bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of large‐scale spatial variation of pelagic fish on hydroacoustic estimates of their population density in Windermere (northwest England)
Authors: Baroudy E. , Elliott J. M.
Published: July 2006

From July 1989 to December 1992, an echo sounder provided monthly estimates, usually for both day and night, of pelagic fish densities in the north and south basins of Windermere, the largest natural lake in England. Sampling was along contiguous transects, 3 in the north basin and 5 in the south basin. It was impossible to separate records for Arctic charr (Salvelinus alpinus) from those for brown trout (Salmo trutta), but previous sampling by gill‐nets and anglers showed that charr formed about 90% of this mixed population in the north basin and 60–75% in the south basin. In each basin, estimates of population density for the combined transects did not agree with estimates obtained by treating the transects as a contiguous sample of 9 sampling units; only the latter, of course, provided a measure of the precision of each estimate. Analyses of the contiguous samples showed that the variance was significantly greater than the arithmetic mean in most samples, indicating that the fish were distributed nonrandomly in a patchy or clumped pattern. The relationship between the large‐scale spatial variance and mean for these samples was well described by a power function; the parameter estimates did not vary significantly between basins, day and night samples or years. As the power in this equation did not differ greatly from 2 (value for pooled data was 1.70 ± 0.11, n= 136), the variance was stabilized by a log transformation of the data, and the geometric mean, rather than the arithmetic mean, provided the best estimate of population density when some measure of precision was required. These conclusions may be applicable to other echo‐sounding estimates of population abundance, and similar comparisons should be made for pelagic fish in other lakes.
Habitat selection by rainbow trout Oncorhynchus mykiss in a California stream: implications for the Instream Flow Incremental Methodology
Authors: Vondracek B. , Longanecker D. R.
Published: July 2006

We quantified microhabitat selection of rainbow trout (Oncorhynchus mykiss) at 2 flows (low= 1.13 m3. s−1 and high =4.95 m3. s−1) in the Pit River, California. Flows were controlled by an upstream dam and habitat availability was similar during 4 sampling periods at low flow and 2 periods at high flow. A principal components analysis reduced 6 microhabitat variables to 3 new variables that explained 80% of the observed variance. The 3 components loaded heavily on velocity variables, depth variables and substrate. Microhabitat selection generally differed among macrohabitats (i. e., pools, runs, and riffles). Rainbow trout selected different microhabitats at high flow relative to low flow in response to the availability of deeper, faster water. At low flow, depth and velocity selection were positively correlated with seasonal temperature change for adults but not juveniles. Rainbow trout apparently sought shelter in interstitial spaces in the substrate of runs and riffles during the day in early winter. Generally, large rainbow trout were observed in pools, intermediate‐sized fish in runs, and small trout in riffles. The largest fish occurred in slow, deep areas of pools, where they moved slowly without orientation to flow and were not observed feeding, whereas small fish generally faced upstream and fed in all habitat types. Foraging forays were directed up in the water column at velocities similar to the mean water column velocities at holding positions. Rainbow trout were the most abundant species in 76% of the population survey stations. Other species that might have influenced microhabitat selection by rainbow trout were uncommon.
Microhabitat use by fish in the upper Rio Matarraña, Spain, 1984–1987
Authors: Grossman G. D. , de Sostoa A.
Published: July 2006

Abstract– We evaluated the microhabitat use and abundance of Barbus graellsii, Bardus haasi, Chondrostoma toxostoma, Noemacheilus barbatulus, Oncorhynchus mykiss and Rutilus arcasii between 1984 and 1987 in the upper Rio Matarraña, Spain. The mean abundance classes for all species ranged from 1.8 to 3.0 (where 1=1–6, 2=6–10, 3=11–20 and 4=>20 specimens, respectively). Mean abundance was consistently higher in 1984–1985 (2.4–3.0) than during 1986–1987 (1.8–2.8). The decreases noted in 1986–1987 were attributable to declines in abundance of O. mykiss (introduced in winter 1984) and B. haasi. Barbus graellsii and Ch. toxostoma, however, remained abundant throughout the entire 4‐year study. We only observed N. barbatulus and R. arcasii irregularly in the study site. Analyses of microhabitat availability data indicated that the study site contained more silt and less algae/debris during spring 1985 and early and late summer 1986 than in the majority of the remaining season. The converse was true for late summer 1985 (i. e., less silt and more algae/debris than the majority of seasons). Principal component analyses showed that B. graellsii and Ch. toxostoma generally occupied deeper microhabitats with low to average velocities, higher amounts of depositional substrata and lower quantities of erosional substrata. B. haasi tended to avoid microhabitats with rubble substrata and occurred in those with higher amounts of algae/debris. O. mykiss occupied shallower areas with slightly higher velocities and a heterogeneous substratum. With the exception of B. haasi, microhabitat use by assemblage members was similar from 1984 to 1987. B. haasi, however, was not as strongly affected by depth in the latter two years of the study as it was during 1984–1985. Seasonal and annual analyses of intraspecific microhabitat use showed that most changes were due to variations in microhabitat availability. Nonetheless, all species exhibited minor seasonal shifts in microhabitat use. Size‐related analyses indicated that both smaller B. graellsii and Ch. toxostoma occupied shallower microhabitats with slower velocities than larger specimens. Intersite differences in microhabitat use for B. graellsii and Ch. toxostoma showed that most differences in substratum use were attributable to disparities in substratum availability. Both species occurred closer to the substratum in the site with higher velocities (i. e., upper reach), although this response was more pronounced in Ch. toxostoma. Interspecific analyses indicated that B. graellsii and Ch. toxostoma did not consistently occupy statistically differentiable microhabitats, although both species occurred farther from the substratum and refuges than did B. haasi. O. mykiss occupied shallower microhabitats with more gravel than either B. graellsii or Ch. toxostoma. The lack of microhabitat shifts by native species during the study period indicates that interactions with either B. haasi or O. mykiss did not play a strong role in microhabitat use by the remaining assemblage members.
Variation in agonistic encounters in a dominance hierarchy of freely interacting red‐spotted masu salmon (Oncorhynchus masou ishikawai)
Authors: Nakano S.
Published: July 2006

