Sublittoral abundance and food consumption of Baltic gobies

Two small demersal fishes, the sand goby Pomatoschistus minutus and the common goby Pomatoschistus microps , were quantified on soft bottoms at 20–40 m depth in the Baltic Sea, using a camera placed above the bottom. The largest numbers of gobies were seen following the settlement of young in late summer and autumn. Most recorded fishes were sand gobies. An annual average of 4·7 individuals m⁻²(0·24 g dry mass m⁻²) was recorded in 1983–1985 and 2·5 individuals m⁻²(0·13 g m⁻²) in 1997–1998. Using these densities, the annual goby food consumption was estimated to 100 kJ m⁻² in 1983–1985 and 50 kJ m⁻² in 1997–1998, corresponding to most of the annual macrobenthos production available to the gobies. The resulting goby production, assumed equal to 25% of the food consumed, must have been an important food source for the larger fishes occasionally recorded in the photographs.     

A strong species-area relationship for eukaryotic soil microbes: island size matters for ectomycorrhizal fungi

While the effects of habitat size and isolation have been successfully studied for macro-organisms, there is currently debate about their relative importance in explaining patterns of microbial species richness. In this study, we examine the species richness of a dominant group of eukaryotic soil microbes, ectomycorrhizal fungi, on 'tree islands' of constant age and host composition that range in size from < 10 to > 10 000 m². Our results show that ectomycorrhizal species richness is significantly reduced on smaller and more isolated tree islands, and the species–area slope that we observe (0.20–0.23) is similar to average slopes reported for macro-organisms. Additionally, species' occurrence patterns across tree islands and investment trends in fungal fruit bodies suggest that a trade-off between competition and dispersal could play an important role in structuring ectomycorrhizal assemblages.     

Tree population dynamics in Kibale National Park, Uganda 1975–1998

Changes in species composition, stem abundance, and basal area of trees taller than or equal to 10 m in a medium altitude tropical rain forest at the Ngogo study area, Kibale National Park, Uganda are described for the period between 1975 and 1998 ( n  = 23 years). Two enumeration episodes were conducted in 263 plots of 5 m by 50 m during 1975–80 and 1997–98. During this period, species richness decreased by 3% (from 92 to 89). Species diversity (H') also declined slightly from 2.97 to 2.86. The number of trees recorded in the sample plots decreased by 8% (from 2545 to 2329), while basal area decreased from 49.48 m² ha⁻¹ to 48.68 m² ha^−1. However, stem abundance and basal area increased for some species.     

Is Atlantic salmon production limited by number of territories?

Thirty Atlantic salmon Salmo salar parr (mean 135 mm total length, L _T) in the River Alta, Norway, were radio‐tagged and tracked during a 11–13 day period. The parr stayed within defined home ranges with a 95% probability of localization within an average area of 1286 m²(241–3484 m²). On average, each parr had overlapping home ranges with 7·7 other parr, and the overlap between pairs of fish covered on average 24% of their home range areas. Mean length of the river stretch used was 90 m (22–383 m). On average, during 38%(16–77%) of the tracking surveys, the fish had moved >10 m since the previous survey. Mean total distance moved during the whole study was 402 m (208–862 m). The Atlantic salmon were most often recorded in riffles, but 27% of the parr alternated between riffles and pools. The extensive movements, flexible habitat utilization and relatively large home ranges, together with the fact that all the parr had home ranges partly overlapping with other radio‐tagged parr, indicate a flexible and variable behaviour and, thereby, a more complex social structure than a rigid defence of a fixed territory. Thus, Atlantic salmon production seems not to be limited by the highest potential number of territories for large parr in a given area.     

Biogeography of vascular plants on habitat islands, peninsulas and mainlands in an eascentral Swedish agricultural landscape

The increase of island species richness with area can be explained by an increase in habitat diversity or by an equilibrium of species immigration and extinction. We examined vascular plant species richness in 39 sites (24 habitat islands, 7 'habitat peninsulas' and 8 comparable 'mainland' sites). We sampled at three scales: whole sites, meadows within sites and quadrats (4 m × 4 m) within meadows. All sites (10–10⁴ m²) contained natural vegetation within arable fields in eascentral Sweden. There was a strong correlation between species richness and area for whole sites and for meadows There was no correlation, however, between species richness in quadrats and site area. The difference between site and meadow results on one side and quadrat results on the other suggests that species richness increases with whole site area primarily because large sites are more diverse than smaller ones. Speciearea relationships did not differ between islands, peninsula and mainland sites. Thus, patterns of species richness on our sites were more consistent with habitat diversity than an immigratioextinction equilibrium.     

