Consultancy Report 

Clients: ETSU,Harwell, for DTI 

Nuclear Electric plc 

EXPERIMENTS ON THE USE OF 

SOUND AS A FISH DETERRENT 

A W H Turnpenny, K P Thatcher 

R Wood and P H Loeffelman* 

* Energy Engineering Services Company 

3750A Hacienda Boulevard, Ft. Lauderdale, Florida 33314, USA 

For the attention of: 

Dr M Davies, ETSU 

Mr C J L Taylor, Nuclear Hectric plc 

FCRO40193 

April 1993 

a 

Obiectives 

The aim of the project was to assess the effectiveness of underwater sound signals for 

repelling fish from areas of water, �orpotential application to fish exclusion at power station 

or other water intakes. Sound systems offer potential advantages over physical screening 

systems, of low capital and runningcosts, no hydraulic head loss and, elsewhere, have been 

shown to be highly effective, with diversion efficiencies of 80-100%. Two candidate 

systems were selected for trial: an empirical signal development process developed by 

Fawley arl Ltd for Nuclear Electric plc and a novel signal development process developed 

by Loeffelman and co-workers in the USA. 

Background 

Many of Britain’s large nuclear or fossil-fuelled power stations are sited on the coast or on 

estuaries. Fish catch at these stations may include species of economic andor conservation 

importance: cod (Gadus morhua), bass (Dicentrarchus labrax), salmon (Salmo salar), sea 

trout (Salmo trutta) and Twaite shad (Allosafallax). Substantial quantities of other species, 

notably whiting (Merlangius merlangus), sprat (Spratm spratw) and herring (Clupea 

harengus) are also captured, potentially causing operational difficulties. Any future tidal 

power barrages in Britain would also be sited on estuaries and would, potentially, have an 

impact upon the same range of species. 

Passage of fish through hydroelectric turbines or their entry into the cooling water systems 

of power stations leads to increased mortality rates in fish stocks. This may place an 

additional pressure on fish populations, some of which are already under pressure from 

exploitation by fisheries and through habitat loss, and their exclusion is therefore desirable. 

Nuclear Electric plc wish to improve this aspect of the environmentalperformance of their 

power stations wherever practical and cost-effective solutions can be devised. The 

Department of Trade and Industry are funding generic research into fish diversion methods 

for the benefit of possible future tidal barrage developments on Britain’s estuaries. For tidal 

barrage application, fish diversion methods form only part of an integrated arrangement of 

diversion systems and fish passes which would be required to encourage fish to cross a 

barrage line, other than via the turbines. 

Physical screening methods do not present a viable option for fish protection at large power 

plants owing to the very high water flows involved and the high capital costs incurred. Most 

behavioral fish deterrent systems, based on light, sound, electrical or hydraulic stimuli, have 

met with limited or no success. The most successful system tested to date on a British power 

station is a bubble curtain which was recently installed and tested at Nuclear Electric’s 

Heysham 2 Power Station. This gave a predicted annualcatch reduction of around 40% for 

fish and 60%for shrimps. 

&ly trials with acoustic systems either failed to produce a response in fish, or proved 

unreliable for long term application. More recent trials conducted in the UK at Nuclear 

Electric plc’s Oldbury on Severn power station produced some positive results, yielding an 

estimated 39%reduction in bass catch. In this work signals were developed by an empirical 
Es-2 

method. Fish were subjected to a series of underwater sounds in a tank and a signal that 

appeared to disturb the fish was then used for field trials. 

The Loeffelman signal development process is based on signal synthesis using information 

gained from the spectral analysis of recorded fish sounds. The method assumes that fish will 

be sensitive to sounds having similar frequency and temporal characteristics to those that they 

emit, so that deterrent signals can be targeted to particular fish species. 

In both systems the chosen signal is played back through a durable underwater sound system. 

For the Loeffelman method, groups of fish were placed within an acoustically isolated 

chamber, and their sounds recorded using a sensitive hydrophone coupled to a digital audio 

tap recorder. All sounds that could not be attributed to background noise or mechanical 

sources and were believed to be fish communication sounds, were then analyzed for spectral 

composition and temporal patterning. Potentiai deterrent signals were then developed from 

characteristics of these fish calls. 

For the empirical method, 16 different signals were composed, comprising either pure sine 

wave tones or mixed tones, delivered as constant, pulsed, swept frequency or swept 

amplitude (crescendo) forms. These were recorded as a series on tap for playback during 

experiments. First, a screening trial was carried out in which the tape was played to a group 

of fish. From this, fish responses were scored and one or more candidate deterrent signals 

were chosen for more comprehensive testing. 

The signal, derived by either method, was tested on fish under laboratory conditions. Initial 

attempts to duplicate a floating cage experimental arena, as used by Loeffelman for initial 

trials of deterrent signals, failed owing to low water clarity and siltation problems. Further 

experiments were carried out in test pools at the Fawley laboratory and at a salmon farm in 

south west Scotland. A Model 220 Argotec electromagnetic transducer, capable of producing 

180dB re lpPa@Im, was employed as the underwater sound source for the trials. Fish used 

for the experiments were: adult Atlantic salmon, adult and juvenile brown trout, adult cod, 

adult whiting, adult and juvenile bass, and adult eels. In addition recordings were made of 

sounds produced by herring, although none were available for experimental testing of 

deterrent signals. 

For each trial, a group of fish was placed within the tank and their distribution observed 

during control periods with no signal applied, and during experimental periods with the 

candidate signal played through the sound system. Sound levels were monitored and 

modifications made to take account of the acoustic environment. 

~ 

To test for habituation, trials were repeated 10 times, with intervening control and rest 

periods, over a period of 1-2 days. The data were then examined for any deterioration in 

response to sound through the trial series. 
Es-3 

Results 

Signals were developed by the Loeffelman method for salmon, adult brown trout, whiting 

and cod; no sound was detected from juvenile trout, although it did prove possible to apply 

the adult-derived signalto the juveniles. No sounds were produced by either bass or eels and 

so no deterrent signal could be developed using this technique for either species. Significant 

positive avoidance responses were observed with all the species tested. No habituation to the 

signals was observed in response to any of the signals. In brown trout, there was evidence 

of a learnt response, in which the fish remained away from the sound source after the initial 

few trials. 

Of the sixteen Nuclear Electric signals tested, four were identified as useful signals for 

further trials. Of these, only the two signals comprising a sweep of frequencies from 100-500 

Hz were observed to produce significant avoidance responses. However, dl species tested, 

with the exception of eel, were shown to respond to one or both of the swept signals. No 

significant habituation was observed to either Signal. 

Discussion 

Both series of trials met the objectives of this stage of the project. In the case of the 

empirical method, these were to consolidate the findings of the earlier preliminary trials 

conducted on behalf of Nuclear Electric plc, and to expand the range of species tested. The 

earlier success with bass at Oldbury on Severn Power Station, achieved using the 100 to 

500Hz swept signal, was repeated, and the signal was found to offer an effective, broad 

spectrum deterrent, capable of repelling a'range of species. Of the species tested, only eels 

failed to show any useful response to this signal. 

The objective in the case of the Loeffelman method was see if the method already tested on 

North American fish species would work on UK estuarine fish species. Good results were 

obtained with the species tested. Unfortunately, in these trials the method was limitedby the 

failure to detect sounds in two out of the seven species tested, so that no signal could be 

developed for these two species. 

Comparison of the two methods, setting aside the problem in the Loeffehan method 

associated with lack of vocalization, showed that there was little to choose between the 

effectiveness of the signals developed on a given species. The Loeffelmanmethod yielded 

stronger reactions with brown trout, whilst the empirid method resulted in stronger 

responses in salmon, cod and whiting. Since the scope for response was constrained by the 

walls of the experimentalpools, it is not possibleto state whether one or other method would 

move a particular species further away from the sound source, in a free-field situation. 

The sound field within the pools was variable, depending upon the water depth and the sound 

frequency being used. This makes a direct assessment of the threshold sound level required 

to repel fish difficult from the results of the present study. However, sound levels 

throughout the pools were maintained at >30 to 4OdB re 1pPa above ambient, in the 

frequency range 100 to 300Hz, and it would be wise to achieve at least this differential in 

any field trials. 
Es-4 

In contrast to the findings of some previous investigations, no habituation to the test signals 

was detected, based on either signal development method, over a 1 to 2 day trial period. 

This absence of habituation is ascribed to the continually-changing nature of the successful 

sound signals, in terms of either frequency or amplitude. The experiments revealed some 

evidence that fish can learn to stay away from the sound source after an initial exposure to 

the signal. 

Conclusions 

1. Both the Loeffelman signal development process and the empirical screening method 

were successful in producing signals which could be shown to have a statistically significant 

deterrent effect in laboratory trials. 

2. The empirical system yielded one signal in particular, based on a sweep of 

frequencies, which was shown ,tobe effectivewith all species tested, except the eel. None 

of the signals tested was found to be effective against eels. 

3. A limitation of the Loeffelman approach was that two out of seven species did not 

produce sound under the test conditions, and so no deterrent signal could be developed. 

4. No evidence of habituation was detected in the trials. There was some indication that 

brown trout learnt to stay away from the sound source. 

5. Based on the effectiveness of the signals in these laboratory trials, a properly 

developed and sited acoustic fish deterrent system is expected to significantly reduce fish 

impingement at water intakes. 

Recommendations 

1. For non-selective deterrence of a wide range of fish species and life stages, the 

swept-frequency signal approach developed under the Nuclear Electric plc contract is 

recommended. Where the signal must be applied to one or more selected speciedlifestages, 

the Loeffelman signal development process should be tried. 

2. In view of the successful completion of the laboratory trials, it is recommended that 

field trials should be undertaken on an estuarine power station where conditions would also 

be representitive of a potential tidal barrage power generating site. Nuclear Electric plc’s 

Rinkley Point B power station meets the requirements for such a trial. An initial planning 

survey would need to be undertaken over the summer months; the autudwinter period, 

when fish catch on the stations cooling water intake screens is highest, would be optimal for 

the trials. 

A W H Turnpenny 

for: 

FAWLEY aquatic research laborabri% Ltd 

Marine and Freshwater Biology Unit 

Fawley, Southampton SO4 1TW 
1. Introduction 

1.1. The need for fish deterrents 

1.2. Underwater sound: elementary concepts and definitions 

1.3. Sound production and hearing in fish 

1.3.1. General 

1.3.2. Sound production mechanisms 

1.3.3. Hearing in fish 

2. Materials and methods 

2.1. Sources of experimental fish 

2.2. Recording and analysis of fish sounds 

2.3. Signal development 

2.3.1. The Loeffelman approach 

2.3.2. The empirical method 

2.4. Fish response trials 

2.4.1. The sound generating system 

2.4.2. Observation of fish behaviour 

3. Results 

3.1. Atlantic salmon (Salmo sdar) 

3.1.1. Loeffelman method 

3.1.2. Empirical method 

8 

8 

9 

9 

9 

9 

10 

10 

10 

16 

16 

16 

17 
3.2. Brown trout (Salmo trutta) 17 

3.2.1. Loeffelman method 17 

3.2.2. Empirical method 18 

3.3. whiting (Merlongiw merlangw) 18 

3.3.1. Loeffelman method 18 

3.3.2. Empirical method 19 

3.4. Cod (Gadus morhua) 19 

3.4.1. Loeffelman method 19 

3.4.2. Empirical method 19 

3.5. Bass (Dicentrachus labrax) 20 

3.5.1. Loeffelman method 20 

3.5.2. Empirical method 20 

3.6. Eel (Anguilla anguilla) 20 

3.6.1. Loeffelman method 20 

3.6.2. Empirical method 20 

3.7. Herring (Clupea harengus) 21 

3.7.1. Loeffelman method 21 

3.7.2. Empirical method 21 

4. Discussion 21 

4.1 Limitations of experiments 21 

4.1.1. Acoustic conditions 21 

4.1.2. Confinement of fish 22 

4.1.3. Use of farm-raised fish 22 
4.2 Performance of methods 23 

4.2.1. Empirical method 23 

4.2.2. Loeffelman method 24 

4.2.3. Comparison of the Loeffelman method versus 

the empirical method 24 

5. Conclusions 25 

6. Recommendations 26 

References 28 

Tables 

Figures 

Appendix 
1 

I. INTRODUCTION 

This report describes a seriesof experimental studies into the potential use of acoustic stimuli 

to deter fish from water intakes at thermal and hydroelectric power stations. It combines the 

results of two parallel projects, funded independentty by Nuclear Electric plc and ETSU (on 

behalf of the Department of Trade and Industry: DTI) respectively. 

The Nuclear Electric element of the study looked at an empirical.signal development process 

used with some success in earlier trials at Oldbury-on-Seven power station (Thatcher and 

Irving, 1992). The aim was to enlarge the range of candidate signals for testing, and to apply 

these in more rigorous laboratory trials and to a wider range of estuarine and marine fish 

species than was possible in the initial preliminary studies. The trials were also required to 

investigate the degree to which fish might become habituated to the sound signals, 

consequently reducing their effectiveness. 

The DTI-funded part of the study was to apply the novel signal development process 

developed in North America by Loeffelman and co-workers (Loeffelman et al., 1991; 1993; 

Klinect etal., 1992), to examples of British estuarine fish in laboratory trials, and to compare 

the results with the findings of the Nuclear Electric study. To simplify comparison, both 

funding bodies agreed that the results should be combined in a single report. 

The species of fish which were of interest in this study were the Atlantic salmon (&lmu 

salar), sea trout (Slmutrutta), the shads (Absa fillax, A alma), the Europeaneel (Anguilla 

anguilla), bass (Dicentrarchuslabrad, herring (CrUpea harengus), whiting (Merlangiks 

mrlangus)and cod (Gadusmrhua). All of these species are considered to be of conservation 

and/or commercial importance in Britain today and are potentially vulnerable to capture by 

nuclear, fossil-fuelled and tidal generating stations. 

