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1.
Mitsuhiro Nagata Yasuyuki Miyakoshi Hirokazu Urabe Makoto Fujiwara Yoshitaka Sasaki Kiyoshi Kasugai Mitsuru Torao Daisei Ando Masahide Kaeriyama 《Environmental Biology of Fishes》2012,94(1):311-323
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. 相似文献
2.
Gregory T. Ruggerone Beverly A. Agler Jennifer L. Nielsen 《Environmental Biology of Fishes》2012,94(1):149-163
Increasing production of hatchery salmon over the past four decades has led to concerns about possible density-dependent effects
on wild Pacific salmon populations in the North Pacific Ocean. The concern arises because salmon from distant regions overlap
in the ocean, and wild salmon populations having low productivity may compete for food with abundant hatchery populations.
We tested the hypothesis that adult length-at-age, age-at-maturation, productivity, and abundance of a Norton Sound, Alaska,
chum salmon population were influenced by Asian hatchery chum salmon, which have become exceptionally abundant and surpassed
the abundance of wild chum salmon in the North Pacific beginning in the early 1980s. We found that smaller adult length-at-age,
delayed age-at-maturation, and reduced productivity and abundance of the Norton Sound salmon population were associated with
greater production of Asian hatchery chum salmon since 1965. Modeling of the density-dependent relationship, while controlling
for other influential variables, indicated that an increase in adult hatchery chum salmon abundance from 10 million to 80
million adult fish led to a 72% reduction in the abundance of the wild chum salmon population. These findings indicate that
competition with hatchery chum salmon contributed to the low productivity and abundance of Norton Sound chum salmon, which
includes several stocks that are classified as Stocks of Concern by the State of Alaska. This study provides new evidence
indicating that large-scale hatchery production may influence body size, age-at-maturation, productivity and abundance of
a distant wild salmon population. 相似文献
3.
Artificially grown native species are released into natural environments to increase biological resources or to recover threatened populations. Such stocks typically have enhanced survivability and may outcompete wild conspecifics as so-called native invaders. In addition, it is likely that the competitive effects of native invaders on native species are more intense than those of nonnative invaders. To test these hypotheses, an enclosure experiment was conducted using young-of-the-year wild and hatchery (normally grown to a relatively large size to increase survival after stocking) native masu salmon, Oncorhynchus masou, and nonnative brown trout, Salmo trutta (which attain a smaller size than masu salmon). Competitive effects between these fishes were evaluated in terms of stomach fullness and specific growth rate of the wild masu salmon. The magnitude of the relationship between stomach fullness and growth between the experimental treatments revealed a similar pattern, suggesting that competition for foraging habitat most affected their growth. Wild masu salmon were negatively affected by hatchery conspecifics, and the effects were greater than those caused by brown trout. We propose that these outcomes were caused by competitive dominance as a consequence of body size differences. In conclusion, the results support the hypothesis that size-enhanced hatchery masu salmon have the potential to function as native invaders, and the negative effects of artificial stocks on wild masu salmon could be greater than those caused by a nonnative invader. 相似文献
4.
Early marine trophic interactions of wild and hatchery chum salmon (Oncorhynchus keta) were examined as a potential cause for the decline in harvests of adult wild chum salmon in Taku Inlet, Southeast Alaska.
In 2004 and 2005, outmigrating juvenile chum salmon were sampled in nearshore habitats of the inlet (spring) and in epipelagic
habitat at Icy Strait (summer) as they approached the Gulf of Alaska. Fish were frozen for energy density determination or
preserved for diet analyses, and hatchery stocks were identified from the presence of thermal marks on otoliths. We compared
feeding intensity, diets, energy density, and size relationships of wild and hatchery stocks (n = 3123) across locations and weeks. Only hatchery fish feeding intensity was negatively correlated with fish abundance. In
both years, hatchery chum salmon were initially larger and had greater energy density than wild fish, but lost condition in
early weeks after release as they adapted to feeding on wild prey assemblages. Diets differed between the stocks at all inlet
locations, but did not differ for hatchery salmon between littoral and neritic habitats in the outer inlet, where the stocks
overlapped most. Both diets and energy density converged by late June. Therefore, if density-dependent interactions affect
wild chum salmon, these effects must be very rapid because survivors in Icy Strait showed few differences. Our study also
demonstrates that hatchery release strategies used near Taku Inlet successfully promote early spatial segregation and prey
partitioning, which reduce the probability of competition between wild and hatchery chum salmon stocks. 相似文献
5.
