Challenges to effective fishing and preferred fishing gear in a hydrodynamic freshwater system

Challenges to fishing and preferred gear of multiple used Lake, whose water depth is controlled by opening of its dam gate were investigated. Geographic survey, interview and focused group discussion of fishermen were used to assess factors influencing effectiveness of fishing and the preferred gear of Asejire Lake. Water usage (s) such as frequency of Complete and Partial Opening of Dams Gate (CODG and PODG) were investigated as indices for hydrodynamic condition. Response during focused group discussion with about 33% of fishermen of the Lake were obtained on sources of disturbance to effective fishing (SDEF), most effective gear (MEG)- least environmentally perturbed gear, comparability of catch structure of preferred gear to conventional gear and sustainability of superiority of preferred gears in situations outside hydrodynamic condition (SSPPG). The PODG occurred 1-7times/Month-dry season, 15-18times/Month-wet season; CODG occurred 1-2times/Month in both season; Interval of CODG was 3-17 and 5-12days (dry and wet season). It affected set-net and catch. The SDEF were gear availability, weather condition, dam’s gate opening, religion activities and Health of fisher-folks. 50% respondents accepted opening of dams gate as most important disturbance while religion was least (5% respondents accepted). 60% respondents accepted traps as MEG being the least affected while 75% respondents accepted Gura cage trap as the MEG among traps.90% respondents accepted that among traps, its catch structure was closest (comparable) to conventional gear. However, 75% respondents rejected SSPPG. Opening of dams’ gate creates hydrodynamic condition and it affects fishing. Gura trap was preferred for fishing hydrodynamic condition.

Some considerations on coastal processes relevant to sea level rise

The effects of potential sea level rise on the shoreline and shore environment have been briefly examined by considering the interactions between sea level rise and relevant coastal processes. These interactions have been reviewed beginning with a discussion of the need to reanalyze previous estimates of eustatic sea level rise and compaction effects in water level measurement. This is followed by considerations on sea level effects on coastal and estuarine tidal ranges, storm surge and water level response, and interaction with natural and constructed shoreline features. The desirability to reevaluate the well known Bruun Rule for estimating shoreline recession has been noted. The mechanics of ground and surface water intrusion with reference to sea level rise are then reviewed. This is followed by sedimentary processes in the estuaries including wetland response. Finally comments are included on some probable effects of sea level rise on coastal ecosystems. These interactions are complex and lead to shoreline evolution (under a sea level rise) which is highly site-specific. Models which determine shoreline change on the basis of inundation of terrestrial topography without considering relevant coastal processes are likely to lead to erroneous shoreline scenarios, particularly where the shoreline is composed of erodible sedimentary material. With some exceptions, present day knowledge of shoreline response to hydrodynamic forcing is inadequate for long-term quantitative predictions. A series of interrelated basic and applied research issues must be addressed in the coming decades to determine shoreline response to sea level change with an acceptable degree of confidence. (PDF contains 189 pages.)

A Synoptic View of a Coastal Plain Estuary.

During October, 1972 the Patuxent River Estuary was monitored intensively and synoptically over two tidal cycles to determine the spatial and temporal patterns of various hydrodynamic, chemical and biological features. Forty-one depths at eleven stations along nine transects were sampled simultaneously at hourly intervals for salinity, temperature, dissolved oxygen, chlorohyll a, particulate nitrogen, nitrate, nitrite, total kjeldahl nitrogen, ammonia, particulate carbohydrate, dissolved organic carbon, total hydrolizable phosphorous, dissolved inorganic phosphorous, suspended sediment, particle size distribution, and zooplankton. Tidal velocity was continuously monitored at each depth by recording current meters. Riverine input and meteorological conditions were relatively stable for two weeks preceeding the deployment. This communication describes the calculation of the intrinsic rates of change of the observed variables from their measured distributions in the Estuary. The steady-state, one-dimensional equation of species continuity is employed to separate the advection and tidal dispersion of a hydrodynamically passive substance frbm its intrinsic rate of change at point. A new spatial transform is introduced for the purpose of interpolation and extrapolation of data.The intrinsic rate of change profiles reveal a region of heavy bloom activity in the upper estuary and a secondary bloom near the point in the River that most of the suspended material settles out. The changes in ammonia and nitrates are highly correlated to the productivity patterns. Phosphorous rates are less closely correlated to productivity. The perturbations that the Chalk Point steam electric power plant have on the heat and oxygen balances are easily discernible.

