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Sustainably managed wild fisheries support food and nutritional security, livelihoods, and cultures (1). Harmful fisheries subsidies—government payments that incentivize overcapacity and lead to overfishing—undermine these benefits yet are increasing globally (2). World Trade Organization (WTO) members have a unique opportunity at their ministerial meeting in November to reach an agreement that eliminates harmful subsidies (3). We—a group of scientists spanning 46 countries and 6 continents—urge the WTO to make this commitment...

The ability to distinguish between different migratory behaviours (e.g., anadromy and potamodromy) in fish can provide important insights into the ecology, evolution, and conservation of many aquatic species. We present a simple stable carbon isotope (δ13C) approach for distinguishing between sockeye (anadromous ocean migrants) and kokanee (potamodromous freshwater residents), two migratory ecotypes of Oncorhynchus nerka (Salmonidae) that is applicable throughout most of their range across coastal regions of the North Pacific Ocean. Analyses of kokanee (n = 239) and sockeye (n = 417) from 87 sites spanning the North Pacific (Russia to California) show that anadromous and potamodromous ecotypes are broadly distinguishable on the basis of the δ13C values of their scale and bone collagen. We present three case studies demonstrating how this approach can address questions in archaeology, archival, and conservation research. Relative to conventional methods for determining migratory status, which typically apply chemical analyses to otoliths or involve genetic analyses of tissues, the δ13C approach outlined here has the benefit of being non-lethal (when applied to scales), cost-effective, widely available commercially, and should be much more broadly accessible for addressing archaeological questions since the recovery of otoliths at archaeological sites is rare.

In spite of a relatively optimistic pre-season forecast, the total return of adult sockeye salmon (Oncorhynchus nerka) to the Fraser River (British Columbia, Canada) in 2009 was the lowest recorded since quantitative records began in the late 1940s. A plausible mechanism is proposed that links a sequence of extreme oceanic and climatic events to poor marine survival. It began with record-setting snow packs in the coastal mountain range during the winter of 2007 that led to the development of unprecedented oceanographic conditions in the spring of 2007 from Queen Charlotte Strait in central British Columbia to Southeast Alaska. When combined with equally extreme atmospheric anomalies in the region in the spring of 2007, with a winter wind regime persisting through July, a coastal surface ocean with characteristics that are known to be associated with lower marine survival was established. Most of the sockeye salmon that were expected to return to the Fraser River as adults in 2009 passed through this atypical ocean as juveniles on their migration to the open ocean in 2007. A trophic gauntlet hypothesis is proposed as a new paradigm to describe the oceanic environment faced by sockeye salmon after they emigrate northward from the Strait of Georgia. The hypothesis identifies a new type of high nutrient low chlorophyll region that can explain how oceanographic extremes at critical locations along the migration route beyond the Strait of Georgia can reduce marine survival in some years.

The hatchery program for chum salmon in Hokkaido, northern Japan, constitutes one of the largest salmon hatchery programs in the world. The hatchery program has been conducted for over 120 years, and returns of chum salmon rapidly increased during the last quarter of the 20th century. Since the 1990s, chum salmon returns to Hokkaido have remained at a historically high level, although different fluctuation trends have been observed among regions within Hokkaido. Although such intensive hatchery programs have been conducted for more than 25 generations, there has been no evidence indicating any decline of genetic diversity. The hatchery program for chum salmon in Hokkaido is successful in increasing commercial catches and will likely be the main management tool in future. However, information on naturally spawning chum salmon in Hokkaido remains scarce. Assessment of naturally spawning populations recently commenced, and it has been revealed that naturally spawning chum salmon populations remain in many ri...

Yatsu, A., Chiba, S., Yamanaka, Y., Ito, S-I., Shimizu, Y., Kaeriyama, M., and Watanabe, Y. 2013. Climate forcing and the Kuroshio/Oyashio ecosystem. – ICES Journal of Marine Science, 70: 922–933. The Kuroshio and Oyashio, western boundary currents in the North Pacific, greatly influence climate, ecosystems, and fisheries in the western North Pacific and its adjacent waters. The Kuroshio/Oyashio ecosystem (KOE) shows interannual and decadal variability including regime shifts. Under a collaboration of the Climate Forcing and Marine Ecosystem Response (CFAME) Task Team and Working Group 20 (Evaluations of Climate Change Projections) of PICES, we analysed the observed time-series of physics, nutrients, chlorophyll, zooplankton abundance and phenology, and productivity, biomass, and catch of commercially important species to assess the impacts of Intergovernmental Panel on Climate Change's global change scenarios on KOE. Mechanistic linkages from climate forcing to fish population dynamics were explored for the Japanese common squid (Todarodes pacificus), Japanese sardine (Sardinops melanostictus), walleye pollock (Theragra chalcogramma), and chum salmon (Oncorhynchus keta). Future scenarios of zooplankton, commercial species, and ecosystem changes were presented based on the empirical mechanistic linkages and results of projections for physical conditions and primary production in KOE derived from both empirical knowledge and three-dimensional ecosystem-biogeochemical models. Associated data gaps, uncertainties, and implications for managers were also discussed.

