The
Air Sweep, -
A Fish Herding Tool
Field of the Invention:
"The present invention
relates to a mechanism to herd fish. Its intent is to motivate fish to
move in a predetermined direction.
Background of the Invention
Work by others:
Air curtains are used as components
of different types of fish movement dissuasion/diversion devices. These
include both light, electric fields, and sound.
Air Curtain with Sound:
U.S. Patent 5,730,086
describes a sound based deterrent system that refers to air curtains as
an ineffective substitute. Text from the background in his patent follows:
Sound is an additional means of modifying the behavior of fish. An
overview of the current state of the art sound deterrent systems is provided
in Carlson, T. J. 1994. Use of Sound for Fish Protection at Power Production
Facilities: A Historical Perspective of the State of the Art. Battelle,
Pacific Northwest Laboratories. U.S. DOE Bonneville Power Administration,
Portland, Oreg.
See also the BioAcoustic Fish
Fence (BAFF) system at www.fish-guide.com.
The BAFF is used to divert fish from a major flow, e.g. entering a
turbine, into the minor flow of a fish pass channel. It may be regarded
as analogous to a conventional angled fish screen. It uses an air bubble
curtain to contain a sound signal which is generated pneumatically. Effectively,
this creates a "wall of sound" (an evanescent sound field) field
that can be used to guide fish around river structures by deflection into
fish passes.
Air curtain with Light:
Lights – usually underwater
strobes are used to repel fish from inlets at hydropower dams. In U.S.
Patent 5,850,806, an air curtain is used to assist strobe lights to repel
fish. Specifically: 5,850,806 The system may include
means to generate an air curtain near the flash heads to improve light
dispersion and water jet means to clean the lenses on the flash heads.
… In addition, an air bubble curtain and water jets installed at
or near the flash head allow the system to adapt to changing water conditions
and fish varieties so that the system can be easily optimized for a particular
environment.”
Identically in the related
patent 5,937,791 the air curtain is again used to assist the lights. The
system may include means to generate an air curtain near the flash heads
to improve light dispersion. A study of this use is described at:
http://www.glec-online.com/gl03059.htm.
A typical application of strobe lights with air curtain support is described
by a vendor Smith-Root at: http://www.smith-root.com/barriers/strobe_lights.html
.
Herding with air curtain
only
A herding effect similar to
what is proposed here has been observed in a tank in the following reference:
Fish herding effect by air bubble curtain in a large circular tank.
Akiyama S., Arimoto T. in Inoue M, Nippon Suisan Gakkaishi 58(1): 45-48
Jan 1992.
This article (AA) and earlier
similar studies by were in a toroidal tank. Fish were driven around a
tank by being repelled from of walls pf bubbles that were emitted sequentially
from a series of radial tubes on the bottom of the tank. When there was
a net at the end of the tank, the experiment was 100 percent successful.
When a curtain of air was substituted for the net the ability of the holding
the fish between the two air curtains dropped to about 60 %.
This patent application us
similar to the AA work in that we are using air curtains that are moved
from one pipe to another somewhat parallel giving the impression of a
moving wall of air to influence fish.
This patent application differs
from that work in two ways: Alternative interaction modes and number of
walls.
Alternative Fish/Wall interaction
First, the interaction with
the bubble wall is not specified as repulsion as it was with the AA articles.
Our technology uses two other interactions with a bubble wall. First fish
locate on the bubble wall as a way to locate or navigate. Thus if the
wall moves, the fish will move with the moving wall. Not because it is
repelled from the wall as in the AA wall, but rather because the fish
locate on it passively as they would locate on a rock or the streambed
to station keep in a stream.
Second, fish are attracted
to bubble walls for a number of reasons that are perceived by scientists
as curiosity, and more clearly, cover. Thus the original art of moving
fish through simple repulsion from an air curtain is extended in this
work by a adding other modes of interaction specifically attraction and
visually locating on.
Number of walls:
Second, the AA work there is only one wall of bubbles. In field situations,
any one wall of bubbles may not be as effective as multiple walls made
up of one or more sets of sub walls for two different reasons. First the
use of multiple walls simply provide repeated treatments from one or more
walls so that the effect is repeated again and again from repetitive moving
walls. This is important in that the field efficacy of any one wall may
be small, but with multiple hits the use of multiple walls will effectively
influence more fish through repeated treatments, so the whether the wall
is effective on any one pass is greatly reduced. The use of multiple walls
produces an effective system where a single wall would be deemed ineffective.
If the walls are near each
other, the fish may relate simultaneously to both walls especially as
it locates itself in the hall-like space between them. Thus the movement
of both walls forming a side moving hall like space is qualitative different
from the effects of a single wall. Not only because of the multiple hits,
but separately because fish will locate within a serried of walls differently
than they may respond to a single wall.
