FIELD OF THE INVENTION The invention relates to the control of undesirable aquatic organisms, in particular to the use of acoustic signals to induce lethal lesions in sensory organs of the organisms.

BACKGROUND OF THE INVENTION

A number of aquatic organisms are in various situations deemed undesirable. Examples of such organisms include parasites, pathogenic organisms, invasive species, blooms of native aquatic species and the like.

1. Invasive aquatic alien species

As used herein, the term "invasive aquatic alien species" are animals and plants that are introduced accidently or deliberately into a natural environment where they are not normally found, with serious negative consequences for their new environment.

(http://ec.europa.eu/environment/nature/invasivealien/ind ex_en.htm)

Invasive aquatic plants are introduced plants that have adapted to living in, on, or next to water, and that can grow either submerged or partially submerged in water. Invasive aquatic animals require a watery habitat, but do not necessarily have to live entirely in water.

(https ://www.invasivespeciesinfo .gov/ aquatics/main, shtml) .

Example: Apple Snail (Pomacea insularum)

2. Bloom of aquatic native species Nutrient over enrichment of waters by urban, agricultural, and industrial development has promoted the growth of alga, cyanobacteria as well as other native organisms. These blooms increase the turbidity of aquatic ecosystems, smothering aquatic plants and thereby suppressing important invertebrate and fish habitats. Die-off of blooms may deplete oxygen, killing fish. Some cyanobacteria produce toxins, which can cause serious and occasionally fatal human liver, digestive, neurological, and skin diseases. Cyanobacterial blooms thus threaten many aquatic ecosystems. Climate change is a potent catalyst for the further expansion of these blooms that have recently included other taxa, like Cnidarian, and could include more species in the future. Blooms occur with respect to native aquatic animals as well.

Example: Bloom of Jellyfish

3. Parasites and Pathogens

Parasites and pathogens are part of the natural biology and functioning of natural ecosystems. Nevertheless, pathogens and parasites live at the expense of the host, divert host energy from growth and reproduction into disease resistance and can cause mortality. Pathogens and parasites can drastically reduce host population.

Example: The Sea Lice (Lepeophtheirus salmonis)

Aquatic organisms, in particular undesirable aquatic species, have sensory organs that are responsible for the perception of acoustic pressure and particle motion associated with sound. Such perception of sound is necessary for the organisms to survive, as such perception is necessary for a variety of vital biological and behavioural functions, such as feeding, mating and parasite/host interactions. The sensory organs, for example in parasitic organisms such as sea lice, detect gravitational and inertial forces that among other things allows the parasite to detect the presence of the host organism necessary for the parasite to attach to a host.

The present inventors, in the following studies on the environmental impact of sound on aquatic species, have demonstrated that exposure to low frequency sound may damage the sensory organs of cephalopods and jellyfish:

1 An academic paper (Andre et al., "Low-frequency sounds induce acoustic trauma in cephalopods", Front Ecol Environ 2011) describes the effect of sound exposure on cephalopods using frequencies between 50 - 400 Hz using a repeated sweep.

2. An academic paper (Sole et al., "Evidence of Cnidarians sensitivity to sound after exposure to low frequency noise underwater sources", Nature Scientific Reports 6,

2016) describes the effect of sound exposure on the non-invasive species Cotylorhiza tuberculata and Rhizostoma pulmo using frequencies between 50 - 400 Hz using a repeated sweep. The two academic papers describe an experimental protocol that was shown to induce lesions in sensory organs of the aquatic species being studied. The methods described in the study employed, inter alia in-air loudspeakers directed towards a tank containing subject organisms. A control tank contained control organisms that were not exposed to the loudspeakers.

While the methods used in the studies were sufficient in an experimental setting to demonstrate that lesions may be introduced by environmental sounds, the described methods were not directed towards, and are not practical in a real-world aquatic environment for controlling undesirable species. In particular, the experimental protocols described in the papers do not take into account the particular sound exposure level required to induce lesions and further do not offer a way to control the sound exposure to maximize the acoustic trauma while minimizing the environmental impact (for example to other nearby organisms). There is a need, therefore, for a method of controlling undesirable aquatic organisms that improves upon the technique described in the academic papers by focussing on delivering the required sound exposure level dose by actively controlling the sound production.

In addition to the above studies by the present inventors, various methods have been employed to control undesirable aquatic organisms using sound, as exemplified below. This prior art does not, however, operate by inducing targeted damage to the sensory organs of the undesirable organisms responsible for detecting sound.

1. Jackman (patent W09417657 (Al), Removal of Parasites from Fish, 1993). This patent discusses a method to remove parasites from fish that are residing in or swimming through a walled chamber. It uses sound waves to stun or kill the parasite by resonation or dislodging from the fish. This patent does not concern lesions in sensory organs and it does not disclose acoustic frequency ranges nor exposed levels required to dislodge a parasite.

