WO1998006256A1

WO1998006256A1 - Method and apparatus for electrically attracting aquatic animals

Info

Publication number: WO1998006256A1
Application number: PCT/US1997/013583
Authority: WO
Inventors: Donald H. Edwards; Charles D. Derby; Marc Weissburg
Original assignee: Georgia State University
Priority date: 1996-08-09
Filing date: 1997-08-11
Publication date: 1998-02-19
Also published as: AU4049897A

Abstract

A method and apparatus for attracting an aquatic animal to a trap (10) in a region of water in which the aquatic animal inhabits the trap (10), having an entrance (26) with two spaced-apart electrodes (36, 38) being placed adjacent the trap. An electric field (14) is generated between the electrodes (36, 38). The strength of the electric field (14) is within a range corresponding to a naturally occurring electric field that would be generated by a living organism of the type that would be likely prey for the aquatic animal being attracted, so as to attract the aquatic animal into entrance (26) of the trap (10).

Description

METHOD AND APPARATUS FOR ELECTRICALLY ATTRACTING

AQUATIC ANIMALS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to devices for attracting aquatic invertebrates and, more specifically, to devices for attracting aquatic invertebrates with an electric field.

2. Description of the Prior Art

Current methods of harvesting marine crustaceans (lobsters and crabs) and freshwater crayfish and leeches rely exclusively on chemical attractants (baits). Harvesting, as it is currently performed, accounts for most of the production cost of such aquatic animals. For example, in the crayfish industry, harvesting accounts for 60 to 80 percent of production costs. Crayfish are trapped in cages, and each cage is baited daily with 1/4 to 1/3 pounds offish. Currently, bait purchases account for over 40% of annual costs, whereas labor associated with harvest accounts for only about 20%.

Invertebrate marine fisheries for lobsters and crabs depend on baited traps that are scattered on the sea bottom and catch the animals that are attracted into the traps by the scent of the bait. Freshwater crayfish are similarly caught in baited traps placed in ponds where the animals are raised or in natural waters.

The ability to detect weak electric fields as a sensory capability has been known previously in vertebrates (e.g., sharks and rays, bony fish, urodeles, and monotremes). Recently, responses to weak electric fields have been found in an invertebrate, the crayfish Procambarus clarkii. Behavioral observations indicated that crayfish can detect dipole fields that are similar in intensity to fields produced by small freshwater animals.

There is an enormous fishery that relies on live spiny lobsters as bait. The spiny lobster fishery would benefit from the development of an inexpensive and effective attractant to be used in spiny lobster traps.

No device or method exists which uses an artificial electric field to simulate an electric field naturally given off by a living organism of the type that would normally be prey to an aquatic animal desired for harvesting. SUMMARY OF THE INVENTION

The disadvantages of the prior art are overcome by the present invention which is a method of attracting an aquatic animal to a trap having an entrance and an apparatus therefor. Two spaced apart electrodes are placed adjacent the trap in a region of water in which the aquatic animal inhabits and an electric field is generated between the electrodes. The strength of the electric field is within a range corresponding to a naturally occurring electric field that would be generated by a living organism of the type that would be likely prey for the aquatic animal being attracted, so as to attract the aquatic animal into the entrance of the trap. The invention also comprises an apparatus for attracting an aquatic animal to a trap having an entrance that includes two spaced apart electrodes disposed adjacent the trap and a circuit for generating an electric field between the electrodes.

In another embodiment of the invention, the apparatus includes an insulating member defining a cavity therein, a first electrode disposed within the cavity and a second electrode spaced apart from the first electrode. A circuit generates an electric field between the first electrode and the second electrode. The strength of the electric field is within a range corresponding to a naturally occurring electric field that would be produced by a living organism of the type that would be likely prey for the aquatic animal being attracted.

Three other embodiments of the present invention are all based upon an electric field generated by a battery enclosed in a plastic case and placed in a trap/cage made from a plastic screen. The designs differ in the location of the distal ends of the electrodes and, thus, the location of the maximum field. One embodiment has the electrodes projecting just outside the plastic case, but inside the trap; the next embodiment has them extending to the inside mouth of the opening of the trap/cage; and the other embodiment has the electrodes extending to the outside of the trap.