This paper describes an attempt in 2008 to establish an aerial census of adult chum salmon using a small radio-controlled (RC) helicopter. The Moheji River, located in southern Hokkaido, was chosen because all the salmon in a stretch of the river between a weir and the estuary are seine-netted every morning for artificial propagation. Aerial photographs of the river were taken from a RC helicopter equipped with a digital single-lens reflex camera and polarized filter. To quantify salmon density within the census area, the number of salmon per aerial photograph was counted using image-processing software. Salmon could be clearly identified in photographs taken from an altitude of ∼30 m. Salmon numbers estimated by aerial census and seine-netting were significantly related. The results indicate that a small RC helicopter can be used to generate adult salmon abundance data in Japanese rivers.

Advances in salmon culture practices during the latter part of the 20th century provided the opportunity for mass production of juvenile salmon. Hatchery-produced salmon currently outnumber wild salmon in some regions around the Pacific Rim, raising concerns about their ecological impacts on wild salmon. We convened five regional sessions at an international conference to identify and discuss issues related to ecological interactions between wild and hatchery salmon. Session participants were charged with identifying key interaction types by salmon life stage. Each group was asked to summarize key research needs and identify management actions that might be needed to reduce risks from hatchery programs. Some common themes emerged in all the sessions, including the importance of predation and competition interactions in freshwater environments during juvenile life stages and breeding interactions among adults. Much less is understood about interactions in estuarine and marine ecosystems, even though these environments may be critical in determining recruitment success. Some groups identified a need for field experiments to test hypotheses related to ecological interactions and the need to understand and, where possible, control hatchery straying. Some groups also discussed the importance of carrying capacity in different environments and how hatchery programs may be contributing to density-dependent effects. There is a lack of focused studies on ecological interactions between wild and hatchery salmon in the Western Pacific. The authors of this paper hope to encourage new research efforts to better understand ecological interactions to help inform management efforts aimed at reducing hatchery risks to wild salmon.

To clarify relationships between the abundance and biological characteristics of Pacific salmon Oncorhynchus spp., we analyzed spatiotemporal changes in fork length, body weight, and an index of relative abundance (catch per unit effort, CPUE) for pink salmon (O. gorbuscha), chum salmon (O. keta), and sockeye salmon (O. nerka) collected by research gill-nets from the T/V Oshoro-maru and the T/V Hokusei-maru of Hokkaido University in the North Pacific during 1953-2007. Populations of each species were distributed throughout the western Bering Sea, eastern Bering Sea (EB), western North Pacific (WNP), central North Pacific (CNP), eastern North Pacific (ENP), and Okhotsk Sea. Since 1970, the average body size of chum salmon at ocean ages 0.3-0.4 has generally declined in the WNP and CNP. However, the average body sizes of sockeye and pink salmon have not shown temporal changes. Chum salmon showed significant negative (positive) correlations between CPUE and body size for populations in CNP (ENP) at ocean ages 0.2-0.3 (age 0.1) for both sexes. In general, sockeye salmon also showed significant negative (positive) correlations between CPUE and body size for populations in the EB at ocean ages X.2-X.3 (age X.1) for both sexes, except in CNP at age 2. Our results suggest that better growth by chum and sockeye salmon in the early periods of their ocean life histories might produce higher abundance. This higher abundance, which might also be affected by overlapping distributions among Pacific salmon species and populations in certain seas, in turn appears to cause density-dependent declines in growth in the following ocean life history period due to the limited carrying capacity of the seas. To understand complex dynamics in Pacific salmon species in the North Pacific Ocean, research on interactions among species and populations is needed.

