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.     

Modelling effects of disturbance on population dynamics of generalized crayfish life history strategies

1. Crayfish play a crucial ecological role and are often considered a keystone species within freshwater ecosystems; however, North American crayfish species face disturbance and ecological threats including invasive species and intensified drought.
2. Demographic models can allow examination of population dynamics of a targeted species under a wide variety of disturbance scenarios. In this study, crayfish population dynamics were modelled and their responses to simulated biological invasions and drought were assessed.
3. As life history data on crayfish are relatively rare, models were used to explore the population viability of four generalized species with distinct life history strategies under 11 disturbance scenarios. RAMAS-Metapop was used to construct stage-based demographic metapopulation models parameterized using vital rates from established literature sources.
4. Models indicated that populations respond differentially to disturbance based on life history. However, both r- and K-selected species appear to be highly susceptible to decline when faced with the additive effects of reduced carrying capacity resulting from invasion and reduced survival rates caused by drought.
5. Constructing models that explore a broad array of life histories and disturbance regimes can provide managers with tools to develop generalized, widely applicable conservation strategies in data-depauperate systems.

     

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.     

Effect of food amount and temperature on growth rate and aerobic scope of juvenile chum salmon

Offshore migration of Pacific salmon Oncorhynchus spp. is partly triggered by increasing body size and high motility in the early stages of life. The survival of juvenile salmon may depend on their growth rate during the first few months in the sea, and this factor partly regulates the dynamics of adult populations. Here, we assessed the effects of water temperature and food availability on the growth of juvenile chum salmon O. keta. In addition, by combining the measurements of metabolic performance for growth and activity (Absolute Aerobic Scope: AAS) with a bioenergetics model, we estimated the energy allocation for different activities in the juveniles. Under high temperatures (14 °C), juveniles reared at low food levels (1% body weight) allocated less than half their energy for growth than those reared at high food levels (4% body weight). These findings suggest that high temperature and low food level constrain the growth of juveniles, providing an insight into the effect of the recent increase in warm and low-nutrient water masses on survival of juveniles and catches of adult chum salmon on the Pacific side of Honshu Island, Japan.

     

Changes in rhodopsin-porphyropsin ratio of chum and pink salmon

ABSTRACT:   In order to investigate the changes in rhodopsin-porphyropsin ratio of chum salmon and pink salmon in relation to the change in their habitat, the ratios were analyzed in individual fish prior to stocking, during the sea run, homing, and upstream migration. The ratio in both the species gradually increased during the sea run. However, the ratio decreased after upstream river migration. Moreover, in the sea, the rhodopsin-porphyropsin ratio of chum salmon was always slightly higher than that of pink salmon. The largest difference in the individual variation was observed in the individuals caught with a set net placed near the mouth of a home river.     

人工培育秋大麻哈幼鱼的生长与形态研究

通过对在淡水中培育大麻哈幼鱼生长和形态测定发现:大麻哈幼鱼在2.5%日投喂量时特定生长率较高;大麻哈幼鱼体重与体长的关系符合幂函数,其关系式为W=0.661 L2.1635;随着大麻哈幼鱼的生长,其肥满度有所增加,但增加幅度较小;全长/体长、体长/头长、背吻距/背尾距的比值较体长/体高、头长/吻长、头长/眼径和头长/眼间距的比值变化小,背吻距/背尾距的比值接近1,而大麻哈鱼生殖群体的比值在1.13～1.31之间.     

Changes in GnRH levels in the brain and pituitary gland during migrations of sockeye salmon and chum salmon

Levels of two moleculer types of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH–II (cGnRH–II) in the various brain regions and pituitary gland of sockeye salmon (Oncorhynchus nerka) and chum salmon (O. keta) during smoltification and spawning migration, respectively, were measured using specific time-resolved fluoroimmunoassay (TR-FIA) systems. Changes in sGnRH levels in different brain regions tended to be specifically synchronized with serum thyroid hormone or pituitary gonadotropin (GTH) levels during smoltification and spawning migration, respectively. In contrast, cGnRH–II levels did not show such synchronized changes. SGnRH and cGnRH–II in various brain regions might have different roles during smoltification and spawning migration of salmonid fishes.     

