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1.
Spatial variation in the fish community of the regulated Raia stream (Portugal) was examined during the summer of 1995. Variation in the native fish community (abundance of species-size combinations) was explicitly related to both the abundance of exotic species and habitat variables. The fish community changed in space from assemblages characterised by the high relative abundance of Leuciscus pyrenaicus, Leuciscus alburnoides and the smaller size classes of Barbus bocagei (all Iberian endemics with total length, TL, < 100mm to assemblages characterised by the high relative abundance of Chondrostoma polylepis (Iberian endemic) and B. bocagei with TL > 200mm and of exotics Micropterus salmoides and Lepomis gibbosus (> 100mm TL). The former assemblages used shallow sites far from downstream dams with some current whereas the latter assemblages used deeper sites closer to downstream dams without current velocity and with abundant floating macrophytes. Both exotic species and habitat variables were significant correlates of endemic assemblage composition in the Raia stream and the abundance of M. salmoides > 150mm in TL was the best biotic predictor of endemic assemblage composition. The total variation in the community of endemic fish was partitioned into four components: (i) associated uniquely with exotic species - 12.6%, (ii) associated uniquely with habitat variables - 27.6%, (iii) associated both with exotic species and habitat variables - 14.5%, and (iv) that unexplained - 45.3%. A significant association of exotic species with the endemic fish community remained after accounting for the selected environmental variables and a strong (habitat) x (exotic species) interaction was indicated.  相似文献   

2.
The decline of the endangered Mary River cod, Maccullochella peelii mariensis, of Queensland, Australia, has been attributed to anthropomorphic habitat alterations, however, the relationships between this subspecies and its physical environment are poorly understood. We used radiotelemetry to investigate the movements and use of habitats by nine Mary River cod (total length 420–760mm; weight 1.3–5.5kg) in the Mary River system over a 20 month period. The mean distance moved each month was positively correlated with monthly stream discharge, but the direction of movements was unpredictable. Patterns of movement varied considerably among individuals and appeared to be unrelated to size. Cod established home ranges of between 70 and 820m in length. Five of the tagged cod returned to a previous home range after moving more than 10km, whereas three did not move more than 2km from their capture location for the duration of the study. Cod used large woody debris complexes more than any other type of habitat, and rarely used areas of open water. Managers should give high priority to maintenance of fish passage and protection/rehabilitation of large woody debris habitats if cod populations are to recover.  相似文献   

3.
We examined the benthic fishes and artisanal fishery in the intertidal flats of Inhaca Island, Mozambique. Results of a questionnaire indicated that catches had decreased, and that piscivorous fish have disappeared. Results of a catch sampling study indicated that current catch rates are low, < 2 kg person–1 fishing trip–1. Use of fishing gear was significantly related to season, diel and lunar tidal phase, and habitat. Forty-eight fish species were observed in the catches with eight species comprising 80% of the catch of 1814 specimens. The annual catch was estimated at 26.2t for the whole bay. Highest fishing pressure was observed in the central section of the bay. A demersal fish survey was carried out with a 2-m beam trawl to sample the fish community. Two different areas were sampled, one area with a low, and one with a high fishing pressure. A total of 19889 fishes were caught comprising 93 species. Gobies dominated the catches and accounted for 56% of all specimens. Fishes were small with a mean standard length of 29mm. The Saco area exhibited the highest catch rates and biomass (maximum of 1040 fish 1000 m–2 and 1490g 1000 m–2), and the highest species richness and evenness values. Catch composition was different between the two sampling areas, and was strongly affected by season, but less by habitat. Total fish biomass was estimated at 5.6t for the whole area. Stomach content varied with habitat, and season, and was dominated by benthic invertebrates. The largest estimates of consumption were obtained in the tidal channel and the Zostera beds. Mean consumption of benthic organisms was 1.3g AFDW m–2 yr–1. The area seemed to be overfished. The heavily fished areas exhibited lower catch rates, lower proportion of piscivorous fish, increased proportion of small fish, and a decrease in species diversity.  相似文献   

