bluuebunny/crossref_metadata_2025 huggingface dataset:
Assemblage structure and quantitative habitat relations of small mammals along an ecological gradient in the Colorado Desert of southern California
Authors: Kelt Douglas A.
Published: July 2006

Ecological gradients have intrigued ecologists for many years. In southern California the Deep Canyon Transect spans a range of habitats and elevations from Lower Sonoran Desert sand dunes and creosote scrub to Upper Transition coniferous forest, where relict species typical of the Sierra Nevada are found. I sampled a 1050 n elevational range in this transect to evaluate the ecological distributions of small mammals and to better characterize community structure. Results complement and substantially extend a previous study of this fauna, and provide insights into the habitat associations of species in this complex fauna. Assemblage structure changed greatly between summer and winter, largely due to reduced presence of pocket mice Chuetodipus in winter. Additionally, the distribution of abundance and species richness was different than reported earlier, suggesting that patterns across this gradient may be temporally variable, and strongly influenced by local dynamics. Most taxa exhibited significantly nonrandom use of a large number of habitat variables but this was not a simple consequence of the elevational gradient. A mid‐elevation bulge in species richness was indicated, but likely is not a consequence of mass effects since a number of animals captured in intermediate regions were reproductively active.
Predator–prey interactions between brown trout Salmo trutta and native and introduced ampbipods; tbeir implications for fisb diets
Authors: MacNeil Calum , Elwood Robert W. , Dick Jaimie T. A.
Published: July 2006

An attempt to improve the food base for brown trout Salmo trutta in Northern Ireland was made in 195859 by deliberately introducing English Gammarus pule.x into several Irish rivers. In addition, another amphipod Crangonyx pseudogracilis, was later accidently introduced into Irish waters. Our study represents the first attempt to examine the trophic interactions between a native fish predator (S. trutta) and an array of these native (Gammarus dueheni celticus) and introduced (G. pulex and Cpseudogracilis) amphipods. Feeding experiments, involving young brown trout predators and amphipod prey, revealed that the fish actively selected C. pseudogracilis relative to two alternative Gammarus prey species. Although the trout encountered the Gammarus species more than C pseudogracilis, they were eaten less than Crangonyx. Difficulties in handling and ingestion of Gammarus by trout may be a key component of the preference for the smaller, more easily handled Crangonyx. The microdistribution of the species was altered by the fish, due to predation being greater in particular microhabitats. Our study showed that the introduction of the herbivorous C. pseudogracilis into Irish freshwaters may represent a useful addition to fish diets, particularly for small and or juvenile fish. The repercussions of the deliberate introduction of G. pule.x are less clear. It may improve feeding for fish. but only if it can coexist with indigenous macromvertebrates and thus ultimately improve the range and quantity of possible food items in predator diets. Alternatively, being highly predatory towards other macroinvertebrates including G. d. celticus and C. pseudogracilis, G. pule.x may be deleterious to the diversity of the resident benthic community and hence reduce the diversity of prey available to fish predators.
Variation in floral morphology and individual fecundity in Erythronium dens‐canis (Liliaceae)
Authors: Guitián Javier , Guitián Pablo , Medrano Mónica , Sánchez José María
Published: July 2006

This study investigated the extent to which the reproductive success of plants of Erythronium dens‐canis (Liliaceae), a spring herb of mountain habitats, is dependent on floral morphology. To this end, a series of studies was performed in an area in northwest Spain. The results show that E. dens‐canis plants in this area a) are self‐compatible, b) need pollinator visits (largely Bombus terrestris and Andrena spp.) to produce seed, and c) show high fruit set under natural conditions. Only 20% of among‐plant variance in floral morphology variables was explained by variation in plant size. Floral morphology variables (outer tepal length, stamen length, style length and ovule number) tend to vary in parallel, indicating the existence of an “integrated floral phenotype”. Two floral morphology variables (initial number of ovules and outer tepal length) had statistically significant or near‐significant effects on seed production. A more detailed experimental analysis indicated that small‐flowered plants produce fewer seeds than large‐flowered plants, and that this is attributable to less efficient pollination of small flowers. The results of this study thus suggest that among‐plant variation in floral morphology in E. dens‐canis has implications for reproductive success.
Spatial pattern of the threatened epiphytic bryophyte Neckera pennata at two scales in a fragmented boreal forest
Authors: Kuusinen Mikko , Penttinen Antti
Published: July 2006

The spatial pattern and occurrence of a threatened bryophyte, Neckera pennata. were studied in relation to the abundance and pattern of suitable substrate trees at two spatial scales: 1) in a 4 x 4 km fraction of fragmented, mostly managed southern boreal forest landscape, and 2) in an old‐growth forest stand within this landscape, with abundant occurrence of suitable habitats. To explore in detail the spatial clustering of N. pennata at the forest stand scale, we applied a second order point process analysis based on the Ripley's K‐function for binary point patterns, Neckera pennata proved to be a rare species in the studied landscape: it was found only on 31 Populus tremula trees. At the landscape scale, the distribution of the species was highly aggregated: the species occurred only within a 60 ha old‐growth forest patch in the whole area. At the forest stand scale, N. pennata proved to be a widespread, randomly distributed species without any tendency towards aggregation. It was found on 19 Populus trees, which was only 1.5% of the total 1253 potential substrate trees within the inventory area. The species showed a statistically significant preference towards large trees. The future of the species in the study area is unclear due to 1) the very low population density and 2) the lack of regeneration of Populus within the protected old‐growth forest area hosting the remaining population.
The dynamics of peat accumulation on bogs: mass balance of hummocks and hollows and its variation throughout a millennium
Authors: Malmer Nils , Wallén Bo
Published: July 2006

