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1.
Hake recruitment has been examined in relation to environmental variables in two of the main reproductive areas of the central Mediterranean, the northern and central Tyrrhenian Sea. Seventeen years time series data from trawl surveys revealed high fluctuations in recruit abundance that could not be just explained by spawning biomass estimations. Generalized additive models were developed to investigate hake recruitment dynamics in the Tyrrhenian Sea in relation to spawner abundance and selected key oceanographic variables. Environmental data were explored in attempt to explain survival processes that could affect early life history stages of hake and that accounted for high fluctuations in its recruitment.Thermal anomalies in summer, characterised by high peaks in water temperature, revealed a negative effect on the abundance of recruits in autumn, probably due to a reduction in hake egg and larval survival rates. In the northern Tyrrhenian, recruitment was reduced when elevated sea-surface temperatures were coupled with lower levels of water circulation. Enhanced spring primary production, related to late winter low temperatures could affect water mass productivity in the following months, thus influencing spring recruitment. In the central Tyrrhenian a dome-shaped relationship between wind mixing in early spring and recruitment could be interpreted as an “optimal environmental window” in which intermediate water mixing level played a positive role in phytoplankton displacement, larval feeding rate and appropriate larval drift. Results are discussed in relation to the decline in hake stock biomass and within the present climate change and global warming context.  相似文献   

2.
根据2014年10月、2015年3月、5月和8月在桑沟湾养殖水域开展的海洋调查所获取的营养盐状况调查数据,分析了营养盐含量的季节变化和平面分布,并对该水域营养水平状况进行了评价.结果显示,该海域秋季溶解无机氮(DIN)含量明显高于其他三个季节.夏季NO2-N的平均含量最高,秋季NO3-N的平均含量最高,春季NH4-N的平均含量最高,冬季PO4-P的平均含量最高.与海水水质标准相比,各季节DIN总体水平均低于海水一类标准值,春季和夏季PO4-P总体水平低于海水一类标准值,秋季和冬季PO4-P总体水平则高于海水一类标准值.从平面分布看,春季DIN含量呈湾内低、湾外高的趋势,夏季和秋季呈湾内高、湾外低的趋势,冬季呈自湾内南部水域向北逐渐降低的趋势.春季和冬季PO4-P含量均呈自湾内中部水域向外逐渐下降的趋势,夏季呈自湾内中部水域向外逐渐上升的趋势;秋季则呈湾内高、湾外低的趋势.春季、夏季和冬季N/P比值均高于Redfield比值,无机磷相对缺乏,而秋季N/P比值与Redfield比值基本一致.根据潜在性富营养化评价模式,桑沟湾养殖海域四个季节的营养水平较低,均属贫营养水平.与20世纪八九十年代相比,桑沟湾浮游植物生长的主要限制性因素已由整体的氮限制转变为春、夏季磷限制为主.  相似文献   

3.
Declines in landings of the hairtail Trichiurus japonicas indicate the need for more effective management of this species. Hairtail spawning peaks occur twice yearly in the Bungo Channel, in spring and autumn. Relationships between hairtail stock and brood seasonality were examined to determine if an association between either and a decline in landings existed. Stock assessments show that the biomass of both spring and autumn hairtail broods from within and around the Bungo Channel are decreasing, with a rapid reduction in spring-brood stock abundance after 2007 largely responsible for decreased landings. Yield and spawning per recruitment analyses indicate current fishing pressure to be higher than several reference points. We suggest that fishing pressure needs to be reduced by at least 20% of the current level for this fishery to remain sustainable, as the projected stock abundance and catch demonstrate that the current fishing pressure is unsustainable. Analysis of time-series data of recruits per spawning revealed spring-brood recruitment to have been strong in year classes 2003 and 2005. Of various options available for improved management of this fishery, we propose that fishing pressure should be reduced in the years following the appearance of strong year classes to increase future biomasses and landings.  相似文献   