Abstract– Agonistic behaviour and dominance relationships in red‐spotted masu salmon, Oncorhynchus masou ishikawai, were observed in a mountain stream pool. A linear, size‐structured dominance hierarchy was recognized among individuals, body weight being a more important determinant of dominance status than fish length. Immigrant fish interacted more frequently with residents of similar body size than with larger or smaller fish during the early period following immigration. Thereafter, frequency of interactions rapidly decreased. When a fish was attacked, it reacted in a variety of ways in close accordance with its opponent's dominance rank: responses were to simply flee, flee with lateral display, revolt by performing a counter display or ignore the aggression. Such behavioural modification seems to be established during the successive agonistic encounters, in particular, early encounter periods when frequent interactions took place.
Gut evacuation in barbel (Barbus sclateri G., 1868) and nase (Chondrostoma willkommi S., 1866)
Authors: Encina L. , Granado‐Lorencio C.
Published: July 2006

Abstract– In this study we estimated the rates of summer gut evacuation for two cyprinids with detritivorous‐omnivorous feeding habits, Barbus sclateri, Günther 1868 (barbel) and Chondrostoma willkommi, Steindachner 1866 (nase). This study was performed at two sampling stations in the upper Guadalete River (south Spain). A previous study reported differences in the natural diet of both species. The gut evacuation rate was estimated from the regression of gut contents weight against time. Linear and exponential models best described the pattern of gut emptying in the two species. There was no significant difference in the gut evacuation rate between both sampling stations for barbel. However there was a discrepancy related to the model that provided the best fit to empirical data. In contrast, the same model provided the best fit to the empirical data for nase in both sampling stations, but the gut evacuation rate was significantly different in both sampling stations. The results of these study provide the first data of evacuation rates for Iberian freshwater fish species directly measured in the field.
Patterns of movement of centrarchids in two warmwater streams in eastern Tennessee
Authors: Gatz A. J. , Adams S. M.
Published: July 2006

We studied the movements of redbreast sunfish (Lepomis auritus), bluegill (Lepomis macrochirus), rock bass (Ambloplites rupestris), largemouth brass (Micropterus salmoides), and warmouth (Lepomis gulosus) by tagging fishes with individually numbered tags. We sampled quarterly over a 3‐year period (1985–1988) at six 800‐ to 2300‐m‐long sites in 2 streams near Oak Ridge, Tennessee. Overall, distances between successive captures were < 100 m for approximately two‐thirds of all fishes. Only rarely did we document movements over long distances; distances of 17.0‐17.6 km between successive captures were obtained for 5 fishes (1 redbreast sunfish, 1 largemouth bass and 3 bluegill), and only one other fish moved > 10 km. In general, all species were highly sedentary in both streams, with rock bass and redbreast sunfish being the most sedentary and bluegill and largemouth bass being the least. In most instances, redbreast sunfish showed the same distribution of distances between captures regardless of the interval between captures (1 week, 3 months, 6 months or more). This species also tended to be more mobile in the spring and less mobile in the winter, with large fish exibiting the greatest distances between captures. Some redbreast sunfish showed a very restricted home range, being captured 3 or more times over ≥ 6 months in the same 50‐m section of stream. A few individuals moved 4‐9 km only to return to their original location, but most fish exhibited behaviors intermediate between these extremes. For all species, upstream and downstream movements were equally common, although movements in one direction predominated at some sites for limited periods of time. Knowledge of movement patterns and differences in behavior among species is important not only in understanding the basic ecology of the species but also in designing, conducting and interpreting environmental monitoring studies.
Habitat use by an endangered riverine fish and implications for species protection
Authors: Freeman B. J. , Freeman M. C.
Published: July 2006

