Vertical Distribution Of Fish Research Articles

The effect of hydropower on fish stocks: comparison between cascade and non-cascade reservoirs

Spatial distributions of fish were studied in two types of reservoirs by means of hydroacoustics during the summer. Different patterns of fish distribution were found in non-cascade (Řimov, Želivka) and cascade (Kamýk, Slapy, Stěchovice, Vrane) reservoirs. Maximum biomass and density of fish were observed in the tributary area of the non-cascade reservoir. The biomass declined towards the dam area. Average weight of fish showed the opposite trend—maximum average weight was observed in the dam area and declined towards the tributary area. In the cascade reservoirs fish distribution was found to be more complicated but the maximum biomass and density of fish were observed in the dam areas, whereas the tributary areas were nearly fishless. Poor ecohydrological conditions in the tributaries of cascade reservoirs are likely to be responsible for the low abundance of fish in these areas. This was evident in the example of Vrane reservoir which has two major inflows. Low biomass and density of fish were observed in the cold and low oxygen saturated inflowing cascade Vltava River while higher biomass and density were observed in the warm and well oxygen saturated Sazava River inflow. Average weights of fish followed the same trend as in non-cascade reservoirs—the maximum was in the dam area and it declined towards the tributary area. The vertical distribution of fish is driven by the fully developed stratification of temperature and oxygen during the summer season in non-cascade reservoirs. A significantly lower biomass of fish was observed below the thermocline in vertical surveys in both non-cascade and cascade reservoirs. Summer stratification in cascade reservoirs is weakly developed or is not developed at all due to hypolimnetic releases of cold water and short retention times. High transparency suggests lower primary production in cascade reservoirs.

The effect of trigger depth on self-feeder utilisation, growth and the vertical distribution of tank-held rainbow trout Oncorhynchus mykiss (Walbaum)

This study investigated the effect of placing a self-feeding trigger at either a) 1 cm below the water surface or b) mid-water (35 cm below the surface), on self-feeder usage, growth, feed wastage and fin damage of juvenile rainbow trout, Oncorhynchus mykiss (Walbaum). The vertical distribution of trout was also measured for the first 31 days of self-feeding. Group-held trout (n=10 fish group−1, 5 groups treatment−1), weighing 51.06 g±8.09 g (mean±SD) were held in 200 l cylindroconical tanks (depth=75 cm) for 62 days. Trigger placement had no significant effect upon self-feeder conditioning, and upper trigger group (UTG) and lower trigger group (LTG) fish took an average of 16±7.4 days and 14±9.8 days to reach a stable level of self-feeding, respectively. Specific growth rate was significantly higher in UTG fish (1.83±0.20 vs. 0.95±0.21 for UTG vs. LTG fish, respectively) whilst condition factor and self-feeder utilisation (ration size, 1.21±0.18 vs. 0.52±0.15 kg tank−1 for UTG vs. LTG fish) were also significantly higher in UTG fish. Trigger depth had no significant effect on size heterogeneity, mortality, feed wastage, feed conversion ratio (FCR) or the incidence of caudal and dorsal fin splitting and fin erosion. Dorsal fin splitting decreased with time in UTG but not in LTG fish. Caudal fin erosion increased with time in UTG (upper lobe only) and LTG (both lobes). The vertical distribution of fish also differed between treatments and more LTG fish preferred the lower part of the tank. Placing a self-feeding trigger at a mid-water depth can significantly limit growth, condition factor and self-feeder utilisation in juvenile rainbow trout, in addition to hindering recovery from dorsal fin erosion.

Swimming behavior of juvenile anchovies (Anchoa spp.) in an episodically hypoxic estuary: implications for individual energetics and trophic dynamics

