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1.
Biological features of chinook salmon Oncorhynchus tshawytscha from the Apuka River, the largest river of the northeastern Kamchatka inflowing Olyutorskii Bay of the Bering Sea, are studied.
Chinook salmon from the Apuka River spend mainly a year in the river before downstream migration to the sea. The fish live
in the sea for 1–4 years. The spawning migration of chinook salmon into the Apuka River begins in late May just after ice
melting, and it continues until early August. The main part of the spawners enters the river during June. A hypothesis on
the occurrence of two seasonal races in the Apuka River is proposed. 相似文献
2.
Results of studies of spawning chum salmon Oncorhynchus keta (Walbaum) in Olutorsky Bay and the Apuka River—the largest river in northeast Kamchatka—inflowing Olutorsky Bay of the Bering Sea are presented. It was established that the first individuals of the chum salmon enter the river together with early sockeye salmon and chinook salmon in the first ten-day period of June, and mass-spawning run takes place in July–August. Analysis of biological characteristics of chum salmon caught in the Apuka River and Olutorsky Bay of the Bering Sea enabled us to reveal the inhomogeneity of its spawning school represented by two seasonal forms. 相似文献
3.
The state of gonads, age, structure of scales, and size of specimens of the resident lacustrine form of sock-eyed salmon—kokanee
Onchorhynchus nerka—are analyzed. In stocked, previously fishless, lakes, there are specimens that have survived spawning and have remained active
for a year or several years. No evidence was found of the possibility of repeated spawning. Thus, such fish do not belong
to the spawning stock of the population, and their ecological function is not clear. 相似文献
4.
Chum salmon Oncorhynchus keta from the Tugur River of Khabarovsk krai was studied. It was found that, in the river basin, chum salmon of two ecological
groups reproduces: the first spawns at river sections with a pronounced underflow and the second spawns at river sections
with a groundwater outlet. In the first anadromous migration, usually three maxima of the number of approaches of migrating
fish are observed. The first in time maximum is represented by early (or summer) chum salmon, the second includes migrants
of early and late (or autumn) form, and the third is represented by chum salmon of only late form. Forms of chum salmon from
the Tugur River basin different in dates of the run and the spawning sites differ not only in the ecology of reproduction
but also in biological indices. The later chum salmon is larger; its gonads at entry into the river for spawning are less
mature as compared with early chum salmon. The autumn form of chum salmon reproducing at key spawning grounds is distributed
more widely than the summer form. It is found along the Asian coast from Chukotka in the north to Japan and Korea in the south.
Summer chum salmon occupies only part of the range of the autumn form. 相似文献
5.
Four Special Areas of Conservation (SACs) have been designated in the Republic of Ireland for Twaite shad, Alosa fallax (Lacépède), based on recent historical information on spawning activity—the estuarine reaches of the Rivers Munster Blackwater,
Suir, Barrow–Nore and Slaney. The spawning status of some of these populations is considered to have declined substantially
in recent years, and no known spawning areas of Allis shad, Alosa alosa (L.), are known for Ireland. Data are presented confirming the presence of both Allis shad and Twaite shad in all four SACs.
The majority of the material has come as by-catch from estuarine commercial salmon netsmen. Angling is the principal source
of material from the R. Barrow. Examination of scale and gonad material of Allis shad indicates some degree of readiness for
spawning as well as spawning having taken place. Gonadosomatic index (GSI) data from the R. Barrow for Twaite shad in the
May spawning period (2000–2002) had mean GSIs of 13.7–15% with maxima in the range of 21–28%. GSI values of 18% and 22% have
been recorded in the July period for individual Allis shad from the upper estuaries of the R. Slaney and R. Suir, respectively,
with both fish displaying gonad maturity stage V or VI (after Pina, 2000). Low GSI values have been recorded from other Allis shad in the June–July period displaying gonad condition varying from
stage III (immature) to stage VIII (spent). These findings point to a possibility that Allis shad do engage in spawning activity,
whether mono-specifically or with Twaite shad. The possibility of the latter is supported by gill raker count data presented.
These show clearly defined value ranges for Twaite and for Allis as well as a series of fish with intermediate counts. The
apparently low population levels of Twaite shad within the SACs identify a need to examine what measures might be undertaken
to ensure the favourable conservation status of this species.
Submitted for oral presentation to Fish Diadromy in Europe conference, 27.1.2005.