We investigated habitat specificity of the amber darter (Percina antesella Williams & Etnier 1977), an imperiled fish from restricted portions of 2 rivers in the southeastern United States. Foraging amber darters occupied a narrow range of riffle habitat, consistently avoiding areas < 20 cm deep and with velocity < 10 cm. s−1 near the substrate, occupying areas with cobble or gravel substrate and average water‐column velocity of 30 to 70 cm. s−1. During low to mo'derate flows, approximately 20% or more of the study areas contained suitable habitat for the species. Amber darters appeared rare, and the numbers of individuals were uncorrelated with the concurrent availability of suitable habitat. Protecting the amber darter may require more than maintaining adequate depths and velocities over gravel‐cobble substrates. Until we understand the potential importance of migration and dispersal for maintaining small populations, suitable habitat should be maintained over the longest contiguous stream segments possible.
Effects of stocking of piscivorous brown trout, Salmo trutta L., on stunted Arctic charr, Salvelinus alpinus (L.)
Authors: Damsgård B. , Langeland A.
Published: July 2006

To study the effects on a stunted freshwater population of Arctic charr, Salvelinus alpinus (L.), two groups of large (26–45 cm) individually tagged brown trout, Salmo trutta L., were released and recaptured with gillnets after 1, 7, 11 and 63 weeks. One group of trout was trained on a fish diet before release, and the other, reared on commercial dry pellets, served as a control. Specific growth rates in both groups were negative 1 week after release and approached zero after 63 weeks. Condition factor and internal fat content decreased during the experiment. Although only 11% of the trout stomachs examined contained fish prey, charr represented 79% of the total stomach weight content. Gillnet samples of charr before and 63 weeks after the release of trout indicated a decreasing population size of charr. Individual growth and mean length of charr increased after release of trout, especially for charr at age 4 years. After the release of trout, 35% of the charr were longer than 20 cm as compared with 6% before the release.
On size and growth in freshwater fish
Authors: McDowall R. M.
Published: July 2006

Patterns of growth and size achieved in freshwater fish are examined with relation to the issues of indeterminate and determinate growth and asymptotic growth. Various authors suggest minimum, average and maximum sizes attained by fish, variously pointing to very small gobies and very large sharks, with most fish being about 150 mm long. Growth in fish is distinctive in that typically it continues throughout life, even though it becomes slower with increasing age and the onset of sexual maturity. Growth rates and size achieved by fish are highly flexible and subject to both genetic and environmental controls, so that size reached may vary with environmental variables such as water temperatures and food availability (both food abundance and prey types and sizes). Frequency distributions of 5 disparate freshwater fish faunas (Papua‐New Guinea 267 species and tropical; North America 709 species and subtropical to Arctic; Australia 176 species and tropical to temperate; New Zealand and Great Britain 27 and 39 species and both warm to cool temperate) closely resemble distributions generated by the theoretical model of Hutchinson & MacArthur, and also data on diverse faunas. Frequency distributions in these faunas are closely similar, with a majority of species being small. This similarity would seem to suggest a general explanation. However, examination of the freshwater fish fauna of North America suggests that, rather than showing a predominance of large fish in the Arctic, the fauna has more large fish towards the tropics, though the proportion of large fish there is lower owing to the proliferation of small species in the tropics and a paucity of them towards the Arctic. Analysis shows a shift in the size composition of the fauna with latitude and shows that the general pattern for the whole of North America consists of a composite series of rather different patterns. This suggests that there is probably no meaningful general explanation of the overall patterns seen in these diverse and disparate faunas and that the similarity in overall size distributions between freshwater fish faunas of North America, New Guinea, Australia and New Zealand are of little ecological or evolutionary significance. The generality of Cope's rule is questionable, especially for fish, in which dwarfing and/or evolution towards smaller size are seen to be common phenomena.
The effect of lakes on the stream fish fauna
Authors: Degerman E. , Sers B.
Published: July 2006

The effect of natural lakes on the fish species distribution in surrounding streams was studied using electrofishing survey data from 3281 localities in streams throughout Sweden. The occurrence of lake fish (northern pike, European perch, roach and burbot) was significantly higher close to lakes, both up‐ and downstream, as compared to localities further up‐ or downstream of lakes. Correspondingly, the occurrences of stream fish (brown trout, grayling, European minnow and bullheads) were lower close to lakes. It is suggested that the lower occurrences of the latter close to lakes be due to biotic interaction with lake fish, especially predation from pike and burbot. The results strongly indicate that the effect of lakes on water temperature, drift of plankton and invertebrates or the moderating effect on water fluctuations and quality did not influence the stream fish fauna to the same extent as the presence of lake fish in a zone up‐ as downstream of the lakes. Lakes function as a reservoir of strong predators and competitors.
Microhabitat use by fish in the lower Rio Matarraña, Spain, 1984–1987
Authors: Grossman G. D. , De Sostoa A.
Published: July 2006