4.
Petitpierre E  Garnería I 《Genetica》2003,119(2):193-199
The chromosomes of ten species of Cyrtonus and the genome sizes of six are surveyed. Among the total of 15 chromosomally studied species, 11 have 2n=28 chromosomes and a 13+Xyp male meioformula, three have 2n=40 and 19+Xyp and one 2n=46 and 22+Xyp. All but one species with 28 chromosomes show only metacentric or submetacentric chromosomes, whereas the species with 40 and 46 chromosomes display some telocentrics or subtelocentrics, that are probably derived from the former by centric fissions. However, since the number of major chromosome arms is strikingly higher in these latter species (NF=70 and 78) than in the 28-chromosome species (mostly NF=56), other chromosomal rearrangements such as pericentric inversions or heterochromatin accretions could also be involved. The genome sizes display a narrow range, from 1C=0.6–1.22pg, and they are not significantly correlated with the chromosome numbers. Some possible factors implied in the rough chromosomal evolution of Cyrtonus are discussed in relation to a few other genera of the subfamily Chrysomelinae.  相似文献   

5.
Fall and winter movement and behaviour of 28 cutthroat trout Oncorhynchus clarki was determined using radiotelemetry to evaluate the effects of water temperature and ice conditions. As water temperatures decreased, cutthroat trout moved from more solitary positions to aggregations. With few exceptions, radiotagged fish aggregated with other fish in groups varying from 5 to approximately 70 fish. The percentage of fish aggregating and the mean size of aggregation was negatively correlated with water temperature. The mean distance moved by radiotagged cutthroat trout from 1 September to 12 January was 1.0km. After forming aggregations, fish tended to stay within a 120m length of stream until the end of tracking in mid-January. Fish that were less sedentary after their initial overwintering movement usually moved when their habitat was occluded by anchor ice. These fish moved thirty times farther and six times more often than fish in stable overwintering areas. In Dutch Creek multiple freezing events caused several ice related habitat exclusions and movements associated with large decreases in air temperature. Several bull trout and mountain whitefish were observed in groups with cutthroat trout.  相似文献   

6.
During the spring and summer months of 1995, 1996 and 1997, gillnet and longline surveys were conducted in conjunction with tag and recapture experiments to outline spatial and seasonal distribution of young sandbar sharks, Carcharhinus plumbeus, in Delaware Bay for essential fish habitat mapping, to assess abundance of young sandbar sharks, and to quantify growth during the summer nursery season. Sandbar sharks (n = 943) ranging from 40 to 120cm fork length (48 to 130cm total length) were captured; yearly totals were 199, 314 and 430 in 1995, 1996 and 1997, respectively. Individuals were captured between June and October in water temperatures ranging from 15.4° to 28.5°C and salinities ranging from 22.8 to 30.3 ppt. Presence of neonates and catch per unit effort data indicate that pupping begins in late June near the southwestern coast of the Bay. Juveniles were present from early June through September and their spatial distribution in the Bay appeared uniform. Of 782 sandbar sharks tagged and released during the three years, 50 were recaptured. Mean distance from tag to recapture location and mean days-at-liberty of sandbar sharks recaptured in Delaware Bay during the year of tagging were 10km and 18 days, respectively. Some sharks were recaptured as far as 957km from the release location. Length distributions show young-of-the-year sandbar sharks grow about 2–3cm in length during the nursery season.  相似文献   

7.
A denitrifying photosynthetic bacterium (PSB), Rhodobacter sphaeroides S was immobilized on a porous ceramic plate (10×10×0.5cm) using a small amount of agar. In the bioreactor (3.5 l liquid) using this plate, repeated batch treatments of sewage wastewater (acetic acid as a carbon source) were carried out under aerobic conditions (DO 5mg/l) for two weeks. The simultaneous and effective removal of chemical oxygen demand (COD), ammonium, and nitrate was observed. In continuous treatment at a relatively high dilution rate of 0.20 h–1 (retention time, five hours), the same simultaneous treatments were observed for about one month.  相似文献   