Guest editors: S. Dufour, E. Prévost, E. Rochard & P. Williot
Fish and diadromy in Europe (ecology, management, conservation) 相似文献
6.
Effects of Salmon-Borne Nutrients on Riparian Soils and Vegetation in Southwest Alaska 总被引:1,自引:0,他引:1
Spawning Pacific salmon (Oncorhynchus spp.) contribute marine-derived nutrients to riparian ecosystems, potentially affecting characteristics of the associated
soils and vegetation. We quantified these effects by comparing soil and vegetative characteristics upstream and downstream
of natural migratory barriers on ten spawning streams in southwest Alaska. Mean δ15N values—indicative of salmon-borne nutrients—were significantly higher in the O horizon and surface mineral soils downstream
of barriers (near spawning reaches) than in soils upstream of barriers (near non-spawning reaches). However, the mean total
N concentration in surface mineral soil was lower downstream than upstream. Mean foliar δ15N values were higher downstream for three plant species (Picea glauca, Salix alaxensis and Arctagrostis latifolia) with contrasting physiognomies. Mean overstory stem density was 100% higher downstream, primarily due to a fivefold difference
in the density of large-diameter willows (Salix spp.). Mean understory stem density was 47% lower downstream, also driven by a difference in willow density. Mean ground
layer non-vascular and dwarf shrub species covers were 28% and 73% lower downstream, respectively. Of the ten soil and vegetative
characteristics that differed upstream to downstream, two (O horizon and Picea glauca δ15N) were correlated with the density of spawning salmon. Collectively, the data suggest that salmon-borne nutrients alter riparian
soils and vegetation, while factors unrelated to salmon are responsible for the ultimate expression of many community characteristics. 相似文献
7.
Flores AM Shrimpton JM Patterson DA Hills JA Cooke SJ Yada T Moriyama S Hinch SG Farrell AP 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2012,182(1):77-90
Maturing adult sockeye salmon Oncorhynchus nerka were intercepted while migrating in the ocean and upstream in freshwater over a combined distance of more than 1,300 km to
determine physiological and endocrine changes associated with ionoregulation. Sockeye migrating through seawater and freshwater
showed consistent declines in gill Na+/K+-ATPase (NKA) activity, plasma osmolality and plasma chloride concentration. In contrast, plasma sodium concentration became
elevated in seawater as fish approached the river mouth and was then restored after sockeye entered the river. Accompanying
the movement from seawater to freshwater was a significant increase in mRNA for the NKA α1a subunit in the gill, with little
change in the α1b subunit. Potential endocrine signals stimulating the physiological changes during migration were assessed
by measuring plasma cortisol and prolactin (Prl) concentrations and quantifying mRNA extracted from the gill for glucocorticoid
receptors 1 and 2 (GR1 and GR2), mineralocorticoid receptor (MR), growth hormone 1 receptor (GH1R), and prolactin receptor
(PrlR). Plasma cortisol and prolactin concentrations were high in seawater suggesting a preparatory endocrine signal before
freshwater entry. Generally, the mRNA expression for GR1, GR2 and MR declined during migration, most notably after fish entered
freshwater. In contrast, PrlR mRNA increased throughout migration, particularly as sockeye approached the spawning grounds.
A highly significant association existed between gill PrlR mRNA and gill NKA α1a mRNA. GH1R mRNA also increased significantly,
but only after sockeye had migrated beyond tidal influence in the river and then again just before the fish reached the spawning
grounds. These findings suggest that cortisol and prolactin stimulate ionoregulation in the gill as sockeye salmon adapt to
freshwater. 相似文献
8.
Ola Ugedal Tor F. Næsje Eva B. Thorstad Torbjørn Forseth Laila M. Saksgård Tor G. Heggberget 《Hydrobiologia》2008,609(1):9-23
The River Alta, northern Norway (70°N), was regulated for hydropower in 1987. Densities of juveniles and catches of adult
Atlantic salmon have been studied since 1980–1981 to examine the effects of regulation. The need to control environmental
variables during electrofishing was emphasized, as flow variables explained up to 42% of the variation in estimated juvenile
densities. The number of spawning redds was counted along the river from 1996 to 2005. The annual number of spawning redds
was correlated with the catch of multi-sea-winter salmon (predominantly females). In the upper 7 km section, just downstream
of the power station outlet, juvenile densities were reduced by 80% from pre-regulation levels to minimum levels in 1992–1996.
