pacific salmon

Sex chromosomes in fish provide an intriguing view of how sex-determination mechanisms evolve in vertebrates. Many fish species with single-factor sex-determination systems do not have cytogenetically-distinguishable sex chromosomes, suggesting that few sex-specific sequences or chromosomal rearrangements are present and that sex-chromosome evolution is thus at an early stage. We describe experiments examining the linkage arrangement of a Y-chromosomal GH pseudogene (GH-Y) sequence in four species of salmon (chum, Oncorhynchus keta; pink, O. gorbuscha; coho, O. kisutch; chinook, O. tshawytscha). Phylogenetic analysis indicates that GH-Y arose early in Oncorhynchus evolution, after this genus had diverged from Salmo and Salvelinus. However, GH-Y has not been detected in some Oncorhynchus species (O. nerka, O. mykiss and O. clarki), consistent with this locus being deleted in some lineages. GH-Y is tightly linked genetically to the sex-determination locus on the Y chromosome and, in chinook salmon, to another Y-linked DNA marker OtY1. GH-Y is derived from an ancestral GH2 gene, but this latter functional GH locus is autosomal or pseudoautosomal. YY chinook salmon are viable and fertile, indicating the Y chromosome is not deficient of vital genetic functions present on the X chromosome, consistent with sex chromosomes that are in an early stage of divergence.     

Alaskan brown bears (Ursus arctos) aggregate and display fidelity to foraging neighborhoods while preying on Pacific salmon along small streams

The interaction between brown bears (Ursus arctos) and Pacific salmon (Oncorhynchus spp.) is important to the population dynamics of both species and a celebrated example of consumer‐mediated nutrient transport. Yet, much of the site‐specific information we have about the bears in this relationship comes from observations at a few highly visible but unrepresentative locations and a small number of radio‐telemetry studies. Consequently, our understanding of brown bear abundance and behavior at more cryptic locations where they commonly feed on salmon, including small spawning streams, remains limited. We employed a noninvasive genetic approach (barbed wire hair snares) over four summers (2012–2015) to document patterns of brown bear abundance and movement among six spawning streams for sockeye salmon, O. nerka, in southwestern Alaska. The streams were grouped into two trios on opposite sides of Lake Aleknagik. Thus, we predicted that most bears would forage within only one trio during the spawning season because of the energetic costs associated with swimming between them or traveling around the lake and show fidelity to particular trios across years because of the benefits of familiarity with local salmon dynamics and stream characteristics. Huggins closed‐capture models based on encounter histories from genotyped hair samples revealed that as many as 41 individuals visited single streams during the annual 6‐week sampling season. Bears also moved freely among trios of streams but rarely moved between these putative foraging neighborhoods, either during or between years. By implication, even small salmon spawning streams can serve as important resources for brown bears, and consistent use of stream neighborhoods by certain bears may play an important role in spatially structuring coastal bear populations. Our findings also underscore the efficacy of noninvasive hair snagging and genetic analysis for examining bear abundance and movements at relatively fine spatial and temporal scales.     

Goosander predation and its potential impact on Atlantic salmon smolts in the River Tana estuary, northern Norway

In the summers of 1981 and 2000, 288 goosanders Mergus merganser were sampled in the estuary of the River Tana in northern Norway, which has the largest wild Atlantic salmon Salmo salar stock in the world. Based on 2308 otoliths found in their stomach contents, sandeels Ammodytes sp. were found to be the dominant prey, and only one pair of Atlantic salmon otoliths was found. This suggested that goosanders were not significant predators on Atlantic salmon smolts in the estuary, probably because of the high abundance of sandeels and other marine prey fishes, at least in these particular years.     

Urine of ovulated female masu salmon attracts immature male parr treated with methyltestosterone

Methyltestosterone-treated immature male masu salmon Oncorhynchus masou parr were attracted to both the urine of ovulated females and the ether soluble basic substances extracted from the urine, but not to immature female urine. It is suggested that the male response to the sex attractant (releaser pheromone) in the urine is under the control of androgens.     

Fecundity and egg size variation in North American Pacific salmon (Oncorhynchus)

We examined regional and latitudinal variation in fecundity and egg weight for five species of Pacific salmon ( Oncorhynchus ) along the Pacific coast of North America. Data were examined for 24 chum salmon, 15 pink salmon, 34 sockeye salmon, 44 chinook salmon, and 40 coho salmon populations from published sources, unpublished Canadian hatchery records, our own laboratory investigations, and other unpublished sources. Substantial regional variation in fecundity and egg weight was observed, with salmon on the Queen Charlotte Islands and Vancouver Island in British Columbia generally having lower fecundity and larger egg size than nearby mainland populations. The relative distance of freshwater migration to the spawning grounds generally had a marked effect on both fecundity and egg size, with populations spawning in the upper portions in the drainages of large rivers like the Fraser River in British Columbia having reduced fecundity and egg size compared with coastal spawning populations. Fecundity was generally higher and egg size generally lower in more northern populations of sockeye, chinook, and coho salmon compared with southern ones. We suggest that egg size tends to be lower in northern populations of some species as a result of increased fecundity due to their older ages at maturity and a limited amount of energy that can be expended on egg production.     