8.
We used ultrasonic telemetry to examine movement patterns of 11 bat rays, Myliobatis californica, in Tomales Bay, California. Tomales Bay is long (20km) and narrow (1.4km), and is hydrographically separated into outer and inner bay regions. The outer bay (the outermost 8km) is characterized by oceanic conditions while the shallow inner bay (the innermost 12km) features wide seasonal temperature shifts. Five rays were tracked monthly from October 1990 to November 1991 and six rays (four of which carried temperature-sensing transmitters) were tracked daily from 30 June to 16 July 1992. Mean bat ray movement rate was 8.84mmin–1 (range 4.49 to 13.40mmin–1) and was not significantly affected by size (p=0.592), tidal stage (p=0.610), or time of day (p=0.327). Movement direction was unrelated to tidal stage (p=0.472) but showed a highly significant diel pattern (p<0.001). From 2:50–14:50h, rays moved toward the warmer and shallower inner bay, while from 14:50–2:50h they moved toward the cooler and deeper outer bay. These telemetry data, along with known bat ray foraging patterns and respiratory temperature-sensitivity, argue for behavioral thermoregulation as the primary influence on this movement pattern.  相似文献   

9.
Hydrological variables have influenced fish recruitment in lakes, reservoirs and rivers. We evaluated how annual and seasonal hydrological variables were related to year-class strength (i.e., residuals from catch curves) of sportfish across eight Florida waterbodies (four rivers and four lakes). Multiple regression equations computed for black bass Micropterus spp. were combined across rivers and year-class strength was negatively related to spring median flow rates and in some cases positively related to winter median flow rates (all p0.10). Conversely, Lepomis spp. residuals combined from the rivers indicated that year-class strength was positively related to median flow rates in the fall prior to spawning and negatively related to post-spawn fall median flow rates (all p0.10). Fish recruitment combined across lakes were not related to water levels in this study, although within lake relationships did occur in some instances. Ecological implications of this work include regulations such as minimum flows and levels (MFLs) regarding sportfish species. Impacts of hydrology on year-class strength of sportfish were stronger in rivers than in lakes for these Florida systems. High flows at least once every 3years in the fall may allow inundation of floodplain habitat, providing favorable environmental conditions for Lepomis spp. reproduction. Setting MFLs during periods of drought (i.e., 3years or more) should consider impacts to short-lived species such as Lepomis spp.  相似文献   

10.
Ninety four scalloped hammerhead sharks, Sphyrna lewini (53 females and 41 males) ranging in size from 121 to 321cm total length (TL), were collected from surface gillnetters operating off northeastern Brazil and throughout the southwestern equatorial Atlantic Ocean between January and December 1996. A common regression for TL and eviscerated weight (EW) was calculated as, logEW = –11.786 + 2.889 logTL. Females and males were categorised into reproductive stages (4 and 2, respectively) according to morphological changes in their gonads. Size at sexual maturity for females was estimated to be 240cm, while males appeared to mature at between 180 and 200cm. Gravid females had between 2 and 21 embryos or pups, varying in TL from 3 to 38cm. There was no relationship between maternal length and size of litter. Copulation and parturition appear to occur outside the sampled area and possibly closer to the coast. With the exception of slightly lower uterine and ovarian fecundities, the results support the few existing data on the reproductive cycle of S. lewini in other areas.  相似文献   

