Consumption choice by bears feeding on salmon

Consumption choice by brown (Ursus arctos) and black bears (U. americanus) feeding on salmon was recorded for over 20,000 bear-killed fish from 1994 to 1999 in Bristol Bay (sockeye salmon, Oncorhynchus nerka) and southeastern Alaska (pink, O. gorbuscha and chum salmon O. keta). These data revealed striking patterns of partial and selective consumption that varied with relative availability and attributes of the fish. As the availability of salmon decreased, bears consumed a larger proportion of each fish among both years and habitats. When availability was high (absolute number and density of salmon), bears consumed less biomass per captured fish, targeting energy-rich fish (those that had not spawned) or energy-rich body parts (eggs in females; brain in males). In contrast, individual fish were consumed to a much greater extent, regardless of sex or spawning status, in habitats or years of low salmon availability. The proportion of biomass consumed per fish was similar for males and females, when spawning status was statistically controlled, but bears targeted different body parts: the body flesh, brain and dorsal hump in males and the roe in females. Bears thus appeared to maximize energy intake by modifying the amount and body parts consumed, based on availability and attributes of spawning salmon.     

Sex ratio control in pink salmon (<Emphasis Type="Italic">Oncorhynchus gorbuscha</Emphasis> and chum salmon (<Emphasis Type="Italic">O. keta</Emphasis>) populations: The possible causes and mechanisms of changes in the sex ratio

Long-term changes in the sex ratio have been studied in pink salmon (Oncorhynchus gorbuscha and chum salmon (O. keta) populations of Kamchatka and Sakhalin. It has been demonstrated that these changes are an adaptation to population dynamics: an increase in the population size is accompanied by a shift towards a higher proportion of males; a decrease in population size, by a shift towards a higher proportion of females. The correspondence between morphological and molecular characters in populations of the two species has been analyzed in order to determine the mechanism of sex ratio control. In some pink salmon and chum salmon populations, there is a discrepancy between sex identifications based on morphological characters and molecular markers. This discrepancy is assumed to be accounted for by sex inversion mechanisms, which may be population-or region-specific. In two cases, it has been found that the sex ratio discrepancy in populations is related to the numbers of fish in subsequent generations. These findings suggest that sex inversion may be related to population size control.     

Daily feeding rhythm and rations of Pacific salmon of the genus Oncorhynchus in the period of marine prespawning migrations

The daily feeding rhythm and rations of the humpback salmon Oncorhynchus gorbuscha, the sockeyed salmon O. nerka, and the chum salmon O. keta during marine prespawning migrations is investigated with consideration of materials collected at daily stations in waters off eastern Kamchatka in June–July 1999 and 2001 (from catches of drift nets). The bulk of humpback salmon and sockeyed salmon food consists of euphausiids, hyperiids, large copepods, pteropods, and fish juveniles. In the food of chum salmon, pteropods dominated. In a 24-h period, salmon manifest a pronounced evening peak of stomach fullness, while at night feeding discontinues. Samples collected in the morning consisted of fish who had just started feeding after the night pause. In addition to nightly period of rest, all species manifested a daytime decrease in foraging activity, though less pronounced than in the night. The daily rhythm of Pacific salmons’s feeding depends on the vertical migrations of their food items (representatives of sound-scattering layers). During the marine feeding period, the most intensive feeding is recorded in the humpback salmon and chum salmon. The daily ration of the humpback salmon is lower than that of the chum salmon but includes animals of higher food value. Due to a high digestion rate in combination with a large stomach volume, the chum salmon can consume a large quantity of low-calorific food in a short time. The daily ration of the sockeyed salmon is considerably lower than that of other salmon species.     