1.1 The Need �or Fish Deterrents 

Earlier studies commissioned by ETSU, on behalf of the DTI, into the risk of damage to fish 

passing through tidalpower turbiies (Solomon, 1988; Turnpenny et al., 1992) identified the 

need for developing methods of repelling or guiding fish away from turbine intakes. The 

need arises since diadromous species would need to cross the tidalbarrage to enter the river 

or sea, depending on the direction of migration, in order to compIete the life cycle: in doing 

so,some would be at risk of passing through the turbines and being damaged by blade contact ’ 

or hydraulic conditions. In view of the large flows of water involved, and the high debris 

loads carried by estuarine waters, physical sereedng methods are deemed to be both 

impractical and uneconomical: impractical owing to the high maintenancerequirements, and 

uneconomicbecause of the high capital cost of installation, coupled withgenerating head loss. 

Solomon (1988) estimated the cosfs of installing travelling meens to be of the order E28 

million per unit for a barrage on the Severn estuar)r, with an oved figure for the barrage 

of f5,600 million. Any type of fish diversion method would, of course, fcmn part of an 

integrated system of diversion facilities and fish passes, designed to promote the passage of 

fish via routes other than the turbines. 
2 

Steam-electric power stations, whether nuclear or conventional, require large volumes of 

water for condenser cooling. Those sited on the open coast or on estuaries commonly use 

once-through rather than tower-assisted cooling systems. The cooling water requirement is 

typically of the order 5Om3s-' for a 1300MWenuclear station, or 40m3s1for a similarly-sized 

conventional thermal station. Fish and other organisms become entrained in the cooling 

water flows of both types of power stations, and whilst the quantities are not sufficiently 

large to have caused any discernible impact on fish stocks (Turnpenny and Coughlan, 19921, 

Nuclear Electric plc are seeking to reduce these catches where practicable by a means that 

is robust, inexpensive, easy to deploy, and that is effective. This objective is driven by an 

aim to improve the environmental performance of their power stations, and not by current 

regulatory requirements. 

A number of behaviourally-based frsh protection systems have been used at water intakes, 

though with varying success. Behavioural systems have the potential advantage of excluding 

fish without the need for physical screening structures, which are both costly to install and 

maintain, and prone to blockage. They rely upon generating, in front of the intake, stimuli 

which fish can detect and avoid or, in some cases, stimuli which attract fish away from the 

intake. By appropriate design of the stimulus field, it may be possible to guide fish to safe 

havens or fish passes. Such systems may be based on electric fields, air bubble curtains, 

strobe lights, moving lights, mercury vapour lights, underwater sound generators or 

turbulence generators (e.g. louvre screens). In the case of louvre screens, there is a physical 

screening structure which creates an impediment to water flow, though the gaps are much 

larger and provide lower head loss than a conventional passive screening system. The 

principles of operation and typical applications of these behavioural methods are described 

in a number of reviews (e.g. Turnpenny, 1988; Turnpenny et aZ., 1992; Solomon, 1988; 

Solomon, 1992). Unfortunately, whilst good results have been obtained with some of these 

systems in specific applications, in general the track record of behavioural systems has been 

poor, either in terms of unpredictable performance, or poor reliability. To date, the best 

results on a British power station were obtained in a recent trial of a bubble curtain at 

Nuclear Electric plc's Heysham 2 Power Station. The potential annual reduction in fish and 

shrimp catch with this system were estimated to be 40% and 60% respectively. 

Acoustic deterrent methods have been tried for many years but, until recently, with limited 

success. Sound generating systems of various kinds have been used, including pneumatic 

poppers, and a variety of other mechanical devices capable of producing high underwater 

sound levels (Patrick et aZ.,1988). These have met with some limited success as fish 

deterrents, though results have b&n species-specific, owing to the different sound 

characteristics needed to deter different species. Mechanical sound generators can be tuned 

to alter the sound characteristics but offer little flexibility once in place. The reliability of 

some systems has also precluded their use for continuous service applications. 

In the UK there has been some experience with acoustic deterrents. Early trials using low 

frequency sound (50Hz)were undertaken by the Central Electricity Generating Board at 

Oldbury-on-Severn power station in the 1960s (Ray et ul., 1976) to deter salmon (Salmo 

sulur) smolts. These trials did not successfully deter fish, probably since the sound signal 

used and the level at which it could be generated using the equipment available 

(underwater 
3 

loudspeakers) were inappropriate. No attempt was made to test the efficacy of the signal on 

captive salmon smolts before it was applied in the field. 

More recent UK trials were carried out in 1992 at Nuclear Electric’s Oldbury-on-Severn 

Power Station Vhatcher and Turnpenny, 1992;Thatcher and Irving, 1992). In these trials, 

specimens of bass (Dicmrurchus labrax)and whiting(Merlangius merlangus) were subjected 

to a selection of acoustic signals in a laboratory tank. A signal which apped to disturb 

the behaviour of the fish was then generated via an underwater loudspeaker system placed 

in front of the cooling water intakes of the power station. This resulted in a minor (11%) 

but non-significant (p>0.05) reduction in the catch of all fish species but a significant 

@<0.02) reduction (39%)in bass catch. The signal used was a sine wave, continuously 

varying in frequency from 100 to 500Hz,played at sound pressure levels of around 58 dB 

above background noise level. The placement of the loudspeakers immediately in front of 

the intakes was probably far from optimal, since water velocities in the area (up to 65 cm 

s-l) were well above the swimming capabilities of many of the fish present; thus many fish 

would not have been able to escape by the time they encountered the signal. 

An alternative signal development has been studiedin the USA, and patented by Loeffelman 

(US Patent No. 4,955,005; UK Patent No. 2 223 386 A), in which recordii1gs are made of 

fish communication sounds. The sounds produced are examined by spectral analysis and 

time series amlysis to determine the main characteristics of the fish calls. New signals are 

then developed electronically, based on key features of the fish sounds, and are played 

through an underwater sound system in front of the water intake. The sound pressure levels 

used are designed so as to be high enough to avoid masking by background noise. The basis 

of this method is that the fish sounds indicate the sensitive portion of the hearing range for 

particular fish, and the temporal patterning to which fish are most responsive. By listening 

to specimens of the population at the application site, the signals can be customized to their 

particular characteristics. Combined with a sound system using military-grade underwater 

loudspeakers, in North American trials the system has been shown to offer a combination of 

high fish diversion efficiency, for example 80-100%for salmonid fish, with a durability of 

hardware appropriate to continuous service in hostile underwater conditions (Loeffelman et 

al., 1991; 1993; Klinect et al., 1992). The aim of the present project was to assess whether 

selected British estuarine fish species could be repelled using an underwater sound system. 

1.2 Underwater Sound: Elementary Concepts and Definitions 

Tounderstand the experimental trials,some basic understandmg of thephysics of underwater 

sound will be helpful. Both Tavolga (1971) and Hawkins (1986) give succinct introductions 

I to this subject, insofar as it is relevant to fish hearing and sound production. The following 

brief summary covers the key points that will be encountered later in the text. 

Any object moving or vibrating in water will produce underwater sound. This sound is 

characterized by minute (of the order nanometres) to-and-frodisplacements of particles, and 

oscillatory changes in pressure above and below hydrostatic pressure. Sound can thus be 

measured in terms of the partick velocity, Le. the vibrational velocity of the moving 

particles, and the sound pressure @). Particle velocity is measured in metres per second 

and sound pressure in pascals (Pa). More commonly, owing to the vast range of levels 

encountered in nature, sound pressure is expressed on the logarithmic decibel scale, relative 
4 

to a reference quantity: 

sound pressure level (SPL) = 20 loglop/predB 

Here, prefis a reference pressure, normally taken as 1 pPa for water, with SPL being 

expressed as d33 re 1pPa. A ten-fold increase in SPL is equal to 20 dB,a hundredfold is 

40 dB, and so on. Table 1.1 gives typical SPLs for various sources in air and water to give 

the reader some feel for the levels involved. It should be pointed out that, since underwater 

acoustics are based on a 1pPa reference level as opposed to 20pPa in air, a given level of 

sound expressed in the units that would be used underwater is thus 26dB higher than the 

identical level expressed in the units that would be used in air. 

Sound, measured as either SPL or particle velocity, diminishes with distance from source. 

Far away from the source, either quantity declines as the inverse of the distance from that 

source, Le. by a factor of 2, or 6 dB,for a doubling of distance. Here, SPL and particle 

velocity are directly proportional to one another. Closer to the source, a different 

relationship exists. In the simple situation of a pulsating sphere (a monopole source) in open 

water, the sound waves emanating close to the source will be spherical; particle velocity is 

much higher for a given sound pressure, and declines with the inverse square of the distance. 

With increasing distance away from the source, the waves become planar and the linear 

relationship then applies. For the pulsating sphere model, the limit of the inverse-square 

relationship is reached at distance of X/27r, where X is the wavelength. The volume enclosed 

within this boundary is known as the near-field and that beyond it thefar-field. Table 1.2 

gives examples of wavelengths at different sound frequencies in water, and their associated 

near-field distances. It should be noted that these relationships apply to idealized, free 

acoustic field conditions, such as in deep, open water and close to reflecting surfaces they 

become more unpredictable. Air /water interfaces, and the walls of experimental tanks, are 

examples of reflecting surfaces. 

The propagation of sound waves in water is dependent upon the depth of water relative to 

the wavelength. If the water depth is less M4,then the wave amplitude will attenuate rapidly 

with distance from source. On the other hand, in deep water, low frequency sound will 

propagate successfully over hundreds of miles. Table 1.2 shows the water depths required 

to propagate fully different frequencies. 

1.3. Sound Production and Hearing in Fish 

1.3.1 General 

Sound production is a very common phenomenon in fish, with over 50 families known to 

contain sound-producing species (Myrberg, 1981). Many of the sounds produced are known 

to have a communicatory function with other fish of the Same or different species, related 

for example to agonistic (e.g. territorial) or reproductive behaviour or warning of perceived 

danger. Other sounds are incidental, �or example the hydrodynamic and muscularcontraction sounds caused by fish swimming or turning, mechanical sounds of grinding 

teeth, or sounds associated with release of gas from the swimbladder, although some of these 

sounds may have a biological signifimce. There is evidence, for example, that predators 

can be attracted by the swimming sounds of prey fish schools (Moulton, 1960). Temporal 
5 

patterns of sound delivery, as well as frequency range and amplitude, is an important 

determinant of how sounds are interpreted by the receiving fish. For example, in the male 

haddock (Melanogrammus aeglefinus), which emits repeatable patterns of sound pulses at 

different stages during its courtship behaviour, it has been demonstrated that these sounds, 

played back to a maturing female, will elicit reciprocal courtship behaviour. Other species 

also distinguish courtship calls from those of other species, simply from the interpulse 

intervals (Hawkins, 1986). 

There exist very extensive reviews of hearing and sound production in fishes. Good general 

reviews are given by Marshall (1962), Tavolga (1971) and Hawkins (1986), while Fish and 

Mowbray (1970) review sound production (or lack of it) in families of fishes from the 

western North Atfantic. For the present purpose, it will be sufficient to state some of the 

generalizations apparent from these reviews, and to draw upon some of the more specific 

information relevant to the species featured in the present investigations. Table 1.3 

summarizes available published information about sound production and sonic mechanisms 

found for these species. 

1.3.2 Sound Production Mechanisms 

Marshall (1962) distinguishesfive kinds of sound production in fishes, including swimming 

sounds, gas-bubble sounds, stridulation, vibration of the swimbladder and sounds produced 

by quick movements of the head. Whilst later authors (e.g. Tavolga, 1971) have elaborated 

on this classification, the additional classes of sound production are merely subdivisions of 

Marshall’s categories. The following information is taken from Marshall. 

Swimminr Sounds 

Studies of swimming sounds have been made largely in relation to schools of fish in open 

water. When idling, no swimming noise is detectable, but during active periods of 

swimming(’streaming’), noise is generated, especially during veering or turning manoeuvres. 

In anchovy schools (Anchoviella sp.), the greatest sound intensity was emitted at below 500 

Hz,and up to 1,600 Hi, when streaming, and at below 8OOHz when veering, with a 

maximum of 2,OOO Hz. 

The origins of the sounds may be various: movement of water over the body surface, 

breaking of the water surface, tailbeat movements, muscular contractions and friction 

between moving body parts. 

+ Gas Bubble Sounds 

Fish with ducted swimbladders (phystostomes), for example the clupeid fishes (herrings, 

shads) and eels (Angfidae), may produce sound when gas is released into the water. The 

sound has been described as a mouse-like squeak. Thisnormally occurs as fish rise in the 

water mlurnn and have to release excess pressure, but can occur as a result of alarming fish, 

especially when in captivity. 
6 

Stridulation 

Stridulatory sounds are produced by the friction of neighbouring skeletal parts, commonly 

the upper and lower pharyngeal teeth, though other spines or bones may be involved. The 

sounds produced are described as ’rasping, scraping, scratching or whining in character’. 

The swimbladder (if present) appears to contribute a resonant quality to sounds of this type. 

The frequency range of stridulatory sounds is relatively wide, 50 to 4,800 Hz,with most of 

the energy concentrated in the upper frequencies. 

Vibration of the Swimbladder Wall 

Swimbladder sounds are typically low-pitched, drum lie sounds, resonant in quality. They 

may be heard as thumping or knocking sounds, delivered in short bursts. The frequency 

range is commonly 50 to 1,400 Hz, but with most of the energy concentrated at the low end 

of this range. Muscles attached to the internal or external wall of the swimbladder are 

responsible for generating the vibration, in most cases acting against a spring mechanisms 

provided by the elasticity of the bladder walls, body wall musculature or connective tissues. 