Masahide Kaeriyama Hyunju Seo Hideaki Kudo Mitsuhiro Nagata 《Environmental Biology of Fishes》2012,94(1):165-177
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. 相似文献
6.
Maksimovich AA 《Zhurnal evoliutsionno? biokhimii i fiziologii》2008,44(1):51-59
A complex of adaptive changes occurring in the Pacific salmon fry in the process of migration to the sea is described, including behavior, ion content in carcasses, and morphological changes in Stannius bodies, gill epithelium, and nephron tubular epithelium. Participating in experiments with transfer from fresh water into a two-layer aquarium (the lower layer - sea water, the upper layer - fresh water) were smolts of chum salmon and underyearlings of masu salmon as well as the trachurus and leiurus forms of the three-spined stickleback Casterosteus aculeatus. All fish, regardless of their salt preference, at once after placement into the two-layer aquarium, occupied the sea water zone, at the very bottom of the aquarium. After 1 h, there started brief excursions of masu salmon and chum salmon to the upper, fresh water layer; however, both forms of the three-spined stickleback did not participate in these excursions. After 12 h, the chum salmon settled down in the lower, sea water layer, while the masu salmon - in the upper, fresh water layer. Both forms of the three-spined stickleback never left the sea water layer and felt quite comfortably on the aquarium bottom. It seems that the high tolerance of the both stickleback forms to wide salinity limits allows them to choose the convenient position regardless of the water salt composition. By analyzing the material obtained for three years (2001-2003) on structure and functions of the gill epithelium chloride cells (CC), we have come to the conclusion that the fresh water fry of two salmon species, chum and masu salmons, caught at the same time and practically in the same water reservoirs can be divided into three groups. The underyearlings of the masu salmon as a rule are characterized by the thickened epithelium of secondary gill lamellae, but by a very small number of CC. In smolts of chum salmon, on the contrary, the epithelium is sufficiently thin, but enriched in the CC that demonstrate an active structure in the very beginning of migration to sea. However, with approaching the sea (and with an increase of terms of migration) the CC activity drops, but their amount does not change. And only after migration to the sea the CC activity rises again, although their amount seems to remain unchanged. The described peculiarities of behavior and of the ion composition regulation in the migrating salmon fry confirm the hypothesis that the salmons evolutionized in fresh water, that the Oncorhynchus genus appeared in large spaces of saltish waters, such as the Japan Sea at the period of the early Pleistocene, and that learning of fry of the Oncorhynchus genus (for instance, of O. gorbuscha and O. keta) is the most specialized in the salmons migrating to the sea, whereas the fresh water species of chars (Salvelinus) and of trouts (Salmo) are more primitive. 相似文献
7.
Genetic implications of hatchery rearing in Atlantic salmon: effects of rearing environment on genetic composition 总被引:5,自引:0,他引:5
W. W. Crozier 《Journal of fish biology》1998,52(5):1014-1025
In an experiment to investigate genetic consequences of hatchery rearing in salmon, allozyme variation at five polymorphic loci was examined in Atlantic salmon of known initial genetic composition, which were reared throughout freshwater life in the hatchery or stocked into the wild as swim-up fry. The genetic composition of the juveniles in the hatchery remained homogeneous from fertilization up to stocking, and from stocking to 2+ in the wild, however, those remaining at the hatchery developed genetic differences among smolting and nonsmolting 1+ parr. These differences were attributed to conditions leading to early smolting at 1+ among the hatchery fish, with 1+ smolts diverging from the gene pool from which they were derived, whereas those stocked into the wild did not smolt until a year later and retained the original genetic composition. The results are discussed in relation to hatchery rearing of salmon and implications for the use of reared fish in stocking and enhancement programmes. 相似文献
8.
We review studies of interactions between hatchery and wild Pacific salmon in the Russian Far East. This includes the role of hatchery practices that result in premature migration to the sea and increased mortality, and data on feeding and territorial competition between juveniles of hatchery and wild origin. In the course of downstream migration many juvenile hatchery salmon are eliminated by wild salmon predation. During the marine period, Japanese hatchery chum salmon (Oncorhynchus keta) distribution overlaps the distribution of Russian wild salmon. Consequently, replacement of wild populations by hatchery fishes, as a result of abundant juvenile hatchery releases combined with extensive poaching in spawning grounds, is apparent in some Russian rivers. Interactions between the populations occur in all habitats. The importance of conservation of wild salmon populations requires a more detailed study of the consequences of interactions between natural and artificially reared fishes. 相似文献
9.
