Seasonal variations in and effect of incubation water temperature on vertebral number in naturally spawning chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis>

Seasonal variations and reaction norms for vertebral number (V _N) in response to incubation water temperature were estimated in adult and juvenile naturally spawning chum salmon Oncorhynchus keta. The mean V _N of adults varied according to spawning time; the early-spawning population had higher V _N values than the late-spawning population. Moreover, the mean V _N values in the early-spawning population decreased with seasonal changes, whereas V _N values in the late-spawning population remained stable. Chum salmon embryos in three full-sib families were incubated at five different temperatures until hatching, and the V _N values of the resulting juveniles were analyzed. The V _N reaction norm to incubation water temperature showed a V-shaped curve that was lowest at an intermediate temperature. The mean V _N at the same incubation temperature varied among the three families. These results suggest that V _N values in chum salmon are influenced by genetic components and incubation water temperatures. V _N may be a useful parameter for estimating the environmental conditions during ontogenesis and the genetic background by detecting population changes.     

Estimation of heritability of vertebral number in chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis>

Hereditary causes of variation in the vertebral number of chum salmon were analyzed to estimate heritability for populations in the Chitose and Shikiu Rivers, Hokkaido Island, northern Japan. A total of 70 families were produced by diallel cross mating and then heritability was estimated using two statistical tests: a two-way ANOVA and a parent-offspring regression. Heritability estimates ranged from 0.26 to 1.91 and showed a strong correlation between the values from the two different tests. Estimates from female components were substantially higher than those from male components, which can be attributed to the maternal effect. Heritability in the Shikiu River population was shown to be higher than that in the Chitose River population. These results indicate that the heritability of vertebral number in chum salmon is generally high, and also that vertebral number is controlled by hereditary causes.     

Density‐dependent effects of eastern Kamchatka pink salmon (Oncorhynchus gorbuscha) and Japanese chum salmon (O. keta) on age‐specific growth of western Alaska chum salmon

Hatcheries release >4.5 billion juvenile Pacific salmon (Oncorhynchus spp.) into the North Pacific Ocean annually, raising concerns about competition with wild salmon populations. We used retrospective scale analysis to investigate how the growth of chum salmon (O. keta) from western Alaska is affected by the abundance of chum salmon from Japanese hatcheries and wild pink salmon (O. gorbuscha) from the Russian Far East. Over nearly five decades, the growth of Kuskokwim River chum salmon was negatively correlated with the abundance of Japanese hatchery chum salmon after accounting for the effects of sex and spring/summer sea‐surface temperature in the Bering Sea. An effect of wild eastern Kamchatka pink salmon abundance on the growth of Kuskokwim River salmon was detectable but modest compared to the intraspecific competitive effect. A decrease in Japanese hatchery chum salmon releases in 2011–2013 was not associated with increased growth of Bering Sea chum salmon. However, the abundance of wild chum salmon from the Russian Far East increased during that time, possibly obscuring reduced competition with hatchery chum salmon. Our results support previous evidence that chum salmon are affected by intraspecific competition, and to a lesser extent interspecific competition, in the North Pacific, underscoring that the effects of salmon hatchery production transcend national boundaries.     

Spatiotemporal change in growth of two populations of Asian chum salmon in relation to intraspecific interaction

Spatiotemporal changes in growth patterns of chum salmon Oncorhynchus keta that returned to the Ishikari (Japan) and Namdae (Korea) rivers in 1984–1998 were investigated using scale analysis. Juvenile chum salmon from both populations left coastal marine areas after spring at a size of over 8 cm fork length (FL). In summer, juvenile salmon from the Namdae River entered the Okhotsk Sea at a larger FL than did Ishikari River juveniles. There were no significant differences in annual growth between populations of 1-, 2-, and 4-year-old fish. For 3-year-old fish, however, Namdae River salmon had significantly higher synchronous and sympatric growth than did Ishikari River salmon. Mean FL of adults was also larger in Namdae River salmon than in Ishikari River salmon. Analysis of covariance (ANCOVA) results showed (1) negative linear relations between FL and catch, (2) homogeneous slopes of those relations at regional and species levels, and (3) nonhomogeneous slopes at the population level, indicating that density-dependent effects on growth were most significant at this level. We concluded that growth of chum salmon was concurrently influenced by stronger effects of intrapopulation competition and weaker effects of inter- and intraspecific interactions in the Bering Sea.     