Sounds Produced bv Ouick Head Movement 

In various species, notably blennies, thumping sounds are made by sudden downward or 

sideways movements of the head. These sounds are reported to play an important part in the 

pre-spawning behaviour of certain species. 

1.3.3 Hearing in Fishes 

The sensitivity of fish to sounds is normally described in the form of an audiogram, which 

relates the detectable sound level threshold (in terms of SPL or particle velocity) to different 

frequencies. An example is shown in Figure 1.1, which gives the audiograms for four 

separate species of fish. It is perhaps unsurprising that the sensitive frequency range is in 

general below 1,OOO Hz,correlating in broad terms with sound spectra emitted by fish 

(Section 1.3.2). 

Figure 1.1 demonstrates clearly that marked differencesin hearing sensitivity occur amongst 

different species, and that the centre and bandwidth of optimum sensitivity also varies. 

Acoustic deterrent signals must be designed to take account of these characteristics. Few 

species are sensitive to sounds at frequencies above 2 or 3 kHz. If the fish do not hear the 

signal, the deterrent will not stimulate the fish to change its swimming behaviour. Sound 

sytems designed to produce signals targeted at the fish’s optimum sensitivity will be more 

effective at achieving this. Because lower SPLs are necessary to stimulate the fish when the 

sound frequencies are correctly targeted, smaller, lower cost underwater speakers can be 

used, resulting in more economical guidance system installations. 

The usual method of determining fish audiograms is by conditioning the fish to respond to 

loud sound stimuli, at a particular frequency, and then to lower the sound level 

progressively, until the response ceases. Unfortunately, since this method is labour-intensive, 

relatively few fish species have been investigated by this means. 
* 

7 

Differences in sensitivityamongst different species are related to the anatomy of the hearing 

mechanisms (Hawkins, 1986). Sound in al�species is detected by the otolith organs of the 

inner ears, which are paired structures embedded in the cranium on either side of the midbrain. The lateral line organs are also sensitive to low frequency sound (20 to 500 Hz),but 

only in the near field (see Section 1.21, since they are detectors of particle motion rather than 

sound pressure. An important factor determining overall hearing sensitivity is the presence 

of a swimbladder and the proximity of it to the inner ear. in the flatfishes (plaice, 

Pleurunectes platessa; dab, Lirnanda limanda), for example, which are quite insensitive to 

sound, there is no swimbladder. The swimbladder, in those species possessing one, acts as 

a pressure transducer, converting sound pressure to particle velocity. Thus species without 

a swimbladder, or in which the swimbladder has no close connection with the inner ear,are 

insensitive to sound pressure and rely upon detection of particle displacement. 

An important feature of hearing ability is the need to distinguish sounds that are of interest 

to the fish from background noise. Auditory masking occurs when a tone is surrounded by 

background noise of the same or close frequencies. In sensitive species such as the cod, this 

may make hearing difficult in noisy environments and, indeed, the cod requires a sound’to 

be of the order of 20 dB above background noise level to detect,it (Hawkins, 1986). 

Frequency-selectiveauditory filters are known to be present in a number of species and assist 

in auditory discrimhation. It has also been shown that this mechanism can be used to 

discriminate between frequencies, with the goldfish (Carassius auratus), for example, able 

to distinguish tones differing in frequency by only 3-5%. Auditory masking is an important 

factor when considering the feasibility of, and sound levels required for, acoustic fish 

deterrence. 

Loeffelman et aZ. (1993) demonstrated the influence of masking in field trials at a fish ladder 

in Michigan, USA. When the signal was only a few dB greater than the ambient sound 

pressure levels in a concrete pool in the ladder, up-migrating adult steelhead trout 

(Oncurhynchus mykiss) were not deterred. By placing the signal in a quieter pool and 

increasing the sound level over ambient (133dB re $Pa) to 158 dB re lpPa, 73% of fish 

were stopped from moving up the ladder. Sound levels in most natural waters ranges from 

80 to 100db re lpPa for all frequencies. Advanced sound systems are capable of producing 

SPLs sufficiently greater than these ambient levels. A speaker weighing 25kg, for instance, 

is capable of producing 170dB re 1pPa @lm. 

It is also important to evaluate the influence of site conditions on the signal designed for the 

fish’s hearing ability. Bottom substrate, bathymetry and other physical factors will cause 

frequencies to propagate with less sound pressure and over shorter distances than in a free 

field (Le. open water). In some cases a signal may fail to propagate at all owing to lack of 

depth, or wave cancellation due to reflecting surfaces. By knowing the fish’s sensitive 

hearing range, the signal frequencies may be adjusted to site conditions for good propagation, 

without fatling outside this range. 

In view of the important role of the swimbladder in the hearing process, it might be guessed 

that swimbladder size - and hence resonant frequency - would have a significant influence 

on the audiogram, with the expectation that small fish would have mdum sensitivity at 

a higher frequency than larger fish of the same species. This argument might be applied 

equally well to sound production. According to Hawkins (1986), experimental studies have 
8 

shown that the resonant frequency of the swimbladder is generally well above the hearing 

range of the fish and therefore that it is detuned to provide moderate amplification over a 

wide frequency range. This would serve to facilitatecommunication over a wider range of 

fish sizes than would a tuned swimbladder. The finding has potentially important 

implications for fish deterrence and suggests that an acoustic deterrent signal would not be 

too dependent on the sizes of fish to be deterred. Nevertheless, sound production does seem 

to be (inversely) related to size. Loeffelman et aZ. (1993) have shown that in Pacific salmon 

(Oncorhynchus spp.), smolt sounds were approximately700Hz higher than adult sounds. A. 

Turnpenny recently observed 25mm chinook salmon (0.ts~tsch)producing sounds at 

a sound system installation using the Loeffelman method in North America: these fish 

produced sounds at predominant frequencies around 1.5kHz higher than adults. Fish (1954) 

also gives sound spectra for eels (AnguiZZu rostrutu) of 545 and 700mm length respectively, 

showing that the larger specimen produced sounds 100 to 400Hzlower than the smaller one, 

Given these direct observations linking the frequency of sound production to fish size, it is 

clear that, if the Loeffelman hypothesis is correct, that fish hearing capability corresponds 

with sound production spectra, then the development of deterrent signals should take 

account of fish size and life stage. 

2 MATERIALS AND METFtODS 

2.1 Sources of Experimental Fish 

Fish for the experiments were obtained as follows: 

Atlantic salmon (adults, 40- 60 cm length): Otter Ferry Salmon Ltd, Argyll, Scotland; 

Brown trout (juveniles, 10 - 12 cm and adults, 30 - 40 cm length): Itchen Valley Trout 

Farm, Alresford, Hampshire; 

Cod (juveniles, 30 - 40cm length): MAFF Fisheries Laboratory, Lowestoft, Suffolk; rodand-line caught, by anglers at Lowestsoft; 

Whiting (adult, 30 - 40cm length): as for cod. 

Bass (juveniles, 7 - 20 cm): seine-netted, R. Itchen Estuary by MAFF/NRA; (adults, 30 ­ 40cm): from stock held at MAW, Lowestoft. 1 

Eels (adults, 40 -80 cm length): fixed engine fishery, Stolford Flats, Somerset (Mr �3 

Sellick); also, from stock held at MAFF, Lowestoft. 

Herring (adults 20-30cm length): from stock held by the Sottish Marine Biological 

Association, Dunstafhage, Oban, Argyll, Scotland. 

Attempts were made, in collaboration with the National Rivers Authority (Severn Trent 

Region), to collect Twaite shad for the study but these were unsuccessful. 
9 

2.2 Recording. and Analysis of Fish Sounds 

This applied to the Loeffelman method only and the equipment and methodology was as 

described by Loeffelman et al. (1993). 

Groups of fish were placed in an acoustically-isolated recording chamber (Flexwrap 

Corporation), of approximate size 120 Q x 25 (W) x 120 (D) cm. This was normally 

operated indoors to avoid interference from low frequency wind noise. Sound production was 

detected by a miniature Bruel and Kjaer (�3 & K) Model 8103 hydrophone placed within the 

recording chamber. This was coupled to a B & K Model 2635 charge amplifier and 

Rockland System 90 spectrum analyzer. An Aiwa HD-S1 digital @AT) tape recorder was 

used to make audio recordings of each sampling session, which was normally of 45 minutes 

duration. The overall layout of the recording equipment is shown in Figure 2.1. Observers 

listened in continuously throughout the recording session and recorded the times of any 

sounds produced. Any fish behaviour or outside interferences which might have produced 

sound artefacts was noted; for example, fish bumping into the hydrophone, the fall of 

condensation droplets into the water, or fish breaking the surfaceof the water. A continuous 

visual record was also made by means of a television camera and recorder (PanasonicM7000 

camcorder) placed in front of the recording chamber. Recorded sounds and video records 

could be synchronised by means of timebases on both media. 

Analysis of the sounds was carried out on recorded signals. For each sound which was 

clearly not caused by an artefact, the sound spectrum was printed out, together with the 

amplitude-time trace. Only where several sounds having similar characteristics were 

obtained, and for which no extraneous cause could be found, were they deemed to be valid 

fish calls. 

2.3 Signal Development 

2.3.1 The Loeffelman Approach 

Signals were synthesized on an IBM@XT PC fitted with a Roland SCC-1 GS Sound Card. 

Information obtained from analyses of fish calls (amplitude, frequency content, waveform, 

call duration, call interval) was used to formulate the test signal. The signal was then tested 

by playing it back to the fish using an underwater sound system in a test tank (see Section 

2.4). In some cases, the signal was subsequently modified during the playback phase, when 

environmental conditions did not allow adequate propagation of key frequencies. In such 

cases, the frequency range was shifted up or down by the minimum amount required to 

* ensure propagation. 

2.3.2 The EmDiriCat Method 

The alternativeapproach used a standard series of sound signals which could be played back 

to each test species, with no customization, other thanto determine empirically which signal 

worked best (if at all). The standard signal set comprised 16discrete sound patterns, differing 

in frequency, amplitude or temporal patterning. Their descriptions are given in Figure 2.2, 

with examples of time series. The signals used were an extension of those used in earlier 
10 

work carried out on behalf of Nuclear Electric during 1991-2. One of these (Signal No. 7) 

was tested and found to reduce significantly bass impingement at Oldbury-on-Severn Power 

Station (Thatcher and Turnpenny, 1992; Thatcher and Irving, 1992). 

A number of different signal classes can be distinguished, as follows: 

Group 1 Signals 1to 3: pure tones, fixed frequency and amplitude; 

Group 2 Signals 4 to 6: pure tones, fixed frequency, delivered in discrete, 

repetitive bursts; 

Group 3 Signals 7 & 8: continuously-varied frequency, fixed amplitude; 

Group 4 Signals 9 & 10 fixed frequencies, continuously-varied amplitude; 

Group 5 Signals 11 to 14 continuously varying frequencies and amplitude; 

Group 6 Signals 15 & 16 broad frequency band signals. 

No modification of this signal series was made during the trials. 

2.4 Fish Response Trials 

2.4.1 The Sound GeneratinP System 

The sound generating system is shown schematically in Figure 2.3. Signals were composed 

as described in Section 2.3, and either played directly by the signal generator or sound card, 

or first recorded onto magnetic tape and played back via the sound system from this source. 

The Kemo filter was used primarily in this set-up to provide additional signal amplification 

(up to 10 x) when necessary, rather than as a bandpass filter. Amplification was provided 

by a Ross Power Amplifier, capable of producing about 1000 W RMS power output. The 

underwater transducer (loudspeaker) used to generate the sound in the water was an Argotec 

Model 220. This is the largest of the transducers used by Loeffelman and co-workers in 

north-American sound experiments (Loeffelman et al., 1991, 1992, 1993; Beet et 

al.,1992). The unit is capable of producing sound levels of up to 180 d3 re lpPa @ lm, 

over a frequency range from 50 to 1OOOHz. 

2.4.2 Observation of Fish Behaviour 

The effectiveness of the signals for repelling fish was determined in behavioural trials. The 

initial intention was to use an underwater observation chamber, of the kind described by 

Klinect et al. (1992). A polyethylene-covered chamber was constructed with dimensions of 

9mC) x 1.2m(W) x 0.3m@) and suspended in a sea water dock adjacent to the Fawley 

laboratories. Underwater television cameras were used to observe fish movements. This 
* 

11 

approach was, unfortunately, made unworkable by problems of visibility, which Klinect et 

u2. had not experienced in their solely freshwater experiments. The problems at Fawley were 

caused by poor water clarity, but also deposition of fine sediments onto the outer surfaces 

of the observation chamber. Thus it was not possible to make any reliable observations of 

fish behaviour by this method. 

At first, the idea of conducting the behaviourd experiments in tanks or pools was rejected, 

on account of the complex acoustics of most small containments (Hawkins, 1986). However, 

following the lack of success of the open water trials it became necessary to use other means 

and, in recent experiments in Norway, Knudsen et ul. (1992) successfully demonstrated fish 

aversion to low frequency sound (10-150Hz), using a 4m x 5m x 2.5m@) concrete pool. 

A pool was tried and gave good results, so was finally adopted for all the behavioural 

trih. 

Salmon Farm Trials 

The pool experiments were first developed at an onshore salmon farm in south west Scotland 

(Otter Ferry Salmon Ltd,Argyll). Owing to the difficulties of transporting large numbers 

of adult salmon to the Fawley laboratory and keeping them there, it was decided to carry out 

all the salmon work at the fish farm. For this purpose, a circular, below-ground concrete 

pool of 15m diameter and 2m depth was made available. Water was provided from a 

pumped supply of sea water abstracted from the adjacent Loch Fyne. Water clarity was good 

and, since the pool was coated with a pale-coloured paint and had been cleaned prior to the 

trials, any fish within the pool could be seen clearly from above. 

Before the start of the experiments, the pool was stocked with 200 farm-raised Atlantic 

salmon, of nominal 600g weight. The Model 220 transducer was placed on the floor of the 

pool, against the side wall. The rest of the sound system and instrumentation was located 

in a trailer, adjacent to the pool. 