2. Iwamoto et al in Japan (patent WO2013051725 (Al) Sanitation Management Method of Farmed Fish and Device Thereof). This patent concerns the use of ultrasonic sounds for the removal of parasites from fish in a tank.

3. Skogseth (patent WO2013095153 (Al), System and Method for Inhibiting Parasites to Infest and Attach to Aquatic Animals). This patent describes the use of acoustic waves to inhibit parasites from infesting and/or attaching to aquatic animals using sounds below 100 Hz, but does not teach any effect on the sensory organs of the organisms.

4. Skogseth (N0335513B1) This patent describes the use of acoustic waves to inhibit parasites from infesting and/or attaching to aquatic animals using sounds between 3 - 300 Hz. This patent does not disclose particular sound exposure levels required to inhibit attachment and does not describe targeted inducement of lesions in the sensory organs of undesirable organisms or any other physical effects due to sound exposure.

5. Menezes (US 4922468). This patent describes using sound as stimuli to cause

unwanted aquatic organisms to depart an area.

6. Hydroacoustics Inc (WO2011/090925) describes the repelling of sea mammals from a

region of water by using sound stimuli such as an air gun.

7. Suomala (US 493007) describes a sound device for modifying fish behaviour.

8. Airmar Tech (WO 95/00016) describes an acoustic system for repelling marine

mammals. SUMMARY OF THE INVENTION

The present invention has as one of its objects to overcome the disadvantages of the prior art, and to provide a new and at least alternative method for controlling undesirable aquatic

organisms. It has been shown in various experiments that sound exposure can induce lesions on a variety of species. None of these experiments allows for a precise control of the delivered sound

exposure level to the organisms or the frequencies required to induce lesions, and in fact, they do not attempt to establish a required SEL nor to deliver a specific SEL. The present

invention improves on the previous work by controlling the exposure dose and limiting the

dose to those frequencies that have most effect on the organism of interest. This control

allows the inducing of lesions on the target organisms while minimizing unwanted potential environmental impact.

This invention incapacitates, kills or leads to the death of undesirable aquatic organisms in an infected aquatic zone by producing lesions in their sensory organs through the use of acoustic signals, for example continuous acoustic signals.

According to one aspect, the invention relates to the control of undesirable aquatic organisms generally. According to another aspect, the invention relates to the control of particular, identified species. Even more particularly, one aspect of the invention relates to the control of sea lice specifically.

The lesions induced by the invention are lethal to, or incapacitate, the targeted organisms. The invention uses specific continuous acoustic signals in the frequency range for which an undesirable organism is sensitive in order to trigger lesions on sensory organs responsible for the perception of sound. Those organs include, but are not limited to, statocysts; otholith organs;

sensory setae; lateral lines and other water flow detectors; chordotonal organs; tympanal organs; starch-statolith of undesirable aquatic organisms. The induced lesions incapacitate or degrade the organisms' ability to perceive their surrounding environment and lead them to die.

As used herein, the term "lesions" means an induced physical change in one or more sensory organs of an undesirable species, in particular sensory organs responsible for the perception of acoustic pressure and particle motion associated with sound, as described in table 1 below. The term "lesion" further refers to a change or damage to the sensory organ severe enough to be incompatible with the life of the exposed individuals. For example, as discussed below, the sensory organs of certain species comprise a number hair like structures or mechanosensory cells. The term "lesions" may thus be defined and quantified for such organs as the percentage of hair cells or mechanosensory cells bearing sensilia that have been extruded, expulsed, missing or otherwise damaged after sound exposure (permanent/irreversible trauma). The number of extruded cells determines the threshold that defines a lesion to be lethal or have lethal consequences on the exposed animals.

The field of underwater bioacoustics is constantly evolving. Little is known about acoustic perception of many marine organisms and hence about the effects of noise exposure to sensory organs. The sensitivity to sound of many species within the scope of the invention is not yet definitively established. The present inventors have, however, as discussed above, demonstrated acoustically induced lesions in the statocysts of jellyfishes {Cotylorhiza tuberculata and Rhizostoma pulmo) and apple snails (Pomacea insularum), as well as in the sensory setae of copepodids and adults of sea lice (Lepeophtheirus salmonis). The present invention is therefore believed to be effective for any aquatic species (in any of their life cycle stages) with sensory organs sharing similar morphological and physiological characteristics.