Thus compared to the Japanese
work, this technology: uses three modes of interaction with any bubble
curtain, as opposed to one, It also addresses the use of multiple curtains
for both the repetitive effect and for the Hall effect of relating to
or locating on multiple walls at the same time.
In summary, the fish management
industry’s use of air curtains, or sound, lights, or electric fields
in combination with air curtains for that matter is limited to almost
exclusively used to repel fish. AA is the only human example of using
air curtains to herd fish.
Finally, humpback whales working
together will dive under schools of herring. One or more whales will swim
in a circle while blowing bubbles under the herring. When the bubbles
rise they form a bubble-curtain and a poor acoustical reverberation chamber.
At depth, the whales then make loud noises which bounces of the bubble
curtain scaring the herring into a tight ball in the center. The whales
then come up through the middle with their mouths open, capturing large
amounts food. This invention differs from that behavior in that we are
moving the air curtain as a herding mechanism, not using it in any manner
as a containment device for either fish or sound.
List of Figures
Figure
1. Typical bubble tube array in a plan view of a water body.
Figure 2: Fish
Localizing, and interacting with the bubble curtains - a Profile view.
Figure 3: A Preferred
embodiment - Necklace Formation
Figure 4.: An Alternative
embodiment – A Barrier formation
Figure 5: An Alternative embodiment – V Formation
Object of the Invention
The object of the invention
is to use repetitive patterns of air curtains to herd fish in a preferred
direction or to a preferred point in open field conditions. This is accomplished
by having them interact with patterns of bubble curtains emitted from
combinations of multiple stationary tubes below the fish, then moving
the pattern. When the pattern moves, the fish relating to this pattern
will move along with the pattern. By controlling the direction of the
pattern movement it is possible to herd fish in a given direction. Only
a percentage of the fish will interact with any part of the pattern. It
is a related objective to use a repeated structure in the pattern –
such as a series of curtains to have a repetitive effect on the fish increasing
herding effectiveness.
In the context of the fixed
array or tubes, there will be a controller that will generate the patterns
through controlling which tubes emit air. In the context of the tubes
and controller there will be an air compressor to supply required air.
Summary of the Invention:
This invention uses multiple
air bubble curtains, which fish relate to, or locate on, to move fish
by moving the air curtains. Fish can be induced into moving in a predetermined
direction by slowly moving a pattern of air curtains. The preferred realization
shown in Figure 1 is comprised of a compressor 1 on the bank and bottom
4 of a body of water 6 supplying air through a controlled set of valves
2 to an array of tubes on or near the bottom of said body of water. Air
is released in patterns from active tubes 8 when the valves permit. The
air pattern is moved by shifting the air emission from the one inactive
tube 9 to another adjacent tube. The fish 5 interact with these air bubble
curtains. Under program control the pattern can be shifted and some of
the fish will move with the pattern.
Figure 2 shows a section view.
The proposed mechanism is to create an air curtain pattern 7 that appears
stationary to fish 5, but the pattern actually moves by slowly moving
the air emission from one active tube 8 tube air to the next inactive
tube 9 to the next etc. to make the apparent wall of air bubbles appear
or feel stationary to the fish but actually move slowly in a direction
at an angle to the tubes releasing the air.
The invention consists of a
plurality of tubes 8 and 9 to create a pattern of air curtains that through
their sequential operation will move fish because the resulting air curtain
will be perceived by the fish 5 as stationary. Fish relate to, interact
with, or locate themselves 5 on the air curtains 7. By slowly sequencing
which tube is emitting air 8 we can induce the fish into thinking they
are interacting with stationary air curtains, but through sequential operation
of the tubes the wall will be emitted form first one then the next then
a thereby inducing fish to move in a preferred direction. Figure 4 shows
the moving curtain pattern can emanate from a space 10 where it is desired
to preclude fish. The patterns moves out from 10 into the water body 6.
This becomes a barrier device, with any one air curtain having minimal
effect, but the sequence of many curtains having significant efficacy.
For example, to move fish to
an entrance to a fish passage at 3 in Figure 1, large necklace-like ellipse
shaped of rings of leaky air hoses would be placed on the bottom over
an area about 70 fish lengths in dimension. The hoses would be tangent
to the entrance of the fish passage. Air would be pumped into the outer
ring. After a while air would be pumped into the second outermost ring.
Then air would be reduced in the outer ring. Next air would be slowly
turned on in the third most outermost ring , while it is diminished in
the second most outermost ring, and cut off in the outer ring. Next air
would be slowly turned on in the fourth most outer ring, diminished in
the third most outer ring, and cut off in the second most outer ring.
This slowly moving example
pattern will move fish interacting with the bubble curtain inward toward
the target fish passage. This might continue for say 23 rings then the
pattern could be augmented with a second air curtain starting again at
the outer ring. Thus with 48 tube rings, two patterns would always be
present in this example. In practice the number of active rings and speed
of movement, and pattern shape would be determined by fish response, visibility
and current conditions.
