scholarly journals Quantification of Chaoborus and small fish by mobile upward-looking echosounding

2018 ◽  
Vol 78 (1) ◽  
Author(s):  
Roman Baran ◽  
Michal Tušer ◽  
Helge Balk ◽  
Petr Blabolil ◽  
Martin Čech ◽  
...  
Keyword(s):  
Surface Layer ◽  
Czech Republic ◽  
Water Column ◽  
Small Proportion ◽  
Fish Larvae ◽  
Juvenile Fish ◽  
Target Strength ◽  
Small Fish ◽  
Římov Reservoir ◽  
Acoustic Recording

Chaoborus larvae inhabit frequently the water column of lakes, when they can be mistaken for small fish. Because larvae ascend up to the blind zone of downward-looking echo sounding at night, quantitative acoustic estimation of them is possible only with upward-looking approach. For this reason, the mobile hydroacoustic upward-looking system (120 and 38 kHz split-beam echosounder) in combination with a direct catch method (trawling) was tested to investigate the night community of invertebrates and juvenile fish in the surface layer of the Římov reservoir (Czech Republic). In the target strength range of invertebrates (smaller than -59 dB), the 38 kHz echosounder recorded only a small proportion of targets while the 120 kHz echosounder recorded distinct peaks corresponding to high densities of Chaoborus (target strength, TS range -70 to -60 dB, average TS -66 to -64 dB). At 120 kHz frequency, the TS distribution of smaller cohort of juvenile fish (<25 mm in length) overlapped the TS-distribution of Chaoborus. The number of these smaller juvenile fish was so small compared with the number of Chaoborus that they did not seriously bias acoustic Chaoborus estimate. The correlation between the density of Chaoborus with small contamination of juvenile fish larvae from trawling and acoustic recording made with the 120 kHz echosounder was high (R2= 0.88), but the acoustic densities from trace counting appeared to underestimate Chaoborus abundance when the density was > 1.5 ind.m-3. 

In Vivo Fluorescence of Chlorophyll A: Estimation of Phytoplankton Biomass and Activity in Římov Reservoir (Czech Republic)

1993 ◽  
Vol 28 (6) ◽  
pp. 29-33 ◽  
Author(s):  
V. Vyhnálek ◽  
Z. Fišar ◽  
A. Fišarová ◽  
J. Komárková
Keyword(s):  
Czech Republic ◽  
Chlorophyll Fluorescence ◽  
Primary Production ◽  
Chlorophyll A ◽  
Phytoplankton Biomass ◽  
In Vivo Fluorescence ◽  
Fluorescence Of Chlorophyll A ◽  
Římov Reservoir ◽  
Natural Phytoplankton

The in vivo fluorescence of chlorophyll a was measured in samples of natural phytoplankton taken from the Římov Reservoir (Czech Republic) during the years 1987 and 1988. The fluorescence intensities of samples either with or without addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron, DCMU) were found reliable for calculating the concentration of chlorophyll a during periods when cyanobacteria were not abundant. The correction for background non-chlorophyll fluorescence appeared to be essential. No distinct correlation between a DCMU-induced increase of the fluorescence and primary production of phytoplankton was found.

scholarly journals A model for the evolution of the thermal bar system

2012 ◽  
Vol 24 (2) ◽  
pp. 161-177 ◽  
Author(s):  
DUNCAN E. FARROW
Keyword(s):  
Surface Layer ◽  
Water Column ◽  
Thermal Balance ◽  
Spring Warming ◽  
Entire Water Column ◽  
Horizontal Extent ◽  
Thermal Bar ◽  
Stable Surface Layer ◽  
Near Shore ◽  
New Framework

A new framework for modelling the evolution of the thermal bar system in a lake is presented. The model assumes that the thermal bar is located between two regions: the deeper region, where spring warming leads to overturning of the entire water column, and the near shore shallower region, where a stable surface layer is established. In this model the thermal bar moves out slightly more quickly than predicted by a simple thermal balance. Also, the horizontal extent of the thermal bar region increases as it moves out from the shore.

scholarly journals Distribution and population structure of the rockfish Helicolenus dactylopterus (Pisces: Scorpaenidae) in the western Mediterranean

2001 ◽  
Vol 81 (1) ◽  
pp. 129-141 ◽  
Author(s):  
Enric Massutí ◽  
Joan Moranta ◽  
L. Gil de Sola ◽  
B. Morales-Nin ◽  
Llucia Prats
Keyword(s):  
Population Structure ◽  
Juvenile Fish ◽  
Western Mediterranean ◽  
Small Fish ◽  
Depth Range ◽  
Southern Area ◽  
Northern Areas ◽  
Helicolenus Dactylopterus ◽  
Spatio Temporal ◽  
And Cluster Analysis

