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Aquatic Ecology Course Zoo 374 Freshwater Ecosystems Only 3% of the world's water is fresh. And 99% of this is either frozen in glaciers and pack ice or is buried in aquifers. The remainder is found in lakes, ponds, rivers, and streams. Freshwater ecosystem Freshwater ecosystems cover 0.8% of the earth's surface. They generate nearly 3% of its net primary production. Freshwater ecosystems contain 41% of the world's known fish sp. There are 3 types of freshwater ecosystems: Lentic: slow-moving water, including pools, ponds and lakes. Lotic: rapidly-moving water: streams & rivers. Wetlands: areas where the soil is saturated or inundated for at least part of the time. Importance of fresh water ecosystems Fisheries Aquaculture Sources Lakes Rivers Lakes Some studies about distribution, origin and morphometry of the world’s large lakes were done. Natural lakes, fresh and salt with a surface area greater than 500 sq km were included. They are 253 known lakes. Large lakes occur on all continents except Antarctica, but nearly half of them are found in North America These data show that the large lakes of the world occupy a surface area of 1,456,000 sq km and they have an estimated volume of 202,000km3 Large lakes account for about 90% of the total surface area and volume of water held in all lakes , . of the world Fisheries management in Fresh water ecosystem Firstly, we have to know the difference between : Natural aquatic ecosystems Modified aquatic ecosystems Natural aquatic ecosystems * Fishes and other aquatic resources are captured from a great variety of freshwater ecosystems, most of which are natural. • Natural aquatic ecosystems include lakes, swamps and floodplains, collectively called standing waters, and rivers and streams, collectively called running waters. *Distribution of natural waters - The distribution pattern of natural freshwaters among the continents is uneven which has important implications for aquatic production, inland fisheries and aquaculture. - For example, the greatest occurrence of standing waters is in the relatively unproductive northern areas of the Northern Hemisphere. In contrast, the distribution of running waters in the form of perennial rivers is more homogeneous, with the exceptions of the great deserts of North and Southwest Africa, the Arabian Peninsula and Australia. - The status and trends of aquatic ecosystems, both natural and modified, are closely linked to the condition of adjacent terrestrial ecosystems. Modified aquatic ecosystems • Nearly all inland water bodies have been modified to some extent through human intervention. For instance, the enriching effects of excess fertilizers and livestock wastes in the runoff from farmland and lakes have caused biological environmental impacts on rivers and streams. * New ecosystems have been created by the physical modification of natural aquatic ecosystems, such as rivers and streams that have been dammed to form reservoirs and irrigation systems for agriculture. • Reservoirs themselves can be engineered in special ways to facilitate, for example, fish passage and fish capture or otherwise to stimulate increased production through habitat enhancement for a specific species. * Natural and modified ecosystems are further transformed in their particular community structures through biodiversity - by the introduction of new species - and by periodic stocking. SO.,,,,,,, * All modifications affect the fisheries potential of aquatic ecosystems. Many are subtle, with long-term irreversible effects and may eventually prove negative. * Large reservoirs are among the most conspicuous man-made aquatic ecosystems. Many small water bodies seem natural but, in fact, are reservoirs that have been created primarily as community water supplies, to water livestock or to irrigate crops……….. Such water bodies can have multiple uses, including fisheries and aquaculture but, to be successful, they require well-planned integrated watershed management. Rice paddies are a prime example of an agricultural crop system that produces a second crop - fish - which in turn enhances the rice production. Fish resources in lakes The degree of resource utilization differs greatly from lake to lake and according to two main types of fisheries: demersal/inshore and pelagic/offshore. Currently, the demersal/inshore resources are heavily exploited or overexploited. In Asia, there is a relatively advanced national capacity for the development of enhanced fisheries but less experience in social and political issues. African large lakes are receiving adequate biological attention through a number of international activities, with research focusing particularly on lakes Victoria ,Tanganyika and Malawi. However, governmental support in some African countries is still low, with little money allocated from national budgets for their development. Fish resources in lakes (Cont.) Africa, especially East Africa, is endowed with numerous lakes that support very important fisheries, in turn providing a livelihood to millions of people and contributing significantly to food supply. In many of these lakes fisheries are reaching a state of maturity and consequently management problems are rising. For 11 lakes, shared by 11 countries of eastern Africa, fisheries employs close to half a