Divergent trends in anadromous salmonid populations in Norwegian and Scottish rivers

The Atlantic salmon (Salmo salar) is a charismatic anadromous fish of high conservation and economic value. Concerns have been expressed regarding the long-term viability of fisheries throughout the species''s distributional range because of abundance variations that cannot currently be explained or predicted. Here, we analyse long-term catch data obtained over a wide geographical range and across a range of spatial subscales to understand more fully the factors that drive population abundance. We use rod catch data from 84 Norwegian rivers over 125 years (1876–2000) and 48 Scottish rivers over 51 years (1952–2002). The temporal correlation in catches is very long-term, with trends persisting over several decades. The spatial correlation is relatively short-range, indicating strong local-scale effects on catch. Furthermore, Scottish salmon populations exhibit recent negative trends in contrast to some more positive trends in Norway—especially in the north.     

Ecological subspecies and locally temporal populations of anadromous fish

Intraspecific organization and structure of anadromous fish populations (in terms of species of the Oncorhynchus, Salvelinus, and Tribolodon genuses) were investigated. It was shown that the ecological, genetic, and morpho-physiological differences in ecology-temporal (seasonal) races of these fish reached the rank of ecological subspecies. The expediency of more careful and detailed study of intraspecific organization, ecological and locally temporal differentiation of fish, and consideration of the results of these researches was shown in the development of a polymorphic species concept as well as optimization of fish industry—the sustainable organization of fishing, artificial fish breeding, and introduction of fish.     

Catchability: a key parameter for fish stock assessment

Summary Catchability is a concept in fishery biology which reflects the efficiency of a particular fishery. Its quantitative magnitude is expressed by the catchability coefficient, which relates the biomass abundance to the capture or fishing mortality. This paper is a comprehensive review of catchability including the development of our knowledge, interpretation and estimation.Catchability patterns indicate that the catchability coefficient has been used in two main lines: (a) increased efficiency of fishing effort and (b) its relation to population fishery processes for assessment and management purposes. It involves various aspects of the fishery, such as individual and population biology, characteristics of the fishing gear, amount of fishing, fishing strategies, and environmental fluctuation, among others.The concept is proposed of an integrated model of the catchability coefficient, which incorporates various of the aspects mentioned above. It is illustrated with two examples of its application: the red grouper (Epinephelus morio) fishery from the Campeche Bank, Gulf of Mexico, and the sardine (Sardinops caeruleus) fishery from the Gulf of California.     

Response of fish assemblages to water quality in boreal rivers

The relationship between fluvial fish assemblages and environmental variables including water quality was studied by nonmetric multidimensional scaling (NMS) and generalised regression neural network (GRNN). Fish assemblages in the studied boreal rivers in Central Finland showed a higher response to water quality than to other environmental variables such as altitude and river width. Of the water quality parameters, total phosphorus, oxygen saturation in winter and solids had the highest influence on fish assemblages. Brown trout (Salmo trutta L.) responded to water quality strongly by favouring pristine waters. Among other fish species, the responses were lighter, and the relative contribution of environmental variables varied. Percentage of fishless sites, i.e. no catch in electrofishing, was 4.4% when pH ≥ 6, and 38.2% when pH < 6. However, the most effective way to influence the fish assemblage composition, and to raise the fish-based FIFI integrity index value, would be to reduce loading of solids and phosphorus, rather than depressing acidification.     

DNA viruses associated with diseases of marine and anadromous fish

The association of DNA-containing viruses with diseases of marine and anadromous fish is reviewed. One section of the review describes those diseases with a proven viral etiology. Available information on the physical, chemical, and biological properties of the viruses is included. Another section deals with those diseases where a viral etiology is suspected but not established. The primary evidence associating viruses with many of these diseases is the observation of virus particles in electron micrographs of thin sections of tissue samples from diseased fish. Finally, the possible role of pollutants, and other stress factors, in predisposing fish to viral infection is discussed as are the problems associated with studying diseases of wild fish populations.     