Comparative Study of Substrate–Inhibitor Specificity of Brain Cholinesterase Activity of Pacific Salmon Fish of the Salmonidae Family

Salmon fish of the Salmonidae family, representatives of the Pacific salmon Oncorhynchus genus, the humpback salmon O. gorbuscha Wielb., dog salmon O. keta, coho salmon O. kisutch, blueback salmon O. nerka, and chinook salmon O. tschawytscha, and also of noble salmons genus, Salmo—black salmon S. salar, caught in the northwest water area of the Pacific ocean, are studied in the work. Iodides of acetyl-, propionyl-, and butyrylthiocholine were used as substrates. Carbamate proserine and 5 organophosphorus inhibitors were studied as inhibitors. Testing of homogeneity of cholinesterase activity in the brain tissue has revealed only one enzyme in the coho salmon, while several enzymes, in the dog salmon and humpback salmon, which can be an enzymologic argument for the favor of hypothesis about the presence of interspecies groups among Pacific salmons of the Oncorhynchus genus. Interspecies differences in substrate specificity of the brain tissue in the studied salmonid species are found. The fish enzymes of the fishes have shown a high sensitivity to proserine. Only in the case of diisopropylfluorophosphate, both interspecies and intergenus differences are revealed.     

Fitness and behavioral correlates of pre-stress and stress-induced plasma cortisol titers in pink salmon (Oncorhynchus gorbuscha) upon arrival at spawning grounds

Semelparous Pacific salmon (Onchorynchus spp.) serve as an excellent model for examining the relationships between life history, behavior and individual variation in glucocorticoid (GC) stress hormone levels because reproductive behaviors are highly variable between individuals and failure to reproduce results in zero fitness. Pink salmon (O. gorbuscha) were intercepted upon arrival at the spawning grounds across three time periods. Pre-stress and stress-induced plasma cortisol concentrations were assessed in relation to behavior, longevity and reproductive success. Results revealed differences between sexes and with arrival time. The study period marked a year of high reproductive success and only nine females (12% of sample) failed to spawn. Female pre-spawn mortalities were characterized by significantly elevated stress-induced cortisol concentrations and decreased longevity as well as pre-stress cortisol above the normal range in pink salmon from the study area. Interestingly, reproductive behaviors were only associated with pre-stress cortisol levels. For females, aggression and mate interaction time were reduced in individuals with elevated pre-stress cortisol concentrations. In males, a similar negative relationship between pre-stress cortisol concentration and mate interaction time was detected. The observed behavioral correlations are likely a factor of social status where dominant individuals, known to have higher reproductive success, are characterized by lower cortisol levels relative to subordinate conspecifics. Findings show both elevated pre-stress and stress-induced cortisol concentrations at arrival to the spawning grounds to be associated with reduced survival.     

Life-history styles and somatic allocation in iteroporous arctic charr and semelparous pink salmon

Synopsis RNA/DNA ratios were used to estimate recent somatic allocation of spawning arctic charr,Salvelinus alpinus, and pink salmon,Oncorhynchus gorbuscha. Smaller arctic charr morphs had lower ratios than larger morphs. Larger male pink salmon had lower ratios than smaller males. Thus recent somatic allocation (anabolic metabolic activity and growth) is coupled with cumulative lifetime growth in iteroparous arctic charr, but is uncoupled in semelparous pink salmon. These data suggest that somatic investment in these species is being differentially effected by the energetic costs of reproduction.     

Evidence of successful recruitment of non-native pink salmon Oncorhynchus gorbuscha in Iceland

In mid-May 2022, pink salmon Oncorhynchus gorbuscha smolts were caught in the rivers Botnsá, Grímsá, and Langá in Iceland. This observation provides the first evidence of successful spawning and the completion of the freshwater phase of the life cycle in Icelandic rivers. It is the most western record of O. gorbuscha smolts in Europe, further west than Russia, Norway, and the UK. Smolts originating from Iceland potentially support the recruitment of this species in the North Atlantic and may lead to the establishment of a self-sustaining population in Iceland.     

Annual changes in the population size of the salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae) on high-seas Pacific Salmon (Oncorhynchus spp.), and relationship to host abundance