Species richness and endemism of plant and bird communities along two gradients of elevation, humidity and land use in the Bolivian Andes

Abstract.  We studied the patterns of species richness and range–size rarity (as a measure of endemism) of two plant groups (Pteridophyta, Bromeliaceae) and birds along two gradients of elevation, humidity and human land use in a forested Andean valley. Both transects covered the transition from an arid valley bottom through a cloud forest zone to relictual high-elevation Polylepis forest, but transects differed in overall precipitation. Plants were surveyed in 88 plots of 400 m² each, while birds were detected primarily through visual observations and tape recordings over areas of 0.3–1.5 km². Global range sizes of all species were mapped on 1°-grids and range-size rarity was calculated as the mean inverse range size of all species recorded in elevational steps of 200 m. Patterns of species richness and range–size rarity were mainly unrelated between and within study groups. Monotonic increases and decreases and hump-shaped patterns were observed for species richness as well as range–size rarity. Several of these patterns can be interpreted in the light of the ecological requirements of each taxonomic group, e.g. dependence of fern species richness on humidity or of bird richness on habitat complexity. Species richness of ferns and birds peaked at higher elevations along the less rainy transect, possibly as a result of higher levels of solar radiation and ecosystem productivity. Patterns of species richness and endemism of the study groups are causally unrelated and cannot be used to predict those of other groups at the spatial scale of this study. Human impact was highest in areas of mostly low to intermediate species richness, but was often high in zones of high endemism.     

Seagrass patch size affects fish responses to edges

1.  Patch area and proximity of patch edge can influence ecological processes across patchy landscapes and may interact with each other. Different patch sizes have different amounts of core habitat, potentially affecting animal abundances at the edge and middle of patches. In this study, we tested if edge effects varied with patch size.
2.  Fish were sampled in 10 various-sized seagrass patches (114–5934 m²) using a small (0·5 m²) push net in three positions within each patch: the seagrass edge, 2 m into a patch and in the middle of a patch.
3.  The two most common species showed an interaction between patch size and the edge–interior difference in abundance. In the smallest patches, pipefish ( Stigmatopora nigra ) were at similar densities at the edge and interior, but with increasing patch size, the density at the edge habitat increased. For gobies ( Nesogobius maccullochi ), the pattern was exactly the opposite.
4.  This is the first example from a marine system of how patch size can influence the magnitude and pattern of edge effects.
5.  Both patch area and edge effects need to be considered in the development of conservation and management strategies for seagrass habitats.     

Seasonal changes in the habitat use and movements of adult European grayling in a large subarctic river

In late summer (13 August–13 September 1998), at water temperatures of 12·0–15·7° C, grayling ( n =14) stayed mainly in the riffle-section where they were captured in a large regulated river in northern Finland, moving little between consecutive days. In autumn (2–30 October 1998), at 1·7–6·7° C, the fish ( n =16) migrated to potential overwintering sites 0–14 km up- or downstream by mid October, moving mainly short distances thereafter. The daily movement rates, and the total ranges covered by the fish in late summer and autumn were 54±32 m (mean± s.d ) and 1053±1636 m, and 190±168 m and 3135±1850 m, respectively. In autumn the fish used deeper habitats (most suitable range 150–400 cm) with lower current velocities (20–80 cm s⁻¹) and finer bottom substrata (mainly sand) than in late summer (depth 100–325 cm, velocity 30–110 cm s⁻¹, and cobble-boulder substrata).     