4.
流沙湾是中国海水珍珠“南珠”的主产区和广东省重要的贝类养殖区。为评估湾内养殖活动的环境效应,于2015~2016年对流沙湾海区进行了夏(8月)、秋(11月)、冬(2月)、春(5月) 4个季节的浮游植物和海水理化因子调查。共检出浮游植物171种,包括硅藻门43属122种、甲藻门 10属44种、蓝藻门2属2种、金藻门2属2种和裸藻门1属1种。流沙湾内湾浮游植物细胞丰度为(0.05~79.04)×104个/L,夏季>春季>秋季>冬季,且夏季丰度远大于其他三季,内湾和外湾差异不显著。春季须状角毛藻(Chaetoceros crinitus)、红海束毛藻(Trichodesmium erythraeum)和明壁圆筛藻(Coscinodiscus debilis)为主要优势种,夏季优势种主要为中肋骨条藻(Skeletonema costatum),秋季优势种主要为拟弯角毛藻(Chaetoceros pseudocurvisetus)、奇异棍形藻(Bacillaria paradoxa)、洛氏角毛藻(Chaetoceros lorenzianus),冬季主要优势种为威氏圆筛藻(Coscinodisus wailesii)、柔弱根管藻(Rhizosolenia delicatula)、岛脆杆藻(Fragilaria islandica)。其中,奇异棍形藻为春、秋、冬季的优势种,红海束毛藻为春、夏、秋季的优势种。冗余分析表明,流沙湾浮游植物优势种在春季与水温和氨氮密切相关,夏季受透明度显著影响,而在秋、冬季受亚硝酸氮含量影响显著。流沙湾不同养殖区的浮游植物多态性和丰度有明显季节差异。与2012年相比,流沙湾外湾的养殖覆盖率提高了近50%,内湾的珍珠贝养殖减少了近90%,养殖品种、规模和分布格局都发生了明显变化,目前流沙湾的浮游植物群落特征正是对其变化的一种响应。夏季鱼类网箱养殖提高了水域营养盐水平并降低了浮游植物多样性。大规模的扇贝养殖则导致了扇贝养殖区浮游植物丰度的降低。  相似文献   

5.
The neon flying squid (Ommastrephes bartramii), which is the target of an important North Pacific fishery, is comprised of an autumn and winter–spring cohort. During summer, there is a clear separation of mantle length (ML) between the autumn (ML range: 38–46 cm) and the winter–spring cohorts (ML range: 16–28 cm) despite their apparently contiguous hatching periods. We examined oceanic conditions associated with spawning/nursery and northward migration habitats of the two different‐sized cohorts. The seasonal meridional movement of the sea surface temperature (SST) range at which spawning is thought to occur (21–25°C) indicates that the spawning ground occurs farther north during autumn (28–34°N) than winter–spring (20–28°N). The autumn spawning ground coincides with the Subtropical Frontal Zone (STFZ), characterized by enhanced productivity in winter because of its close proximity to the Transition Zone Chlorophyll Front (TZCF), which move south to the STFZ from the Subarctic Boundary. Hence this area is thought to become a food‐rich nursery ground in winter. The winter–spring spawning ground, on the other hand, coincides with the Subtropical Domain, which is less productive throughout the year. Furthermore, as the TZCF and SST front migrate northward in spring and summer, the autumn cohort has the advantage of being in the SST front and productive area north of the chlorophyll front, whereas the winter–spring cohort remains to the south in a less productive area. Thus, the autumn cohort can utilize a food‐rich habitat from winter through summer, which, we hypothesize, causes its members to grow larger than those in the winter–spring cohort in summer.  相似文献   

6.
为了探明陵水湾浮游动物饵料情况,本研究依据2014年11月(秋季)、2015年5月(春季)、8月(夏季)和2016年1月(冬季)陵水湾4个航次的调查资料,分析了该海湾浮游动物的种类组成、优势种、丰度和生物量、生物多样性等群落结构特征及其影响因素。调查共发现浮游动物94种和浮游幼虫21类,其中桡足类(Copepoda)最多,有38种,其次是水螅水母类(Hydromedusae)11种,毛颚类(Chaetognatha)8种,其余类群种类数在1~6种之间。浮游动物群落主要由广温广盐类群、暖水沿岸类群和暖水外海类群组成,优势种主要分布在前两个类群,无全年优势种;浮游幼虫是陵水湾的重要类群,丰度呈现为冬季(低温)高于春季(高温)。与亚热带海域不同,低温已不再是制约陵水湾海洋生物生长的主要因子。浮游动物丰度和生物量均呈现为秋季最高,春季最低,冬季高于夏季。浮游动物群落物种Shannon-Wiener指数(H¢)和均匀度指数(J¢)的变化趋势一致,表现为春夏季高,秋冬季低,湾外高,湾内低。聚类分析结果表明,陵水湾浮游动物可分为湾内和湾外两个群落,主要受地形阻隔所致。盐度与浮游动物丰度和生物量均呈显著负相关关系,是浮游动物季节变化的主要影响因子之一。根据陵水湾浮游动物年均生物量估算出浮游动物提供的渔产潜力为2.24×10~4 kg。陵水湾浮游动物丰度呈现剧烈的季节变化,有必要对其进行长期的跟踪监测。  相似文献   