Pacific salmon (Oncorhynchus spp.) play an important role as a keystone species and provider of ecosystem services in the North Pacific ecosystem. We review our studies on recent production trends, marine carrying capacity, climate effects and biological interactions between wild and hatchery origin populations of Pacific salmon in the open sea, with a particular focus on Japanese chum salmon (O. keta). Salmon catch data indicates that the abundance of Pacific salmon increased since the 1976/77 ocean regime shift. Chum and pink salmon (O. gorbuscha) maintained high abundances with a sharp increase in hatchery-released populations since the late 1980s. Since the 1990s, the biomass contribution of hatchery returns to the total catch amounts to 50% for chum salmon, more than 10% for pink salmon, and less than 10% for sockeye salmon (O. nerka). We show evidence of density-dependence of growth and survival at sea and how it might vary across spatial scales, and we provide some new information on foraging plasticity that may offer new insight into competitive interactions. The marine carrying capacity of these three species is synchronized with long-term patterns in climate change. At the present time, global warming has positively affected growth and survival of Hokkaido populations of chum salmon. In the future, however, global warming may decrease the marine carrying capacity and the area of suitable habitat for chum salmon in the North Pacific Ocean. We outline future challenges for salmon sustainable conservation management in Japan, and recommend fishery management reform to sustain the hatchery-supported salmon fishery while conserving natural spawning populations.

Lacustrine sockeye salmon (Oncorhynchus nerka) are listed as an endangered species in Japan despite little genetic information on their population structure. In order to clarify the genetic diversity and structure of Japanese populations for evaluating on the bottleneck effect and an endangered species, we analyzed the ND5 region of mitochondrial DNA (mtDNA) and 45 single nucleotide polymorphisms (SNPs) in 640 lacustrine sockeye salmon in Japan and 80 anadromous sockeye salmon in Iliamna Lake of Alaska. The genetic diversity of the Japanese population in both mtDNA and SNPs was significantly less than that of the Iliamna Lake population. Moreover, all Japanese populations had SNP loci deviating from the HWE. In spite of low genetic diversity, the SNP analyses resulted that the Japanese population was significantly divided into three groups. These suggest that Japanese sockeye salmon populations should be protected as an endangered species and genetically disturbed by the hatchery program and transplantations.

The Sakhalin taimen Parahucho perryi is an endangered salmonid with a natural range limited to the Russian Far East and Japan. We constructed a classification tree to determine the environmental factors shaping the historical global distribution of this species and then predicted its potential geographic range. The distribution was most strongly influenced by a spatial autocorrelation term, indicating that it is highly contiguous. Large drainage basins with low topographic relief and large floodplains had a higher probability of taimen occurrence. The boundary of the global distribution was delineated by mean monthly precipitation within the range of 54–96 mm. The presence of Sakhalin taimen was predicted in many drainage basins where it has never been recorded. We also modeled the status of 48 taimen populations in Japan, where it was possible to classify them into three categories: currently stable (7), endangered (5), and extinct (36). The most significant factor differentiating the 12 extant ...

We used multiple regression and path analysis to examine the effects of regional and larger spatial scales of climatic/oceanic conditions on the growth, survival, and population dynamics of Hokkaido chum salmon (Oncorhynchus keta). Variability in the growth of chum salmon at ages 1 to 4 was estimated from scale analysis and the back-calculation method using scales of 4-year-old adults returning to the Ishikari River in Hokkaido, Japan, during 1943–2005. Growth of chum salmon at age 1 was less during the period from the 1940s to the mid-1970s compared to the period from the mid-1980s to the present. On the other hand, growth of chum salmon at ages 2, 3, and 4 has declined since the 1980s. Path analysis indicated that growth at age 1 in the Okhotsk Sea was directly affected by warmer sea surface temperatures associated with global warming. The increased growth at age 1 led directly to higher survival rates and indirectly to larger population sizes. Subsequently, in the Bering Sea, the larger population size was directly associated with decreased growth at age 3 and indirectly associated with shorter adult fork lengths despite the lack of relationships among sea surface temperature, zooplankton biomass, and growth at ages 2 to 4. Therefore, higher growth at age 1 related to global warming positively affected the survival rate of juvenile chum salmon in the Okhotsk Sea. The higher survival rates in turn appear to be causing a population density-dependent effect on growth at ages 2 to 4 and maturation in the Bering Sea due to limited carrying capacity.