11.
The freshwater trout minnow, Galaxias truttaceus, is restricted to the small catchments of the Goodga and Kalgan Rivers in Western Australia. Its large geographic separation from populations in south-eastern Australia, and subsequent reproductive isolation and variation in the prevailing environmental conditions, has created marked differences in biology (and morphology) between the eastern and western populations of G. truttaceus. The biology (spawning period, longevity, growth rates, diet and parasitism) of G. truttaceus in the Goodga River is described and then compared with information on the biology of diadromous and landlocked populations in south-eastern Australia (i.e. Tasmania) (see Humphries 1989). In the Goodga River, ca. 34 and 8% of males and females, respectively, attain maturity at the end of their first year, while only four mature males and one mature female 0+ fish were found in the Tasmanian populations. Adults migrate upstream prior to spawning which peaks during April and May. Larvae, which hatch at ca. 6.5mm (cf. 7.5–9.0mm in Tasmania), move downstream into Moates Lake for a few months before re-entering the river. Of the 810 G. truttaceus collected, ca. 53, 34, 10, 2, 1, 0.2 and 0.1% belonged to the 0+, 1+, 2+, 3+, 4+, 5+ and 7+ age classes, respectively. In contrast, the Tasmanian populations have a much higher proportion of older fish. At the end of their first, second and third years, the males on average attain 60, 84 and 95mm total length (TL), respectively, whereas females attain 63, 89 and 103mm TL, respectively at those ages. Only one fish > 140mm TL was captured, which contrasts with the Tasmanian fish, where a substantial proportion are > 140mm TL. The diet of fish > 40mm TL consisted of between 65 and 96% terrestrial fauna (mainly coleopterans and hymenopterans) in the different seasons. Larval fish diets were largely comprised of copepods.The occurrence of the introduced cestode Ligula intestinalis in ca. 7% of G. truttaceus represents the first record of this parasite in Western Australia. It was found to cause gonadal retardation and gross morphological deformities, the latter of which possibly increases the risk of avian predation.  相似文献   

12.
The population density and summer daytime habitat characteristics of the endangered torrent catfish, Liobagrus reini, in the Urano River, a tributary of the Chikuma River in Nagano, central Japan, were investigated. A total of 105 individuals were captured in 2001–2003, and the estimated population density 100m–2 in the whole study area ranged from 0.20 to 2.96. Liobagrus reini were captured from under cobbles and boulders, interstices in bedrock, and in clumps of roots of terrestrial vegetation along banks. Compared with the distribution of physical factors in the study area, the fish selected shallow habitats with the riverbed covered by cobbles and boulders. Boulders and larger cobbles were chosen by larger individuals as a habitat. Habitat selection was not correlated with current velocity, and some individuals were sampled near (<1m) the riverbank with no current. For the conservation of L. reini, the preservation of natural riverbanks and areas with boulders and large cobbles in the riverbed is concluded to be important.  相似文献   

13.
We intensively sampled fish in rivers and streams within a single major drainage basin (the Blackwater River) and across major drainages in British Columbia to assess the factors influencing distribution of chiselmouth, Acrocheilus alutaceus, and to develop models for predicting chislemouth presence. Chiselmouth were typically absent from sites with maximum temperatures below 20°C or 2100 annual degree days, both within a single drainage and between larger drainages. Indices of stream size (bankfull channel width and basin area) were the most significant predictors of chiselmouth presence within the Blackwater drainage (p=0.016 and p=0.032, respectively), and inclusion of thermal variables only marginally increased classification success. In contrast, bankfull channel width and basin area were poor predictors of chiselmouth presence in mainstem habitat within larger drainage basins throughout British Columbia. Inclusion of thermal variables (particularly degree days > 12°C) doubled correct classification rates of chiselmouth presence across larger drainage basins. These habitat associations suggest that water temperature is the primary constraint on presence of chiselmouth populations in larger drainages across a landscape, while selection of different habitat types (mainstem habitat over smaller tributaries) determines distribution within any given basin.  相似文献   

14.
We investigated short-term movements of neonate and juvenile sandbar sharks, Carcharhinus plumbeus, on their nursery grounds in Delaware Bay. The majority of sharks tracked limited their movements to water less than 5m deep, remained within 5km of the coastline, and occupied oblong activity spaces along the coast. In addition to site-attached coastal movements observed, several sharks moved entirely across Delaware Bay or spent considerable time in deeper portions of the central bay. Sharks tracked on the New Jersey side of the bay tended to spend more time in deeper water, farther from shore than sharks tracked on the Delaware side. Observation-area curves estimated that optimal tracking time for sandbar sharks in Delaware Bay was 41h. Indices of site attachment showed that movement patterns of tracked sandbar sharks varied from nomadic to home ranging. There was no significant difference in rate of movement for day/night, crepuscular periods, or between juveniles and neonates. In general, young sandbar sharks patrolled the coast and appeared to be site attached to some extent, but were capable of making longer excursions, including movement entirely across Delaware Bay.  相似文献   