Spatial and temporal patterns of abundance of coral reef gobies (Teleostei: Gobiidae)

This study investigated the spatial and temporal patterns of abundance of four substratum-associated species of Gobiidae on a heterogeneous reef flat comprised of four distinct habitat zones, and examined microhabitat use within each zone. Asterropteryx semipunctatus had the widest distribution and was the most abundant species in each habitat zone, followed by Amblygobius bynoensis , Valenciennea muralis and Amblygobius phalaena . Significant temporal and spatial differences in mean density were evident. The highest density of A. semipunctatus (312 individuals 10 m^–2) was recorded in a habitat zone dominated by algal-covered rubble, whereas A. bynoensis and V. muralis were most abundant (mean summer density 5·5–5·8 individuals 10 m^–2) in habitats containing both sand and hard substrata. In contrast, A. phalaena was uncommon (mean density ≤ 0·4 individuals 10 m^–2) in all four habitat zones. Significant seasonal differences in abundance were due to the large influx of recruits in summer. Ontogenetic shifts in habitat use were not evident at either the macrohabitat ( i.e. among habitat zones) or microhabitat scale ( i.e. substratum use within zones). At the microhabitat scale, V. muralis consistently exhibited a strong positive association with sand and was rarely associated with hard substrata. In contrast, the two Amblygobius species were commonly associated with both sand and hard substrata, but patterns of microhabitat use differed among habitat zones. Substratum composition at the microhabitat scale may influence spatial patterns of abundance at larger spatial scales by providing essential resources and, or influencing carrying capacity and predation risk.     

Swimming activity of seabass: comparing patterns obtained in natural environment and in re-circulating tanks under high density

Seabass ( Dicentrarchus labrax ) swimming activity was compared between natural environments and aquaculture facilities. Behaviour under natural conditions was assessed in a saltmarsh pond (250 m², 18 × 14 × 0·8 m) using acoustic telemetry. From several surveys, we documented the diel activity rhythm and demonstrated group effects on swimming patterns and amplitudes by comparing activity of solitary fish with that of a fish living in a group of 60. Consequences of weather variability were also analysed and revealed a high sensitivity of fish to atmospheric conditions for both swimming and demand‐feeding behaviour. Behaviour in fish tanks was also studied using acoustic telemetry, as part of the EUREKA EU1 960 'Aqua‐Maki 2' project investigating aspects of fish culture in re-circulating tanks under high density. A re-circulating hexagonal tank (5·4 × 5·4 m, 1·8 m depth, 48 m³) was equipped with positioning and demand‐feeding systems, oxygen and temperature probes. Initial density was 50 kg m³ in March and rose to 90 kg m³ at the end of the experiment in May. During this period, the movements of nine fish were continuously recorded for 24 h each, reaching a total of six 24 h episode at eight days interval. Swimming activity was analysed in terms of activity rhythms and space occupation specially around feeding events. The two data set and main results will be presented and compared to assess seabass behavioural plasticity and sensitivity to husbandry conditions.     

Community structure of an assemblage of tidepool fishes on a tropical eastern Pacific rocky shore, Colombia

The composition, abundance, species richness and diversity of a rocky intertidal fish assemblage in the central zone of the Pacific coast of Colombia were determined. From July to December 2002, 10 tidepools with volumes ranging from 0·087 to 1·350 m³ were surveyed. A total of 893 fishes belonging to 14 species and 12 families were found. The most abundant species were Bathygobius ramosus and Abudefduf concolor , representing 71% of all fishes collected. Bathy gobius ramosus , Malacoctenus zonifer and Gobiesox adustus were residents, Abudefduf concolor , Abudefduf troschelii , Microsphatodon bairdii , Chaenomugil proboscideus , Halichoeres aestuaricola and Echidna nocturna were transients, and Apogon dovii , Sargocentron suborbitalis , Cerdale sp, Rypticus nigripinnis and Ctenochaetus marginatus were considered as accidental visitors. The temporal and spatial variation of assemblage structure was tested. The fish assemblage structure did not differ between months and there was not a clear relationship between tidepool surface area and depth, and community variables. Diversity and species richness were negatively correlated with tidepool height. It is suggested that the tidepool assemblage was stable and resilient in time on short (annual) scales. The constancy in time and space could have been a consequence of eurytopic features of the organisms and the lack of drastic seasonal changes in the tropics.     

