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1.
The abundances, population dynamics and production of the rotifer community of Lough Neagh were examined for a three year period. Keratella cochlearis was the most abundant species accounting for over 40% of biomass followed by Polyarthra dolichoptera and Notholca acuminata. The mean standing crop for the rotiferan zooplankton increased in successive years (41, 51, 75 mg dwt m–2) as did production (1037, 1322, 1417 mg dwt m–2 y–1). The seasonal pattern of biomass expression and production varies markedly in different years. Instantaneous birth rates tend to be lower but more consistent for the more abundant species, instantaneous death rates show periods of negative mortality indicating an inadequacy of the model employed but explicable as hatching of resting eggs. K. cochlearis as the most successful species is explained as its perennial appearance and adaptation to the low annual temperature cycle found in the lough. The population succession and the annual occurrence of species differs in each year.  相似文献   

2.
A study was made of the effects of a Ligula intestinalis infestation on the biology and distribution of gudgeon in Lough Neagh, Northern Ireland. During the summer months, when the majority of the gudgeon population was restricted to the inshore areas of the lough, Ligula was present in all age (size) classes of the host although levels of infestation were highest in the oldest individuals. While there was no significant effect on the length-weight relationship of the gudgeon, the presence of the parasite did adversely affect gonad size in both sexes. Ligula also influenced the distribution of the gudgeon population by decreasing the swimming depth of infested individuals and by delaying their autumnal migration to the deeper offshore parts of the lough.  相似文献   

3.
Stomach contents of pollan caught monthly throughout the year were examined. Stomach fullness was significantly correlated with water temperature. Adult pollan fed on bottom fauna, mainly chironomid larvae, in October-March, chironomid pupae in April and on Daphnia spp. in May-September. Immature (0+ and 1 +) fish also ate other cladocerans and copepods. While there is no evidence for selection of any benthic prey species, adult pollan appear to be highly selective feeders on Daphnia spp. in summer.  相似文献   

4.
5.
Synopsis Following the introduction of roach, Rutilus rutilus, to a large eutrophic lake in ca. 1973, a subsequent increase in the abundance of this cyprinid through the 1970s was accompanied by a decline in the numbers of one of the lake&s most abundant overwintering waterfowl, the tufted duck, Aythya fuligula, and an increase in overwintering piscivorous great crested grebes, Podiceps cristatus. We suggest that these contrasting trends are causally related and that competition for benthos and increased prey availability are the mechanisms responsible for the changes in the tufted duck and grebe populations respectively. In agreement with these hypotheses, a reduction in the roach population during the mid 1980s was accompanied by a recovery of tufted ducks and a decline of grebes.  相似文献   

6.
Rippey  Brian  Jewson  David H. 《Hydrobiologia》1982,91(1):377-382
Oxygen is transported 30 mm into the sediment at an 8 m depth site in eutrophic Lough Neagh by the irrigational activities of the benthic fauna. Faunal activity also mixes the upper 20 mm of sediment. Sediment oxygen uptake rate, redox potential-depth profile and the chlorophylla concentration were measured in the upper sediment layers from February to November 1979. Chlorophylla input to the sediment, following the Spring phytoplankton maximum, remained in the 0–1 cm sediment layer but did cause the redox potential profile to change from one with potentials around 400 mV in the upper 50 mm to one with a strong gradient over the 0–30 mm region. The start of benthic faunal activity in May caused the chlorophylla to be mixed into the 1–2 cm layer and also caused oxygen to be transported into the sediment at a rate sufficient to change the redox potential back to its initial state. The biodiffusion coefficient for solids in the upper 20 mm was estimated to be 6 × 10−8 cm2 s−1. Oxygen transport in the pore, waters of the upper sediment layers was considered to be best described as advection, caused by the irrigational activities of the benthic fauna.  相似文献   

7.
Long runs of seasonal rotifer population data allow analysis of seasonal occurrence using mathematical tools. The application of Fourier analysis to a 15 year dataset describes seasonality in simple mathematical terms. This facilitates comparison of population expression with potential population driving variables and provides a basic modelling tool. Results show that annual patterns of occurrence and density have linkages with annual maximum and minimum environmental temperature, although the exact relationships are not clear.  相似文献   

8.
Scales from Lough Neagh pollan display a large number of checks, making age determination difficult. Sclerite counts showed that an annual check is formed on scales in May and a second accessory check in most young fish in October. The method of ageing from scales was supported by inspection of length-frequency plots and by following the growth of pollan in their first 2 years of life. The body-scale relationship was curvilinear. Back-calculation showed that pollan of both sexes attain a fork length of 29 cm in 5 years (1 ∞=28.9 cm; k = 0.65; l 0= -0.06 year). There is no evidence that annual growth rates have changed since 1965. Possible environmental causes of scale check formation are discussed.  相似文献   

