Environmental effects of tidal power generating schemes

Summary The Severn Estuary has been proposed as a site for a tidal power generating barrage. The character of the existing environment would be changed but, if the risks of accumulating pollutants and eutrophication can be avoided, the reduction in turbidity and tidal scour could increase species diversity and productivity. The interests of wading birds and wildfowl could be accommodated by special reserve areas. The main unknowns are the hydrographic and sedimentological regimes that would follow construction of a barrage, and prediction of biological changes depends on knowing the physical and chemical nature of the altered environment.     

Effect of seed passage through vertebrate frugivores'' guts on germination: a review

The capacity of seeds to germinate after ingestion by frugivores is important for the population dynamics of some plant species and significant for the evolution of plant-frugivore interactions. In this paper the effects of different vertebrates on seed germination of nearly 200 plant species are reviewed, searching for patterns that predict the circumstances in which germination of seeds is enhanced, inhibited, or unaffected by the passage through the digestive tract of a seed disperser. It was found that seed dispersers commonly have an effect on the germinability of seeds, or on the rate of germination, or both, in about 50% of the plants they consume, although the diversity of animal species tested so far is still rather low (42 bird species, 28 non-flying mammals, 10–15 bats, 12 reptiles, 2 fishes). Enhancement of germination occurred about twice as often as inhibition.

In spite of the morphological and physiological differences in their digestive tracts, the different animal groups tested have similar effects on seed germination, although non-flying mammals tend to influence germination slightly more often than the other groups. Data on fishes are still too scarce for any generalization. Seed retention time in the dispersers' digestive tract is one factor affecting germination, and helps to explain the variation in seed responses observed among plant species, and even within a species. However other factors are also important; for example, the type of food ingested along with the fruits may affect germination through its influence on chemical or mechanical abrasion of the seed coat. Seed traits such as coat structure or thickness may themselves be responsible for some of the variation in seed retention times. Seeds of different sizes, which usually have different transit times through frugivores, and seeds of either fleshy or dry fruits, show often similar germination response to gut passage.

Seeds of different plants species differ strongly in their germination response after ingestion, even by the same frugivore species. Congeneric plants often show little consistency in their response. Even within a species variation is found which can be related to factors such as the environmental conditions under which germination takes place, seed morphology, seed age, and the season when the seeds are produced.

The effect of gut passage on germination differs between tropical and temperate zones. Seed germination of both shrubs and trees (data on herbaceous species are still scarce) in the temperate zone is more frequently enhanced than in the tropics. This result supports the hypothesis that enhanced germination may be more advantageous in unpredictable or less constant environments. Significant differences in frugivore-mediated germination are also found among different life forms. In both tropical and temperate zones, trees appear to be consistently more affected than shrubs or herbs. This might be due to an overall higher thickness of the seed coats, or to a higher frequency of seed-coat dormancy in tree species.

The influence of frugivory upon the population dynamics of a species has to be evaluated relative to other factors that influence germination and seedling recruitment at a particular site. Whether seed ingestion by dispersers is really advantageous to a plant (as has commonly been assumed) can only be assessed if we also determine the fate of the ingested seeds under natural conditions, and compare it to the fate of seeds that have not been ingested.     

Barriers to fish passage and barriers to fish passage assessments: the impact of assessment methods and assumptions on barrier identification and quantification of watershed connectivity

Barriers (culverts and dams) can impede fish passage and affect the overall habitat connectivity of rivers. However, a challenge lies in how to conceptualize and adequately measure passability at barriers. We hypothesize that estimates of barrier and watershed connectivity are dependent on assumptions about the nature of passability, and how it is measured. Specifically, we compare passability estimates in Terra Nova National Park, Canada for individual barriers for two barrier assessment methods (a rapid assessment and one based on FishXing software), two salmonid species, different fish sizes and swimming speeds, and varying hydrological conditions. Watershed connectivity was calculated using the Dendritic Connectivity Index (DCI). Lastly, we test to see what the impact of the various factors is on the practical goal: prioritizing barriers for restoration. Our results show that barrier passability estimates can vary drastically for some barriers (0–100%). In general, the rapid field-based assessment tended to give more conservative estimates of passability than those based on FishXing. Estimates of watershed connectivity were not as sensitive to the assumptions and methods used (DCI: 40–83). Fish size had the greatest effect on DCI. Importantly, variation in DCI had little impact on the restoration priorities. The same barrier was retained as the top priority >96% of the time. Thus, managers wishing to assess barriers for restoration need to carefully consider how passability is to be measured, but can reduce the impact of these decisions by considering barriers in their watershed context using a connectivity index such as the DCI.     

