Animal husbandry – Aquatic animal culturing – Fish culturing
Reexamination Certificate
1999-09-02
2001-01-09
Carone, Michael J. (Department: 3643)
Animal husbandry
Aquatic animal culturing
Fish culturing
C043S009200, C043S009600, C043S017100, C367S139000
Reexamination Certificate
active
06170436
ABSTRACT:
This invention relates to methods of and apparatus for reducing or avoiding the by-catch of marine mammals during fishing operations.
Nets, especially gill-nets, are essentially large transparent diffuse structures and difficult to perceive for dolphins and other small cetaceans, though fish trapped in such or behind nets can be detected by the animal's sonar, and the animal's pursuit of prey may result in its own entrapment in the net. This by-catch is problematical especially where a species is already endangered or where mortality rates are recognised as excessive. In this context harbour porpoise by-catch in bottom set gill-nets is a particular problem.
Various measures have been suggested and some even tried to prevent or reduce such by-catch. The methods fall into two categories
i) Passive enhancement of the acoustic reflecting properties of the net.
ii) Active acoustic alarms or beacons intended to warn or scare away the animals at risk.
Category i) passive experiments involving modification of the net fibre material or the addition of assorted materials, i.e. ‘bead chain’ attached to the structure have shown very little benefit.
Category ii) active devices may be treated as low power beacons or alarms which act as ‘lighthouses’ to mark the position of the net obstruction or as very high power acoustic harassment devices (AHDs) which are intended to create an uncomfortable exclusion zone immediately surrounding them. AHD devices with source levels which may approach 210 dB re 1 &mgr;Pa at 1 m in seawater, are typically applied to protect static fish farm facilities from pinniped predation and may require an electricity generator or a direct connection to shore power.
To be cost effective, deterrent devices must be inexpensive both to deploy and to run, and they must remain effective for reasonable periods of time. Active devices require very high electro-acoustic efficiency to maximise their operating life on batteries (and minimise the down-time needed for battery replacement). However, effectiveness must also take into account the rate at which animals may habituate to, learn to ignore or take advantage from the emitted sounds.
Active ‘pinger’ beacon or alarm devices typically comprise a waterproof pressure housing attachable to the net which contains a power source (usually conventional dry cells) and an acoustic signal generator, typically generating a ‘ping’ around 10 kHz with an acoustic output around 120-140 dB re 1 &mgr;Pa at 1 m in seawater. The frequency is chosen to be audible to the cetacean but inaudible to the fish. However, the long term effectiveness of this approach is unknown.
The present invention, however, provides methods and devices having significant advantages both from a cost-effectiveness point of view and from the point of view of their absolute effectiveness in deterring specific marine mammals or alerting them to the nets so that they are able to avoid them.
The invention in one aspect comprises a method for reducing or avoiding by-catch of marine mammals during fishing operations using nets comprising disposing on or in relation to the nets a series or array of acoustic devices which emit a deterrent signal appropriate to a particular marine mammal on actuation by the approach of the mammal in question.
The acoustic devices may comprise active sensors that detect marine mammal emitted stimuli and respond with a suitable response emission. They may be arranged so as not to be triggered by their own back-scattered emission, and, further, arranged each to trigger an adjacent device to produce a ripple-effect response to a detected marine mammal stimulus.
The response emission may include acoustic emissions at different frequencies, which may be emitted at different times during a single emission period (e.g. by ramping a single frequency up or down over a period) or at the same time (e.g. by emission of multiple tones or harmonics).
Different response emissions may be emitted depending on the detected marine mammal stimuli. The devices may emit different responses from a set of stored responses, and may emit more than one response from the set in response to a particular stimulus.
The devices may detect the effect of response emission and adapt the emissions so as to improve or optimise their effect. The devices may for example detect reduction in emitted stimuli, such reduction reinforcing selection of particular response emissions that effect such reduction.
It is also possible, however, to use passive devices, comprising discrete acoustic reflectors capable of returning an echo directly back towards an echolocating marine mammal. The unsatisfactory passive devices tested to date have utilised materials with cross-sections significantly smaller than the shortest wavelength of the ensonifying signal transmitted by the marine mammal. In such cases the incident energy is scattered inefficiently or directed away from the animal. According to this invention discrete passive reflectors have minimum cross-sections exceeding 3 times the short wavelengths exploited by echolocating small cetaceans and are constructed with a shape which ensures that significant echo energy is returned directly towards the animal.
An ellipsoidal deep water net float, designed with a suitably shaped air cavity, has the required target strength characteristics, i.e. its echoes must appear slightly ‘brighter’ than those from the largest fish sought as prey by the cetacean at risk, but according to the invention, must be deployed with its long axis in the vertical plane and be disposed in a series or array in which their acoustic properties, rather than the flotation properties, are utilised. In addition these floats are modified to have neutral buoyancy so as to produce least distortion to the geometry of the net to which they are attached. Further, the internal air cavity of the float has an acoustic resonance selected to provide a spectral echo ‘signature’ when ensonified which is detectable to the animal and very uncharacteristic of a typical prey echo. This resonant acoustic signature can also be stimulated by suitable signals emitted by active alarm devices and hence extend the influence of these.
The invention also comprises an acoustic device adapted for attachment to a fishing net and comprising a detector for detecting acoustic signals and a transducer for emitting acoustic signals and signal generating means adapted to generate signals for emission by the transducer and control means adapted to cause the transducer to emit signals on detection of a signal by the detector.
The signal generating means may be programmable to generate pre-selected signals, and may generate Morse code.
The device may comprise device condition monitoring means and be adapted to emit condition information.
The device may be adapted to emit on detection of an echo sounder signal and/or a coded interrogation signal.
The device may comprise an immersion sensor, which may be a capacitative sensor, and which may condition the emission of signals by the device.
The device may be a device which is primarily adapted to emit warning or deterrent signals to marine mammals, and may be one adapted to detect marine mammal emitted signals and respond with a suitable response emission.
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Goodson Anthony David
Newborough Darryl
Woodward Bryan
Bradley James E.
Carone Michael J.
Felsman Bradley Vaden Gunter & Dillon, LLP
French III Fredrick T.
Loughborough University Innovations Ltd
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