A field‐based assessment of oxygen supply to incubating Atlantic salmon (Salmo salar) embryos

Oxygen fluxes through artificially created salmon redds within four UK rivers were quantified and assessed against survival to hatching of Atlantic salmon embryos. All sites recorded high spatial variability in survival. Minimum survival to hatching was zero at all sites. Maximum survival to hatching ranged from 35% to 91%. Mean survival to hatching ranged from 8·7% to 71%. Intra‐ and inter‐site variations in rates of oxygen supply were observed. Generally, interstitial dissolved oxygen concentrations declined over the incubation period from a maximum recorded directly after redd creation, although localized fluctuations were recorded. Similarly, interstitial flow velocities declined over the incubation period from a maximum directly after redd creation to a minimum at hatching. With respect to the causes of embryo mortalities, oxygen supply was shown to be a stronger determinant of survival than interstitial oxygen concentration or interstitial flow velocity. To improve delineation of potential causes of embryo mortalities in the field, the statistical analysis was integrated within mass transfer theory of the processes controlling respiration to determine the likely mechanisms inhibiting respiration. Based on this analysis, mortalities were assessed to have resulted from periods of lethal oxygen concentrations, from periods of interstitial flow velocities that were insufficient to remove metabolic waste, or from combinations of oxygen concentration and interstitial flow that did not support respiratory requirements. A set of oxygen‐supply‐related thresholds for assessing incubation habitat quality are proposed. Copyright © 2007 John Wiley & Sons, Ltd.     

The effect of copper-treated net pens on farmed salmon (Salmo salar) and other marine organisms and sediments

Samples of Atlantic salmon (Salmo salar), saithe (Pollacius virens), blue mussel (Mytilus edulis), brown seaweed (Ascophyllum nodosum) and sediment were collected from six different fish farms. Five of the farms used net pens treated with copper-containing coatings, whereas one farm did not use copper-containing coating (this was used as a reference location). Samples of muscle, liver and gills of Atlantic salmon and saithe, blue mussel and brown seaweed were freeze dried, homogenised, wet digested and analysed for copper by flame atomic absorption spectrometry. The results showed no significant differences in copper concentrations among the samples from the different locations. The copper contents of some of the samples appeared to be in the upper part of the normal concentration range. From a nutritional point of view, the use of copper-coatings on net pens did not affect the quality of the seafood products either within, or around the net pen.     

Incubation,hatching and survival of eggs of Atlantic salmon (Salmo salar) in spawning redds influenced by groundwater

Many west coastal and northern Norwegian rivers run through deep, confined valleys with permeable layers of glacial and alluvial deposits. Groundwater flows through these permeable layers and enter lakes and rivers as underwater seepage and springs. Groundwater inflow to inland Norwegian rivers may constitute 40–100% of total water discharge during low flow periods in late summer and winter. Juvenile salmonids may take advantage of groundwater upwellings and actively seek out such patches. In regulated rivers groundwater influx may create refuges during low flow or hydropeaking episodes. The importance of groundwater for salmon redd site selection and egg survival is also clear, although less known and documented in regulated rivers.Eggs of Atlantic salmon (Salmo salar) are deposited in redds in river bed gravels lacking fine sediments and with high oxygen levels. Egg development is therefore dependent on the interaction of a number of environmental factors such as groundwater influx, oxygen and temperature. Atlantic salmon in the regulated River Suldalslågen, Western Norway, spawn relatively late compared to other Norwegian rivers, with a peak in early January. Newly emerged fry are found from the end of May to the beginning of June, i.e. “swim up” one month earlier than expected using models for egg and alevin development and river water temperatures. The most plausible explanation is that groundwater has a higher and more stable temperature than surface river water. In field experiments, fertilized salmon eggs were placed in boxes close to natural spawning redds in the river bed at sites influenced and those not influenced by groundwater. A difference of up to 40 days in 50% hatching was found, and “swim up” occurred at the end of May in boxes influenced by groundwater.Preliminary studies have revealed that groundwater also plays an important role in survival of salmon eggs in the River Suldalslågen when dewatered in winter. Eggs placed in boxes in groundwater seepage areas during winter in the dewatered river bed survived even when covered by ice and snow. The survival from fertilization until 30 April, one month before hatching, was 91%, the same survival as found for eggs placed in boxes in the wetted river bed. However, mortality from fertilization to hatching was higher compared to the eggs placed in wetted river bed, 57 and 91% respectively.Groundwater creates a horizontal and vertical mosaic of temperatures in spawning redd areas leading to potentially greater variation in spawning sites, time of hatching and “swim up”. This is likely to increase egg survival during low flow periods in regulated rivers. In conclusion, the interaction between groundwater and surface river water should therefore be considered when managing fish populations in regulated rivers.     

