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1.
The species and size composition of euphausiids consumed by Pacific hake ( Merluccius productus ) along the south-west coast of Vancouver Island were monitored during the 1989, 1990 and 1995–97 summer feeding seasons. Thysanoessa spinifera and Euphausia pacifica were the only euphausiid species eaten by hake. Hake persisted in selecting krill longer than 17 mm and consistently preferred T. spinifera, even though there was a substantial reduction in euphausiid abundance, a change in species composition and a shift in the size distribution to smaller individuals after the 1992–93 warm water years. The biomass of euphausiids available to hake after 1993 averaged 27% of that for 1991, the pre-ENSO year, and was 12% of the 1991 value in 1996. Hake predation was not responsible for the reduction in euphausiid abundance, as it was already low at euphausiid sizes smaller than those eaten by hake.  相似文献   

2.
The diet of Notoscopelus japonicus , one of the dominant mesopelagic fishes in the transitional waters of the western North Pacific, was examined in 106 specimens collected over the continental slope off the Pacific coast of northern Japan during April and October 1996. The prey comprised mainly crustaceans, such as copepods, ostracods, euphausiids and amphipods. Euphausia pacifica was the dominant prey, representing 83.1% by number and 72.4% by wet weight of the total diet. Between April and October, there was no shift in prey species consumed, but prey size decreased significantly and prey number per fish stomach increased in October. These results indicate that, in October, N. japonicus consumed larger numbers of smaller E. pacifica , rather than shifting to other prey taxa. The pronounced importance of E. pacifica in the diet was ascribed to its co-occurrence with N. japonicus at night in the surface layer and during the daytime in the near-bottom layer.  相似文献   

3.
This study evaluates the influence of oceanic variability on plankton and fish production in a coastal upwelling system off southern Vancouver Island, British Columbia, Canada. A trophodynamics model is used to hind-cast plankton and fish production as estimated by empirical seasonal patterns in upwelling, sea surface temperature, solar radiation, and by biomasses of Pacific hake (Merluccius productus) and Pacific herring (Clupea pallasi). Simulation results indicate that interannual and longer-term variability in coastal plankton production occurs, and that the patterns are primarily determined by the dynamics in the initiation and intensity of coastal upwelling. Fish properties are greatly influenced by zooplankton, with simulated hake production being correlated with summer euphausiid production, and measured herring condition being correlated with autumn zooplankton production. An evaluation of transfer efficiencies indicates that interannual variability in the diatom-to-fish transfer is high (CV = 78%), with the majority of this variability occurring in the diatom-to-zooplankton component of the transfer. Seasonal dynamics of the diatom-to-zooplankton transfer result from the effects of upwelling on diatom production, and subsequent trophodynamic phasing with copepods and euphausiids.  相似文献   

4.
The abundance and stomach contents of salmonids (Oncorhynchus spp.) and the biomass of prey organisms were examined in the central subarctic Pacific and Bering Sea in the summer of 1991 and 1992. Salmonids were caught by surface longline using the same level of fishing effort. Chum (O. keta) and pink (O. gorbuscha) salmon were the predominant species, representing 44% and 36% sof the total catch (n = 1275) in 1991. In 1992, chum salmon composed 85% of the total catch (n = 603), but the catch of pink salmon decreased to 1% of the total catch due to the odd/even year fluctuation of Asian pink salmon abundance in the study area. It was found that chum salmon changed their dominant diet from gelatinous zooplankton (pteropods, appendicular-ians, jellyfishes, chaetognaths, polychaetes and unidentified materials) in 1991, when pink salmon were abundant, to a diet of crustaceans (euphausiids, cope-pods, amphipods, ostracods, mysids and decapods) in 1992, when pink salmon were less abundant. Local crustacean biomass (wet weight; mg m-3) had significant negative correlation with the CPUE (catch number per 30 hachi) of pink salmon in 1991 (r = -0.586; P = 0.026) and that of chum salmon in 1992 (r =–0.616; P = 0.014). There may be a limitation in the available prey resource for production of salmonids.  相似文献   

5.
ABSTRACT:   The feeding habits of Lampanyctus jordani , an abundant mesopelagic fish in the subarctic North Pacific, was examined based on the stomach contents of 721 specimens collected over the continental slope off the Tohoku area, Pacific coast of northern Japan during April and October from 1996 to 1998. The prey items comprised mainly crustaceans such as copepods, amphipods, euphausiids and decapods. Euphausiids were the most important items in the diet both during April and October. During April, when the annual maximum of zooplankton biomass occurred and the Oyashio Intrusion Current prevailed, L. jordani fed intensively and consumed a high proportion of Euphausia pacifica . These seasonal variations also influenced the feeding intensity and dietary diversity. Feeding intensity, measured by the stomach contents index, was higher during April than October, reflecting the higher biomass of zooplankton in the Tohoku area during spring. The dietary diversity of L. jordani was lower during April than October, indicating that L. jordani shifted to a wider variety of prey when the availability of E. pacifica was limited.  相似文献   