The population size of the salmon louse, Lepeophtheirus salmonis, was monitored annually in the summers of 1991–1997 by examining six species of Pacific salmon (Oncorhynchus spp.) caught by surface long-lines in oceanic offshore waters of the North Pacific Ocean and Bering Sea. The annual copepod population size on all salmonids caught was estimated by combining the calculated number of copepods carrying on each salmonid species. The copepod population fluctuated markedly from year to year, which resulted largely from marked annual changes in abundance of pink salmon (O. gorbuscha). Since pink salmon were most frequently and heavily infected and since their abundance changed every year, the copepod population was high in the years when this salmonid species was abundant, but low when it was rare. On the contrary, chum salmon (O. keta) did not show high prevalence and intensity of infection, but the annual abundance of this host species was consistently high, i.e. chum salmon carried many copepods every year. Copepods on other salmonid species (sockeye salmon O. nerka, coho salmon O. kisutch, chinook salmon O. tshawytscha, and steelhead trout O. mykiss) constantly formed a small percentage of the total copepod population. Both chum and pink salmon are the most important hosts in terms of their substantial contribution to support the copepod population, but the importance as hosts of each species is definitely different between the species. Chum salmon is a stable important host supporting the copepod population at a relatively high level every year, while the number of copepods on pink salmon annually exhibits marked fluctuations, and this salmonid species is regarded as an unstable important host.     

Morphological Bases for Evolution of Functions

The morphological and morphometrical changes in the renal proximal tubular cells of the salmonOncorhynchus gorbuscha during spawning migration are described for the first time. The evaluation of the ultrastructural changes in the kidney of the adult humpback salmon allows concluding that the proximal tubular cells are affected by significant osmotic loads during spawning migration. Various destructive processes in the proximal tubular cells indicate a decrease of their functional activity in the fresh water. The analysis of the results of the study of the humpback salmon kidney ultrastructure during the anadromous migration allow suggesting that reduction of the amount of the most active cell organelles in the proximal tubule, such as mitochondria and the basolateral membrane system, is associated with a decrease of the number of ion pumps that operate less intensively in the fresh water. Such mechanism of the kidney functioning in the euryhaline fish appears to be formed in the course of evolution as an adaptation to the freshwater environment. The morphological and morphometrical changes in the proximal tubules of nephrons were described for the first time in Pacific salmon smoltsOncorhynchus keta, O. gorbuscha,O. Kisutch, andO. masou in environments with different salinity. The most marked response to the transfer to the sea water or to the calcium-enriched sea water was observed in the chum salmon smolts. In 48 h, the tubular diameter reached its peak, more than 72 μm, the tubular lumen also was very large, while the epithelium height was only slightly greater than that in the fresh water control. In spite of the considerable morphological changes, as soon as in 24 h (the Ca²⁺-enriched sea water) and in 48 h (the sea water) the ion content in smolt carcasses was within the physiological norm for the environment with enhanced salinity. These results indicate a high efficiency of the osmoregulatory system in smolts during their transfer from the fresh to the sea water.     

Evidence of potential establishment of pink salmon Oncorhynchus gorbuscha in Scotland

In spring 2022, pink salmon Oncorhynchus gorbuscha smolts were recorded in the UK. Fish were caught in the Rivers Thurso and Oykel in Scotland between 13 and 17 March. To the authors’ knowledge, this is the first observation of O. gorbuscha smolts in Europe outside the Scandinavian and Kola peninsulas, including other tributaries of the White and Barents Seas. It also provides evidence of successful spawning in 2021 and completion of the freshwater phase of the life cycle, and indicates the possibility for potential establishment of an O. gorbuscha population in Great Britain.     

Incomplete congruence between morphobiological characters and sex-specific molecular markers in Pacific salmons: 1. Analysis of discrepancy in five species of the genus <Emphasis Type="Italic">Oncorhynchus</Emphasis>

The congruence between molecular markers, identifying the presence of the Y chromosome, and secondary sexual characters was examined in Asian populations of five Pacific salmon species: pink salmon (Oncorhynchus gorbuscha), chum salmon (O. keta), sockeye salmon (O. nerka), chinook salmon (O. tschawytscha), and sima (O. masou). It was demonstrated that in all species examined, the presence or absence of sex-specific molecular markers was to a considerable degree congruent with secondary sexual characters, but in some cases, an incongruence was found. These findings suggested that the mechanism underlying this phenomenon was similar or identical in all species examined. Possible genetic and physiological explanations of this phenomenon are discussed.     

