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1.
Otoliths of pre-recruit orange roughy (Hoplostethus atlanticus) were sampled from different deep-water habitats (‘flat’ and ‘hill’) and areas (north and south) on the Porcupine Bank. Age-based profiles for stable isotopes of carbon (δ13C) and oxygen (δ18O) in these otoliths were developed, which provide a fish life-history record of water depth and metabolic activity. These profiles were consistent among all individuals implying endogenous (ontogenic) influences on the pattern. The data indicate that post-larval orange roughy are mesopelagic active foragers, early juvenile fish move into a low energy deep-demersal phase, and older pre-recruit orange roughy assume the habitat depth and metabolic rate typical of adults. Comparison of otolith stable isotope profiles among areas and habitats on the Porcupine Bank suggest that juvenile orange roughy from South ‘hill’ and ‘flat’ habitats experience differing temperature and metabolic status at certain life stages. This may reflect oceanographic and ecological divergence between the two environments and suggests fine-scale population structure that may reduce resilience to exploitation.  相似文献   

2.
White steenbras Lithognathus lithognathus (Teleostei: Sparidae) is an overexploited marine fish species endemic to South Africa. Overexploitation in recreational, subsistence and commercial fisheries has resulted in stock collapse and the need for improved management of the species. Adults are thought to undertake large-scale annual spawning migrations, yet studies of their movement indicate low levels of connectivity among coastal regions. To address this, mitochondrial DNA sequencing and genotyping of microsatellite loci in the nuclear genome were conducted to determine the genetic stock structure and level of gene flow in this species. Genetic diversity was high throughout the species’ core distribution, with no evidence of isolation by way of distance or localised spawning. Low, non-significant pairwise fixation indices (FST, RST and Jost’s Dest) indicated low genetic differentiation and high levels of gene flow. The observed results, and agreement between mitochondrial and microsatellite DNA, confirm that white steenbras exists as a single genetic stock with high levels of gene flow throughout its distribution.  相似文献   

3.
It is a common observation that the mean length in a fish population progressively decreases as the biomass is reduced by fishing. However, this has not happened with the population of orange roughy (Hoplostethus atlanticus) on the Chatham Rise, New Zealand, even though the biomass is estimated to have declined by almost 80%. Because orange roughy are slow growing it might be expected that mean age (or its proxy, mean otolith weight) would be a more sensitive indicator of biomass decline than mean length. A simulation study shows that this is not true. With equal sample sizes, all three indicators are equally sensitive; on an equal cost basis, mean length is more sensitive than the others. A log transformation increases the sensitivity of age and otolith weight, but it is not clear whether this increase is sufficient to outweigh the much greater costs of measuring age and otolith weight, compared to length. Under the assumption of constant recruitment, it is more likely than not (P = 0.55–0.8) that a change in mean length would have been detected in the Chatham Rise population, given the estimated biomass decline.  相似文献   

4.
Heating otoliths of the orange roughy (Hoplostethus atlanticus; Trachichthyidae) by the break‐and‐burn method causes a crystal transformation from aragonite to calcite. However, the change does not affect the legibility of the check rings. Orange roughy otolith check rings fall into two classes: a diffuse deposit (that is not visible in the break‐and‐burn method, but may have an annual periodicity) and structural check rings (which appear as fine lines on the surface, but as dark bands in the body of the otolith). Structural check ring deposition is irregular, but fortuitous aggregations of structural check rings might be mistaken for conventional annual check rings.  相似文献   