Mechanism of body cavity temperature regulation of chum salmon (Oncorhynchus keta) during homing migration in the North Pacific Ocean

Vertical movement patterns of five chum salmon (Oncorhynchus keta) during homing migration were examined using archival tags. The standard deviation of the depth and ambient and body cavity temperatures during daytime were larger than those during night‐time. Vertical movements through the thermocline with a periodicity of less than 1 h were observed during daytime in addition to the diel vertical movement patterns in the open ocean. During these periods of frequent short‐term vertical movements, the difference between the body cavity temperature and ambient temperature was large while the variance of the body cavity temperature was less than that of the ambient temperature. From the results of a random simulation, the variation of the body cavity temperature was shown to decrease due to these periodic high frequency movements in comparison with random vertical movements. The whole‐body heat‐transfer coefficient k (s^?1), which was estimated by a heat budget model, was 1.48 × 10^?3. The k of chum salmon was larger than that of bigeye tuna (Thunnus obesus) by about one order of magnitude for the cooling of the body. The k of chum salmon did not change like tuna, which are physiologically adapted to conserve body cavity temperature. This indicates that the regulation of body cavity temperature by chum salmon is dependent on the vertical movements only. The maintenance of the body cavity temperature is concluded to be advantageous for their maturation and growth from the relationship between energy input and output during their homing migration.     

Freshwater habitat associations between pink (Oncorhynchus gorbuscha), chum (O. keta) and Chinook salmon (O. tshawytscha) in a watershed dominated by sockeye salmon (O. nerka) abundance

To understand the interplay between habitat use and contemporary anadromous Pacific salmon, Oncorhynchus spp., distributions we explored the habitat associations of three species, pink (O. gorbuscha), chum (O. keta) and Chinook salmon (O. tshawytscha) in streams of the Wood River system of Bristol Bay, Alaska, where sockeye salmon (O. nerka) are numerically dominant. We developed models to investigate the occurrence of nondominant salmon in relation to habitat characteristics and sockeye salmon density, using four decades of salmon presence and abundance data. The frequency of occurrence and abundance of nondominant species increased with watershed drainage area and stream depth and decreased with sockeye salmon density. The range of occurrence varied from nonexistent to perennial for the other species in sockeye‐dominated streams. Increasing watershed area resulted in larger stream habitat area and deeper habitats, allowing for the sympatric occurrence and persistence of all salmon species. The relationships between habitat and the presence of these Pacific salmon help define their requirements but also remind us that the patterns of presence and absence, within the overall ranges of salmon species, have yet to be fully understood.     

An evaluation of the potential influence of SST and currents on the oceanic migration of juvenile and immature chum salmon (Oncorhynchus keta) by a simulation model

Using a salmon migration model based on the assumption that swimming orientation is temperature dependent, we investigated the determining factors of the migration of juvenile and immature chum salmon (Oncorhynchus keta) in the North Pacific. We compared the predictions of the model with catch data of immature and juvenile chum salmon collected by Japanese research vessels from 1972 to 1999. The salmon migration model reproduced the observed distributions of immature chum salmon and indicates that passive transport by wind‐driven and geostrophic currents plays an important role in the eastward migration of Asian salmon. These factors result in a non‐symmetric distribution of Asian and North American chum salmon in the open ocean. The directional swimming component contributes to the northward migration in summer. The model results indicate that during the first winter Asian chum salmon swim northward against the southward wind‐driven currents to stay in the western North Pacific. This suggests that Asian chum salmon require more energy to migrate than other stocks during the first winter of their ocean life.     