Mechanisms of seawater acclimation in a primitive,anadromous fish,the green sturgeon

Relatively little is known about salinity acclimation in the primitive groups of fishes. To test whether physiological preparative changes occur and to investigate the mechanisms of salinity acclimation, anadromous green sturgeon, Acipenser medirostris (Chondrostei) of three different ages (100, 170, and 533 dph) were acclimated for 7 weeks to three different salinities (<3, 10, and 33 ppt). Gill, kidney, pyloric caeca, and spiral intestine tissues were assayed for Na⁺, K⁺-ATPase activity; and gills were analyzed for mitochondria-rich cell (MRC) size, abundance, localization and Na⁺, K⁺-ATPase content. Kidneys were analyzed for Na⁺, K⁺-ATPase localization and the gastro-intestinal tract (GIT) was assessed for changes in ion and base content. Na⁺, K⁺-ATPase activities increased in the gills and decreased in the kidneys with increasing salinity. Gill MRCs increased in size and decreased in relative abundance with fish size/age. Gill MRC Na⁺, K⁺-ATPase content (e.g., ion-pumping capacity) was proportional to MRC size, indicating greater abilities to regulate ions with size/age. Developmental/ontogenetic changes were seen in the rapid increases in gill MRC size and lamellar length between 100 and 170 dph. Na⁺, K⁺-ATPase activities increased fourfold in the pyloric caeca in 33 ppt, presumably due to increased salt and water absorption as indicated by GIT fluids, solids, and ion concentrations. In contrast to teleosts, a greater proportion of base (HCO₃ ⁻ and 2CO₃ ²⁻) was found in intestinal precipitates than fluids. Green sturgeon osmo- and ionoregulate with similar mechanisms to more-derived teleosts, indicating the importance of these mechanisms during the evolution of fishes, although salinity acclimation may be more dependent on body size.     

An assessment of a tow net used to sample coarse fish fry in rivers

The design and use of a tow net for sampling coarse fish fry in rivers are described, and its performance over a year is discussed with regard to species selectivity and size selectivity. The extent to which it can be used to provide data on the comparative abundance of the fry and their mean lengths and associated variances are described.     

The law of the sea and management of anadromous fish stocks

Abstract

Unilateral declarations of 200‐mi fishing zones by coastal states are likely to find universal recognition in new articles of international law. These probably will conform to the Single Negotiating Text currently under discussion in continuing sessions of the Third Conference on the Law of the Sea. The articles of this Text are clearly designed to protect and strengthen the fisheries rights of coastal states. Ironically, the new rules may prove counterproductive in respect of the major salmon stocks that migrate beyond 200‐mi limits. Effective protection of state‐of‐origin rights on the high seas beyond these limits will be difficult. Distant water fishing fleets experiencing reduced access to 200‐mi coastal zones will be tempted to increase, their efforts on stocks found in the remaining high seas. Salmon interception by neighboring states will also remain a problem. The article analyzes protective strategies and accommodations that may be pursued by states of origin.     

Intestinal transport following transfer to increased salinity in an anadromous fish (Oncorhynchus mykiss)

The ability to transition from freshwater to seawater environments is an intrinsic requirement of the life history of some fish species, including the anadromous rainbow trout (Oncorhynchus mykiss). The differences between hyper- and hypoosmoregulation are developed quickly (in hours to days), and at all scales, from gene expression to organ function. In this study, intestinal ion and water transport was examined in O. mykiss following acute transfer from freshwater (FW) to 70% seawater (SW). Plasma [Mg2+] increased at 24h post-transfer but recovered by 72 h. In the intestinal fluids, total CO? was found to increase with SW exposure/acclimation, while [Na+] decreased after 24h of SW exposure. Overall, in vitro experiments demonstrated the importance of base secretion to epithelial water uptake, and suggested that the primary physiological adjustments occurred 24-72 h after acute SW transfer. The mRNA expression of ion transporters important for intestinal osmoregulation and maintenance of acid-base balance was also investigated. A Na+/H+ exchanger (NHE2) and anion exchanger (SLC26a6) were hypothesized to be involved in the transport of acid-base equivalents, Na+, and Cl?, but were not uniformly expressed across tissue samples, and expression, where present, did not change following salinity transfer. NHE1, however, was expressed in all examined tissues (gill, kidney, anterior intestine, and pyloric cecae), but exhibited no changes in expression following acute salinity transfer.     