On signals of phase transitions in salmon population dynamics

Critical slowing down (CSD) reflects the decline in resilience of equilibria near a bifurcation and may reveal early warning signals (EWS) of ecological phase transitions. We studied CSD in the recruitment dynamics of 120 stocks of three Pacific salmon (Oncorhynchus spp.) species in relation to critical transitions in fishery models. Pink salmon (Oncorhynchus gorbuscha) exhibited increased variability and autocorrelation in populations that had a growth parameter, r, close to zero, consistent with EWS of extinction. However, models and data for sockeye salmon (Oncorhynchus nerka) indicate that portfolio effects from heterogeneity in age-at-maturity may obscure EWS. Chum salmon (Oncorhynchus keta) show intermediate results. The data do not reveal EWS of Ricker-type bifurcations that cause oscillations and chaos at high r. These results not only provide empirical support for CSD in some ecological systems, but also indicate that portfolio effects of age structure may conceal EWS of some critical transitions.     

Interannual variation of linear-weight indices,age structure,and rate of growth of chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> and factors affecting it (the Bol’shaya River basin,western Kamchatka)

The interannual variation in the size-age composition and the rate of growth of autumnal chum salmon Oncorhynchus keta in the Bol’shaya River basin (western Kamchatka) was studied. Data of biological analysis and results of back calculations of the linear growth of O. keta were analyzed for the period of 1993 to 1999. Possible reasons of interannual changes in indices such as the numerical ratio of the main age groups (3+ and 4+), average values of the length and weight of spawners, and the linear growth of O. keta are discussed. It was established that the main factor responsible for the variation of the growth and dynamics of the O. keta population in the Bol’shaya River are the numbers of the western Kamchatka pink salmon O. gorbuscha.     

Adaptive strategies and life history characteristics in a warming climate: Salmon in the Arctic?

In the warming Arctic, aquatic habitats are in flux and salmon are exploring their options. Adult Pacific salmon, including sockeye (Oncorhynchus nerka), coho (O. kisutch), Chinook (O. tshawytscha), pink (O. gorbuscha) and chum (O. keta) have been captured throughout the Arctic. Pink and chum salmon are the most common species found in the Arctic today. These species are less dependent on freshwater habitats as juveniles and grow quickly in marine habitats. Putative spawning populations are rare in the North American Arctic and limited to pink salmon in drainages north of Point Hope, Alaska, chum salmon spawning rivers draining to the northwestern Beaufort Sea, and small populations of chum and pink salmon in Canada’s Mackenzie River. Pacific salmon have colonized several large river basins draining to the Kara, Laptev and East Siberian seas in the Russian Arctic. These populations probably developed from hatchery supplementation efforts in the 1960’s. Hundreds of populations of Arctic Atlantic salmon (Salmo salar) are found in Russia, Norway and Finland. Atlantic salmon have extended their range eastward as far as the Kara Sea in central Russian. A small native population of Atlantic salmon is found in Canada’s Ungava Bay. The northern tip of Quebec seems to be an Atlantic salmon migration barrier for other North American stocks. Compatibility between life history requirements and ecological conditions are prerequisite for salmon colonizing Arctic habitats. Broad-scale predictive models of climate change in the Arctic give little information about feedback processes contributing to local conditions, especially in freshwater systems. This paper reviews the recent history of salmon in the Arctic and explores various patterns of climate change that may influence range expansions and future sustainability of salmon in Arctic habitats. A summary of the research needs that will allow informed expectation of further Arctic colonization by salmon is given.     

Sex‐selective Predation by Threespine Sticklebacks on Sea Lice: A Novel Cleaning Behaviour

Cleaning interactions have been described in a wide range of fish species and other taxa. We observed a novel cleaning behaviour during a study of the transmission dynamics of sea lice (Lepeophtheirus salmonis) between juvenile pink salmon (Oncorhynchus gorbuscha) and threespine sticklebacks (Gasterosteus aculeatus) in the Broughton Archipelago, British Columbia, Canada. Experiments showed that sticklebacks significantly reduced the number of sea lice on individual juvenile salmon. Adult female lice were preferentially consumed by sticklebacks, and gravid female lice also experienced egg string cropping. Overall, 76% of gravid female lice experienced either consumption, egg string cropping, or both by sticklebacks. This preference by sticklebacks for female parasites may stem from female lice being larger than males and the added nutritional value of egg strings on gravid females. Cleaning by sticklebacks can potentially have an impact on sea louse populations on wild juvenile salmon.     

