Recruitment of pelagic fish in an unstable climate: studies in Sweden's four largest lakes

Pelagic fish population biology was studied in the large Swedish lakes V?nern, V?ttern, M?laren and Hj?lmaren. It is crucial for fish fry in temperate regions to hatch early in the growth season to survive, and achieve large size before winter, and it is suggested that the key factors are to match the spring development of phyto- and zooplankton, but to avoid predation. This is more easily accomplished by the studied spring spawners smelt (Osmerus eperlanus) and pike-perch (Stizostedion lucioperca) than autumn spawners, such as vendace (Coregonus albula). It is shown that hatching of vendace fry shortly after ice-break-up is beneficial for year-class strength. In oligotrophic large lakes with few predatory species a rapid increase in water temperature after ice-break is also promoting recruitment, whereas this is not the case in eutrophic lakes where predation pressure from other species may become too high. The results indicate that autumn spawners will have difficulties in adapting to global warming and it is also suggested that the life history can explain the large variations observed in year-class strength between years.     

Fish status survey of Nordic lakes: effects of acidification,eutrophication and stocking activity on present fish species composition

The status of fish populations in 3821 lakes in Norway, Sweden and Finland was assessed in 1995-1997. The survey lakes were chosen by stratified random sampling from all (126 482) Fennoscandian lakes > or = 0.04 km2. The water chemistry of the lakes was analyzed and information on fish status was obtained by a postal inquiry. Fish population losses were most frequent in the most highly acidified region of southern Norway and least common in eastern Fennoscandia. According to the inquiry results, the number of lost stocks of brown trout (Salmo trutta), roach (Rutilus rutilus), Arctic char (Salvelinus alpinus) and perch (Perca fluviatilis) was estimated to exceed 10000. The number of stocks of these species potentially affected by the low alkalinity of lake water was estimated to exceed 11000. About 3300 lakes showed high total phosphorus (> 25 microg L(-1)) and cyprinid dominance in eastern Fennoscandia, notably southwestern Finland. This survey did not reveal any extinction of fish species due to eutrophication. One-third of the lakes had been artificially stocked with at least one new species, most often brown trout, whitefish (Coregonus lavaretus s.l.), Arctic char, rainbow trout (Oncorhynchus mykiss), pike-perch (Stizostedion lucioperca), grayling (Thymallus thymallus), pike (Esox lucius), bream (Abramis brama), tench (Tinca tinca) and European minnow (Phoxinus phoxinus). The number of artificially manipulated stocks of these species in Fennoscandian lakes was estimated to exceed 52000. Hence, the number of fish species occurring in Nordic lakes has recently been changed more by stockings than by losses of fish species through environmental changes such as acidification.     

The environmental consequences of alien species in the Swedish lakes Mälaren, Hjälmaren, Vänern and Vättern

Twenty alien species have become established in the lakes M?laren, V?nern, V?ttern and Hj?lmaren. Intentional introductions include fish and the signal crayfish from North America, ornamental plants, and the Canada goose. Unintentional introductions include the crayfish plague introduced with infected crayfish, the zebra mussel, and Chinese mitten crab introduced with ballast water. The introduction of pathogens and parasites, in particular the crayfish plague, to the lakes has had the greatest environmental and socioeconomic effects and has contributed to the decimation of the indigenous noble crayfish. The stocking of brown trout and salmon with origins from different biogeographical regions has contributed to the extinction of relict indigenous fish species in L. V?nern. Although major ecosystem damage caused by the introduction of alien species, with the exception of the crayfish plague, has not occurred in the four large Swedish lakes, local problems of considerable dignity occur occasionally.     

杭州西湖水生高等植物的恢复与水生生态修复

在过去的50年，西湖一直被富营养化问题所困扰。迄今为止，采用了各种工程措施进行治理，耗资数亿，但收效不明显。为了进一步解决西湖富营养化问题，提出需要用生态方法去解决生态问题，通过生态学手段，恢复、重建高等水生植物带落，增加水生生物多样性，改善西湖水生生态系统的结构和功能，控制藻类来修复西湖水生生态系统。科学地选择先锋种类组合、消除草食性鱼类的影响、合理地控制水位是西湖水生植被恢复过程中的三个重要措施。     

Study on PCBs,PCDD/Fs,organochlorine pesticides,heavy metals and arsenic content in freshwater fish species from the River Turia (Spain)