Table 1 below lists a number of types of aquatic species and various sensory organs of such species responsible for detection of sound: SPECIES/GROUPS SENSORY SYSTEM

BIVALVES STATOCYST CNIDARIANS Organ of equilibrium found in usually aquatic invertebrates, that is typically a fluid- filled E CHIN ODE RMS vesicle lined with sensory hairs cells (setae in some crustaceans), which detect the position of suspended statoliths, calcareous structures that stimulate sensory cells and help indicate CEPHALOPODS position when the animal moves.

CRUSTACEANS

FISHES OTOLITH ORGAN AND SEMICIRCULAR CANALS (vertebrate inner ear)

AMPHIBIANS

REPTILES Vertebrate ear is the organ that sends information about sound to the brain, as well as

vestibular information about the orientation of the head in space. Fishes present only inner ear and it subsumes both hearing and balance (functions). Amphibians and reptiles have a middle ear with a tympanic membrane, and reptiles also have an external auditory meatus (or canal) which extends from the tympanic membrane to the external surface of the head. The inner ear has several regions, including three semicircular canals and three otolith organs— the saccule, utricle, and lagena

CRUSTACEANS SENSORY SETAE INSECTS POLYCHAETES Stiff hair, bristle, or bristlelike structures distributed all around the invertebrate body that allow them to receive vital environmental information.

ARACHNIDS

FISH LATERAL LINE AND OTHER FLOW DETECTORS

AMPHIBIANS

Sensory structures within a longitudinal canal in the animal's skin that extends along

REPTILES

each side of the body and within several canals in the head. They have hairlike structures at

CEPHALOPODS their surface that project into a gelatinous membrane called a cupula. Enable the animals to

CTENOPHORES sense objects that reflect pressure waves and low-frequency vibrations (to detect prey, to

CNIDARIANS swim in synchrony with the rest of its school, to sense its environment, to supplement the

ARTHROPODS animal's sense of hearing).

Some amphibians retain the lateral line system of their ancestral fishes.

Scale sensilia are small tactile mechanosensory organs located on the head of squamate reptiles (lizards and snakes), that act as tactile and hydrodynamic receptors capable of sensing the displacement of water.

Cephalopods have sensory cells with cilia that project from the body surface and make direct contact with surrounding water. The ciliated cells of this "lateral line system" are sensitive to local water movements and are able to perceive hydrodynamic pressure.

Ctenophores and Cnidarians, both in the polyp and the medusa stage, possess sensory organs, located in their tentacles and acting as mechanoreceptors, able to detect vibrations in water associated to prey movement, and changes in their surrounding environment.

Cnidocysts of cnidarians contain mechanoreceptors that modulate the sensitivity of nematocysts. The mechanoreceptors associated with the cnidocysts send axons into the central nervous system and sub-serve a somatosensory function.

Arthropods use surface receptors in the form of mechanosensory setae to function in both touch and hydrodynamic sensing. These receptors can also be deflected by solid objects or water flow.

CRUSTACEANS CHORDOTONAL ORGANS

Propioceptive organs that monitor joint movement, direction of movement and static position. Chordotonal-type mechanosensitive cell are external mechanosensory cells typical located on the chordotonal organs of Crustaceans

INSECTS TYMPANAL ORGANS

Tympanate ears (pressure detectors) are typical peripheral auditory systems of insects, All have fundamentally similar structures— tympanum backed by a tracheal sac and a tympanal chordotonal organ— , ancillary structures, and number of cliordotonal sensilla. Some aquatic insects (Hemipterans) present a complex tympana, non-homogeneous in thickness and sometimes have cuticular structures on the tympanum itself that affect vibration, for instance, have a club-like appendage. Insects use their ears in different behavioural contexts, mainly intraspecific communication for mate attraction, predator avoidance, and parasitic host localisation.

PLANTS STA CH-STATOLYTH

In plants, including aquatic species, the statocyst consist on cell containing any of various movable inclusions, such as plastids, starch grains, or other statoliths and are thought to function in geotropic responses. As an organ elongates and becomes displaced from vertical, the amyloplasts (starch- filled plastids within the cell) sediment to the new lower side of the cell due to their high density relative to the cytoplasm, acting as a statolith.

TABLE 1

The sensory organs of aquatic species responsible for sensing sound are sensitive to sounds in a range of frequencies. The following references describe the sensitivity ranges for various types of organisms:

BIVALVES

Louise Roberts, Samuel Cheesman, Michael Elliott. Sensitivity of the mussel Mytilus edulis

to substrate borne vibration in relation to anthropogenically generated noise.

https://hydra.hull.ac. Uk/assets/hull:12417/content

Here sensitivity of the marine bivalve Mytilus edulis to substrate borne vibration

was quantified by exposure to vibration under controlled conditions. Sinusoidal excitation by tonal signals at frequencies within the range 5 - 410 Hz was

applied during the tests, using the staircase method of threshold determination. GASTROPODS