The distribution and spatio–temporal variation of Helicolenus dactylopterus (Pisces: Scorpaenidae) population was studied from 816 bottom trawls developed along the Iberian coast. Multifactor analysis of variance was used to test the differences in abundance and biomass and cluster analysis was applied to detect differences in population structure. The results showed a bathymetric and latitudinal gradient in abundance and population structure along three geographic sectors in the surveyed area. In the southern area, the species was more frequent and showed a wider bathymetric distribution range than northwards. The depth range with the maximum frequency of occurrence was also wider in the southern area than northwards. Similar trends were observed in terms of abundance and biomass, with the highest and lowest indices in the southern and northern areas, respectively. The age composition of the catches showed that the population consisted mainly of young-of-the-year and juvenile fish. This fraction of the population is well represented, at a mesoscale, along the whole surveyed area, but adults are well represented only at a local scale, at the deepest strata surveyed in the southern area. In this case, recruits of age 0 and juveniles up to 4-y old were restricted to depths shallower than 500 m, while adult fish older than 6 y of age appeared below this depth. In the southern area, seasonal changes in the population structure were also observed, with modes of small fish (3–6 cm) from March to June, as a consequence of the species recruitment to the bottom. Some direct and indirect factors of biogeographic, environmental and anthropogenic origin affecting the observed gradient are discussed.

scholarly journals Limited mid-water scavenging of trawl discards

2003 ◽  
Vol 83 (4) ◽  
pp. 731-734 ◽  
Author(s):  
Karim Erzini ◽  
Pedro Monteiro ◽  
Artur Araújo ◽  
Margarida Castro
Keyword(s):  
Water Column ◽  
Deep Water ◽  
Small Fish ◽  
Sea Birds ◽  
Trawl Fishing ◽  
Southern Portugal ◽  
Catch Rates ◽  
Electric Fishing ◽  
Scavenging Rates

The consumption or scavenging of fish in the water column at depths from 75 to 275 m in Algarve (southern Portugal) trawl fishing grounds was evaluated. Longlines were used to suspend baits throughout the water column while electric fishing reels were used to simulate sinking discards. Eighteen species were caught, with higher catch rates near the surface than near the bottom. However, scavenging rates were generally highest near the bottom and lowest in the middle of the water column. At depths less than 100 m the majority or all the fish were scavenged throughout the water column, while at depths greater than 200 m most of the fish were untouched after periods of time greater than would be required for them to sink to the bottom. Since other studies have shown that most small fish discards are scavenged at the surface by sea birds and most of the discarded species that sink are either too large or not attractive to pelagic predators, these results suggest that mid-water scavenging of trawl discards in deep water is relatively unimportant.

The herring swimbladder: loss and gain of gas

1984 ◽  
Vol 64 (2) ◽  
pp. 441-459 ◽  
Author(s):  
J. H. S. Blaxter ◽  
R. S. Batty
Keyword(s):  
Pressure Vessel ◽  
Atmospheric Pressure ◽  
Juvenile Fish ◽  
Gas Diffusion ◽  
Sea Surface ◽  
Target Strength ◽  
Experimental Conditions ◽  
Neutral Buoyancy ◽  
Sea Bed ◽  
Ecological Implications

The herring is a physostome with no gas secretion mechanism in the swimbladder. The swimbladder volume was measured in fish from about 3–33 cm in length. It was rarely large enough to give the fish neutral buoyancy at the sea surface. Swimbladder volumes were also measured after periods of up to 1 week at pressures from 1·9 to 5·5 ATA (0·9–4·5atm above atmospheric pressure) in a laboratory pressure vessel and in a sub-surface cage in the sea. The swimbladder gas was lost within a few hours in the larval herring and in a few days in smaller juvenile fish; no change was found in older fish under experimental conditions. The findings were in accord with measurements of the guanine content of the swimbladder wall which was low in those fish which lost gas quickly. This supports the view that gas diffusion is limited by guanine crystals. While it seems likely that larger fish can exist for several weeks without the need to replenish the swimbladder gas some large spawning herring were caught at sea with empty swimbladders, suggesting a long stay near the sea bed. Analysis of swimbladder gas showed that oxygen tended to diffuse out more quickly than nitrogen. Behaviour experiments showed that fish with artificially emptied swimbladders could refill them by swallowing air at the surface, in some cases very quickly and efficiently. Fish with empty swimbladders and no access to the surface suffered a high mortality. The ecological implications of these results and their relevance to the interpretation of sonar ‘target strength’ measurements are discussed.

