Relación entre la abundancia y estructura de la comunidad de peces y el régimen hidrológico, en lagunas de la alta cuenca del río Salado

This thesis explored the relationship between hydrological variability and associated changes in fish communities in the upper Salado river lakes (Pampa plain, Argentina). The sampling design included five sites along the river connected lakes being explored for fish, hydrological and environmental data during different hydrological conditions. The temporal dynamic of main environmental characteristics of these lakes show that hydrology largely regulates some of the most important factors influencing fish ecology. Changes in fish communities associated with this hydrological and environmental dynamic allow to speculate a first approach towards the functioning of the system as a whole. Following oscillation between droughts and floods, study lakes have shown significant changes on abundance of major fish species, as well as on their recruitment success, which finally leaded to marked changes in fish community structure. Interestingly, trophic structure of communities did not change as much. iOdontesthes bonariensis/i was more abundant during droughts and in saltier sites but also displayed an improvement in recruitment success during these harsh abiotic conditions. Conversely, the abundance of iParapimelodus valenciennis, Cyphocharax voga/i and iCyprinus carpio/i as well as its recruitment success, were largely favoured by lower water residence times and total salinity. This dichotomy is mainly based on different life history strategies of these species against flor and environmental variability and it support the existence of different functional groups among the fish species of upper Salado river lakes. iOligosarcus jenynsii/i did not showed as evident functional response. In conclusion, hydrological and environmental variability can be considered as one of the main factors regulating the functioning and structure of fish communities in these very shallow lowland river lakes of the Pampa plain. Following these results some implications for an eventual regulation of the river regime are discussed.

Observations on the ecology of Hepsetus odoe, Bloch, 1794 (Pisces: Hepsetidae) in Epie Creek floodplain, Niger Delta, Nigeria

The distribution, abundance, age and growth, the food and feeding habits, condition factor and reproduction of Hepsetus odoe in the Epie Creek Floodplain (Nigeria) was studied. H. odoe occur in the creek, swamp channel and lake. It is a very common, abundant and one of the major commercial species. A total of 457 specimens weighing 76.90 kg were caught during the period of investigation. The catches were more abundant in the dry season than in the wet season. The total length ranged from 10 cm to 46 cm while the weight varied between 50 g and 900 g. Six distinct components or year classes were observed using Bhattacharya's method. A growth exponential value 'b' was 3.35 with condition factor, 'k' values ranging from 0.69 to 0.83. The main diets of Hepsetus odoe were fish, including crustaceans (shrimps) and insects. The mean fecundity was 6060 plus or minus 358 eggs (range 2,769 to 6.667 eggs). The ova diameter of H. odoe was found to range from 2.2 mm to 2.6 mm with overall mean = 2.4 plus or minus 0.1)

Some aspects of the ecology and reproduction of the small pelagic cyprinid, Rastrineobola argentea in Lake Victoria

This study concentrated on the reproductive biology of the small pelagic cyprinid Rastrineobola argentea. The results indicate that this fish is an inshore spawning species, which agrees with other recent studies. It was also found that in areas where fishing intensity was likely to be relatively high, the size at first maturity of R. argentea was reduced, which is likely to be an effect of the fish altering its reproductive strategy according to life history theory. The CPUE results showed a general trend of decreasing with distance from shore, however areas less than one kilometer from the shore were not sampled. Evidence was also found suggesting that the cestode parasite, Ligula intestinalis had an adverse effect on the maturation and fecundity of R. argentea. Some management options concerning the findings in this study are also briefly discussed. (PDF has 82 pages)

Ecology and fishery in the Cross River Estuary - a research project

A literature review of 50 titles including nearly all relevant publications ensures adequate basis on the present level of knowledge. The proposal includes (a) the determination of the biozoenosis and selected environmental factors, and (b) of fishery and stock data of the main fish and shellfish species. The ecological research studies physical and chemical variables of the estuarine waters (flow velocity and direction, water temperature, conductivity, pH, dissolved oxygen, salinity, nutrients such as ammonium, nitrite, phosphate, silicate, pollutants such as hybrocarbons, pesticides and heavy metals, biochemical oxygen demand, chemical oxygen demand), plankton (bacterio-phyto-and zooplankton), benthos, sediment. The fishery biological and fishery investigations include: number of villages and fishermen, number of boats and gears by type, length and weight data of the main fishery objects with concentration on the shrimps, species and numbers of fish parasites. The ecological variables were monitored at fixed stations on sections in the Cross-River Estuary, Calabar and Great Kwara Rivers two times per month during spring and neap tides. The fishery biological and fishery variables were obtained during spring and neap tide too. For the determination of the detailed methodology the ecological and fishery part of the progeamme should be started with frame surveys based on a larger number of stations. These frame surveys should be repeated from time to time. Both parts of the programme are based on three years duration. It seems already appropriate to continue the work with selected representative stations, villages and variables in form of a long-term data chain