9.
The annual cycle for roach ( Rutilus rutilus ) and perch ( Perca fluviatilis ) in Lough Neagh, Northern Ireland can be divided into warm 'growing' and cold 'non-growing' seasons. Summer water temperatures declined between 1991–1993, as did the sizes of 0+ fish of both species. Small overwinter increases in length occurred after poor summers due, in roach, to size-selective mortality. Fat content was size-dependent and increased over the summer in both species. All sizes of roach but only small perch lost fat overwinter. Dead roach collected towards the end of the 1992/3 winter had significantly less fat than live individuals. The allocation of energy to growth (and ultimately reproduction) and to fat (and overwinter survival) was modelled as a tradeoff, assuming that fat has twice the energy density of protein and using observed summer and winter changes in body composition. The predicted allocation optima were close to observed values but, for roach, this entailed a substantial survivorship cost.  相似文献   

10.
The length–weight relationship for Lough Neagh pollan was log W= 3·2 log L –2·24. Covariance analysis indicated that there were no differences between the sexes, with maturity, or between years. While a seasonal cycle in relative condition was in phase with gonad development during late summer and autumn, changes in somatic condition presented a more complex pattern. Somatic condition increased in spring, as did the quantity and diversity of food consumed. Despite good conditions for feeding and growth, there was an autumn fall in somatic condition, caused by the diversion of energy to gonad growth.  相似文献   

11.
12.
Studies had been carried out on the local non-migratory whitefish. Spawning behaviour and light conditions on the spawning ground are recorded. After artificial spawning, embryonal development took place under controlled conditions and the larvae were reared. Detailed characteristics of swim bladder creation and differentiation of the digestive tract are given. Distribution and number of pollan larvae near the spawning area and in the open lake were examined. Data are presented concerning the growth rates of larvae and fry in captivity and under lake conditions. Ecological data related to other coregonids are discussed and compared with the present study.  相似文献   

13.
The homogeneous distribution of the phytoplankton in a shallow (mean depth 8·6 m) unstratified lake, L. Neagh, Northern Ireland, facilitated the study of the interaction of components controlling gross photosynthesis per unit area. These included the photosynthetic capacity, the phytoplankton content of the euphotic zone, and a logarithmic function describing the effective radiation input. These factors were analysed for two sites, the open lake and Kinnego Bay, which respectively had standing crops of up to 90 and 300 mg chlorophyll a m?3 and maximum daily rates of gross integral photosynthesis of 11·7 and 15·6 g O2 m?2 day?1. Values are reduced by the high contribution to light attenuation by non-algal sources, which increases at low standing crops particularly in winter, when values of integral photosynthesis decrease to 0·5 g O2 m?2 day?1. This relative change is the result of self-shading behaviour of the phytoplankton altering the crop content of the euphotic zone at different population densities. Changes in the irradiance function, incorporating day length, are largely responsible for the changes in daily rates of integral gross photosynthesis; as daily irradiance is also a determinant of water temperature, it exerts further influence through the photosynthetic capacity which was strongly correlated with temperature. Much of the gain in gross photosynthesis resulting from higher photosynthetic capacity may not be reflected in a higher net column photosynthesis, because of the greater proportional rise in respiration with temperature. The balance in the water column between respiration losses and photosynthetic input may frequently alter since the ratio of illuminated to dark zones is between 1/4 to 1/5 in the open lake, and small shifts in any of the controlling features may result in conditions unfavourable for growth. This is analysed especially for the increase of diatoms in spring, when small modifications of the underwater light field can delay growth.  相似文献   

14.
Between 1932–1947 and from 1960 onwards, elvers have been trapped near the mouth of the River Bann, Northern Ireland, and released into Lough Neagh. Each period of elver transport has been followed by a marked increase in the proportion of male silver eels migrating from the lough. Catches of silver eels were sampled on several nights each year from 1965–1974, and the lengths of a total of 20358 eels measured showed a progressive increase in the percentage of male eels from 9.3-86.0 % during this period. Various reasons for this change were examined. The different ages at which male and female eels migrate to the sea was not important. There was no evidence to support the hypothesis that male elvers normally remain in estuarine conditions, and their transport to the lough was therefore unnatural. An increasing fishing effort for yellow eels, such as occurred following the introduction of trawling in 1960, would favour males since small eels were returned to the lough. It was not thought, however, that this was a major cause of the change in sex ratio. Instead, elver transport appeared to be directly implicated, possibly by the overstocking of Lough Neagh, and the phenotypic determination of progressively more male eels, but the evidence for this suggestion was inconclusive.  相似文献   

15.
SUMMARY. Cell phosphorus and anthrone-reactive carbohydrate contents were measured over a 6-month period in the phytoplankton of Lough Neagh, N. Ireland. When all the soluble reactive phosphorus had disappeared from the water column, cell phosphorus contents began to decrease, reaching a minimum value of 0.4% ash-free dry weight. At this time, cell carbohydrate contents greatly increased and phosphorus sorption assays showed rapid uptake of orthophosphate. Following a presumed sediment phosphorus release, cell carbohydrate and phosphorus uptake rate decreased greatly and there was a subsequent increase in cell phosphorus content to 1.6% ash-free dry weight. As the cell phosphorus content declined, blue-green algal filaments became progressively shorter. On the basis of these responses it is likely that phosphorus limitation occurred over a 4-week period.  相似文献   