In this study samples of common trout, European eel and barbel have been analysed for the levels of heavy metals such as lead (Pb), cadmium (Cd), zinc (Zn), copper (Cu), and the metalloid arsenic (As). Polychlorinated biphenyls (PCBs), including three non-ortho substituted PCBs, 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and DDT and its two main metabolites were also analysed in some selected samples, in order to evaluate the extent of contamination of the River Turia basin. All samples presented detectable levels of the elements analysed, presenting zinc the highest concentrations. European eel was the species found to highly accumulate these contaminants. Regarding organochlorinated compounds, seven samples exhibited detectable levels of the most toxic PCDD/Fs congener, the 2,3,7,8-TCDD. Non-ortho PCBs were not detected or not quantified in almost all samples and the sum of the individual PCB congeners determined were low compared to other aquatic ecosystems with similar fish species.     

Mercury in sediment and fish communities of Lake Vänern, Sweden: recovery from contamination

The past effluents of mercury (Hg) into Lake V?nern were considerable. The consequences of, and recovery from these have been monitored through continuous measurements of mercury in sediment and fish. Mercury levels in lake sediments in the vicinity of the main source of mercury, a chloralkali plant on the northern shore, have only decreased by slightly more than a half since the mid-1970s, despite a radical decrease in effluents from the source, already during the 1960s. The mercury levels in pike (Esox lucius) have decreased to a similar extent during this time period. They are now about 30% higher in the worst affected parts of the lake compared to the least affected parts. Lower levels have been measured in perch (Perca fluviatilis) and salmonoid fish in the lake. Despite the increased presence of mercury in the sediment of Lake V?nern, the mercury levels in the fish of the lake are relatively low compared to fish in lakes situated in the same region, but not affected by any local mercury effluents. As calculated, the total fish biomass of L. V?nern holds less than 1000th of the amount of mercury contained in the upper, biologically active layers of the bottom sediment of the lake. This demonstrates the potential influence of various environmental factors and motivates continued monitoring of mercury levels in the lake in the future.     

Challenges in assessing biological recovery from acidification in Swedish lakes

Since the 1980s, Swedish lakes have in general become less acidified. Assessment of biological recovery is, however, hampered by poor pre-acidification data, confounding effects of climate change, and few lakes with annual sampling of fish and other organisms. Only three critically acidified, but non-limed, lakes had two decades of fish monitoring. The lakes had not yet recovered to pre-industrial chemical targets. Fish had low species richness compared to other organism groups. Roach (Rutilus rutilus) and/or European perch (Perca fluviatilis) were the dominant fish species, and the acid-sensitive roach had been lost from one of the lakes. Calcium decreased, possibly approaching pre-acidification concentrations, but exceeded minimum levels needed to sustain some Daphnia species. High or increasing levels of total organic carbon, likely due to reduced acidification and climate change, might influence the biological communities in unexpected ways, for example, facilitating more frequent occurrence of the invasive algae Gonyostomum semen.     

Analysis of the effects of rotational larviciding on aquatic fauna of two Guinean rivers: the case of permethrin.

Within the Onchocerciasis Control Programme about 50,000 km of west African rivers have been regularly sprayed with larvicides to control the vector of dermal filariasis caused by Onchocerca volvulus. Since the beginning of the programme invertebrates and fish data were collected to monitor adverse effects on non-target organisms. The regular series of biological and hydrological data collected in two Guinean rivers were analysed to evaluate the effects of rotational larviciding with particular attention to permethrin, as preliminary acute toxicology tests and semi-field experiments suggest it has stronger effects on non-target fauna in respect to other larvicides. Invertebrates and fish variations in biomass and species richness are seasonal and flow-related and the results presented here do not support any evidence of specific effects of permethrin application on the biological targets monitored. Larvicide applications influence community structures, putting pressure on some taxonomic groups, causing, for example, the rarefaction of some taxa. In spite of the above results, the scarcity of some invertebrate systematic units does not result in a significant reduction of total invertebrate density because of the corresponding increase in other systematic units. In nature the studied aquatic communities would rarely be in equilibrium because of frequent natural stresses, such as drought and spate events, the biological variations discussed are to be considered ecologically acceptable.     

