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Fish Counter
Automatic fish counters are automatic devices for measuring the number of fish passing along a particular river in a particular period of time. Usually one particular species is of interest. One important species studied by fish counters are Atlantic salmon. This species is of interest owing to its ecologically vulnerable status and anadromous lifestyles. Methods of operation Fish counters can be divided into three principal types: resistive counters, optical counters, and hydroacoustic counters. Resistive counters A resistive counter is associated with an in-river structure, an example constituting a Crump weir. The resistivity of a fish is lower than that of water. So, as fish cross this barrier, they pass embedded electrodes, and the difference in resistivity disturbs the field established in the vicinity of the electrodes, altering inter-electrode resistance. With three electrodes these disturbances can then be measured by a Wheatstone bridge, or other means, to detect t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atlantic Salmon
The Atlantic salmon (''Salmo salar'') is a species of ray-finned fish in the family Salmonidae. It is the third largest of the Salmonidae, behind Siberian taimen and Pacific Chinook salmon, growing up to a meter in length. Atlantic salmon are found in the northern Atlantic Ocean and in rivers that flow into it. Most populations are anadromous, hatching in streams and rivers but moving out to sea as they grow where they mature, after which the adults seasonally move upstream again to spawn. When the mature fish re-enter rivers to spawn, they change in colour and appearance. Some populations of this fish only migrate to large lakes, and are "landlocked", spending their entire lives in freshwater. Such populations are found throughout the range of the species. Unlike Pacific species of salmon, ''S. salar'' is iteroparous, which means it can survive spawning and return to sea to repeat the process again in another year. Such individuals can grow to extremely large sizes, althoug ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fishing Weir
A fishing weir, fish weir, fishgarth or kiddle is an obstruction placed in tidal waters, or wholly or partially across a river, to direct the passage of, or trap fish. A weir may be used to trap marine fish in the intertidal zone as the tide recedes, fish such as salmon as they attempt to swim upstream to breed in a river, or eels as they migrate downstream. Alternatively, fish weirs can be used to channel fish to a particular location, such as to a fish ladder. Weirs were traditionally built from wood or stones. The use of fishing weirs as fish traps probably dates back prior to the emergence of modern humans, and have since been used by many societies around the world. History The English word 'weir' comes from the Anglo-Saxon ''wer,'' one meaning of which is a device to trap fish. A line of stones dating to the Acheulean in Kenya may have been a stone tidal weir in a prehistoric lake, which if true would make this technology older than modern humans. In Ireland, fish traps in a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aquatic Ecology
An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic (slow moving water, including pools, ponds, and lakes); lotic (faster moving water, for example streams and rivers); and wetlands (areas where the soil is saturated or inundated for at least part of the time). Types Marine ecosystems Marine coastal ecosystem Marine surface ecosystem Freshwater ecosystems Lentic ecosystem (lakes) Lotic ecosystem (rivers) Wetlands Functions Aquatic ecosystems perform many important environmental functions. For example, they recycle nutrients, purify water, attenuate floods, recharge ground water and provide habitats for wildlife. Aquatic ecosystems are also used f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Closed Circuit Television
Closed-circuit television (CCTV), also known as video surveillance, is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors. It differs from broadcast television in that the signal is not openly transmitted, though it may employ point-to-point (P2P), point-to-multipoint (P2MP), or mesh wired or wireless links. Even though almost all video cameras fit this definition, the term is most often applied to those used for surveillance in areas that require additional security or ongoing monitoring (Videotelephony is seldom called "CCTV"). Surveillance of the public using CCTV is common in many areas around the world. In recent years, the use of body worn video cameras has been introduced as a new form of surveillance, often used in law enforcement, with cameras located on a police officer's chest or head. Video surveillance has generated significant debate about balancing its use with individuals' right to privacy even when in public. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spawn (biology)
Spawn is the Egg cell, eggs and Spermatozoa, sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquatic mammals and marine reptile, reptiles, reproduce through the process of spawning. Spawn consists of the reproductive cells (gametes) of many aquatic animals, some of which will become fertilized and produce offspring. The process of spawning typically involves females releasing Ovum, ova (unfertilized eggs) into the water, often in large quantities, while males simultaneously or sequentially release spermatozoa (milt) to fertilize the eggs. Most fish reproduce by spawning, as do most other aquatic animals, including crustaceans such as crabs and shrimps, molluscs such as oysters and squid, echinoderms such as sea urchins and sea cucumbers, amphibians such as frogs and newts, aquatic insects such as mayflies and mos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fish Trap