This study concerns the mass balance in hummocks and hollows on three ombrotrophic boreonemoral bogs in both a short (ca 10 yr) and long (1000 yr) time scale. Nitrogen, 14C. and −210Pb are used to establish detailed time scales and to estimate productivity and decay losses in tour different microtopographical units: hummocks with either Sphagnum or lichens and hollows with either Sphagnum lawns or bare hollows. The accumulation of N and 210Pb was greater in hummocks than in hollows. The litter input was higher in Sphagnum hummocks (170‐210 g m−2yr−1) than in lawns (110‐145 g m −2‐ yr−1) while its decay rate (0.011 ‐0.014 yr−1) did not differ. The arotelm was deeper in Sphagnum hummocks than in lawns but because of less compaction in lawns, neither residence time (80 100 yr) nor decay losses (70‐75%) differed. Productivity in lichen hummocks and bare hollows was insignificant and the mass balance negative. It is concluded that the higher productivity in Sphugnum hummocks maintains the microtopography on the mire surface. The mass balance in hummocks will determine not only the development in hollows but also the rise of the ground water mound, and the height increment of a bog. The addition of mass to the catotelm has generally been less in hollows than in hummocks. Since 800 BP the overall input to the catotelm has decreased from about 150 to < 50 g m −2 yr−1 due to longer residence time increasing losses through decay in the acrotelm from < 20% to 70% and is the result of either climatic changes or autogenic processes in the bog ecosystem. Before recent centuries the whole bog surface must have been covered with Sphagnum mosses, forming an overall input of litter as large as in the recent Sphagnum hummocks and lawns. Due to the present lesser cover of peat forming mosses (20‐50% of the surface), the recent overall input of peat‐forming litter is only 50‐65 g m−2 yr−1. The bogs no longer act as sinks for carbon since the input of carbon only just covers the losses as CH4 and CO2.
Occurrence of epiphytic macrolichens in relation to tree species and age in managed boreal forest
Authors: Uliczka Helen , Angelstam Per
Published: July 2006

For the maintenance of biodiversity some epiphytic macrolichens have been used to identify forests with high conservation value. To understand what these macrolichens indicate, we studied the relationships of tree species and age with the abundance of a set of 33 macrolichens (20 of them in use as indicator species) at 90 localities in a 150 km2area in south‐central Sweden.

We sampled the four most common tree species Scots pinePinus sylvestris.Norway sprucePicea abies, birchBetulaspp, and aspenPopulus tremulafor macrolichens at 0‐2 m from the base. Of the 33 target species we found 17, six of them were indicators in use for this region. In 30, out of 40 tested, cases there was a positive relation between lichen abundance and age of the tree.

On all tree species the number of the studied lichen species increased with age. The colonisation rate of the species was fastest on birch. All species occurring on birch were also found on at least one of the coniferous trees, while aspen had six species not found on other trees. Pine and spruce with a slow growth rate had more signal lichen species than fast growing trees.

We could not detect a competitive situation between common and rare species as the most abundant or largest lichens did not exclude other species. The length of the longest fruticose lichen was positively correlated with the number of species on the tree. Shade had a negative effect on the number of species.

We conclude that the indicator macrolichens encountered in this study showed a preference for old trees or aspens. This result, and the low number of indicator species, points at the importance of promoting these trees for the preservation of biodiversity in the boreal forest.
Leaf litter and the small‐scale distribution of carabid beetles (Coleoptera, Carabidae) in the boreal forest
Authors: Koivula. Matti , Punttila. Pekka , Haila Yrjö , Niemelä Jari
Published: July 2006

Management practices favoring conifers at the expense of deciduous tree species, and the eradication of deciduous trees, especially aspen Populus tremula, from managed forests have resulted in population declines in several species in Fennoscandia. In addition to species depending on decaying wood of deciduous trees, earlier evidence suggests that leaf litter, especially that of aspen, is favored by many carabid species. We ran a four‐year experiment in order to compare carabid assemblages of unchanged forest floor with artificially created leaf‐litter plots in central Finland. A total of 18 plots (5 m in diameter) were established in three forest stands without aspen a few kilometers apart. Each stand had 3 litter plots (litter added) and 3 control plots, Pre‐treatment samples were compared with those collected alter litter addition.

The litter addition affected the carabid‐assemblage structure by increasing the catches of some species and decreasing the catch of one species. The number of carabid species was similar in control and litter plots. The litter effect was smaller than variation among forest stands and year‐lo‐year fluctuations. There was a strong temporal constancy among the plots: ‘rich’ plots remained ‘rich’ from year to year and similarly, ‘poor’ plots remained ‘poor’.