Spatial and temporal variability of Atlantic salmon (Salmo salar L.) spawning activity in braided river channels: a preliminary assessment

The distribution of Atlantic salmon redds was recorded during two spawning seasons (2005 and 2006) along a 4?km braided reach of the river Feshie in the Cairngorm mountains, Scotland. Within this complex reach, four main channels types were differentiated on the basis of geographical water sources, channel morphology and hydrochemistry: (1) the main braided channels of the river Feshie; (2) groundwater channels fed by seepage at the edge of the floodplain; (3) hillslope tributary channels and (4) mixed channels downstream of confluences of two or more of types 1?C3. The 2005 season was characterised by high and variable flows. In total, 223 redds were observed which were mainly (64%) located in groundwater channels, with relatively few (9%) in the more extensive sections of main channel. The second year had much lower and more stable flows. Here, a total of 337 redds were observed. The largest number were again located in the groundwater channels (44%), though spawning was more evenly distributed in the other channel types, including the main river (19%). It is hypothesised that the apparently more suitable characteristics of groundwater-fed channels relate to a more stable, richer environment for embryo development and juvenile growth, whilst hydraulic conditions and sediment stability in the main channel may create more adverse conditions for successful recruitment.     

Prediction of the consumption rates for juvenile Atlantic salmon (Salmo salar L.) on the scale of habitat patches: Development of empirical models based on stomach contents

Rivers and streams are unstable environments in which estimation of energetic costs and benefits of habitat utilization are the daunting exercise. Empirical models of food consumption may be used to estimate energetic benefits based on abiotic and biotic conditions in patches of habitat. We performed thirty daily surveys of fish stomach contents to estimate the consumption rates for juvenile Atlantic salmon (Salmo salar) in a river. The data were used to assess whether variations of daily consumption rates existed within the river, and to develop empirical models that could predict fish consumption rates using abiotic and biotic conditions as independent variables. Daily consumption rates based on stomach content surveys in the field (range: 0.15–1.49 g dry/(100 g wet day)) varied significantly depending on habitat patch (500–1000 m²), summer period, and sampling year. Variables such as water temperature, numerical density of salmon, water depth and moon phase explained 83–93% of the variations in daily food consumption rates. Daily consumption rates tended to increase with water temperature and depth, and were also higher near a full moon. However, they tended to decrease with the numerical density of salmon. Our work suggests that empirical models based on independent variables that are relatively simple to estimate in the field may be developed to predict fish consumption rates in different habitat patches in a river.     

Empirical models to identify mechanisms driving reductions in tissue mercury concentration during culture of farmed southern bluefin tuna Thunnus maccoyii

Two empirical models are presented to elucidate the mechanisms driving reductions in the mercury concentration of southern bluefin tuna (SBT) during culture. Model 1 predicts temporal fluctuations in mercury concentration in response to growth dilution. Model 2 predicts the combined effects of growth dilution and linear mercury accumulation. Model 2 was found to be the more accurate model. Over a typical farming period of 136 days, growth dilution resulted in a reduction in mean mercury concentration of SBT edible tissues from 0.51 mg/kg down to 0.33 mg/kg. Extended culture beyond 136 days resulted in an increase in mercury concentration due to the combined effects of mercury accumulation and seasonal lipid depletion. Results indicate that under current industry practice, cultured SBT can be consumed twice as frequently as that of wild caught SBT while maintaining total dietary mercury intake below national recommendations.     