To provide morphological bases for functional studies, the development of the photoreceptor cells in the retina of the cuttlefish Sepia esculenta from newly hatched juveniles to the adults was examined by light and electron microscopy. Four layers were distinguished in the retina: the rhabdomeric layer, subrhabdomeric layer, inner segmental layer, and plexiform layer. With the development of the retina, the structure of the plexiform layer becomes stronger. Morphometric data on the rhabdomeric microvilli from the newly hatched to the adult retinas are presented. The thickness of the rhabdomeric layer and the total surface area of the rhabdomeric microvilli present beneath a unit surface area of the retina show an exponential increase with developmental days; the diameter of the lens shows a linear increase with days. The results of our research show that the visual acuity and sensitivity of S. esculenta continuously increased with development.

From the 1970s to 1990s, a reduction in the body size of Japanese chum salmon (Oncorhynchus keta) was observed. To investigate this body size reduction in the North Pacific, we developed a bioenergetics model for chum salmon coupled with the results from a lower trophic ecosystem model embedded into a three-dimensional global model. In the bioenergetics model, respiration and consumption terms are assumed to be functions of water temperature and prey zooplankton density, which are the determining factors of the reduction of body size. The model reproduced the body size of the 1972 and 1991 year classes of chum salmon. The reproduced body size of the 1972 year class was larger than that of 1991 year class, and this result agrees with observations from the Bering Sea. Our model also reproduced the body size trend from l970 to 2000. The prey density, especially in the eastern North Pacific, had a greater influence on the change of body size than did the SST. This suggests that the size reduction of Japanese chum salmon in the 1990s was partly affected by changes in prey zooplankton density. In the context of the global warming scenario, we discuss changes in the migration route of chum salmon and predict that the population of Japanese chum salmon experience significant declines over this century.

While documentation of climate effects on marine ecosystems has a long history, the underlying processes have often been elusive. In this paper we review some of the ecosystem responses to climate variability and discuss the possible mechanisms through which climate acts. Effects of climatological and oceanographic variables, such as temperature, sea ice, turbulence, and advection, on marine organisms are discussed in terms of their influence on growth, distribution, reproduction, activity rates, recruitment and mortality. Organisms tend to be limited to specific thermal ranges with experimental findings showing that sufficient oxygen supply by ventilation and circulation only occurs within these ranges. Indirect effects of climate forcing through effects on the food web are also discussed. Research and data needs required to improve our knowledge of the processes linking climate to ecosystem changes are presented along with our assessment of our ability to predict ecosystem responses to future climate change scenarios.

Despite the importance of olfactory receptor neurons (ORNs) for homing migration, the expression of olfactory marker protein (OMP) is not well understood in ORNs of Pacific salmon (genus Oncorhynchus ). In this study, salmon OMP was characterized in the olfactory epithelia of lacustrine sockeye salmon ( O. nerka ) by molecular biological and histochemical techniques. Two cDNAs encoding salmon OMP were isolated and sequenced. These cDNAs both contained a coding region encoding 173 amino acid residues, and the molecular mass of the two proteins was calculated to be 19,581.17 and 19,387.11 Da, respectively. Both amino acid sequences showed marked homology (90%). The protein and nucleotide sequencing demonstrates the existence of high-level homology between salmon OMPs and those of other teleosts. By in situ hybridization using a digoxigenin-labeled salmon OMP cRNA probe, signals for salmon OMP mRNA were observed preferentially in the perinuclear regions of the ORNs. By immunohistochemistry using a specific antibody to salmon OMP, OMP-immunoreactivities were noted in the cytosol of those neurons. The present study is the first to describe cDNA cloning of OMP in salmon olfactory epithelium, and indicate that OMP is a useful molecular marker for the detection of the ORNs in Pacific salmon.

It is generally accepted that anadromous Pacific salmon (genus Oncorhynchus) imprint to odorants in their natal streams during their seaward migration and use olfaction to identify these during their homeward migration. Despite the importance of the olfactory organ during olfactory imprinting, the development of this structure is not well understood in Pacific salmon. Olfactory cues from the environment are relayed to the brain by the olfactory receptor neurons (ORNs) in the olfactory organ. Thus, we analyzed morphometric changes in olfactory lamellae of the peripheral olfactory organ and in the quantity of ORNs during life history from alevin to mature in chum salmon (Oncorhynchus keta). The number of lamellae increased markedly during early development, reached 18 lamellae per unilateral peripheral olfactory organ in young salmon with a 200 mm in body size, and maintained this lamellar complement after young period. The number of ORNs per olfactory organ was about 180,000 and 14.2 million cells in fry and mature salmon, respectively. The relationship between the body size (fork length) and number of ORNs therefore revealed an allometric association. Our results represent the first quantitative analysis of the number of ORNs in Pacific salmon and suggest that the number of ORNs is synchronized with the fork length throughout its life history.