The significant influence of leaf litter on carabid abundance can be attributable to both abiotic factors (microenvironmental conditions, especially humidity and temperature), and biotic ones (changes in niche structure, improved food supply). Leal litter seems to have an effect on carabid distribution patterns, and deciduous trees scattered among conifers are likely to be of importance on carabid fauna in boreal forests.
Patterns of turtle species’geographic range size and a test of Rapoport's rule
Authors: Hecnar Stephen J.
Published: July 2006

There has been a recent resurgence of interest in documenting and explaining patterns of species' range sizes with the goal of determining if general patterns exist. Much recent debate has centered on whether Rapoport's rule, the tendency for range size to increase with increasing latitude, is a general rule or a local effect. I calculated the sizes of turtle species ranges from distribution maps and used published natural history data to examine how range size varies with latitude, and to determine if differences in range size exist among continents, and if correlations with body size, available land area, habitat and diet breadth exist. The distribution of turtle range sizes extended over six orders of magnitude and formed a lognormal distribution with many species having moderate or small ranges and few species having large ranges. Range size was positively correlated with available land area, habitat breadth, diet breadth, and body size. Multiple regression accounted for only 39% of the variance in range size indicating that other important factors remain unknown. At both global and continental scales, range size is largest near the equator and decreases with increasing latitude, the apposite of Rapoport's rule. However, range size did increase latitudinally above 25‐30°N in both the Neararctic and Palearctic suggesting that the pattern would be more accurately considered a local effect than a general rule. Larger range sizes at low latitudes may occur because more land area in the tropics provides much suitable habitat for ectotherms and there are few large scale physical barriers to dispersal. Rapoport patterns result from the occurrence of a small number of wide‐ranging cold tolerant species that have reinvaded northern latitudes after Pleistocene glaciation. Patterns of the longitudinal and latitudinal extents of species ranges and their positions illustrate the importance of climate, mountain ranges, deserts, and coastlines, as barriers potentially affecting range size.
The winter distribution of seed‐eating birds: habitat structure, seed density and seasonal depletion
Authors: Robinson Robert A. , Sutherland William J.
Published: July 2006

To understand the reasons for population change we need to understand the mechanisms through which it occurs. Throughout western Europe there have been declines in farmland birds. These declines have been paralleled by major changes in agricultural management. Which have resulted in major changes in habitat structure. This paper describes the habitat selection at two scales (within and between fields) of a number of seed‐eating farmland birds. Habitat preferences for most species were related to the density of seeds present. Which differed markedly between habitats. Seed density declined with distance from hedgerow in cultivated fields but not stubble fields. Yellow hammers were restricted to foraging close to hedgerows, whilst skylarks foraged in the centre of fields, but moved closer towards the edges as the winter progressed and seed densities declined. This work has clear consequences for agricultural management and the conservation of declining bird populations.
Comparative feeding, growth and movements of Atlantic salmon (Salmo salar) parr from riverine and estuarine environments
Authors: Cunjak R. A.
Published: July 2006

Abstract–The diet composition, movcments and growth of Atlantic salmon parr rearing in the estuary of Western Arm Brook, Newfoundland were compared with those of parr from riverine habitats over 2 years. Estuarine parr consumed a variety of prey, including many freshwater taxa (mainly insects), which indicated a dependence on freshwater drift from the river. Prey of estuarine origin (amphipods and sticklebacks) were increasingly consumed between spring and autumn. Prey volume per fish and number of prey per fish increased significantly for estuarine parr between spring and autumn, suggesting an improvement in food availability. Riverine parr, however, realized a general decrease in both parameters between spring and autumn. The recapture of 16% (n= 131) of the 829 parr marked in the estuary in 1987 and 1988 indicated a directed movement toward the head of the estuary and river mouth, as also suggested by the diet analysis. Parr from outer estuary sites were very mobile compared with parr from the estuary site closest to the river mouth, which behaved more like parr in the river proper in displaying strong site fidelity. Movement patterns of parr were primarily along the shoreline. Individual growth rates were highly variable in both environments but especially in the estuary. The mean growth of estuarine parr was 0.23 mm. d−1between May and October with some evidence of fastest growth having occurred in late spring and early summer (approx. 0.4 mm. d−1); mean growth rate of riverine parr was slower, at 0.12 mm. d−1. The results are discussed in the context that estuarine rearing by salmon parr represents an alternative life‐history tactic for the species in river systems in eastern Canada.
Physical habitat utilization of fish in a Sonoran Desert stream, Arizona, southwestern United States
Authors: Rinne J. N.
Published: July 2006

Abstract– The physical habitat utilization of 7 species of native fishes in a Sonoran Desert stream, Aravaipa Creek, Arizona is described. The species occupied significantly different depths and velocities of water. Longfin dace (Agosia chrysogaster), speckled dace (Rhinichthys osculus) and loach minnow (Tiaroga cobitis) used similar depths and velocities. Two of the three larger species (Sonora sucker [Catostomus insignis] and roundtail chub [Gila robusta]) used areas of greater depth and reduced velocity. Desert sucker (Catostomus clarki) grouped with loach minnow and speckled dace in the velocity of water occupied, but utilized deeper waters. The spikedace (Meda fulgida) aligned very closely with desert sucker in use of all 3 physical habitat variables.
The life‐history patterns of Barbus bocagei sclateri (Günther, 1868) in a tributary stream of the Guadalquivir River basin, southern Spain
Authors: Harrera M. , Fernández‐Delgado C.
Published: July 2006