Simulating the Lateral Transport of lchthyoplankton in the Potomac Estuary

Previous simulations of potential ichthyoplankton entrainment by power generating stations on the Potomac estuary have not included the influence of lateral transport in distributing eggs and larvae over the nursery area. Therefore, two-dimensional, vertically-averaged hydrodynamic and kinematic models of passive organism transport were developed to represent advective and dispersive processes near the proposed Douglas Point Nuclear Generating Station. Although the more refined model did not substantially alter the estimate of ichthyoplankton entrainment, it did reveal that lateral inhomogeneities in hydrodynamics could engender several fold differences in entrainment probabilities on opposite sides of the estuary. Models of higher resolution and greater biological detail did not project greater total entrainment by the Douglas Point plant, because the volume of nontidal flow past the site was large in comparison to the proposed rate of cooling water withdrawal.

Ein Vorschlag zur Senkung des Schlepppwiderstandes von Grundschleppnetzen

Mathematical modelling shows that the projection area of the trawl twine influencing its hydrodynamic resistance can be reduced by approx. 30 % through increasing the mesh size of the trawl wings and the conical parts of the trawls, in combi-nation with the use of thinner twine. The interrelation between fuel consumption and projection area of the trawl twine as well as the influence of the enlarged meshes of the wings and first panels on the catch composition can only be measured by trials on fishing boats.

T90-Steert: Letzte Untersuchungen vor der Übernahme ins EU-Regelwerk

After due consideration the EU Commission has decided in December 2005 to admit cod-ends made of netting turned 90 de-grees (T90) as an allowable alternative for the cod fishery of the Baltic. The construction was included as one of two admissibles versions into the newly issued EU regulation 2187/2005 on technical measures for the conservation of fishery resources of the Baltic. This contribution describes some of the investigations preceeding that decision with which some of the previous demurs could be dispelled. In the course of these experiments it was detected that the cod-end netting material plays an important role for the mesh selection of a T90 cod-end, whereas the netting twine diameter is negligible. Problems with modern twine mate-rial have to be taken in consideration for constructional changes of T90 cod-ends. A relation of 1 to 2 in the circumferences in meshes at the joining round between last row of the belly and extension/cod-end turned out to be acceptable. Both the hauling technique (sidetrawler or sterntrawler) and an extensive use in the commercial fishery proved to be of no relevance for to the selection of T90 cod-ends. Taken alone, the different hydrodynamic conditions in a cod-end are insufficient to fully explain the selection phenomena. This was demonstrates by the material-related differences in selectivity of T90 cod-ends.

Distribution, growth, and mortality of sailfish (Istiophorus platypterus) larvae in the northern Gulf of Mexico

Ichthyoplankton surveys were conducted in shelf and slope waters of the northern Gulf of Mexico during the months of May–September in 2005 and 2006 to investigate the potential role of this region as spawning and nursery habitat of sailfish (Istiophorus platypterus). During the two-year study, 2426 sailfish larvae were collected, ranging in size from 2.0 to 24.3 mm standard length. Mean density for all neuston net collections (n=288) combined was 1.5 sailfish per 1000 m2, and maximum density was observed within frontal features created by hydrodynamic convergence (2.3 sailfish per 1000 m2). Sagittal otoliths were extracted from 1330 larvae, and otolith microstructure analysis indicated that the sailfish ranged in age from 4 to 24 days after hatching (mean=10.5 d, standard deviation [SD]=3.2 d). Instantaneous growth coefficients (g) among survey periods (n=5) ranged from 0.113 to 0.127, and growth peaked during July 2005 collections when density within frontal features was highest. Daily instantaneous mortality rates (Z) ranged from 0.228 to 0.381, and Z was indexed to instantaneous weight-specific growth (G) to assess stage-specific production potential of larval cohorts. Ratios of G to Z were greater than 1.0 for all but one cohort examined, indicating that cohorts were gaining biomass during the majority of months investigated. Stage-specific production potential, in combination with catch rates and densities of larvae, indicates that the Gulf of Mexico likely represents important spawning and nursery habitat for sailfish.