A comparison of anthropogenic mercury pollution in Kastela Bay (Croatia) with pristine estuaries in Ore (Sweden) and Krka (Croatia)

Anthropogenic mercury pollution was studied in Kastela Bay (Croatia), 10 years after chloralkaline plant (PVC) stopped production. The concentration of total mercury determined in sediments which are composed mainly of calcite and quartz, are in the range 14,280-30,400 ng/g. The values are higher than reported in the literature for Elbe and Seine estuaries and also above 25,000 ng/g used for criterion in remediation project in Minamata Bay. The concentration of methylmercury 6.05-36.74 ng/g are typical for slightly to highly contaminated estuarine sediments. The low ratio of methylmercury to total mercury found in sediments of Kastela Bay is in the range 0.04-0.18%. It can be explained that in this region predominate conditions which do not promote in-situ methylation. Sediments were found to be highly anoxic. Concentrations of total mercury in unfiltered surface waters are in the range 69-145 ng/l and in unfiltered bottom waters in the range 230-1,418 ngl(-1). High concentrations found in bottom waters suggest that either resuspension or partial dissolution of sediments takes place. An experiment performed on filtered and unfiltered waters showed that about 85% of total mercury in surface water and almost 100% in bottom water was retained on 45 microm filters. To demonstrate contrasts, two pristine estuaries from norths and south Europe were studied. Silicious sediments of Ore estuary (Sweden) and calcareous sediments of Krka estuary (Croatia) have total mercury concentrations close to accepted background level. The ratio of methylmercury to total mercury is < or = 1% in all samples with one exception. The highest observed ratio (2.70%) was in the surface sediment from E2 station in Krka estuary measured in March 2000. This location is suitable for studying methylmercury formation in pristine environment.     

In situ biomonitoring of caged, juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Lower Duwamish Waterway

Contaminated sediments may have wide-ranging impacts on human and ecological health. A series of in situ caged exposure studies using juvenile Chinook salmon was conducted in the Lower Duwamish Waterway (LDW). Chemical analysis of sediment, water, and fish tissue were completed. Additionally, in 2004, DNA adducts in hepatic and gill tissues were measured. Gills contained significantly higher DNA adducts at stations B2 and B4, prompting further analysis of gills in 2006 and 2007. Fluorescent aromatic compounds (FACs) in bile, and CYP1A1 in hepatic tissue were also measured during 2006 and 2007, respectively. FACs in field-caged fish were comparable or significantly higher than wild-caught fish LDW fish and significantly higher than lab fish after only 8-10 days, demonstrating the equivalency of exposure to that of migrating salmon. Furthermore, selected biomarkers appear to be capable of detecting spikes in contamination between sampling years, emphasizing the need for multiple year data collection.     

A hydrographic time series station in the Wadden Sea (southern North Sea)

In the tidal inlet between the East Frisian islands of Langeoog and Spiekeroog, southern North Sea, a time-series station was set up in autumn 2002 as part of the research programme BioGeoChemistry of Tidal Flats run by the University of Oldenburg. The purpose of the station is to provide continuous data on physical, biological and chemical parameters. In addition to instruments recording basic hydrographic and meteorological parameters, the time-series station is equipped with acoustic Doppler profilers for measuring surface waves and current profiles. Compact optical spectrometers are being used for spectral measurements of seawater transmission and for daylight reflectance. Additional sensors were installed for measuring oxygen, nutrients and methane in the seawater. The data shall help to quantify the flux of dissolved and suspended matter between the backbarrier tidal flat and the open sea and to characterise the material transformation in the tidal flat area by biogeochemical processes over the tidal cycle. Due to its novel design, operation of the station is also possible during winter and under extreme weather conditions (gales, storm surges, and sea ice) when data sampling with conventional platforms such as research vessels, buoys, or smaller poles could not be performed in the past. In this way, time series of data are obtained, which include events that are most relevant to the evolution of this coastal area. The performance of the station and its equipment are presented with data covering 6 years of operation. Time series of air and water temperature as well as seawater salinity demonstrate the multiyear dynamics of these parameters in the East Frisian Wadden Sea. Hydrographic data collected under specific meteorological conditions such as gales and storm surges exemplify the all-weather capabilities of the station and its value for studying hydrographic processes in the Wadden Sea.     

