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International Council for theExploration of the Sea

CM 1997/Q:19Theme Session: By-Catch of Marine Mammals:Gear Technology, Behaviour, and Kill Rates (Q)

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AN EXPERIENCE ON THE QUANTIFICATION AND MAPPING OF DOLPHIN BY-CATCHES IN THESICILIAN CHANNEL AND TESTING OF AN ACOUSTIC-BASED POSSIBLE SOLUTION

Mazzola S.I, Patt i B. 1, Bonanno A. 2, Cuttitta A. 1, Basilone G. 1, Tesler W. 3, Toistoganova L. 3

1. Istituto di Tecnologia della Pesca edel Pescato. Via L. Vaccara, 61.91023 Mazara dei Vallo, Italy.FAX ++39-923-906634. E-mail: mazzola@itpcnr.itpp.pa.cnr.il.

2. Dipartimento di Energetica ed Applicazioni della Fisica. Viale delle Scienze. 90100 Palermo, Ilaly.3. Laboratory of Fishery Acoustics of VNIRO. Moscow, Russia.

Keywords: dolphin by-catch, Sicilian Channel, underwater acoustic devices.

Summary

This study assembles the results of the EC project coded MED93/011, aiming at gathering information about dolphin-small pelagicfishery interaction in Sicilian waters. Il was conducted following two different lines of investigation:I. the quantification and mapping of dolphin by-calches which occurred during small pelagic fishery operations;2. the study of the effecIs of acoustic signals, different by nature and structure. on dolphin behaviour evaluating lhe possibility of repelling

dolphins from an area of the sea where fishing operations are taking place.To achieve the first objective, we collected data throughinterviews with the fishermen from the main Sicilian small pelagic fisheries.

Data showed relative higher kill rates of dolphins in the western side of Sicilian waters and in fishing areas around Lampedusa island (SicilianChannel).

While following the second line of investigation, we carried out experiments in a dolphinarium aimed at selecting acoustic stimulicapable of keeping dolphins away from a certain area of the sea. The statistical analysis of the results allowed us to select a set of signals to be usedfor controlling dolphin behaviour at sea. In addition, we developed an electroacoustic prototype capable of emilling underwater acoustic signals.Finally, we implemented an experiment at sea while fishing vessels were at work to verify the operation and the effectiveness of our acousticsignals in repelling dolphins from a certain sea area. The experiments carried out at sea demonstrated that the acoustic signals used to provokepsychologically repelling stimuli (bolllenose dolphin and killer whale calls) worked weil only for a short time. This facI suggests that in the futurephysiological methods could be studied for the purposes of repelling dolphins.

INTRODUCTION

Increasing attention has been paid in the last decades to the ways in which fisheries may affect marinemammal populations and to the ways in which marine mammals might compete with, or cause damage to, fisheries(Northridge, 1991).

Recently most researchers affirrn that marine mammal by-catches due to fishing operations are a source ofmortality which can cause serious problems for various marine mammal populations (Notarbartolo-di-Sciara, 1990). Onthe other hand, fishermen say that a large number of cetaceans compromises the abundance of fish while causingserious damage to their nets (Viale, 1985; Mazzola er ai., 1996).

In particular in Sicilian seas, the interaction between dolphins and the fishing activities is intense. In thisinteraction both sides, competing for the same resource, gain and lose something. Dolphins become entangled andwounded in fishing nets and are sometimes shot by fishermen, while fishermen suffer both damage to their nets andlosses in the size of their catches.

The problem of cetacean by-catches in fishing operations is world-wide. The present study, by assemblingthe results of the EC project coded MED93/011 (Mazzola et al., 1996), examines this problem in Sicilian waters.

MATERIALS AND METHODS

We developed this project along two parallel lines of investigation with distinct objectives:I) the quantification and mapping of dolphin by-catches during activity of small pelagic fishery (equipped with

encircling nets and pelagic trawl nets);[I) the study of the effects of acoustic signals, different in nature and structure, on dolphin behaviour to evaluate the

possibility of repelling dolphins from an area of the sea where fishing operations are taking place.

