Abstract:
The inventive subject matter describes systems and methods for the remote placement of electrified fish barriers are illustrated and described herein. The inventive subject matter describes a floating electrical barrier that is responsive to the presence of detected fish. The inventive subject matter also describes a multiplicity of electrical barriers that are arranged to create an electrical field that entrains certain species of fish. The inventive subject matter also describes a movable barrier that is used to guide fish from location to location using electrical fields.

Description:
BACKGROUND 
       [0001]    The present inventive subject matter relates to the systems and methods for the remote placement of movable electrified fish barriers. 
         [0002]    The protection and preservation of natural resources includes the management of fish and game. Fish move about lakes, rivers, streams and reservoirs for a variety of reasons, including migration, spawning, and searching for food. 
         [0003]    Water intakes divert water for drinking, irrigation, and industrial uses. The introduction of fish into intakes is generally regarded as unwanted, and, in some cases, is expressly prohibited by federal government mandates such as the “Endangered Species Act” and the EPA “Clean Water Act.” Many rivers have  hydroelectric, fossil fuel and nuclear power plants with water intakes to the hydroelectric turbines and for cooling. It is desirable to keep the fish out of these intakes and away from dangerous conditions. Many large bodies of water are linked by inland waterways, including natural rivers and man made canals. Some of these bodies of water have diverse fish and wild life that are foreign to each other. Because migration across such natural divides can upset the ecological balance, government mandates often require that construction and use of such waterways incorporate a method or apparatus for controlling ecologically harmful migration through these waterways. As a consequence, all water diversions require governmental licenses and/or permits, and require periodic re-licensing. The water diversions must be upgraded to satisfy any changes in government regulations at the time of re-licensing. For these, and a variety of other economic, commercial, cultural and ecological reasons, it is often necessary to govern the migration and random motion of fish. 
         [0004]    As the need for governing the movement and migration of fish has been recognized, means for achieving this goal have also been developed. Electric fish barriers, such as described in U.S. Pat. No. 4,750,451 to Smith, have become a common and useful means for governing the migration and travels of fish in lakes, locks, rivers, dams, fisheries and other restricted or controlled areas. 
         [0005]    Furthermore, electrofishing barriers and techniques of electrofishing have also been used freshwater lakes and streams and are the subject of U.S. Pat. Nos. 5,445,111; 5,327,854; 4,672,967; 4,713,315; 5,111,379; 5,233,782; 5,270,912; 5,305,711; 5,311,694; 5,327,668; 5,341,764; 5,551,377; and 6,978,734 which are incorporated herein by reference. Also, electrofishing has been the used to stimulate yields of fishing in conjunction with the use of trawl nets as described in U.S. Pat. Nos. 3,110,978 and 4,417,301 which are also incorporated herein by reference. Systems for controlling electricity in aquatic environments have been described in U.S. Pat. No. 5,460,123 which is incorporated herein by reference. 
         [0006]    In electric fish barriers, an electrical irritation or shock is only felt by a fish when there is a voltage differential across the fish thereby driving an electrical current through a fish. Accordingly, the most significant factor in controlling the motion of fish is not the field strength, with respect to ground, where the fish is located, but the voltage gradient where the fish is located. Field voltage gradient is the rate of change in voltage of an electric field per linear measure. Although the instantaneous axis of the linear measurement can be in any direction, the maximum field gradient is measured across a unit length of a one dimensional line oriented perpendicular to the two dimensional surface representing an equipotential voltage plane. The instantaneous voltage differential across unit distance is thus the electric field gradient, or voltage gradient. The higher the voltage gradient, the greater the total voltage drop across a fish, and consequently, the greater the electrical current that will pass through a fish. 
         [0007]    Because a gradient times a linear distance equals a voltage potential, it can be understood that the longer a fish, the greater the total voltage drop across the fish. Similarly, because resistance is inversely proportional to the cross sectional area of a resistor, and because a large fish typically has a proportionally larger cross sectional area, the larger the fish, the lower the resistance of the fish. The size of a fish, therefore, affects the electrical current flow through the fish for several reasons as illustrated above. 