This was followed by partial recovery during 1997–2005, although not entirely back to pre-regulation levels. In contrast,
the general trend in the middle part of the river was a linear increase in juvenile densities during 1981–2005. Decreased
juvenile densities in the upper section was subsequently followed by reduced catches of adult salmon in this part of the river.
The relative catches of smolt year classes migrating to sea in the upper section was reduced by up to 75% from 1991 onwards.
Spawning and recruitment in the upper section have increased in recent years, probably back to the introduction of catch-and-release
angling and an increase in salmon runs. However, present day smolt production in the upper section is still reduced compared
to the middle part of the river, 18 years after regulation. The decreased densities of juvenile salmon in the upper section
were probably caused by several factors, of which stranding mortality due to sudden drops in the water level and increased
winter mortality due to changed environmental conditions, especially reduced ice-cover, may be the most important. In conclusion,
the regulation caused a considerable reduction of the salmon production in the upper 16% of salmon reaches, but did not affect
the salmon population negatively further downstream. This study illustrates that apparently small environmental disturbances
can cause large changes in Atlantic salmon abundance in high latitude populations.
Guest editors: R. L. Welcomme & G. Marmulla
Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries 相似文献
9.
10.
E. D. Pavlov E. V. Mikodina M. A. Sedova N. G. Emel’yanova G. N. Markevich 《Journal of Ichthyology》2010,50(4):321-329
Morphology of gonads and structure of sex cells in females and males of the resident sockeye salmon Oncorhynchus nerka—kokanee—from Tolmachevskoe Reservoir are investigated. Anomalies in structure of sex cells and structure of oocytes are found.
Partial or mass resorpbion of cells in the ovaries of males and testes of males is found, leading to sterility of gonads.
The relationship between anomalies found in structure of the sex system of kokanee, changes in biological parameters of fish
and the increase of the population abundance is discussed. 相似文献
11.
Quetzalli Yasu Abadia-Chanona Marcial Arellano-Martinez Bertha Patricia Ceballos-Vazquez Francisco Benitez-Villalobos Geoff A. Parker 《Invertebrate reproduction & development.》2013,57(4):268-289
ABSTRACTReproductive studies of an intertidal free-spawning population of Chiton articulatus (Mollusca: Polyplacophora) from Puerto Angel, Oaxaca, Mexico were undertaken during 2011. We used gonad histology and gonadal indices to assess the relative gonad expenditure of the sexes (RGES) and other reproductive traits, accounting for individual and seasonal variation within this population. At this location, C. articulatus is gonochoric, without sexual dimorphism, except internally by gonad colour (testis is ‘salmon’ coloured and ovary olive green). Annual and monthly sex ratios (m/f) do not differ significantly from 1:1. Highest population-level gonadosomatic index (GSI) corresponded to maximum (peak) ripe stage (i.e. maximum gonad investment), with a first peak in May with a high value (8.4 ± 0.5) and a second peak during August-September with a lower value (4.7 ± 0.3). GSI fluctuated throughout year implying that gonad expenditure may be seasonally constrained, but with overall synchrony between sexes of ripe and spawning stages. July to December was the main reproductive season with some facultative spawning occurring off-season. Ripe and spawning RGES did not differ between sexes, suggesting that either sperm competition is intense and/or that sperm limitation is high. Early spawning individuals may quickly replenish their gametes for a second phase of gamete release later.Abbreviations: RGES: relative gonad expenditure of the sexes; GSI: gonadosomatic index; GDS: gonad developmental stages; MiMI: microscopic maturity index; SST: sea-surface temperature. 相似文献
12.
This study was conducted in order to evaluate seasonal migratory behaviour and reproductive pattern of lake sturgeon in a
confined region of the Mattagami River system in northern Ontario where river flow is regulated by hydroelectric works. Radio
tracking and the systematic sampling of lake sturgeon using gill nets indicated that the distribution of fish throughout the
study site varied on a seasonal basis. This distribution was related to the migration of individuals to potential spawning
sites in the spring, a post-spawning dispersal to feeding areas and late summer migration to an area of concentration on the
Groundhog River which is a tributary of the Mattagami River. There was a high proportion of fish (about 50%), within the size
range of reproductively active fish, found in the vicinity of suitable spawning habitat during early May. Measurement of the
gonadosomatic index (GSI) and plasma sex steroid hormone levels revealed a divergent pattern of reproductive development between
the sexes. Female sturgeon exhibited a prolonged period of ovarian regression following spawning. Resumption of ovarian development
was not evident until September and was characterized by an increased GSI and plasma levels of testosterone and 17β-estradiol.