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
10.
R. Czerniawski M. Pilecka‐Rapacz J. Domagala 《Zeitschrift fur angewandte Ichthyologie》2011,27(4):984-989
Survival rate and growth parameters of Atlantic salmon fry and sea trout fry were determined after stocking in the wild. Before release (22 May 2009) into the wild the larvae were reared for 10 weeks in the hatchery in three groups: (i) fry fed on live zooplankton , (ii) fry fed on larvae of live nekton, and (iii) fry fed on prepared pellet food. In autumn (15 September 2010) the fish were caught in the wild; the survival rate and growth parameters of both Atlantic salmon and sea trout were the highest in the zooplankton‐fed group, whilst the pellet‐fed group had the lowest survival rate and growth value parameters. Most effective food for hatchery‐reared fishes to be used as stock was the natural living zooplankton. The general conclusion is that the live diet supplied in the rearing period has a positively impact on fish survival in the wild. 相似文献
11.
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
12.
There has been very little effort to understand genetic divergence between wild and hatchery populations of masu salmon (Oncorhynchus masou). In this study, we used mitochondrial (mt) NADH dehydrogenase subunit 5 gene (ND5) and six polymorphic nuclear microsatellite DNA loci to compare the genetic variability in three hatchery broodstocks of
masu salmon with the variability in eight putative wild masu populations sampled in five rivers including one known source
river for the hatchery broodstocks. Both ND5 and microsatellites showed no significant genetic divergence (based on FST estimates) between four annual collections from the source river population, suggesting no change in genetic diversity over
this time period. The FST estimates, an analysis of molecular variance (AMOVA), and a neighbor-joining tree using both DNA markers suggested significant
differentiation between the three hatchery and all eight putative wild populations. We conclude that genetic diversity of
hatchery populations are low relative to putative wild populations of masu salmon, and we discuss the implications for conservation
and fisheries management in Hokkaido. 相似文献
13.
Behavioural experiments using artificial and natural stream channels were undertaken to determine whether there were differences in dispersal between newly emerged male and female masu salmon. Eyed eggs from a cross with wild spawners were planted in the middle pool of an artificial channel. After emergence, more males than females moved into an upstream trap, while fewer males moved downstream. In a natural stream, eyed eggs were marked with alizarin complexone to distinguish them from naturally spawned eggs and these were planted into artificial redds. More newly emerged male fry remained at the planted site than female fry. In contrast, more females moved downstream than males. These results imply that differences in dispersal patterns between male and female masu salmon fry are genetically controlled. 相似文献
14.
The purpose of this review is to provide a global perspective on Oncorhynchus salmonine introductions and put-and-take fisheries based on modern stocking programs, with special emphasis on freshwater
ecosystems. We survey the global introductions of nine selected salmonines of the genus Oncorhynchus: golden trout, cutthroat trout, pink salmon, chum salmon, coho salmon, masu/cherry salmon, rainbow trout/steelhead, sockeye
salmon/kokanee, and chinook salmon. The information is organized on a geographical basis by continent, and then by species
and chronology. Two different objectives and associated definitions of ‘success’ for introductions are distinguished: (a)
seed introduction: release of individuals with the purpose of creating a wild-reproducing, self-sustaining population; and
(b) put-and-take introduction: release of individuals with the purpose of maintaining some level of wild population abundance,
regardless of wild reproduction. We identify four major phenomena regarding global salmonine introductions: (1) general inadequacy
of documentation regarding introductions; (2) a fundamental disconnect between management actions and ecological consequences
of introductions; (3) the importance of global climate change on success of previous and future introductions; and (4) the
significance of aquaculture as a key uncertainty in accidental introductions. We conclude this review with a recognition of
the need to terminate ongoing stocking programs for introduced salmonines worldwide. 相似文献
15.
Interspecific relationships between Atlantic salmon and coho salmon were studied at early life stages in laboratory and semi-natural stream channels. During emergence, the survival and dispersal patterns were similar for the two species in single or mixed populations. Survival of Atlantic salmon fry was reduced in the presence of older coho fry. However, no predation was observed. Microdistribution differed between the two species, with Atlantic salmon fry more numerous in riffles when coho were present.