         [0008]    The maximum transfer of energy from water to a fish occurs when the fish&#39;s electrical conductivity matches the electrical conductivity of the surrounding water. In most circumstances, a fish&#39;s body is normally more conductive than fresh water. As a result, the fish&#39;s body acts as a “voltage divider” when swimming through fresh water, and the gradient of an electrical field in the body of a fish will typically be less than the voltage gradient in the same space filled by fresh water. That is, the voltage gradient is altered in a region proximate a fish in the zone of an electric fish barrier. Nevertheless, all other factors remaining equal, the voltage gradient in the body of a fish will be roughly proportional to the voltage gradient in the same region of fresh water when no fish are present. Accordingly, if the voltage gradient in a region of water is doubled, the voltage gradient across the fish (and the electrical current through the fish) will also double. The effectiveness of an electric fish barrier on a particular fish, therefore, depends on the voltage field gradient produced by the electric fish barrier. 
         [0009]    The voltage gradients in the region of water may be adjusted to cause a physiological reaction in the fish. If a voltage gradient in a region of water is too weak, the fish will not feel appreciable discomfort, and will travel undaunted by the electric fish barrier. An “annoying region” will cause a fish to turn around and travel the preferred route. Conversely, early experiments have demonstrated that if a moderately annoying region of the electric barrier is too narrow to allow a fish to turn around, then the rapidly swimming fish passes quickly through the “annoying” region and then into the “painful region”. The rapid transition from the annoying to the painful may induce large fish to react so violently in their attempt to change direction that they have actually snapped their own spine. As a result of these observations, an ideal fish barrier will normally have a wide region with a moderately annoying voltage gradient, increasing at a rate that causes increasing discomfort to fish of various sizes and species, but allowing ample room for a fish experiencing discomfort to turn around before passing completely through the annoying region and into a painful or lethal region. The awareness of the field gradient should, therefore, not be a sudden discovery, but a gradually growing annoyance. Whether a fish barrier is effective, ineffective or harmful is thus a function of the shape of the boundary, the thickness and the intensity of a voltage gradient produced by an electric fish barrier. 
         [0010]    The current passing through a fish depends on a variety of factors such as the conductivity of the water at both ends of the fish, the total resistance in a conductive path of water, and the size and species of a fish being repelled, etc. Typically, higher gradients are necessary to control the travel and migration of smaller fish, and lower gradients are effective for larger fish. The effectiveness of a particular strength gradient also depends on the species of fish, and whether the motion of the water reliably flows in a direction to orient the fish along the axis of the strongest gradient, which is perpendicular to the equipotential voltage plane. However, a voltage gradient of one hundred volts per meter has been observed to establish a good base-line voltage gradient for effectively and yet safely deterring average size fish from entering a prohibited area. It is understood that higher and lower voltage gradients may be appropriate according to a variety of factors. First, the electric field is generated fixed barrier that typically runs along the bottom of a riverbed. 
         [0011]      FIG. 1  illustrates a multi-stage fish barrier known in the prior art for regulating the traffic of fish in shallow waterways. According to this example, fish  9  within a waterway  10  seek to migrate up river (against the water flow), and the electric barrier is configured to direct them to an alternative route  11 . Five electrodes  13 - 17  rest on a substrate  12  within riverbed  10 . The five electrodes  13 - 17  separate the stream or river into four separate voltage gradient regions  18 - 21 . The electrodes  13 - 17  are advantageously formed from elongated members, such as cables or extruded bars. Although copper conducts electricity well, galvanic effects between copper and water can prematurely erode copper cables, requiring frequent replacement. Additionally, in water having a sulfur content, the ionized copper can form copper sulfate compounds in water, which can be poisonous to fish. For these reasons, a ferrous metal is usually preferred for forming the elongated members of the electrodes  13 - 17 , such as steel cables, beams, or railroad track segments. The elongated members  13 - 17  are oriented perpendicular to the direction of water flow, which, in most confined river areas, also creates a geometrically parallel orientation among the elongated members. 
         [0012]    The electrodes  13 - 17  of  FIG. 1  are arranged at one meter intervals, and the voltage levels are controlled such that the relative voltage between two electrodes is continually increasing. Electrode  13  is at a zero or ground potential, and electrode  14  is at a one hundred volt peak potential, so that the peak differential between electrodes  13  and  14  is a one hundred volt differential. Electrode  15  is at a three hundred volts peak potential, so that the peak differential between electrodes  14  and  15  is a two hundred volt differential. Electrode  16  is at a six hundred volts peak potential, so that the peak differential between electrodes  15  and  16  is a three hundred volt differential. Electrode  17  is at a one thousand volts peak potential, so that the peak differential between electrodes  16  and  17  is a four hundred volt differential. 