Abstract– The age, growth and reproduction of Barbus bocagei sclateri (Günther, 1868) were studied from November 1987 to September 1989 in a tributary stream of the Guadalquivir River basin. The maximum ages observed were 8 + in males and 11 + in females. The seasonal growth began in April and lasted 4–6 months. The males matured during their third year of life (2 +) and females during their fifth/sixth year (4 +/5+). There was a significant difference in the overall sex ratio of 1. 3: 1 (961 males to 740 females). Reproductive activity started in April/May and lasted until June/July. The end of the reproduction period coincided with a fall in the percentage of oxygen saturation. During this reproductive period, females spawned 2 batches of eggs. The relationship between fecundity (Fec) and fork length (FL, mm) was: Fec= 7.54 × 10−4 FL3.06 The maximum contribution to the fecundity of the population was observed in the 6 + female group. The reproductive effort was also maximum in this age. Compared with the rest of the European barbel populations studied, the life‐history patterns of this stock are characterized by low annual growth, early maturity, reduced longevity and high fecundity.
Modular microcomputer software to estimate fish population parameters, production rates and associated variance
Authors: Kwak T. J.
Published: July 2006

Abstract– Microcomputer software to estimate fish population parameters, production rates, and associated variances was developed using established procedures. Pop/Pro Modular Statistical Software is a series of portable programs written in English that run on Macintosh(R) or IBM(R) (and compatible) computers. Population parameters can be estimated using either a single‐census mark‐recapture method or a removal method. Production and component parameters can be estimated with either the instantaneous growth rate method or the increment summation method. Output may be stratified by fish length, age or sampling interval and includes variance estimates for all parameters. The software was developed for use with fish data but may be applicable to other taxa.
Reproductive timing in three southern Appalachian stream fishes
Authors: DeHaven J. E. , Stouder D. J. , Ratajczak R. , Welch T. J. , Grossman G. D.
Published: July 2006

We quantified the reproductive biology of mottled sculpin (Cottus bairdi), rosyside dace (Clinostomus funduloides) and longnose dace (Rhinichthus cataractae) in Coweeta Creek, North Carolina, USA, a fifth order stream. These species are abundant in coldwater streams through out the southern Appalachian mountains, the southernmost limit of their range. We collected fishes from Coweeta Creek every second month (between July 1984 and January 1986) and quantified the seasonal reproductive cycles of females, using both histological techniques and the relative gonadal index (RGI). Both techniques indicated that I) C. bairdi reproduced between March and May, 2) CI. funduloides spawned between May and August and 3) R. cataractae were reproductively active between June and July. These conclusions were supported by the following: 1) the presence of reproductive coloration, 2) gravid females, 3) courtship displays, 4) the presence of nest‐guarding C. bairdi males and 5) the timing of young‐of‐the‐year recruitment. The reproductive characteristics of these 3 species were correlated with different environmental variables. The mean monthly RGI values for both C. bairdi and R. cataractae were inversely correlated with both maximum and minimum daily water temperatures. The mean RGI values for C. bairdi also were negatively correlated with photoperiod, whereas the values for R. cataractae and CI. funduloides were positively correlated with the change in daily photo period.
Movement of brook trout (Salvelinus fontinalis) in four small subalpine streams in northern Colorado
Authors: Riley S. C. , Fausch K. D. , Gowan C.
Published: July 2006

We studied the movement of brook trout (Salvelinus fontinalis) in four small streams in northern Colorado using mark‐recapture methods and weirs. The recapture rates of marked adult trout were low for all streams, and large numbers of unmarked adult trout, apparently immigrants, were found each year. Significantly more trout, immigrated into sections that were experimentally modified by installing low log dams, which increased depth, pool volume and the amount of overhead cover. The number of immigrant and resident trout was significantly related to the amount of cover in the sections. Resident trout were larger than immigrants in all streams in the last year of sampling. Most mobile brook trout moved upstream during summer on the two streams where weirs were operated, and upstream migrants were significantly larger than downstream migrants on both streams. We suggest that a high degree of movement may be an adaptive response by brook trout to the heterogeneous nature of small mountain streams.
Annual variations in the diet of juvenile chinook salmon (Oncorhynchus tshawytscha) in the Waitaki River and the demonstration channels, 1982–1986
Authors: Rutledge M. J. , Power G.
Published: July 2006