Total and organic mercury concentrations in the muscles of Pacific albacore (Thunnus alalunga) and bigeye tuna (Thunnus obesus)

Muscles of 115 North Pacific albacore (ALB, Thunnus alalunga) and 75 Pacific bigeye tuna (BET, Thunnus obesus), collected from 2001 to 2006, were analyzed. No ALB, but 13 large BET had organic mercury (OHg) concentrations exceeding 1 μg g⁻¹ wet weight. For both ALB and BET, total mercury (THg) and OHg concentrations were significantly and positively correlated with fork length (FL) and body weight. The muscle Hg bioaccumulation rates of BET were higher than those of ALB, particularly in the adult fish. Moreover, the lines had crossover points among the two species that imply the young BET (FL < 110 cm) contains lower muscle Hg concentrations than ALB of the same size. The suggested weekly dietary intake of ALB and small-BET meats is 340 g, and of BET meat it is 150 g for a 60-kg person based on the provisional tolerable weekly intake (PTWI) of methylmercury set by the WHO.     

The effect of copper-treated net pens on farmed salmon (Salmo salar) and other marine organisms and sediments

Samples of Atlantic salmon (Salmo salar), saithe (Pollacius virens), blue mussel (Mytilus edulis), brown seaweed (Ascophyllum nodosum) and sediment were collected from six different fish farms. Five of the farms used net pens treated with copper-containing coatings, whereas one farm did not use copper-containing coating (this was used as a reference location). Samples of muscle, liver and gills of Atlantic salmon and saithe, blue mussel and brown seaweed were freeze dried, homogenised, wet digested and analysed for copper by flame atomic absorption spectrometry. The results showed no significant differences in copper concentrations among the samples from the different locations. The copper contents of some of the samples appeared to be in the upper part of the normal concentration range. From a nutritional point of view, the use of copper-coatings on net pens did not affect the quality of the seafood products either within, or around the net pen.     

Stable isotope ratios of carbon,nitrogen and oxygen in killer whales (Orcinus orca) stranded on the coast of Hokkaido,Japan

We analyzed δ¹³C, δ¹⁵N and δ¹⁸O in the muscle and liver from killer whales stranded on the coast of Japan. The δ¹⁵N values in the muscle samples from calves were apparently higher than those in their lactating mothers, suggesting that nursing may result in the higher δ¹⁵N values in the muscle samples of calves. The δ¹⁵N value in the muscle samples of male and female whales, except for the calves, were positively correlated with the δ¹³C values and body length, suggesting that the increases in δ¹⁵N were due to the growth of the whales and increase in their trophic level. In contrast, the δ¹⁸O values in the muscle samples of female whales except for the calves were negatively correlated with the δ¹³C and δ¹⁵N values. The δ¹⁸O may be lower in whales occupying higher trophic positions (δ¹⁵N), although it might also be affected by geographic and climatic conditions.     

A two-stage time series model for monthly hydrological projections under climate change in the Lim River basin (southeast Europe)

ABSTRACT

Climate change projections of precipitation and temperature suggest that Serbia could be one of the most affected regions in southeastern Europe. To prepare adaptation measures, the impact of climate changes on water resources needs to be assessed. Pilot research is carried out for the Lim River basin, in southeastern Europe, to predict monthly flows under different climate scenarios. For estimation of future water availability, an alternative approach of developing a deterministic-stochastic time series model is chosen. The proposed two-stage time series model consists of several components: trend, long-term periodicity, seasonality and the stochastic component. The latter is based on a transfer function model with two input variables, precipitation and temperature, as climatic drivers. The Nash-Sutcliffe model efficiency for the observed period 1950–2012 is 0.829. The model is applied for the long-term hydrological prediction under the representative concentration pathway (RCP) emissions scenarios for the future time frame 2013–2070.     

Segmentation-based approach for trend analysis and structural breaks in rainfall time series (1851–2006) over India

ABSTRACT

This study analysed long-term rainfall data (1851–2006) over seven climatic zones of India at seasonal and annual scales based on three techniques: (i) linear regression, (ii) multifractal detrended fluctuation analysis (MFDFA) and (iii) Bayesian algorithm. The linear regression technique was used for trend analysis of short-term (30 years) and long-term (156 years) rainfall data. The MFDFA revealed small- and large-scale fluctuations, whereas the Bayesian algorithm helped in quantifying the uncertainty in break-point detection from the rainfall time series. Major break points years identified through Bayesian algorithm were 1888, 1904 and 1976. The MFDFA technique identified that high fluctuation years were between 1871–1890, 1891–1910 and 1951–1970. Linear regression-based analysis revealed 1881–1910 and 1971–2006 as break-point periods in the North Mountainous Indian region. A similar analysis was carried out for India as a whole, as well as its seven climatic zones.     