Diel swimming behaviors of juvenile anchovies (Anchoa spp.) were observed using stationary hydroacoustics and synoptic physicochemical and zooplankton profiles during four unique water quality scenarios in the Neuse River Estuary, NC, USA. Vertical distribution of fish was restricted to waters with DO greater than 2.5 mg O2 l−1, except when greater than 70% of the water column was hypoxic and a subset of fish were occupying water with 1 mg O2 l−1. We made the prediction that an individual fish would select a swim speed that would maximize net energy gain given the abundance and availability of prey in the normoxic waters. During the day, fish adopted swim speeds between 7 and 8.8 bl s−1 that were near the theoretical optimum speeds between 7.0 and 8.0 bl s−1. An exception was found during severe hypoxia, when fish were swimming at 60% above the optimum speed (observed speed = 10.6 bl s−1, expected = 6.4 bl s−1). The anchovy is a visual planktivore; therefore, we expected a diel activity pattern characteristic of a diurnal species, with quiescence at night to minimize energetic costs. Under stratified and hypoxic conditions with high fish density coupled with limited prey availability, anchovies sustained high swimming speeds at night. The sustained nighttime activity resulted in estimated daily energy expenditure over 20% greater than fish that adopted a diurnal activity pattern. We provide evidence that the sustained nighttime activity patterns are a result of foraging at night due to a lower ration achieved during the day. During severe hypoxic events, we also observed individual fish making brief forays into the hypoxic hypolimnion. These bottom waters generally contained higher prey (copepod) concentrations than the surface waters. The bay anchovy, a facultative particle forager, adopts a range of behaviors to compensate for the effects of increased conspecific density and reduced prey availability in the presence of stratification-induced hypoxia.

A video analysis procedure for assessing vertical fish distribution in aquaculture tanks

This paper describes an economical and efficient video analysis procedure for registering vertical fish distribution in aquaculture tanks. The procedure can be summarized in three steps: (1) A digital underwater camera is used to film a section of a tank wall marked with one or more vertical black lines. (2) Automatic image analysis is used to identify those parts of the lines that are not obstructed by fish in the individual image-frames. (3) The visible parts of the lines are compared with the known extent of the lines and the percentage coverage is calculated. The procedure does not require uniform or stable lighting conditions, only that the black stripes are clearly visible. A case study demonstrates that the procedure can be used to document how fish in a classical conditioning learning procedure react to a sudden fright stressor in the first trial and how the fish gradually become habituated to the stressor and start to associate it with feeding in subsequent trials. Since the procedure offers a good description of vertical distribution over time, is cost effective and easy to implement, we believe that it is likely to become a standard for describing fish behaviour in aquaculture tanks.

Echo integration of nonuniform fish densities

Echo integration is a well recognized method for measuring backscatter intensity and for estimating fish density. EI is appropriate for high and low fish densities as long as the target distribution is uniform across the beam. This is generally the case in mobile applications that use a downward looking transducer. However uniform fish distribution across the beam cannot be assumed in riverine applications that use a stationary side looking system. Observed distributions are often very nonuniform especially when migrating fish are surface or bottom oriented. EI may still be possible if the relative vertical fish distribution is known and reasonably constant over time. A priori estimates of the vertical fish density distribution could be from split-beam observations when densities are lower or from video observations. A model for the EI of nonuniform fish densities is developed, typical results are simulated to test the model and its application is discussed.

The fuzzy relationship between trawl and acoustic surveys in the North Sea

AbstractAdding information on the horizontal and vertical distribution of fish both on and between trawl stations is reason enough to perform acoustic surveys routinely in tandem with annual groundfish trawl surveys. Ideally, acoustic and trawl density indices could be combined to maximize information on fish distribution and provide more reliable estimates of stock size. The core of the problem boils down to the question: “how does what we see on an echosounder relate to what we catch in a net?” The fuzzy logic “model-free estimation” approach presented here sidesteps the need to understand specific mechanisms that determine the nature and variability of any relationship between acoustics and trawl catches. Fuzzy logic models that describe and predict the relationship linking acoustics and environmental variables (inputs) with trawl catches (output) are developed, and the sensitivities and robustness of the approach are discussed. In the models examined, the static environmental variables location and depth proved to be better predictors of trawl catches in the North Sea than the acoustic energy in the first 5 m off the bottom. We suggest that finding the “hidden” relationship between acoustics and trawls will require closer attention to partitioning the acoustics data by species/assemblages and understanding the key gear and behavioural differences responsible for producing the high between-gear variability.