We quantified microhabitat use in Barbus graellsii, Cyprinus carpio, Chrondostoma toxostoma, Esox lucius, Gobio gobio and Leuciscus cephalus during 1984–1987 in the lower Rio Matarraña, Spain. Fluctuations in numerical abundances of assemblage members increased during 1986–1987. These increased fluctuations were due to decreases in the abundances of Ch. toxostoma, E. lucius and G. gobio during the latter 2 years of our study. Only C. carpio increased slightly in abundance during this period. An analysis of microhabitat availability data indicated that 16 seasonal samples could be assigned to 1 of 6 groups ranging from: seasons with zero velocities, shallower depths and an algal/debris substratum to those with high velocities and depths and a substratum composed of algae/debris, rubble and gravel. Most seasonal changes in the substratum were attributable to conditions inhospitable to the growth of benthic algae (i. e., high velocities or low oxygen levels) rather than to actual changes in the underlying lithospheric substratum. Principle component analyses indicated that most species were overrepresented in deeper microhabitats with depositional substrata. Ch. toxostoma, however, tended to occur over rubble substrata in both shallow and deep microhabitats. Most seasonal changes in microhabitat use were produced by seasonal variations in microhabitat availability. However, all species except E. lucius exhibited seasonal variations in microhabitat use that typically involved velocity, depth and substratum composition. Although smaller specimens of most species were found closer to the substratum in 1984–1985, they tended to occupy shallow areas in 1986–1987. Canonical analyses of discriminants and univariate data demonstrated that the distance from the substratum was the best predictor of interspecific differences in microhabitat use. Species could be arrayed along a vertical gradient with L. cephalus and Ch. toxostoma occupying mid‐water column positions, B. graellsii and C. carpio occurring in lower‐water column microhabitats and E. lucius and G. gobio strongly associated with the substratum. Changes in interspecific microhabitat use were not correlated with changes in species abundances, and hence, interspecific competition did not appear to strongly influence microhabitat use during our study.
Variations in the population dynamics of the European eel Anguilla anguilla (L.) along the course of a Cantabrian river
Authors: Lobón‐Cerviá J. , Utrilla C. G. , Rincón P. A.
Published: July 2006

Abstract– The size, density and production rate of eel were determined at 16 contrasting sites of 4 streams along the course of a Cantabrian river over the years 1990–1993. In addition, the diel cycles of feeding activity were determined monthly in another tributary over the year 1991–1992. Eels in the Esva were small, short‐lived and mostly males (>99%). The seasonal patterns of eel density, feeding activity and condition were tightly fitted with each other, size‐independent and regulated mainly by water temperature. Mean eel size increased with distance from the river mouth, but at each site, it remained similar between seasons and years. In contrast, density decreased upstream and showed marked seasonal and annual fluctuations. For all the sites, the number of eels increased in spring and summer and peaked by late autumn, coincident with higher water temperature and lower discharge. Mortality and migration rates were correlated with eel numbers for each stream, suggesting a densitydependent regulation. Production rates were correlated with distance from the river mouth, which explained only 10.2% of the variation, but they were also correlated with the initial and mean numbers, suggesting that site‐specific factors acting upon density also influence production. Average production for the first year was 158.6 kg–ha–1. year–1 (range 56.5–378.0) but decreased to 104.2 and 89.7 in the next 2 years. The reduction in the numbers of eels rather than the later reduction in mean size was responsible for this decrease. Monthly water temperature, distance from the river mouth and the initial number and size of eels for each site explain most of the variation observed in the population parameters along the course of the Esva River.
Laboratory studies of substrate and microhabitat selection in the southern cavefish (Typhlichthys subterraneus Girard)
Authors: Schubert A. L. S. , Noltie D. B.
Published: July 2006

Abstract– The southern cavefish (Typhlichthys subterraneus Girard) is a small troglobitic fish found in a few disjunct populations in the central United States. Protecting and managing these populations requires a knowledge of southern cavefish microhabitat requirements, including their preference for substrate. We conducted tests of their preferences for cobble, gravel, pea gravel, and sand substrates in two‐way and multiple choice experiments for extended periods using time‐lapse video photography. Cobble proved to be the substrate these fish preferred to occur within. In nature, this preference may provide cavefish increased foraging opportunities and/or refuge from high flows associated with flooding. Our results indicate the need to (1) maintain coarse substrate as an integral part of cavefish habitats, and (2) direct cavefish censusing attempts towards such key areas.
Visual habitat choice in cyprinid fishes: an experimental approach
Authors: Podolsrky D. , Uiblein F. , Winkler H.
Published: July 2006

Abstract– The mechanisms leading to spatial segregation along optical habitat dimensions in closely related, co‐occurring fishes were investigated. In two experimental series, six laboratory‐reared cyprinid species were faced to six novel optical patterns. These were positioned either laterally, at the bottom, or at the water surface, in one of three compartments of a large tank. When a bottom pattern was presented, the primarily bottom‐dwelling species Vimba elonguta and Abranzis brama chose the test compartment at high frequencies, indicating a significant preference. More surface‐oriented species like Chalcalburnus chalcoides mento and Scardinius erythrophthalmus developed similar preferences in response to surface patterns. V. elongata, A. brama, and Rutilus rutilus showed significant preferences for a photograph of submerged plants. Also, V. elongata developed preferences for several optical patterns. These data confirm earlier studies on V. elongata habitat selection and foraging behaviour which suggest a highly exploratory lifestyle. S. erythrophthalmus and Leuciscus cephalus showed significant avoidances for laterally positioned optical patterns associated with reduced interindividual distances, indicating marked neophobic responses. The establishment of species‐specific preferences or avoidances during the two experimental series was influenced by learning processes.
Effect of sudden increase in discharge in a large river on newly emerged Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) fry
Authors: Saltveit S. J. , Bremnes T. , Lindå O. R.
Published: July 2006