5.
Experiments on sand mounds in oscillatory flow, undertaken in controlled, large-scale laboratory conditions, have produced well-defined data sets for model comparison. Three bathymetries with different levels of submergence, including a surface-piercing case, were tested. The maximum slope was about 1:5.5. Sediment transport is due to bed load with ripple formation. The principal time-dependent bulk parameters are the vertical distance of the centre of gravity above the base and the volume of the mound. A semi-implicit finite-volume depth-averaged hydrodynamic model is used to drive morphodynamics, using van Rijn's sediment flux model generalized to take account of bed slope, and some justification is given for depth-averaged modeling in these conditions. Starting the model runs with the conditions at the end of the first cycle avoided initial atypical physical behaviour. In general good predictions were obtained with an angle of repose reduced from the standard value of about 30° for stationary beds to 15°. For these situations, morphodynamics was largely unaffected by a hydrodynamic roughness height in the range 2.5D50 to 51D50, with larger values accounting for ripple roughness. The reduced angle of repose may be physically expected with mobile beds but this specific value is only expected to be suited to this form of bed motion. In one case an exaggerated ripple formed near the top of the mound reducing agreement with experiment. For the submerged case with normal ripple structure excellent predictions were obtained. For the initially surface-piercing mound, the time of submergence was better predicted with a 30° angle of repose, presumably due to the prominent influence of the near stationary bed near the wet/dry interface, although long term predictions were better predicted with 15°. The occurrence of vortex shedding in the first cycle modeled was in agreement with experimental observation.  相似文献   

6.
《Oceanologica Acta》1999,22(6):593-602
Major commercial fisheries for orange roughy (Hoplostethus atlanticus) occur on seamount features, which are widely distributed throughout the New Zealand region. When the fishery developed in the late 1970s to early 1980s, it occurred mainly on flat bottom, but over time has become more focused on seamounts. In the 1995–1996 fishing year, it is estimated that about 70 % of the catch of orange roughy within the New Zealand EEZ was taken from seamounts. Seamounts on the Chatham Rise have been fished for over ten years. Examination of commercial catch and effort data show strong declines in catch rates over time, and a pattern of serial depletion of seamount populations, with the fishery moving progressively eastwards to unfished seamounts along the southern margins of the Rise. Catch rates on seamounts in other regions of New Zealand have also generally shown a similar pattern of rapid decline. There is growing concern over the impact of trawling on seamounts, and the effects this can have on the benthic habitat and fauna, and the long-term sustainability of associated commercial fisheries.  相似文献   

7.
利用电子显微探针元素分析技术(EPMA)对黄海南部野生银鲳和鮸鱼的耳石进行了锶和钙沉积特征的初步分析。定量线分析结果表明,两种鱼类耳石的Sr/Ca之间存在显著的种间差异。银鲳耳石Sr/Ca比,在耳石核心及相邻处为低值区(5.86±0.92);3段Sr/Ca高值区分别为近核心部(7.88±1.28)、第1龄处(9.44±1.82)及耳石边缘(7.91±1.38);揭示银鲳孵化和早期发育应需要盐度适中的生境,当龄鱼在后期的生长中需洄游经过两段高盐生境(其中之一在第1龄时)。鮸鱼耳石Sr/Ca比波动表现为耳石核心处(7.72±0.97)高于其余部分,反映了鮸鱼孵化及初期发育阶段可能生活在高盐度生境,而当龄鱼随后阶段的生长和发育过程则会洄游至盐度有所降低的生境中进行。  相似文献   

8.
Occasional population outbreaks of the crown‐of‐thorns sea star, Acanthaster planci, are a major threat to coral reefs across the Indo‐Pacific. The presumed association between the serial nature of these outbreaks and the long larval dispersal phase makes it important to estimate larval dispersal; many studies have examined the population genetic structure of A. planci for this purpose using different genetic markers. However, only a few have focused on reef‐scale as well as archipelago‐scale genetic structure and none has used a combination of different genetic markers with different effective population sizes. In our study, we used both mtDNA and microsatellite loci to examine A. planci population genetic structure at multiple spatial scales (from <2 km to almost 300 km) within and among four islands of the Society Archipelago, French Polynesia. Our analysis detected no significant genetic structure based on mtDNA (global FST = ?0.007, P = 0.997) and low levels of genetic structure using microsatellite loci (global FST = 0.006, P = 0.005). We found no significant isolation by distance patterns within the study area for either genetic marker. The overall genetically homogenized pattern found in both the mitochondrial and nuclear loci of A. planci in the Society Archipelago underscores the significant role of larval dispersal that may cause secondary outbreaks, as well as possible recent colonization in this area.  相似文献   