In contrast, male lake sturgeon began testicular recrudescence within one month of spawning with the GSI reaching prespawning
levels by September; reproductive hormones were at prespawning levels by the end of June. It seems that hydroelectric works
has complex effects on sturgeon in the Mattagami system. The extensive migratory behaviour of lake sturgeon within the study
area make it prone to impingement or entrainment whereas the altered river flow appears to enhance reproductive development.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
After rearing to adulthood at sea, coho salmon (Oncorhynchus kisutch) return to freshwater to spawn once and then die on or near their spawning grounds. We tested the hypothesis that spawning
coho salmon return marine N and C to beaver (Castor canadensis) ponds of the Copper River Delta (CRD), Cordova, southcentral Alaska, thereby enhancing productivity of the aquatic food
webs that support juvenile coho salmon. We sampled three types of pond treatment: (1) natural enrichment by spawning salmon,
(2) artificial enrichment via addition of salmon carcasses and eggs, and (3) ponds with no salmon enrichment. All ponds supported
juvenile coho salmon. Seasonal samples of stable isotopes revealed that juvenile coho salmon, threespine sticklebacks (Gasterosteus aculeatus), caddisfly larvae, leeches, and chironomid midge larvae were enriched with marine N and C. The aquatic vascular plants bur
reed (Sparganium hyperboreum), pondweed (Potamogeton gramineus), and mare’s tail (Hippuris vulgaris) were enriched with marine N only. Riparian vegetation (Sitka alder Alnus viridis ssp. sinuata and willow Salix spp.) did not show enrichment. Artificial additions of adult carcasses and eggs of coho salmon increased the δ15N and δ13C values of juvenile coho salmon. In this dynamic and hydrologically complex coastal environment, spawning coho salmon contributed
marine N and C comprising 10–50% of the dietary needs of juvenile coho salmon through direct consumption of eggs and carcass
material. Invertebrates that have assimilated marine N and C yield a further indirect contribution. This perennial subsidy
maintains the productivity of the ecosystem of the coho salmon on the CRD. 相似文献
14.
Richard E. Brenner Steve D. Moffitt William S. Grant 《Environmental Biology of Fishes》2012,94(1):179-195
The straying of hatchery salmon may harm wild salmon populations through a variety of ecological and genetic mechanisms. Surveys
of pink (Oncorhynchus gorbuscha), chum (O. keta) and sockeye (O. nerka) salmon in wild salmon spawning locations in Prince William Sound (PWS), Alaska since 1997 show a wide range of hatchery
straying. The analysis of thermally marked otoliths collected from carcasses indicate that 0–98% of pink salmon, 0–63% of
chum salmon and 0–93% of sockeye salmon in spawning areas are hatchery fish, producing an unknown number of hatchery-wild
hybrids. Most spawning locations sampled (77%) had hatchery pink salmon from three or more hatcheries, and 51% had annual
escapements consisting of more than 10% hatchery pink salmon during at least one of the years surveyed. An exponential decay
model of the percentage of hatchery pink salmon strays with distance from hatcheries indicated that streams throughout PWS
contain more than 10% hatchery pink salmon. The prevalence of hatchery pink salmon strays in streams increased throughout
the spawning season, while the prevalence of hatchery chum salmon decreased. The level of hatchery salmon strays in many areas
of PWS are beyond all proposed thresholds (2–10%), which confounds wild salmon escapement goals and may harm the productivity,
genetic diversity and fitness of wild salmon in this region 相似文献
15.
K. V. Kuzishchin A. M. Malyutina M. A. Gruzdeva K. A. Savvaitova D. S. Pavlov 《Journal of Ichthyology》2009,49(6):441-453
In the Kol basin, one of the typical salmon rivers of Western Kamchatka, special traits of reproduction ecology of masu salmon Oncorhynchus masou are studied (characteristics and behavior of spawners during spawning, localization of spawning grounds, topography and hydrology of redds, and interaction with other species of salmonids). The masu salmon spawns in the Kol basin in tributaries of the upper reaches of the river and only in downwelling. Spawning grounds of masu samlmon are confined to stretches with overhanging banks, log jams creating shelters for spawners and favorable hydrological conditions for spawning and egg development. All over its range, masu salmon requires similar conditions for reproduction. In the north of its range, in Kamchatka, masu salmon retains the properties of the most warm-water species in the genus Oncorhynchus and selects for spawning the grounds characterized by the highest temperature in the period of spawning and development. 相似文献
16.