Abstract– Downstrcam displacement of salmonid fry due to flow increase, from 12–15 m3/s to >100 m3s, was documented in the river Suldalslåen, Western Norway. In May only fry of brown trout (Sulmo trutta) occurred in the drift, while from the beginning of June only newly emerged Atlantic salmon (Sulmo sular) were found. The maximum number of Atlantic salmon fry drifting during a single day was estimated to be 17 000 individual. Their density in the drift was higher during the night than during the day, and their appearance in the drift coincided with the predicted period of emergence. Total brown trout numbers in the drift were estimated to vary between 4000 and 16 000 per day. Fry displaced downstream from the lowermost part of the river were lost from the population. The total losses were estimated to be between 75 000 and 100 000 Atlantic salmon fry which represents between 5.6 and 11.1%) of juvenile mortality during the first year of life.
New data on the ecology of kutum, Rutilus frisii (Nordmann, 1840) from the Caspian Sea
Authors: Holčik Juraj
Published: July 2006

Abstract– In the anadromous cyprinid kutum, Rutilus frisii (Nordmann, 1840) from the Anzali Lagoon, Iran, the following hitherto unrecorded characters were found. The complex life‐style of juvenile kutum is reflected directly in their body size and preferred habitat, and indirectly in their growth rate and the formation of scale annuli. The early juveniles did not move downstream to the feeding grounds in the sea as they are supposed to do in populations inhabiting the Caucasian coast of the Caspian sea, but most of them spend one or two years in fresh or brackish water. Moreover, most kutum scales carried one or two juvenile marks. It appears that the time spent in fresh water is inversely proportional to the age of the kutum. On average about 43% of fish 2 years old and older, spent their first year in fresh or brackish water, while 57% spent two years there. The rate of growth in length is substantially different in both groups. Fish that enter the sea in their second year of life grew faster but their life span seems to be shorter than those which spent two years in fresh or brackish water.
Territoriality of male cichlid fishes in Lake Tanganyika
Authors: Kohda Masanori
Published: July 2006

Abstract– Intra‐ and interspecific territoriality of males in six maternal mouthbrooding cichlid species was observed in Lake Tanganyika. Males of all species usually swam, foraged and courted visiting females in restricted ranges (2–10 m across) which were separated from those of conspecific males. Each swimming area contained a nest site. Males of all species attacked conspecific males near or beyond the borderline of the swimming area (mating territory) and attacked various kinds of potential egg eaters from a narrow area only around the nest site (nesting territory). Males of three species attacked cogeneric fishes, i. e. food competitors, inside mating ‐ but outside nesting territories (feeding territory). Thus, males maintained two or three different kinds of territories. Territoriality of the cichlids was compared with that of damselfishes.
Annual biomass and production of brook charr (Salvelinus fontinalis) introduced into a historically fishless lake
Authors: Kelso J. R. M. , Shaw M. A.
Published: July 2006

Brook charr 15 months old were introduced in 1985 into one of two self‐contained basins of Batchawana Lake, Ontario, Canada, where they survived and reproduced. Population survival rates (ages ≥ 1) remained high (>50%) from 1986 to 1992. Annual growth rates peaked (Gx=3.1) the year following their introduction, and remained between 0.8 and 1.6 thereafter. Brook charr biomass (B) was highest, ∼ 55 kg ∼ ha−1in 1987 and 1990, and production (P) gradually declined from 80–90 in 1986–1987 to ∼ 30 kg‐ha−1‐year−1in 1990–1991. Initial high P:B ratios for brook charr, ∼ 3.0, declined and stabilized to ∼ 1.3 in the third year after introduction.
Fish species richness in lakes of the northeastern lowlands in Germany
Authors: Eckmann R.
Published: July 2006

Fish species richness was assessed by electrofishing and gillnetting in 16 lakes of the northeastern lowland in Germany (the Schorfheide biosphere reserve). The lakes range from 0.03 to 10.55 km2 and support between 5 and 14 fish species. Species richness is significantly correlated with lake area in an exponential and a power model. Richness is also correlated with shoreline development and total dissolved solids. This supports the hypothesis that larger areas contain more species within a taxonomic group due to increased habitat diversity. The slope of the species‐area curve is low compared with most other studies of fish species richness in lakes, and the intercept value is high. This is interpreted as the result of high habitat and food diversity, lack of stress from abiotic factors, and the small regional species pool from which these lakes can be colonized. Two species inventories, one from the beginning of this century and one from the 1950s, are available for comparison. Average species richness did not change during the last decades. Species turnover rates were not related to the degree of anthropogenic eutrophication or to the intensity of fishery exploitation in these lakes. On the species level, however, one effect of accelerated eutrophication is apparent, the disappearance of 4 bottom‐living species from one to 6 of the study lakes.
Food resource partitioning of Arctic charr, Salvelinus alpinus (L.) and three‐spined stickleback, Gasterosteus aculeatus L., in the littoral zone of lake Takvatn in northern Norway
Authors: Jørgensen L. , Klemetsen A.
Published: July 2006