Size-assortative mating in salmonids: negative evidence for pink salmon in natural conditions

Driven by competition and mate choice, size-assortative mating has been seen in many organisms. The breeding system of salmonid fish, Oncorhynchus spp., has been extensively investigated and many examples of size-assortative mating have been found. However, assortative mating is not always observed and many reported examples involved cases with a large dichotomy in size classes or were conducted in artificial arenas where other factors influencing mate choice and competition were controlled. This study investigated size-assortative mating in a population of naturally reproducing pink salmon, O. gorbuscha. We made direct observations of courtship behaviour over 3 years on fish of known sizes. To determine the extent to which these observations corresponded to reproductive success, we assessed the parentage of the offspring produced by the fish in the first 2 years of the study using DNA fingerprinting. Size-assortative mating was not seen in the behavioural observations. Parentage results showed that our measure of dominance (proximity of males to ripe females) corresponded with successful matings, suggesting that the fish that we observed as dominant were in fact involved in more matings or more successful matings. We also saw no size-assortative mating in male and female pairs that produced adult offspring. We are not suggesting that the processes that can lead to size-assortative mating are not occurring, but that many other factors, such as female ripeness, male availability, predation threat and changing environmental conditions, may minimize the importance or mask the occurrence of size-assortative mating under natural conditions.     

Conditions of reproduction and population dynamics of Pacific salmons (<Emphasis Type="Italic">Oncorhynchus</Emphasis>): The northeast of Sakhalin Island

The efficiency of reproduction of Pacific salmon (Oncorhynchus) in the rivers of the northeastern Sakhalin coast is characterized based on long-term observations. The rivers of the northern, central, and southern parts differ in the type of their channel, faunistic composition of aquatic biota, and prevalent salmon species. The northern rivers have a plain type of channel with rather low spawning efficiency of salmons and relatively poor freshwater ichthyofauna. The central area houses the largest rivers (Tym’ and Nabil’ Rivers) running to the Nyiskii and Nabil’skii Gulfs; the rivers there have developed channels of a plain type, high diversity of resident ichthyofauna, low spawning efficiency of the pink salmon Oncorhynchus gorbuscha, and high (in the past) abundance of the fall chum salmon O. keta. Characteristic of the southern rivers with their prevalently mountain–foothill type of channels are poor fish population and high spawning efficiency of the pink salmon. The population dynamics of the salmonids in the northeastern coast of Sakhalin is described. The total number of breeders entering the rivers of the northeastern coast that provides an efficient reproduction is estimated as 3.5?9.0 million individuals for the pink salmon and 0.04–0.60 million individuals for the chum salmon (fall race).     

Reproduction efficiency and some characteristics of the spawning grounds of the pink salmon <Emphasis Type="Italic">Oncorhynchus gorbuscha</Emphasis> in the small salmon watercourse in southern Sakhalin

The peculiarities of the distribution of the freshwater ichthyofauna, bottom sediments and conditions at the spawning grounds, and the egg survivability rate of Oncorhynchus gorbuscha were studied in 2003?2012 in a typical salmon river on Sakhalin Island (Goluboi Ruchei brook, Aniva Bay, southern Sakhalin). The sites characterized by the highest survivability rate of the embryos of the pink salmon are inhabited by the freshwater fish community where the juveniles of masu salmon O. masu and whitespotted char Salvelinus leucomaenis dominate. The lengthway bed slope at this site is steeper compared to the sites with lower survivability rates (0.010?0.020 vs. 0.004?0.020?). The maximal positive correlation of the egg survivability rate to the flow velocity of the underflow has been registered for the depth of 30?40 cm, and the maximal negative correlation of the egg survivability rate has been registered to the bottom sediment temperature.     

Inheritance of Alpha-Glycerophosphate Dehydrogenase in the Pink Salmon, ONCORHYNCHUS GORBUSCHA (Walbaum)

Genetic crosses of alpha-glycerophosphate dehydrogenase (alpha-GPDH) phenotypes in the pink salmon, Oncorhynchus gorbuscha (Walbaum), reveal that this enzyme is encoded by a single locus with two codominant alleles (Slow and Fast). The significance of single gene control of alpha-GPDH is discussed in relation to the purported tetraploid nature of the salmonids.