Frings H, Frings M (1967) Underwater sound fields and behavior of marine invertebrates. I n:

Tavolga 473 WN (ed) Marine Bio-Acoustics Pergamon Press, Oxford

Up to 500Hz (Hezabranchus aplysia) CNIDARIANS Frings H, Frings M (1967) Underwater sound fields and behavior of marine invertebrates. I n:

Tavolga 473 WN (ed) Marine Bio-Acoustics Pergamon Press, Oxford

Up to 100Hz (sea anemone) CTENOPHORES

No literature on sound sensitivity range. ECHINODERMS

No literature on sound sensitivity range. CEPHALOPODS

Mooney TA, Hanlon RT, Christensen-Dalsgaard J, Madsen PT, Ketten DR, Nachtigall PE.

2010. Sound detection by the longfin squid (Loligo pealeii) studied with auditory evoked potentials: sensitivity to low-frequency particle motion and not pressure. J. Exp. Biol. 213, 3748-3759 - Responses were obtained between 30 and 500 Hz with lowest thresholds between 100 and 200 Hz.

Hu, M., Yan, H. Y., Chung, W.-S., Shiao, J.-C. and Hwang, P.-P. (2009). Acoustical evoked potentials in two cephalopods inferred using the auditory brainstem response (ABR) approach. Comp. Biochem. Physiol. 153A, 278-283

Using ABR we found that auditory evoked potentials can be obtained in the frequency range 400 to 1500 Hz (Sepiotheutis lessoniana) and 400 to 1000 Hz {Octopus vulgaris), respectively.

Kaifu K, Akamatsu T, Segawa S (2011) Preliminary evaluation of underwater sound detection by the cephalopod statocyst using a forced oscillation model. Acoust sci Technol. 32:255-260.

Reported perception thresholds of Sepia officinalis, Octopus vulgaris, and O. ocellatus fit the model well at low frequencies, whereas at frequencies above 150 Hz, the empirically measured threshold increased more steeply than the predicted increment

CRUSTACEANS

Randall Hughes, David A. Mann, and David L. Kimbro. Predatory fish sounds can alter crab foraging behaviour and influence bivalve abundance. Proc Biol Sci. 2014 Aug 7; 281(1788): 20140715. doi: 10.1098/rspb.2014.0715 Best sensitivity was at 75 Hz with decreasing sensitivity up to 1600 Hz.

Goodall C, Chapman C, Neil D (1990) The acoustic response threshold of the Norway lobster, Nephrops norvegicus (L.) in a free sound field. I n: Wiese K, Krenz WD, Tautz J, Reichert H, Mulloney B (eds) Frontiers in Crustacean Neurobiology. Basel, Boston, Berlin: Birkhauser Verlag, pp. 106-113

Peak sensitivity was broadly tuned to frequencies between 200 Hz and 400 Hz. A more complex response: excitation to frequencies between 100 Hz and 300 Hz, and inhibition at higher frequencies (4350±1000 Hz)

Lovell, J. M., Findlay, M. M., Moate, R. M. and Yan, H. Y.(2005). The hearing abilities of the prawn Palaemon serratus. Comp. Biochem. Physiol. 140A, 89-100.

- P. serratus is responsive to sounds ranging in frequency from 100 to 3000 Hz.

Nathan J. Edmonds, , Christopher J. Firmin, Denise Goldsmith, Rebecca C. Faulkner, Daniel T. Wood. A review of crustacean sensitivity to high amplitude underwater noise: Data needs for effective risk assessment in relation to UK commercial species. Marine Pollution Bulletin. Volume 108, Issues 1-2, 15 July 2016, Pages 5-11.

http://dx.doi.Org/10.1016/i.marpolbul.2016.05.006.

- 5-400 Hz

FISHES

Mann DA, Cott PA, Hanna BW, Popper AN. 2007. Hearing in eight species of northern Canadian freshwater fishes. J Fish Biol 70, 109-120 (doi :10.1111/j.l095-8649.2006.01279.x)

- 100 to 1600 Hz.

Casper, B. M., Lobel, P. S. and Yan, H. Y. (2003). The hearing sensitivity of the little skate, Raja erinacea: a comparison of two methods. Environ. Biol. Fish. 68, 371-379. The best hearing sensitivity for R. erinacea (bottom-dwelling elasmobranch) between 100 and 300 Hz.

Egner, S. A. and Mann, D. A.(2005). Auditory senstivity of sargent major damselfish Abudefduf saxatilis from post-settlement juvenile to adult. Mar. Ecol. Prog. Ser. 285, 213- 222.

All fish were most sensitive to the lower frequencies (100 to 400 Hz). The frequency range over which fish could detect sounds was dependent upon the size of the fish; the larger fish (>50 mm) were more likely to respond to higher frequencies (1000 to 1600 Hz).