Effluent profile of commercially used low-phosphorus fish feeds

Excess phosphorus (P) in aquaculture feeds contributes to the eutrophication of natural waters. While commercially available low-P (LP) fish feeds have been developed, there is uncertainty about their potential to reduce effluent P while maintaining fish growth relative to regular P (RP) feeds. We therefore simulated commercial aquaculture conditions and fed for 55 days rainbow trout (approximately 190 kg/raceway, n = 3 raceways/diet) RP (1.4% total P) and LP (1.0%) feeds then determined effluent P levels, fish growth, and feed costs. Excretions of fecal-P and soluble-P, but not particulate-P, in effluents were greater in RP than in LP ponds. Fish growth, bone-P and plasma-P were similar between diets, demonstrating that LP feeds can lower effluent P levels without compromising growth. Costs were 0.97 dollars/kg fish production for LP feeds, and 0.74 dollars/kg for RP. Because feed is the largest variable cost in commercial aquaculture, the use of LP feeds can significantly increase production costs.     

Vitellogenin content in European eel (Anguilla anguilla) in Flanders, Belgium

As part of a large-scale monitoring program of bioaccumulating contaminants in the European eel (Anguilla anguilla) in Flanders (Belgium), we investigated potential effects of xenoestrogens in these fish. The present paper describes the results of the plasma vitellogenin (VTG) content, measured in 142 eels sampled at 20 different locations, in relation to the internal pollution levels. To validate the blood VTG assays, a small number of eels (n=8) was exposed to 10 microg ethinylestradiol/l (EE2) for 9 days. In this experiment, VTG was detected as a protein with a molecular weight of 214 kDa and confirmed by Western blotting. Compared with the solvent controls, significantly higher concentrations of VTG were measured in EE2 exposed eel. However, the VTG content was relatively low compared with other fish species exposed to high concentrations of estrogens. The plasma VTG content of eels from the field study was very low, despite a very high internal load of endocrine disrupters. These results, together with previously published studies, suggest that immature yellow European eel might not be the best sentinel species to study the effects of estrogenic compounds on VTG levels of wild fish populations.     

Offshore windmills and the effects of electromagnetic fields on fish

With the large scale developments of offshore windpower the number of underwater electric cables is increasing with various technologies applied. A wind farm is associated with different types of cables used for intraturbine, array-to-transformer, and transformer-to-shore transmissions. As the electric currents in submarine cables induce electromagnetic fields there is a concern of how they may influence fishes. Studies have shown that there are fish species that are magneto-sensitive using geomagnetic field information for the purpose of orientation. This implies that if the geomagnetic field is locally altered it could influence spatial patterns in fish. There are also physiological aspects to consider, especially for species that are less inclined to move as the exposure could be persistent in a particular area. Even though studies have shown that magnetic fields could affect fish, there is at present limited evidence that fish are influenced by the electromagnetic fields that underwater cables from windmills generate. Studies on European eel in the Baltic Sea have indicated some minor effects. In this article we give an overview on the type of submarine cables that are used for electric transmissions in the sea. We also describe the character of the magnetic fields they induce. The effects of magnetic fields on fish are reviewed and how this may relate to the cables used for offshore wind power is discussed.     

Mapping Biological Resources in the Coastal Zone: An Evaluation of Methods in a Pioneering Study from Norway

For many years, the planning and management of terrestrial areas has been supported by a detailed knowledge of the distribution of habitats and their associated species. However, the detailed mapping of biological resources in extent coastal areas, such as the Norwegian coastal zone, is unrealistic due to its enormous coastline. Here, we present a useful and feasible approach and a set of simple, cost-effective methods which are suitable for providing a broad-scale overview of marine habitats and fish resources. This approach was developed in conjunction with a pioneer study conducted along the southern coast of the Skagerrak, where we combined knowledge gathered from local fishermen with scientific knowledge of important species and nature types to establish a coastal sea mapping program. GIS modeling tools were used in both the mapping program and to integrate local and scientific knowledge into digital maps made available to local area management. This multi-faceted approach, which combines local knowledge and scientific methods, provides valuable information with respect to marine biodiversity, and has been used extensively by local environmental management.     