The numbers of particular prey in stomach samples of juvenile chinook salmon varied between sites, months and years in two controlled flow demonstration channel sites and the mainstem lower Waitaki River. During 4 growing seasons, 1982–1986, Deleatidium, Aoteapsyche, Hydroptilidae, Elmidae, Chironomidae and Amphipoda were important components of the diet. Salmon also ate a variety of other items of aquatic and terrestrial origin. Diets were quite similar and tended to change in the same way in all sites simultaneously, perhaps in response to discharge. Smaller prey (Chironomidae, Hydroptilidae and early instar Aoteapsyche) were more numerous in stomach samples in seasons of lower, more stable, discharge. Fewer but larger prey were consumed during high flows. The salmon sampled in March 1986 originated from the high egg deposition of 1985 and grew during a season of low discharge. They were exceptionally small and their diet consisted of large numbers of small prey. There was no evidence of progressive annual changes in the habitat or the diet of salmon in the demonstration channels. However, it would be prudent to arrange for flow fluctuations that would be sufficient to flush finer substrate sediments in a controlled flow residual river, thus maintaining the diversity of prey for juvenile salmon.
Within‐stock variations of life‐history traits in juvenile Atlantic salmon (Salmo salar)
Authors: Prévost E. , Chadwick E. M. P. , Claytor R. R.
Published: July 2006

Variations in space (geographical location) and time (year) of phenotypic traits linked to life‐history (size, growth, condition and sexual maturation) were analysed within the population of Atlantic salmon (Salmo salar L.) 1 + parr of Little Codroy River (southwest Newfoundland). The hydrographic system was divided into 10 zones: 4 for the mainstem and 6 for the tributaries. Despite the small size of the river studied, a highly significant spatial heterogeneity was observed. Within the mainstem, size, growth and rate of maturation of males tended to decrease when progressing upstream. When compared with the tributaries as a whole, the mainstem had smaller salmon juveniles, both at the end of the first winter (mainstem: 67.6 mm; tributaries: 73.3 mm) and at 1 + age (mainstem: 80.6 mm; tributaries: 88.3 mm), and the proportion of maturing fish among 1 + males was lower (mainstem: 48.6%; tributaries: 74.2%). According to the feature considered, from 20% to 70% of the spatial effect was due only to differences between the mainstem and the tributaries as a whole. A strong year effect was also revealed. Life‐history traits seemed to fluctuate over time independently from one tributary to another, whereas patterns in their yearly variations were basically consistent among zones in the mainstem. The potential role of genetic and environmental factors in explaining changes in space and time of biological characteristics of parr is discussed. Within a small system such as Little Codroy River, spatio‐temporal life‐history variations of Atlantic salmon juveniles were most likely driven by environment.
Growth and mortality of juvenile sunfishes (Lepomis sp.) under heavy predation
Authors: Belk M. C.
Published: July 2006

The relationship among growth, energy storage and mortality of juvenile bluegills (Lepomis macrochirus, Rafinesque) experiencing heavy predation was experimentally investigated in a large reservoir where piscivorous largemouth bass (Micropterus salmoides, Lacépède) were abundant. I conducted experiments evaluating interspecific competition, density‐dependent growth and lipid content and habitat‐specific growth and mortality rates of juvenile bluegills in this reservoir. Enclosure experiments showed that the growth rates of bluegills were unaffected by presence of other Lepomis species but decreased with increasing bluegill density. However, at densities corresponding to those found in the reservoir, the growth rates of bluegills were high, and competition appeared to be relatively unimportant. The percentage lipid content of bluegills was unaffected by the presence of other species, density of bluegills or habitat. The growth rates of bluegills in vegetated refuge areas were significantly higher and mortality rates were significantly lower compared with open water habitats. The low densities and high growth rates of juvenile bluegills in refuge environments suggests that there is a strong lethal effect of predators on this population of bluegills.
Distribution, growth and transformation timing of larval Geotria australis in New Zealand
Authors: Tedd P. R. , Kelso J. R. M.
Published: July 2006

Lamprey, Geotria australis, are widely distributed in New Zealand and are common in streams and rivers of the west coast of both islands, the southern tip of the North Island, the Banks Peninsula and the southern coast of the South Island. In fresh water, lamprey are found in association with all substrate types but are most commonly (> 50% of the sample sites) found in association with finer gravels. There is insufficient evidence to determine any change in historically abundant adult spawning migrations. Spawning, back calculated from larval growth rates, probably occurs late November‐December, and emergence at 9.63 mm occurs in January. We estimate that, on average, ammocoetes grow 0.068 mm/day throughout the year, and metamorphose and emigrate to sea between January‐May, 3.5 years after spawning at 101 mm (SD = 6.7).
Instream size segregation and density of Geotria australis ammocoetes in two New Zealand streams
Authors: Kelso J. R. M. , Todd P. R.
Published: July 2006

Geotria australis occurred almost to the upstream limit of detectable discharge in two New Zealand streams. The length, and consequently age, of larvae differed over the course of the stream and smallest animals ‐ presumed to be age 0 ‐ predominated upstream. Metamorphosing larvae (mean length 99.5 mm) typically occurred in downstream reaches, where flows were higher and substrate was coarser. We estimated that annual larval survival was 47% for age 0 to 1 and 77% for age 1 to 2. Differences in the relation between length and weight occurred both between years within a stream and between streams; thus, we assume growth is generally variable. The density of ammocoetes in New Zealand streams ranged from 0 to 104 m−2 and was significantly related to substrate type and depth in a multiple linear regression model. Because of the predictable nature of lamprey distribution and abundance, we believe it should be possible to estimate the absolute abundance of ammocoetes in a catchment with only a limited assessment of substrate properties.
A further assessment of trophic and spatial inter‐relations of galaxiids and salmonids in New Zealand
Authors: Glova G. J. , Sagar P. M.
Published: July 2006