“Tubes” are defined
here as conventional tubes, hoses, pipes, or patterns of emission from
a structure or substrate, plate or field that resembles tubes that leak
air in a linear or near linear fashion more or less continually along
their length. They are placed at a depth near or below the target fish
– typically on or in the bottom of the water body.
“Fish” are here
defined as individual fish, many fish, schools of fish, or one or more
crustaceans.
“Parallel” in this
application refers to geometrically parallel, near geometrically parallel,
or long non-intersecting straight or curvilinear configuration.
An air curtain is defined as
a bubble of air released from tubes underwater.
Description of a Preferred
Embodiment:
Figure 1 shows the preferred
embodiment as an array of necklace like non-overlapping loops that have
a common tangent point. Fish will be driven slowly to this tangent point
by sequentially putting air into the outer ring followed by an adjacent
inner ring, then another adjacent inner ring, in sequence adjacent inner
rings thereby gently herding the fish toward Point A in Figure 1. The
process of sequentially aerating ring after ring moving the apparent wall
slowly toward the desired point. There may be one or more activated rings
active at a time forming what is perceived by the fish to be moving walls
in a stationary hall with walls formed by consecutive air curtains. The
invention counts on the fish not perceiving or not caring that the walls
of the hall slowly move toward Point A. This embodiment may be useful
to direct fish toward a bypass facility for fish at a dam, or alternatively
to a netting or capture point.
In view of the many possible
embodiments to which the principles of my invention can be put, it should
be recognized that the detailed embodiment is illustrative only and should
not be taken as limiting the scope of my invention. Rather, I claim as
my invention all such embodiments as may come within the scope and spirit
of the claims and equivalents thereto. An alternative embodiment would
have the air curtains emanating from a point or area that want to be protected
from fish presence. This is shown in Figure 4.
Another alternative embodiment
shown in Figure 3. The moving curtains 7 rising from the active tubes
intersect in a series of V formations. The V appears stationary to the
fish, but in fact, moves slowly herding the fish up away from the apex
of the V. This would be useful for herding fish through a channel in a
larger body of water. Clearly this could be used in reverse slowly inducing
fish to move away from the axis of the V.
From the foregoing, it is apparent
that the present invention is effective in herding fish in any direction
at right or steep angle to angle to the tubes, and provides numerous advantages
over the prior art. Having illustrated and described the principles of
my invention with reference to a preferred embodiment, it should be apparent
to those skilled in the art that the invention can be modified in geometry,
arrangement, and detail without departing from such principles. For example,
while the invention has been illustrated with reference moving fish to
a point, it will be recognized that other tube arrangements can alternatively
be used to move fish slowly in other patterns. Similarly, while the invention
has been disclosed with reference to parallel arrays of tubes and thus
air curtains, it will be recognized that certain principles thereof are
equally applicable to other intersecting or non-intersecting
In view of the many possible
embodiments to which the principles of my invention can be put, it should
be recognized that the detailed embodiment is illustrative only and should
not be taken as limiting the scope of my invention. Rather, I claim as
my invention all such embodiments as may come within the scope and spirit
of the claims and equivalents thereto.
Theory of the invention:
Fish guidance is a rich field
of endeavor both to attract fish for capture and to repel fish from harmful
engineering structures. This invention uses two behaviors of fish to move
fish, first, interaction with a bubble curtain, and second, fish locate
themselves relative fixed objects so as to station-keep or navigate in
a current.
First: Behavior Interaction with Bubble Curtains – many small rising
bubbles from small pipes or linear leaky tubes influence some fish behavior
through avoidance of such as was documented in the AA approach cited above,
attraction to, locating on, or as a protective cover.
Avoidance: When used as a fence, the efficiency of this mechanism as a
fish trespassing inhibition device in the field, may be fair to poor –
depending on the species. However, the avoidance of the bubble curtains
– or the fence function of the air curtain is not generally zero
as has been demonstrated in the AA article cited above. Thus, if the air
curtain could be moved, some fish would move to avoid it. Since this behavior
has been documented, it is not part of this patent.
Attraction: At times, fish,
are attracted to bubble curtains and appear to play with it. Again, if
they play with the curtain and it moves, or appears to the fish to move,
the underlying theory of this invention suggests that they would move
with the curtain.
Cover: Fish often interact with irregularities in water space boundaries
for reasons of perceived protection, cover, or other unknown reasons.
Predation avoidance is a component of fish behavior. This device uses
the cover seeking and cover providing aspects of a bubble curtain to herd
fish.
Thus, any interaction with
the air curtain may allow for movement of the fish if the air curtain
or curtains can be moved without changing the interaction behavior between
the fish and the moving air curtain.