The experimental method was based upon the observation that the salmon stocked into the 

pool aligned themselves with the circular current, which was generated by the tangential 

inflow of water at the side wall and the exit of water via a central drain (Figure 2.4). Left 

undisturbed, the majority of fish adopted stablepositions on the streamlines. When disturbed 

by an outside stimulus, for example an object thrown into the water, the stablepattern would 

break down, with the fish changing orientation and moving away from the stimulus source. 

Since the floor of the pool was divided up into sectors, visible as joints in the concrete floor 

sections, it was possible for observers standing around the edge of the pool to count the 

numbers of fish in each sector. This was repeated at intervals over time, comparing the 

numbers of fish present in the sector containing the underwater speaker, and in the two 

adjacent to it (Sl, 52 and 53 in Figure 2.4), for periods with sound on ('test') and sound off 

('control'). Thus, a positive response was shown by a significantly reduced number of fish 

present in these threesectors in the test versus control periods. More detailed visual records 

were, at the same time, made by a camcorder (Panasonic M7000)mounted on a tripod to 

view fish in a small area (about 5m x 3m of pool floor) close to the sound source. 
* 

12 

The detailed protocol used was as follows: 

i) All aerators were removed and the water supply to the pond was cut off to eliminate 

these sources of noise. The inertia of the water mass would keep the water moving 

around the tank for at least 1 hour after this, so that the fish would retain their 

orientation on the streamlines. 

ii) Three observers took up position at the edge of the pool to monitor sectors S 1,S2 and 

S3. This was done cgefully to avoid disturbing the fish. A fourth person took charge 

of the sound system and called out times to the three observers. 

iii) At 30 second intervals over a five minute period, the number of fish in each of the 

sectors S1 to S3 was counted, with sound off (control). 

iv) Flow was restored and, after a five minute rest period, was cut off again. 

v) Step (iii) was repeated but with sound on (test). 

vi) Steps (iii) to (v) were repeated ten times to complete the experimental series. 

vii) Flow and aeration were restored. 

The trials were, in fact, conducted in two runs of five control-test pairs, on consecutive days 

(8th and 9th December, 1992). The transducer was moved about one-third of the way 

around the edge of the pool for the second day's trials to avoid bias in the results associated 

with transducer position. 

The data from the trials were analyzed to determine the mean and standard deviation of the 

number of counts per observation sector for successive test and control periods. A test for 

significant difference between test and control counts was made using the Student t-test for 

equal sample sizes (Clarke, 1969). The possibility of the fish becoming habituated to the 

signals was examined by plotting the percentage reduction (positive or negative) in fish count 

in the observation area as a whole (S1 to S3 inclusive) versus the number of test exposures. 

A linear regression line was then plotted through the resulting time-series, the goodness of 

fit being shown by the correlation coefficient .r (Clarke, 1969). A positive slope to the 

regression line, or a value of the x-coefficient which was not significantly different from 

zero, was deemed to be evidence of no significant habituation. 

Additional analysis was performed on video tape images, to show changes in fish behaviour 

between test and control periods. The video tapes were played back through a video cassette 

recorder in freeze-frame mode. Clear acetate sheets were fixed over the video screen, and 

the positions and alignments of fish marked onto the sheet with permanent marker pens. 

Observations were repeated at'15 second intervals over one test and one control period, 

recording the data on separate acetate sheets for each. The sheets were then removed and 

fish alignment angles measured by protractor. 
13 

' 

Laboratory Trials at Fawlev 

As the method of assessing fish responses to sound that was used at the fish farm worked 

well, a similar approach was adopted for laboratory trials at Fawley. A suitable belowground pool was not available, so an above-ground swimming pool was purchased and set 

up within the laboratory buildings Figure 2.5). This was smaller than that used at the fish 

farm, being 5m diameter and 1.2 m deep. A circular flow was generated by means of a 

submersible pump (4.2 1 s" flow rate) placed at the centre of the pool, with the outlet 

arranged to discharge at the edge of the pool, tangential to the wall. Water would continue 

to circulate for at least one hour after the pump was turned off. As in the fish farm trials, 

an Argotec Model 220 transducer was placed on the floor of the pool against the side wall. 

Observation of fish behaviour was carried out remotely in the laboratory trials. A 

monochrometelevision camera (Sony CCD, Model AVC DS-CE), fitted with a 4.5mm focal 

length, wide-angle lens, was fixed to an overhead beam above the pool and the area of view 

covered about 90% of the entire pool area. A pair of 500W halogen floodlights mounted 

above and to either side of the pool provided even illumination. Since water turbidity at 

Fawley is high, before entering the pool the raw water was passed first through a sand filter 

and then through a cartridge filter (56ympore size), to improve clarity. Using this method, 

fish could be seen clearly on a remote television screen. The results video-recorded for 

subsequent analysis. A timer function on the video recorder imprinted the time (to 1/1OOth 

second) onto the video image. 

A minimum of 10 and maximum of 40 fish were introduced into the pool the day before 

experimentation began. The experimental protocol was similar to that used on the fish farm 

but adapted to the remote observation and recording methodology. An identical 

experimental sequence was used, with fish counts being made every 30 seconds over five 

minute test and control periods with no water flow or aeration, separated by five minute rest 

periods during which water flow was restored. Again, ten pairs of test and control sequences 

were run in each experimental series. The main difference was the method of scoring fish 

numbers. The intention was, having mapped the sound field in the tank, to score fish 

numbers in relation to SPL isopleths, with the aim of determining the threshold SPL for 

avoidance of each signal type. Sound was mapped at the start of the trials, as shown in 

Figure 2.6, showing a clear SPL gradient across the tank and, initially, counts of fish 

between each of these isopleths were made. It subsequently became apparent that, although 

the experimental system had remained identical throughout the experiments in all other 

respects, changes in water level of only a few centimetres markedly altered the distribution 

of SPLs within the tank. As SPLs had not been mapped individually for each trial, no 

reliance could be placed upon the relationship between SPL and fish distribution. Instead, 

fish positions were counted in relation to the map shown in Figure 2.7. The curved lines 

shown are based on concentric circles drawn around the transducer centre at radial 

increments of 0.83m. Counts were made by placing an acetate overlay of this map on the 

television monitor scrcen and replaying, in freeze-frame mode, the video tapes of the 

experiments. The number of fish within each zone was counted and recorded at 30 second 

intervals. Thus, the records represent fish distance from the sound source rather than 

distribution in relation to sound level. 

Analysis of the data was broadly similar to that in the fish farm trials. However, rather than 
14 

looking just at an overall reduction of fish numbers within the vicinity of the transducer, the 

mapping procedure allowed the fishes’ distance away from the transducer to be determined 

for both test and control conditions, even though this distance was bounded by the wall of 

the tank. The average displacement from the transducer for test ad control states was 

therefore used as the measure of response. 

To calculate this, it was first necessary to correct the frequency counts obtained from the 

video tape analyses for the differences in area of each of the six map zones. This was done 

by dividing the raw count figures by the correction factors shown in Figure 2.7. The 

average distance away (m) from the transducer for an experimental run was calculated as: 

6 

X <:Di 

AverageDistance= i= 

6 

where is the average fish count for the zone i, and Di is the distance (m)from the 

transducer to the middle of zone i. 

Since the fish distances could not be normally distributed, owing to the boundary imposed 

by the tank wall, a test of significance for differences between control and test distributions 

was carried out using the non-parametric Kolmogorov-Smirnov test, following the procedure 

for large sample sizes (>40) described by Campbell (1974). Thus, the difference in average 

distance from the sound source between test and control pairs gives a measure of response, 

and the Kolmogorov-Smirnoff test ascribes the significance level to any differences in 

distribution pattern. 

The test for habituation closely resembles that used in the fish farm trials. For each testcontrol trial pair, the difference in the average distance from the sound source was plotted 

against the number of exposures. A linear regression line was fitted to the points to reveal 

any trend, and a negative slope, coupled with an x-coefficient which differed significantly 

from zero, was deemed to be evidence of habituation, or vice versa. A limitation of this 

approach is that it does not allow for the possibility that fish may learn to stay away from 

the sound source, remaining away in control as well as experimental periods. This would 

have the effect of reducing the difference seen between control and experimental periods. 

To cater for this, where the habituation test was positive, control and experimental distances 

were both plotted to reveal possible learning trends, applying a regression line to test for 

significance. 

Subiective Scorin? of Fish Behaviour 

Certain aspects of the fish behaviour seen by the observers could not readily be quantified, 

for example the speed at which fish moved away from the sound source when the signal was 

applied. A true impression can only be gained from viewing the Video tape records of the 

experiments. 

In an attempt to convey some of these aspects of behaviour, a subjective scoring system was 
15 

adopted to record the observers’ impressions of the strength of response to the sound signal. 

Five categories were defined: 

Category 1: Extreme startle reaction away from the sound source, some fish 

leaping out of the water. 

Category 2: Clear startle reaction away from the sound source, but no fish leaping 

out of the water. 

Category 3: Steady swimming away from the sound source but no obvious startle 

reaction. 

Category 4: Slight response to the sound signal but not a sustained movement of 

fish away from the sound source. 

Category 5: No response seen. 

Differences in Procedure with the Fixed Signal Approach 

In the work carried out for Nuclear Electric, a signal selection procedure was applied prior 

to the application of the protocol described above. A tape recording of the sixteen candidate 

signals, each lasting for one minute with a one minute resting interval between, was played 

to the fish via the underwater sound system in the test pool. From these, the signal which 

evoked the most obvious behavioural response, based on the subjective scoring system 

described above, was selected for the full test protocol. In some cases, where good . 

responses were generated by two or more signals, more than one was tested using the full 

protocol. 

Sound Mapping 

Sound mapping was carried out by generating sine wave signals of constant amplitude arid 

frequency through the transducer. Sound pressure levels were measured at different points 

in the pool and at lo%, 50%and 90%depth. This was repeated for frequencies of 100, 200 

and 300Hz (210 and 275 Hz at Otter Ferry) . Values at mid-depth (50%)only are shown 

in the present report. SPLs at 10 and 90,%were within lOdB of mid-depth values. 

The equipment was the same as that used for listening to fish sounds (Section 2.2). The 

hydrophone was attached to a long boom to allow access to different areas of the pool. SPLs 

were read from the display of the Rockland spectrum analyzer, which had been set up with 

the calibration parameters of the hydrophone. 

* 

The results are presented, in summary form only, in Figure 2.6, for both the Otter Ferry 

and Fawley test pools. 
16 

3. RESULTS 

To aid comparison between the two signal development methodologies, the results are shown 

species by species. .Most but not all species were tested by both methods, therefore the 

comparison has not been possible in all cases. 

Table 3.1 summarises category scores for all species tested, against each of the 15 signals 

in the empirical series. 

3.1 Atlantic Salmon (Salmo salur) 

Experiments on Atlantic salmon (carried out at Otter Ferry salmon farm) were not included 

in the Nuclear Electric project brief and therefore centred primarily on the Loeffelman 

method. Preliminary screening observations only were made using the Nuclear Electric 

signal series, since available time did not allow the full test protocol. 

3.1.1 Loeffelman Method 

Sound Production and Sound Signal Development 

Large numbers of sounds were recorded from salmon. Many of these were associated with 

quick head movements, of the kind described by Marshall (1962). Figure 3.1 shows a 

typical example of the sound spectrum and wave-train time series associated with one of 

these sounds. A low frequency peak at <lOHz represents the head movement. Most of 

the sound energy was concentrated below 300Hz, with a signal duration of 1.5 to 2s. 

The sound signal used in the trials was a two frequency sine wave tone at 210 and 275Hz, 

delivered as a repeated 2 second crescendo at maximum power output. 

Behavioural Response 

Recorded counts from the experiments are given in Table Al.l (Appendix). A summary of 

the data obtained by the counting method is given in Figure 3.2. Mean counts per sector 

for the observation area were approximately twice as high with sound off as with sound on, 

yielding a highly significant difference on both test dates (Figure3.2a). Overall counts were 

lower on the second day of the trials (9th December): this was attributed to bright sunlight 

on that day, which encouraged fish to remain in shadow, on the side of the pool away from 

the transducer; the previous day was overcast and fish were uniformly distributed around 

the pool. An effective response was obtained throughout the trials, with no evidence of 

habituation (Figure 3.28). The subjective response was classified as Category 3, with most 

fish swimming steadily away from the transducer but some fish, presumably entering points 

of high sound pressure, reacting more violently and, on occasions, jumping out of the water. 

A fact which the results in Figure 3.2 obscure is that, although some fish were recorded in 

the observation area around the transducer when the signal was applied, they were not 

holding station on the streamlines as were the majority of fish counted in the control periods. 

They were swimming past in a disorientated fashion, apparently looking for a means of 

escape which was not available to them within the confines of the pool. Figure 3.3, which 
17 

compares the alignment of fish relative to strmline direction for test and control periods, 

gives some indication of the chaotic orientation of the fish when the sound was on. 

3.1.2 Empirical h�ethod 

Results for the initial screening process only are available for Atlantic salmon and are shown 

in Table 3.1. Strong reactions (Category 2: moderate startle) were shown with signals 7, 12, 

14and 15. 

3.2 Brown Trout (Sulmo trutla) 

3.2.1 toeffelman Method 

Sound Production and Sound Signal Development 

Though sound production in brown trout was less prolific than in salmon, a number of 

sounds were successfully recorded and analyzed, a typical sound spectrum and time series 

for a 30cm trout being shown in Figure 3.4. The sounds were heard as dull thumps or 

clicks, with energy principally below 400H2,indicating the swimbladder as the likely origin. 

Pulses were brief, of the order 150ms. 