The trophic and spatial inter‐relations between 2 small native fish (Galaxias vulgaris Stokell and G. paucispondylus Stokell, Galaxiidae) and juveniles of 2 introduced fish (Oncorhynchus tshawytscha Walbaum and Salmo trutta L., Salmonidae) were investigated in a New Zealand stream. Interspecific overlap in timing of feeding among these four fish species was greatest between pre‐dusk and pre‐dawn (1730‐0530). Aquatic invertebrates were consumed exclusively by all fish species except O. tshawytscha, which also preyed on Trichoptera imagos, particularly at night. Dietary similarities were least between galaxiids, moderate between galaxiids and salmonids, and greatest between salmonid species. Both galaxiid species were found primarily in riffles, with G. vulgaris occupying slightly deeper (≤0.3 m) and slower (0.5–0.8 m. s−1) waters than did G. paucispondylus (≤0.2 m deep and 0.7‐1.0 m. s−1 water velocity); salmonids were mostly in pools and runs, with O. tshawytscha occupying slightly slower (0.1‐0.2 m. s−1) and deeper (≤0.5 m) waters than those occupied by S. trutta (0.2–0.5 m. s−1 water velocity and ≤0.4 m deep). The interspecific differences in feeding and microdistribution presumably reduce interaction between sympatric populations of galaxiids and salmonids.
Winter movements of burbot (Lota lota) during an extreme drawdown in Bull Lake, Wyoming, USA
Authors: Bergersen E. P. , Cook M. F. , Baldes R. J.
Published: July 2006

Winter movements of burbot (Lota lota) were monitored in Bull Lake, Wyoming during a record low water storage period in the winter of 1985–1986. Burbot with surgically implanted ultrasonic transmitters were commonly sedentary during the drawdown. The fish that did move were most active during dusk and at night in winter and during the day in spring. Burbot did not appear to occupy well defined home ranges or show discernible movement patterns. Movement into shallow water during winter was attributed to colder water temperatures and the onset of the spawning season. Burbot were always found associated with silt substrates during the drawdown. Aerial photographs of the exposed bottom revealed that virtually all suitable spawning and nursery habitat for burbot was eliminated by the 13.4‐m drawdown.
Digestion of larval American shad by cyprinids
Authors: Rottiers D. V. , Johnson J. H.
Published: July 2006

Cyprinids have pharyngeal teeth for grinding food before swallowing and a continuous gut with no discrete stomach. This digestive tract structure, as well as the feeding behavior traits shown by cyprinids, makes it difficult to identify and measure the amount of food consumed by these fishes. The relations among quantity of food in cyprinid gut, time after feeding and predator size were described by log‐linear multiple regression. The number of intact American shad (Alosa sapidissima (Wilson)) larvae eaten in laboratory experiments was estimated by extrapolating the regression for the amount of food in the gut over time for predators of various size. The numbers of larval American shad in guts of fish captured in the Juniata River, Pennsylvania, were not significantly different from those estimated with the equations derived from laboratory data. In view of their abundance in rivers and their potential digestion rate for larval fish, cyprinids can be expected to have a marked influence on reducing the numbers of larval American shad.
Timing of spawning in cultured and wild Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in the River Vosso, Norway
Authors: Lura H. , Sægrov H.
Published: July 2006

Spawning time and size of wild and nonnative cultured female Atlantic salmon (Salmo salar L.) were studied in the River Vosso, Norway. Cultured immigrants were smaller, and peak spawning occurred 21 and 26 days earlier relative to wild salmon in 1991 and 1992, respectively. It was calculated that hatching and initial feeding of offspring of cultured females peaked 12 and 9 days earlier in spring 1992 and 19 and 8 days earlier in spring 1993 relative to offspring of wild females. Spawning time of the cultured salmon is similar to most Norwegian salmon populations and to cultured fish in other streams. In the River Vosso it also overlaps with that of brown trout (Salmo trutta L.), which may increase hybridization. The early time of breeding in nonnative fish indicates local adaptation in this trait in wild salmon. The consequences of early breeding of cultured fish are unpredictable in relation to spring temperatures but probably reduce their relative breeding success. The smaller size may also reduce the success of cultured females.
Reproductive life history of the North American madtom catfish,Noturus hildebrandi(Bailey & Taylor 1950), with a review of data for the genus
Authors: Bakar J. A. , Heins D. C.
Published: July 2006

Abstract–The female reproductive traits of a small, North American catfish were studied over a two‐year period in a population at the southern extreme of the species’range. The reproductive season was long forNoturus, possibly from February to September. Females matured at age 1 and probably reproduced in only a single year. Clutch sizes were 16–68 oocytes in females 33–47 mm SL, and only one lifetime clutch may be produced. Clutch size, dry mass and volume were related to female size, but ripening oocyte size was not. Clutch mass averaged 23% of total body mass just prior to spawning. Compared to a northern population, females had greater SL‐adjusted body masses, clutch sizes and clutch volumes but smaller oocytes. Oocyte size accounted for 73% of the difference in clutch sizes and clutch volume 14%. Concerns about the comparability of present data forNoturusare expressed. The need to include many life‐history traits, from several populations of each species, using standardized methods in analysis of functional responses is discussed.
The effect of depth on the interaction between perch (Perca fluviatilis) and minnow (Phoxinus phoxinus)
Authors: Eklöv A. G. , Greenberg L. A. , Kristiansen H.
Published: July 2006