Coho juveniles had a pelagic and gregarious distribution, in contrast to the benthic behaviour of the Atlantic salmon. In laboratory streams, Atlantic salmon fry moved out or adopted a subordinate cryptic behaviour which allowed them to escape predation while negatively affecting their growth. 相似文献
Coho juveniles had a pelagic and gregarious distribution, in contrast to the benthic behaviour of the Atlantic salmon. In laboratory streams, Atlantic salmon fry moved out or adopted a subordinate cryptic behaviour which allowed them to escape predation while negatively affecting their growth. 相似文献
16.
《Journal of morphology》2017,278(7):948-959
Mature male Pacific salmon (Genus Oncorhynchus ) demonstrate prominent morphological changes, such as the development of a dorsal hump. The degree of dorsal hump formation depends on the species in Pacific salmon. It is generally accepted that mature males of sockeye (O. nerka ) and pink (O. gorbuscha ) salmon develop most pronounced dorsal humps. The internal structure of the dorsal hump in pink salmon has been confirmed in detail. In this study, the dorsal hump morphologies were analyzed in four Pacific salmon species inhabiting Japan, masu (O. masou ), sockeye, chum (O. keta ), and pink salmon. The internal structure of the dorsal humps also depended on the species; sockeye and pink salmon showed conspicuous development of connective tissue and growth of bone tissues in the dorsal tissues. Masu and chum salmon exhibited less‐pronounced increases in connective tissues and bone growth. Hyaluronic acid was clearly detected in dorsal hump connective tissue by histochemistry, except for in masu salmon. The lipid content in dorsal hump connective tissue was richer in masu and chum salmon than in sockeye and pink salmon. These results revealed that the patterns of dorsal hump formation differed among species, and especially sockeye and pink salmon develop pronounced dorsal humps through both increases in the amount of connective tissue and the growth of bone tissues. In contrast, masu and chum salmon develop their dorsal humps by the growth of bone tissues, rather than the development of connective tissue. 相似文献
17.
Yasuyuki Miyakoshi Hirokazu Urabe Hayato Saneyoshi Tomoya Aoyama Hiroyuki Sakamoto Daisei Ando Kiyoshi Kasugai Yoshio Mishima Masayuki Takada Mitsuhiro Nagata 《Environmental Biology of Fishes》2012,94(1):197-206
Since the late 20th century, the biomass of Pacific salmon Oncorhynchus spp. has increased. Hokkaido, northern Japan, is one of the main areas of chum salmon O. keta production in the North Pacific and intensive hatchery programs support the recent high abundance. However, proper management
of naturally spawning populations is necessary to conserve healthy stocks of this species. In 2008, we started a program to
assess the naturally spawning chum salmon populations in Hokkaido. Of the total of approximately 1,500 rivers in Hokkaido,
238 rivers with lengths of longer than 8 km (excluding those rivers used for hatchery broodstock collection) were surveyed
in 2008 and 2009. The number of non-enhanced rivers found to contain naturally reproducing chum salmon was 59 (31.4% of surveyed
rivers) and 50 (37.6% of surveyed rivers) rivers in 2008 and 2009, respectively. Including the rivers where hatchery broodstock
were collected and rivers shorter than 8 km that contain naturally spawning chum salmon, chum salmon ascended at least 191
and 175 rivers in Hokkaido in 2008 and 2009, respectively. Repeated foot surveys indicated that the run timings of naturally
spawning chum salmon may be affected by coastal commercial fisheries. This study showed that naturally spawning chum salmon
remain in many rivers in Hokkaido where hatchery programs have been intensively conducted. 相似文献
18.
Aggregate hatchery production of Pacific salmon in the Kamchatka region of the Russian Federation is very low (< 0.5% of total
harvest, with five hatcheries releasing approximately 41 M juvenile salmon annually), but contributions in certain rivers
can be substantial. Enhancement programs in these rivers may strongly influence fitness and production of wild salmon. In
this paper we document significant divergence in demographic traits in hatchery salmon populations in the Bolshaya River and
we estimate the proportion of hatchery chum salmon in the total run in the Paratunka River to demonstrate the magnitude of
enhancement in this system. We observed a reduction in the expression of life history types in hatchery populations (ranging
from 1 to 9 types) compared to wild populations (17 types) of sockeye salmon in the Bolshaya River. We found similar trends
in Chinook salmon in the same river system. This reduced life history diversity may make these fish less resilient to changes
in habitat and climate. We estimate hatchery chum salmon currently contribute 17-45% to the natural spawning population in
the Paratunka River. As hatchery fish increase in numbers at natural spawning sites, this hatchery production may affect wild
salmon production. It is important to investigate the risk of introgression between hatchery and wild salmon that can lead
to reduction in salmon fitness in Kamchatka rivers, as well as the potential of ecological interactions that can have consequences
on status of wild salmon and overall salmon production in this region. 相似文献
19.