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 Ishikari River juveniles. There were no significant differences in annual growth between populations of one-, two-, and four-year-old fish. For three-year-old fish, however, Namdae River salmon had significantly higher synchronous and sympatric growth than Ishikari River salmon. Mean FL of adults was also larger in Namdae River salmon than in Ishikari River salmon. ANCOVA results showed (1) negative linear relations between FL and catch, (2) homogeneous slopes of those relations at regional and species levels, and (3) non-homogeneous 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 intra-specific interactions in the Bering Sea., 鱗分析と体サイズのバックカリキュレーション法に基づき，1984-1998 年に北海道石狩川と韓国ナンダエ川へ回帰したシロザケの成長パターンの時空間変動を明らかにした。その結果，石狩川系幼魚が沿岸から小型で直接オホーツク海へ移動するのに対して，ナンダエ川幼魚は日本海を回遊後オホーツク海へ大型で移動することが明らかとなった。シロザケ4 歳魚の体サイズはベーリング海で3 歳時に種内あるいは個体群間より個体群内で強い密度依存効果を受けることが示唆された。

Hatchery programmes involving the mass release of cultured fish have been implemented worldwide to supplement wild populations and to increase harvests. Hokkaido Island is one of the most active regions for Pacific salmon hatchery programmes, with ca. 1.2 billion (109) juveniles released annually along a coastline of ca. 3000 km. During the last quarter of the 20th century, coastal catches of chum and pink salmon increased dramatically, whereas those of masu salmon did not. In addition to the development of hatchery technologies, several possible hypotheses may explain these catch trends, including climate change, closing of high-seas fisheries, rehabilitation of water quality, habitat loss caused by damming and channelling, and increased pressure from recreational fisheries. Even when these other factors have been accounted for, it is difficult to evaluate whether all hatchery programmes have actually increased net populations. To use these programmes more effectively, it is necessary to evaluate both their river- and species-specific benefits and compare hatchery programmes with other management tools, such as fishery controls and habitat rehabilitation. Future hatchery programmes should incorporate active, adaptive learning approaches to minimize the risks associated with artificial propagation and to promote sustainable salmon stocks.

Coastal-ocean–open-ocean migrations, prey–predator relations and long-term population dynamics of chum salmon (Oncorhynchus keta) and Japanese sardine (Sardinops melanostictus), associated with large-scale climate and oceanographic conditions, are reviewed. After early marine life in coastal waters in northern Japan, chum salmon of Japanese origin spend their first summer in the Okhotsk Sea, then move to the Western Subarctic Gyre for the first winter at sea. Thereafter, they migrate between summer feeding grounds in the Bering Sea and wintering grounds in the Alaskan Gyre for a period of usually up to four years, and finally return to their natal rivers to spawn. Carrying capacity (K) for chum salmon at an unfished equilibrium level was estimated from a Ricker spawner–recruitment curve, and the residual carrying capacity ( RCC = ( K - abundance ) K - 1 ). was positively correlated with body size at age 4, and negatively correlated with age at maturity. Marine survival of Hokkaido chum populations was affected by body size at release, but neither by Aleutian low pressure activity nor sea-surface temperature (SST) around coastal Hokkaido in spring, although there is some correlation between survival rate and coastal SST. Juveniles of the Pacific stock of Japanese sardine become broadly distributed in the Kuroshio Extension (KE) as far east as 180° longitude during spring. Adults disperse as far as the central Pacific and the southern areas of the Okhotsk Sea and Western Subarctic Gyre in years of high abundance. Somatic growth and age at maturation of sardine are density-dependent. We used catch, biomass and residuals of observed recruitment numbers from a Ricker curve (LNRR) as a measure of sardine population dynamics. LNRR was highly correlated with SST of KE in winter, which shifted in 1970 and 1988. Recent biomass and catch remain at extremely low levels due to a combination of adverse environmental conditions and intensive fishing. We suggest that Japanese populations of chum salmon and Japanese sardine have a broader geographic range than North American populations, perhaps because of differences between western and eastern boundary current systems, and associated larval drift (sardine) or avoidance of intra-species competition (chum salmon).