9.
Kingklip Genypterus capensis inhabit deep continental shelf and slope waters off southern Africa and are now largely harvested as a bycatch in trawl and longline fisheries for Cape hakes Merluccius spp. Regional differences in growth, vertebral count and otolith morphology indicate that kingklip may consist of three stocks. In this study, allozyme markers are used to test whether the two southern stocks, the putative Cape and South Coast stocks, are genetically distinguishable. Standard electrophoretic methods detected Mendelian polymorphisms at six (23%) of 26 enzyme-encoding loci in five samples extending from about 29°S on the West Coast to about 25°E on the South Coast. No deviations from Hardy-Weinberg proportions were observed in the samples or in the pooled sample. Gene diversities (heterozygosity) ranged from HS = 0.039 to 0.042 among samples, and averaged 0.041. Genetic differentiation among localities was remarkably small, FST = 0.003, and did not differ significantly from zero. A Bayesian analysis of population structure, based on detecting departures from Hardy-Weinberg proportions and gametic phase equilibria between loci, indicated with a high likelihood that the five samples were drawn from a single genetic population. In combination, these results are consistent with the occurrence of a single population off South Africa. However, the most conservative management strategy is to set harvest quotas individually on the Cape and South Coast stocks.  相似文献   

10.
Orange roughy form dense spawning aggregations in specific small areas in deep water on the Namibian shelf between late June and early August each year. The biomass in three such areas, where most commercial fishing occurs (the Johnies, Frankies and Rix Quota Management Areas, or QMAs) has been assessed acoustically each year since 1997. Acoustic estimates of the aggregated portion of the biomass (the only component that can be assessed reliably using acoustics) were obtained for all three QMAs in 1997 and 1998, but only for Frankies in 1999 owing to increased problems with target identification as the biomass declined. The methodology developed for these surveys, including the equipment used, survey design, target identification, data processing and error analysis are described. Some important biases that should be corrected for when estimating absolute abundance of orange roughy acoustically are addressed. Individual sources of error were quantified as well as possible, and input to an error model that simulated the error process and produced probability density functions of absolute biomass, from which the mean absolute biomass and its standard error could be computed for each survey, effectively correcting for identified sources of bias and quantifying the overall uncertainty. The correction factors ranged from 1.58 to 1.71 and the CVs increased by factors of 1.2–2.1. Target strength uncertainty and negative bias attributable to the dead zone close to the bottom were considered to be the most serious errors. The acoustic estimates indicate a substantial decline in orange roughy biomass in all three QMAs since 1997, in accord with indices from contemporaneous swept-area surveys and the catch rate of the commercial fleet. Acoustic estimates have already been used extensively to manage the resource and are likely to remain important in the future.  相似文献   

11.
The vortex shedding from near-bed piggyback pipelines in a steady flow has been investigated experimentally in a large water flume. A specially arranged PIV system with upward-illumination of pulsed laser arrays from the flume bottom was employed for the flow visualization and quantitative measurement of the lee-wake flow in a sub-critical regime around the piggyback pipelines in the proximity of a plane boundary. Based on dimensional analyses, a dimensionless maximum swirling strength (Wm) is used for analyzing the vortex shedding intensity and its frequency. Time-averaged swirling strength analyses indicate that the lee-wake patterns for the near-bed piggyback pipelines are dependent on the configuration factors, including the gap-to-diameter ratio (e/D), the spacing-to-diameter ratio (G/D), and the diameter ratio of two pipes (d/D), etc. The swirling strength in the lee-wake is obviously asymmetric for piggyback pipelines with bed proximity. For the fixed values of G/D and d/D, the maximum swirling strength decreases with the decrease of e/D. Moreover, for the examined G/D range (0 ≤ G/D ≤ 0.5), minimum values of Wm and corresponding VIV amplitude for the piggyback pipelines are evidently within the same range of spacing-to-diameter ratio G/D ≈ 0.05–0.20.  相似文献   