Diel patterns in pelagic fish behaviour and distribution observed from a stationary, bottom-mounted, and upward-facing transducer

AbstractDiel variation in pelagic fish distribution influences hydroacoustic abundance estimates. To study and quantify diel patterns in behaviour and spatial distribution in pelagic fish without causing avoidance reactions or attraction to any floating equipment or vessel we used a bottom-mounted, upward-facing transducer. Light intensities were measured as skylight and underwater light (at 5-m depth). The study was performed in a coastal area in the Baltic Sea, late July to mid-August in 2001 and 2002. The results provided additional information on fish behaviour and distribution valuable for future survey planning and in the analyses of hydroacoustic data from regular surveys in this area. At night, the data on hydroacoustic backscattering (sA) were less variable, the vertical distribution of fish was more even, with fewer fish in the deepest layer, and the percentage of single-echo detections was higher. The tilt angle of fish seemed to differ day and night, but trawling and target-strength distribution results taken together also implied a partial diel change in the fish assemblage in the midwater layers. The processes of formation and disintegration of schools happened rapidly and coincided with day and night transition periods.

ESTABLISHMENT OF A METALIMNETIC OXYGEN REFUGE FOR ZOOPLANKTON IN A PRODUCTIVE LAKE ONTARIO EMBAYMENT

Hypolimnetic oxygen injection is a management tool used to improve water quality by preventing anoxia and associated phosphorus release from the sediments. An additional benefit would be formation of a low-oxygen refuge for large-bodied herbivorous zooplankton in the metalimnion. The magnitude and timing of hypolimnetic oxygenation was deliberately manipulated during summer 1997 in Irondequoit Bay, a eutrophic Lake Ontario embayment (New York, USA), to maintain metalimnetic dissolved oxygen (DO) concentrations in the range of 1–2 mg/L. We assessed the vertical distributions of fish and zooplankton in 1997, a year with controlled oxygenation, and 1996, a year with oxygenation but without a deliberate attempt to create amenable refuge conditions. After initiation of oxygenation, June through early August metalimnetic DO in 1997 was 1.8 ± 0.5 mg/L (means ± 2 se), whereas metalimnetic DO in 1996 was 3.8 ± 1.0 mg/L. Hydroacoustic surveys in 1997 and gillnet catches in both years indicated that >96% of planktivorous fish, alewives (Alosa pseudoharengus) and emerald shiners (Notropis atherinoides), were restricted to depths with DO > 4.0 mg/L. A refuge effect in 1996 was slight and evidenced only by significantly larger zooplankton in the metalimnion while densities of Daphnia galeata medotae and D. retrocurva were similar or significantly greater in the epilimnion. In 1997, the refuge effect was strong despite an almost twofold increase in planktivorous fish abundance compared to 1996. Overall zooplankton densities were similar in the epilimnion and metalimnion while zooplankton size and densities of both daphnids were significantly greater in the metalimnion. Densities of an invertebrate predator, Mesocyclops edax, were also significantly higher in the metalimnion compared to the epilimnion. Despite high fish abundance in 1997, mean summer (late May through August) chlorophyll a decreased 29% compared to 1996, consistent with expectations from grazing by large Daphnia protected in the refuge. Presence of large-bodied zooplankton in 1997 despite high planktivore abundance demonstrated that successful creation of a low-oxygen refuge from fish predation was possible in an open Great Lakes embayment where traditional biomanipulation via fish removal was not practical.

Diel variation in the vertical distribution of fish and plankton in Lake Kinneret: a 24-h study of ecological overlap

Diel vertical migration (DVM) behaviour is a predator avoidance mechanism observed within many zooplankton species in the presence of zooplanktivorous fish. A 24-h survey was carried out in June 1998 to investigate diel variation in the vertical distribution of fish, zooplankton and phytoplankton (chlorophyll) in Lake Kinneret, Israel. Fish revealed diel variation in vertical distribution but had no spatial overlap with zooplankton, and consequently no apparent influence on zooplankton dispersal. Zooplankton revealed some diel variation in distribution being affected by thermocline and oxycline position and movement of the internal the internal seiche wave. Cyclopoid species closely follow the movement of the seiche wave implying that, due to their greater motility, they are following conditions that are suitable to them. The Cladocera species and small rotifers only partly, which may be part of their phototaxic behaviour. Physical forces like convection, horizontal and vertical forcing probably have a role in contributing to a homogeneous distribution of the plankton by preventing stratification or interfering with the more motile zooplankton which may be attempting to migrate.