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In order to reach the objectives set by the first work line we had planned to conduct census investigations andsighting campaigns in different Sicilian fisheries. The census data acquisition was designed based on the co-operationof fishermen associations and was to be carried out by means of log-books and interviews with fishermen. Weencountered a problem we had not anticipated, namely, an unwillingness of small pelagie Sicilian fishermen tocooperate. We tried to overcome this problem by changing the procedure for collecting data regarding the interactionbetween dolphins and fisheries. Therefore, col1ected data was obtained solely through interviews with the fishermen. Intotal over 90 interviews were held including most Sicilian Channel and South Tyrrhenian Sea (western part only) smal1pelagie fisheries, and namely: Isola delle Femmine, Terrasini, Castellammare, S. Vito, Trappeto, Trapani, Mazara deIVallo, Porto Empedocle, Sciacca, Porto Palo and Lampedusa. The main small pelagie fisheries in the area consideredwere loeated in Terrasini, Trapani and Sciacca (Western Sicily). These fisheries alone represent nearly 80 % of totalgross tonnage of a11 vessels using fishing gears in this area (Mazzola et al., 1995b).The information co11ected was obtained exclusively from older, experieneed fishermen with reliable and long historicalmemory about the local fisheries. This choice was based on their knowledge of the eulture and traditions of the Sicilianfisheries. We also conducted 45 interviews and inspections for dolphin by-eatches in fisheries using different gears(pelagie drift net and gill net).

The second Hne of investigation was developed in three successive steps.First, we carried out tests in a dolphinarium to study the behaviour and reaetions of dolphins to different

--aeoustie stimuli; We chose·the bottlenose dolphin (Tursiops truncatus) as the subject of the experiment because it 1S oneof the most common species found in the sea area we studied. The aim of these experiments was to find signals thatcould be used for repelling dolphins from fishing nets to prevent their entanglement and the destruction of the fishinggears. Experiments took place in the Moscow Dolphinarium of the Severtsov' Institute of Evolutional Morphology andEcology of Animals of the Russian Academy of Sciences between Oetober 3rd and 20th, 1994. Different types ofacoustie stimuli were used during the experiments. Some of them had a biological origin such as recordings of soundsemitted by killer whales (Orcinus orca) and by bottlenose dolphins (Tursiops truncatus). Other signals had an anthropieorigin: beating two pieces of metal and signals generated by the synthesiser (pure tones, modulated by frequency andamplitude tones, pulses simulating sounds of squids and meander of different frequencies). The methodology used inthe experiments was to watch the behaviour of the dolphin under the effect of different signals emitted into the water,taking into account many subjective faetors. The reactions were earefully viewed and classified by three independentobservers (zoopsychologists) and data was statistica11y analysed by different methods (t-test, ANOVA). Theexperiments in the dolphinarium led to the seleetion of two types of acoustie stimuli to be used to control dolphinbehaviour (Mazzola et al., 1995a). The first one was asound emitted by specimen of aphalina (the Russian name forthe bottlenose dolphin in the Black Sea) kept into the pool and the second was the recording of sounds emitted by killerwhales. We expeeted a negative reaction (repulsion) to the latter signal because of analogies with similar experimentson different marine mammal species (Cummings and Thompson, 1971). The repelling behaviour to the sound emittedby aphalinas could be explained by a sort of territoriality.

Seeondly, the results of the dolphinarium experiments encouraged us to design and built an electroacoustiedevice to repel dolphins from a eertain area, and suggested the implementation of a portable prototype to be used laterin the experiments we carried out at sea.

Fina11y, we implemented an experiment at sea during real fishing operations to verify the functioning and theefficieney of our aeoustic prototype. Instead of using small pelagic nets we conducted the experiments using gill netsfor coastal fishery because of the great advantage these offer when installing and controlling the acoustic prototypes.

The experiments took place in an area along the North-western coast of Sicily where the loeal fishermenassociations are very sensitive to this problem and beeause in the spring and summer seasons the presence of dolphinsis very common. Sound signals used for dolphins repelling were "Trune 1", "Ore 36" (selected during dolphinariumexperiment) and a dolphin sound reeorded in the S.Vito waters during the experiment, "TruncSVito"; moreover, thereference signal "SO", aperiodie sound aimed at increasing detectability of the fishing nets (llatakeyama et al., 1994;Lien et al., 1990), was emitted by the electroacoustie prototype (see Table 1). Experiments were held in S.Vito 10 Capo(TP), on the north-western eoast of Sicily (Fig. 1).