The original signal developed comprised 200 and 3mHz sine waves, delivered as a 2s 

crescendo at maximum power output. Since it was found that the signal, in this form, 

propagated poorly in the test pool (see below), the signal was modified subsequently to 200 

plus 300Hz. 

Despite many hours of listening to and recording juvenile trout (1Ocm nominal length), in 

group sizes of up to 40, no calls were heard. The greater success with the adult trout may 

have been related to the time of year when the recordings were made - November - the 

spawning time for this species. 

Behavioural Response 

Figure 3.5 shows results obtained with the original 200/300Hz signal. The results indicate 

no significant response. The observers also reported this as a Category 5 response (no 

visible reaction), and repeated the experiment three times with no more success. It was then 

that the sound level was monitored, showing that the signal would not propagate properly, 

perhaps owing to destructive interference. The 100/300Hz signal was then tested and found 

to propagate well. 

The response of the adult brown trout to the 200/300Hz signal is shown in Figure 3.6. A 

Category 2 response ws observed (startle reaction), With a highly significant (p<O.OOI) 

redistribution of fish away from the sound source. The habituation test shown in Figure 3.6b 

appears to show a marked reduction through the trial series, the regression line indicating 

a significant (p<0.05) degree of habituation. However, further inspection of the data show 

that the declining differences between control and test distances from the signal source were 

not the result of the fish moving progressively closer to the transducer but because during 

the control periods, the fish remained progressively further away. This suggests that the 
18 

fish were leanzing to stay away from the aversive stimulus. 

As no sound signal had been obtained for thejuvenile trout, the adult trout 100/300Hz signal 

was also tested on the juvenile trout. The response was classified as Category 3, with 

occasional startle reactions by individuals, but never by the whole group. The movement of 

fish away from the sound source was highly significant @<0.001), and whilst the level of 

response was somewhat erratic through the experimental series (Figure 3.3, there was no 

indication of significant habituation. 

3.2.2 Empirical Method 

Adult brown trout showed some, though little, reaction to the empirical series (Table 3.1). 

Signals 8 and 11 were selected for full trials and the results are shown in Figures 3.8 and 

3.9. Both were Classified as Category 4 responses (slight). Statistid analysis showed no 

significant response to Signal 11, and a small but significant (p<0.05) response to Signal 

8. Although a slight downward trend is seen in the habituation regression line (Figure 3.8b), 

it is not statistically significant. 

Figure 3.10 shows the results for juvenile trout. Signal 7 was selected as the most promising 

(Table 3.1). In the full trials, the response was classified as Category 3 (steady movement 

away). Startle reactions were occasionally seen for the odd fish, but never for the whole 

group. A small but highly significant @<0.001) redistribution of fish away from the 

transducer was seen. A downward trend in the habituation regression is evident (Figure 

3. lob) but this was non-significant. 

3.3 Whiting (Merlangiur merlannus) 

3.3.1 Loeffelman Method 

Sound Production and Sound Signal Development 

Few sounds were recorded from whiting. A sample spectrum and time series are shown in 

Figure 3.11. Sound energy was concentrated at frequenciesbelow 500Hz,with a protracted 

'bump' lasting over Is. 

Two sound signals were composed and tested for whiting. One was a dual frequency 

360/390Hz signal; the other, 410/480Hz. Both were delivered as a repeated 2s crescendo. 

Behavioural Response 

Results for the 410/480Hz signal are shown in Figure 3.13. A highly significant (p<0.001) 

positive response was obtained, with fish moving away from the sound source. There did, 

however, appear to be a degree of habituation with this signal (Figure 3.12), although this 

proved not to be statistically significant. 

Using the second signal, comprising the 360/390& mix,good results were also obtained 

(Figure 3.13), though with no evidence of habituation. 
19 

Both signals gave a response classified as category 3, with the fish showing a steady 

movement away from the transducer but no startle reaction. 

3.3.2 Empirical Method 

In screening trials, whiting reacted most strongly to Signal 7 vable 3. l),and this signal was 

selected for the full trials. 

Results of a full trial are shown in Figure 3.14. The signal evoked a dramatic response 

(Category l), with fish leaping out of the water when the signal was applied. A highly

significat (p <0.001) shift of fish away from the transducer was observed, with no evidence 

of habituation. 

This trial was repeated in full and yielded similar results (Figure 3.15). 

3.4 Cod lGadm morhual 

3.4.1 Loeffelman Method 

Sound Production and Sound Signal Development 

Cod were prolific in their sound production. Figure 3.16 shows an example of a cod sound, 

which contained, predominantly, frequencies below 200Hz. The sound duration was of the 

order of 1-2 seconds in most cases. 

The test signal was composed of frequencies 140 and 170Hz,delivered as a 2 second 

crescendo. 

Behavioural Response 

The response was classified as Category 3, showing steady movement away from the sound 

source. The observers described it as "the best example of this type of response". 

Curiously, the results of the statistical analysis show a less obvious, though statistically 

significant (p <0.05), redistribution of fish away from the sound source (Figure 3.17). 

The reason' for this apparently limited effect is that the fish remained mobile throughout the 

experiment, first moving away from the transducer, then making exploratory movements 

back towards it, before turning away again. 

3.4.2 Empirical Method 

In preliminary screening, cod showed Category 2 reactions to Signals 7 and 14 (Table 3.1), 

and both these signals were fully tested. Results are shown in Figures 3.18 to 3.20. 

Cod responded obviously to Signal 7, giving a clear startle reaction (Category 2). Significant 

movement of fish away from the sound source (p <0.05 to 0.01) is shown by Figures 3.18 

and 3.19. No significant habituation occurred. 
20 

Signal 14 failed to evoke a useful response when tested in full (Figure 3.20), with only a 

minor (Category 4) reaction seen. 

3.5 Bass Dicentrarchus labrax) 

3.5.1 Loeffelman Method 

Many hours were devoted to listening for bass sounds from juvenile and adult fish, under a 

wide range of conditions (highllow salinity, highllow dissolved oxygen, varying temperature) 

but none were detected. Unfortunately, it was not therefore possible to apply the Loeffelman 

method to this species. 

3.5.2 Empirical Method 

Signals 7 and 8 both showed a Category 2 reaction in the screening trials (Table 3.1), and 

both were tested in full (Figures 3.21, 3.22). Both were classified similarly in the full trials, 

though it was noted that the more obvious agitation lasted only for about 1 minute, 

In statistical terms, both signals proved to have a significant effect (p <0.05 - 0.01). 

There was no significant fall-off in response over the trial series. 

3.6 Eel (Anguilla anguilla) 

3.6.1 Loeffelman Method 

As for bass, many hours were spent listening to eels, under a similarly wide range of 

condition, but with no positively attributable sounds. Again, it was not, therefore, possible 

to apply the Loeffelman method. 

3.6.2 Empirical Method 

Eels showed Category 2 responses for Signals 1 and 7 in screening trials, and both were used 

in full trials. 

Reactions of the eels to either signal were minimal (Category 4)in the more protracted trials. 

As the transducer was the only source of cover in the pool, all the eels, on being placed in 

the pool, dived for cover under the Model 220. They continued to remain within Zone 1, 

even when the sound was turned on, thus there was no need to apply the statistical analysis 

used for other species. 

The slight reaction which was seen was in those eels which were in direct contact with, or 

very close to the transducer. These showed some signs of being startled when the sound was 

turned on, but moved only a very short distance away. 
21 

3.7 Herring (Clupea harengzis) 

3.7.1 Loeffelrnan Method 

An opportunity to listen to herring sounds was provided by the Dunstaffnage Marine 

Laboratory at Oban, where numbers of herring are held for experimental work. It was not 

possible to conduct behavioural trials since neither the time nor facilities were available to 

do so. 

A number of herring sounds were recorded, and a typical signal is shown in Figure 3.23. 

This showed the frequency content to be concentrated in the sub-200% range, with a sound 

duration of about 250ms. 

4 DISCUSSION 

Since this Report encompasses two studies which began as separate projects, it is necessary 

to consider separately how each has matched up to its own objectives. Equally, since they 

both had the same overall objective of demonstrating the feasibility of moving fish using 

sound, it is desirable to compare in the same terms how each method performed. 

However, as both methods were tested in a comparable manner, before discussing either 

method in detail, it will be helpful to discuss any methodological limitations which are 

common to both studies. 

4.1 Limitations of the Experiments 

4.1,l Acoustic Conditions 

The unpredictable acoustic conditions of small water bodies, such as pools and tanks, 

considerably restrict the interpretation of fish responses to sound. The unpredictability arises 

from the occurrence of reflections, from all the tank boundaries, including thewater surface, 

and from the possible constructive and destructive interference of reflected waves. This was 

evident from the failure of some signals to propagate well in the present trials. 

Depth is also an important consideration, since long wavelengths will not propagate in 

shallow water. Table 1.2 gives minimum propagation depths for different frequencies, 

showing that in the Otter Ferry trials, where water depth was 2m,the lowest frequency that 

would propagate well is 200H2,while for the 1.2m Fawley pool, frequencies below 350Hz 

would be strongly attenuated. Depth is also important with regard to transducer function: in 

shallow water, low frequency transducers tend to cavitate or de-gas the water at high 

amplitudes. In the trials, the Model 220 transducer was driven to the maximum output level 

that could be achieved without distortion. With a lOOHz signal, this yielded a maximum 

output level of 138 dB re 1pPa @lm in the Fawley test pool, and a slightly higher level of 

142dB re 1pPa @lm in the Otter Ferry pool. Levels of 180dB re ZpPa elm at this 

frequency could be expected in open water conditions with a depth of 4m or more. 
22 

The fact that good directional responses were found for most species, despite these 

limitations, indicates that even better responses could be expected under deep, open water 

conditions but that, nevertheless, sound should work as a deterrent in less-than-ideal 

circumstances. It is interesting to note that the Empirical Series Signal 7 produced only a 

moderate response with bass in the present laboratory trials, whdst when fitted to a power 

station in far from ideal conditions, a 39% reduction in bass catch was achieved (Thatcher 

and Irving, 1992). 

In view of the changeable acoustic field within the test pools, it would be unwise to overinterpret the findings on how fish redistributed themselves in relation to the sound pressure 

level distributions. The chief point is that the fish, where significant responses were 

demonstrated, moved away from the sound source. The most important factor, in acoustic 

terms, was that the sound levels throughout the tank were maintained at a high level relative 

to the ambient background noise level, which was in the range 65 to 70dB re 1 pPa at all 

times, both at Fawley and Otter Ferry. This represents a differential between test and 

control SPL of at least 30 to 40dB re lpPa in all trials, for frequencies of 100 to 300Hz. 

Whilst lower SPLs might prove effective, it would be wise in any future field trials to aim 

to exceed, in the proposed fish exclusion zone, both the minimum absolute and differential 

(relative to background) sound levels used in the present trials. 

4.1.2 Confinement of Fish 

An obvious limitation of the present trials was that sound levels were high throughout both 

the experimental pools, albeit with some gradation, and the fish had no means of escaping 

from the sound field altogether. As a consequence, fish trying to flee the sound field had 

two choices: either move as far away as possible from the source, or search for a way out. 

Most fish tended to do both to a greater or lesser extent. The confused result for cod with 

the Loeffelman signal, for example, was not because the fish did not react to the sound but 

because the main behaviour was to search the tank. 

In open water, where the system can be placed so as to offer the fish a free choice of 

movement, a more fruitful response might be expected. The high diversion efficiencies 

reported by Loeffelman et al. (1991;1993) would tend to confirm this. 

Whilst the full details of the observations on fish behaviour have been presented in this 

Report and attempts have been made to apply quantitative measures to the responses, again 

it would be unwise to over-interpret the significance of variations in response seen with 

different signals used on the same fish species. Any form of positive result, Le., significant 

movement of fish away from the sound source, indicates that the fish have the capacity to 

react appropriately to that signal: a more impressive high-speed reaction will not necessarily 

imply a more effective deterrence in the field, where a more considered response by the fish 

might actually be more effective. 

4.1.3 Use of Farm-Raised Fish 

The salmon and trout used in this study were farm-raised; all other species were taken from 

the wild. 
23 

Some differences are to be expected with farm-&sed fish. At the salmon farm in Scotland, 

for example, the fish were grown on in ponds supplied by a pulsed aeration system, resulting 

in their continuous exposure to high level, low frequency noise (no measurement was made 

of this). 

Knudsen et al. (1992) compared the behaviour of wild and hatchery-raised Atlantic salmon 

and found differences in their escape responses when confronted with high sound levels. 

They used a tank with a sloping bottom and found that, whereas hatchery-raised fish would 

make for the most distant part of the pool. when escaping, wild fish would make for the 

deepest part. This may not be important per se, but illustrates that behaviour cannot be 

assumed to be the Same for farmed and wild fish. 

4.2 Performance of the Methods 

4.2.1 The Empirical Method 

The objectives of this part of the work were to consolidate the preliminary laboratory 

findings presented by Thatcher and Turnpenny (1992) and Thatcher and Irving (1992) by 

developing a more objective test method which also assessed habituation, and to extend the 

approach by testing a wider variety of signals on a range of estuarine species. These 

objectives were met, with the development of a repeatable test methodology, which was then 

applied to a variety of species with a broader range of candidate signals. 

The most obvious finding from the empirical trials was that, of the sixteen signals under test, 

few generated any significant reaction. Some assessment of the success obtained with the 

various signals can be made by totalling the Response Category scores given in Table 3.1 for 

the screening trials. Here, the lower the number, the more effective was the signal over a 

range of species. This information is more easily absorbed when the scale is reversed by 

subtracting the totals from the maximum available score of 35, as shown in Figure 4.1. In 

this scheme, signals which produced no response at all, with any of the species tested, yield 

an overall zero value. On this basis, all signals but numbers 3,4 and 10 evoked some 

response in fish. Other signals produced varying degrees of response, but outstanding 

amongst them all were the Group 3 Signals, numbers 7 and 8. When subjected to the full 

test protocol, only these two signals produced a statistically-verifiable deterrence response 

Figure 4.1). The success of these signals over the others may be owing to the combination 

of high signal amplitude and the frequency sweep: a swept frequency band offers nonspecific frequency targeting, while maintaining maximum amplitude across the whole 

frequency band. All other signals in the series either had reduced amplitude during part of 

the delivery cycle (crescendo or pulsed signals), reduced frequency coverage (fixed frequency 

signals) or reduced amplitude since the signal was spread over a range of frequencies at the 

same time (e.g. broad band signals). 