6.
Long-term variability in zooplankton biomass in the subarctic Pacific Ocean   总被引：11，自引：0，他引：11  
Zooplankton collections from the subarctic Pacific were analyzed from two periods (1956–1962 and 1980–1989). In this report, we document: 1) a positive correlation between the intensity of winter winds and subsequent summer zooplankton biomass in the subarctic gyre within these periods; and 2) a doubling of zooplankton biomass and a similar increase in pelagic fish and squid abundance between these two periods of time. Some possible explanations for these changes are considered.  相似文献   

7.
黄海中部小黄鱼的食物组成和摄食习性的季节变化   总被引：21，自引：6，他引：21       下载免费PDF全文
根据2001年3月至2002年1月在黄海中部海域进行的4个季节的定点底拖网调查,应用聚类分析、单因素方差分析和列联表检验等方法,对小黄鱼(Pseudosciaena polyactis Bleeker)的食物组成和摄食的季节变化进行研究.结果表明,小黄鱼摄食的饵料种类有30余种,甲壳类(磷虾类和虾类)和鱼类是其主要的饵料类群,二者在食物中所占的重量百分比之和为97.45%.优势饵料种类有太平洋磷虾(Euphausia pacifica)、脊腹褐虾(Crangon affinis)、细螯虾(Leptochela gracilis)和赤鼻棱鳀(Thryssa kammalensis).小黄鱼的摄食强度有显著的季节变化,秋季最高,春季和冬季较低.食物组成也随季节的不同而有所变化,夏季主要以虾类为食,其它季节则主要以磷虾类为食.聚类分析的结果表明,小黄鱼春、夏季的食物组成与秋、冬季相比,存在较大差异.通过与历史资料进行比较发现,黄海小黄鱼的食物组成发生了较大的变化,其中鳀鱼(Engraulis japonicus)在食物中所占的比例有明显的下降.  相似文献   

8.
ABSTRACT:   Seasonal changes in distribution and abundance of euphausiids off south-eastern Hokkaido (41°−43°N), Sanriku (38°−41°N), and Joban (36°−38°N) were investigated using cylindrical-conical nets every two months from March 1997 to February 1998. Twenty-six species of seven genera of euphausiids occurred during the survey. Among them, subarctic-transitional Euphausia pacifica was the most abundant throughout the year in coastal waters, as their relative contribution to the total abundance of euphausiids was 89–92%. This species occurred in each coastal water throughout the survey and was abundant from winter to early summer (February–June) off Sanriku and Joban and in autumn in south-eastern Hokkaido. Thysanoessa inspinata occurred off south-eastern Hokkaido and Sanriku throughout the survey, mainly in spring (April) but rarely occurred off Joban. Three other subarctic Thysanoessa species occurred mainly off south-eastern Hokkaido from winter to spring. Conversely, warm- and transitional-water epipelagic species occurred exclusively off Sanriku and Joban in autumn. The characteristics of seasonal distributional patterns of euphausiids are discussed in relation to the spatial and temporal changes of oceanographic conditions and several predators off north-eastern Japan.  相似文献   

9.
The biomass distribution, community structure and species composition of the dominant micronektonic animals were determined in the western tropical Pacific, using day/night sampling from upper 200 m depth with a commercial midwater otter trawl in fall‐winter of 1994, 1995 and 1997. Night‐time micronekton biomass was significantly higher than daytime biomass except for a few cases. All the night‐time catches had similar taxonomic composition, dominated by myctophid fishes, small squids, shrimps and euphausiids. Night‐time micronekton biomass in the upper 200 m was assumed to be higher in the North Equatorial Counter Current than in the North Equatorial Current, reflecting the zooplankton biomass distribution which micronektons feed on at night. A total of 42 species of myctophid fishes, 34 species of squids, 27 species of shrimps and six species of euphausiids were collected. Community types of each dominant taxonomic group were classified by cluster analysis based on the species composition. A station located north of the subtropical convergence zone was distinct from other tropical stations south of the convergence zone, having significantly different species composition in three of the four dominant taxonomic groups (myctophids, squids and shrimps). The interaction between the larvae of commercially important fishes and micronektonic animals is discussed.  相似文献   