Quantifying seascape structure: extending terrestrial spatial pattern metrics to the marine realm

Spatial pattern metrics have routinely been applied to characterize and quantify structural features of terrestrial landscapes and have demonstrated great utility in landscape ecology and conservation planning. The important role of spatial structure in ecology and management is now commonly recognized, and recent advances in marine remote sensing technology have facilitated the application of spatial pattern metrics to the marine environment. However, it is not yet clear whether concepts, metrics, and statistical techniques developed for terrestrial ecosystems are relevant for marine species and seascapes. To address this gap in our knowledge, we reviewed, synthesized, and evaluated the utility and application of spatial pattern metrics in the marine science literature over the past 30 yr (1980 to 2010). In total, 23 studies characterized seascape structure, of which 17 quantified spatial patterns using a 2-dimensional patch-mosaic model and 5 used a continuously varying 3-dimensional surface model. Most seascape studies followed terrestrial-based studies in their search for ecological patterns and applied or modified existing metrics. Only 1 truly unique metric was found (hydrodynamic aperture applied to Pacific atolls). While there are still relatively few studies using spatial pattern metrics in the marine environment, they have suffered from similar misuse as reported for terrestrial studies, such as the lack of a priori considerations or the problem of collinearity between metrics. Spatial pattern metrics offer great potential for ecological research and environmental management in marine systems, and future studies should focus on (1) the dynamic boundary between the land and sea; (2) quantifying 3-dimensional spatial patterns; and (3) assessing and monitoring seascape change.

Predicting the distribution of Vibrio vulnificus in Chesapeake Bay

Vibrio vulnificus is a gram-negative pathogenic bacterium endemic to coastal waters worldwide, and a leading cause of seafood related mortality. Because of human health concerns, understanding the ecology of the species and potentially predicting its distribution is of great importance. We evaluated and applied a previously published qPCR assay to water samples (n = 235) collected from the main-stem of the Chesapeake Bay (2007 – 2008) by Maryland and Virginia State water quality monitoring programs. Results confirmed strong relationships between the likelihood of Vibrio vulnificus presence and both temperature and salinity that were used to develop a logistic regression model. The habitat model demonstrated a high degree of concordance (93%), and robustness as subsequent bootstrapping (n=1000) did not change model output (P > 0.05). We forced this empirical habitat model with temperature and salinity predictions generated by a regional hydrodynamic modeling system to demonstrate its utility in future pathogen forecasting efforts in the Chesapeake Bay.

Sediment Quality Triad assessment in Kachemak Bay: characterization of soft bottom benthic habitats and contaminant bioeffects assessment

A baseline environmental characterization of the inner Kachemak Bay, Alaska was conducted using the sediment quality triad approach based on sediment chemistry, sediment toxicity, and benthic invertebrate community structure. The study area was subdivided into 5 strata based on geophysical and hydrodynamic patterns in the bay (eastern and western intertidal mud flats, eastern and western subtidal, and Homer Harbor). Three to seven locations were synoptically sampled within each stratum using a stratified random statistical design approach. Three sites near the village of Port Graham and two sites in the footprint of a proposed Homer Harbor expansion were also collected for comparison. Concentrations of over 120 organic and metallic contaminants were analyzed. Ambient toxicity was assessed using two amphipod bioassays. A detailed benthic community condition assessment was performed. Habitat parameters (depth, salinity, temperature, dissolved oxygen, sediment grain size, and organic carbon content) that influence species and contaminant distribution were also measured at each sampling site. Sediments were mostly mixed silt and sand; characteristic of high energy habitats, with pockets of muddy zones. Organic compounds (PAHs, DDTs, PCBs, cyclodienes, cyclohexanes) were detected throughout the bay but at relatively low concentrations. Tributyltin was elevated in Homer Harbor relative to the other strata. With a few exceptions, metals concentrations were relatively low and probably reflect the input of glacial runoff. Relative to other sites, Homer Harbor sites were shown to have elevated concentrations of metallic and organic contaminants. The Homer Harbor stratum however, is a deep, low energy depositional environment with fine grained sediment. Concentrations of organic contaminants measured were five to ten times higher in the harbor sites than in the open bay sites. Concentration of PAHs is of a particular interest because of the legacy of oil spills in the region. There was no evidence of residual PAHs attributable to oil spills, outside of local input, beyond the confines of the harbor. Concentrations were one to ten times below NOAA sediment quality guidelines. Selected metal concentrations were found to be relatively elevated compared to other data collected in the region. However, levels are still very low in the scale of NOAA’s sediment quality guidelines, and therefore appear to pose little or no ecotoxicity threat to biota. Infaunal assessment showed a diverse assemblage with more than 240 taxa recorded and abundances greater than 3,000 animals m-22 in all but a few locations. Annelid worms, crustaceans, snails, and clams were the dominant taxa accounting for 63 %, 19%, 5%, and 7 % respectively of total individuals. Specific benthic community assemblages were identified that were distributed based on depth and water clarity. Species richness and diversity was lower in the eastern end of the bay in the vicinity of the Fox River input. Abundance was also generally lower in the eastern portion of the study area, and in the intertidal areas near Homer. The eastern portions of the bay are stressed by the sediment load from glacial meltwater. Significant toxicity was virtually absent. Conditions at the sites immediately outside the existing Homer Harbor facility did not differ significantly from other subtidal locations in the open Kachemak Bay. The benthic fauna at Port Graham contained a significant number of species not found in Kachemak Bay. Contaminant conditions were variable depending on specific location. Selected metal concentrations were elevated at Port Graham and some were lower relative to Kachemak Bay, probably due to local geology. Some organic contaminants were accumulating at a depositional site.