If a single signal were required for multi-species deterrence, Signal 7 would clearly be the 

one to choose: it had the largest Fish Response Score (Figure 4.I) and yielded a 

Category 3 or better response from all of the species on which it was tested (Table 3.1). 

In no trial was there any evidence of fish becoming habituated to the signal. 
24 

The one failure with the empirical method was the European eel. The lack of any significant 

deterrence effect may have been a result of using inappropriate signal frequencies. In the 

absence of any published information on hearing or sound production in this species, the 

question cannot be resolved. A second possibility is that, since eels taken from low salinity 

or fresh waters are benthic in habit and their swimbladders are not fuily inflated, they may 

not be sensitive to sound pressure. This would limit any sound detection to the near-field of 

the transducer, perhaps explaining the slight response observed for eels in close contact with 

the transducer. There is no doubt that the cover provided by the transducer provided 

stronger attractive influence on eels that the aversive stimulus of the sound. 

4.2.2 The Loeffelman Method 

The main objective with these trials was to confirm that the method, as developed by 

Loeffelman and co-workers, would work with estuarine species of interest within the UK. 

Of seven species investigated in the trials (Atlantic salmon, brown trout, cod, whiting, eel, 

bass, herring) only four could be fully tested using the Loeffelman method, since no relevant 

sounds were detected for bass and eel, despite protracted 'listening'. For four species, 

sounds were successfully recorded and analyzed and, in all cases, effective deterrent signals 

were developed and statistically proven. In herring dso, sounds were recorded that would 

have enabled signal development, but there was no opportunity to conduct behavioural trials 

on this species. 

No habituation to the test signal was detected in any of the species tested. In brown trout, 

there was evidence that fish learnt to stay away from the sound source. 

4.2.3 Comparison of the Loeffelman versus the EmDiricai Method 

For those species which do not readily (if at all) produce sound, the Loeffelman method is 

clearly not applicable and this must be recognised as a potential limitation of the method. 

Most species in the present study did produce sound, with only bass and eel remaining silent. 

If their close American relatives (Table 1.3) are any indication, these species may be sound 

producers, given the right conditions. According to Loeffelman (pers. comm.), fish tend to 

be more vocal at warmer temperatures, whereas the present studies were conducted in wintertime. It would be worth making further attempts with these species during the summer 

months. There may also be differences between males and females of the same species, and 

some life stages may be more talkative than others, as found in the present study with brown 

trout. 

With regard to the relative efficacy of the signals produced by the two methods, the results 

must be treated with caution, owing to the limitations stated above. A comparison can only 

be made for those species which could be tested by both methods, Le., the salmonid and 

gadid species. Both produced statistically-signifTcant (p=0.05or better) movement of these 

away from the sound source. A summary of the responses obtained by each method is 

shown in Table 4.1. For salmon, the Empirical Series signal produced a stronger response 

(Category 2 versus 3) than the Loeffelman signal, though for brown trout adults and juveniles 

more marked reactions were obtained using the Loeffelman method. Cod and whiting 
25 

reacted more strongly to the Empirical Series signals. Overall, the Empirical Series scored 

more successes, chiefly because more species could be tested. 

The principal difference between the two methoiis is the degree of customization: the signal 

(No. 7)selected as being most effective from the Empirical Series offers, potentially, a 

broad-spectrum deterrent which might be expected to work for a range of fish species in an 

indiscriminate way. This range might need to be shifted up or down to cater for fish with 

higher or lower frequency hearing optima. The Loeffelman method, on the other hand, is 

sharply focused on individual species. The degree of discrimination was obvious during the 

trials, when signals developed for one species were tried out on others, invariably producing 

negligibleeffect. As much may be inferred from the Empirical Series screening trials, where 

a number of signals which were generally similar to those derived by the Loeffelman method, 

typically comprising one or more tones applied as a crescendo (e.g. Signals 9 and 10) evoked 

virtually no response in any of the fish tested (Table 3.1). The Loeffelman method may be 

used for multiple species and lifestages by combining signals designed for individual species 

into a signal train or, in some cases, by electronically mixing the signals into one signal. 

Trials currently being undertaken by Loeffelman and co-workers on the Sacramento River 

in northern California are taking advantage of the selective potential of the method, where 

a high frequency signal (about 1.5kHz) is being used to deter down-migrating juvenile 

chinook salmon: this frequency is believed to be well above the hearing range of adults 

returning up-river and therefore should disturb their migarations. The results from this trial 

are not yet available. The method could also be used to guide species during sequentially 

timed migrations by having different signals running at different times of the year. The 

sound system offers this flexibility. 

Habituation of fish to the sound signals was not found with either method in the present 

study. Habituation to sound has been found to occur in Atlantic salmon (Knudsen et al., 

1992), presumably as a result of the different nature of the sound signals used in their study. 

These authors used a sound which was constant in both frequency and amplitude, whereas 

either or both were continuously varied in the successful gignals used in the present study. 

The replicate experiments in the present study were carried out over a period of a day or 

more and the absence of habituation on this timescale should ensure that a sound system will 

remain effective for any population migrating past a water intake. The findings for brown 

trout may also indicate that a more resident population may quickly learn to stay away from 

the sound field. This would therefore meet the requirements for fish protection at coastal 

and estuarine thermal or hydroelectric plants, as well as other types of water intake. 

5. CONCLUSIONS 

5.1 Both the Loeffelman signal development process and the empirical screening method 

were successful in producing signals which could be shown to have a statistically-significant 

(p<0.05) and, in most cases highly significant (p<O.OOl) deterrent effect in laboratory 

trials. 

5.2 The empirical approach yielded one signal, based on a constant amplitude, swept 

frequency range, which was shown to be effective with all the fish species tested, apart from 

eel. Neither method was successful with eels, 
5.3 A limitation experienced with the Loeffelman approach was that two out of the seven 

species tested did not produce sounds in the trials, and therefore no signal could be developed 

for them. This risk may be reduced by developing better protocols to ensure that sound 

production from a particular lifestage is encouraged. This limitation has not been apparent 

in previous North American work by Loeffelman and co-workers. 

5.4 No evidence of habituation was detected in the trials. In one species (brown trout), 

the fish quickly learnt to remain away from the sound source, a feature which would enhance 

the protection of populations resident near water intakes. 

5.5 Based on the effectiveness of the signals in these laboratory trials, a properly designed 

and installed sound system should should be capable of guiding fish past water intakes. For 

tidal barrage applications, this would need to be be designed as part of a complementary 

system of acoustic deterrents and fish passes that would encourage fish to pass via routes 

other than the turbines. 

6. RECOMMEXDATIONS 

6.1 Signal Development Method 

6.1.1 For broad spectrum applications, where it is desired to deter the widest range of fish 

species and life stages possible, the swept frequency signal developed under the Nuclear 

Electric plc contract is most appropriate. In the present trials, this type of signal produced 

a sound field which was repulsive to all species tested, apart from eels. However, the 100 

to 500Hz sweep used might not be appropriate to allspecies: there is scope for defining the 

optimum range for the particular suite of species and life stages using the Loeffelman 

method. 

6.1.2 For applications where it is neccessary to deter selectively particular life stages or 

species, the Loeffelman method potentially offers a higher degree of targeting, provided that 

the overlap in auditory spectra is small. This approach is currently being tested in North 

American trials, where it necessary to deter downstream-migratingjuvenile fish while, at the 

same time, not deterring upstream adult migrants of the same species. Multiple signals can 

be compiled into a single signal trainbut, for non-specific deterrence, it would be easier in 

practise to use a swept signal for this purpose. 

6.1.3 To make the best use of the heffelman method, further investigation of factors and 

conditions which lead fish to vocalize is required. These may relate to environmental 

conditions such as temperature, salinity and daylength, or the physiologidanatomical state 

of the fish, which may be related to lifestage, sex or season. 

6.2 Field trials 

6.2.1 The results of these laboratory trials have met the chief objective of.showing that a 

selection of British estuarine species which are of conservation or fisheries interest can be 
moved in a predictable way using approPriate underwater sound signals. It is therefore 

recommended that the programme should be taken on to the next phase of proposed testing 

on an estuarine or mastally sited nuclear power station. NuclearElectric plc's Hinkley Point 

B Power Station is the preferred option, for the following reasons: 

i) Nuclear Electric plc have in excess of 12years data on seasunal catch rates of 

fish, which would aid in statistical planning of the trial. 

ii) The cooling water intakes are located offshore in high tidal-velocity, turbid 

waters; no other type of behavioural fish deterrent system would be feasible under these 

conditions and so the system would be highly relevant to this type of site and a severe test 

of the system's durability; the conditions are also typical of those at potential tidal barrage 

sites in the UK. 

iii) There is tunnel access to the offshore intalce structure at the site, and an 

electrical power supply, adequate for the needs of the acoustic deterrent system hardware. 

The autumn-winter period is one of seasonally-high fish catch, and would be optimal for the 

trial. 

6.2.2 Before conducting such a trial, it will be necessary to carry out a full planning 

survey at the test site to assess the flow geometry and acoustic conditions. Only then will it 

be possible to specify the number and size of the underwater transducer units and associated 

driving system required. The sound system will need to generate sound levels >40dB above 

ambient levels. 

It is recommended that the planning survey should be carried out in the summer months, with 

a view to system inscallationIater in 1993 for testing in the same year. 

6.2.3 Since a broad spectrum deterrent, effective against a wide range of species, is required 

for this site, it is recommended that the Empirical Series 7 signal be adopted for this trial. 
28 

REFERENCES 

Campbell, R 'C, 1974. Statistics for Biologists. Cambridge,University Press, 385 pp. 

Clarke, G M, 1969. Statistics and Experimental Design. London, Arnold, 161 pp. 

Day, F, 1884. The Fishes of Great Britain and Ireland (Volume ZI). London, Williams and 

Norgate, p.234-236. 

Fish, M P, 1954. The character and significance of sound production among fishes of the 

western North Atlantic. Bingham Oceanographic Collection, Bulletin 14 (3), pp3­

109. 

Fish, M P and Mowbray, W H, 1970. Sounds ofwestern North Atlantic Fishes: a 

Reference File of Biological Underwater Sounds. London, John Hopkins, 207 pp. 

Hawkins A D, 1986. Underwater sound and fish behaviour. In: The Behaviour of Teleost 

Fishes, (Ed. Pitcher, T J), London Croom Helm, pp 114-151. 

Klinect D, Loeffelman P H and Van Hassel J H, 1992. A new signal development process 

and sound system for diverting fish from water intakes. Proc. Amer. Power 

Conference, Illinois Institute of Technology, April 13-15, 1992, Chicago, Illinois. 

Knudsen, F R, Enger, P S and Sand, 0, 1992. Awareness reactions and avoidance 

responses to sound in juvenile Atlantic salmon. J. Fish Bid, 40 (4), pp523-534. 

Loeffelman P H, Van Hassel J H, Klinect D A, 1991. Using sound to divert fish from 

turbine intakes. Hydro Review, October, 1991 pp 30-43. 

Loeffelman P H, Klinect D A and Van Hassel J H, 1993. A behavioural guidance system 

for fish using acoustics customized to target fish hearing. Can. J. Fish.Aquat. Sci. , (in press). 

Marshall, N B, 1962. The biology of sound-producing fishes. Symp. Zool. SOC.London, 

7,pp 45-60. 

Moulton, J M, 1960. Swimming sounds and the schooling of fishes. Biol. Bull. Woods 

Hole, 119, p210. 

Patrick P H, McKinley R S, Christie A E and Holsapple J G, 1988. Fish protection: sonic 

deterrents. In: 'Proceedings: Fish Protection at steams and Hydro electric Power 

P�ants', pp 4.1-4.12. Electrical Power Research Institute. EPRI CS/EA/AP-5663-

SR. 
29 

Ray S S, Snipes R L and Tomijanovich P A, 1976. A state-of-the-art report on intake 

technologies. Rept. to Office of Res. and Dev., US Envir. Protect. Agency, 

Washington DC. EPA-60. 0/7-76-02 0. 

Solomon D J, 1988. Fish passage through tidal energy barrages. Energy Technology 

Support Unit, Harwell. Contractors Report Number ETSU TID 4056, 76 pp. 

Solomon D J, 1992. Diversion and entrapment of fish at water intakes and outfalls. 

National Rivers Authority, R&D Report No. 1, NRA, Bristol BS12 2UD. 

Tavolga, W N, 1971. Sound production and detection. In: Fish Physiology (eds. Hoar, WS 

and Randall, D J), London, Academic, pp.135-263. 

Thatcher K P and Turnpenny A W H, 1992. Acoustic fish deterrent system: preliminary 

observations, 1991. Report to National Power plc and Nuclear Electric pfc. 

FAWLEY arl Report No. FCR 008/92. FAWLEY arl Ltd, Southampton SO4 1W, 

ZIX. 

Thatcher K P and Irving P, 1992. Fish deterrent trials at Oldbury Power Station, November 

1991 to January 1992. Report to National. Power plc and Nuclear Electric plc, 

FAWLEY arl Report No. FCR009/92. Fawley arlLtd, SouthamptonSO4 lTW, UK. 

Turnpenny A W H, 1988. The behaviourial basis of fish exclusion from coastal power 

station cooling water intakes. CEGB Research Report No. RD/L/3301/R88. 