Larval Fishes in Relation to Water Masses of the Central North Pacific Transitional Areas, Including the Shelf Break of West-Central Alaska

Larval fishes and corresponding physical data were sampled along two transects from Seward, Alaska to Oahu, Hawaii in February 1991. The first transect was west along the shelf break (SH) off Kodiak Island, 57°38′ to 55°20′ N, between 149 and 156°W. The second transect, North Hawaii (NH), was south along 158°W from 54°40′N, at Shumigan Islands off the Alaskan Peninsula, to 22°00′ N, near the island of Oahu, Hawaii. No other cruise has specifically sampled fish larvae along a similar transect from Alaska to Hawaii in the winter. Myctophidae, Gonostomatidae and Sternoptychidae dominated our catches. A variety of methods have been used to assign faunal provinces and to define distribution of fishes, from descriptive to empirical to statistical to physical. The result is that zoogeographic zones in the North Pacific have been defined in several ways, depending on the taxa and area studied. The multiplicity of nomenclature complicates comparisons, however the difference may be a matter of semantics. We used Roden's (1991) salinity and temperature limits as an objective method for determining water mass boundaries and analyzing faunal provinces. The subtropical domain had the highest diversity, as expected; however, the subarctic front was a close second. Diversity was the lowest in the subarctic domain and the transition zone. The counter-intuitive low values of diversity and evenness in the transition zone are explained by the vertical distributions of fish in these water masses. When temperature divisions are used to calculate diversity, a true “transition zone” appears between 8 and 19°C. The “transition” of taxa apparently occurred north of the physically derived transition zone. This may be a situation unique to the relatively wide transition zone of February 1991. If not, then future analysis should include frontal zones as part of one large transition zone to reflect the broader subarctic-subtropical transition zone. Regardless of the label or the method used to assign faunal provinces, the distribution of larval fishes is regulated by water mass characteristics.

Acoustic telemetry versus monitored longline fishing for studying the vertical distribution of pelagic fish: bigeye tuna ( Thunnus obesus) in French Polynesia

This study compares detailed, nearly continuous, observations on bigeye tuna, Thunnus obesus equipped with electronic tags, with discrete observations on a larger number of individuals from fishing experiments in order to validate the use of instrumented longlines to study the vertical distribution of fish. We show that the depth distributions obtained from the two different observation techniques regarding different environmental variables (temperature, dissolved oxygen (DO), prey distribution) are similar. Bigeye tuna do not seem to be attracted by baits in the vertical dimension (no modification of their vertical distribution by the fishing gear), which allows the use of instrumented longlines to study the vertical behaviour of pelagic species. This technique, when used with appropriate deployment strategy, could therefore represent an alternative to electronic tags (acoustic or archival tags) when there is a need to determine the vertical distribution of fish species by size or sex, in different environments for the study of fishery interactions.

Seasonal development of a turbid hydrothermal lake plume and the effects on the fish distribution

Measurements of the suspended particle concentration in a lake demonstrate the presence of a turbid hydrothermal plume. The plume, generated from a warm source develops upward carrying a suspension of particles from the bottom. It is found that the vertical structure of the plume depends on the stratification of the water column, which in turn depends on the seasonal meteorological conditions. During the stratified period of the lake, the plume is constricted to the hypolimnion zone. At the beginning of the summer season, the plume reaches the bottom of the metalimnion meanwhile at the end of this season the plume does not. In the mixed period of the lake, the plume develops in the whole water column and reaches the surface of the lake, where particles accumulate and spread around the center. Measurements of the vertical fish distribution in the stratified period show that the plume can constrict the fish habitat due to an increase of suspended particles transported by the plume.