The leucocytes of fish: A review

The data available in the literature concerning fish thrombocytes, lymphocytes, monocytes, macrophages and granulocytes is discussed and the dearth of reliable information concerning the functional identity of most fish leucocytes is underlined. The methods of applying nomenclatures to fish leucocytes encountered in the literature is discussed in some detail and found to be unsatisfactory. An attempt is made to simplify the confused and conflicting reports by applying the concepts which have recently arisen in the field of mammalian immunology. Nomenclatures are assigned to cells on a functional and morphological basis where sufficient data exists.
Thrombocytes are responsible for clot formation and are considered to be distinct, separate and unrelated to lymphocytes. Lymphocytes are recognised as immuno-competent cells though as yet little information exists on their role in immune mechanisms. Recent work is furnishing interesting results in this direction, especially in the origin of lymphocyte populations and their co-operative responses in immunity. Previous references to monocytes and macrophages in fish are confused and the literature is discussed in the light of the new classification of the Mononuclear Phagocyte System.
Very few experimental data exist concerning granulocytic leucocytes in fish, indeed the presence of such cells with granulocytic functions still requires proof. Cells with morphological similarity to mammalian granulocytes do exist in fish but information essential for an understanding of their role in defence mechanisms is lacking. The state of the literature concerning the eosinophil, basophil and mast cell in fish is so confused that an entirely new approach to a study of these cells is warranted. It is hoped that this review will supply guidelines for future research.     

Viable gut passage of cyanobacteria through the filter-feeding fish Atlantic menhaden, Brevoortia tyrannus

We examined the contents of the alimentary tract of juvenileAtlantic menhaden, an obligate filter-feeding fish, with epifluoresencemicroscopy. All plankton taxa and detrital material observedin plankton samples from the sampling area could also be foundin the esophagus of the fish. The corresponding plankton taxawere absent from the pre-feces sampled in the hindgut with theexception of cyanobacteria, which were found intact and fluorescingas they do in nature. The survival of cyanobacteria during gutpassage and their presence in menhaden feces may enhance bothnutrient availability and the delivery of these cells to thebenthos. Additionally, diatoms frustules were found in the pre-feces,which may affect the sequestration of biogenic silica. Theseresults may have bearing on the formation of cyanobacteria blooms,nutrient flow in estuaries and the delivery of material to thesediment.     

Mean flow and turbulence characteristics of a full-scale spiral corrugated culvert with implications for fish passage

A micro-acoustic Doppler velocimeter (ADV) was used to measure three-dimensional mean velocity and turbulence characteristics in a full-scale culvert with spiral corrugations. The culvert was set up in a test bed constructed to examine juvenile salmon passage success in various culvert types. The test culvert was 12.2 m long and 1.83 m in diameter and set at a 1.14% slope. The corrugations were 2.54 cm deep by 7.62 cm peak to peak with a 5° right-handed pitch. Cross-sectional grids of ADV measurements were taken at discharges of 0.028, 0.043, 0.071, 0.099, 0.113, 0.227, and 0.453 m³/s at nine locations. In the uniform flow region, the centerline velocity profiles were consistent with fully rough turbulent flows and the friction factor was independent of Reynolds number and was very close to theoretical results. Secondary flow induced by the spiral corrugations caused asymmetries in the velocity and turbulence distributions creating a reduced velocity zone (RVZ) on the right side of the culvert as seen looking upstream, which small fish could utilize to aid their upstream passage. Velocity and axial components of turbulence in the RVZ were found to be much less than in mid-channel or on the left of the culvert, and the difference became greater at increased flow rates. In addition, cross-stream and vertical velocity components within the RVZ were small relative to the downstream axial component, while lateral and vertical turbulence intensities were comparable to the axial component. Observations from a concurrent fish passage study showed that more juvenile fish migrate through the right side of the culvert within the RVZ.     