         [0013]    Since the distance between the electrodes  13 - 17  remains a constant one-meter, the voltage gradient in each region  18 - 21  is greater than the previous region. In region  18 , the gradient is one hundred volts per meter. In region  19 , the gradient is two hundred volts per meter. In region  20 , the gradient is three hundred volts per meter. In region  21 , the gradient is four hundred volts per meter. As a fish advances into a progressively higher voltage gradient, the electrical current passing through that fish increases proportionally. Through the multi-stage barrier of  FIG. 1 , fish of a size or species that are not annoyed by a lower voltage gradient will be progressively exposed to higher voltage gradients, eventually forcing all migrating fish to turn around and select the alternative path  11  in their upstream travels. Although the multi-step barrier of  FIG. 1  can be effective in a shallow stream, the incremental regulation of voltage gradients is not reliably formed by single-step or multi-step designs of the prior art in deeper water applications. 
         [0014]      FIG. 2  is a prior art cross sectional view of a stream or river nine meters deep, illustrating the equi-gradient field lines of an electric field produced by two elongated members  30 ,  31  on a riverbed. The direction of river flow is along the w-axis. The elongated members  30 ,  31  are separated by fourteen meters in the direction of river flow, and disposed at the bottom of a river  32 , perpendicular to the direction of flow. The conductivity of the river water is 500.mu. Siemens. A one kilovolt differential is generated between the two elongated members  30 ,  31 . 
         [0015]    As discussed above, the basic operational parameter of an electric fish barrier is the voltage gradient of an electric field, and a gradient of 100 volts per meter is a common benchmark for an operational system. If the field gradient between the two conductors  30 ,  31  were completely linear, one thousand volts over a fourteen meter range would produce a continuous gradient of seventy-one volts per meter. As the field gradient patterns of  FIG. 2  indicate, however, the field gradient is not uniform between the two conductors  30 ,  31 . A field gradient of sufficient strength must extend all the way to the surface to prevent passage of fish past the barrier. Because fish can travel on the surface where the gradient is weakest, the strongest gradient value to extend all the way to the surface is an important value for profiling the efficacy of a fish barrier. The strongest voltage gradient extending to the river surface in  FIG. 2  was measured at 25 volts per meter. On the bottom of the riverbed, near the conductive elongated members  30 ,  31  viewed end-wise, the higher field gradients more closely resemble concentric cylinders formed around the respective elongated conductive members  30 ,  31 . As one approaches the conductive members  30 ,  31 , the path leading to a conductive member  30 ,  31  is distinguished by a voltage potential that changes rapidly over distance, which equates to a high voltage gradient. 
         [0016]    Because effective blocking of fish from migrating up or downstream would require a minimum gradient of 100 volts per meter everywhere in a cross-sectional plane to the direction of flow of the river, calculations were performed normalizing the surface gradient at one hundred volts per meter according to the prior art design of  FIG. 2 . At this normalized value, the calculations disclose that a peak voltage difference of 4.032 kilovolts between the elongated members  30 ,  31  would be required to produce a surface gradient of one hundred volts per meter. At the level of 4.032 kilovolts potential between the elongated members  30 ,  31 , the electrical current produced by the normalized electric field pattern in a river nine meters deep and one meter wide would be 52.5 amps at a conductivity of 500 micro Siemens. Although certain fish species have shown a deterrent effect at a voltage threshold of 100 Volts per meter (1 V/cm), it has been observed that certain mammalian species may be deterred at a voltage threshold much less than 1 V/cm. For example California sea lions tested at Moss Landing Marine Labs are able to detect underwater DC electric fields of 0.14 v/cm at pulse frequencies of 2 Hz and pulse width from 80 to 290 μs (0.00008 to 0.00029 secs). The sea lions are apparently deterred when the field pulse widths are increased to an amount of approximately 320 μS. 
         [0017]    Likewise, Manatees, (e.g. marine mammals of the order Sirenia, also known as “sea-cows”) are believed to be affected by electric fields. These animals can be found in shallow waters, bays, canals and coastal areas. The manatee has a streamlined body, with two flippers and one paddle-shaped tail. Their true color is gray, although it may appear brownish gray. Adult manatees can grow up to 12 feet in length and weigh around 1,800 pounds. 