The effects of climate events on the feeding ecology and trophic dynamics of Pacific salmon (Oncorhynchus spp.) in offshore waters of the central Gulf of Alaska were investigated during early summers (1994–2000), based on analyses of stomach contents, and carbon and nitrogen stable isotopes (δ13C and δ15N). Gonatid squids (mainly Berryteuthis anonychus) were the dominant prey of all salmon species except for chum salmon (O. keta). During the 1997 El Nino event and the 1999 La Nina event, squids decreased sharply in the diets of all Pacific salmon except coho salmon (O. kisutch) in the Subarctic Current, and chum salmon diets changed from gelatinous zooplankton (1995–97) to a more diverse array of zooplankton species. A δ13C and δ15N analysis indicated that all salmon species occupied the same branch of the food web in 1999–2000. We hypothesize that high-seas salmon adapt to climate-induced changes in their prey resources by switching their diets either within or between trophic levels. To understand the effects of climate change on Pacific salmon in the Gulf of Alaska, biological oceanographic research on B. anonychus and other important prey resources is needed.

We examined the genetic population structure of chum salmon, Oncorhynchus keta, in the Pacific Rim using mitochondrial (mt) DNA analysis. Nucleotide sequence analysis of about 500 bp in the variable portion of the 5′ end of the mtDNA control region revealed 20 variable nucleotide sites, which defined 30 haplotypes of three genealogical clades (A, B, and C), in more than 2,100 individuals of 48 populations from Japan (16), Korea (1), Russia (10), and North America (21 from Alaska, British Columbia, and Washington). The observed haplotypes were mostly associated with geographic regions, in that clade A and C haplotypes characterized Asian populations and clade B haplotypes distinguished North American populations. The haplotype diversity was highest in the Japanese populations, suggesting a greater genetic variation in the populations of Japan than those of Russia and North America. The analysis of molecular variance and contingency χ2 tests demonstrated strong structuring among the three geographic groups of populations and weak to moderate structuring within Japanese and North American populations. These results suggest that the observed geographic pattern might be influenced primarily by historic expansions or colonizations and secondarily by low or restricted gene flow between local groups within regions. In addition to the analysis of population structure, mtDNA data may be useful for constructing a baseline for stock identification of mixed populations of high seas chum salmon.

This study investigated the continuous record of eutrophication in Lake Onuma based on the geochemical properties of two lake sediment cores obtained from the deepest part of the lake in 2011. Based on a tuff layer deposited during the eruption of Mt. Komagatake, and on the correlation between fluctuations in δ13C and δ15N values, two sediment cores, ON11-2-2 and ON11-6, were dated to the 1920s and 1890s, respectively. The δ13C value and C/N ratio for the lake sediments show values within the ranges for planktonic material and river sediment, suggesting that the lake sediment is a mixture of these sources and that their mixture ratio was almost constant since the 1920s. On the other hand, the δ15N of two cores show a similar trend with increasing δ15N from the 1950s–1960s to the present time. It is attributed to the increase in the δ15N value of planktonic material reflecting anthropogenic nitrogen inflow to the lake.

The chum and pink salmon catches in Hokkaido, Japan have increased dramatically since the 1970s and the 1990s, respectively. In contrast, masu salmon catches have been steadily decreasing. Despite intensive hatchery development in Hokkaido, naturally spawning salmon populations persist based on results from a recent river survey. This paper focuses on the challenges of maintaining hatchery salmon populations while protecting natural chum, pink and masu salmon populations in Hokkaido. Two important initiatives related to meeting this ambitious goal are managing hatcheries in a way that minimizes negative interactions between natural and hatchery salmon populations, and initiating new efforts at restoring and rehabilitating degraded freshwater habitats. In addition, in order to maintain a balance of demand and supply in the domestic market through the exportation of extra salmon, Hokkaido has decided to enter full assessment to gain Marine Stewardship Council (MSC) certification of the Hokkaido chum salmon trap net fishery. This would involve a fundamental shift in fisheries management as practiced in Japan, specifically elevating the importance of managing the fishery in a way that conserves natural salmon populations. A key component of a new salmon management strategy is the establishment of a zone management framework based on the designation of stream units to spatially separate natural salmon from hatchery salmon to minimize negative effects of hatchery fish and to utilize effectively hatchery salmon for commercial fisheries. This effort is allied with similar initiatives in other Pacific Rim countries that are focusing on management reform to restore natural ecosystem function and maintain the coexistence of wild and hatchery salmon.