Vittoria Todisco Emil Fridolfsson Charlotte Axén Elin Dahlgren Maciej J. Ejsmond Marc M. Hauber Kjetil Hindar Petter Tibblin Markus Zöttl Linda Söderberg Samuel Hylander 《Journal of fish biology》2024,104(3):807-824
Thiamin is an essential water-soluble B vitamin known for its wide range of metabolic functions and antioxidant properties. Over the past decades, reproductive failures induced by thiamin deficiency have been observed in several salmonid species worldwide, but it is unclear why this micronutrient deficiency arises. Few studies have compared thiamin concentrations in systems of salmonid populations with or without documented thiamin deficiency. Moreover, it is not well known whether and how thiamin concentration changes during the marine feeding phase and the spawning migration. Therefore, samples of Atlantic salmon (Salmo salar) were collected when actively feeding in the open Baltic Sea, after the sea migration to natal rivers, after river migration, and during the spawning period. To compare populations of Baltic salmon with systems without documented thiamin deficiency, a population of landlocked salmon located in Lake Vänern (Sweden) was sampled as well as salmon from Norwegian rivers draining into the North Atlantic Ocean. Results showed the highest mean thiamin concentrations in Lake Vänern salmon, followed by North Atlantic, and the lowest in Baltic populations. Therefore, salmon in the Baltic Sea seem to be consistently more constrained by thiamin than those in other systems. Condition factor and body length had little to no effect on thiamin concentrations in all systems, suggesting that there is no relation between the body condition of salmon and thiamin deficiency. In our large spatiotemporal comparison of salmon populations, thiamin concentrations declined toward spawning in all studied systems, suggesting that the reduction in thiamin concentration arises as a natural consequence of starvation rather than to be related to thiamin deficiency in the system. These results suggest that factors affecting accumulation during the marine feeding phase are key for understanding the thiamin deficiency in salmonids. 相似文献
17.
Return migration of Atlantic Salmon in the River Tana: Phases of migratory behaviour 总被引:3,自引:0,他引:3
F. Øklamd § J. Erkinaro † K. Moen ‡ E. Niemelä ¶ P. Fiske R.S. McKinley | E. B. Thorstab 《Journal of fish biology》2001,59(4):862-874
From a total of 174 multi-sea-winter Atlantic salmon radio tagged in the Tanafjord (northern Norway, 70°N) during 1992 and 1993, 48 Atlantic salmon were followed from entering the River Tana until spawning. Three phases were identified: (1) migratory, direct or stepwise migration to, or close to the position held at spawning; (2) search, movements both up and down river at or close to the position held at spawning; (3) holding, a period without movements prior to spawning. During the migratory phase, Atlantic salmon migrated directly to near the spawning area, or stopped between one and nine shorter periods during the upstream migration. Number of stops increased with increasing migratory distance in 1993, but no such correlation was found in 1992. The highest migratory speeds were recorded in the lower parts of the river. A distinct change in migratory pattern was found in 67% of the Atlantic salmon near or at the area held at spawning. Most common was a search phase of erratic movements with more than one down river movement. After the movement terminated, 96% of the Atlantic salmon had a period when no or little movement was recorded until spawning (on average 55 days in 1992 and 51 days in 1993). There was no preference for staying at, up or down river from the spawning area during this holding period. Early ascending Atlantic salmon migrated to spawning areas further from the mouth than the later arriving Atlantic salmon in 1993, but not in 1992. The proportion of time spent on the migratory phase increased, while the proportion of time spent on the holding phase decreased with increasing distance to the spawning area. 相似文献
18.