Habitat use by a Midwestern U.S.A. riverine fish assemblage: effects of season, water temperature and river discharge

The hypothesis that temperate stream fishes alter habitat use in response to changing water temperature and stream discharge was evaluated over a 1 year period in the Neosho River, Kansas, U.S.A. at two spatial scales. Winter patterns differed from those of all other seasons, with shallower water used less frequently, and low‐flow habitat more frequently, than at other times. Non‐random habitat use was more frequent at the point scale (4·5 m²) than at the larger reach scale (20–40 m), although patterns at both scales were similar. Relative to available habitats, assemblages used shallower, swifter‐flowing water as temperature increased, and shallower, slower‐flowing water as river discharge increased. River discharge had a stronger effect on assemblage habitat use than water temperature. Proportion of juveniles in the assemblage did not have a significant effect. This study suggests that many riverine fishes shift habitats in response to changing environmental conditions, and supports, at the assemblage level, the paradigm of lotic fishes switching from shallower, high‐velocity habitats in summer to deeper, low‐velocity habitats in winter, and of using shallower, low‐velocity habitats during periods of high discharge. Results also indicate that different species within temperate river fish assemblages show similar habitat use patterns at multiple scales in response to environmental gradients, but that non‐random use of available habitats is more frequent at small scales.     

River flow and fish abundance in a South African estuary

The ichthyofauna of the Thukela Estuary, a small (55 ha), shallow (<1·5 m) system on the KwaZulu-Natal coast (mean annual river runoff of 3865 × 10⁶ m³, from a large catchment of 29 000 km², is seasonal: peak inputs occurring between November and March), was dominated by the juveniles of marine taxa that used the estuary as a nursery area. A striking feature of the above community was the decline in fish abundance with increasing river input, with flow values >100 m³ s⁻¹ leading to increased loss of species from the system. This decline was linked to the lack of saline intrusion into the estuary and increased freshwater flooding through the system.     

Hydroacoustic measurement of swimming speed of North Sea saithe in the field

Saithe Pollachius virens , tracked diurnally with a split-beam echosounder, showed no relationship between size and swimming speed. The average and the median swimming speeds were 1·05 m s⁻¹(±0·09 m s⁻¹) and 0·93 m s⁻¹, respectively. However, ping-to-ping speeds up to 3·34 m s⁻¹ were measured for 25–29 cm fish, whose swimming speeds were significantly higher at night (1·08 m s⁻¹) than during the day (0·72 m s⁻¹). The high average swimming speed could be related to the foraging or streaming part of the population and not to potential weakness of the methodology. However, the uncertainty of target location increased with depth and resulted in calculated average swimming speeds of 0·15 m s⁻¹ even for a stationary target. With increasing swimming speed the average error decreased to 0 m s⁻¹ for speeds >0·34 m s⁻¹. Species identity was verified by trawling in a pelagic layer and on the bottom.     

Effect of increased flow on the behaviour of Atlantic salmon parr in winter

The effect of increased flow on movement and microhabitat use of Atlantic salmon Salmo salar parr in winter was investigated using radiotelemetry. To simulate hydropeaking operations, flow was increased four‐fold from 1·3 m³ s⁻¹ to 5·2 m³ s⁻¹ for 24 h periods. Flow did not affect fish habitat use or displacement and had little effect on fish activity within diel periods. During high flow periods in late winter, fish reduced night‐time activity. Stranding rates during flow reduction were also very low (only one fish).     

Movement patterns of Cephalopholis cruentata in a marine reserve in St Lucia, W.I., obtained from ultrasonic telemetry

Home range size and shape, and within home range movement patterns were determined from 10 adult graysby Cephalopholis cruentata implanted with acoustic transmitters on two reefs within the Soufriere Marine Management Area, St Lucia. The mean home range area was 2120 m²(range 1200 to 4000 m²) and non‐circular in shape. All fish demonstrated a clear preference for a specific area in their home range where, on average, 72·9% of an individuals position were located. Time spent in this favoured area was correlated with reef complexity. Fish with greater activity and displacement possessed a larger home range. Activity and displacement were higher by night than by day, and consistent with this, fish spent less time in the preferred area of their home range by night than by day. Tagged individuals demonstrated a strong tendency to avoid sand habitat present at reserve boundaries.     

Distribution and density of populations of goldsinny wrasse (Ctenolabrus rupestris) on the west coast of Scotland