These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS FIG. 1 is a schematic diagram of an embodiment of the present invention.

FIGS 2, 3 and 4 are schematic representations of the second, third and fourth embodiments of the present invention which show the electric field in different positions relative to the trap entrance. DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: "a," "an," and "the" includes plural reference, "in" includes "in" and "on."

As shown in FIG. 1, one embodiment of the invention is a trap 10 for aquatic animals (shown) that includes an outer insulating member 20 that defines a cavity 23 therein. The insulating member has a non-conducting base portion 24 and a nonconducting cage 22 supported by the base portion 24 which is constructed of suitable wood or plastic material. A first electrode 36 is disposed within the cavity and a second electrode 38 is spaced apart from the first electrode 36. (The second electrode 38 could be disposed either within or outside the trap 10, depending upon the application.) A circuit schematically represented by the numeral 30 generates an electric field 14 between the first electrode 36 and the second electrode 38. The first electrode 36 is disposed so as to generate an electric field 14 having field lines converging adjacent the entrance 26 of the trap 10. The term "adjacent" may mean within or outside the trap 10 or the entrance 26. The strength of the electric field 14 is within a range corresponding to a naturally occurring electric field that would be produced by a living organism of the type that would be likely prey for the aquatic animal being attracted.

The trap 10 includes element 44 for supporting bait 12 adjacent the entrance 26 of the trap 10. The bait 12 is of a type that is attractive to the aquatic animal. The structure 44 could be any commonly used in baiting traps for aquatic animals. The first electrode 36 includes a conducting ring 40 disposed adjacent the bait supporting structure 44 so that electric field 14 lines converge adjacent the bait 12. Preferably, the negative pole of the electric field 14 converges nearest the bait 12. Alternately, the electric field 14 lines converge adjacent the entrance 26 to the trap. A conducting lead 42 electrically interconnects a battery 32 and the conducting ring 40 so that the conducting ring 40 is in electrical communication with the battery 32. As would be obvious to one skilled in the art, rather than using a battery, any electrical power supply could be employed to generate the electric field 14.

To attract aquatic invertebrates, the electric field 14 should have a strength in the range of from 50 microvolts per centimeter to 9000 microvolts per centimeter and preferably be about 100 microvolts per centimeter. The frequency of the current should range from D.C. to about 10Hz.

Figs.2-4 depict three more embodiments of the present invention in which a two-volt to nine-volt battery is placed in a conventional trap for aquatic invertebrates. The field generated by the battery attracts invertebrates in accordance with the invention, with the embodiments differing only in the location of the electrodes and, thus, the location of the maximum field relative to the entrance of the trap.

Figs. 2-4 illustrate a simple construction with a plastic-coated screen trap 100 having an entrance 126 defining a cavity 123 in which is disposed a bait 112 within a bait box or element 144. A battery 132 in the cavity 123 adjacent the bait 112 is positioned within a non-conducting plastic case 160. An uninsulated wire electrode 136 extends from the positive pole of the battery 132, through the case 160 into the cavity 123. A wire electrode 138 similarly extends from the negative pole of the battery 132. The energized battery 132 generates an electric field 114 between electrodes 136, 138 within the cavity 123.

In Fig. 3, the trap 200 has electrodes 236, 238 that extend into the cavity 223 and terminate adjacent to the entrance 226. The electrodes 236, 238 are formed of insulated wires, except for their bare metal tips at the distal ends thereof, and are attached to the respective positive and negative poles of the battery 232 to generate electric field 214.

Fig. 4 shows a structure similar to the embodiments of Figs. 2 and 3, except that the electrodes 336, 338 extend through the entrance 326 so as to generate the electric field 314 exteriorly of the trap 300.