10.
I explored the biological basis of variation in recruitment (age 3 abundance), growth and age‐specific adult survival rate for the major populations [West Coast Vancouver Island (WCVI), Strait of Georgia, Central Coast, North Coast and Haida Gwaii] of Pacific herring (Clupea pallasi) that inhabit British Columbian waters. The analyses were based on a synthesis of time series of empirical observations of herring population characteristics (egg deposition, age‐specific abundance and size) and prey, competitor and predator biomass/abundance. Recruitment was not correlated among populations. Recruitment variability was explained for WCVI herring only, as a consequence of prey (the euphausiid Thysanoessa spinifera) biomass during August in each of the first 3 years of life, and the biomass of piscivorous Pacific hake (Merluccius productus) during the first year of life. Recruit mass and adult mass‐at‐age were correlated among populations and over ages within populations. Recruit mass was affected by T. spinifera biomass in August of the first and third years of life. Adult mass‐at‐age variability was determined mainly by size at the beginning of the growth season, but also by T. spinifera biomass in August. Age‐specific adult survival rates were not correlated among the five populations. Survival rates decreased with age; there were additional population‐specific effects of somatic mass and T. spinifera biomass in August. The analyses were repeated using physical oceanographic explanatory variables. Only recruit mass variation was explained significantly by physical oceanographic variables, and the biological‐based explanation of recruit mass variability accounted for more of the variation.  相似文献   

11.
ABSTRACT:   Biomass and production of Euphausia pacifica off south-eastern Hokkaido (41–43°N), Sanriku (38–41°N), and Joban (36–38°N) were investigated every two months from March 1997 to February 1998. High biomass was found in summer–autumn off south-eastern Hokkaido, and in the late winter–early summer off Sanriku and Joban. Annual mean biomass was 381, 314 and 258 mg C/m2 off south-eastern Hokkaido, Sanriku, and Joban, respectively. The total production (sum of flesh, moults and eggs) during the survey period off south-eastern Hokkaido (3829 mg C/m2) was comparable with that off Sanriku (3872 mg C/m2); both were much higher than that off Joban (2243 mg C/m2). Somatic production during the survey period contributed the highest proportion (51.5–70.9%) to the total production in each coastal area. The somatic production–biomass ratio in each coastal area (5.2–6.9) was an intermediate value among 25 populations of 16 euphausiid species previously reported. This effect resulted from the negative factor of stagnated growth of adults during summer–winter, coupled with positive factors including continuous occurrence of larvae which show high growth rate throughout the year off Sanriku and Joban, and the numerous larvae occurring in October off south-eastern Hokkaido.  相似文献   

12.
ABSTRACT:     The biomass of bighand thornyhead Sebastolobus macrochir was increased by the high recruitment success of the 1999–2002 year classes off the Pacific coast of northern Honshu, Japan. In this study, the growth of bighand thornyhead was examined over a 9-year period from 1996 to 2004 in this area. The growth of the 1999 year class and the 2000–2002 year classes was reduced at 3 and 2 years old, respectively, while the 1999–2002 year classes were smaller than the 1993–1998 year classes. In 2-, 3- and 4-year-old fish, the relationship between abundance and mean standard length was expressed by negative linear regressions, while fish became smaller when abundance of the year class was larger. Mean bottom temperatures were stable at depths of 350–900 m; variations in water temperature were small in the main distribution area of bighand thornyhead. We discuss the factors affecting the growth of bighand thornyhead via changes in the demersal fish community and feeding habits.  相似文献   

13.
Large‐scale shifts occurred in climatic and oceanic conditions in 1925, 1947, 1977, 1989 and possibly 1998. These shifts affected the mix and abundance of suites of coexisting species during each period of relative environmental stability—from primary producers to apex predators. However, the 1989 regime shift was not a simple reversal of the 1977 shift. The regime shifts occurred abruptly and were neither random variations nor simple reversals to the previous conditions. Timing of these anomalous environmental events in the North Pacific Ocean appears to be linked to physical and biological responses in other oceanic regions of the world. Changes in the atmospheric pressure can alter wind patterns that affect oceanic circulation and physical properties such as salinity and depth of the thermocline. This, in turn, affects primary and secondary production. Data from the North Pacific indicate that regime shifts can have opposite effects on species living in different domains, or can affect similar species living within a single domain in opposite ways. Climatic forcing appears to indirectly affect fish and marine mammal populations through changes in the distribution and abundance of their predators and prey. Effects of regime shifts on marine ecosystems are also manifested faster at lower trophic levels. Natural variability in the productivity of fish stocks in association with regime shifts indicates that new approaches to managing fisheries should incorporate climatic as well as fisheries effects.  相似文献   