         [0018]    As shown in the prior art, a fixed electrical barrier is taught for the deterrence of certain fish and mammalian species. Whereas a fixed electrical barrier has certain advantages for the guidance and deterrence of certain fish and mammalian species, it cannot be positioned in a body of water to change the relative position of the field. 
         [0019]    Furthermore, is may be necessary to temporarily entrain fish or marine mammals in a specified locations due to changing conditions in that body of water. 
         [0020]    For marine mammals such as seals, certain voltage gradients in the water produce a deterrent effect where the marine mammal seeks to avoid the electric field. These levels are approximately 0.32 V/cm gradient, a pulse width of 1 millisecond, and a frequency of 2 hz (a duty cycle of 0.5%). At this voltage gradient and duty cycle, the marine mammal is deterred, but the local fish are apparently unharmed. The benefit is that lower voltage gradients are effective at deterring pinnipeds and do not affecting fish. Lower voltage gradients generally result in lower power dissipation in the water. In view of the lower power dissipation, the use of mobile barriers can be considered both practical and feasible in the deterrence of marine mammals. Therefore, what is desired is a floating apparatus that provides a electric field gradient to entrain marine mammals. The floating apparatus may be configured individually or in multiple units to provide field configuration. 
         [0021]    Furthermore, the units may be configured remotely and/or in response to schools of fish to automatically entrain fish in specific locations. 
       SUMMARY 
       [0022]    The present inventive subject matter overcomes problems in the prior art by providing for systems and methods for the remote placement of electrified fish barriers are illustrated and described herein. The inventive subject matter describes a floating electrical barrier that is responsive to the presence of detected fish. The inventive subject matter also describes a multiplicity of electrical barriers that are arranged to create an electrical field that entrains certain species of fish. The inventive subject matter also describes a movable barrier that is used to guide fish from location to location using electrical fields. 
         [0023]    These and other embodiments are described in more detail in the following detailed descriptions and the figures. 
         [0024]    The foregoing is not intended to be an exhaustive list of embodiments and features of the present inventive subject matter. Persons skilled in the art are capable of appreciating other embodiments and features from the following detailed description in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a prior art diagram of a graduated electrical field barrier. 
           [0026]      FIG. 2  is a prior art diagram depicting the electrical field intensity between fixed anodes and cathodes. 
           [0027]      FIG. 3  is a side view of an embodiment of the inventive subject matter with a single craft having an anode a cathode, and a pulsator. 
           [0028]      FIGS. 4   a  and  4   b  are top views of an embodiment of the inventive subject matter having two crafts each having a pulsator with an interconnecting electrical cable. 
           [0029]      FIG. 5  is a top view of an embodiment of the inventive subject matter depicting two crafts being positioned relative to a school of fish. 
           [0030]      FIG. 6  is a top view of an embodiment of the inventive subject matter depicting two crafts entraining fish such that the fish are guided from a spillway to a raceway. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Representative embodiments according to the inventive subject matter are shown in  FIGS. 1-6 , wherein similar features share common reference numerals. 
         [0032]    The term “aquatic animal” generally refers to an animal that lives in a conductive medium, including, but not limited to fish, mammals, and other species. 
         [0033]    The term “boat” is generally known to those in the arts as a large floating object capable of containing electronics needed to produce an electrical field as described in this application. The electrical field being dependent on the 
         [0034]    The term “electrical stimulation” refers to an electrical field impressed on the tissue of a fish in water. This electrical field will have a range in values that is dependent on the size and orientation of the fish. 
         [0035]    The term “entrainment response” refers to a physiological reaction by an aquatic animal to the imposition of an electric field on the body of the aquatic animal. The term “pulsator” shall mean a device that can output a range of voltages and currents in a waveform that is programmed either by hardwire switch (e.g., a pulse generator) or by software (e.g. a computer controlled voltage generator). A pulsator creates a voltage differential between the anode lead (e.g. first electrode) and the cathode lead (e.g. second electrode) when the first and second electrodes are inserted into a conductive medium (i.e. water). 
         [0036]    Now referring to  FIG. 3  which illustrates the side cross-sectional view of the floating electrified fish barrier  300 . The watercraft  310  contains a pulsator  320 , which is connected to a first electrode  330  and a second electrode  340 . The first electrode  330  and the second electrode  340  are placed proximate to aquatic animals, mammals and/or schools of fish  350 . 