12.
《Journal of Sea Research》2004,51(3-4):191-197
As a preliminary investigation into the genetic structure of Irish Sea plaice we genotyped samples of juvenile plaice from six inshore areas within the Irish Sea across eight microsatellite loci and compared them with fish from two sites from the Dutch Wadden Sea (North Sea stocks). Genetic variability in all samples was generally low for that typically observed at microsatellite loci. The number of alleles per locus varied between two and nine (average 5.5) and the observed heterozygosity ranged from 0.080 up to a maximum of 0.909 (average 0.382). Few significant heterozygote deficits were observed, even when the data set was pooled. The majority (98%) of genetic variation present was within, rather than between, populations. None of the pairwise comparisons of population differentiation (FST) were significant (P>0.05) and a Bayesian analysis of population structure provided no evidence for a partitioning of the samples. Since juveniles arriving at nursery grounds in the Irish Sea are not distinct, it is likely that adult plaice form a single stock (perhaps with some weak differentiation). However, if plaice eggs and larvae do not disperse as predicted by a particle tracking model, then it is possible that the juveniles represent a mixture of several distinct stocks. Further work is therefore required to determine whether the phenotypic variation observed between female plaice from the eastern and western Irish Sea is the product of reproductive isolation or of the environment.  相似文献   

13.
In the South-Western Indian Ocean (SWIO), four eel species of the genus Anguilla (i.e. Anguilla bicolor bicolor, Anguilla nebulosa labiata, Anguilla marmorata and Anguilla mossambica) were identified, while their respective oceanic spawning area remained unknown. Based on collected larvae, glass eel captures and hydrodynamical conditions, previous studies raised the hypothesis that the eel spawning area might be common to all of those freshwater eel species, and located East of Madagascar. An original modeling approach, based on backward simulations, is developed to assess how the ocean circulation in the SWIO determines the location of the spawning areas and whether a common spawning area for each recruitment site where glass eels were found is possible. We use a hydrodynamical model, which reproduces realistically the 3D open ocean circulation in the region, associated with a Lagrangian model that calculates the possible migration pathways of larvae, represented by passive particles. Some biological parameters, provided by previous otolith microstructures analysis, are taken into account to constrain our simulations. Results suggest the existence of a common spawning area located between 13°S and 19°S and westwards of 60.5°E, although these boundaries vary on the interannual timescale. Salinity fronts were reported beside the boundaries, reinforcing this assumption. We explore the impact of hydrodynamic conditions on recruitment and migration durations from three specific regions within the common spawning area. They all allow migration to each recruitment sites consistent with duration estimated from otolith microstructure analyses. Nevertheless, there is substantial variability on intra-seasonal to interannual timescale in simulated migration durations and arrival success, with specific amplitude to each recruitment site and spawning location.  相似文献   

14.
Terrigenous sediment in the nearshore environment can pose both acute and chronic stresses to coral reefs. The reef flat off southern Molokai, Hawaii, typically experiences daily turbidity events, in which trade winds and tides combine to resuspend terrigenous sediment and transport it alongshore. These chronic turbidity events could play a role in restricting coral distribution on the reef flat by reducing the light available for photosynthesis. This study describes the effects of these turbidity events on the Hawaiian reef coral Montipora capitata using in situ diurnal measurements of turbidity, light levels, and chlorophyll fluorescence yield via pulse-amplitude-modulated (PAM) fluorometry. Average surface irradiance was similar in the morning and the afternoon, while increased afternoon turbidity resulted in lower subsurface irradiance, higher fluorescence yield (ΔF/Fm′), and lower relative electron transport rates (rETR). Model calculations based on observed light extinction coeffecients suggest that in the absence of turbidity events, afternoon subsurface irradiances would be 1.43 times higher than observed, resulting in rETR for M. capitata that are 1.40 times higher.  相似文献   