14.
Information on prey availability, diets, and trophic levels of fish predators and their prey provides a link between physical and biological changes in the ecosystem and subsequent productivity (growth and survival) of fish populations. In this study two long‐term data sets on summer diets of steelhead (Oncorhynchus mykiss) in international waters of the central North Pacific Ocean (CNP; 1991–2009) and Gulf of Alaska (GOA; 1993–2002) were evaluated to identify potential drivers of steelhead productivity in the North Pacific. Stable isotopes of steelhead muscle tissue were assessed to corroborate the results of stomach content analysis. We found the composition of steelhead diets varied by ocean age group, region, and year. In both the GOA and CNP, gonatid squid (Berryteuthis anonychus) were the most influential component of steelhead diets, leading to higher prey energy densities and stomach fullness. Stomach contents during an exceptionally warm year in the GOA and CNP (1997) were characterized by high diversity of prey with low energy density, few squid, and a large amount of potentially toxic debris (e.g., plastic). Indicators of good diets (high proportions of squid and high prey energy density) were negatively correlated with abundance of wild populations of eastern Kamchatka pink salmon (O. gorbuscha) in the CNP. In conclusion, interannual variations in climate, abundance of squid, and density‐dependent interactions with highly‐abundant stocks of pink salmon were identified as potential key drivers of steelhead productivity in these ecosystems. Additional research in genetic stock identification is needed to link these potential drivers of productivity to individual populations.  相似文献   

15.
象山港三种不同养殖方式对浮游动物群落的影响   总被引：1，自引：0，他引：1  
为探究不同营养类型养殖方式对半封闭海湾浮游生态系统的影响,于2015年在象山港的鱼类网箱养殖、牡蛎筏式养殖和海带筏式养殖3种养殖区内外分别进行大、中型和中、小型浮游动物群落及相关环境因子的四季研究。结果显示,牡蛎养殖区内大、中型浮游动物群落结构变化明显,夏、秋季优势种太平洋纺锤水蚤的优势度下降,冬季优势种腹针胸刺水蚤的优势度上升;网箱养殖区内浮游动物群落变化不明显,变化主要为大、中型浮游动物优势种,春、冬季腹针胸刺水蚤的优势度下降,秋季优势种种类组成变化明显;海带养殖区内浮游动物群落和优势种变化均不明显。此外,3种养殖方式对浮游动物的生物量、丰度和α多样性均未产生明显影响。结合象山港的水文特征和养殖区内外的环境因子,研究表明,牡蛎养殖区浮游动物群落变化是牡蛎滤食行为和铁港水交换能力差的综合结果,而浮游动物优势种变化可能与水体总磷含量较高有关;因目前网箱养殖规模小且西沪港水动力条件较好,网箱区内局部环境和浮游动物的变化较小;海带养殖因面积小且仅春、冬季养殖,不足以对水质和浮游动物产生影响。此外,本研究显示不同环境中,大、中型浮游动物群落结构的变异较中、小型浮游动物明显,这可能与中、小型浮游动物群落的稳定性较高有关。  相似文献   

16.
钱塘江富阳段鱼类资源现状   总被引：3，自引：0，他引：3  
2014年11月—2015年12月对钱塘江富阳江段3个断面鱼类资源进行了逐月采样调查,对该水域鱼类种类组成、优势种、群落多样性指数和捕捞量进行分析。结果显示:共采集鱼类48种,隶属8目13科37属,其中鲤科鱼类种类最多,占总种类数的64.58%,优势种为鲢、鲤、鲫和光泽黄颡鱼。各月中,4月份捕获的鱼类种数最多,占总种数的52.08%;9月份鱼类捕获量最高,占总渔获量的17.85%。Margalef丰富度指数4月份较高,2月份较低;Shannon-Wiener多样性指数和Pielou均匀度指数在7月份较高,9月份较低,而Simpson多样性指数与之相反。富阳段鱼类捕捞强度较大,渔获物中小个体鱼类占主要部分。与历史记录比较,富阳江段鱼类群落组成已经发生了显著变化,除本地种光泽黄颡鱼外,增殖放流鱼种已成为了优势或重要种群。  相似文献   

17.
Seasonal and spatial variation in a prairie stream-fish assemblage   总被引：5，自引：1，他引：5  
Abstract – Stream-fish assemblage and environmental data for 13 sites in the upper Brazos River, Texas, USA during 1997 and 1998 were used to assess the relationship between environmental conditions, and seasonal and spatial variation in fish species abundance and distribution patterns. There was considerable spatial variation in environmental conditions among sites. Spatial variation in species diversity and species composition was related to variation in conductance (salinity), depth and current velocity among sites and streams. Species diversity increased downstream and species composition shifted from primarily cyprinodontids upstream to cyprinids downstream. Among all dominant species, spatial components of variation in fish abundance were greater than seasonal components, suggesting that assemblage structure is determined more by average or persistent differences in environmental conditions among sites than by seasonal variation in environmental conditions.  相似文献   