Preparation of hatchery—reared chum fry for life at sea: osmoregulation dynamics

The development of saltwater tolerance was studied in chum fry reared in the Malkinsky hatchery (central Kamchatka, 200 km from the Sea of Okhotsk). Hypo-osmoregulatory ability of fry was assessed by dynamics of plasma sodium concentration, 24 and 48 h after their transfer from fresh water to seawater (30%o), and by fry survival in seawater of 40%o salinity. Complete osmoregulation function in young chum was developed in seawater only in late June, despite their earlier development of silver body color and fairly high migration activity. No correlation was found between the weight of fish and their osmoregulatory abilities. The reasons for late smoltification of hatchery-reared chum have not yet been clearly defined. One explanation might be the combined effect of low nocturnal temperatures and considerable daily fluctuations in temperature (more than 8^oC) during the period of egg incubation (in fall), as well as during smoltification of chum juveniles (spring-early summer). Data on the osmoregulatory ability of chum smolts could be useful in forecasting their survival in the early marine period of life.     

Effect of temperature on short-term storage of eggs and sperm of chum salmon (Oncorhynchus keta)

Chum salmon (Oncorhynchus keta) gametes were stored separately for intervals up to 460 h at temperatures ranging from 3 to 15°C. Estimates of time to 90 and 50% fertilization success (FS) were obtained for either stored eggs, stored milt, or stored eggs and milt. When both gametes were stored, the combined loss of gamete viability resulted in shorter times to 90 and 50% FS than when either eggs or milt were stored alone. Gamete storage at colder temperatures significantly prolonged viability; for example, when both gametes were stored, the time to 90% FS ranged from 19.6 h (15°C) to 123.9 h (3°C). Loss of viability of stored gametes in these trials was similar to that found in other studies with Oncorhynchus species at low storage temperatures (3–6°C), but gametes showed significantly greater viability when stored at higher temperatures (9–15°C). This increased viability in the current study appears to have resulted from the provision of (1) higher air-to-gamete ratios, and (2) greater interface area between air and gametes in the storage containers, two factors that would enhance gamete respiration during storage.     

Monitoring the spawning behaviour of chum salmon with an acceleration data logger

Abstract –  The continuous observation of salmon behaviour in some wild environments can be extremely difficult. We recorded spawning behaviour of female chum salmon ( Oncorhynchus keta ) in the field simultaneously using visual observation and fish-borne data loggers with two-axis accelerometer sensors. Using only acceleration records, behaviours were successfully classified into the eight well-known components of spawning behaviour: swimming, nosing, exploratory digging, nest digging, probing, oviposition, covering and post-spawning digging. To understand how the female chum salmon modulates spawning behaviours in relation to changes in environmental conditions, we compared the behaviours of salmon during normal flow of clear water to those of salmon during the heavy flow of turbid water after a storm. Salmon in the normal flow showed all eight behaviours, whereas salmon in the heavy flow showed only three behaviours: swimming, nosing and exploratory digging. The proportion of time spent on swimming was greater in the heavy flow than in the normal flow (mean of 98.47% vs. 92.84%). Moreover, the proportion of tail beating in swimming was greater in the heavy flow (77.86%) than in the normal flow (15.63%). Our results indicate that the behaviour of female chum salmon was strongly affected by the heavy flow of turbid water after a storm. The recording of accelerations is a promising method for clarifying the spawning behaviour of salmonids in the wild where continuous visual observation is too difficult.     

Thyroid hormone concentrations in the gonads of wild chum salmon during maturation

Changes in gonadal and plasma concentrations of thyroid hormones were examined at various stages of maturation in chum salmon (Oncorhynchus keta) caught in the Bering Sea and the Bay of Alaska. Plasma concentrations of thyroxine (T₄) were less than 5 ng ml⁻¹, and those of 3,5,3′-triiodo-L-thyroxine (T₃) were less than 2 ng ml⁻¹ I in both males and females, regardless of the degree of sexual maturity or the gonadosomatic index (GSI). There was no clear relationships between circulating thyroid hormone levels and tissue levels. The ovarian T₄ concentrations were undetectable (less than 0.2 ng g⁻¹) or less than 2 ng g⁻¹ when GSI was lower than 1%, but increased thereafter and reached a plateau of 8–10 ng g⁻¹ when GSI became 2%. The ovarian T₃ concentrations were about 5 ng g⁻¹ when GSI was 1%, increased to a maximum level (20 ng g⁻¹) when GSI was about 2%, and decreased to a constant level of 10 ng g⁻¹ thereafter. The T₄ and T₃ content in single oocyte increased proportionally to the oocyte volume, indicating a constant incorporation of the hormones into the oocyte. The T₄ concentrations in the testis were 1 ng g⁻¹ or less regardless of the GS1. On the other hand, the T₃ concentrations were highest (15 ng g⁻¹) when the GSI was less than 1%, decreased thereafter when spermatocytes appeared in the testis, and became about 5 ng g⁻¹ I in testes containing spermatozoa, raising the possibility of a role for T₃ during early gamete and/or gonad maturation of testes.     