The food resource partitioning of Arctic charr (Salvelinus alpinus L.) and three‐spined stickleback (Gasterosteus aculeatus L.) were investigated in the littoral zone of lake Takvatn in northern Norway in the ice‐free period June–November. Charr and sticklebacks had different feeding habits. Sticklebacks ate several small benthic prey items that were never eaten by charr, and the sticklebacks' diet were dominated by the benthic microcrustaceans Chydoridae and Ostracoda, chironomid larvae and stickleback eggs. Small charr (<17 cm) consumed a wide spectrum of chironomid pupae, terrestrial insects and zooplankton. Intermediate (17–20 cm) and small charr had quite similar feeding habits, while large charr (>20 cm) frequently ate both benthos, pelagic and terrestrial food. The diet overlap between small charr and sticklebacks was never larger than 0.6 (Schoener's index). The segregation in feeding habits indicates that small charr and sticklebacks are segregated in microhabitat when they are both in the littoral zone.
Phenology and spatial and temporal distribution of larval fishes in a partially channelized warmwater stream
Authors: Peterson M. S. , VanderKooy S. J.
Published: July 2006

We studied the phenology and spatial and temporal dynamics of larval fish abundance with light traps from 5 locations along the length of Luxapalilia Creek, a partially channelized warmwater stream in northeastern Mississippi over 2 spawning seasops (March through August 1992 and 1993). The dominant, early spring spawners were catostomids (early‐April to late‐May) and darters (mid‐March to early‐June) whereas summer spawners were mainly cyprinids (mid‐May to August) and centrarchids (late‐May to August). The relative abundance of larvae collections differed based on: 1) site, 2) location, 3) date, 4) year, and 5) in larval stage. Total numbers of larvae and CPUE were high in mid‐ to late summer in downstream locations in both years when: 1) temperatures were high, 2) water velocities were low, and 3) depths were shallow compared to upstream locations. More mature larvae (meso‐ and metalarvae) were more common in the downstream locations whereas less mature larvae (yolk‐sac and protolarvae) were more abundant at the upstream locations. The downstream channelized portion of Luxapalila Creek resembled a lentic habitat with littoral zones characterized by slow water velocities, shallow depths, fine sediments, and vegetation. Larvae of darters (Etheostorna and Pcrcina), which require gravel bars and swift currents, were not collected in great numbers downstream, although members of the Ictiobinae (Carpoides and Ictiobus), cyprinidae and centrarchidae (Lepomis spp., Pomoxis spp. and Micropterus spp.) were more abundant downstream than upstream. This suggests that the natural, upstream locations acted as sources of larvae for the channelized downstream location.
Year class variation in fluctuating asymmetry in perch (Perca fluviatilis L.) from an acidic aluminium‐rich lake
Authors: Øxnevad S. A. , Østbye K. , Vøllestad L. A.
Published: July 2006

Fluctuating asymmetry is the random deviation from perfect bilateral symmetry owing to developmental perturbation, proposed as an indicator of sublethal environmental effects. This was measured in perch (Perca fluviatilis L.) from an acidic aluminium‐rich lake. Eleven paired meristic and morphometric characters were scored for fluctuating asymmetry. Level of fluctuating asymmetry differed significantly between year classes for two of the meristic characters, lower extra gill rakers and upper extra gill rakers, and also for an index summarizing number of asymmetric meristic characters per individual. This year class variation in fluctuating asymmetry is probably due to large variation in water quality during early development of perch embryos in spring. For future work on fluctuating asymmetry on fish we recommend the use of as many year classes as possible in the analyses.
Fattv acid content of some freshwater fish in lakes of different trophic levels – a bottom‐up effect?
Authors: Ahigren G. , Sonesten L. , Boberg M. , Gustafsson L. B.
Published: July 2006

Abstract– Various sizes of roach, perch, pike, zander (pike‐perch) and crucian carp were collected from lakes of different trophic levels in order to study the variation of lipids and fatty acids (FA) within and between species. Freeze‐dried samples of the dorsal muscle were analysed quantitatively for total lipid content and FA content. The results indicate that total lipid and FA contents can vary considerably, both within and between species. In contrast to herbivorous fish, carnivorous‐piscivorous fish FA patterns were more constant and independent of size ‐ fry excepted. Lipid and FA contents of roach from two oligotrophic lakes were significantly higher than in roach from a eutrophic lake. Differences in basic food webs may be responsible for these results. In the oligotrophic lakes, the algal flora was dominated by species classified as high quality food for grazers, e. g. flagellates and diatoms. It was shown in earlier papers that these algal groups contain two long‐chained FA of φ 3 type (eicosapentaenoic acid and docosahexaenoic acid) which are used as criteria indicating high nutritional value. Conversely, the eutrophic lake was dominated by blue‐greens, a group of autotrophs lacking these long‐chained φ 3 FA. Blue‐greens have generally been classified as poor food for grazers. (The fatty acids are described by three numbers, x:yφz, where x=number of carbon atoms, y=number of double bonds, and z=position of the first double bond counted from the methyl end of the molecule.)
Lake‐use by juvenile Atlantic salmon (Salmo salarL.) and other salmonids in northern Norway
Authors: Halvorsen M. , Jørgensen L.
Published: July 2006