Levels of polychlorinated biphenyls and organochlorine pesticides in some edible marine organisms from the Central Adriatic Sea

Concentrations of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCs) were found in tissue of marine organisms such as Mediterranean mussel, Norway lobster, red mullet, common cuttle-fish, European flying squid, European anchovy, European pilchard and Atlantic mackerel, coming from two sites along the Abruzzo coast of the Adriatic Sea. Species were selected due to their habitat, trophic level, feeding behaviour and their use in the Italian diet. Mussels, filter feeder and sedentary organisms, were used in order to test water pollution whereas Norway lobster and red mullet (benthic fish) were used in order to test sediment pollution. The concentration of ?PCBs exceeded that of ?OCs in the samples analysed. The highest concentrations of ?PCBs (1415 ng/g lipid weight) and ?OCs (507 ng/g lipid weight) were found in pilchard while the lowest concentrations of the same pollutants were found in cephalopods. Our results have shown that species such as anchovy, pilchard and mackerel, were the most polluted due to their location at the last level of the trophic chain. All samples contained different concentrations of PCBs and among these, congeners 153 and 138 were the most representative. Among the OCs, except for the cuttle-fish, the highest concentrations were found for p,p(')-DDE and p,p(')-DDD that are metabolite of DDT. The prevailing DDE presence, compared to DDT (high DDE/DDT ratio), suggested that the biotransformation rate of pollutants was very efficacious in fish and above all in crustaceans. Results have also been interpreted in terms of geographical distribution and organisms' biological cycle. None of the samples analysed exceeded the tolerance limits established by the OCs Italian legislation.     

Four decades of research on the Swedish large lakes Mälaren, Hjälmaren, Vättern and Vänern: the significance of monitoring and remedial measures for a sustainable society

The large lakes of Sweden, M?laren, Hj?lmaren, V?ttern and V?nern, have been subjected to water-quality monitoring for almost four decades. Physicochemical variables, plankton and benthic invertebrates have been regularly assessed. Hydrological and sediment conditions, macrophytes, fish, primary production, bacteria and attached algae have been periodically investigated. The human impact, including industrial activities, was reflected in excessive amounts of organic matter, nutrients, metals and persistent organic compounds. From the late 1960s all municipal sewage works in the catchments of the lakes were upgraded to the highest technical standard, including chemical precipitation of phosphorus, and phosphorus discharge from the sewage works was thereby reduced by 90-95%. In addition, industries were obliged to restrict discharge of harmful substances. The reactions of the lakes to the remedial measures are discussed as well as the value of various indicators. The studies were instrumental in designing a national lake monitoring program. Additionally, results from large lake monitoring have contributed to the establishment of national water-quality criteria including, physical, chemical, and biological indicators.     

Spatial distribution of ciguateric fish in the Republic of Kiribati

Ciguatera is food poisoning caused by human consumption of reef fish contaminated with ciguatoxins (CTXs). The expanding international trade of tropical fish species from ciguatera-endemic regions has resulted in increased global incidence of ciguatera, and more than 50 000 people are estimated to suffer from ciguatera each year worldwide. The Republic of Kiribati is located in the Pacific Ocean; two of its islands, Marakei and Tarawa, have been suggested as high-risk areas for ciguatera. The toxicities of coral reef fish collected from these islands, including herbivorous, omnivorous and carnivorous fish (24% [n = 41], 8% [n = 13] and 68% [n = 117], respectively), were analyzed using the mouse neuroblastoma assay (MNA) after CTX extraction. The MNA results indicated that 156 fish specimens, or 91% of the fish samples, were ciguatoxic (CTX levels >0.01 ng g⁻¹). Groupers and moray eels were generally more toxic by an order of magnitude than other fish species. All of the collected individuals of eight species (n = 3-19) were toxic. Toxicity varied within species and among locations by up to 10 000-fold. Cephalapholis argus and Gymnothorax spp. collected from Tarawa Island were significantly less toxic than those from Marakei Island, although all individuals were toxic based on the 0.01 ng g⁻¹ threshold. CTX concentrations in the livers of individuals of two moray eel species (Gymnothorax spp., n = 6) were nine times greater than those in muscle, and toxicity in liver and muscle showed a strong positive correlation with body weight. The present study provides quantitative information on the ciguatoxicity and distribution of toxicity in fish for use in fisheries management and public health.     