Turnpenny A W H and Coughlan, J., 1992. Power generation on the British coast: thirty 

years of marine biological research. Hydroexol. Appl. (4)1,pp 1-11. 

Turnpenny A W H, Davis M H, Fleming J M and Davies J K, 1992. Experimental studies 

relating to the passage of fish and shrimps through tidal power turbines. Unpublished 

report to National Power plc and AEA Technology, Harwell. 
Figure 1.I.Audiograms of Teleost Fish 

140 

100 

80 

60 

50 100 200 500 1,000 2,000 5,000 10,000 

Frequency (Hz) 

Adapted from Hawkins, 1986 
Figure 2.1 Equipment Usedfor the Recording . 

and Analysis of the Fish Sounds 

(a) Fish Recording Apparatus (from Klinect et al, 1991) 

Charge

Amplifier 

B&K 

Model 8103 

Transducer 

fnOX7520 i Rockland 1 

Digital Spectrum Oscilloscope Analyser 

Loudspeaker 

AlWA HD-SI 

DAT 

Recorder 

(b) Block Diagram of fnstrumentation 
Figure 2.2 Description of Signals in the Empirical Series 

used for the Nuclear Electric Trials 

(a) Example of pure sine wave @ i63 Hz . 

pool 

,. . . . . . . . . , 

-19.7 rSiC 1:-13 .ZE-3 58.5 m 

Example of 163Hz crescendo 

..... .... 

-394. rSEC 

(e) Definitions of a31 16 signals 

1. Sine wave, 163Hz 

2. Sine wave, 217Hz 

3. Sine wave, 294Hz 

4. Sine wave, 163Hz, 10 cycle burst 

5. Sine wave, 217Hz, 10 cycle burst 

6. Sie wave, 294'&, 10 cycle burst 

7. Sine wave, sawtooth sweep from 100 to 

500Hz, 4.5Hz sweep rate 

. 8. sine wave, Sawtooh sweep from 100 to 

500% ,2.5% sweep rate 

9. Sine wave, 163Hz, 1s crescendo 

1.1714 SIC 

10. Sinewave, &xed 163,217 and 294Hz, 1s 

crescendo 

1 1. Sine wave, 163-197 Wz sweep crescendo 

12. Sine wave, 217-253'Hzsweep crescendo 

13. Sine wave, 294-340 Hzsweep crescendo 

14. Sine wave, 163, 217 and 294 Hz sweep . 

crescendo 

15. Sine wave, multi-frequency 139 to 

463Hz, 500mspulses 

16. Sine wave, multi-frequency 139 to 463Hz, 

1s crescendo 
.................... 

\ 

/ 

.................., 

I 
Figure 2.4. The Otter Ferry Test-Pool 

Used for Atlantic Salmon Trials 

s3 

9 

Observation 

a 

Observation 

Point 

3 

\ 

15m 

/ 

Obsewafion 

Point 

Point 

i 

Point 

2 

Ground level 
Figure 2.5.The Fawley sound Pool . 

(a) Plan View 

\ 

5rn 

Submersible 

' DLight 2 

\ 

I' 

Tangential 

discharge 

(b) Section nOverhead TV Camera 
Figure 2.6. Isopleths of Sound Pressure Level 

easiared at 50% Depth in the Fawfev Sound Pool 

(a) Signal - 300Hz Sine Wave 

(b) Signal - 100 Hz SineWave 
Fiaure 2.6. Isopleths of Sound Pressure Level 

Measured at 50% Depth in the Otter Ferrv Sound 

poof 

(e) Signal - 210 Hz Sine Wave 

level = 6570dB RMS 

Backgroundsound level = 6570 dB RMS 
Figure2.7. Concentric Zones Used for Scorinq 

of Fish Distribution in the Fawlev Sound Pool J 

Area adjustments 

Area 2 = 1,21(Area 1) 

Area 3 = 1.27(Area 1) 

Area 4 = 1.69(Area1) 

Area 5 = 1.64(Area 1) 

Area 6 = 1,03(Area1) 
Figure 3.1 (a) Spectrum and (b) Time Series 

for Atlantic Salmon Sounds, Fish Size - 600g 

i i i i i i i i i 

110.00 

d0R 

3

...... : : : : :

.... 

30 . _,__I_.._....

0.00 Frequency/Hz 1000.0 
Figure 3.2 

Summary of Results for Atlantic Salmon Deterrence 

Signal: 210Hz and 275Hz,2second crescendo 

(Responsecategory 3) 

Tbe experimentwas performed in a 15m diameterx 2m deep pool. Observationswere 

made of the numbers of fish present within a defined area (45 sq. m) closeto #e Model 

220 transducer. Countswere made every 30s over ten Sminute test periods, 

alternatingwith control and rest periods. 

Fish Counts with and without Sound 

m Otter Ferry, 8-95ecember,l992 3 70 

Mean counts and significance of differences: 

{see Appendix t, TableAI. I for full&ta) 

8th December9th December 

Sound OR 15.2(3.6) 13.0(7.3) 

Sound on: 7.0 (2.3) 7.7 (4.3) 

p<O.OOI p<O.OOI 

Habituation 

8th December 

-so -
Figure 3.3 

Fish Orientation Relative to Streamlines, 

with and without sound 

Atlantic Salmon,OtterFeny,9th December 1992 

25 Sound Off 

-90 -80 -70 -60 -33 -40 -30 -20 -10 0 10 20 30 40 53 50 7u 80 90 -85 -75 4s -55 -45 -3s -25 -15 -5 5 15 25 35 45 55 65 IS 85 

Angle from flow 

Sound On 

-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 

-85 -75 -65 -55 -45 -35 -25 -15 -5 5 I5 25 35 45 55 65 75 115

Angle hm flow 
Figure 3.4.(a) Spectrum and (b) Time Series 

for Brown Trout Sounds, Fish Size - 30cm 

dBR 

30 

0.00 Frequency///Hz 1000.0 

Relative Amplitude 

0 Timeims 
Figure 3.5 

Distributionof Fish in the Fawley Pool, with and without Sound Signals 

Species: Brown Trout (adult) Salmo trutta 

(Response Category 5) 

Signal Description: 200& 300 Hz, 2 second crescendo 

(a) Adjusted Distribution of Fish 

901 

1 2 3 4 5 6 

Zone Number 

Sound Off USound On 

Kolmosrorov-SmimoffTwoSample Test for Significant Differencein Fish Distribution 

Mean Distance of fish From Sound Source (metres)

Sound Off: 1.49 Sound On: 1.58 

5.00 13.26 32.95 196.15 193.62 0.95 I 0.93 I 0.02 

6.00 11-06 15.33 207.21 208.95 1.00 I 1.00 I 0.00 

Sum 207.21 208.95 Max Difference 0.03 

Siginficance Level: Not Significant 

(b) HabituationTest 

Differencein Distancefrom Transducer inTest andControlPeriods 1.5 

-1.5 1 ' 

1 2 3 4 5 6 7 8 9 ie 

Number of Exposures 

r-squared = 0.34 No1Significant 
Figure 3.6 

Distribution of Fish in the Fawtey Pool,with and without Sound Signals 

Species: Brown Trout (adult) Saimo frutta 

(Response Category 2) 

Signal Description: 100 & 300 Hz,2 second crescendo 

(a) Adjusted Distributionof Fish 

601 

1 2 3 4 5 6 

Zone Number 

Sound Off L1Sound On 

KolmogorovSmimoffTwo-Sampie Test for Significant Difference in Fish Distribution 

Mean Distance of Fish From Sound Source (metres) 

Sound Off: 2.23 Sound On: 2.79 

5.00 28.59 46.56 181.71 158.14 0.90I 0.831 0.07 

6.00 21-05 33.37 202.76 191.50 1.00 1 1 .ooI 0.00 

Sum 202.76 I91-50 Max Difference 0.20 

Siginficance Level: p<0.001 

(b)Habituation Test 

Differencein Di&n& from Transducer inTest and Control Periods 3, 

-3 I ' I 1 2 3 4 5 6 7 8 9 10 

Number of i3posures 

r-squared = 0.70 p~O.aOl: 
Figure 3.6 (continued) 

(c) Testing for a Lemt Response 

1 2 3 4 5 6 7 8 9 10 

Number of Exposures 

Sound On Control 

Test for effect shown infigure 3.6(b)being a learnt response. 

R Squared 0.59 Significantat p 0.01 
Figure 3.7 

Distributionof Fish in the Fawley Pool, with and without Sound Signals 

Species: Brown Trout (juvenile) Saimo frutta 

(ResponseCategory 3) 

Signal Description: 100& 300 Hz, 2 second crescendo 

(a) Adjusted Distribution of Fish 

300 

250 

5 200 C

g 150 

Q

& loo 

50 

0 

6 

Sound Off USound On 

KolmogorovSmimoff TwoSampie Test for Significant Difference in Fish Distribution 

Mean Distance of Fish From Sound Source (metres) 

Sound Off: 3.61 Sound On: 3.92 

Siginficance Level: p<o.001 

(b) Habituation Test 

Difference in Distance from Transducerin Test and Control Periods 8 

- 6 ' 

1 2 3 4 5 6 7 8 9 Number of Exposures 10 

r-squared = 0.01 Nol Significant 
Figure 3.8 

Distribution of Fish in the Fawley Pool, with and without Sound Signals 

Species: BrownTrout (adult) Salmo truth 

(Response Category 4) 

Signal Description: NE Signal #8 

(a) Adjusted Distribution of Fish 

80 

70 

50 

x

Em 

340 

230 

U 

20 

10 

0 

1 2 3 4 5 6 

Zone Number 

Sound Off USound On 

Kotmosorov-Smirnoff Two-Sample Test for Significant Difference in Fish Distribution 

Mean Distance of Fish From Sound Source (metres) 

Sound Off: I.74 Sound On: 2.18 

5.00 I 16.44 28.78 207.71 187.32 0.96 I 0.93 0.03 

6.00 I 7.95 13.39 215.66 200.71 1.00 1 1.00 1 0.00 

Sum I 215.66 200.71 Max Difference 0.16 

Siginficance Level: pe0.05 

(b) Habituation Test 

Difference inDistance from Transducer in Test and Control Periods 2 

-2 I ' 

1 2 3 4 5 6 7 8 9 10 

Numberof Exposures

r-squared = 0.38 Not Significant 
Figure 3.9 

Distributionof FisR in the Fawley Pool, with and without Sound Signals 

Species: Brown Trout (adult) Saimo frutta 

(Response Category 4) 

Signaf Description: NE Signal #I1

(a) Adjusted Distribution of Fish 

501 

I 2 3 4 5 6 

Zone Number 

Sound Off 0Sound On 

KolmonorovSmimoffTwoSample lest for Significant Difference in Fish Distribution 

Mean Distance of Fish From SoundSource (metres) 

Sound Oft 2.10 SoundOn: 2.22 

SiginficanceLevel: Not Significant 

(6)Habituation Test 

Differencein Distance from Transducer inTest and Control Periods 15 

-1.5 I ' 

1 2 3 4 3 6 7 8 9 10 

Numberof Exposures 

r-squared=0.02 Not Significant 
Figure 3.10 

Distributionof Fish in the Fawby Pool, with and without Sound Signals 

Species: Brown Trout (juvenile) Salmo frutta 

(Response Category 3) 

Signal Description: NE Signal #7 

(a) Adjusted Distributionof Fish 

n 

0 

I 2- 3 4 5 6 

Zone Number 

SoundOff SoundOn 

Kolmogorov-Smirnoff Two-Sample Test for Significant Difference in Fish Distribution 

Mean Distance of Fish From Sound Source (metres) 

Sound Off: 2.96 Sound On: 3.22 

Siginficance Level: p<o.O01 

(b) HabituationTest 

DifferenceinDistancefrom Transducer inTest and Control Periods 3 

-3 

1 2 3 4 5 6 7 8 9 10 

Numberof Exposures 

r-squared= 0.14 Mot Significant 
Figure 3.11 (a) Spectrum and (b) Time Series 

for Whiting Sounds, Fish Size - 30cm 

dBR 

30 

(b) 

RelativeArnplitt 

Time/s 1.5 
I 

Figure 3.12 

Distribution of Fish in the Fawley Pool, with and without Sound Signals 

Species: Whiting (adult) Merlangius merlangus 

(Response Category 3) 

Signal Description: 410& 480 Hz,2 second crescendo 

(a) Adjusted Distribution of Fish 

90r I

80 

70 

8 60 

@= 

540 

ti= 

20 

IO 

0 

1 2 3 4 5 6 

Zone Number 

Sound Off Sound On 

Kolmogorov-SmimoffTwoSample Test for SignificantDifference in Fish Distribution 

Mean Distance of Fish From Sound Source (metres) 

Sound Off: 3.11 Sound On: 3.59 

Siginficance Level: p<o.o01 

c 
Figure 3.13 

Distribution of Fish in the Fawley Pool, with and without Sound Signals 

Species: Wbiting (adult) Merlangius metfangus 

(Response Category 3) 

Signal Description: 360& 390 Hz,2 second crescendo 

(a) Adjusted Distribution of Fish 

100 

90 

80 

). 70

Em 

s50 

z40 

E30 

20 

10 

0 

Zone Number 

Sound Off aSound On 

Kdrnogorov-Smirnoff TwoSample Test forSignificant Diffemnce in Fish Distribution 

Mean Distance of Fish From Sound Source (metres) 

Sound OR 3.26 Sound On: 3.60 

Siginficance Level: p<O.OI 

2 

h

wl­ E

8

C

9 O ­

ii 

m

= 

a - -1 

a 

-2 8 
Figure 3.14 

Distributionof Fish in the Fawley Pool, with and without Sound Signals 

Species: Whiting (adult) Meriangius mertangus 

(Response Category 1) 

Signal Description: NE signal#7 

(a) Adjusted Distribution of Fish 

n 

IO 

0 

1 2 3 4 5 6 

Zone Number 

Sound Off aSoundOn 

Kolmogorov-Smirnoff Two-Sample Test for Sisnificant Difference in Fish Distribution 

Mean Distance of Fish from Sound Source (metres) 

SoundOR 2.83 SoundOn: 3.36 

5.00 44.48 7037 155.15 133.66 0.91 1 0.81 1 0.10 

6.00 15.04 31.23 170.19 164.89 1.oo I 1.00 I 0.00 

Sum 170.19 164.89 Max Difference 0.27 

Siginficance Level: p<O.ool 

(b) Habituation Test 

Differencein Distancefrom Transducer inTest and Control Periods 

2, 

h

VI E

0)

-0 

c 

8 0 rn 

1 2 3 4 5 6 7 8 9 10 

Numberof Exposures 

r-squared = 0.01 Not Significant 
Figure 3.15 

Distribution of Fish in the Fawley Pool,with and without Sound Signals 

Species: Whiting (adult) Mefiangius rnerlangus 

(ResponseCategory 1) 

Signal Description: NE Signal #7 

(a) Adjusted Distribution of Fish 

60 

50 

2;a

c

$ 30 

Q)

1;: 20 

10 

0 

6 

Zone Number 

Sound Off tII Sound On 

Kolrnogorov-Smirnoff TwoSampie Test for SignificantDifference in Fish Distribution 

Mean Distance of Fish From Sound Source (metres) 

Sound Off: 3.18 Sound On: 3.98 

Siginficancetevei: p<O.OOI 

(b) Habituation Test 

Difference in Distance fromTransducerin Test and Control Periods 3 

- 2

W 

E 

$ I c:

B o

9 

n 

8 -' Q) 

Q -2 

-3 1 2 3 4 5 6 7 8 9 10 

Number of Exposures 

r-squared = 0.23 Mot Significant 
Figure 3.16.(a) Spectrum and (b) Time Series 

for Cod Sounds, Fish Size - 45cm 

dBR 

30 

Relatlve li. 