A review of indicators of estuarine tidal wetland condition

This review critically evaluates indicators of tidal wetland condition based on 36 indicator development studies and indicators developed as part of U.S. state tidal wetland monitoring programs. Individual metrics were evaluated based on relative scores on two sets of evaluation factors. A rigor score evaluated metric development based on conceptual relevance, indicator development method, degree of independent validation, and temporal and spatial extent tested. An applicability score evaluated metrics based on cost of data collection, probable spatial extent of applicability, technical complexity, and indicator responsiveness. The majority of indicators could be classified as biotic condition indicators (81%), with vegetation (37%) and macroinvertebrate (28%) metrics composing the largest proportion. Most metrics provided a conceptual model or scientific justification (97%), were developed by correlation to environmental gradients (46%), were tested over multiple seasons or years (49%) and at multiple sites (88%). Few were independently validated (18%). Average rigor score was 10 (on a scale of 0–25) and ranged between 1 and 21. Highest rigor scores were for trematode community metrics (community similarity index, species richness) and metrics of grass shrimp (Palaemonetes pugio) individuals (gene expression, relative fecundity, embryo hatching success, larval survival). Most metrics had a high cost of data collection (63%), required field and laboratory processing (84%), would be applicable across the U.S. (72%), and were responsive to the variable of interest (44%). Mean applicability score was 4.9 (range: 2–8). Highest scores were found for metrics that only required field collection of data using simple or no instrumentation. Lowest scoring metrics required expensive equipment, specialized taxonomic knowledge, complex laboratory analysis, and/or culturing of organisms. Scores for individual metrics were grouped by indicator, then averaged and rescaled between 0 and 100 to provide a composite evaluation of the indicator they measured. Among major indicator types, biotic indicators had the highest rigor scores (mean = 44, range 20–79), followed by indicators of chemical/physical characteristics (mean = 36, range 16–56), landscape condition (mean = 31, range 24–37), and hydrology/geomorphology indicators (mean = 21, range 4–52). In contrast, biotic indicators scored lowest for applicability (mean = 58, range 25–100) and indicators of landscape condition scored highest. The results of this review suggest that the development and selection of tidal wetland indicators could be vastly improved by employing a standardized development methodology that provides uniform information about each indicator. In addition, tidal wetland indicator research should focus on the development of indicators of ecological processes and disturbance regimes.     

Surface phenotypic characteristics and virulence of Spanish isolates of Aeromonas salmonicida after passage through fish.

Eleven strains of Aeromonas salmonicida were passaged twice by intraperitoneal injection through rainbow trout and reisolated from the kidney of moribund fish. The surface characteristics and virulence of the strains changed following passage through fish. None of the in vitro tests used could effectively predict the in vivo virulence.     

Offshore renewable energy and nature conservation: the case of marine tidal turbines in Northern Ireland

The global demand for renewable energy continues to increase rapidly and with it the necessity to develop and test new technologies to deliver the power. Offshore renewable energy sources that harness wind, wave or tidal power are of major interest. Technological advances in these directions have not been matched by a clear understanding of the environmental impacts of the new devices, with most existing research concentrated on the impacts of offshore wind farms. Decisions often continue to be made without the support of a clear evidence base. Here we use an underwater tidal turbine, SeaGen, constructed and operated within the Strangford Lough marine protected area in Northern Ireland, as a case study to explore the potential impacts of the turbine as points of concern and argumentation in the decision-making processes. We use information obtained from official documents and one-to-one interviews with the main stakeholders. Our results demonstrate that during the construction and operation of the turbine the perceptions and views of different stakeholders sometimes disagreed but were often surprisingly similar in relation to both likelihood and intensity of the potential impacts of the turbine on marine biodiversity, ecosystem services and human well-being in general. The overall consensus of views was refined and evolved under an adaptive management approach over the 10 years of the discussions and decision-making processes. The results are discussed in relation to cumulative gains in knowledge, future arrays of many underwater turbines and multiple use of oceans within social ecological systems to maintain the conservation of marine biodiversity.     

A study of the fish community structure in a tidal creek.

The fish assemblage in a mangrove tidal creek was studied in monthly collections between August 1998 and July 1999 in the quadrature low tide and high tide, using a fyke net of 30 m x 1.5 m and meshes of 8 and 10 mm. Simultaneously with the biological collections, temperature, salinity, pH, water transparency, and current speed data were obtained. The collections resulted in the capture of 36,873 fish representing 22 families and 52 species. Immature individuals abounded (63.8%), and among the adult specimens there was a larger number of females. The species Anchoa parva, Harengula clupeola, Genidens genidens, and Bairdiella ronchus, contributed to 84.9% of the total capture of fish, however the contribution in mass was of 55.2%, indicating a predominance of small individuals. A smaller number of fish and species seem to occupy the area in the period between August and December, in comparison to the period between February and July, when the larger aggregations appear, mainly of the species Anchoa parva, Harengula clupeola, Opisthonema oglinum, Genidens genidens, Diapterus rhombeus, and Bairdiella ronchus. The environmental factors, pH, water transparency, and rainfall seem to have an influence in the structure of the observed biological patterns.     

Renin-angiotensin system in elasmobranch fish: A review.