The Trophic Diatom Index: a new index for monitoring eutrophication in rivers

A index for monitoring the trophic status of rivers based on diatom composition (‚trophic diatom index’, TDI) has been developed, in response to the National Rivers Authority (England & Wales)'s needs under the terms of the Urban Wastewater Treatment Directive of the European Community. The index is based on a suite of 86 taxa selected both for their indicator value and ease of identification. When tested on a dataset from 70 sites free of significant organic pollution, this index was more highly correlated with aqueous P concentrations than previous diatom indices. However, where there was heavy organic pollution, it was difficult to separate the effects of eutrophication from other effects. For this reason, the value of TDI is supplemented by an indication of the proportion of the sample that is composed of taxa tolerant to organic pollution. The index was tested on the R. Browney, N-E. England, above and below a major sewage discharge. TDI values indicated that the effect of inorganic nutrients on the river downstream of the discharge was slight as the river was already nutrient-rich, but there was a large increase in the proportion of organic pollution-tolerant taxa. This indicates that the river was already so eutrophic upstream of the discharge that tertiary treatment to remove P would not be effective unless other aspects of the discharge were also improved.     

Seasonal occurrence of helminths in the anadromous fish Coilia nasus (Engraulidae): parasite indicators of fish migratory movements

To understand the seasonal migration of the anadromous Coilia nasus , we attempted to identify the parasites infecting C. nasus and determine their seasonal occurrence. From June 2007 to July 2008, a survey of 775 C. nasus individuals from the estuary of the Yangtze River and the coast of the East China Sea revealed more than 7,300 parasites associated with the gills and alimentary tracts of C. nasus . The following 6 helminth taxa were identified, i.e., the monogeneans Heteromazocraes lingmueni and Helciferus tenuis, the digenean Elytrophallus coiliae, the acanthocephalan Acanthosentis cheni , and larvae of the nematodes Anisakis simplex and Contracaecum sp., all of which are marine or brackish-water parasites. The absence of freshwater helminths suggested that the parasites acquired in freshwater may have been accidentally, and easily, lost by the time the fish had reached the estuary and coast. Contrary to seasonal occurrence of the parasites' life cycles, the lowest mean abundance and prevalence of H. lingmueni and A. cheni occurred in August, which suggested the immigration of C. nasus from freshwater to the Yangtze estuary, with lower parasite burdens. The highest mean abundance and prevalence of the nematodes A. simplex and Contracaecum sp. in May and June, and the lowest in August, indicated the arrival of the fish from the coast and the Yangtze River, to the estuary, respectively. These findings suggested that a majority of the fish prepared for spawning migration in the estuary in spring and early summer and returned to the estuary after spawning in the lower and middle reaches of the Yangtze River in late summer.     

A probabilistic model characterizing fish assemblages of French rivers: a framework for environmental assessment

1. Management of running waters and assessment of water quality trends require the use of biological methods. Among potential indicators, fish assemblages are of particular interest because of their ability to integrate environmental variability at different spatial scales. 2. The French Water Agencies and the Ministry of the Environment initiated a research programme to develop a fish-based index that would be applicable nation-wide. Such an index should encompass the relative importance of geographic, ecoregional and local factors influencing the distribution of riverine fishes. 3. An effective way of using the information available from fish assemblages to establish such an index is through the use of the 'reference condition approach' which involves testing a fish assemblage exposed to a potential stress against a reference condition that is unexposed to such a stress. 4. Logistic regression procedures were applied, using a fish data set of 650 reference sites fairly evenly distributed across French rivers and defined by some easily measured regional and local characteristics, to elaborate the simplest possible response model that adequately explains the observed patterns of occurrence for each species of a fish assemblage at a given site of any given river. This allows us to predict a 'theoretical' assemblage at a site. 5. The models were validated using a second independent data set of 88 reference sites. Using a third data set of 88 disturbed sites, the observed assemblages were then compared against the reference condition as defined by the 'theoretical' assemblages. The amount of deviation between the expected and observed assemblages within these sites is used as a measure of degradation. 6. This approach could be used as a framework for adapting and calibrating a multimetric index, thereby serving as a practical technical reference for conducting cost-effective biological assessments of lotic systems.     