Population structure and stock identification of chum salmon Oncorhynchus keta from Japan determined by microsatellite DNA variation

Variation at 14 microsatellite loci was surveyed in 26 chum salmon Oncorhynchus keta populations from Japan, one population from West Kamchatka and three populations from North America to determine population structure. Microsatellites were then applied to estimate stock composition of chum salmon in mixed-stock fisheries. The genetic differentiation index (F _st) over all populations and loci was 0.031, with individual locus values ranging from 0.010 to 0.081. Seven regional populations were observed in Japanese chum salmon, with late-run populations from the Pacific Coast of Honshu the most distinct. Japanese populations displayed greater genetic diversity than did those in North America. Transplantation history in some Japanese river populations influenced their present genetic characteristics. Analysis of simulated mixtures from fishery sampling suggested that accurate and precise regional estimates of stock composition should be produced when the microsatellites were used to estimate stock compositions. Stock compositions for a 2005 sample of maturing, migrating chum salmon off the north-west coast of Hokkaido near the border of the Sea of Japan and the Sea of Okhotsk indicated that this region may be a migration corridor for Hokkaido populations from the Sea of Japan coast. Microsatellites have the ability to provide fine-scale resolution of stock composition in Japanese coastal fisheries.     

Current status of natural spawning of chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> in rivers with or without hatchery stocking on the Japan Sea side of northern Honshu,Japan

Information on the status of natural spawning is needed on the Japan Sea side of northern Honshu, Japan for ecosystem-based sustainable management of chum salmon resources. We conducted on-site visual surveys in October–December of 2015 and 2016 that targeted spawning chum salmon redds in all rivers?>?5 km long (total 94 rivers) in Akita, Yamagata, Niigata (including Sado Island), and Toyama prefectures. The ratio of rivers found to host natural reproduction to the total number of surveyed rivers was 93.6% (44/47) in stocked rivers and 74.5% (35/47) in non-stocked rivers. These results show that there is a wide occurrence of natural reproduction of chum salmon in these rivers, regardless of the history of hatchery stocking. The density of spawning redds (number of redds/1000 m²) as an indicator of chum salmon escapements did not differ (P?=?0.54) between stocked rivers (mean 3.5, N ?=?49) and non-stocked rivers (mean 2.4, N? =?36),when rivers where no redds were observed were excluded from the analysis. These results suggest that chum salmon escapements into non-stocked rivers may not be negligible. Conservation measures for wild fish are needed in stocked and non-stocked rivers to promote enhancement programs based on natural reproduction.     

Effect of treatment of chum salmon Oncorhynchus keta (Walbaum) eggs with 1,3;1,6‐β‐D‐glucans on their development and susceptibility to Saprolegnia infection

The effects of six 1,3;1,6‐β‐D‐glucooligo‐ and polysaccharides with different structures (ranging from 1 to 10 kDa in molecular mass and containing 10–25% of β‐1,6‐linked glucose residues) from brown algae, Saccharina cichorioides, on development of the chum salmon, Oncorhynchus keta (Walbaum), were evaluated. Exposure of chum salmon eggs to 1,3;1,6‐β‐D‐glucans with a molecular mass of more than 2 kDa increased the survival of embryos and juveniles and their resistance to Saprolegnia infection by up to 2.5‐fold, leading to a weight gain in juveniles of 40–55% compared with The control chum salmons. The 1,3;1,6‐β‐D‐glucans with molecular mass of 6–8 kDa and used at a at concentration of 0.5 mg mL^?1 rendered the best stimulative effect.     