Second: The Optomotor Response.
The optomotor response refers to the maintaining of a position relative
to a moving visual stimuli. Here the moving visual stimulus is the slowly
moving air curtain. Fish, or fish schools, locate themselves in the water
by references to visual objects that the fish taken as fixed otherwise
it would be moved downstream by the current. This station-keeping or navigation
relative to a moving visual stimulus is called the Optomotor response
and has been documented since the 1930’s. It has been demonstrated
repeatedly in the academic literature, see for example, Sherer and Harrison,
1979, The optomotor response test in Toxicity for Freshwater Fish,
Scherer, E. Ed. Canadian Special Publication Fisheries Aquatic Science,
44, 179, 1979.
Normally, the visual cues are
stationary objects in a fish’s environment such as rocks, bottom
irregularities, walls, and similar fixed objects. This invention counts
on the Optomotor response (also called the optokinetic response) inducing
the fish to locate themselves – whether navigating or station keeping
relative to a bubble curtain that appears and or feels stationary to the
fish. The bubble curtain is created to act as a strong visual and perhaps
pressure cue that the fish will perceive as stationary. The underlying
theory of this invention is that they would continue to locate themselves
relative to one or more bubble curtains if the curtain is moved slowly
enough.
Schooling: The optokinetic
function may be related to schooling behavior. The curtains will allow
for schools on one side of a curtain to be clearly defined, however a
curtain will make the schooling behavior more difficult if the fish cannot
see or feel their neighbors. Thus, it is expected that the location function
will work indirectly through schooling behavior as the fish school positions
relative to one or more air curtains.
So the two different responses
to an air curtain can be used – interaction and locating. Assume
that the air curtain emanates from a plurality of nearly parallel tubes
that are sufficiently close together. This invention moves the apparent
bubble curtain by slowly shifting the air-flow for the bubbles from one
tube to a second and on to a third in a pattern or patterns. Assume that
the shifting pattern moves between tubes that is slow enough so that the
air curtain emanating from the tubes appears or feels stationary to fish.
If the fish are interacting with, or locating themselves relative to the
air curtain, then they will move as the air curtain moves. The fish may
relate to more than one wall at a time. The fish between multiple patterns
may be influenced by the multiple bubble curtains in the same way they
might locate on more than one rock, or be hidden by more than one wall
at the same time.
The curtains are expected to
be sequential with the spacing and speed of apparent movement to be determined
in the field. Each curtain may have air come up from more than one set
of tubes. The tubes are expected to be very roughly parallel on any flank
as seen by the fish, but may actually be shaped to move fish in a particular
direction or to a particular point.
Inefficiency: It is assumed
that the bubble curtain will affect only a percentage of the fish or fish
schools. Some literature such as the AA paper suggests that this could
be as high as 100 % addressing the avoidance behavior alone for some species
in a quite academic test setting. This invention is different from the
single sweep of the AA experiment. It will work well with only a few percent
of the fish responding. Since there are almost no moving parts in the
invention other than some land based air valves 2 and compressor 1, the
patterns can be swept again and again at only the cost of the compressed
air. Assuming the moving bubble patterns were 1 % effective at motivating
each fish, then if one pattern per minute were used to sweep an area,
then two thirds of the fish would be moved in two hours. Clearly fish,
or even fish schools, do not move independently, nor is sequential response
of the same fish expected to be independent. This is not a Markovian system,
however, it is clear that with this device, low response rate per sweep
does not preclude efficacy.
Claims:
I claim:
- A new method of herding
or guiding fish in open water including generating a series of parallel
air curtains air from tubes on the bottom, and by controlling the pattern
of air emissions from these tubes so as to induce fish to move in preferred
direction at a steep, or right, angle to the air curtains.
- The method of claim 1 in
which the air curtains moving at the fish to act as a repetitive deterrent
to the fish crossing the curtains to an exclusion zone or point.
- The method of claim 1 except
that the pattern of the tubes is not parallel, but intersect so as to
induce fish to move in a direction between or among intersecting air
curtains along a path formed by the loci of the intersections.
- The method of claim 3.
except that the air curtains move out from an intersection so that fish
are induced to move away from a central area between the intersecting
curtains.
Patent Abstract
This invention is the use
of multiple, similar, air curtains that are used in patterns to move
fish by moving the pattern. As the pattern moves, the fish follow for
various reasons, such as attraction, behavior interaction such as play
or hiding, and optokinetic navigation on the moving air curtain. The
moving pattern is repetitive so that if one pattern does not motivate
a particular fish, it might be influenced by the next. The repetitive
moving patterns continues indefinitely slowly, statistically, sweeping
the fish in a particular direction. This device uses a very low response
rate of fish response to produce a steady sweeping of fish in a particular
direction or to a particular point.
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