EROD activity in gill filaments of anadromous and marine fish as a biomarker of dioxin-like pollutants

The applicability of a gill filament-based ethoxyresorufin O-deethylase (EROD) assay, originally developed in rainbow trout, was examined in Atlantic salmon (Salmo salar), Arctic charr (Salvelinus alpinus), Atlantic cod (Gadus morhua), saithe (Pollachius virens) and spotted wolffish (Anarhichas minor). All species but spotted wolffish showed strong EROD induction in tip pieces of gill filaments following 48 h of exposure to waterborne beta-naphthoflavone. Atlantic salmon parr, smolts held in freshwater and smolts transferred to seawater showed EROD induction of similar magnitude. Arctic charr, differing 11-fold in body weight, showed similar EROD activities as expressed per gill filament tip. Laboratory exposure of saithe to water and sediments collected at polluted sites, resulted in strong EROD induction. In conclusion, the gill filament assay seems useful for monitoring exposure to aryl hydrocarbon receptor agonists in various species. Furthermore, smoltification status, water salinity and body size proved to have minor influence on gill filament EROD activity. However, the results in spotted wolffish show that some species may be less suitable for monitoring using the gill assay. Assessment of gill filament EROD activity in fish exposed to polluted water and sediments in the laboratory proved to be an easy and cost-effective way to survey pollution with dioxin-like chemicals.     

Re-colonization of Atlantic and Pacific rivers by anadromous fishes: linkages between life history and the benefits of barrier removal

The last two decades have seen a rapid increase in barrier removals on rivers of the Northern Hemisphere, often for the explicit purpose of expanding the abundance, spatial distribution, and life history diversity of migratory fishes. However, differences in life history such as seasonal timing of migration and reproduction, iteroparity versus semelparity, and the extent of natal homing are likely to affect the capacity for expansion and re-colonization by taxa such as alosines, lamprey, and salmonids. We first review some basic life history traits that may affect re-colonization by migratory fishes, and then present selected examples from Atlantic and Pacific basins to illustrate these patterns and their implications for the success of barrier removal as a measure to advance the goal of fish conservation. We conclude that diadromous fishes have the capacity to rapidly re-colonize newly available habitats, though the life history patterns of each species, the proximity to source populations in the same or nearby river systems, and the diversity of habitats available may control the patterns and rates of re-colonization.     

Putting pharmaceuticals into the wider context of challenges to fish populations in rivers

The natural range of fish species in our rivers is related to flow, elevation, temperature, local habitat and connectivity. For over 2000 years, humans have altered to varying degrees the river habitat. In the past 200 years, we added to the environmental disruption by discharging poorly treated sewage, nutrients and industrial waste into our rivers. For many rivers, the low point arrived during the period of 1950s–1970s, when rapid economic development overrode environmental concerns and dissolved oxygen concentrations dropped to zero. In these more enlightened times, gross river pollution is a thing of the past in the Developed World. However, persistent legacy chemical contaminants can be found in fish long after their discharge ceased. Changes in habitat quality and morphology caused and continue to cause the disappearance of fish species. The range of fish stressors has now increased as temperatures rise, and non-native fish introductions bring new diseases. The threat from pharmaceuticals to fish populations remains hypothetical, and no studies have yet linked change in fish populations to exposure.     

Global scale patterns of fish species richness in rivers

Explanations of spatial and temporal variation in species richness is a central theme in community ecology Until recently, most research has focused on small-scale phenomena, often emphasizing on local environmental factors and, thus, poorly reflecting large-scale processes that organize species richness In this paper, we analyze variations in species richness of indigeneous freshwater fish on a worldwide scale We show that factors related to species-area and species-energy theories statistically explain most of the variation in freshwater fish species richness across continents Historical events supposed to influence present distributions offish are of little assistence in explaining variations in fish species richness at the global scale Our model, which uses easily measured factors, should also be of practical value to aquatic conservation biology and natural resource management