A field survey of populations of goldsinny wrasse ( Ctenolabms rupestris ) was undertaken on selected areas of rocky coast of west Scotland. Observations by sub-aqua diving were used to determine distribution, habitat preference, and population density, and their seasonal variations. Availability of the preferred refuge type (crevices on rock faces, or between boulders, where two or more entrances exist) was essential in determining goldsinny presence. Goldsinny were not always present in areas or at depths where the influences of freshwater runoff (low temperatures and salinities) were likely, even if the preferred habitat type was available. In areas remote from these influences, and where there were suitable refuges, depth of water (0–44 m), macroalgal cover and high current speeds (2.1–3.6 ms⁻¹) did not affect goldsinny distribution. Observed densities of goldsinny reached a peak in summer months with a maximum of 4.0 m⁻² in areas of shallow boulder scree, but only 1.0 m⁻² in shallow areas with little scree, or at deeper study sites. Numbers of goldsinny observed actively swimming decreased after October, with a rapid disappearance in November. A gradual reappearance was recorded in late April, and early May. Changes in activity may be influenced by both water temperature and photoperiod. Young-of-the-year goldsinny were first observed in August in shallow water (0–8 m) areas typified by rock/boulder scree and/or high macroalgal cover. Where adults also inhabited these nursery areas, 0+ fish could make up over 50% of the total population. After their first winter, juvenile goldsinny may migrate away from inshore sites.     

Depth distribution and biological characteristics of the European eel Anguilla anguilla in Lough Ennell, Ireland

Using a longline survey, a total of 196 European eels Anguilla anguilla were collected at different depths in Lough Ennell (maximum depth 30 m), central Ireland. The catch per unit of effort of A. anguilla that were caught from 1 to 25 m depths was lowest at 0·5–5·0 m and greatest at the deepest depth range (22·5–25·0 m). Sub-samples of A. anguilla from depths of <15 m showed little or no difference in size, sex ratio, age, growth rate, condition factor, length–mass relationship, gonado-somatic index, fin index or eye index with fish from depths of >15 m. All fish examined were female yellow-phase A. anguilla that had ages from 7 to 20 years (mean ± s . d . = 10·3 ± 2·9 years), with growth rates from 24·0–60·8 mm year⁻¹ (mean ± s . d . = 40·7 ± 8·5 mm year⁻¹). Variations in the growth rates were greater in the shallow group than that of the deep group. This study suggested that deeper regions are important feeding habitats for A. anguilla and that fish in this lake were growing moderately fast compared to similar habitats and areas in the species' range.     

Elevational parallels of latitudinal variation in the proportion of lianas in woody floras

Aim  To determine if elevational variation in the proportion of lianas in woody floras parallels the variation observed on latitudinal gradients. This is to be expected if the poleward decrease in the importance of lianas is related to the vulnerability of their wide vessels to freeze embolism.
Location  Coastal ranges of south-central Chile (latitude 37°–40° S) and western South Island of New Zealand (41°–43° S).
Methods  The presence of all woody species was recorded in plots of 2500 m² (Chile) or 100–400 m² (New Zealand) on four elevational gradients in temperate rain forest. Each species was classified as a tree, shrub or liana. Original data were obtained from 22 plots at two sites in Chile. In New Zealand, two surveys comprising a total of 296 plots were extracted from the National Vegetation Survey data base.
Results  Liana species richness declined more or less monotonically on all four gradients, whereas richness of trees and shrubs showed more varied elevational patterns. The proportion of woody species contributed by the liana life-form was negatively correlated with elevation on all four gradients, falling from 15 to 35% of the woody flora at c . 200 m a.s.l. to nil well below the tree line. The elevational and latitudinal limits of liana species were marginally significantly correlated in Chile, but not in New Zealand.
Main conclusions  The elevational parallel of the well-documented decline in liana representation with increasing latitude is consistent with the hypothesis that cold intolerance is a strong control on the global distribution of the liana life-form.     

Reproductive migration of brown trout in a small Norwegian river studied by telemetry

The movement of 34 large (39–73 cm standard length) brown trout Salmo trutta was monitored using radio telemetry for up to 74 days in Brumunda, a small Norwegian river (mean annual discharge 3·3 m³ s⁻¹) flowing into the large Lake Mjøsa. The maximum range of movement in the river was 20 km. No clear relationships existed between individual movement and water discharge, temperature and barometric pressure. Brown trout migrated at all levels of water discharge. At low discharge (<2 m³ s⁻¹) movements were nocturnal. A weir 5·3 km from the outlet restricted ascending brown trout at low ( c . 6° C), but not at high ( c . 8° C) water temperatures. Spawning occurred in September to October and tagged individuals spent 2–51 days at the spawning sites. Mean migration speed from tagging to when the fish reached the spawning area, and from when they left the spawning areas and reached the lake was 1·0 and 2·3 km day⁻¹, respectively. All tagged brown trout that survived spawning returned to the lake after spawning.