A total of 15 vessels of the S. Vito fishery were involved in the program, between April 21 and June 10,1996. Eight stations, on their usual fishing grounds were selected (Fig. 1). Two of them were chosen for soundemissions, using a signal emitted by the prototype (sonobuoy, at station 6) and by the transducer submerged in thewater direetly from the vessel (at station 3); the remaining stations, covering a wider area, served as a background tobetter interpret the pattern of dolphin ineursions and their consequences. .

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Table 1. Description of signals emitted during experiments at sea

Signal "Trune 1", is a fragment (with the duration of 3.2 s) of the reeording of whistles and sonar clicks of 3 aphalinasrecorded in the pool on Oetober 14, 1994. It consisted of a small part of a whistle (- 0.5 s), a whole whistle (0.6 s),the main part of a third whistle (1.5 s) and some sonar clicks. All whistles have more than 4 harmonics in the dynamicrange of 30 dB with linearly increasing frequency (1 oetave per 1 s) up to 30 kHz.

Signal "Orc 36", is a 5.8 sec fragment of killer whales eall reeordings. The fragment includes 3 whistles and somesonar clieks. Whistle 3 begins 0.1 sec after starting whistle 2. The duration of whistles 1 and 2+3 is 0.8 sec and 1.5 secrespeetively. Whistles 1,2 and 3 have more than 5, 8 and 8 harmonies respeetively, with sharply inereasing in thebeginning and a stable part up to 10 kHz .

Signal "Trune S.Vito" is a fragment (with the duration of 3 sec.) of the recording of aphalina whistles and sonarclieks reeorded in south Tyrrhenian sea (close to S.Vito, Trapani) on May 18,1996. It eonsists of some sonar elieksand three whistles with duration respeetively 0.5 sec, 0.4 sec. and 0.6 sec. The first and third whistles showed, in thedynamic range of 10 dB, a slope of - 1 octave per sec. while the second one showed a steeper slope (- 1 octave per0.8 sec.).

- Signal "SO" is a -D.3 'sec, ,fragment 'of the recording-'of the reference signal emitted by'the sonobuoy. It consists of 8pulses (duration 5 ms) emitted periodically (T=30 ms). The signal emitted is not a pure tone due to the non-linearityof the deviee but the sonogram shows that the energy of eaeh of the eight pulses is largely located near 70 kHz.

Fig. 1. Study area and position of stations of the experiment at sea.

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The activity of the S.Vito entangling net fishery goes on as folIows: each evening at sunset fishermen reachtheir usual fishing place and drop their nets perpendicularly to the eoast, at a depth ranging from approximately 10 to150 meters. Fishermen usually set out their nets at sunrise. For the purpose of our experiments all fishermen were askedto use the same fishing gear.

Every day, six fishermen were asked to cast their nets at 6 out of the 8 above-mentioned sites in the studyarea (stations n.1-2-4-5-7-8). When permitted by sea conditions, two extra entangling nets were dropped by two other

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vessels at stations n. 3 and n. 6. Station 3 was used for emission during the whole night, picking up and recordingsignals from the vessel, using standard electronic devices. Station n. 6 was chosen to test the electroacustic prototype,which continuously emitted the SO signal .

. A test and control strategy was devised, i.e., on each day it was possible to emit signals both from the vesselat station n. 3 and from the buoy at station n. 6 (a total of 10 days; one or two observers were on board the vessel), thefollowing day trials were carried out at the same stations (3 and 6) without emitting sounds, in order to get further datafor comparisons.

All fishermen were asked to fil! out and return a questionnaire. This permitted us to gather informationabout:

haul duration;catch (by main species);

• dolphin sighting;damage of the net (number of tears produced by dolphin raids), indicator of dolphin-fishing activity interactions.

RESULTS

The interviews with fishermen revealed that the most common dolphin species in the study area was the'. Tursiops .truncatus. Occasionally, some specimen of Stenella coeruloealba. and Delphinus delphis were found. The

distribution of dolphin by-catches as obtained by the interviews is shown in Fig. 2 .

Fig. 2. Map of dolphin by-catches in the small pelagic fishing sea areas considered. Numbers in round bracketsare the mean number of specimen per vessel in the last three years.