Sundström LF Lõhmus M Devlin RH 《Evolution; international journal of organic evolution》2005,59(7):1560-1569
Substantial evidence from the animal kingdom shows that there is a trade-off between benefits and costs associated with rapid somatic growth. One would therefore expect growth rates under natural conditions to be close to an evolutionary optimum. Nevertheless, natural selection in many salmonid species appears to be toward larger size and earlier emergence from spawning redds, indicating a potential for increased growth rate to evolve. We tested how selection for genetic variants (growth hormone transgenic coho salmon, Oncorhynchus kisutch, with more than doubled daily growth rate potential relative to wild genotypes) depended on predator timing and food abundance during the early period of life (fry stage). In artificial redds, fry of the fast-growing genotypes showed a highly significant developmental shift, emerging from gravel nests approximately two weeks sooner, but with an 18.6% reduced survival, relative to wild-genotype fry. In seminatural streams, fry of the fast-growing genotypes suffered higher predation than those of wild genotypes when predators were present at the time of fry emergence, but this difference was less pronounced when food was scarce. In streams where predators were introduced after emergence, fry survived equally well regardless of food availability. Surviving fry grew faster in habitats provided with more food, and fast-growing genotypes also grew faster than wild genotypes when predators arrived late and food was abundant. Fewer fish migrated downstream past a waterfall when food availability was high and in the presence of predators, and wild-genotype fry were more likely to migrate than fry of the fast-growing genotypes. After being returned to the experimental streams after migration, fast-growing genotypes survived equally well as those of the same genotypes that did not migrate, whereas migrating wild genotypes experienced higher mortality relative to those of the same genotypes that did not migrate. Comparisons of growth rates between siblings retained under hatchery conditions and those from habitats with the fastest growth in the experimental stream revealed that growth rates were similar for wild genotypes in both environments, whereas the fast-growing genotypes in the streams only realized 90% of their growth potential. The present study has shown that a major shift in developmental timing can alter critical early stages affecting survival and can have a significant effect on fitness. Furthermore, ecological conditions such as food abundance and predation pressure can strongly influence the potential for fast-growing variants to survive under natural conditions. The large-scale removal of many predatory species around the world may augment the evolution of increased intrinsic growth rates in some taxa. 相似文献
20.
Bioenergetics modeling was used to estimate zooplankton prey consumption of hatchery and unmarked stocks of juvenile chum salmon (Oncorhynchus keta) migrating seaward in littoral (nearshore) and neritic (epipelagic offshore) marine habitats of southeastern Alaska. A series of model runs were completed using biophysical data collected in Icy Strait, a regional salmon migration corridor, in May, June, July, August, and September of 2001. These data included a temperature (1-m surface versus surface to 20-m average), zooplankton standing crop (surface to 20-m depth versus entire water column), chum salmon diet (percent weight of prey type consumed), energy densities, and weight. Known numbers of hatchery releases were used in a cohort reconstruction model to estimate total abundance of hatchery and wild chum salmon in the northern region of southeastern Alaska, given average survival to adults and for two different (low and high) early marine littoral mortality rate assumptions. Total prey consumption was relatively insensitive to temperature differences associated with the depths potentially utilized by juvenile chum salmon. However, the magnitudes and temporal patterns of total prey consumed differed dramatically between the low and high mortality rate assumptions. Daily consumption rates from the bioenergetics model and CPUE abundance from sampling in Icy Strait were used to estimate amount and percentage of zooplankton standing crop consumed by mixed stocks of chum salmon. We estimated that only a small percentage of the available zooplankton was consumed by juvenile chum salmon, even during peak abundances of marked hatchery and unmarked mixed stocks in July. Total daily consumption of zooplankton by all stock groups of juvenile chum salmon was estimated to be between 330 and 1764 g/km2d1 from June to September in the neritic habitat of Icy Strait. As with any modeling exercise, model outputs can be misleading if input parameters and underlying assumptions are not valid; therefore, additional studies are warranted, especially to determine physiological input parameters, and to improve abundance and mortality estimates specific to juvenile chum salmon. Future bioenergetics modeling is also needed to evaluate consumption by the highly abundant, vertically migrating planktivorous that co-occurred in our study; we suggest that these fishes have a greater impact on the zooplankton standing crop in Icy Strait than do hatchery stock groups of juvenile chum salmon. 相似文献