In laboratory experiments with crayfish, it has been observed that field strengths as low as 100 microvolts/cm elicit local search and intense digging and grabbing behaviors at the electrodes. These behaviors are not seen in the absence of the field. The percentage of animals grabbing or digging increased with field strength to reach a level of about 80% at field strengths near 300 microvolts/cm. Animals were more sensitive to low frequency (1-4 Hz) than high frequency (10 Hz) stimulation. Observations indicated that the first two pairs of walking legs must be in close proximity to the electrodes for a response to be evoked. Initial physiological evidence suggested the presence of electrosensitive neurons in these appendages. Data from single unit extracellular recordings showed that the firing rates of some neurons were modulated when stimulated by dipole fields of 100-400 microvolts/cm. These responses show graded increases or decreases in firing rate with increasing field strength, and were sensitive to field polarity. This suggests that electrosensitivity in crayfish functions in a similar context to passive electroreception in order animals, namely as a way to locate cryptic prey. The following is a proposed experiment: A standard baited crayfish trap will be used and will consist of an insulated wire-mesh cone-shaped cage mounted on a wooden base. An interior cylindrical cage is placed inside the exterior cage which contains a platform to hold bait, and below that, a dry cell battery. One pole of the battery is connected to a wooden screw in the center of the wooden base and the other pole of the battery is connected through a wire to a metal ring at the top of the cylindrical cage. The battery and conducting leads are insulated so that the only exposed metal linked to the poles of the battery is the metal ring at the top of the interior cage and the screw exposed on the bottom of the wooden base. The battery will set up an electric field between the screw in the wooden base and the conducting ring, which is believed will attract crayfish at a distance by the bait odor and will follow the converging field lines to the entrance to the trap at the top, and then enter the trap to try to eat the conducting ring.

Crayfish (Procambarus clarkii) are sensitive to, and are attracted by, weak dipole electric fields which provide a new attractant for these and possibly other invertebrate animals to lure them into traps. This sensory capability has not previously been described for any invertebrate. Crayfish are attracted to weak dipole electric field sources (field strengths at least as low as 100 μ V/cm) which they then try to dig up and eat. Preliminary data also indicate that crayfish orient along the field lines to stronger sources and then move towards the sources from distances of 10 cm. As in vertebrates, this sense is useful to crayfish and other invertebrates in localizing hidden prey.

Laboratory experiments have also been performed on Caribbean spiny lobsters (Panulir s argus). This is a commercially important species that lives throughout the Caribbean, including the Florida Keys. Two types of laboratory experiments have been performed that indicate that spiny lobsters are electroreceptive. Animals were tested in 80-liter sea water aquaria. In the first experiment, a 2V battery was buried under the gravel in an aquarium containing spiny lobsters. The animals began digging at the batteries and pulled them from the gravel with their legs and mouth. In the second experiment, electric fields were produced using a spaced-apart pair of wire electrodes inserted into the gravel at the bottom of an aquarium. An approximately 4-Hz, 400 mV signal was applied across the wire leads. The animals responded to the wires with vigorous grabbing behaviors when the field was turned on. Their response was more intense than in the control condition in which the wires were present, but no electrical field was generated. The invention may be used to attract many types of marine animals. The ability to locate living, dying or recently dead animals suggests that this ability is likely to be found in a broad population of marine and freshwater invertebrates, including, crayfish, crabs, lobsters, annelids including medicinal leeches and earthworms, and perhaps mollusks, including octopus, squid, snails, clams and scallops.

Electrical dipole fields provide another, and potentially less costly and more effective, means of attracting animals of interest that possess an electric sense. Supplementing existing chemical attractants with an electrical attractant would provide an attractant that is more like normal prey, by giving off both chemical and electrical cues to its location.

A suitably designed device that provides an appropriate electrical signal to supplement the chemical signal would significantly increase the catch provided by the chemical signal alone. Such a device would create a low-level dipole electric field from a source inside a non-conducting cage that extends some distance outside the cage. The field source might be as simple as a battery encased in an insulating material with leads to a pair of electrodes near the entrance to the cage. The device might also include an oscillator circuit that would enable time-varying fields to be created that oscillate at the frequency preferred by the targeted species. Field strength for crayfish would be in the range of a few hundred to a few thousand microvolts/cm at 20 cm from the cage at frequencies from DC to 10 Hz. The field could also be supplemented by time-release chemical attractants suitable for the targeted species.

The above described embodiments are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.