Japanese chum salmon stock enhancement: current perspective and future challenges

This study reviews the present status of the Japanese chum salmon Oncorhynchus keta stock enhancement program and considers the ecological sustainability of wild populations while providing fishery production, exemplified by the hatchery-based Kitami region set net fishery. The return rate and the number of returns have been historically high in the Sea of Okhotsk, but have decreased in other regions since 2005. Natural spawning of chum salmon occurred in at least 160 rivers in Hokkaido. The genetic diversity of Japanese chum salmon was similar to or higher than that of other Pacific Rim populations. Numbers of alleles were high at microsatellite loci, but the loss of rare haplotypes was observed in all populations. The estimated N _e /N ratio for the Kitami region was >0.15 % including hatchery and wild fish under the present high fishing pressure. Four regional populations were inferred in Hokkaido, however, genetic differentiation was weak and some river-populations were nested. Substantial changes in run timing were observed, but it has recovered gradually owing to the recent practice of escapement. Our analyses highlight the importance of juvenile quality and the vital roles of escapements in enhanced and non-enhanced rivers. New research is needed to minimize the genetic risks associated with hatchery programs.     

Changing salmon: An analysis of body mass,abundance, survival,and productivity trends across 45 years in Puget Sound

Pacific salmon and trout (Oncorhynchus spp., Salmonidae) of the Puget Sound region of Washington State, USA, have experienced recent and longer‐term (multidecadal) variability in abundance while supporting robust fisheries. As part of the post‐season salmon management process, population‐specific estimates of total adult abundance to Puget Sound (Strait of Juan de Fuca) for pink (O. gorbuscha), chum (O. keta), coho (O. kisutch), sockeye (O. nerka), and Chinook (O. tshawytscha) salmon and steelhead trout (O. mykiss) are calculated annually. We compiled annual estimates of body mass, abundance and survival of hatchery‐ and naturally produced salmon from 1970 to 2015 to compare spatial and temporal patterns across species. Average weights of adult salmon and steelhead returning to Puget Sound, with the exception of coho salmon, have decreased since the 1970s. Temporal trends in abundance, survival and productivity varied by species and origin (hatchery vs. naturally produced). Generally, abundance and survival rates of natural‐origin species decreased whereas those of hatchery‐produced species did not, which is in contrast with other studies' general conclusions of decreasing survival among Puget Sound salmonids. Species diversity has decreased in recent years, with salmonids that rely on a short freshwater rearing phase in the natural environment (hatchery‐produced fish and naturally produced pink and chum) representing >90% of total returns in most years. This new information reveals patterns of body size, abundance, survival and productivity across species, life history and rearing type over the past 45 years and, in doing so, demonstrates the strength in multidecadal, multifactor time series to critically evaluate salmonid species.     

Detection of hybrids between masu salmon <Emphasis Type="Italic">Oncorhynchus masou masou</Emphasis> and amago salmon <Emphasis Type="Italic">O. m. ishikawae</Emphasis> occurred in the Jinzu River using a random amplified polymorphic DNA technique

Identification of masu salmon Oncorhynchus masou masou and amago salmon O. m. ishikawae was accomplished using a random amplified polymorphic DNA (RAPD) technique. Of 80 primers screened, three primers amplified subspecies-specific fragments (OPA11-1095 ^*, OPB5-1618^* and OPD5-2038 ^*). Based on fragment patterns, 33 hybrids were detected among 150 upstream-migrating individuals in the Jinzu River, central Japan, a long-time habitat of masu salmon, to which amago salmon were recently introduced. All of the individuals examined in the 2000–2002 cohorts were identified as F ₁ and F _x as well as pure masu and amago forms. These results indicated continuing hybridization, the genetic pollution of the native masu salmon population by amago salmon possibly being a serious problem in the Jinzu River. Both standard length and body weight in F ₁ hybrids tended to be less than in pure masu salmon. However, F _x hybrids showed similar body sizes to masu salmon.     

Body size trends along vertical and thermal gradients of chum salmon in the Bering Sea during summer

Relationships between the vertical distribution and thermal habitat, and body size of chum salmon Oncorhynchus keta were studied in the Bering Sea in summer using trawl surveys at various depths. Chum salmon abundance decreased with increasing depth, but the patterns of decrease differed between size groups. The abundance of small salmon fell rapidly with depth, whereas that of large salmon decreased gradually to 40 m depth, and abruptly below that. The average fork length of chum salmon collected from each trawl correlated positively with trawl net depth and negatively with water temperature. Since the optimal temperature for growth decreases with body size in this species, the observed body size‐related vertical habitat use by chum salmon may indicate size‐dependent thermal preferences.     