A review of the biology, ecology and management of Scirpus Olneyi. Volume 1: An annotated bibliography of selected references

This annotated bibliography of selected literature on Olney's three7square (Scirpus olneyi Gray )compiled basically for two reasons: 1) to assist a task force in its pursuit of an explanation for the substantial reduction in marsh acreage at the Blackwater National Wildlife Refuge in Dorchester County, Maryland, and 2) to serve as the author's foundation for the initiation of ecological research on this species as partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Botany Department of the University of Maryland. Both purposes are directly related in that the Author's research will be of use to the task force, along I with its other technical information and research results, in under-standing and possibly correcting the marshland loss problem at the Refuge. (PDF contains 100 pages)

Aspects of ecology of Owena reservoirs: implication on fish production

The article gives physical description of Owana reservoir, Nigeria. The reservoir was chemically and thermally stratified partial mixing of the water was observed during the rains. The concentration of major ions in the water showed distinct peculiarities. The captions (Na super(+), K super(+)Ca super(H),Ca super(Z), Mg super(++)) SO sub(4) super(2-) were relatively low. The water had high dissolved oxygen, it was acidic and also had low values of alkalinity, conductivity and total dissolved solids. About 61 plankton taxa belonging to 21 species were identified. The reservoir supports a commercial fishery of about fifteen fishermen with about fifteen species of fish caught daily with the aid of traps set and cast nets. Effective management of the lake will enhance fish production

Intersexual and spatial heterogeneity in trophic attributes of the sleeper, Bostrychus africanus (Eleotridae) in the Qua Iboe Estuary, Nigeria

There was variation in the ingestion of the food objects by the sexes. Despite the similarity in rank-order of the food objects, the ingestion of the objects vary significantly (rg=0.320, P>0.05). Dipterans adult and Hymenoptera were the only food objects not eaten by the males whereas insect remains and unidentified bivalves were absent from the trophics spectrum of the females. There was significant increase in feeding intensity by females than males. There was significant increase in GRI by specimens from Nipa Creek whereas individuals from mangrove creek recorded higher MGF and vice-versa. Dipterans adult. Hymenoptera, insect remains, Neritina glabrata and unid bivalves were absent from dietaries for nipa creek whereas a complete array of the food objects were eaten in the mangrove creek. The present findings highlights the importance of the mangrove ecosystem as the native vegetation encompassing great diversity of food resources and living conditions than the succeeding alien nipa vegetation

Social Organisation of the Short-finned Pilot Whale, Globicephala macrorhynchus, with Special Reference to the Comparative Social Ecology of Delphinids

As a contribution to the understanding of comparative social trends within the cetacean family Delphinidae, a 22-month study was conducted on the shortfinned pilot whale, Globicephala macrorhynchus, which has been suggested to have a unique social system in which males and females in the same group are related and mating occurs outside of the group. The individual identification of 495 pilot whales, analysed in daily group association patterns, allowed identification of 46 pods. They were classified as productive or non-productive based on the presence or absence of immature animals. Productive pods were a significantly larger, although 12% of them lacked adult males. Two classes of whales (residents and visitors) were defined by patterns of occurrence,suggesting differential patterns of habitat use. Resident pods occasionally travelled together (41% of all groups) and associations between age and sex classes showed that in mixed-pod groups, the highest ranked associations of the reproductive females were with males from other pods, while within pods, adult males and females associated less. During summer, the proposed peak conception period, pilot whale groups were significantly larger and contained individuals from a significantly greater number of pods. These findings support the hypothesis that males and females mate when associating with individuals from other pods. A comparative analysis of sexual dimorphism, brain size, and testes size, habitat, prey and group size within the 17 delphinid genera identified a correlation between sexual dimorphism and body size, but relative measures of brain size and testes size did not correlate with broad ecological or social classifications. However, a comparison of three delphinid societies identified two distinct male mating systems: males of the small, mono-morphic Tursiops truncatus live in age/sex segregated groups and mate with a number of discrete female communities. Males in the large sexually dimorphic Glob icephala spp. and Orcinus orca mate with associated female pods and yet remain with their female kin. This corresponds to the avunculate social system described in some human societies. It could evolve from a promiscuous mating system where there is little guarantee of paternity and where males that live with their kin increase their inclusive fitness.