Juveniles of chum salmon (Oncorhynchus keta) held at high population density were apparently smaller than those held at medium and low population densities. The effects of high population density on pituitary growth hormone (GH) cells in juvenile chum salmon were examined using immunocytochemical and in situ hybridization techniques. The ratio of GH-immunoreactive (ir) area to the whole pituitary was almost constant in all of the high, medium and low population density groups, although the number and sizes of GH-ir cells were decreased in the high population density group. Image-analysis of GH-ir cells indicated the presence of a population of heterogenous cells, in which medium or rather strongly stained smaller cells and as extreme weakly stained larger cells. The medium or rather strongly stained smaller cells predominated in the high population density group, while weakly stained larger cells in the low population density group. In situ hybridization study showed somewhat different distributions and intensities of hybridization signals for mRNAs encoding GH I and II precursors. The area showing signals for GH II mRNA in the high population density group was significantly smaller than those in the medium and low population density groups. In contrast, the sizes of areas showing signals for GH I mRNA did not differ among the groups, although the intensity was slightly higher in the high population density group. These results indicate that high population density decreased the number of weakly immunoreactive larger GH cells, and also suppressed expression of the gene encoding GH II precursor, which may result in retarded somatic growth.

Gonadotropin-releasing hormone analog (GnRHa), testosterone (T) or 17α, 20β-dihydroxy-4pregnen-3-one (DHP) was implanted in lacustrine sockeye salmon (Oncorhynchus nerka) to examine their effects on homing behavior prior to spawning. Maturing adult fish in Lake Shikotsu were captured by a set net adjacent to their natal hatchery in September and October, 1997. They were tagged, implanted with hormones and released at the center of lake. More than 70% of released fish returned to the hatchery. In September, GnRHa-implanted fish returned significantly earlier than the controls regardless of sexes. DHP also shortened homing duration in the females but not in the males. T tended to reduce homing duration in the males, however it did not have any significant effect in the females. In October, fish in all groups quickly returned within a few days after the release. Hence, the shortening effect of GnRHa on homing duration was not seen. The October fish may be already well primed by endogenous hormones. The present study showed that, in September, GnRHa consistently shortened homing duration, whereas sex steroid actions varied depending on sex in lacustrine sockeye salmon.

Adult sockeye salmon (Oncorhynchus nerka) in Lake Shikotsu were captured in September, October and November adjacent to their natal hatchery prior to spawning. They were sampled for hormones, tagged and released in the center of lake. Fish were again sampled at recapture to characterize changes in steroid hormone levels in individual migrants as well as homing percentage and duration in each month. All males returned faster than females early in the breeding season, although a half of the tagged males did not return to the natal site late in the season (November). A high percentage of females always returned, and homing duration shortened late in the season. In males, the shortening of homing duration coincided with an increase in serum testosterone (T) and 11-ketotestosterone levels. In females, the shortening of homing duration corresponded to an elevation of serum T and 17α,20β-dihydroxy-4-pregnen-3-one (DHP) levels, and a drop in serum estradiol-17β levels. Sustained administration of gonadotropin-releasing hormone analog (GnRHa, via implants) in September greatly shortened homing duration, especially in females. GnRHa treatment caused a dramatic increase in serum DHP levels in both sexes on average. Individual GnRHa-treated males which rapidly returned, however, showed higher serum T levels and lower serum DHP levels than slower returning males. The present study indicates sexual differences in homing profiles as well as shortening of homing duration following GnRHa implantation in lacustrine sockeye salmon in Lake Shikotsu which may be reflective of changes in serum steroid hormone levels.