Community Structure of Fishes and Habitat Complexity on a Tropical Rocky Shore

The relationship between the variables of reef fish community structure (fish richness, fish diversity and total number of fishes) and those of habitat complexity (total surface area, substratum diversity, topographic complexity, number of holes, percent cover of turf algae, zoanthids, millepores, massive corals, bare rock, encrusting calcareous algae, urchins, other sessile organisms and Sargassum) were examined on three different rocky shores (FA, FB and FT) at Arraial do Cabo, a tropical region located on Brazilian southeastern coast (23 ◦ S, 42 ◦ W). Fish abundance and vertical distribution were assessed by a visual census technique using strip transects. Percentage cover of benthic organisms and other substratum types were calculated by replicated transects using a chain laid down on the substratum. Topographic complexity was determined by the chain link method and number of holes were estimated by direct counts on replicated transects. More than 91 fishes belonging to 37 families were seen in all study sites during one year of visual census effort. FA and FB sites had similar fish community structure and habitat complexity characteristics, while FT showed different habitat characteristics and higher fish diversity and richness, plus total number of fishes. Vertical distribution of fishes along the rocky shores studied seemed to be predictable and was determined by factors such as feeding habits and behavior, availability of refuges and social interactions. The habitat variables that best explained the higher diversity and number of fishes observed in FT site were total surface area of rocky shores and the abundance of benthic sessile invertebrates; these conditions were typical of rocky shores more exposed to wave surge.

How vertical fish distribution may affect survey results

At a selected location in the Barents Sea, acoustic observations were made and bottom- and pelagic-trawl data were collected over a 10-day period. A large proportion of fish were found in the acoustic bottom dead zone. Only during a few hours in the daytime were high acoustic values obtained, mainly consisting of large haddock ascending from the bottom. Small haddock and redfish dominated the acoustic recordings at night. The bottom-trawl catches showed greater variability and higher average catch rates during the day than at night, but the diel variations were relatively less pronounced than those of the acoustic recordings. The largest reductions in catch rates from day to night were observed in small haddock and redfish. This was consistent with the observation that these species were pelagic at night. The acoustic observations and the bottom-trawl catch rates were found to be correlated with diel cycles in observed light level and semi-diel cycles in current speed. The results are interpreted in terms of the variable availability and eYciency of the bottom trawl and of the variable availability of the echosounder. ? 1999 International Council for the Exploration of the Sea

Effects of summer upwelling on the abundance and vertical distribution of fish and crustacean larvae off central Florida's Atlantic coast

The abundance and vertical distribution of various fish and crustacean larvae in response to seasonal upwelling at a study site off the east central Florida coast were examined. Upwelling was recorded at the site from mid July to late August 1986 during which the intruded water was confined to near-bottom layers with a well-defined thermocline present near mid-depth. Near-bottom temperatures of 20–23°C were generally 3–6°C below temperatures recorded near the surface during this time. Densities of larval fish, penaeid shrimp, stomatopods, brachyuran zoeae, brachyuran megalopae and porcellanid zoeae were quantified at near-surface and near-bottom levels prior to, during and following the upwelling event. Densities of brachyuran zoeae and penaeid larvae dominated the other four groups in both levels of the water column throughout the 14-week study. Only brachyuran megalopae and penaeid larvae occurred in significantly higher numbers in upwelled water. All six larval groups were found in higher densities near the bottom through most of the study period. Combining these results with findings from related physical studies suggests that upwelling may play an important role in transporting these and other larval forms shoreward in this region.

Large scale distrlbution of acoustical scattering layers at the Norwegian continental shelf and the Eastern Norwegian Sea

Abstract Vertical and horizontal distributions offish and micronekton were mapped in a zigzag pattern from Lofoten, northern Norway to Stadt, southwestern Norway, in March 1992. Pearlsides (Maurolicus muelleri) were present whenever depth was sufficient for daytime requirements (i.e. > 150–200 m). They performed diel vertical migrations, characterized by ascent at dusk, followed by nocturnal descent, and a dawn ascent before downward migration to day depth. Nocturnal descent among pearls ide has previously been explained by preference for warm water to speed up digestion, but this could not explain the results in this study as relevant vertical temperature gradients were minor. A deep scattering layer consisting of mesopelagic fish, pelagic shrimps and other macroplankton was present outside the shelf. This layer was located beneath ca 300 m by day, while the tendency to carry out diel vertical migrations varied strongly between water masses. Blue whiting (Micromesistius poutassou) associated with the lay...