         [0037]    The watercraft  310  floats on the surface of the water  360  which is inherently conductive. The pulsator  320  is connected to a remote control device  370  that can be used to control the pulsator  320  and/or the propulsion and steering mechanism  380  that is integral to the watercraft  310 . 
         [0038]    The watercraft  390  also has a fish finder  390 . The fish finder  390  can detect and/or characterize fish using acoustical (e.g. sound), optical, or electrical sensing techniques. The term “fish finder” should not be limited to a system that can locate only fish, rather, this term should be construed broadly to include not only fish, but, aquatic mammalian species, crustaceans, and swimming humans. 
         [0039]    Operationally, the watercraft  310  induces an electrical field  335  between the first electrode  330  and the second electrode  340 . The electrical field  335  is of a sufficient field strength to induce the desired effect on the subject species of fish. For example, certain salmonid species may exhibit the desired response to the electrical field  335  when the voltage gradient is 0.1 to 4.0 volts per in (0.1-4.0 v/in). This electrical field  335  can be generated by commercially available electrical generators, such as, the Smith-Root™ brand of electric field pulsators. By manipulation of the electric field, (e.g. the strength, the direction, and intensity), an entrainment response can be invoked in the target aquatic species. 
         [0040]    Additionally, the watercraft can be position proximate to groupings of fish (e.g. schools) such that the maximal effect of the electrical field can be induced on these schools of fish  350 . The positioning may be done manually via a remote control  370  or locally via a control unit  375  connected to the fish finder  390 . 
         [0041]    Now referring to  FIG. 4   a  which illustrates a pair of watercraft  305  interconnected by a connection cable  395 . In this configuration the electrical field  335  is generated between the first watercraft  310   a  and the second watercraft  310   b.  For example electrodes  340   a,    330   a  can be configured as the anode and electrodes  340   b,    330   b  c can be configured as cathodes. In this configuration, the field is present between the first watercraft and the second watercraft. 
         [0042]    As shown in  FIG. 4   b , is an alternate configuration involving the two watercraft  310   a , 310   b . The watercraft  310   a,    310   b  may be configured such that the electrodes  330   a,    330   b,    340   a,    340   b  define a perimeter around the watercraft  310   a,    310   b.  By energizing the electrodes in a rotating pattern (e.g.,  340   a (+)/ 330   a (−),  330   a (+)/ 330   b (−),  330   b (+)/ 340   b (−),  340   b (+)/ 340   a (−),  340   a (+)/ 330   a (−), etc.), the resultant field encircles objects within the perimeter. This electrical field creates, in essence, a “electrical fence” that can be used to entrain fish within the fixed perimeter. 
         [0043]      FIG. 5  depicts the entrainment and movement of fish using electrical fields. The watercraft  310   a,    310   b  start at a first location  410  with the electrical field energized to contain the fish  350  within the perimeter. As the watercraft  310   a,    310   b  moves to the second location  420 , the fish  350  are guided by the sensing of the increasing electrical fields. For example, as the watercraft  310   a,    310   b  move forward, fish  350  that are closest to the rear electrical field  405  will cause the fish  350  to be moved forward due the fish&#39;s  350  natural aversion to an electrical field. 
         [0044]    Now referring  FIG. 6 , the fish  350   a,    350   b,    350   c  are entrained and guided by the use of a moving electrical field. The fish  350   a,    350   b,    350   c  swim towards the water spillway  520 . At a point  510   a,  the fish  350   a  encounter the electrical field  335   a  created by the watercraft  310   a,    310   b,  and due to the electrical field the fish are repulsed away from the watercraft  310   a,    310   b,  and at the same time are forced towards the spillway  520  due to the natural force of the water. As the watercraft  310   a,    310   b,    310   c  moves, the fish are guide to an alternative water discharge point, for example a fish raceway  530 . 
         [0045]    As previously indicated, the watercraft  310   a,    310   b  may be guided by the use of onboard and/or remote fish detection devices, such as sonar, optical cameras, electrical fish detectors, and/or other detection mechanisms. 
         [0046]    Persons skilled in the art will recognize that many modifications and variations are possible in the details, materials, and arrangements of the parts and actions which have been described and illustrated in order to explain the nature of this inventive concept and that such modifications and variations do not depart from the spirit and scope of the teachings and claims contained therein. 
         [0047]    All patent and non-patent literature cited herein is hereby incorporated by references in its entirety for all purposes.