The relationships between individual growth and scale pattern were examined for juvenile sockeye salmon (Oncorhynchus nerka) marked with passive integrated transponder (PIT) tags to assess the usefulness of scale analyses for estimating somatic growth. The relationship between absolute somatic growth and increment of scale radius was linear. The relationship between increment of scale radius and number of circuli was also linear. Path analysis showed that the number of circuli was directly correlated with absolute growth. A negative path coefficient (n0.200) between absolute growth and number of circuli indicated that circulus spacing was positively correlated with somatic growth. The relationship between circulus spacing and absolute growth was linear (circulus spacing (μm) = 0.528 × absolute growth (mm) n 9.57). Results indicate that somatic growth affects circulus spacing directly. Circulus spacing was useful for comparing mean growth from the above equation, while back-calculation was useful for estimating individual growth. Resume : Nous avons examinO les relations entre la croissance individuelle et le dOveloppement des Ocailles chez des saumons rouges (Oncorhynchus nerka) juvOniles marquOs avec des Otiquettes ‡ transpondeur passif intOgrO (PIT) en vue diOvaluer liutilitO de lianalyse des Ocailles pour estimer la croissance somatique. La relation entre la croissance somatique absolue et liaccroissement du rayon des Ocailles Otait linOaire. La relation entre liaccroissement du rayon des Ocailles et le nombre dianneaux Otait aussi linOaire. Lianalyse causale a montrO que le nombre dianneaux Otait directement correlO ‡ la croissance absolue. Un coefficient de cheminement nOgatif (n0,200) entre la croissance absolue et le nombre dianneaux indiquait que liespacement des anneaux Otait positivement correlO ‡ la croissance somatique. La relation entre liespacement des anneaux et la croissance absolue Otait linOaire (espacement des anneaux (μm) = 0,528 × croissance absolue (mm) n 9,57). Les rOsultats indiquent que la croissance somatique affecte directement liespacement des anneaux. Liespacement des anneaux a OtO utile pour comparer la croissance moyenne ‡ partir de liOquation ci-dessus, tandis que le calcul rOtrospectif a OtO utile pour estimer la croissance individuelle. (Traduit par la ROdaction)

Mature male Pacific salmon (Genus Oncorhynchus) develop a dorsal hump, as a secondary male sexual characteristic, during the spawning period. Previous gross anatomical studies have indicated that the dorsal humps of salmon are mainly composed of cartilaginous tissue (Davidson [1935] J Morphol 57:169-183.) However, the histological and biochemical characteristics of such humps are poorly understood. In this study, the detailed microstructures and components of the dorsal humps of pink salmon were analyzed using histochemical techniques and electrophoresis. In mature males, free interneural spines and neural spines were located in a line near to the median septum of the dorsal hump. No cartilaginous tissue was detected within the dorsal hump. Fibrous and mucous connective tissues were mainly found in three regions of the dorsal hump: i) the median septum, ii) the distal region, and iii) the crescent-shaped region. Both the median septum and distal region consisted of connective tissue with a high water content, which contained elastic fibers and hyaluronic acid. It was also demonstrated that the lipid content of the dorsal hump connective tissue was markedly decreased in the mature males compared with the immature and maturing males. Although, the crescent-shaped region of the hump consisted of connective tissue, it did not contain elastic fibers, hyaluronic acid, or lipids. In an ultrastructural examination, it was found that all of the connective tissues in the dorsal hump were composed of collagen fibers. Gel electrophoresis of collagen extracts from these tissues found that the collagen in the dorsal hump is composed of Type I collagen, as is the case in salmon skin. These results indicate that in male pink salmon the dorsal hump is formed as a result of an increase in the amount of connective tissue, rather than cartilage, and the growth of free interneural spines and neural spines.

Mature male Pacific salmon (Genus Oncorhynchus) develop a dorsal hump, as a secondary male sexual characteristic, during the spawning period. Previous gross anatomical studies have indicated that the dorsal humps of salmon are mainly composed of cartilaginous tissue (Davidson [1935] J Morphol 57:169-183.) However, the histological and biochemical characteristics of such humps are poorly understood. In this study, the detailed microstructures and components of the dorsal humps of pink salmon were analyzed using histochemical techniques and electrophoresis. In mature males, free interneural spines and neural spines were located in a line near to the median septum of the dorsal hump. No cartilaginous tissue was detected within the dorsal hump. Fibrous and mucous connective tissues were mainly found in three regions of the dorsal hump: i) the median septum, ii) the distal region, and iii) the crescent-shaped region. Both the median septum and distal region consisted of connective tissue with a high water content, which contained elastic fibers and hyaluronic acid. It was also demonstrated that the lipid content of the dorsal hump connective tissue was markedly decreased in the mature males compared with the immature and maturing males. Although, the crescent-shaped region of the hump consisted of connective tissue, it did not contain elastic fibers, hyaluronic acid, or lipids. In an ultrastructural examination, it was found that all of the connective tissues in the dorsal hump were composed of collagen fibers. Gel electrophoresis of collagen extracts from these tissues found that the collagen in the dorsal hump is composed of Type I collagen, as is the case in salmon skin. These results indicate that in male pink salmon the dorsal hump is formed as a result of an increase in the amount of connective tissue, rather than cartilage, and the growth of free interneural spines and neural spines.