Onset and persistence of cyanobacterial blooms in a large impounded tropical river, Australia

2004 ◽  
Vol 55 (1) ◽  
pp. 1 ◽  
Author(s):  
Myriam Bormans ◽  
Phillip W. Ford ◽  
Larelle Fabbro ◽  
Gary Hancock
Keyword(s):  
Surface Layer ◽  
Water Column ◽  
Mixed Layer Depth ◽  
Phosphorus Uptake ◽  
Bottom Layer ◽  
Climatic Conditions ◽  
Cyanobacterial Blooms ◽  
Cylindrospermopsis Raciborskii ◽  
Surface Mixed Layer ◽  
Tropical River

The dynamic interplay between physical, chemical and biological factors in the development and persistence of cyanobacterial blooms in impounded rivers is an important topic. Over a 3-year study period, variable climatic conditions were recorded in the Fitzroy River, Queensland, Australia, which is a typical, impounded lowland tropical river. Post-flood turbidity reduced the available light in the well-mixed water column to levels insufficient for cyanobacterial growth. Only when the water column stratified and the slowly sinking particles dropped from the surface layer did the ratio of surface mixed layer depth to euphotic depth approach 1, allowing cyanobacterial growth. By the time the light climate became favorable, most of the dissolved nutrients had been scavenged from the water column by settling particles or sequestered by fringing macrophytes and other biogeochemical processes. Cyanobacterial blooms dominated by Cylindrospermopsis raciborskii persisted for several months until the next flood flushed the system. The cyanobacterial species dominating that environment were very small and had high specific phosphorus uptake rates. Their nutrient requirement was met by transfer across the oxycline driven by regular high wind mixing events, entraining nutrient-rich bottom waters. Nutrient fluxes from the sediments into the anoxic bottom layer were sufficient to replace the bottom nutrients lost to the surface layer.

Escape Responses of Herring Larvae to Visual Stimuli

1989 ◽  
Vol 69 (3) ◽  
pp. 647-654 ◽  
Author(s):  
R.S. Batty
Keyword(s):  
Startle Response ◽  
Larval Fish ◽  
Fish Larvae ◽  
Adult Population ◽  
Juvenile Fish ◽  
Reciprocal Inhibition ◽  
Contralateral Side ◽  
The Body ◽  
Different Types ◽  
Trunk Musculature

Predation is now considered the main cause of mortality in larval and juvenile fish (Hunter, 1984) and is therefore the most important factor controlling recruitment to the adult population. Marine fish larvae are prey for many different types of predator including medusae, crustaceans and larger fish. When predatory attacks are sensed both adult and larval fish may respond by making a 'C-start', a very fast, simultaneous contraction of the trunk musculature that deforms the body into a C-shape within 20 ms (Eaton & Hackett, 1984). This startle response is mediated by the Mauthner cells, a pair of prominent neurones in the hind brain or by other reticulo-spinal cells located in the same region. As a result of reciprocal inhibition and decussation of the cell axon, stimulation on one side of the body results in contraction of all the muscle on the contralateral side.

A Large-Volume Pump System for Studies of the Vertical Distribution of Fish Larvae Under Open Sea Conditions

1986 ◽  
Vol 66 (4) ◽  
pp. 845-854 ◽  
Author(s):  
R. P. Harris ◽  
L. Fortier ◽  
R. K. Young
Keyword(s):  
Water Column ◽  
Large Volume ◽  
Larval Fish ◽  
Fish Larvae ◽  
Physical Structure ◽  
Small Scale ◽  
Fine Scale ◽  
Pump System ◽  
Open Sea ◽  
Temporal And Spatial

A large-volume pump system (2.8 m3 min-1) for sampling fish larvae under open-sea conditions is described. Comparative efficiency trials by day and night showed that the pump was generally as efficient, or in some cases more efficient, in capturing larvae than vertically hauled 200 μm WP2 nets, though there was some evidence of visual avoidance by particular larval size classes during daylight. The pump system is particularly appropriate for investigating fine-scale vertical aggregations (1–10 m3) of larval fish in relation to the distribution of their food organisms.INTRODUCTIONStudies of the distribution of larval fish and their food organisms in relation to physical structure in the water column require sampling techniques capable of resolving fine-scale temporal and spatial distributions. As an alternative to conventional nets, large-volume pumps, sampling at rates in excess of 1 m3 min-1; provide such a capability. Major benefits of using large pumps in addition to temporal and spatial resolution are that a wide range of sizes of plankton including larval fish can be sampled simultaneously in relation to physical and chemical properties of the water column; there is reliable control of the volume of sample filtered and problems of clogging of towed nets are avoided; long series of sequential samples can be taken in studies of small-scale distribution; and instrumentation with in situ CTD and fluorometers at the intake enables real-time control of sampling in relation to physical structure.General engineering considerations for using such pumps have been reviewed in detail by Miller & Judkins (1981), and a particular area of application has been in power-plant entrainment studies in shallow fresh water (Portner & Rhode, 1977; Bowles & Merriner, 1978; Gale & Mohr, 1978; Ney & Schumacher, 1978; Elder et al. 1979; Leithiser, Ehrlich & Thum, 1979; Cada & Loar, 1982).

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