7.
Embryonic mortality, egg production and the spawning stock biomass of Pacific anchovy, Engraulis japonicus , off Southern Korea during 1983–1994, and their biological response to oceanographic features in spring and summer, were analysed. The instantaneous mortality rate (IMR) of embryonic stages decreased in spring and increased in summer, with a range of 0.33–1.23 day–1 in spring and 0.78–1.69 day–1 in summer. Egg production in summer was three times that during spring and production was low in the late 1980s. Mean lengths of yolk-sac larvae and adult females were greater in spring than in summer, whereas spawning fraction and spawning stock ratio (spawning biomass:adult biomass) were lower in spring than summer. Estimated mean spawning stock biomass ranged from 141 × 103 to 380 × 103 MT in spring and from 221 × 103 to 557 × 103 MT in summer. Statistically, the seasonal and long-term trends of embryonic mortality, egg production and spawning stock biomass of Pacific anchovy can be explained largely by spring warming, summer cooling and by less abundant zooplankton in the late 1980s.  相似文献   

8.
Biomass and duration of the over-wintering period of the Rügen spring spawning herring stock (RHS) in the Sound (ICES Subdivison 23) were investigated as well as possible hydrographical factors affecting relative distribution and triggering southwards migration towards the spawning grounds. Monitoring was performed during 27 surveys over a 6-year period (1993–1998). Abundance of 45–165 000 t in August–February, 5–60 000 t in March–May, and <2000 t in June–July was found. This indicates a longer over-wintering period than hitherto assumed. The year classes 1988, 1991 and 1994 were relatively strong occurring in the Sound from age 2 (winter-rings) and abundance in autumn 1993 and 1996–1997 was relatively high. Relative year class strengths are in accordance with variations in larval indices at the spawning grounds. Decreasing abundance in late spring in the Sound was concordant with observed peaks in commercial landings and (subsequent) peak larval indices at the spawning grounds. Larger size groups seem to migrate southwards in spring before smaller herring size groups. Peak herring densities occur in the northern Sound in autumn and they do not concentrate near the southern Drogden threshold in spring before southwards spawning migration. Highest densities were found from 8 to 22 m below sea surface, and just below or in the halocline in areas with stratified water column. Indications of inflows to the Baltic triggering southwards migration can be observed at some occasions, however, these results are not conclusive because of relatively few biomass estimates in 1996–1998. The identified patterns in herring occurrence agree with some conclusions on migration routes for RHS from previously reported tagging studies, but the present investigations indicate prolonged over-wintering in the Sound. This report quantifies the abundance and distribution of herring in the Sound over the year on basis of repeated investigations, and investigates possible influence of hydrographical factors on distribution and migration.  相似文献   

9.
吴金浩  刘桂英  王年斌  李爱 《水产科学》2011,30(11):708-710
2008—2009年春、夏、秋、冬4个季节,对青堆子湾进行了水质调查。调查结果表明,青堆子湾海域各个季节的化学需氧量、无机氮、无机磷等含量均符合Ⅱ类海水水质标准,一般表现为夏、秋季含量高于春、冬季;青堆子湾海域春、夏、秋、冬季的氮、磷比值分别为35.5,169.7,22.3和77.9,均大于Redfield比值(16),水体大部分时间磷比较缺乏。利用现有的营养状态质量法对青堆子湾的富营养化水平现状进行了评价,结果显示青堆子湾春夏秋冬4个季节的营养状态质量指数分别为2.34、6.99、3.95、1.80,夏季和秋季呈现富营养化水平,但控制因子各不相同,夏季富营养化主要控制因子是叶绿素a,而秋季富营养化是化学需氧量、总氮、总磷及叶绿素a共同作用的结果。  相似文献   