15.
Prior to the 1950s, thornback ray (Raja clavata L.) was common and widely distributed in the seas of Northwest Europe. Since then, it has decreased in abundance and geographic range due to over-fishing. The sustainability of ray populations is of concern to fisheries management because their slow growth rate, late maturity and low fecundity make them susceptible to exploitation as victims of by-catch. We investigated the population genetic structure of thornback rays from 14 locations in the southern North Sea, English Channel and Irish Sea. Adults comprised < 4% of the total sampling despite heavy sampling effort over 47 hauls; thus our results apply mainly to sexually immature individuals. Using five microsatellite loci, weak but significant population differentiation was detected with a global FST = 0.013 (P < 0.001). Pairwise Fst was significant for 75 out of 171 comparisons. Although earlier tagging studies suggest restricted foraging distances from home areas, the absence of genetic differentiation between some distant populations suggests that a substantial fraction of individuals migrate over wide areas. Autumn/winter locations appear to have a lower level of differentiation than spring/summer, which could be due to seasonal migration. Management and conservation of thornback ray populations will be challenging as population structure appears to be dynamic in space and time.  相似文献   

16.
运用6对微卫星分子标记分析了山东蓬莱(SP)、山东黄岛(SH)、江苏前三岛(JQ)、韩国统营(Korea)等魁蚶4个地理群体的遗传结构。结果表明,4个魁蚶群体在6个位点的等位基因数(a)为11.3333—14.3333,平均有效等位基因数(ae)为6.2977—9.5873;平均杂合度观察值(Ho)为0.4083—0.5641,平均杂合度期望值(He)0.7849—0.8753,各位点平均多态信息含量(PIC)值为0.7703—0.9102,遗传多样性非常丰富。聚类分析结果表明黄岛群体与前三岛群体聚在一起,蓬莱群体与统营群体聚在一起最后聚类。本研究结果可为今后魁蚶种质资源保护和遗传育种提供遗传学资料。  相似文献   

17.
The West Coast dusky kob Argyrosomus coronus is a commercially exploited fish with a distribution confined to the Angola–Benguela Frontal Zone (ABFZ) of the southeastern Atlantic Ocean. A previous study revealed that during a recent period of local warming the species extended its distribution into Namibian waters, where it hybridised with the resident and congeneric Argyrosomus inodorus. Environmental changes are a major threat to marine biodiversity and when combined with overfishing have the potential to accelerate the decline of species. However, little is known regarding the evolutionary history and population structure of A. coronus across the ABFZ. We investigated genetic diversity, population structure and historical demographic changes using mtDNA control region sequences and genotypes at six nuclear microsatellite loci, from 180 individuals. A single, genetically homogeneous population was indicated across the distributional range of A. coronus (φST = 0.041, FST = 0.000, D = 0.000; p > 0.05). These findings imply that the oceanographic features within the ABFZ do not appear to significantly influence population connectivity in A. coronus, which simplifies management of the species. However, reconstruction of the demographic history points to a close link between the evolutionary history of A. coronus and the environmental characteristics of the ABFZ. This outcome suggests the species’ vulnerability to the rapid environmental changes being observed across this region, and highlights a pressing need for transboundary management to mitigate the impacts of climate change in this global hotspot of seawater temperature changes.  相似文献   

18.
刘勇  程家骅 《海洋学报》2014,36(6):124-130
鱼类产卵群体的相关研究一直是渔业领域关注的热点,对鱼类的产卵期、产卵场的研究是鱼类生态习性研究方向的重要组成部分。本文在前期研究证实鱼类体长-体重关系幂指数可以指示鱼类产卵期的基础上,利用2004年4个季节的东海大面积调查数据,尝试利用同一时间点上的各个调查点幂指数信息来分析鱼类产卵场分布特征,结果发现,成熟产卵个体仅在春季出现,而未成熟产卵个体4季均有分布,以此推测小黄鱼存在"跳过产卵"现象。另外发现,单靠幂指数大小,不能区分各个产卵成熟阶段,也不能区分产卵个体与非产卵个体;而怀卵个体出现站点的幂指数平均值偏低于匀速生长,空间上也具有类似特征,即幂指数相对低的地方一般对应怀卵个体相对集中的水域。本文依据幂指数分布,推断小黄鱼成熟产卵群体有3块相对集中水域,即舟山渔场近海、济州岛西南侧和江外与舟外渔场临近水域。  相似文献   