Behavioral context of echolocation and prey-handling sounds produced by killer whales (Orcinus orca) during pursuit and capture of Pacific salmon (Oncorhynchus spp.)

Availability of preferred salmonid prey and a sufficiently quiet acoustic environment in which to forage are critical to the survival of resident killer whales (Orcinus orca) in the northeastern Pacific. Although piscivorous killer whales rely on echolocation to locate and track prey, the relationship between echolocation, movement, and prey capture during foraging by wild individuals is poorly understood. We used acoustic biologging tags to relate echolocation behavior to prey pursuit and capture during successful feeding dives by fish-eating killer whales in coastal British Columbia, Canada. The significantly higher incidence and rate of echolocation prior to fish captures compared to afterward confirms its importance in prey detection and tracking. Extremely rapid click sequences (buzzes) were produced before or concurrent with captures of salmon at depths typically exceeding 50 m, and were likely used by killer whales for close-range prey targeting, as in other odontocetes. Distinctive crunching and tearing sounds indicative of prey-handling behavior occurred at relatively shallow depths following fish captures, matching concurrent observations that whales surfaced with fish prior to consumption and often shared prey. Buzzes and prey-handling sounds are potentially useful acoustic signals for estimating foraging efficiency and determining if resident killer whales are meeting their energetic requirements.     

Responses of immature male masu salmon parr to the urine of mature males

Responses of male masu salmon Oncorhynchus masou parr to mature male urine were investigated in a Y-maze trough. Immature masu salmon made fewer entries into the channel conditioned by mature male urine than that with control water. This phenomenon may suggest that immature males avoid sexually active males in the spawning season.     

Mass loss and macroinvertebrate colonisation of Pacific salmon carcasses in south-eastern Alaskan streams

1. We examined the spatial and temporal dynamics of pink salmon ( Oncorhynchus gorbuscha ) carcass decomposition (mass loss and macroinvertebrate colonisation) in south-eastern Alaskan streams. Dry mass and macroinvertebrate fauna of carcasses placed in streams were measured every two weeks over two months in six artificial streams and once after six weeks in four natural streams. We also surveyed the macroinvertebrate fauna and wet mass of naturally occurring salmon carcasses.
2. Carcass mass loss in artificial streams was initially rapid and then declined over time ( k =–0.033 day^–1), and no significant differences were found among natural streams.
3. Several macroinvertebrate taxa colonised carcasses, but chironomid midge (Diptera: Chironomidae) and Zapada (Plecoptera: Nemouridae) larvae were found consistently and were the most abundant (on average 95 and 2%, respectively, of the invertebrates found). Chironomid abundance and biomass increased over time, whereas Zapada abundance and biomass did not. Significant differences in abundance were found among natural streams for Baetis (Ephemeroptera: Baetidae) and Sweltsa (Plecoptera: Chloroperlidae) larvae, while no significant differences were found for chironomid and Zapada abundance or biomass.
4. Our results suggest that salmon carcasses initially undergo a high rate of mass loss that tapers off with time. Chironomid and Zapada larvae are likely to be important in mediating nutrient and energy transfer between salmon carcasses and other components of the freshwater-riparian food web in south-eastern Alaskan streams.     

Variation in responses to spawning Pacific salmon among three south-eastern Alaska streams

1. Pacific salmon are thought to stimulate the productivity of the fresh waters in which they spawn by fertilising them with marine‐derived nutrients (MDN). We compared the influence of salmon spawners on surface streamwater chemistry and benthic biota among three south‐eastern Alaska streams. Within each stream, reaches up‐ and downstream of barriers to salmon migration were sampled during or soon after spawners entered the streams. 2. Within streams, concentrations of dissolved ammonium and soluble reactive phosphorus (SRP), abundance of epilithon (chlorophyll a and ash‐free dry mass) and biomass of chironomids were significantly higher in reaches with salmon spawners. In contrast, biomass of the mayflies Epeorus spp. and Rhithrogena spp. was significantly higher in reaches lacking spawners. 3. Among streams, significant differences were found in concentrations of dissolved ammonium, dissolved organic carbon, nitrate and SRP, abundance of epilithon, and the biomass of chironomids and Rhithrogena. These differences did not appear to reflect differences among streams in spawner density, nor the changes in water chemistry resulting from salmon spawners. 4. Our results suggest that the ‘enrichment’ effect of salmon spawners (e.g. increased streamwater nutrient concentrations) was balanced by other concurrent effects of spawners on streams (e.g. sediment disturbance). Furthermore, the collective effect of spawners on lotic ecosystems is likely to be constrained by conditions unique to individual streams, such as temperature, background water chemistry and light attenuation.