Johnstone, A. D. F. and Hawkins, A. D. (1978). The hearing of the Atlantic Salmon, Salmo salar. J. Fish Biol. 13, 655-673.

The fish responded only to low frequency tones (below 380 Hz)

Mann, D. A., Higgs, D. M., Tavolga, W. N., Souza, M. J. and Popper, A. N. (2001). Ultrasound detection by clupeiform fishes. J. Acoust. Soc. Am. 109, 3048-3054

- able to detect sounds up to 180 kHz.

AMPHIBIANS

Lombard R.; Fay R., Werner YL. Underwater hearing in the frog Rana Catesbeiana. J. exp. Bio/. (1981), 91, 57-71

- 0Hz-4 kHz.

Andreas Elepfandt, Use Eistetter, Andrea Fleig, EIke Gunther, Michaela Hainich, Susanne Hepperle and Burkhardt Traub. Hearing Threshold and frequency discrimination in the purely aquatic frog Xenopus Laevis (Pipidae): Measuremements by means of Conditioning. The Journal of Experimental Biology 203, 3621-3629 (2000)

- 200-4000 Hz. REPTILES

To date, no one has examined hearing in fully aquatic snakes and lizards. These are terrestrial examples: http://www.anapsid.orR/reptjleheannR.html Lizards

Most of the lizards for whom data has been collected show that most hear in the same range as does the green iguana (Iguana iguana), whose picks up sounds in the 500-4,000Hz range,

Snakes

Responses to groundborne vibrations are low in sensitivity and frequency, in the 50-1 ,000Hz range; their peak sensitivity is at 200-300 Hz range,

Christensen, C. B., Christensen-Dalsgaard, J., Brandt, C. and Madsen, P. T. (2012). Hearing with an atympanic ear: good vibration and poor soundpressure detection in the royal python, Python regius. J. Exp. Biol. 215, 331-342.

They were also most sensitive to low frequencies between 80 to 160 Hz and their sensitivity decreased at higher frequencies.

PLANTS

Takahashi H, Suge H, Kato T. 1992. Growth promotion by vibration at 50 Hz in rice and cucumber seedlings. Plant Cell Physiol. 32:729-732.

- 50Hz

Gagliano M. 2012. Green symphonies: a call for studies on acoustic communication in plants. Behav Ecol. 24:789-796. roots growing in the direction of a sound source

The demonstrated and/or reasonably expected effect of the invention on the various sensory organs shown in table 1 is summarized in table 2 below: SPECIES/GROUPS KNOWN AND EXPECTED EFFECT OF THE INVENTION

BIVALVES The invention induces damage on hair cells of statocyst inner cavity sensory

CNIDARIANS epithelia.

ECHINODERMS

CEPHALOPODS

CRUSTACEANS

APPLE SNAIL As a Mollusc gastropod the apple snail possesses statocysts. The statocysts are (Pomacea insula rum) spherical vesicles containing calcareous structures, statoliths, composed of calcium carbonate. They function as balancing organs, used by the snail to detect its position with regard to the ground. They are located inside the snail's body close to the pedal ganglion.

The invention induces damage on hair cells of statocyst inner cavity sensory epithelia. They present expulsed apical poles, or the whole body of the hair cells is totally extruded into the statocyst cavity and present flaccid, fused or missed sensory cilia. Some of the cilia have been expulsed leaving a hole on the hair cell. The crown of microvilli that normally is surrounding the unique cilia is fused or totally lost. These effects are incrementing with time after low frequency and high intensity exposure. The almost or total expulsion of the sensory cells is a definitive signal of that the acoustic impact is acute and the lesion on the sensory epithelia is immediate.

JELLYFHISH Jellyfish present rhopalia. Rhopalia are sensitive bodies located around the bell (Cotylorhiza margin in medusa with a number typically being in multiples of four. Each tuberculata)

rhopalium presents a statocyst at its terminal end containing many refractive (Rhizostoma pulmo)

crystals. The statocyst role is relevant for the gravity- sensing function of the rhopalium; the statocyst together with the adjacent sensory areas work as a gravity organ in rhopalia. When the medusa is tilted, gravity pulls up the statocyst, bending the body of the rhopalium, so that cilia on the sensory cells in the sensory plate make contact with or are removed away from the overlying epithelium (hood). The mechanical stimuli trigger the upright positioning behaviour, which occurs by asymmetric contraction of the swimming muscle to restore the balance against the gravitational force.

The invention induces ultrastructural changes and acoustic damage to the Cnidarians statocyst sensory epithelia. Regardless of the species, all exposed individuals present the same lesions in the statocyst sensory epithelium and the same incremental effects versus time. Damaged hair cells become extruded or missing or present bent, flaccid or missed kinocilia and stereocilia.