Spatial variations in feeding and condition of juvenile pink and chum salmon off Vancouver Island, British Columbia

Spatial variations in feeding and condition of juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon, and their implications for growth, were examined on the Vancouver Island continental shelf in early summer 1992. Juvenile pink salmon off northern Vancouver Island had more material in their stomachs, were in better condition, and had higher potential growth rates (from a bioenergetics model) than pink salmon off southern Vancouver Island. These variations were consistent with spatial differences in zoo-plankton biomass, there being more plankton in the northern region. There was a significant positive relationship between condition of pinks and the amount of material in their stomachs, suggesting a positive feedback on feeding success. Juvenile chum in the north also had more material in their stomachs than chum to the south. However, condition factor was not significantly different between southern and northern regions nor was there a significant relationship between condition factor and the weight of stomach contents for chum on the southern shelf. A bioenergetics model suggests that chum in the south were food limited. Stable carbon isotope data also indicated different feeding histories for some chum in the southern region, which may have been recent migrants onto the continental shelf from near-shore areas, or possibly a nearby hatchery. Estimation of the energy required by juvenile salmon to migrate north in a continental shelf area with low zooplankton biomass and a weak northerly current (inner shelf), compared with an area with higher zooplankton biomass but a strong southerly current (outer shelf), indicated sufficient surplus energy only in the inner shelf, consistent with observations of northward migrations predominantly through this area. Spatial variations in current velocity and zooplankton biomass can affect feeding, condition, and potential growth of juvenile pink and chum salmon off Vancouver Island.     

Capture versus tagging impacts on chum salmon freshwater spawning migration travel times

The spawning migration travel times of chum salmon, Oncorhynchus keta (Walbaum), fitted with gastrically implanted radio tags vs external spaghetti tags were tested for a short [≈60 river km (rkm)] and long migration route (≈730 rkm) on the Koyukuk River, Alaska, USA. Using a novel application of statistical arrival curve models to infer travel times for uncaptured fish, migrations by chum salmon not directly handled during the study were also assessed. Results demonstrated negligible differences in travel times within migration routes between fish fitted only with spaghetti tags and fish fitted with radio tags, indicating low impacts on migration travel behaviour associated with gastric tags once deployed. Conversely, travel times for unhandled fish as inferred by statistical arrival models may have been 12%–24% shorter than those for fish captured with gillnets for tagging. These results suggest that, if present, chum salmon migration behaviour impacts may be more strongly associated with fish capture than tag deployment.     

Effect of riverbed conditions on survival of planted eyed eggs in chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis>

Wild stocks of chum salmon Oncorhynchus keta are supplemented by hatchery fry enhancement programs in northern Honshu, Japan. To maintain these programs, there is a need to reduce expenses and labor. Eyed egg planting is more cost effective than hatchery production of fry. Therefore, we evaluated the effect of environmental conditions on survival of chum salmon eyed eggs planted using Whitlock–Vibert boxes. We measured the percent cumulative weight of fine sediments, Fredle index (FI) as a measure of permeability, vertical hydraulic gradient, water depth (WD), and flow velocity at planting locations. Egg-to-fry survival averaged 92.7% (range: 57.2–100%) in 2013 (N = 19) and 71.5% (range: 6.4–100%) in 2014 (N = 23). Survival was significantly positively correlated with FI and flow velocity, negatively associated with percent cumulative weight of fine sediments and WD. Vertical hydraulic gradient had no effect on survival. Our results suggest that a higher FI (i.e., low amount of fine material and larger particle size), higher flow velocity, and shallower WD reduce the mortality of planted chum salmon eyed eggs. This is likely a result of increased permeability in the substrate and restriction of fine sediment intrusion into the incubation zone.     