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Sicilian waters have been divided in sectors. The numbers shown in parentheses refer to the mean number ofspecimen caught per vesseJ in the last three years. Interaction between dolphins and fishing operations seems to bestronger in sectors I through IV (corresponding to the Western Sicilian sea waters) and in sector VI (Lampedusafishery). Near the Southem Sicilian coasts the phenomenon is nearly totally absent. For a more complete evaluation ofthese results, some special features of the single fisheries are taken into account, and, in particular the fishing activityexpressed in days per year. The duration of the fishery season varies in the different fisheries, and this information isnecessary to compare the situation in each single sector. In sector land II fishermen come from the following fisheries:lsola delle Femmine, Terrasini, Castellammare, S. Vito, Trappeto. The fishing season here is about 3 months long in

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summer. In sector 111 the fishing season is about 4 months long in summer. The most important fishery operating inthis area is Trapani. Sector IV and V are mainly exploited by Sciacca, Mazara and Porto Empedocle fisheries. Most ofthe fishing activity is concentrated in spring and summer, but sector V is exploited particularly in Autumn when pelagictrawl nets for fishing younger specimen are used. The different number of by-catches in the two last sectors is thereforeaffected by the different procedures and gears used. In sector VI (Lampedusa fishery) the fishing season lasts about 8months. In sector VII the activity is mostly concentrated in summer and it is 4 month long. In this sector we have notregistered by-catches.

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During the experiment carried out at sea, a total of 259 questionnaires were collected, each onecorresponding to a fishing action performed by avesseI. Because of bad weather conditions in the first part of the seaexperiment period, it was only possible to perform (at stations 3 and 6) a total of ten sound emission trials.

Fig. 3 shows mean total catch per fishing day for the whole time period of the sea experiments andcorresponding trend in net damage caused by dolphins raids calculated considering "control" stations only. It ispossible to see the peculiar absence of dolphin raids which characterised the first days (April 21-27) of sea experimentsas measured by net damage in the study area. Aperiod of bad weather conditions followed. On May 17 weather clearedand the program of sound emissions started in a regular fashion. It is interesting to note that, even though during theinvestigation period two distinct mean yield levels seem to exist, with a first group characterised by relatively highcatches (up to May 12), the observed pattern of catches was linked with net damage (tears) caused by the dolphin raids,as the two series are negatively correlated .

Fig. 3. Total catches and nets damages in control stations.

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This result supports our choice of the variable "number of tears" as an indicator of the interaction betweenfishing activities and dolphins; in addition, it seems to confirm what fishermen affirm about the inverse relationshipbetween catches and dolphin raids.

The next step was so to further investigate the spatial distribution of catches and corresponding damage tofishing gears. In Fig. 4 are shown shows average catches by species in the control station during the first week of theexperiment, before the beginning of dolphins raids. It is worth to note that catches in the study area was quitehomogeneous in the selected stations, even though observed values in the eastern area were slightly over the average.

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Fig.4. Catch by species in control stations. 1" time period: May 21-27. Horizontal line is the overall averagecatch.

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Fig.5 refers to the period between April 28 and May 5, 1996, when the dolphin raids and correlated netdamages began (see Fig. 3) and some days before starting the emission of sounds at sea. Total catches are showntogether with the corresponding fishing gear damages caused by the dolphin raids. This time, total catches were lowerin the stations inside the Gulf of Castellammare (7-5-1) than outside. We remark that this sea area is a very peculiarone, as it is facing a natural land reserve and boltom trawl fishing has been forbidden since 1990._0bserved differencesin total catches were strictly related to the average number of tears in the nets, so that lower catches correlate to greaterdamages. It seems that, for some unknown reason, dolphins in that period preferred the area inside the Gulf for theirraids.

Fig. 5. Total catch and damages in nets (daily average number of tears) in control stations (2nd time period:04/28 - 05/12).

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The observed pattern of the 2nd period strengthened during the last time interval (05/17-06/10), when dolphinraids generated more damages and simultaneously yield decreased greatly (15-30 Kg, see Fig. 6); this was particularlytrue for the stations inside Gulf of Castellammare (stations 3-6-5-1). Decrement in catch was homogeneous for all themain detected species (see legend in FigA), which are the most economically important in that area.

During that same time period (Fig. 7), when repelling signals were emitted at station n. 3, average yieldincreased (from 10 Kg to 22 Kg) and damages caused by dolphins lessened (from 11.3 to 5.8 tears). At lower

intensities, the same phenomenon occurred in the reference site (station 6), for the trials when the SO signal wasemitted.