Effects of protamine hydrochloride from chum salmon milt on lipid metabolism in rats

Protamine is a basic protein whose sulfate is used in medical applications as a carrier for injectable insulin and as a heparin antagonist, while its hydrochloride is used as an antibacterial ingredient for some food products. We previously showed that protamine hydrochloride derived from chum salmon milt inhibited pancreatic lipase and reduced plasma triacylglycerol levels in an oral fat tolerance test in humans. The present study evaluated the effect of chum protamine hydrochloride on lipid metabolism in rats. The single oral administration of protamine hydrochloride (500 mg/kg) reduced plasma triacylglycerol levels in a corn oil tolerance test, and repeated oral administration at a dose of 0, 150, 500, or 1,500 mg/kg with a high fat diet for 7 weeks significantly reduced body weight gain, liver weight, and epididymal adipose tissue, whereas total calorie intakes were not significantly different. These findings could be caused by the suppression of lipid digestibility leading to a significant increase in fecal lipid excretion due to the fact that protamine hydrochloride could bind with bile acids to make a complex that is difficult to digest. Protamine hydrochloride, with a considerable history as food, can be considered to be promising as an anti-obesity functional food material.     

The relationship between migration speed and release date for chum salmon Oncorhynchus keta fry exiting a 110-km northern Japanese river

The relationship between release date and migration speed was examined for hatchery chum salmon Oncorhynchus keta fry exiting the Nishibetsu River in eastern Hokkaido, northern Japan so that future releases might be scheduled so that fry arrive at the ocean during periods favoring high survival. Separate marked groups of chum salmon released in early April, mid-April, and early May in 2008, late March and mid-April in 2009, and mid-April in 2010 were recaptured with a rotary screw trap 12 km above the river mouth. Chum salmon in later release groups tended to migrate downstream faster than fish in earlier release groups. Those released after mid-April arrived in the lower river on average 9 days after release, while those released before mid-April arrived on average 26–28 days after release. Most marked fish arrived in the lower river during late April to mid-May. These results suggest that chum salmon are adapted to adjust their migratory speed so as to arrive at the ocean during a relatively discrete period, presumably during a time of high productivity favoring good survival.     

Upstream migration of chum salmon through a restored segment of the Shibetsu River

Abstract –  A segment of the Shibetsu River was restored to reconstruct the ecological condition of the previously canalized river stretch to a more natural, meandering state. In this study, we investigated the upstream migration of chum salmon ( Oncorhynchus keta ) using radio transmitters to track the horizontal position of fish and data loggers to detect the vertical swimming depth of fish, simultaneously. The monitored salmon travelled near the bottom of the water column and along the riverbanks, and tended to hold in deep, slow current areas in the canalized river. In the restored segment, the fish swam at more shallow depths and against stronger currents. Although the three tracked fish all reached the confluent point and chose to enter the restored segment, they did not remain in the segment for long. This indicates that the restored area facilitates the upward migration of the chum salmon.     

Relationship between zooplankton abundance and the early marine life history of juvenile chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> in eastern Hokkaido,Japan

Interannual variations in abundance, timing of outmigration from rivers, growth rate and condition of juvenile chum salmon (Oncorhynchus keta) were studied in the Nemuro Strait (eastern Hokkaido, Japan) during 1999–2002 to establish a possible relationship to zooplankton abundance. The otolith microstructure of juveniles was examined each year in late June to determine their time and size at sea entry (i.e., outmigration), and to estimate the early marine growth rates. Salmon outmigration peaked in mid- or late May, which coincided, in three of the four study years, with the peak release of juveniles into rivers within the study area. Abundance, growth rate and condition of fish were higher in 2001, when—compared to other years—smaller fish experienced higher growth rates, coinciding with greater zooplankton abundance for that year. Our results suggest that high zooplankton abundance positively influenced juvenile chum salmon growth and the condition of the fish during their early marine life despite their small size at sea entry.     