Abstract–The utilization of lakes, and inlet and outlet streams by juvenile Atlantic salmon (Salmo salarL.), brown trout (Salmo truttaL.) and Arctic charr (Salvelinus alpinus(L.), were investigated in 16 watercourses northern Norway, all known to inhabit salmon stocks. In lakes, fish were caught by small mesh size gill nets, while in rivers fish were caught electrofishing. In the shallow littoral (0‐3 m depth) there were juvenile salmon in 15 of 19 investigated lakes, juvenile trout in 17 and juvenile charr in seven. Trout dominated significantly in numbers in the shallow littoral of seven lakes, while salmon and charr dominated in three lakes each. When trout and salmon were frequent in the shallow littoral, charr was usually not present in this habitat, but were found in the profundal zone in most of the lakes. Atlantic salmon parr utilized both shallow and deep lakes, and used both stones and macrophytic vegetation as shelter. The utilization of lakes by salmon parr seemed to be closely related to utilization of small inlet streams for spawning. In most inlet and outlet streams salmon dominated over trout in numbers, while charr were absent. This is the first documentation of lake‐use by naturally occurring salmon parr in Scandinavia.
Experimental studies on planting artificial stream channels with unfed and six weeks fed salmon (Salmo salar L.) and trout (S. trutta L.) fry/parr
Authors: Crisp D. T.
Published: July 2006

Abstract– Experimental comparisons were made between release as unfed fry and release as six weeks fed parr, upon the growth and final population density of young salmon and trout over a ten week period. Salmon and trout released into experimental channels as unfed fry at densities of about 19 fish. m‐2 showed rapid reduction in numbers, chiefly by downstream dispersal, accompanied by negligible growth. After substantial reduction in numbers, there was a reduced rate of dispersal and rapid growth. Salmon and trout retained in a hatchery at high density (80 to 200 fish. m‐2) and fed for six weeks on proprietary food showed slow, but measurable, growth. After release into the channels these fish adjusted their numbers, mainly by downstream dispersal, and showed an increased growth rate. At the end of a ten week period, salmon introduced as fed parr had approximately twice the population density of salmon introduced as unfed fry. No similar difference in population density could be shown for trout. For both species, the fish introduced as fed parr had a lower mean weight after ten weeks than had the fish introduced as unfed fry.
Age and growth of yellow eel, Anguilla anguilla (L.), determined by two different methods
Authors: Poole W. R. , Reynolds J. D.
Published: July 2006

Abstract– Ageing and calculation of growth rate of eels has always been controversial, and remarkably little validation has been reported. This article describes the growth of yellow eels from three lakes in the Burrishoole system, Ireland, as determined by back‐calculation from otoliths prepared by burning and cracking. Eels captured by fyke net ranged in length from 25.0 cm to 98.5 cm and the ages ranged from 6 to 49 years. Back‐calculated growth was slow, with mean annual increments of 2.08 cm, 1.40 cm and 1.97 cm for the three lakes. Yellow eels captured in the Burrishoole system in 1987 and 1988 were marked by Pan Jet inoculated alcian blue dye and released back into the three lakes. Recaptures made over the following three years yielded considerable growth data. Mean annual growth rates recorded were 2.30 cm, 1.07 cm and 0.97 cm. These data compare favorably with the calculated growth rates, thereby validating the otolith analysis for the eels in the Burrishoole system.
Migratory dynamics of stream‐spawning longnose gar (Lepisosteus osseus)
Authors: Johnson B. L. , Noltie D. B.
Published: July 2006

Abstract–Literature evidence suggests that lake‐dwelling longnose gar (Lepisosteus osseus) enter tributary streams to spawn, Until the present study, the dynamics of this breeding migration had never been investigated quantitatively. During the summers of 1991 and 1992, longnose gar were captured as they entered Weaubleau Creek, Missouri, a tributary of Harry S. Truman Reservoir. The in‐stream spawning migration began in early April and ended in late May, and was positively correlated with stream flow and water level, and negatively correlated with water temperature. In‐stream residence times ranged from 15 to 94 days, with males exhibiting longer residence times than females. Once in‐stream, longnose gar travelled as far as 10 km upstream and occupied certain pools at greater relative frequencies. Although the reason for this preferential utilization is not completely understood, it may relate to pool depth and riffle proximity. Longnose gar disperse from the spawning stream great distances, with gar captured in Weaubleau Creek being recaptured up to 48 km away. This information should provide fisheries biologists the means to consider the reproductive ecology of this species in their conservation and management decisions.
Growth, population composition and reproduction of Bream Abramis brama (L.) in Lake Volvi, Macedonia, Greece
Authors: Valoukas V. A. , Economidis P. S.
Published: July 2006

Abstract– Growth, population composition and reproduction of bream were studied in Lake Volvi from 1989 to 1991. Females had a higher growth in length (L∞=507 mm, k=0.094) than males (L∞=452 mm, k=0.102). Growth can be characterized as medium, due to low food sources (zooplankton and chironimids). Large specimens are scarce because of high fishing mortality and low growth rate. All males greater than three years old, longer than 135 mm and all females greater than four years old and longer than 150 mm were sexually mature. These values of age and size of first maturity are the lowest that have been reported for this species. The size of the spawning egg is independent of the body size.
Reproductive biology of Cyprinella camura, the bluntface shiner, in Morganfork Creek, southwestern Mississippi
Authors: Farr M. D.
Published: July 2006