Genetic population structure of fishes: implications for coastal zone management

The pattern for distribution of genetic variation within and between populations is referred to as the genetic population structure of the species. To avoid depletion of genetic resources sustainable management should be based on knowledge of this structure. We discuss key aspects of genetic population structure in the context of identifying biological units for fisheries management, suggesting three basic types of structuring: distinct populations; continuous change; and no differentiation. The type of structure determines how units for genetically sustainable management are to be identified. We also review what is currently known regarding the genetic population structure of fishes exploited in the Swedish part of the Baltic Sea, and conclude that sufficient genetic information is lacking for most of the species. This is a serious problem, particularly considering that populations of several commercially exploited fishes are declining and some exhibit recruitment problems. For six species, Atlantic herring, Atlantic salmon, brown trout, European eel, turbot, and pike, sufficient genetic data are available to provide at least basic information on genetic structure and genetic units for biologically sustainable use. Current management practices do not sufficiently consider these data.     

EOX and organochlorine compounds in fish and ringed seal samples from Lake Ladoga, Russia

Information about the pollution of Lake Ladoga, the largest lake in Europe, has been controversial. Various effluents and drainage waters affect the quality of the lake water. Wastewaters have caused eutrophication of parts of Lake Ladoga, but concentrations of persistent organic pollutants in the lake's food webs are poorly understood. In this study, concentrations of some organochlorine compounds, chlorophenols (CPs), and extractable organic halogen (EOX) were determined in smelt (Osmerus eperlanus), vendace (Coregonus albula), pikeperch (Lucioperca lucioperca), whitefish (Coregonus lavaretus), and the Ladoga seal (Phoca hispida ladogensis) from the northern part of the lake. The concentrations of organochlorine compounds in fish were low. Concentrations were between 0.07 and 0.15, 0.65 and 1.0, and 0.29 and 0.48 mg/kg lipids for hexachlorobenzene, total polychlorinated biphenyl (PCB) and p,p'-DDE, respectively. The results indicated biomagnification from smelt and vendace to pikeperch and ringed seal. In ringed seals, concentrations of PCB and DDT were 12 and 29 times higher than in fish used by ringed seals as major food sources.     

Contaminants and their effects on estuarine and coastal organisms in the United Kingdom in the late twentieth century

The biological effects of contaminants in British estuaries and coastal waters have been studied for over 100 years. Until the 1970s. the major pollution impact on estuarine organisms was probably caused by poorly treated sewage which led to severe oxygen deficits and consequent asphyxiation of many water-breathers. However, since the introduction of improved sewage treatment in the last 30 years, a number of continuing impacts have come to light which represent true toxic effects of micro-contaminants. Sublethal changes observed in various bioassays and biomarkers are widespread in both fish and invertebrates, and in the most urbanised and industrialised estuaries, these effects are probably having impacts at the population and community levels. For example, there is good evidence to show that tributyltin from some antifouling paints has not only affected the sexuality and reproductive success of individual estuarine and coastal molluscs, but has also damaged some benthic communities of which molluscs are but a part. Although there are data to show that some contaminant concentrations are now declining, we do not yet have enough data in most cases to decide whether organisms have also begun to recover. This paper reviews the entire field of contaminant effects in UK estuarine and marine waters, focusing especially on the years 1985-2000, and makes some recommendations for future research and monitoring programmes.     

Assessment of DDT and mercury levels in fish and sediments in the Iriri River,Brazil: Distribution and ecological risk

Abstract

In order to assess the risk of exposure of human populations to dichlorodiphenyltrichloroethane (DDT) and mercury, muscles of five fish species were analysed, along with the surface sediment of 14 Iriri River sampling sites. The fish specimens were sacrificed by the spinal section, prior to sex identification, body weight determination and total length. Considering the fish specimens studied, 11% of them showed concentrations of mercury higher than the maximum established by the World Health Organization for safe human consumption. A positive correlation between fish body weight and mercury concentration was observed, besides a positive correlation between the fish size and Hg concentration. Significant differences (P?<?0.05) were found between mean concentrations of DDT and metabolites among species of fish studied. In the Plagioscion squamossissimus species, the highest concentration of total DDT (151.4?ng/g) was found, while in Eugerres Brasilianus species, the lowest. However, the DDT levels in fish muscle of studied species are below the maximum set by FAO-Alimentarius CODEX. In the sediments, total DDT ranged from 11.58?ng/g to 48.4?ng/g, which is associated with the historical DDT use in the Amazon. According to sediment quality guidelines, these levels have a moderate toxic effect in almost all of the studied region.