A 14?500 year record of the accumulation of atmospheric mercury in peat: volcanic signals, anthropogenic influences and a correlation to bromine accumulation

A 14?500 calendar year record of mercury accumulation rates has been obtained from an ombrotrophic peat bog in the Swiss Jura mountains. The range of natural (pre-industrial) mercury accumulation rates varied from 0.3 to 8.0 μg m⁻² yr⁻¹. During the Late Glacial and Holocene, climatic and volcanic signals were evident in the mercury record. Mercury accumulation rates increased by a factor of ca 5 during the Younger Dryas cold period. Short-term spikes in mercury accumulation rates, which correspond in time to known volcanic eruptions, occur during the late Boreal and Older Atlantic periods, when volcanic influences on mercury deposition appear to have been intensified due to increased atmospheric humidity. A correlation of mercury to bromine accumulation is observed throughout the pre-anthropogenic period. During the Holocene, mercury accumulation only exceeded the range of this correlation for a few short periods of elevated mercury deposition which correspond to known volcanic eruptions during the Older Atlantic. During historical times, mercury accumulation rates have exceeded the range of the correlation of mercury to bromine continuously since ca 1330 AD. This excess in mercury accumulation is interpreted as an indication of pollution. During the industrial period, mercury accumulation rates reached 107.6 μg m⁻² yr⁻¹, of which 84% was mercury that exceeded the correlation range. Mercury accumulation rates peaked again during the 1970s, with 78.8 μg m⁻² yr⁻¹. Early 20th century pollution appears to have been dominated by non-Swiss emissions from coal burning, whereas Swiss mercury emissions appear to have been the dominant pollution source during the mid and late 20th century. Current mercury accumulation rates at the site are similar to those ca 10 years ago, with modern deposition rates being ca 15 times their prehistorical average. Anthropogenic emissions of reactive brominated compounds could be contributing to increased atmospheric deposition rates of mercury.     

Designing and testing a network of passive seismic surveying and monitoring in Dehdasht (South Western Iran)

From August 2016 to July 2017, a passive seismic survey was conducted in South Western Iran as a part of a pilot project aimed to improve the imaging in geologically complex areas. Passive seismic methods have shown to be a useful tool to infer the physical properties of the underground geological structures where traditional hydrocarbon exploration methods are challenging. For this purpose, a dense passive seismic network consisting of 119 three-component borehole seismic stations was deployed over an area of 400 km² around the city of Dehdasht. This paper focuses on the details of the network design, which was devoted to high-resolution seismological applications, including local earthquake tomography and seismic attenuation imaging. In this regard, we describe the instrument types and the station installation procedures used to obtain high-quality data that were used to retrieve three-dimensional models of P- and S-wave velocity and P-wave attenuation in the area using tomographic inversion techniques. We also assess the network performance in terms of the seismic ambient noise levels recorded at each station site, and we revise the horizontal orientation of the sensors using surface waves from teleseismic earthquakes.     

Trace elements in the sediments of a large Mediterranean marina (Port Camargue,France): Levels and contamination history

The study of trace elements (Cu, Zn, Pb, As, Hg) and butyltin concentrations in the sediments of Port Camargue enabled assessment of the levels and history of the contamination of the largest European marina linked with the use of antifouling paints. Surface sediments near the boat maintenance area were heavily contaminated with up to 1497 μg g⁻¹ of Cu, 475 μg g⁻¹ of Zn, 0.82 μg g⁻¹ of Hg, 94 μg g⁻¹ of Pb and over 10,000 ngSn g⁻¹ of tributyltin (TBT). High concentrations of Hg and TBT indicate ongoing sources of these elements despite the ban on their use as biocides in paints. Sediment cores provided records of contamination since 1969. The peak concentrations of As, Hg, Pb and TBT in the sediment profile reflect their presence on boat hulls when the marina was built at the end of the 1960s. Degradation of TBT in the sediments near the boat maintenance area is slow compared to other less contaminated area of the marina.