The impact of varying nutrient regimes in earthen freshwater ponds on the comparative ecology of diurnally occurring candidate live feeds

The daytime composition and relative abundance of zooplankton species were studied in three treatments of two replicate earthen ponds each with nutrient sources and water replenishment regimes. Treatment -A (200m super(2) surface area supplied 900kgha super(-1) pig manure only). Treatment -B (200m super(2) surface area supplied 70kgha super(-1) month super(-1) pig manure, 50kgha super(-1) month super(-1) N.P.K. [15:15:15] and 30kgha super(-1) month super(-1) Urea) and Treatment-C (1500m2 surface area supplied 1150kgha super(-1) month super(-1) commercial grade 40% crude protein compounded feed). Water replenishment for Treatment A was daily tidal deluge from the New Calabar River while that for treatment B and C was from column-well and occasional rains. No zooplankton species were recovered from the pig-manure only treatment (A) while only Diffugia constricta and Difflugia urceolata were the two protozoans that occurred together in treatments B (combined fertilization) and C (compounded feed only) in contrast, Difflugia acuminate and three rotifers, Collurella uncinata, Diurella stylata and Keratella quadrata occurred only treatment B. similarly, Arcella arenaria, Arcella costata, Centropyxis aculeate, Difflugia pyriformis, Branchionus calyciflorus, Lepadella patella, Polyarthra trigla and Onchocanmptus mohammedi were recovered from treatment C. Arcella costata was the most abundant zooplankton in the entire experiment, while Arcella arenaria was very abundant in treatment C, Collurella uncinata was very abundant in treatment B. The inference is that combined fertilization of earthen freshwater ponds tend to be more suitable for the culture of rotifers such as Brachionus calyciflorus, popular in fish larva nursery, while those supplied compounded feed could be used to produce protozoans where desirable

Aquatic ecology, economy and society: the place of aquatic ecology in the sustainability agenda

This article explores aspects of sustainability and the importance of sustainable development, including the place of the crucially important resource of fresh water and of freshwater ecosystems. It examines the treatment of natural resources by the economic system that underpins global business, outlines some progress towards more sustainable approaches to business, and recommends steps to re-establish science as the driver of wise policies that contribute to sustainable development.

Symposium on Llangrose Lake: the ecology and conservation of a large nutrient-rich lake in South Wales

This paper summarises a meeting which discussed the ecology and conservation of Llangorse Lake in South Wales. The meeting was organised by the British Ecological Society (Aquatic Ecology Group), in association with the Countryside Council for Wales (CCW), Brecon Beacon National Park Authority (BBNPA) and Environment Agency Wales. It took place on 22 October 1998.

The ecology of Bassenthwaite Lake (English Lake District)

Bassenthwaite Lake is, in many ways, different from the other major lakes in the English Lake District: it is the most northerly, the shallowest, has the largest catchment and the shortest mean retention time. There is also considerable temporal variation in lake level. This article summarises the limnological features of Bassenthwaite Lake, the catchment and physical characteristics before describing the water chemistry, phytoplankton, macrophytes, zooplankton, invertebrates, fish, mammal and invertebrate population. The authors then describe the ecological pressures faced by Bassenthwaite Lake such as nutrients, sediments and introduced species.

Interrelated contributions to freshwater science over 78 years: A guide to published work from the Freshwater Biological Association, Institute of Freshwater Ecology and Centre for Ecology and Hydrology, 1929-2006

This article introduces a new listing of published scientific contributions from the Freshwater Biological Association (FBA) and its later Research Council associates – the Institute of Freshwater Ecology (1989–2000) and the Centre for Ecology and Hydrology (2000+). The period 1929–2006 is covered. The authors offer also information on specific features of the listing; also an outline of influences that underlay the research, and its scientific scope.

Structure of the limbs and its significance for the ecology and systematics of the family Chydoridae. [Translation of: Voprosy Gidrobiologii, p385, 1965]

For an explanation of the dynamics of numbers of chydorids, appearing a massive group in the littoral of fresh water bodies, the structure of the limbs of 29 species was studied.