10.
Kenji Taki 《Fisheries Science》2007,73(5):1094-1103
ABSTRACT:   Seasonal and interannual variations in abundance of Euphausia pacifica off north-eastern Japan were examined using Remodeled Norpac net samples collected from April 1993 to February 2000. Spawning occurred mainly during April–June and August–October in every year. When abundance of eggs was high in May, those of larval and immature stages in May–June and small adults (≤15 mm) during July–October tended to be high. There were high positive correlations between monthly average abundance of eggs in May–June and average abundance of small adults during July–October. However, there was low or negative correlation between monthly abundance of eggs in April and average abundance of small adults during July–October. Recruitment time to adult takes approximately 3 months, so these results suggest that small adults during July–October are mainly derived from spawning in May–June, but rarely from spawning in April. The apparent decrease in abundance of small adults from summer to winter was observed every year despite active spawning during August–October, which would recruit to adults in late autumn–winter. The possible effects on recruitment and mortality are discussed in relation to starvation and predation caused by low temperatures and low available food abundance.  相似文献   

11.
为了解流沙湾养殖活动对浮游动物群落的影响,于2015—2016年对流沙湾海区进行了夏(8月)、秋(11月)、冬(2月)、春(5月)4个季度的浮游动物调查,分析了浮游动物群落特征及其与环境因子的相关性。共记录浮游动物18大类119种、浮游幼体17种。浮游动物种类组成以桡足类(45种)和端足类(20种)为主,其次为毛颚类(15种)、水螅水母类(12种)、等足类(6种)等。十足目幼体(Decapod larvae)为春、夏两季的主要优势类群,亚强次真哲水蚤( Subeucalanus subcrassus)、微驼隆哲水蚤(Acrocalanus gracilis)为秋季主要优势种,夜光虫(Noctiluca scintillans )为冬季主要优势种。年均浮游动物丰度和生物量分别为151.53个·m^-3 和73.48 mg·m^-3 。多维尺度分析(nMDS)结果表明,除春季外,流沙湾内湾浮游动物群落组成与外湾差异明显。典范对应分析(CCA)显示,溶解氧、磷酸盐、透明度、温度和硝酸盐等环境因子是影响浮游动物优势种分布的主要因素。在流沙湾海区,鱼类小网箱的养殖活动在夏秋两季对浮游动物群落组成和结构影响较大;贝类养殖区的浮游动物的丰度和生物量明显降低,但浮游动物群落组成及多样性与其它采样点差异不大。  相似文献   

12.
Eastern Bering Sea pollock have two distinctly different stable spawning grounds—along the shelf and in the eastern and central Aleutian Islands between 400 and 500 m water columns. Pollock spawning behavior supports the hypothesis that the shelf and deepwater “basin” spawning pollock are completely independent reproductive stocks. Deepwater pollock inhabit the shelf and, once mature at age 5–6 years, migrate from the shelf onto the continental slope into the Zhemchug, Pribilof, and Bering canyons by the end of winter. Bering Sea pollock recruitment and year class abundance have high annual variability, but there are no clear relationships between pollock year class strength and water temperature, ice distribution or survival on early ontogenesis stages (eggs and larvae). Young-of-the-year fish survival varies dramatically during winter supporting the hypothesis that the Bering Sea pollock recruitment and strength of year class have high annual variability depending on young-of-the-year fish survival during winter. The annual change of physical oceanography condition, productivity and species composition of zooplankton community are associated with great differences in pollock seasonal migrations and distribution, reproduction, survival of recruits at early stages of development and finally with abundance of year classes and total biomass. Implementation of ecosystem-based fishery management most important for application of pollock research both of Russian national program and on base of International Agreements.  相似文献   