EDUARDO G. MARTINS SCOTT G. HINCH DAVID A. PATTERSON MERRAN J. HAGUE STEVEN J. COOKE KRISTINA M. MILLER MICHAEL F. LAPOINTE KARL K. ENGLISH ANTHONY P. FARRELL 《Global Change Biology》2011,17(1):99-114
Mean summer water temperatures in the Fraser River (British Columbia, Canada) have increased by ~1.5 °C since the 1950s. In recent years, record high river temperatures during spawning migrations of Fraser River sockeye salmon (Oncorhynchus nerka) have been associated with high mortality events, raising concerns about long‐term viability of the numerous natal stocks faced with climate warming. In this study, the effect of freshwater thermal experience on spawning migration survival was estimated by fitting capture–recapture models to telemetry data collected for 1474 adults (captured in either the ocean or river between 2002 and 2007) from four Fraser River sockeye salmon stock‐aggregates (Chilko, Quesnel, Stellako‐Late Stuart and Adams). Survival of Adams sockeye salmon was the most impacted by warm temperatures encountered in the lower river, followed by that of Stellako‐Late Stuart and Quesnel. In contrast, survival of Chilko fish was insensitive to the encountered river temperature. In all stocks, in‐river survival of ocean‐captured sockeye salmon was higher than that of river‐captured fish and, generally, the difference was more pronounced under warm temperatures. The survival–temperature relationships for ocean‐captured fish were used to predict historic (1961–1990) and future (2010–2099) survival under simulated lower river thermal experiences for the Quesnel, Stellako‐Late Stuart and Adams stocks. A decrease of 9–16% in survival of all these stocks was predicted by the end of the century if the Fraser River continues to warm as expected. However, the decrease in future survival of Adams sockeye salmon would occur only if fish continue to enter the river abnormally early, towards warmer periods of the summer, as they have done since 1995. The survival estimates and predictions presented here are likely optimistic and emphasize the need to consider stock‐specific responses to temperature and climate warming into fisheries management and conservation strategies. 相似文献
19.
K. D. Simon Y. Bakar A. G. Mazlan C. C. Zaidi A. Samat A. Arshad S. E. Temple N. J. Brown-Peterson 《Environmental Biology of Fishes》2012,93(4):491-503
Various aspects of the reproductive biology of two archer fishes Toxotes chatareus and Toxotes jaculatrix were studied to describe gonad development, spawning season, sex ratio, and fecundity. Spawning season was assessed using
monthly changes in gonadosomatic index (GSI) and histological inspection of the gonads. Both species exhibit two modes of
oocytes; a mode of small primary growth oocytes and a single mode that increases with size as oocytes sequester vitellogenin
and undergo maturation, showing the synchronous oocyte development typical of total spawners. Based on GSI values and advanced
stages of oocyte maturity, T. chatareus and T. jaculatrix, females appear to spawn from November to December. The average fecundity of female T. chatareus was 55 000 ± 5538 eggs, and T. jaculatrix was 50 000 ± 3440 eggs; fecundity ranged from 20 000 to 150 000 eggs for both species, with relative fecundities of 600 to
1100 eggs/g body weight, and a mean value of 800 ± 32 for T. chatareus; relative fecundity ranged from 500 to 1100 with a mean value of 700 ± 23 for T. jaculatrix. Sex ratio, defined as the proportion of males to females, was 2.2 and 2.5 in T. chatareus and T. jaculatrix, respectively. The apparent abundance of males in samples could be due to females being positioned lower in the water column
and therefore being sampled less frequently. Our results indicate that in both species, spawning occurs between the months
of November and December during the monsoon season, which provides the mangrove coastal waters inhabited by these species
with an abundance of food resources and additional floodplain nursery habitat for larvae and juveniles. 相似文献
20.
Alexander M. Kaev 《Environmental Biology of Fishes》2012,94(1):207-218
In the Sakhalin-Kuril region hatchery culture of pink and chum salmon is of great importance compared to other regions of
the Russian Far East. During the last 30 years the number of hatcheries increased two-fold, and significant advances were
made in hatchery technologies. As a result, chum salmon capture in regions where hatcheries operate (southwestern and eastern
Sakhalin coasts, and Iturup Island) was 9 times as high during 2006–2010 than during 1986–1990, whereas wild chum salmon harvest
markedly declined. Recent dynamics in pink salmon catch appear to track trends in natural spawning in monitored index rivers,
suggesting natural-origin pink salmon play a dominant role in supporting the commercial fishery. It remains uncertain as to
whether hatcheries have substantially supplemented commercial catch of pink salmon in this region, and I recommend continued
research (including implementing mass marking and recovery programs) before decisions are made regarding increasing pink salmon
hatchery production. Location of hatcheries in spawning river basins poses problems for structuring a management system that
treats hatchery and wild populations separately. Debate continues regarding the existence and importance of density-dependent
processes operating in the ocean environment and the role hatcheries play in these processes. Loss of critical spawning habitat
for chum salmon in the Sakhalin-Kuril region has lead to significant declines in their abundance. I conclude by recommending
increases in releases of hatchery chum salmon numbers in the region to help recover depressed wild populations and provide
greater commercial fishing benefits in the region. 相似文献