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It should be stressed that results of Fig. 5-7 present mean values over the relative time periods. It isinteresting to note that repelling signals seem to lose their effectiveness with time, probably as a consequence ofadaptation to the emitted signals (Fig 8), which seems to start after six emitting experiments conducted within twoweeks.

Fig. 8. Total catches and nets damages corresponding to different emitted signals. Results for station 6 (SO) andstation 3 (trunel, orc36, truncSVito) only.

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DISCUSSION AND CONCLUSIONS

The study produced interesting results pertaining to the number of dolphin by-catches in small pelagic nets.In particular, interviews with the fishermen revealed that the problem of the interaction between dolphins and smallpelagic fisheries is important only in the western part of Sicily and in fishing area around Lampedusa island (SicilianChannel), where the by-catches per vessel in the last three years have varied from 1 to 4 specimen. The number ofdolphin by-catches by pelagic drift nets and by gill nets, as detected in our investigation, was 5 to 6 times higher, up to12 to 15 specimen per vessel in the last three years and uniformly distributed throughout the Sicilian waters. The mainspecies of dolphins caught was the bottlenose dolphin, Tursiops truncatus.

The results of the analysis conducted along the second line of investigation pointed out that psychologicalmethods (i.e. these ones we used) can be very effective only for a short period of time. So we may conclude that it isnecessary to propose and develop research projects based on the physiology of the dolphins and, from the acousticpoint of view, on further investigating the possibility of disturbing them by means of acoustic signals.

In order to accomplish all the aforementioned tasks, we adopted an interdisciplinary approach, whereresearchers with different expertise worked together (bio-acousticians, cetacean ethologists, zoo-psychologists,electronic engineers, physicists, etc.). We plan to develop further research projects on these topics using this study asan initial step.

References

Cummings W. c., Thompson P.O., 1971. Gray Whales (Eschrichtius Robustus) avoid the underwater sounds of killerwhales (Orcinus Orca). Fish. Bulletin: Vo1.69, n.3.

Hatakeyama,Y., Ishii,K., Akamatsu,T., Soeda,H., Shimamura,T., and Kojima,T. 1994. A review of studies on allemptsto reduce the entanglement of Dall 's porpoise, Phocoenoides dalli, in salmon gillnets. Rep.Int.WhaI.Commn. (SpecialIssue 15): 549-64.

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Lien,J., Todd,S. and Guigne,J. 1990. Inferences about perception in large cetaceans, especially humpback whales, fromincidental catches in fixed fishing gear, enhancement of nets by 'alarm I devices and the acoustics of fishing gear. pp347-62. In:J.A.Thomas and R.Kastelein (eds.) Sensory Abilities ofCetaceans: Laboratory and Field Evidence. PlenumPress,New York and London. xiiii+710p.

Mazzola S., Miller P., Guerrini A., Bonanno A., Patti B., Tesler W., Tolstoganova L., Khakhalkina E., Bliznyuk Y.,Cannelli G.B., D'Ottavi E., Franzitta G. 1995a. Preliminary data analysis of dolphinarium experiment to study theescaping behaviour of dolphins (tursiops truncatus) under the effects of different sound stimuli. Paper presented at theSymposium on Fishery and Plankton Acoustics, Aberdeen, Scotland, June 1995 (unpublished), 12 pp.

Mazzola S., Guerrini A., Bonanno A., Patti B., Giusto G.B., 1995b. Preliminary study on census data about theinteraction between dolphins and fishing activity in the Sicilian fisheries. European Cetacean Research, vo!. 9, pp. 256-259.

Mazzola S., Bonanno A., Patti B., Tesler W., Tolstoganova L., Cuttitta A., Basilone G., 1996. Quantification andMapping of dolphins by-catches and dolphin-small pelagic fishery interaction. Draft of final report of the EEC ProjectMED93/011.

Northridge S.P., 1991. An updated world review of interaction between marine mammals and fisheries. FAD FisheriesTechnical Paper.No.251, Suppl.1 Rome, FAD, pp58.

Notarbartolo-di-Sciara G., 1990. A note on the cetacean incidental catch in the Italian drifnet swordfish fishery, 1986-1988. Rep./nt.Whaling Commn. 40: 459-460.

Viale D., 1985. Cetaceans in the Northwestem Mediterranean, their place in the ecosystem. Dceanogr. Mar. Bio!. Ann.Rev.23.

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