19.
It has been proposed that the elkhorn coral Acropora palmata is genetically separated into two distinct provinces in the Caribbean, an eastern and a western population admixing in Western Puerto Rico and around the Mona Passage. In this study, the genetic structure of A. palmata sampled at 11 Puerto Rican localities and localities from Curaçao, the Bahamas and Guadeloupe were examined. Analyses using five microsatellite markers showed that 75% of sampled colonies had unique genotypes, the rest being clone mates. Genetic diversity among genets was high (HE = 0.761) and consistent across localities (0.685–0.844). FST ranged from ?0.011 to 0.047, supporting low but significant genetic differentiation between localities within the previously reported eastern and western genetic provinces. Plots of genetic per geographic distances and significant Mantel tests supported isolation‐by‐distance (IBD) within Puerto Rico. Analysis with the software STRUCTURE favored a scenario with weak differentiation between two populations, assigning Eastern Puerto Rican locations (Fajardo and Culebra), Guadeloupe and Curaçao to the Caribbean eastern population and Western Puerto Rican locations (west of Vega Baja and Ponce), Mona and the Bahamas to the Caribbean western population. Vieques and San Juan area harbored admixed profiles. Standardized FST per 1000 km unit further supported higher differentiation between localities belonging to different STRUCTURE populations, with IBD being stronger within Puerto Rico than on larger regional scales. This stronger genetic transition seems to separate localities between putative eastern and western provinces in the Eastern Puerto Rican region, but not around the Mona Passage.  相似文献   

20.
Chronological variation in otolith chemistry can be used to reconstruct migration histories of fish. The use of otolith chemistry to study migration, however, requires knowledge of relationships between the chemical properties of the water and elemental incorporation into otoliths, and how water chemistry varies in space and time. We explored the potential for otolith chemistry of snapper, Pagrus auratus, to provide information on movement history between a large semi-enclosed bay, Port Phillip, and coastal waters in south-eastern Australia. Comparisons of water chemistry across two years demonstrated that ambient barium (Ba) levels in Port Phillip Bay were approximately double those in coastal waters (11 μg L−1 versus 6 μg L−1). Ba levels in otolith margins of wild juvenile snapper were highly positively correlated with ambient levels across 17 sampling locations, and levels in otolith margins of adult snapper collected from Port Phillip Bay were approximately double those of snapper collected in coastal waters. Mean partition coefficients for Ba (DBa) were similar for juvenile (0.43) and adult (0.46) otoliths, suggesting that otolith Ba incorporation relative to ambient levels was similar across life-stages. Low Ba variation across otoliths from adult snapper maintained in tanks for three years indicated that annual temperature and/or growth cycles did not strongly influence otolith Ba variation. We concluded that chronological Ba variation in snapper otoliths would be a reliable proxy for life-history exposure to variable ambient Ba. We used water chemistry data and Ba levels across otoliths of ocean resident snapper to estimate otolith Ba levels indicative of residence in Port Phillip Bay (>10 μg g−1) or coastal waters (<6 μg g−1). Peaks in Ba exceeding 10 μg g−1 were common across otoliths of snapper collected in Port Phillip Bay and a nearby coastal region. The location of strong Ba peaks within otoliths was consistent with residence in Port Phillip Bay during the spring/summer when snapper move into the Bay from coastal waters to spawn. Our results for snapper support the use of otolith Ba as a proxy for ambient levels throughout the life-history, however, confident interpretation of migration history from otolith Ba chronologies will most likely require matching time series of ambient Ba in the water bodies of interest.  相似文献   

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