Chum salmon (Oncorhynchus keta) growth and temperature indices as indicators of the year–class strength of age‐1 walleye pollock (Gadus chalcogrammus) in the eastern Bering Sea

Ecosystem‐based fisheries management requires the development of physical and biological time series that index ocean productivity for stock assessment and recruitment forecasts for commercially important species. As recruitment in marine fish is related to ocean condition, we developed proxies for ocean conditions based on sea surface temperature (SST) and biometric measurements of chum salmon (Oncorhynchus keta) captured in the walleye pollock (Gadus chalcogrammus) fishery in the eastern Bering Sea in three periods (July 16–30, September 1–15 and September 16–30). The main purpose of this paper was to evaluate Pacific salmon (Oncorhynchus spp.) growth as a possible indicator of ocean conditions that, in turn, may affect age‐1 walleye pollock recruitment. Marine growth rates of Pacific salmon are the result of a complex interplay of physical, biological and population‐based factors that fish experience as they range through oceanic habitats. These growth rates can, therefore, be viewed as indicators of recent ocean productivity. Thus, our hypothesis was that estimated intra‐annual growth in body weight of immature and maturing age‐4 male and female chum salmon may be used as a biological indicator of variations in rearing conditions also experienced by age‐0 walleye pollock; consequently, they may be used to predict the recruitment to age‐1 in walleye pollock. Summer SSTs and chum salmon growth at the end of July and September explained the largest amount of variability in walleye pollock recruitment indicating that physical and biological indices of ocean productivity can index fish recruitment.     

Change in chum salmon (Oncorhynchus keta) stomach contents associated with fluctuation of pink salmon (O. gorbuscha) abundance in the central subarctic Pacific and Bering Sea

The abundance and stomach contents of salmonids (Oncorhynchus spp.) and the biomass of prey organisms were examined in the central subarctic Pacific and Bering Sea in the summer of 1991 and 1992. Salmonids were caught by surface longline using the same level of fishing effort. Chum (O. keta) and pink (O. gorbuscha) salmon were the predominant species, representing 44% and 36% sof the total catch (n = 1275) in 1991. In 1992, chum salmon composed 85% of the total catch (n = 603), but the catch of pink salmon decreased to 1% of the total catch due to the odd/even year fluctuation of Asian pink salmon abundance in the study area. It was found that chum salmon changed their dominant diet from gelatinous zooplankton (pteropods, appendicular-ians, jellyfishes, chaetognaths, polychaetes and unidentified materials) in 1991, when pink salmon were abundant, to a diet of crustaceans (euphausiids, cope-pods, amphipods, ostracods, mysids and decapods) in 1992, when pink salmon were less abundant. Local crustacean biomass (wet weight; mg m^-3) had significant negative correlation with the CPUE (catch number per 30 hachi) of pink salmon in 1991 (r = -0.586; P = 0.026) and that of chum salmon in 1992 (r =–0.616; P = 0.014). There may be a limitation in the available prey resource for production of salmonids.     

Effect of acid environments on cortisol and cortisol receptor activity in Atlantic salmon,Salmo salar

The cytosol and nuclear extract of gill tissue obtained from laboratory held Atlantic salmon,Salmo salar manifested saturable cortisol binding of high affinity and low capacity (cytosol: K_a = 0.198 ± 0.024 × 10⁹/M, N_max = 116.8 ± 20.8 fmol/mg protein; nuclear extract: K_a = 0.823 ± 0.057 × 10⁷/M, N_max = 1563 ± 330 fmol/mg protein; n = 4). The cytosol receptor activity displayed high steroid and tissue specificity and a single binding peak at 191,000 Da following gel permeation chromatography. Atlantic salmon exposed for 3 or 8 months to waters from the Medway River (pH about 5.1), the Westfield River (pH about 4.8) and calcium carbonate treated Westfield River (pH about 5.6) showed no gill cytosol receptor activity. Cortisol receptor activity in the gill nuclear extracts from fish in limed Westfield River water in December (3 months) was less than half the activity in the fish treated with Medway River water (p < 0.05) although the plasma cortisol values were not different. In May (8 months), the plasma cortisol of fish in limed water was almost twice that of the fish held in acid Westfield River water (p = 0.058).