18.
Abstract– In this study we asked whether the fish populations of residual pools in a seasonally fluctuating African river varied between years. We used a series of data on the fish of the permanent floodplain pools of the River Sokoto, Nigeria compiled by M. J. Holden (1963) to address this objective. Holden provided estimates for the size and biomass of fish populations in 12 permanent dry season pools over a period of 2 to 3 years. On average, only 22% of the species present in a pool were absent from that pool in the following sampling period. Despite low interannual variability in the species composition of the pools, rank correlation analysis indlcated significant variation in the relative numbers and biomass of the 10 most numerically abundant species in most pools. Altering the spatial scale of analysis to include all possible combinations of 2 and 6 pools did not affect the results. Indices of similarity also indicated relatively high annual variability in the relative abundance of species in the pool communities. We suggest that habitat selection may contribute to the continued occurrence of fish species in pools from year to year, and such factors as changes in the overall abundance of fish species in the system and haphazard trapping during flood decline may contribute to annual variation in their relative abundance.  相似文献   

19.
Pacific and Atlantic herring populations (genus Clupea) commonly experience episodic collapse and recovery. Recovery time durations are of great importance for the sustainability of fisheries and ecosystems. We collated information from 64 herring populations to characterize herring fluctuations and determine the time scales at low biomass and at high and low recruitment, and use generalized linear models and Random Survival Forests to identify the most important bottom‐up, top‐down and intrinsic factors influencing recovery times. Compared to non‐forage fish taxa, herring decline to lower minima, recover to higher maxima and show larger changes in biomass, implying herring are more prone to booms and busts than non‐forage fish species. Large year classes are more common in herring, but occur infrequently and are uncorrelated among regionally grouped stocks, implying local drivers of high recruitment. Management differs between Pacific and Atlantic herring fisheries, where at similarly low biomass, Pacific fisheries tend to be closed while Atlantic fisheries remain open. This difference had no apparent effect on herring recovery times, which averaged 11 years, although most stocks with longer recovery periods had not yet recovered at the end of the observation period. Biomass recovery is best explained by median recruitment and variability in sea surface height anomalies and sea surface temperatures—higher variability leads to shorter recovery times. In addition, the duration of recruitment failure is closely linked with low biomass. While recovery times rely on the nature of the relationship between spawning biomass and recruitment, they are still largely governed by complex and uncertain processes.  相似文献   

20.
渤海鱼类群落结构的年际变化   总被引：3，自引：2，他引：1  
基于2010年和2012–2014年每年8月渤海渔业资源底拖网调查数据,根据优势种、单位个体重、相对资源量、Jaccard种类组成相似性系数和群落结构数量生物量曲线等指标,研究渤海鱼类群落结构的年际变化,结果显示:(1)2010年和2012–2013年,总鱼类和底层鱼类种类数一直呈下降趋势,2014年有所恢复;2010年和2012–2014年暖温种种类数基本上呈下降趋势;(2)底层鱼类优势种由小个体的虾虎鱼(Gobiini sp.)代替大个体的小黄鱼(Pseudosciaena polyactis),中上层鱼类优势种则由植食性为主的黄鲫(Setipinna taty)和斑(Konosirus punctatus)转向浮游动物食性的鳀(Engraulis japonicus);(3)2010年和2012–2014年渤海底层鱼类和总鱼类年间站位相对资源量两两间都不存在显著性差异(P0.05),2013年与2014年间总鱼类及2014年与2010年底层鱼类年间站位相对资源量方差无显著性差异(P0.05),其他年份两两间都为方差不齐(P0.05),底层鱼类和总鱼类站位相对资源量年际存在极端异常值;(4)2010年和2012–2014年单位数量鱼体的个体重逐年下降,渤海鱼类这几年严重趋向小型化;(5)5种组内相似、组间相异贡献率高的鱼类种类,其年度相对资源量和分布变化较大;根据生物量与数量优势度曲线及W统计值判断,2010年渤海鱼类群落结构比较稳定,2012年相对稳定,2013年和2014年处于干扰状态,特别是2013年的鱼类群落结构处于比较严重的干扰状态。综上所述,渤海鱼类群落结构在2010年和2012–2014年发生了较大改变,处于受干扰不稳定状态。  相似文献   

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