13.
长江口渔场渔业生物群落结构的季节变化   总被引:18,自引:4,他引:18  
利用2000~2002年在长江口渔场的底拖网调查资料,运用多样性指数和相似性指数,对该水域的渔业生物群落结构季节变化进行了研究。结果表明:该域的渔业生物群落以鱼类为主要生物类群,占有绝对优势;甲壳类和头足类为其次要组成部分,处于生态劣势。群落生物量以秋季最大,春季最小。渔业生物群落的丰度、多样性以及均匀度以春冬季较高,夏秋季较低,造成这种趋势的原因可能是与带鱼(Trichiurusjaponicus)和小黄鱼(Larimichthyspolyactis)的洄游有关。渔获物组成春冬季之间、夏秋季之间的相似性指数较高。  相似文献   

14.
Abstract  The Argentine sandperch, Pseudopercis semifasciata (Cuvier), is the target of unregulated recreational and artisanal fisheries within the northern Patagonian gulfs of Argentina. Being a reef species, the applicability of conventional large-scale assessment and management approaches appear limited. A more suitable alternative might be offered by spatial approaches, but their effectiveness would depend on the species' degree of mobility. Underwater visual censuses were used to study the annual occupation pattern of shallow rocky reefs by P. semifasciata to evaluate the possible occurrence of spawning migrations and the potential of reserves to protect the stocks. The abundance of P. semifasciata was greatest in winter, intermediate in autumn and lowest in spring and summer, but densities were relatively stable and oscillated ±17–31% around the overall mean for each reef. There was no evidence of spawning migrations as no demographic changes were observed throughout the year. Young sandperches (<1 year old) were never observed on the reefs. Implications of the results for the management of this species are discussed.  相似文献   

15.
为了解北方典型养殖海湾——桑沟湾水域浮游植物群落结构的时空变化特征及其影响因素,于2017年4月(春季)、7月(夏季)、11月(秋季)和2018年1月(冬季)对桑沟湾水域21个站点进行4个航次的大面调查.结果显示,调查期间,该湾共采集到浮游植物31属51种,其中,硅藻(Diatom)24属43种,甲藻(Dinoflag...  相似文献   

16.
岱衢洋鱼类资源及其群落多样性的季节变化   总被引:3,自引:1,他引:2  
根据2010年春季(5月)、夏季(8月)、秋季(11月)与2011年冬季(2月)对岱衢洋进行的共4个航次的底拖网渔业资源调查资料, 对该海域的鱼类资源状况及其多样性进行了分析, 结果表明: 所捕获的38种鱼分别隶属于1门2纲8目21科31属; 暖温性鱼类无论在种类数量还是生物量与尾数密度方面均居主导地位; 凤鲚四季均为该海域的优势种; 在时间分布上, 生物量与资源尾数密度均以夏季为最高, 而冬季则恰好相反, 且该两季的生物量与资源尾数密度间均存在显著差异(P<0.05), 另外, 在空间分布上, 生物量与尾数密度四季总体上均呈北高南低、东高西低的趋势; 生物量与平均底层温度呈二次曲线相关(P<0.01); 春、秋两季的Margalef丰富度指数( D )、Shannon-Wiener多样性指数( H' )和Pielou均匀度指数( J' )均存在显著差异(P<0.05); 与东海近、外海海域鱼类群落的多样性比较, 岱衢洋的Shannon- Wiener多样性指数( H' )较低。  相似文献   

17.
为探讨东海近岸海域浮游动物时空分布特征,根据2013年5月(春季)、8月(夏季)和12月(冬季)东海近岸海域3个航次的浮游动物调查资料,分析了该海域春季、夏季和冬季浮游动物的种类组成、丰度与生物量、优势种季节变化及生态类群。结果显示,3个航次共鉴定浮游动物108种(含未定种),浮游幼体14类,隶属于7门15大类,其中桡足类和水母类的种类和数量占绝对优势,桡足类为最优势类群,共47种,占总种数的43.52%,水母类共19种,占总种数的17.59%。浮游动物种类季节变化较为明显,夏季种类显著高于春季和冬季。各季节浮游动物种类数目与纬度呈负相关。浮游动物平均丰度与平均生物量随季节变化较为明显,其中平均丰度与平均生物量冬季最低,平均生物量夏季最高,平均丰度春季最高。根据浮游动物对水文环境条件耐受性和生活海区的差异性将浮游动物群落分为6个生态类群:近岸低盐种、广温广盐种、高温高盐种、近岸暖温种、暖水种和大洋广布种。其中东海北部近岸海域春、冬季近岸低盐种和广温广盐种占绝对优势,夏季暖水性种群所占比例高;长江口及邻近水域暖水性种群在春、夏、冬三季中均占主导地位;东海中南部近岸海域春、冬季暖水性种群占绝对优势,但夏季高温高盐种、大洋广布种优势明显。各季节中华哲水蚤均为优势种,但其他优势种季节更替较明显,其中春、夏两季优势种更替率为90.9%,夏、秋两季为50%。  相似文献   