million people, with perhaps three times as many engaged in secondary activities and related services, thus supporting about 4 percent of the population of the region as a whole The State of World Inland Fishery Resources Fishes, lampreys, amphibians, crustaceans and molluscs constitute the broad groups of inland resources that directly or indirectly support fisheries (see FAO statistics). Some 11 500 fish species - 41 percent of all fishes - are exclusively freshwater and about 1 percent are diadromous . Due to statistical problems, the state of inland water resources must be implied from other information. Trends in annual capture data provide one line of evidence. Globally, the trend for capture has been for modest annual increases of about 2 percent during the last two decades of the twentieth century. From a continental perspective, trends show increases in Asia, Africa and Latin America, decreases in the Commonwealth of Independent States and Baltic States (former USSR), North America and Europe, and stability in Oceania. The State of World Inland Fishery Resources (Cont.) Another line of evidence on the state of inland resources comes from the status and trends of ecosystems . Generally, it can be inferred that aquatic ecosystems are in a state of decline throughout most of the world. How can this be reconciled with an apparent trend for increases in capture output from inland resources? One reason is a human-induced enriching of aquatic systems from agriculture and urban sources to produce more fish. Another is that the combined effects of fishing and physical and chemical changes in inland waters have caused a shift to species that are more productive per unit of area, weight-wise, but may be of lesser economic value. Better governance -- with attention to aquatic ecosystem management such as habitat enhancement and stocking interventions -- along with broad approaches to management, such as integrated watershed management, also increase inland output. Factors affecting the fisheries and fish production in lakes Natural factors 1) Peripheries erosion 2) Lake area reduction 3) Sea water level rise 4) Lagoon saltation 5) Sea lagoon connection siltation Human related factors 1) Agriculture 2) Industrial sewage discharge 3) Land reclamation 4) Coastal constructions 5) Illegal fishing 6) Recreational activieties 7) Increasing population 8) Number of boats and fishermen 9) Pollution These factors, some of them or even one of them may cause drastic changes in the environmental conditions of lakes all over the world affecting the fisheries of the lakes as well as the fish communities inhabiting these lakes. WHY….. not only lakes ???? Fresh-water habitats are extremely diverse, and include both still-water environments like lakes and ponds, and flowingwater environments like rivers and streams. Still-Water Habitats Lakes and ponds • Like oceans, lakes have pelagic and benthic zones. The temperature of lake water varies depending on depth, and can also change dramatically over seasons. The epilimnion is the topmost layer of lake water. It is significantly warmer than deeper areas due to heating by sunlight. The hypolimnion layer describes deeper, colder lake water. Many of the nutrients in lakes collect at lake bottoms. • Turnover occurs when all the water in a lake is nearly thermally uniform and mixed, distributing nutrients throughout the water. Turnover occurs twice a year in many temperate lakes, but may occur only once in subtropical environments, or not at all in permanently stratified lakes. Still-Water Habitats (Cont.) • Lakes also can be described as either oligotrophic or eutrophic (or in between these two extremes). • Oligotrophic lakes have low levels of nutrients and low productivity. They generally contain cold, highly oxygenated water and support species adapted to these conditions. Eutrophic lakes, on the other hand, have plentiful nutrients and are highly productive. Species that inhabit eutrophic lakes must be tolerant of low oxygen levels and warm temperatures. In general, oxygen levels in lakes depend on the amount of water circulation, the surface area that is exposed to air, and levels of oxygen consumption by living organisms. Still-Water Habitats (Cont.) Flowing-Water Habitats Rivers and Streams The habitats available in rivers and streams differ in several ways from those in lakes and ponds . 1) Because of the current (flowing water), the water is usually more oxygenated . • River species generally have special adaptations for living in water currents. Some species are sessile and live anchored to the river bottom. Other species have evolved adaptations such as suckers or hooks to keep themselves from being washed away. Still other species are strong swimmers. Many of these have flattened bodies that help them resist the pressure of the current. • Compared to lakes, rivers tend to be well-oxygenated because of the constant motion of the water. Temperatures can change quickly in rivers, but do not span as great a range as in lakes or other still water. Because there is less penetration of light in flowing water, plant diversity is generally lower in. 2) Photosynthesizers play a minor role in the food chains here; a large fraction of the energy available for consumers is brought from the land; e.g., in falling leaves. Thank You for your attention