A fish trap is a trap used for fishing. Fish traps include fishing weirs, lobster traps, and some fishing nets such as fyke nets. Traps are culturally almost universal and seem to have been independently invented many times. There are two main types of trap, a permanent or semi-permanent structure placed in a river or tidal area and bottle or pot trap that are usually, but not always baited to attract prey, and are periodically lifted out of the water. A typical contemporary trap consists of a frame of thick steel wire in the shape of a heart, with chicken wire stretched around it. The mesh wraps around the frame and then tapers into the inside of the trap. Fishes that swim inside through this opening cannot get out, as the chicken wire opening bends back into its original narrowness. In earlier times, traps were constructed of wood and fibre. Fish traps contribute to the problems of marine debris and bycatch. __TOC__ History Traps are culturally almost universal and see ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrofishing
Electrofishing is a fishing technique that uses direct current electricity flowing between a submerged cathode and anode. This affects the movements of nearby fish so that they swim toward the anode, where they can be caught or stunned."FISHNET SHOCKINGS" . ''Toronto Star'', December 3, page IN3. Paul Hunter Electrofishing is a common scientific survey method used to sample fish populations to determine abundance, density and species composition. When performed correctly, electrofishing results in no permanent harm to the fish, which return to their natural mobility state in as little as two minutes after being caught. Method Electrofishing relies on two |
Fish Ladder
A fish ladder, also known as a fishway, fish pass, fish steps, or fish cannon is a structure on or around artificial and natural barriers (such as dams, locks and waterfalls) to facilitate diadromous fishes' natural migration as well as movements of potamodromous species. Most fishways enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps (hence the term ''ladder'') into the waters on the other side. The velocity of water falling over the steps has to be great enough to attract the fish to the ladder, but it cannot be so great that it washes fish back downstream or exhausts them to the point of inability to continue their journey upriver. History Written reports of rough fishways date to 17th-century France, where bundles of branches were used to make steps in steep channels to bypass obstructions. A pool and weir salmon ladder was built around 1830 by James Smith, a Scottish engineer on the River Teith, near Deanston, Perthshire ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Swimbladder
The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their current water depth without having to expend energy in swimming. Also, the dorsal position of the swim bladder means the center of mass is below the center of volume, allowing it to act as a stabilizing agent. Additionally, the swim bladder functions as a resonating chamber, to produce or receive sound. The swim bladder is evolutionarily homologous to the lungs. Charles Darwin remarked upon this in ''On the Origin of Species''.Darwin, Charles (1859''Origin of Species''Page 190, reprinted 1872 by D. Appleton. Darwin reasoned that the lung in air-breathing vertebrates had derived from a more primitive swim bladder. In the embryonic stages, some species, such as redlip blenny, have lost the swim bladder again, mostly bottom dwellers like the weather fish. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fish Migration
Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres. Such migrations are usually done for better feeding or to reproduce, but in other cases the reasons are unclear. Fish migrations involve movements of schools of fish on a scale and duration larger than those arising during normal daily activities. Some particular types of migration are ''anadromous'', in which adult fish live in the sea and migrate into fresh water to spawn; and ''catadromous'', in which adult fish live in fresh water and migrate into salt water to spawn. Marine forage fish often make large migrations between their spawning, feeding and nursery grounds. Movements are associated with ocean currents and with the availability of food in different areas at different times of year. The migratory movements m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sonar
Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigation, navigate, measure distances (ranging), communicate with or detect objects on or under the surface of the water, such as other vessels. "Sonar" can refer to one of two types of technology: ''passive'' sonar means listening for the sound made by vessels; ''active'' sonar means emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used for robot navigation, and SODAR (an upward-looking in-air sonar) is used for atmospheric investigations. The term ''sonar'' is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sea Trout
Sea trout is the common name usually applied to anadromous (sea-run) forms of brown trout (''Salmo trutta''), and is often referred to as ''Salmo trutta'' morpha ''trutta''. Other names for anadromous brown trout are sewin (Wales), peel or peal ( Southwest England), mort (Northwest England), finnock (Scotland), white trout (Ireland) and salmon trout (culinary). The term "sea trout" is also used to describe other anadromous salmonids, such as coho salmon (''Oncorhynchus kisutch''), coastal cutthroat trout (''Oncorhynchus clarkii clarkii''), brook trout (''Salvelinus fontinalis''), Arctic char (''Salvelinus alpinus alpinus'') and Dolly Varden (''Salvenlinus malma''). Even some non-salmonid fish species are also commonly known as sea trout, such as Northern pikeminnow (''Ptychocheilus oregonensis'') and members of the weakfish family (''Cynoscion''). Range Anadromous brown trout are widely distributed in Europe along the Atlantic and Baltic coasts, the United Kingdom and the coa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