The renin-angiotensin system (RAS) has been identified recently in elasmobranch fish, and the structure of angiotensin II (ANG II) is unusual ([Asp(1),Pro(3),Ile(5)]-ANG II) compared to other vertebrates. Receptors for ANG II have been identified in blood vessels and in a variety of osmoregulatory tissues including the gill, kidney and rectal gland. In addition, there is considerable binding to the interrenal gland and the stimulation of 1alpha-hydroxycorticosterone production in vitro suggests a physiological role in corticosteroidogenesis. ANG II is a potent vasoconstrictor and this effect does not appear to be mediated by sympathetic activation or catecholamine release. Although the RAS may not be involved in maintaining basal blood pressure, it may be important in situations in which blood pressure is reduced. Understanding of the role of ANG II as an osmoregulatory hormone is only just emerging with putative roles in the control of gill, rectal gland and perhaps, drinking. In addition, the stimulation of corticosteroid secretion may provide another means of controlling osmoregulation. J. Exp. Zool. 284:526-534, 1999.     

The Murray River's 'Sea to Hume Dam' fish passage program: Progress to date and lessons learned

Since its commencement in 2001, a program to facilitate fish passage on a major stretch of Australia's longest river has installed eight structures, testing and modifying their design as they go. What are the results so far and what are the implications for future directions?     

A review of the gobioid fish genusgobioides

The gobioid genusGobioides Lacepède, 1800 shares with the amblyopine gobies (Gobiidae: Amblyopinae) an eel-like, elongate body with a continuous dorsal fin and an affinity for shallow water, muddy bottom habitats. Due to similarities in external morphology and habitat requirements, some workers consideredGobioides allied with amblyopine gobies. Others, however, dispute a close relationship betweenGobioides and the Amblyopinae; morphological and ecological similarities are considered to be homoplasious. Results of this study concur with placingGobioides separate from amblyopine gobies and within the gobiid subfamily Gobionellinae.Gobioides is easily distinguished from the Amblyopinae by its larger eyes (small inGobioides vs. inconspicuous in the Amblyopinae), fewer dorsal and anal-fin rays (14–20 vs. 27–48), and different fin element to vertebra ratios (1∶1 vs. 2∶1).Gobioides reaches lengths of 500 mm SL or greater whereas amblyopines rarely exceed 300 mm SL.Gobioides comprises five species (G. africanus, G. broussoneti, G. grahamae, G. peruanus, andG. sagitta). Although these gobies occupy habitats with similar conditions,Gobioides and amblyopines are nowhere sympatric.Gobioides occurs in tropical and subtropical coastal waters of the eastern and western Atlantic as well as the tropical eastern Pacific Ocean. In the eastern Atlantic.Gobioides is known from Senegal to Zaire. In the western Atlantic.Gobioides is reported from South Carolina to southern Brazil. In the eastern Pacific,Gobioides is known from Mexico to Peru.     

Effects of organic pollutants on fish digestive enzymes: A review

A brief overview of data on the effects of organic pollutants of different chemical natures (organochlorine, organophosphorous and organotin compounds, naphthalene, formalin, nitrosoguanidine, glyphosate, and metylmercury) on the activity of fish enzymes hydrolyzing basic food components is given. It is shown that the xenobiotics listed above have different effects on fish digestive enzymes. The directions of toxicant-induced changes may differ depending on the fish species, type of hydrolyzed substratum, diapason of toxicant concentrations, and experimental conditions.     

Chemotherapy of fish diseases: a review

Fish suffer from environmental, nutritional, viral, bacterial, parasitic, and neoplastic diseases, many of which are similar to those of higher animals. The prevention and treatment of these diseases follow the same principles as diseases of other animals. Fish culture is similar to poultry husbandry in that large numbers of animals are crowded into relatively small areas, feeding is free choice, and medication for systemic infections is usually oral. External treatment of fishes is more common than of poultry, due to a higher frequency of external diseases. Many of the drugs and chemicals used in chemotherapy of fishes are the same as for higher animals. The following is a brief review of the more important drugs and their methods of administration.     

A review of chemical communication in freshwater fish

Since communication between individuals of a species of fish by chemical agents (pheromones) was first demonstrated in 1932, such a process has been suggested in many aspects of fish behavidïo'ur and development. This review describes observations on such mechanisms in shoaling behaviour and beneficial conditioning of water, homing of migratory fish, communication of alarm, 'crowding factor' (which adversely affects growth, survival and fecundity in dense populations), pair formation and spawning, and a range of other social interactions. Some of the chemicals involved have been isolated and identified, but most are indicated by behavioural observations. Pheromones are of great significance in fish behaviour and ecology, and are likely to be an important factor in culture operations.     

Protocol for the assessment of mortality and injuries in fish larvae associated with their downstream passage through hydropower dams

Reviews in Fish Biology and Fisheries - Migratory fishes are one of the groups most threatened by the interruption of river connectivity caused by reservoirs and dams. The downstream displacement...