We tested the hypothesis that small fishes avoid piscivores by increasing their use of shallow water areas, thereby reducing the capture success of the piscivore. Experiments were conducted in 600‐1 aquaria, using perch (Perca fluviatilis) as the piscivore and minnow (Phoxinus phoxinus) as the prey. Two size classes of minnows, presented alone and together, were placed together with perch in aquaria with and without shallow water areas. The capture success of perch and use of depth by minnows changed as predicted by our hypothesis. In addition, we observed a decrease in the shoal size of minnows when perch were present. Perch selected large minnows over small minnows when both size classes were present, probably because large minnows were a more energetically profitable prey size.
The cost of early maturation on growth, body condition and somatic lipid content in a lake pumpkinseed (Lepomis gibbosus) population
Authors: Justus J. A. , Fox M. G.
Published: July 2006

We investigated the implications of early maturation in a central Ontario population of pumpkinseed (Lepomis gibbosus) by comparing the growth trajectory, body condition, lipid to body weight ratio and past growth history of mature and immature females through the 1992 growing season. Pumpkinseeds were sampled from Beloporine Lake from May 28 to July 24 and on November 20, just prior to freeze‐up of the lake. Prior growth history and length at age were determined by backcalculation from scale annuli. Nearly all females age 3 and older had matured in 1992, so we focused on age 2 females (22% mature). Females that matured at age 2 were significantly larger at the end of their first year of life than those that did not mature at age 2, although there was no significant difference between groups in the prior year's growth rate. The mature age 2 females were significantly larger than immatures, at the beginning and end of their third growing season, but not during the June 2 ‐ July 19 breeding season. The condition factor of mature females was higher than that of immature females on all but one collection date. However, the mean somatic lipid‐to‐body weight ratio was higher in immature females on all sample dates and significantly higher over the grwing season. We conclude that the costs of early maturation include lack of length and weight gain during the breeding season, and loss of stored lipid. The latter may be associated with increased overwinter mortality.
Comparison of population dynamics of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in a small tributary of the River Scorff (Brittany, France)
Authors: Baglinière J.‐L. , Prévost E. , Malsse G.
Published: July 2006

The population dynamics of Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) were compared in a small tributary of the River Scorff (Brittany, France) from spawning time to the beginning of the third growing season. The spawning and fry emergence of the two species took place at approximately the same time. In the first autumn, the densityof 0+ juveniles and settling rate from the egg stage were much higher in trout than in salmon. The emigration rate from 0+ population was much higher in trout than in salmon. The size of resident and migrating fish was always smaller in salmon than in trout, whatever the age. The low level of salmon production in the brook, compared with trout, was the result of low survival from egg to 0+ stage in autumn, combined with the small proportion of juveniles migrating after the first growing season. This was not compensated by a high number of migrants the next year. The role of physical habitat, inter‐and intraspecific competition, predation and migration dependence on size and early sexual maturity is discussed. Indications are that small tributaries of the type studied are of great value for recruitment in trout but not very productive for juvenile salmon.
The influence of physical watercourse parameters on the degree of anadromy in different lake populations of Arctic charr (Salvelinus alpinus(L.)) in northern Norway
Authors: Kristoffersen K.
Published: July 2006

The influence of physical watercourse parameters on the degree of anadromy was studied in 15 lake populations of Arctic charr (Salvelinus alpinus(L.)) in northern Norway. The anadromy of the different populations was scored based on the following criteria; marine parasites. fish length and length at maturity. There were significant negative correlations between the anadromy scores and both the length of the outlet rivers of the different lakes and a migration barrier index for the different watercourses (combining migration distance and water velocity). It is hypothsized that these correlations were due to differences in energy expenditure for charr during upstream migration and/or differences in predation pressure on charr during river migration. Short rivers with relatively high water velocity seem to be the most preferable conditions for the anadromous life‐history strategy. There were no correlations between the degree of anadromy and mean river slope or minimum summer water discharge.
Behavioral interactions between black mudfish (Neochanna diversus Stokell, 1949: Galaxiidae) and mosquitofish (Gambusia affinis Baird & Girard, 1854)a
Authors: Barrier R. F. G. , Hicks B. J.
Published: July 2006