Instrumentation in fishing gear research

The general method of study of the performance of any dynamic system is to have an understanding of the various influencing factors. These include the dynamic parameters developed by the system as well as the external factors. In the case of a trawl net under operation there are many hydrodynamic forces acting on it. Since the trawl net is operated much below the water surface, visual observation is rather difficult. Model testing is an alternative method. However, as a model cannot be an exact replica of the original in all respects, model testing has only a limited application and an ultimate test with the actual gear in the true field conditions is necessary.

Features of wave field, its effect to erosion - deposition processes in the Cua Dai (Hoi An), Cai river mouth (Nha Trang) and Phan Thiet Bay in typical local wind conditions

Based on the hydrodynamic model and Shore Protection Manual (CERC - USA) we have calculated wave field characteristics in the typical wind conditions (wind velocity equal to 13m/s in the high frequency direction of the wind regime). Comparison between measured and calculated wave parameters was presented and these results were corresponded to each other. The following main wave characteristics were calculated: -Pattern of the refraction wave field. -Average wave height field. -Longshore current velocity field in surf zone. From distribution features of wave field characteristics in research areas, it could be summarized as following: - The formation of wave fields in the research areas was unequal because of their local difference of hydrometeorological conditions, river discharge, bottom relief… - At Cuadai (Dai mouth, Hoian) area in the N direction of incident wave field, wave has caused serious variation of the coastline. The coastline in the whole region, especially, at the south of the mouth was eroded and the foreland in the north of the mouth was deposited. - At Cai river mouth (Nhatrang) area in the E direction of incident wave field, wave has effected strongly and directly to the inshore and channel structure. - At Phanthiet bay area in the SW direction of incident wave field, wave has effected strongly to the whole shoreline from Da point to Ne point and caused serious erosion.

Tracing sediment transport and bed regime in Nha Trang Bay

Three spatial structure groups of radionuclides in U and Th series, 210Pb-excess and 137Cs, and 40K were found based on analyzing temporal and spatial datum of their content by factor analysis with oblique rotation in Nhatrang bay. U and Th spatial structure with their contours decreased toward the offshore, ran longshore and divided seawater of bay into two parts with strong gradient on both sides. Inside part located from center of Nhatrang bay toward the seashore with three main deposit centers of their contents higher than 23 Bq/kg.dry for 238U and 40 Bq/kg.dry for 232Th, indicated unstability of shoreline. Almost sediments coming from river extended toward the offshore, were stopped and transported toward southeastern. The outside part was less than above mentioned content. The boundary line between two parts superposed with the constantly limit line of turbid plume in the rainy season. Direct influence of the continental runoff was limited by the 9 Bq/kg.dry contour of 238U, 19 Bq/kg.dry contour of 232Th. Longshore current was a predominant process whereas lateral transport as sifting and winnowing process of finer grains in sediments of Nhatrang bay. Areas that had very low content of 137Cs and 210 Pb-excess adjoining shoreline showed areas being eroded. Accumulation of 137Cs and 210 Pbexcess nearby river mouth characterized for fine compositions of sediments controlled by seasonal plumes and sites further toward the south indicated finer materials transported from river and accumulated in lack of hydrodynamic process. Near shore accumulation of 40K revealed the sediments there originated from bed erosion.

Copper-nickel alloys for marine aquacultural engineering

Engineering developments, problems of marine corrosion, fouling and practical innovative applications of copper-nickel alloys in comparison with other materials for marine aquacultural engineering are presented. Coefficient of drag and hydrodynamic force acting on nylon and polyethylene net enclosures have shown a four-fold increase of force in four months at the Cochin harbour due to fouling. Corrosion behaviour of copper-nickel and other copper base alloys are also presented. Effects of copper additions to culture water are reviewed.