18.
Pejerrey Odontesthes bonariensis spawning period takes place during the end of winter and spring and, depending on temperature conditions, during late summer and autumn. Nevertheless, the occurrence and quality of the summer–autumn spawning period have not been well documented and are not considered for aquaculture production. In this context, this study aimed to characterize the reproductive activity of pejerrey reared in captivity under natural conditions of temperature and photoperiod throughout a year in order to summarize the spawning quality of the two spawning periods. The present results showed that pejerrey might spawn from late winter to the end of the spring with a peak in October (mid‐spring) and, also during summer and early autumn, interrupted by a period of 56 days without spawning activity in between. The extension of both spawning periods was almost equal (67 and 69 days). Nevertheless, higher relative fecundity and larger egg size were observed during the first spawning period, associated with higher levels of oestradiol measured in females demonstrating that it is better than the second spawning. The fertilization rate was not affected throughout the reproductive periods. These differences in the reproductive parameters are discussed in order to design specific strategies to increase seed production.  相似文献   

19.
长江口潮下带大型底栖动物群落特征   总被引:1,自引:0,他引:1  
2013年至2014年,对长江口及其邻近水域进行了8个航次104个站点的潮下带大型底栖动物调查,通过Shannon-Wiener多样性指数(H)、Pielou种类均匀度(E)、种类丰度(D)和优势度指数(Y)等指标参数分析了大型底栖动物的物种多样性,应用等级聚类和非度量多维标度排序分析了底栖动物群落结构。结果显示,2013年共采获大型底栖动物49种,2014年40种,每年不同季节种类更替明显。2013年大型底栖动物丰度和生物量最高分别出现在春季和秋季,2014年分别为冬季和夏季,不同年份不同季节的生物量和丰度明显不同。不同年份的特征种均以甲壳动物类群为主,鱼类优势种增多。2013年秋季和2014年春季的大型底栖动物相对于同年度其他季节有更高的多样性,年度变化上多样性指数整体增高。群落结构分析表明,2013年夏秋冬聚为1组,春季为1组;2014年春夏秋聚为1组,冬季为1组。ABC曲线结果显示,潮下带大型底栖动物群落在2013年四季受到中度干扰,2014年春夏秋受干扰不明显,冬季受到中等程度以上的干扰。本研究结果为长江口生态环境保护及修复提供了理论依据。  相似文献   

20.
采用大连湾海域四季底拖网调查数据(2006年夏、冬季和2007年春、秋季),对其鱼类群落结构进行研究,并利用多样性指数法和丰度/生物量比较法(ABC曲线)评价鱼类群落受外界扰动的程度。研究结果表明,该海域四季共采集鱼类31种,隶属于10目24科31属,鱼类区系组成在适温性上以暖温性鱼类为主,在栖息水层上以底层鱼类为主。夏季鱼类生物量(43.16kg/h)和生物数量(950个/h)均明显高于其他3个季节。四季共有优势种为大泷六线鱼和许氏平鲉。鱼类群落多样性指数季节变化范围分别为物种丰富度指数0.76~2.16、多样性指数0.63~1.96、物种均匀度指数0.36~0.91。各季节间生物量和丰度组成的Bray-Curtis相似性均较高。多样性指数法和丰度/生物量曲线法对鱼类群落受外界扰动评价结果一致,均表明鱼类群落受到中度扰动,且秋冬季高于春夏季。本研究可为大连湾海湾生态系统健康评价和生态修复提供科学依据。  相似文献   

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