-

0 Timefs I .5 
Fiaure 3.17 

Distribution of Fish in the Fawley Pool, with and without Sound Signals 

Species: Cod (adu!t) Gadus morhua 

(Response Category 3) 

Signal Description: 140 & 170 Hz,2 second crescendo 

(a) Adjusted Distribution of Fish 

r I 

1 2 3 4 5 6 

Zone Number 

Sound Off L_1Sound On 

Kolmogorou-SmirnoffTwoSample 'Test for Significant Difference in Fish Distribution 

Mean Disbnce of Fish From Sound Source (metres) 

Sound OR 3.02 Sound On: 3.41 

Siginficance Level: p4.05 

(b) HabituationTest 

Difference in Distance from TransducerinTest and Control Periods 1.5 

n l

v 

E 

Q) 0.5 

0 

c ...... -

................. ....... ....... Eo .......................... v)

B 4.5 

Q) 

n 

1 2 3 4 5 6 7 8 9 10 

Number of Exposures 

r-squared = 0.22 Not Significant 
Figure 3.18 

Distributionof Fish in the Fawley Pool, with and without Sound Signals 

Species: Cod (adult) Gadus morhua 

(Response Categmy 2) 

Signal Description: NE Signal#7 

(a) Adjusted Distribution of Fish 

50 

r 

1 2 3 4 5 6 

Zone Number 

Sound Off 0Sound On 

Kofmogorov-SmirnoffTwo-Sample Test for Significant Differencein Fish Distribution 

Mean Distanceof Fish From Sound Source (metres)

Sound OR 3.16 Sound On: 3.74 

Siginficance Level: p<0.05 

(b) Habituation Test 

Differencein Distancefrom Transducer in Testand ControlPeriods 

-1.5 8 

1 2 3 4 5 6 7 8 9 Lo 

Number of Exposures 

r-squared = 0.18 NutSignificant 
Figure 3.19 

Distributionof Fish in the Fawley Pool, with and without Sound Signals 

Species: Cod (adult) Gadus morhua 

(Response Category 2) 

Signal Description: NE Signal # 7 

(a) Adjusted Distributionof Fish 

50 

40 

z-i 

g30 

a 

20 

lL 

10 

0 

Sound Off Sound On 

KolmogorovSmirnoffTwoSample Test for Significant Difference in Fish Distribution 

Mean Distance of Fish From Sound Source (metres) 

Sound Off: 2.84 Sound On: 3.45 

Siginftcance Level: p<o.o1 

L5 

(b) Habituation Test 

Difference in Distance from Transducer inTest and Control Periods 

1 2 3 4 5 6 Number of Exposures 7 8 9 io 

r-squared = 0.11 Not Significant 
Figure 3.20 

Distributionof Fish in the Fawley Pool, with and without Sound Signals 

Species: Cod (adult) Gadus morhua 

(Response Category 4) 

Signal Description: NE Signal #I4 

(a) Adjusted Distribution of Fish 

50 

2 3 4 5 6 

Zone Number 

Sound Off 0Sound On 

KolmworovSmirnoff Two-Sample Test for Significant Difference in Fish Distribution 

Mean Distance of Fish From Sound Source (metres)

Sound Off: 3.41 Sound On: 3.64 

5.00 23.71 30.00 57.70 54.25 0.61 I 0.57 I 0.05 

6.00 35.79 41.61 92.90 95.87 1.00 I 1.00 ] 0.00 

Sum 92.90 95.87 Max Difference 0.11 

Siginficance Level: Not Significant 

(b) Habituation Test 

Difference in Distance from Transducer in Test and ControlPeriods 1.5 

v It\ , 0.5 1 .._....___ \ ....­

r \ 

\ 

\ / 

-1.5 1 ' 

1 2 3 4 5 6 7 8 3 10 

Number of Exposures 

r-squared = 0.03 Not Significant 
Figure 3.21 

Distribution of Fish in the Fawley Pool, with and without Sound Signak 

Species: Bass (adult &juvenile) 

(Response Category 2) 

Signal Description: 

(a) Adjusted Distribution of Fish 

2 3 4 5 6 

Zone Number 

Sound Off USound On 

Kolmogorov-Smimoff Two-SampIe Test for Significant Difference in Fish Distribution 

Mean Distance of Fish From Sound Source (metres) 

Sound Off: 3.49 Sound On: 3.89 

Siginficance Level: p4.05 

(b) Habituation Test 

Differencem Distance from Transducer in Test and ControlPeriods l.5 1 

-1.5 I 1 2 3 4 5 6 7 8 9 10 

Number of Exposures 

r-squared =0.05 Not Significant 
Figure 3.22 

Distributionof Fish in the Fawley Pool, with and without Sound Signals 

Species: Bass (adult &juvenile) Dicentrarchus labra 

(Response Category 2) 

Signal Description: NE Signal #8 

(a) Adjusted Distributionof Fish 

601 

10 

0 

4 2 3 4 5 6 

Zone Number 

Sound Off 0Sound On 

Kolmoaorov-SmimoffTwoSample Test for Significant Differencein Fish Distribution 

Mean Distance of Fish From Sound Source (metres) 

Sound Off 3.37 Sound On: 4.16 

Siginficance Level: p<O.OI 

(b) Habituation Test 

Differencein Distance &om Transducerin Test and Control Periods 2 

h 

V

E I 

Q

0

r:

Bo 

v)

5. 

d

Q -1 

n 

-2 

1 1 3 4 5 6 7 8 9 10 

Number of Exposures 

r-squared= 0.33 Not Significant 
... ... ... ... 

Figure 3.23. (a) Spectrum and (b) Time Series 

for Herring Sounds, Fish Size - 20cm 

110.00 

d8R 

... 

0.00 Frequency/Hz 1ooc 

0 Time/ms 
Figure 4.1 

Fish Response Scores for Empirical Series Signals 

and Signals Yielding Significant Deterrence 

40 

a,6-30 

0 

m 

a, Group 3 

v1 

S 3 

0 20 

Q

u)

2 Group 5 Group 6 

r 

# 10

ii 

0 

1 2 3 4 5 6 7 8 9 10111213141516 

Signal Number 

Note: Numbers above bars indicate the number of full trials 

in which significant (pgO.05) deterrence was achieved. 
Table 1.1 Examples of Sound Levels Produced by Various Sources in Air and Water 

(after Tavolga, 1971) 

Source of Sound 

r 

Jet aircraft takeoff at 100 m 

Threshold for human aural discomfort 

New York subway train at 10 m 

In Air Noisy

- business office ~ ~~ ~~ ~ 

Home hi-fi system 

Average converstaion at 1 m 

Private business office 

Average residence 

Underwater dynamite explosion at 100 m 

25 hp outboard motor at 15 m 

Large chorus of marine catfish 

Noise of ships in a busy harbour 

Large chorus of snapping shrimps at 100 m 

Calm sea (state 0) 

Squirrelfish hearing threshold 

Hearing threshold of ostariophysine fishes 

Sound Pressure Level 

dB re 1 Pa 

134 

124 

94 

84 

74 

64 

54 

44 

134 

124 

94 

84 

74 

64 

54 

34 
Table 1. 2 Sound Wavelengths, Near-Field Distances and Minimum Propagation Depths 

in Water for Various Frequencies 

Frequency Wavelength Near-Field Radius Propagation

m) (m) (m) Depth (m) 

50 30 4.8 7.5 

100 I 15 1 2.4 1 3.8 I 

200 7.5 1.2 1.9 

0.60 0.94 

0.30 0.47 

400 3.7 

800 1.9 

1600 I 0.94 I 0.15 1 0.23 - ~~ 

3200 0.47 0.08 0.12 

Note: wavelengthsare baed on a sound velociq in water of 1XUl metres per second; this may increase io a 

maximum of 1540 metres per second in sea water, giving a wavelength of 15.4 m @ 1OOHz. 
Table 1.3 Sound Production and Sonic Mechanismsin Species of Interest in this Study 

(Source:Fish and Mowbray, 1970, except where otherwise stated). 

Species Description of Sound Production and Sonic Mechanism 

Cod (Gadidae) Loud, low frquency grunts peaking at SOHz, duration ea. 0.2 s, 

Gadusmorhua repeated 3 or 4 times :recorded from captive fish during threat 

displays, flight of displaced fish and spawningprelimbmies. 

Muscular vibration of the mullti-lobed swimbladder is believed to be 

the source; passage of gas over sharp transverse septa between the 

lobes may reinforce the sound. Frequency range 20 to 200Hk. 

Wting (Gadidae) No specific data given. May be similar to cod. 

Merlangius merlangus 

Eel (Angdlidae) No specific data given, but may be similar to A. rostrata. In this 

Anguilla anguilla species, protracted clucking sounds were heard, resembling the "putput" of an outboard motor, spontanwus low knocks and clicking 

during night-time activity and single dull thuds (25 to 1,200Hz)and 

rasps induced by mild shock. Frequency range, 25 to 2,500 Hz. 

Bass (Percichthyidae) No specific data but may be similar to Morone saxatilis of the same 

Dicentrarchus labrax family. Low pitched thumps, single or in bursts of 3 or 4, when 

startled or electroshocked. Sound is generated by the swimbladder, 

which has no special musculature but is probably vibrated by the 

general body musculature. Sound is always coincidentwith suddenly 

increased fish activity. Frequency range not specified. 

Hening (Clupeidae) Hydrodynamicand swimming noise when Swimming fast in large 

Clupea harengus shoals, especially during veering; shrill mouse-like noises due to 

swimbladder venting when fish taken out of water; low knocks and 

thumps stimulated by handling and electroshock. Frequency range 20 

to 300Hz. 

Twaite shad (Clupeidae) No specific data. Data for other Alosa spp. reveal no evidence of 

Aha fallax sound production in captive fish. In the wild, water noise at the 

surface was heard during frenzied swimming activity. Accordiig to 

Day (1884), shads are "reputed to take pleasure from music", though 

there is no evidence that they make it! 

Atlantic salmon (Salmonidae) No data given for salmonids. Loeffelman et al. (1993) recorded 

Salmo salar sounds from Pacific salmon (Oncorhynchus spp.). Frequencies were 

predominantly below 400 to 600 Hz,in pulses of 10 to 30 ms 

duration. 

Brown Trout (Salmonidae) Loeffelman(unpublished)recorded 'soft thump' sounds fromadult 

Salmo trutta brown trout of 60cm length. The predominant frequencies produced 

were in the 75 to 400Hzrange, 
Table 3.1 Response Categories of Different Species to the Empirical Signal Series in Screening Trials. 

(See Section 2.4.2) 

Response Category Summary: 1 = extreme startle; 2 = moderate startle; 3 = steady swimming away; 4 = 

slight reaction; 5 = no Visible reaction. 
Table 4.1 ComparisOn of the &&an Fish Distances from the Sound Source (Test minus 

Control) and Response Categories using Signals Deve3oped by the Loeffelman 

and Empirical Methods. 

species I Loeffehnan Method 

Mean Distance Respnse 

Cm) category 

Atlantic not applicabk 3 

salmon 

Brown trout, Q.56 2 

adult 

Brown trout, 0.31 3 

juvenile 

whiting 0.48 3 

Cod 0.39 3 

Bass not testable not testable 

1 

Ed not testable not testable 

Empirical Method 

MeanDistance 

(m) 

not applicable 

0.44 

i 

0.26 

I 0.80. 

0.61 

0.40 

1 

not applical>le 

Response 

Category 

2 

4 

3 

1 

I 2 

2 

I 

4 

Response Category Summary: 1 = extreme startle; 2 = rn0derai.e startle; 3 = steady 

swimmingaway; 4 = slight reaction; 5 =no visible reaction. Respmses sham are the best 

results recorded in fufl-length trials. 
APPENDIX 

Raw Count Data from Otter Ferry Salmon Trials, December I992 
%cD 

g o

w

zc ­

*-)n. 

0 

3 

3 
rn x

U