Interactive effects of life history and season on size‐dependent growth in juvenile Atlantic salmon

Size‐dependent growth (SDG) is an important process in structuring populations as well as determining life history outcomes. Despite its importance, there have been few investigations from observational studies focusing on the interaction between life history decisions and SDG. In this study, we used data on individually tagged Atlantic salmon from both the laboratory and the field to investigate differences in SDG among two life history groups, parr and smolts. In the laboratory, we found little evidence of SDG in parr but seasonally dependent SDG in the smolt group. Smolts showed at strong compensatory response over the winter months just prior to the smolt transformation window. In the field, we found little evidence of SDG early in ontogeny (i.e., age 0+ fall and winter). There was some evidence of depensatory growth (positive SDG) during the age 1+ spring among both life history groups that may reflect random habitat variation or the monopolisation of resources. After the age 1+ spring, we found that smolts were more likely to show a compensatory effect (negative SDG) than parr. This effect was strongest, as they approached the smolt window in the spring of their age 2+ year. These results suggest (i) SDG is common in Atlantic salmon; however, the form and extent of life history depends on (ii) season and (iii) life history. For individuals that adopt a smolt life history, trade‐offs between freshwater survival and sea survival may lead to a convergent growth pattern, as they approach the smolt migration window.     

Review of population dynamics and management of small pelagic fishes around the Japanese Archipelago

Fisheries Science - Population dynamics of small pelagic fishes (SPF) and their management in Japan were reviewed for Japanese sardine Sardinops melanostictus, Japanese anchovy Engraulis japonicus,...     

EMG telemetry studies on upstream migration of chum salmon in the Toyohira river,Hokkaido, Japan

The movements of 28 adult chum salmon, Oncorhynchus keta (Walbaum) tagged with electromyogram (EMG) transmitters were tracked along the Toyohira river, Hokkaido, Japan, in October of 2007 and 2008 to investigate and evaluate the upstream migratory behavior through the protection bed and fishway of ground sills. The approach time of fish that ascended successfully through the protection bed and fishway was shorter than that of unsuccessful fish. The unsuccessful fish were observed to swim in currents with high water velocity and shallow water depth at swimming speeds that exceeded their critical swimming speed (U _crit) during the approach to these structures. In consequence, unsuccessful fish frequently alternated between burst and maximum sustained speeds without ever ascending the fishway, and eventually became exhausted. It is important that fishway are constructed to enable chum salmon to find a passage way easily, so that they can migrate upstream rapidly without wasting excessive energy.     

A spatial model of population dynamics of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan

We constructed a numerical model reproducing the transport, survival and individual growth of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan during 1978–93. The causes of early life stage mortality, including the influence of the effects of the spatial relationship between the spawning grounds and the Kuroshio on the mortality rate, were investigated. Survival and transport from egg stage to 60 days after spawning were modelled daily in a 1 × 1 degree mesh cell and individual growth in the period was modelled in each region (Kuroshio, Inshore, Offshore and Transition regions). Individual growth and survival from 60 to 180 days after spawning were modelled daily in the Transition region. Environmental data were taken from outside the model system. Our simulation indicates that survival variability in the larval stage (5–25 mm in standard length) is the key factor in determining the year‐class strength. The simulation revealed that strong year classes occurred with good survival in the spawning ground and whilst entrained in the Kuroshio current being transported to the main feeding grounds in the Transition region. The simulation also indicated that survival rates in 1988–93 were low in the Inshore, Kuroshio and Offshore regions, which depressed the year‐class strength during that period.     

Preventive efficacy of sodium hypochlorite against water mold infection on eggs of chum salmon Oncorhynchus keta

ABSTRACT:   To protect chum salmon eggs from water mold infection during incubation, the eggs were treated daily with sodium hypochlorite solution (NaOCl) at 10 mg/L residual chlorine concentration for 15 min during their developmental period from fertilization to eyed stages. The number of infected eggs and number of eyed eggs were observed on day 23 of incubation. The percentage of infected eggs to total eggs was significantly lower with NaOCl treatment (1.8 : 33.4%) than in the control (11.3 : 59.3%, P  < 0.01). The percentage of eyed eggs to total eggs was significantly higher with NaOCl (85.9 : 98.6%) than in the control (66.1 : 97.5%, P  < 0.01). The antifungal activity of NaOCl resulted in improving egg survival. Accordingly, NaOCl is a useful antifungal agent against water mold infection on chum salmon eggs.