Claims

What is claimed is:

1. A method of attracting an aquatic animal to a trap having an entrance, comprising the steps of: a. placing two spaced apart electrodes adjacent the entrance in a region of water in which the aquatic animal inhabits; and b. generating an electric field between the electrodes, the strength of the electric field being within a range corresponding to a naturally occurring electric field that would be generated by a living organism of the type that would be likely prey for the aquatic animal being attracted, so as to attract the aquatic animal into the entrance of the trap

2. The method of Claim 1, wherein the generating step comprises adjusting the electric field so that the electric field has a strength of 100 microvolts per centimeter.

3. The method of Claim 1, wherein the generating step comprises adjusting the electric field so that the electric field has a strength in the range of from 50 microvolts per centimeter to 9000 microvolts per centimeter.

4. The method of Claim 1, wherein the generating step comprises disposing a battery in the trap and connecting one end of each of the electrodes to a respective pole of the battery and placing the distal end of each electrode adjacent the entrance so that electric field lines produced at the distal ends of the electrodes converge adjacent the entrance of the trap.

5. The method of Claim 1, wherein the generating step comprises generating a direct current electric field.

6. The method of Claim 1, wherein the generating step comprises generating an electric field having a frequency in the range of from 0 Hz to 10 Hz. 7. The method of Claim 1, further comprising the step of placing bait adjacent an area near a pole of the electric field.

8. The method of Claim 7, wherein the pole is a negative pole. 9. An apparatus for attracting an aquatic animal to a trap having an entrance, comprising: a. two spaced apart electrodes disposed adjacent the entrance; and b means for generating an electric field between the electrodes, the strength of the electric field being within a range corresponding to a naturally occurring electric field that would be generated by a living organism of the type that would be likely prey for the aquatic animal being attracted, whereby the aquatic animal is attracted to the entrance of the trap when the electric field is generated

10 The apparatus of Claim 9, wherein the generating means comprises a battery

11 The apparatus of Claim 10, wherein the battery has two spaced apart terminals and wherein the electrodes are the terminals of the battery

12 The apparatus of Claim 10, wherein the battery ranges from a two- volt to a nine-volt battery

13 An apparatus for attracting an aquatic animal into a trap through the entrance into the trap, comprising a an insulating member defining a cavity therein, b a first electrode disposed within the cavity, c a second electrode spaced apart from the first electrode, and d means for generating an electric field between the first electrode and the second electrode, wherein the strength of the electric field is within a range corresponding to a naturally occurring electric field that would be produced by a living organism of the type that would be likely prey for the aquatic animal being attracted

14 The apparatus of Claim 13, wherein the insulating member comprises a a non-conducting base portion, and b a non-conducting cage supported by the base portion

15 The apparatus of Claim 14, wherein the electric field generating means is disposed so as to generate an electric field having field lines converging adjacent the entrance 16 The apparatus of Claim 13 , further comprising means for supporting bait of a type that would be attractive to the aquatic animal adjacent the entrance of the trap

17 The apparatus of Claim 16, wherein the first electrode comprises a a conducting ring disposed adjacent the bait supporting means so that electric field lines from the electric field generating means converge adjacent the bait, and b. a conducting lead electrically interconnecting the electric field generating means and the conducting ring so that the conducting ring is in electrical communication with the electric field generating means.

18. The apparatus of Claim 13, wherein the electric field generating means comprises a battery.

19. The apparatus of Claim 13, wherein the electric field generating means comprises an electrical power supply.

20. The apparatus of Claim 13, wherein the second electrode is disposed within the trap.

21. The apparatus of Claim 13, wherein the second electrode is disposed outside the trap.

22. The apparatus of Claim 13, wherein the second electrode is disposed adjacent the insulating member.

23. An apparatus for attracting therein an aquatic animal, comprising: a. an insulating member defining a cavity therein and having an entrance communicating the cavity with the exterior of the member; b. a battery disposed within the cavity, the battery having two spaced apart terminals; c. an electrode extending from each terminal and terminating at a tip exteriorily of the member, each electrode being insulated except for the tip so that when the battery is energized, an electric field is created between the tips, the strength of the electric field being within a range corresponding to a naturally occurring electric field that would be generated by a living organism of the type that would be likely prey for the aquatic animal being attracted, whereby the animal is attracted by the electric field to the entrance of the member.