Fishing – trapping – and vermin destroying – Fishing – Nets
Patent
1996-06-20
1998-08-25
Price, Thomas
Fishing, trapping, and vermin destroying
Fishing
Nets
A01K 7302
Patent
active
057972109
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an apparatus for electro-fishing comprising bottom at a distance in front of the net, operation a pulsed electric field in the water.
BACKGROUND OF THE INVENTION
Apparatuses for electro-fishing of the above-described type are already known from various patent publications. The attention is drawn for example to U.S. Pat Nos. 3,483,649, 3,491,474, 3,110,978, 3,777,388, 4,417,301, 5,111,379, and 5,233,782.
In the apparatuses described in U.S. Pat Nos. 3,483,649 and 3,491,474, the electrodes are embodied as a number of not insulated electrical conductors which are positioned in front of the trawl net over the full width thereof and mutually parallel.
The electrodes which are applied in the apparatuses described in U.S. Pat. Nos. 3,777,388 and 4,417,301 consist of a number of elongated not insulated electrical conductors, which, mutually parallel, extend in the trawling direction, i.e. perpendicular to the front edge of the trawl net. Also in this case all anode conductors and all cathode conductors are powered simultaneously by the pulse generator.
The use of relatively long, mutually parallel extending non insulated electrical conductors as electrodes has a number of disadvantages. In the first place sea water is well-conducting. It may be expected therefore, that the total impedance, which in such an embodiment of the electrodes is connected to the pulse generator, is relatively small with the result that the pulse generator has to produce relatively large current pulses to realize the desired field gradient between the electrodes. A further disadvantage is encountered in the fact that the field strength varies along the length of the electrical conductors, near the pulse generator the field strength will be high and as the distance increases the field strength will decrease. Therefore, a field with the same strength will not be generated everywhere and as a result thereof the fish, which are on or in the bottom, will not everywhere receive the same stimulation.
The electrodes which belong to the apparatus as described in U.S. Pat. No. 3,110,978 comprise one or more anode-components and one or more cathode-components. Irrespective of the number of elements all electrodes are simultaneously powered from the pulse generator. In this publication no details are provided about the embodiment of the electrodes themselves. The use of separate electrode components in this apparatus has not resulted in a decrease of the power to be supplied. In this publication pulses with a peak voltage of 700 V and a peak current of 10,500 Amp are mentioned. To be able to switch such voltages and currents the switching elements in the pulse generator have to fulfil very high requirements.
In the U.S. Pat. Nos. 5,111,379 and 5,233,782 no details are provided about the electrodes, although an embodiment of the pulse generator is considered in more depth. Especially a pulse generator is described destined to supply pulse trains with a number of relatively high frequency pulses, which pulse trains are provided in a relatively low frequent pace to the electrodes. Furthermore, these publications consider in more depth the relation between the strength of the generated electric field and the influence thereof on the fish arriving in said field. Not only the field strength as such is of importance, also the steepness of the pulses, used for generating said field, has influence on the reactions, evoked in the fish.
SUMMARY OF THE INVENTION
The object of the invention is now to provide an apparatus which is specially destined for at least temporarily anaesthetizing or stunning the fish, arriving in the generated field and using therefore a pulse generator with a relatively restricted power output.
In agreement with said object the invention now provides an apparatus as described in the first paragraph, which is characterized in that conducting bodies, each through a separate connection cable connected to said pulse generator, whereby the water contacting surface of each electrically cond
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patent: 3491474 (1970-01-01), Metcalf
patent: 3777388 (1973-12-01), Newman et al.
patent: 4417301 (1983-11-01), Newman
patent: 5111379 (1992-05-01), Sharber et al.
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