The behavior of black mudfish (Neochanna diversus Stokell, 1949: Galaxiidae) and mosquitofish (Gambusia affinis Baird & Girard, 1854: Poeciliidae) was investigated in laboratory tanks. Black mudfish are indigenous to northern New Zealand, and mosquitofish are introduced; both species are sympatric in wetlands in the Waikato region. By comparing position, feeding rates and aggressive behavior of both species, we found that black mudfish were increasingly able to compete with mosquitofish as they grew from fry to adults. Mosquitofish were more aggressive towards mudfish fry and juveniles than were these two life stages towards mosquitofish, but adult mudfish were aggressive towards mosquitofish. Both small (18–24 mm total length (TL)) and large mosquitofish (25–36 mm TL) showed high aggression towards mudfish fry (13–18 mm TL), and fry were eaten by large mosquitofish. However, 3 interspecific differences appear to allow coexistence of these two species. Firstly, mudfish reproduce in winter, whereas mosquitofish reproduce in summer, resulting in mudfish fry being present when mosquitofish are at their lowest abundance. Secondly, mudfish can survive in seasonally dry habitats by aestivation, while mosquitofish cannot. Thirdly, adult black mudfish are nocturnal, whereas mosquitofish are primarily diurnal.
Growth patterns of the otoliths of Stellifer rastrifer (Pisces: Sciaenidae) from the Sergipe River estuary (Sergipe, Brazil)
Authors: Morales‐Nin B.
Published: July 2006

Stellifer rastrifer (Sciaenidae) from the Sergipe River (Brazil) sagittal otoliths show a microstructure that is common to many fish, with microincrements of growth made up of continuous and discontinuous units. The microincrements show thickness and structure variations, which apparently correspond with the rings seen at the macrostructural level.
Brook trout (Salvelinus fontinalis) population dynamics and mottled sculpin (Cottus bairdi) occurrence in relation to acidic episodes in streams
Authors: Carline R. F. , Gagen C. J. , Sharpe W. E.
Published: July 2006

We monitored water chemistry and populations of brook trout (Salvelinus fontinalis) and mottled sculpins (Cottus bairdi) in 5 streams and some tributaries to determine how the severity of acidic episodes (low pH and high Al) influenced density and distribution of these species. Among streams, Linn Run had the lowest pH (4.8) and highest concentrations of total dissolved Al (>400 μg‐l−1) during periods of high discharge. Densities of brook trout and mottled sculpins were low in Linn Run, but high in tributaries, where pH (6.5) and Al (30 μg‐l−1) remained well below lethal levels. Among the other streams, brook trout density was highest where the acidic episodes were least severe and the density of age‐0 brook trout was lowest when precipitation during the early months of the year was above normal. Immigration of brook trout from downstream areas maintained populations in the stream segments subjected to severe episodes. Mottled sculpins were not found in streams with severe episodes.
Observations on a foraging association between two freshwater stream fishes
Authors: Baker J. A. , Foster S. A.
Published: July 2006

On 3 occasions during summer 1977, small groups of a typically run‐ and pool‐dwelling minnow (blacktail shiner,Cyprinella venusta) were observed feeding in a shallow riffle on items dislodged by foraging northern hog suckers (Hypentelium nigricans). Although such nuclear‐attendant following behavior has been documented in marine systems and has been reported from some African freshwater lakes, descriptions from freshwater streams are rare. We describe the interaction and consider the probable development of the search behaviour of the blacktail shiners. We also explore the possible benefits of searching for hog suckers in small groups, as observed, rather than as individuals or in large groups. This feeding strategy may be an important mechanism of food acquisition for some individuals when usual resources are scarce.
Dispersal and growth rate of O‐group salmon (Salmo salar L.) from point‐stocking together with some information from scatter‐stocking
Authors: Crisp D. T.
Published: July 2006

Abstract– Experiments on the dispersal of O‐group salmon from a ‘point‐stocking’ were made in 1988, 1989, 1990 and 1991 in Bollihope Burn, Co. Durham. Experiments on ‘scatter‐stocking’ were made in 1992 and 1993, but the 1992 experiment was aborted for technical reasons. In each year the fish were stocked as fry in spring and their distribution in September was ascertained by electrofishing. Some fish from point‐stocking dispersed up to 50 m upstream or 500 m downstream of the stocking point, but the majority remained close to the stocking point. This gave rise to considerable spatial variation in September population density and fish weight, which could be modelled by semi‐logarithmic curves. Survival from point‐stocking was 19% and 14% in 1988 and 1989, respectively. Approximately 20 to 25% of the September survivors from point‐stocking were found upstream of the release point. Scatter‐stocking gave relatively little variation in population density or fish weight in September, and estimated survival was 27%.
Perceptual constraints on stream fish habitat selection: effects of food availability and water velocity
Authors: Tyler J. A. , Clapp D. P.
Published: July 2006

Abstract–Habitat selection theory assumes that individuals either know the quality of habitatsa priorior can learn it through experience. This work tests the effects of total food supply and of water velocity on the ability of drift‐feeding stream fish (Rhinicthys atratulus) to discriminate between two patches in a laboratory flow‐tank that differ only in the amount of food in the patch. If the fish can discriminate between the patches, their distributions should be predicted by ideal free distribution models; otherwise, their distributions should be random. The results show that at high total food supply levels, fish distributions differ from random in general agreement with ideal free distribution models; total food supply decreases, fish distributions become random, indicating that total food supply levels affect the ability of fish to discriminate between habitats that differ only in food supply. Increased water velocity was expected to affect fish distributions similarly, but its effect was not significant. The results suggest that habitat selection theory should consider both differences between habitats and the ability of fish to perceive those differences.