Abstract– I collected bluntface shiners, Cyprinella camura, once or twice monthly from February to November 1991 in Morganfork Creek, southwestern Mississippi. Examinations of mean largest oocyte diameter (LOD), female mean relative gonadal index (RGI), ovarian developmental condition, and male secondary sexual characteristics indicated that C. camura spawned from late March through mid‐August. There were significant positive correlations between mean LOD and mean daylength, mean maximum temperature, and mean minimum temperature (environmental variable means were calculated for the 28 day period prior to each sampling date). Mean day length and mean RGI were significantly positively correlated, but there was no significant relationship between mean maximum and minimum temperatures and mean RGI. Clutch size, RGI, and mean mature oocyte diameter (MMOD) of mature females were significantly correlated with length (standard length). Mean length, clutch size, and RGI of mature females in individual collections decreased significantly over the reproductive season. The corresponding decrease in mean MMOD was not significant.
Preservation‐induced changes in morphometrics of fishes: influence on prey size‐choice in juvenile walleye,Stizostedion vitreum(Mitchill)
Authors: Peterson M. S. , VanderKooy S. J.
Published: July 2006

Abstract–Juveniles of the Gulf coast population of walleye,Stizostedion vitreum, 22.4–89.9 mm SL (n=111) shrank significantly in SL and throat diameter over 12 months after being fixed in 10% formalin for 1 week and preserved in 50% isopropyl alcohol thereafter. Significant changes in body depth and total length (TL) were also determined for select larval fish prey that juvenile walleye might encounter in nature. The relationship between fresh SL and throat diameter in juveniles of the Gulf coast population of walleye (22.4–172.4 mm SL) is: throat diameter (mm) =−0.8783 + 0.0786 SL (mm) (r2= 0.988,P< 0.0001,n= 135). In laboratory experiments on prey size choice, walleye selected available prey near or less than their mean throat diameter, although several larger prey (7.4% of total) were also consumed. To determine the actual spectrum of prey sizes available to juvenile piscivores, we must adjust the realized size of the predator and prey for changes caused by preservation. Preservation‐induced alterations in morphology translated into errors in the perceived pattern of prey size choice in walleye. The preservation‐induced changes documented in this study, which are also supported by a number of other empirical data sets, must be included when modeling the relationships between feeding ecology, morphology, growth, and ecologically relevant indices (condition factors, relative weights, etc.).
Variation in numbers of eel Anguilla anguilla caught by constant effort in an Irish lake, 1981–1994
Authors: Moriarty C.
Published: July 2006

Abstract– A total of 8,903 eels were collected in 503 fyke‐net samples during the months March to December from 1981 to 1994 in a small bay in Lough Derg, a mesotrophic lake. Variations in catch between months and between years are described. In addition to expected decreases in catch in the colder months, a regular reduction was observed in June. Low catches were observed from 1985 to 1987, coinciding with low water temperatures. A very low catch in August 1994 may have been a chance variation but could have been a first indication of the effects of poor recruitment or of increased commercial fishing effort. The results support the initial hypothesis that a long‐term study is required to determine the extent of variation in an eel population.
Diel patterns in the feeding and habitat use of O‐group fishes in a regulated river: the River Great Ouse, England
Authors: Garner P.
Published: July 2006

Feeding and habitat use behaviour of juvenile O+ fishes, principally Rutilus rutilus (L.) and Leuciscus cephalus (L.) was analysed at 4‐h intervals for a period of 24 h on 29 June, 27 July, and 13 September 1994 at a regulated site on the River Great Ouse, UK. Twenty‐five random point samples were taken by electrofishing during each sampling period from a 250 m reach of the river. Catch per unit effort decreased at night for both R. rutilus and L. cephalus. The number of prey items in the gut and the number of taxa found also decreased at night except for R. rutilus on one occassion. Habitat use remained near constant, with only slight increases in depth and distance from the bank at night. Use of Nuphar lutea by roach increased at night. Chub tended to avoid Nuphar lutea and were positively associated with emergent macrophyte and algal cover both during the day and night.
Diet and dietary overlap in fishes of temporary waters of southwestern Australia
Authors: Pusey B. J. , Bradshaw S. D.
Published: July 2006

The diets of six species of fish occurring in seasonally inundated waters of the southern acid peat flats of southwestern Australia were studied over a 23 month period. Fishes could be allocated to a benthos/lower water column guild or a midwater column/water surface guild. Segregation on the basis of prey size was noted for one species only, and this species had a larger mouth than the remaining species. Seasonal variation in within‐ and between‐guild overlap was observed. Highest overlap occurred in the mid‐wet season when inundation was greatest and all species foraged in extensive areas of very shallow water. Little segregation based on feeding position within the water column was possible, and some prey species (e. g. simuliid larvae) were particularly abundant at this time. Dietary overlap decreased as the dry season progressed and fish became concentrated in smaller areas of habitat. As fish demonstrated lower levels of food acquisition, this change in overlap was suggested to be in response to increased competition for limited food resources.