16.
Clare E. Carter 《Ecography》1980,3(3):214-217
Chironomus anthracinus generally had a one year life cycle at 8 m depth in Lough Neagh, during the study period. In spring 1975 however only a proportion of the population emerged as usual, the rest remaining a second year in the benthos to emerge in 1976. The mean dry weight of larvae just before emergence was 2.8 mg in 1971 and 2.6 mg in 1974 but only 1.6 mg in 1975, and it seems that larvae must reach a weight of at least 1.0 mg in the early spring to emerge that year. Considering temperature, oxygen saturation and standing crop of phytoplankton as factors influencing the life cycle, mean monthly chlorophyll a (phytoplankton) was weakly correlated with mean monthly increase in weight and % monthly weight increase could be related to temperature.  相似文献   

17.
Studies on the chemical composition of adult pollan were carried out monthly from January to December 1977. Sex, weight of scaled fillet, and gonads were examined in 184 fish. Chemical composition which includes water, fat and ash content was analysed in the whole fish, muscle and gonads. This paper attempts to account for the fat and protein flow within fish of both sexes during gonad maturation. Extreme differences between males and females have been recorded in the fat deposition process during summer and spawning period. In spite of our fragmentary knowledge of spawning behaviour in pollan, an explanation is offered for these phenomena. The changes in fat content of female gonads were followed closely throughout the year and the cost of egg production was estimated as a percentage of the amount of fat deposited in the body. Since a similar growth pattern was found for both sexes of pollan, differences in feeding intensity might account for the difference in energy expenditure. Amino acid content was analysed in muscle and gonads and an Essential Amino Acid Index (EAAI) was calculated. There were some changes in EAAI which depended on sex and season. Finally, a new method for evaluation of muscle production expressed as fat and protein is used to determine the most suitable time for fish harvesting.  相似文献   

18.
The physical limnology of Augher Lough (Northern Ireland)   总被引:2,自引:0,他引:2  
SUMMARY.
  • 1 The physical limnology of Augher Lough, Northern Ireland (area=9.25 ha. z=5.5 m), including stratification pattern, heat budget, thermocline erosion rate, eddy diffusion rate in the thermocline and hypolimnion and areal hypolimnetic oxygen deficit is described.
  • 2 Oxygen and temperature profiles, recorded at two sites during 1978 and four sites during 1979, showed that spatial variability of these quantities was low and allowed the following lake characteristics to be estimated. Heat budgel was 5.30 kcal cm-2 (standard deviation=s=0.26) in 1978 and 5.00 (s= 0.26) in 1979. The thermocline depth was 3.5–6.5 m with an erosion rate of 1.9X10-7 m s-1 in 1979. Eddy diffusion coefficients of heat in the thermocline and hypolimnion normally ranged from 0.48X 10-2 cm2 s-1 (s=0.20X10-2) to 5.4X10-2 (s=2.6X10-2), but reached 10X10-2 cm2s-l (s=9X10-2) in early July 1978 after a cooling-mixing episode in the epilimnion. The hypolimnetic oxygen deficit was 680 mg O2 m-2 d-1 (s=76) and varied strongly with depth.
  • 3 A cooling-mixing episode in the epilimnion in June-July 1978 caused the movement of heat down to 8 m, movement of oxygen down to 6 m and increased the eddy diffusion coefficients of heat by an order of magnitude.
  相似文献   

19.
Warke  G. M. A.  Day  K. R.  Greer  J. E.  Davidson  R. D. 《Hydrobiologia》1994,(1):91-100
Breeding cormorants, Phalacrocorax carbo, in Northern Ireland remain seasonally dependent on a coastal environment where they can be censused with accuracy, but numbers in other habitats and at other times of the year are less certain. This study establishes the long term and regional patterns of abundance at breeding and feeding localities, which might in turn be related to diet.Birds were regularly observed and counted at a variety of feeding sites, and some aspects of their breeding success and fledgling diet evaluated at the largest N.Ireland breeding colony.Numbers of breeding birds increased dramatically over a period of eight years but recently show signs of declining. There is likely to be a dynamic relationship between populations of a tapeworm (Ligula intestinalis L.), the numbers of roach (Rutilus rutilus [L.]) and cormorant populations feeding at Lough Neagh, the largest lake in the British Isles. While roach are not a major component in the diet of fledglings, the large numbers of cormorants feeding at the perimeter of L. Neagh suggest that changes in roach populations will affect birds most acutely during or following the winter. We suggest that this might result in a reduction in the proportion of the population volunteering to breed in the subsequent season, but require further data. The longer term effects of one fish species on cormorant populations are unlikely to be critical, since these birds are highly opportunist.In other habitats cormorant numbers are either very stable (estuary) or variable (river) depending on the seasonal and annual availability of their prey. There is no evidence for a systematic seasonal shift in habitat, as suggested by other studies.  相似文献   

20.
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