15.
We assessed small-scale movement patterns of fishes on three eastern Tasmanian reefs by divers visually resighting 1040 individuals of 16 species marked with unique colour-coded tags. With the possible exception of the monacanthid Acanthaluteres vittiger, common species showed high fidelity to site, with individuals generally resighted <100m from the initial tagging site and remaining near the tagging site throughout the 1 year duration of study. The wrasses Pictilabrus laticlavius and Notolabrus tetricus were more sedentary than Notolabrus fucicola and the monacanthids Meuschenia australis and Meuschenia freycineti. Body length, sex, water temperature and time since tagging had little influence on distance moved compared to variation between individuals, other than movement distance increasing with body length for N. tetricus. Movement patterns were generally consistent at all three sites, although mean distance moved by N. fucicola was double at Swanport and Return Point compared to Lobster Point. N. tetricus but not P. laticlavius emigrated from areas artificially cleared of macroalgae. The sedentary nature of most small- to medium-sized reef fish species, particularly labrids, indicates that relatively small (1km diameter) marine protected areas should generally provide conservation benefits for these fishes but few `spillover' benefits in surrounding areas.  相似文献   

16.
Dongtan (or East Tideland) on Chongming Island in China is an important wintering site of Grus monacha (hooded crane). Field observations were conducted in Dongtan in the wintering season of 2000–2001 to determine how tidal fluctuation affects the habitat use and behavior of G.monacha. Scirpus mariqueter (sea-bulrush) was the dominant species in the tidal vegetation; and its corms were the major food source for G.monacha. The corms in the outer zone (far from the dyke) were buried underground shallower than those in the inner zone (near the dyke) because of erosion by tidewater. For easy access to food, G.monacha tended to select the outer zone and the edge of tidal creeks as its foraging sites for the majority of time spent on the tideland. Regression analysis revealed that distance of the foraging sites to the dyke was correlated with tidal height. The cranes did not appear to show territorial behavior, and tended to form large-sized flocks, especially at high tide, because of the effect of the tidewater and the non-uniform distribution of food. Thus, the height of the tide is an important factor responsible for the habitat selection of G.monacha, which was also the major cause of the cranes selecting only the natural tideland at Dongtan on Chongming Island. Unfortunately, the habitats of G.monacha are limited, and even threatened, at Dongtan because the tideland is frequently reclaimed. Appropriate measures should be taken to prevent the tideland being further reclaimed, otherwise the natural wintering grounds of G.monacha will soon disappear.  相似文献   

17.
The phylogenetic relationships of all 16 genera (plus Psenes pellucidus) of the suborder Stromateoidei were estimated cladistically based on 43 osteological, myological, and external characters. Thirty equally parsimonious trees were obtained. Based on the strict consensus tree, Centrolophidae was nonmonophyletic, Psenopsis being placed as a sister group of a clade comprising Amarsipus, Ariomma, nomeids, Tetragonurus, and stromateids. Schedophilus formed a sister group relationship with Seriolella. The relationships among the Centrolophus, Hyperoglyphe, Icichthys, Tubbia, Schedophilus+Seriolella clade, and Psenopsis+Amarsipus+Ariomma+nomeids+Tetragonurus+stromateids clade were unresolved. Amarsipus, which is unique within the suborder in lacking a pharyngeal sac, was nested within the stromateoid clade, being a sister group of the clade including Ariomma, nomeids, Tetragonurus, and stromateids. The absence of a pharyngeal sac in Amarsipus was interpreted as a reversal, its presence in the Stromateoidei therefore being considered as a synapomorphy. Ariomma was placed as the sister group of a clade comprising nomeids, Tetragonurus, and stromateids. Monophyly of the Nomeidae and Stromateidae were supported by 2 and 11 synapomorphies, respectively.  相似文献   