FISHES The invention induces damage on hair cells of the sensory epithelia of the three

AMPHIBIANS semicircular canals and the three otolith organs, the saccule, utricle, and lagena

REPTILES CRUSTACEANS The invention triggers lethal lesions on sensory setae, stiff hair, bristle, or bristle INSECTS like structures distributed all around the invertebrate body

POLYCHAETES ARACHNIDS

SEA LICE The life cycle of L. salmonis includes ten stages, three of which are pelagic. The

(Lepeophtheirus third of these is the infective stage of the salmon louse, the copepodid, which is salmonis)

sensitive to low frequency water accelerations such as those produced by a swimming fish. It carries both chemosensory aesthetes and mechanosensory setae on its antennules, indicating that both mechanical and chemical signals may be important in host-finding. Adult L. salmonis present different types of sensitive setae on their antennae.

Zooplankters such as copepods and protists use external mechanosensors for sensing spatial velocity gradients generated by preys or predators. It is understood that the absence of gravity receptors (i.e. statocysts) in planktonic animals has to do with the specific gravity of the zooplankton body, which is the same or slightly higher than water. Sensing flow-induced changes in orientation, rather than flow deformation, would enable more efficient control of vertical movements. In L. salmonis this external mechanoreceptors are located on the first antenna.

Mechanosensory setae in the antennules allows sea lice to detect the water displacement produced by their host when swimming by. The invention triggers lethal lesions on sensory setae which incapacitate them to perceive their surrounding environment and lead them to die.

FISH The invention induces damage on hair cells of the sensory epithelia of the

AMPHIBIANS lateral line system and flow detectors

REPTILES

CEPHALOPODS

CTENOPHORES

CNIDARIANS

ARTHROPODS

CRUSTACEANS The invention induces damage on external mechanosensory cells typical located on the chordotonal organs

INSECTS The invention induces damage on scolopidial sensilla present on proprioceptive and vibration- sensitive receptor organs and insect ears.

PLANTS containing any of various movable inclusions, such as plastids, starch grains, or other statoliths

TABLE 2 The description of the invention will refer to the term "Sound Exposure Level (SEL)" as the total cumulative squared sound pressure that an organism is exposed to expressed in decibel; it is defined as: SEL = 10 log ₁₀ J _T —^- dtj dB with a reference pressure p ₀ = 1 μΡα and a reference time T ₀ of 1 second.

The cumulative time interval T can be the duration of the exposure to induce lesions. In some cases the SEL is referenced in relation to acceptable levels for marine mammals, measured over a 24 hour period. These levels are referred to by the term SEL24. This invention will refer to the term "Sound Pressure Level (SPL)" as the average sound pressure in a 1 second time interval expressed in decibel; it is defined as: SPL =

10 log ₁₀ j^ dt^ dB with a reference pressure p ₀ as above.

According to one aspect, the invention comprises a method and system whereby one or more undesirable organisms is exposed to continuous acoustic signals over time until a target Sound Exposure Level (SEL) is achieved for the organism, the SEL chosen at a level that induces sufficient lesions in the sensory organs of the organism to disrupt vital functions of the organism necessary for survival. According to one aspect, the target SEL is from 180 to 220 dB re ^Pa ² s , for example 210 dB re ^Pa ² s. This SEL level has surprisingly been shown to induce lesions in a wide variety of undesirable aquatic species. According to one embodiment, the target SEL is achieved by exposing undesirable organisms to a continuous loop of a plurality of individual sounds of a given duration each, for example 1-60 seconds, preferably 5-15 seconds and more preferably 10 seconds. The individual sounds may be single frequency sounds, or may comprise a frequency range. According to one embodiment, the individual sounds are arranged as so-called "third octave sounds" or "third octave bands". As used herein this refers to a sound having a frequency band of one third of an octave, centred upon a particular frequency. The center frequencies of the individual third octave sounds may be chosen to cover the entire sensitivity range of the organism or any subrange within the sensitivity range. According to one aspect of this embodiment, each individual third octave sound has its own target SEL value, chosen such that total sum of all of the individual SEL values equals the total target SEL for the organism. When an individual third octave sound reaches its target SEL value, that sound is dropped from the loop, which continues to repeat until each sound in the loop achieves its respective target SEL. It should be understood that instead of "third octave" sounds, the invention may employ "quarter octave", "half octave", or any other appropriate band width for the individual sounds.

According to another embodiment, a single sound within the sensitivity range of the organism may be played continuously until the target SEL is achieved.