Vertical distribution of fish and krill beneath water of varying optical properties

The distribution of acoustical scattering layers of fish and knll changed markedly in concert with fluctuating fluorescence (chlorophyll a) in upper waters, possibly due to a varying 'shadow effect'. Beneath clear waters on the outer Norwegian shelf (about 300 m depth), mesopelagic fish (Maurolicus muelleri) were located at approximately 150 to 200 m by day. Krill (mainly Thysanoessa inermis) was primarily found below the mesopelagic fish and above planktivorous demersal fish (Norway pout Trisopterus esmarkii). The vertical distributions changed abruptly across a front into water with less light penetration associated with increased fluorescence (chlorophyll a). Mesopelagic fish ascended by about 100 m accompanied by a rise of knll. Demersal fish left the benthic boundary zone, with ascending Norway pout foraging in the lower part of the knll layer. We suggest that the intermediate light conditions inside the front provided an 'antipredation window' (sensu Clark & Levy 1988: Am Nat 131:271-290) and thereby favorable feeding conditions for the planktivore These results indicate that properties of upper layers may impact plankton and fish distributions and their predator-prey interactions throughout the water column on continental shelves.

Abundance, horizontal and vertical distribution of fish in eastern Weddell Sea micronekton

The spatial distribution and species composition of high-Antarctic ichthyonekton was investigated during the EPOS 3 cruise by RV Polarstern in the eastern Weddell Sea during January–February 1989. A multiple rectangular midwater trawl was used to collect samples from the surface to near the sea floor at 11 stations along a 245 kra transect off Halley Bay. Early larval stages of 18 species, representing about 24% of the known Weddell Sea ichthyofauna, were present in the water column. The Antarctic silver-fish, Pleuragramma antarcticum, over-whelmingly dominated the catches comprising 84.5% of the 5022 specimens caught. The abundance of this species markedly increased towards the offshore end of the transect with the highest numbers occurring near the shelf-break front associated with the westerly current of the southern limb of the Weddell Gyre. The increased abundance of P. antarcticum in continental slope waters was attributed to deflection of the East Weddell Coastal Current beyond the shelf/slope break by fringing ice shelves. Most larval and juvenile fish were found in the seasonally warmed upper 0–70 m layer of the Antarctic Surface Water where conditions occurred that appeared to be favourable to both feeding and growth. Cluster analysis indicated that inner-, central-and outer-shelf assemblages were represented and that the species composition was most effectively described by reference to water mass and depth.

Ecological Segregation in Zooplanktivorous Haplochromine Species (Pisces: Cichlidae) from Lake Victoria

Until a few years ago, Lake Victoria possessed a large species flock of haplochromine cichlids, comprised of 250+ species. Very little was known about the possible ecological differentiation within trophic groups, and virtually nothing about the mechanisms structuring the community. This paper deals with zooplanktivorous species from the Mwanza Gulf of Lake Victoria that showed a large overlap in gross morphological characteristics. We found strong evidence that the species were ecologically segregated to a great extent. Species were restricted to certain horizontal and/or vertical zones. Species which segregated relatively little horizontally, did so vertically, and/or by different diet. The two species with the largest diet overlap segregated vertically. Species pairs segregated along at least one of the traditional niche axes: space, food and time. A detailed study of vertical distributions did not yield any evidence for interactive competition for space. Vertical distributions of fish and food at a 14 m deep station correlated well by night. By day the concordance was less clear.

Influence of Trawl Geometry and Vertical Distribution of Fish on Sampling with Bottom Trawl

Studies were initiated at the Institute of Marine Research, Bergen, in 1984 with the aim of improving the reliability of bottom trawl and acoustic survey results for cod and haddock in the Barents Sea. Spread of the wings and doors and height of the trawl were measured during fishing operations, and acoustic recordings of fish densities were obtained. The observations revealed several aspects of geometry and performance of the gear that could reduce its efficiency for sampling different species and size-groups. The acoustic recordings indicated that fish density has a substantial influence on the correlation between estimates of abundance from trawl catches and from acoustic recordings. Furthermore, a day-night discrepancy of integrated acoustic fish abundance was indicated.