18.
Gobies of the genus Elacatinus are regarded as the most specialised cleaner fishes in the western tropical Atlantic, yet there are no studies on these cleaners in the southern portion of West Atlantic. We studied the diversity of clients and the daily cleaning activity of the barber goby, Elacatinus figaro, on rocky reefs in southeastern Brazil (23–24°S). A total of 34 fish client species in 16 families were recorded over 484 cleaning events. The most frequent clients were damselfishes, Pomacentridae (37.9% of cleaning events) and grunts, Haemulidae (16.9%). Planktivores were the most frequently attended trophic category, and two species in that category accounted for about a half (44%) of the total cleaning events. Size of clients ranged 4.5–55cm and most individuals were medium-sized (12–30cm); as the barber goby ranged 2–4.5cm, clients were 1.5 to 15 times larger than the cleaner was. Cleaning activity started at dawn and ended shortly before nightfall, the highest frequency of interactions occurring at early morning (nocturnal clients) and mid-afternoon (diurnal clients). By midday the frequency of cleaning events decreased and their duration increased. A total of 109±3 cleaning events and 30±1min of cleaning activity were estimated per cleaning station per day, both figures low when compared to those recorded for cleaner fishes in tropical areas of the western Atlantic and Indo-Pacific.  相似文献   

19.
The mechanism of uptake of water-insoluble -sitosterol by a newly isolated strain of Arthrobacter simplex SS-7 was studied. The production of an extracellular sterol-pseudosolubilizing protein during growth of A. simplex on -sitosterol was demonstrated by isolating the factor from the cell-free supernatant and its subsequent purification by Sephadex G-150 column chromatography. The M r of the purified sterol-pseudosolubilizing protein determined by SDS–PAGE was 19kDa. The rate of sterol pseudosolubilization (5.2×10–3g l–1h–1) could not adequately account for the rate of sterol uptake (72×10–3g l–1h–1) and the specific growth rate (56×10–3 h–1). However in the unfavourable growth condition, when the cells were treated with sodium azide at the level of 30–60% of MIC, the sterol pseudosolubilization accounted for nearly 74% of the total growth containing 96% free cells. Cellular adherence to substrate particles was found to play an active role in the normal growth of the strain on -sitosterol. Unlike sodium acetate-grown cells, whose surface activity was negligible (60mNm–1), the sterol-grown cells had strong surface activity (40mNm–1). The high lipid content and long chain fatty acids in the cell-wall of -sitosterol-grown cells probably contribute to the high sterol adherence activity of the cells.  相似文献   

20.
We conducted a series of experiments to determine the movements and fidelity of juvenile pinfish, Lagodon rhomboides, in salt marsh creeks within North Inlet Estuary, SC. In Experiment 1, we investigated the fidelity of pinfish (40–100mm SL) at four subtidal locations (9–617m apart) along the axis of a major creek. We trapped and marked 2,297 individuals and recaptured 15–22% of the fishes released at each site, almost all of which (99.7%) had been marked at the same location of recapture up to 3 months earlier. In Experiment 2, we investigated pinfish movements between subtidal and intertidal areas. In the 8 weeks prior to sampling 2 intertidal creeks, we marked 950 juveniles in the adjacent subtidal areas. Sampling of the 2 flooded intertidal creeks showed that 9–20% of the pinfish collected bore marks, and all had been previously marked at the subtidal site immediately adjacent to the intertidal creek. Gut analysis of 60 individuals revealed that juveniles collected from the intertidal areas at high tide had consumed about ten times more food than those collected at the subtidal sites at low tide. In Experiment 3, we determined the fidelity of recently settled pinfish (<35mm SL) and showed that 15% of the 434 marked pinfish remained in the same area; some were at liberty up to 7 weeks. In Experiment 4, we determined home range by tagging and recapturing juvenile pinfish at sites separated by 20m along a 200m subtidal transect. We estimated that during periods when the intertidal zone was not accessible, the average home range was 9.4m with only 10% of tagged fish moving greater than 20m during the 4 month study. Our results indicate that soon after recruitment to the estuary, pinfish establish strong fidelity for sites within salt marsh creeks and exhibit tidal periodicity in both movements and feeding.  相似文献   

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