According to another aspect, the system and method of the invention comprises producing the sounds using calibrated transducers capable of producing sound having frequencies covering all or part of the sensitivity range for the target organism, for example between 0-4000 Hz, for example, 5-1600 Hz, 30-1000 Hz, 50-400 Hz, up to 500 Hz, up to 100 Hz, up to 50 Hz, and 100Hz to 10 kHz. The transducers have a source level at least up to 140 dB re ^Pa ² at 1 m for individual frequencies and 180 dB re ^Pa ² at 1 m for each selected third octave band in the embodiment using the loop of individual sounds. The transducers are driven by amplifiers that can reach the voltages required for these levels; typical peak voltage levels will be below 100 V. The sound production system is calibrated as a whole, and for each individual third octave in the embodiment using the loop of individual sounds.

Calibrated hydrophones record the acoustic pressure in a given frequency range with maximum sound pressure levels at least up to 180 dB re ^Pa ² without saturation. The hydrophone system may be arranged to include a preamplifier if required and an analogue to digital converter (preferably sampling at least at 40 kHz with 16 bit resolution) providing digitized data to a sound exposure control system.

According to another aspect, the invention provides a method of employing acoustic modelling at a treatment site to estimate the sound level at a distance from a transducer, wherein acoustic transmission loss is estimated using the C*log(R) rule, with R the distance in meters between the transducer and the point of interest. For distances closer than 15 meters C = 20 will be used. For distances beyond 15 meters C = 15 will be used. According to this aspect, sound fields from multiple transducers will be summed incoherently. According to yet another aspect, the constant C may be evaluated on site by installing the calibrated transducer and recording its signal with a calibrated hydrophone at various distances. A least square fitting procedure of the log function on the measurements then provides the constant. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail with reference to the drawings, wherin:

Figure 1 is a Schematic overview of a zone containing undesirable aquatic organisms and the exposure system.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 illustrates the system and method according to one aspect of the invention. As shown therein, an aquatic exposure zone 10 is defined, said zone being infected by unwanted organisms. According to one aspect of the invention, zone 10 may have an area in two of three dimensions of from 25 square meter to 20000 square meters, for example 50 by 50 meters (D).

The method of the invention comprises the step of identifying the species of unwanted organisms in the exposure zone, and determining the frequency range of sound to which the organisms are sensitive. Thereafter the organisms are exposed to sound in order to induce targeted lesions in sensory organs of the organsims.

The system of the invention comprises a control module 12. Control module 12 is preferably installed on a buoy or platform close to zone 10. The control module 12 comprises a sound source 14 and an exposure control module 16.

One or more transducers 18 are arranged in or adjacent to zone 10, in communication with the sound source 14 of control module 12, and arranged to produce sounds in zone 10 provided by the sound source 14. The sound is transmitted to the transducers through standard underwater acoustic cables. Sound is transmitted into zone 10 for a sufficient amount of time, at a particular sound pressure level, for the unwanted organisms to receive a sound exposure level (SEL) sufficient to cause lesions in the sensory organs. According to one aspect, the sound exposure level (SEL) is in the range of 180 to 220 ^Pa ² s , for example 210 dB re ^Pa ² s.

According to one aspect of the invention, sound source 14 comprises one or more stored individual sounds having frequencies covering all or part of the frequency range to which the unwanted organisms are sensitive. According to one aspect, the individual sounds stored in the sound source are single frequency sounds. According to another aspect, the individual sounds comprise ranges of frequencies for example from 0-4000 Hz, 5-1600 Hz, 30-1000 Hz, 50-400 Hz, up to 500 Hz, up to 100 Hz, up to 50 Hz, and 100Hz to 10 kHz. The generated sound to which the organisms are exposed may be a combination of all these frequencies together, or preferably, consist of a sequence of frequency bands covering the described frequency range.

According to one embodiment, the sounds that cover a given frequency range comprises a plurality of so-called "third octave sounds" or "third octave bands". The third octave sounds stored in the sound source have a given duration, for example 1-60 seconds, preferably 5-15 seconds and more preferably 10 seconds. The sounds stored are stored in a memory of the sound source and are arranged to be played in sequence in a continuous loop.

The sequence of third octave bands in the loop can be arbitrarily defined, but preferably they are defined such that one of the third octave band centers falls precisely on 1000 Hz. All other centers with the frequency range, for example, between 100 - 1000 Hz, are then computed by

1

repeatedly dividing this starting center by 2s .

One or more hydrophones 20 are arranged in zone 10, in communication with the exposure control module 16 of control module 12 . According to one aspect, a plurality of third octave sounds are provided by the sound source to the transducers. For example, the sound source may provide 10 different third octave sounds. Such third octave sounds are provided as a range of frequencies centred for example on 125, 160, 200, 250, 315, 400, 500, 630, 800, and 1000 Hz.

The third octave sounds are stored and transmitted by the transducers at the level required to reach output sound pressure levels between 140 dB - 180 dB re ^Pa ² at 1 m or higher from the transducer. The sound source includes power amplifiers to drive the transducers. The amplifiers and transducers are all individually calibrated for each third octave frequency band such that the input voltage level is sufficient to obtain a source sound pressure level of preferably 180 dB re ^Pa ² at 1 m. The transducers 18 produce the sounds in the water. The preferred output level of a transducer is for example 180 dB re ^Pa ² at lm. This ensures minimal harm to any marine mammals in or near zone 10. Transducers 18 are positioned inside or very close to the exposure zone. A single transducer 18 may be installed in the centre of the zone, or if that is not possible just outside the zone. If multiple transducers 18 are used then they are distributed either within the zone such that at the entire perimeter of the zone a minimal level of 140 to 180 dB re ^Pa ² is present, or they are installed symmetrically around the exposure zone. The combined transducer dose level is measured with a hydrophone 20 at a control point, or the dose is estimated using the propagation loss model described above (an appropriate C*log(R) ruleY Tn the latter case the sound nressure levels received from the transducers will be summed incoherently. At the preferred output level, transducers should be positioned at least every 25 to 100 m to be effective.

According to one embodiment, the sound source is arranged to cause transducers 18 to play a continuous loop of the stored, third octave sounds of 1-60 seconds, preferably ten-second duration each. This "loop" of consecutive ten-second sounds is then repeated until a particular sound reaches a target SEL dose to the individual organisms. According to aspect, the target SEL levels for the individual sounds is from 180 - 220 dB re ^Pa ² s , preferably 200 dB re ^Pa ² s. Once the target SEL dose is reached for one sound, that sound is dropped from the sequence, which is then continued without this sound. This is repeated until each of the sounds reaches its target SEL dose of for example 200 dB re ^Pa ² s. These bounds are chosen, inter alia, from practical considerations, such as the amount of time the sounds must be played to reach a target SEL value. For example, if the received level at a control point (for example at the center of zone 10) is 170 dB re 1 \iPa ² , then to reach an SEL of 220 dB re ^Pa ² s the sound may need to be played continuously for more than 27 hours. An SEL of 210 dB re ^Pa ² s may be reached in about 3 hours.

When all of the sounds in the sequence reach their target dosages, for example 200 dB re ^Pa ² s, then a combined total SEL will have been delivered to the organisms in zone 10. According to one aspect, this target total SEL could be from 180 to 220 re ^Pa ² s, for example 210 dB re ^Pa ² s. Having thus been exposed to a necessary total SEL, for example a SEL of 210 dB re ^Pa ² s, the hair cells or similar structures of the sensory organs of the organisms will have been inflicted with incapacitating or fatal lesions, as discussed in table 2. The initially required SEL dose for each individual third octave band is, according to one aspect of the invention, set to 200 dB re 1 μPa ² s. When the full dose for all bands is used their combined SEL will reach 210 dB re 1 μPa ² s. With a single exposure per day this level will remain below the recommended SEL24 for marine mammals. The third octaves are centred preferably on 125, 160, 200, 250, 315, 400, 500, 630, 800, and 1000 Hz, but any other sequence covering the bandwidth could be used. For a dose to be effective the SPL throughout the exposure zone should be 150 dB re 1 μPa ² or higher.

Hydrophones 20 record the sound pressure level within the exposure zone and every 10 to 30 seconds and transmit the third octave sound levels to the Exposure Control module through a cabled connection. The hydrophone is installed at least 10 to 50 meters away from any transducer and following standard sound measurement guidelines. The exposure arrangement of control module 12 receives the third octave sound levels from the hydrophones 20 and keeps track of total exposure levels during a single exposure period. The total level for each third octave is compared to the minimally required dose to cause lesions in the organisms in zone 10, and once the dose is reached the centre frequency of that third octave band is transmitted to the Sound Source over a cabled connection. If the hydrophone system is absent and no measurements are available, an estimate of the third octave SEL doses is made based on the calibrated output of the transducer(s) and a transmission loss model described above (an appropriate C*log(R) rule). In that case the SEL is estimated at a point at least 10 to 50 meters away from any transducer. Once all third octave bands have reached their SEL dose, the sound system is switched off.

When the system is installed in an area with marine mammals, a sound ramp-up sequence is optionally played at the start of the exposure. This ramp-up will play a sound consisting of uniform white noise between frequencies 100 Hz - 10 kHz. The level will be increased linearly up to 160 dB re ^Pa ² SPL (calculated over the whole frequency bandwidth) in a 1 minute time period. The ramp up sequence will induce the marine mammals to vacate the exposure zone.