2002 IRISH SCIENTIST YEAR BOOK

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LOUGHBOROUGH UNIVERSITY OF TECHNOLOGY (a) , BORD IASCAIGH MHARA (b) & AQUATEC SUBSEA LTD (c)
A.D. GOODSON (a) , D. RIHAN (b) ,& A. SMERDON (c)
Describing the development of an experimental acoustic dolphin deterrent for use on pelagic pair trawls to study new methods of reducing the by-catch of small cetaceans

Figure 1. AQ528 remotely controlled acoustic deterrent for trawls (Loughborough University/Aquatec Subsea Ltd).

During 1998 and 1999 An Bord Iascaigh Mhara (The Irish Sea Fisheries Board) and the Marine Institute of Ireland undertook a major two year study 1 into developing alternative tuna fishing techniques. One of the techniques identified was the use of pair pelagic (i.e. middle depths and surface) trawls. Recognising the potential for incidental cetacean (i.e. whales, dolphins, porpoises) by-catch in this type of fishery, BIM commissioned, through the offices of Loughborough University Consultants Limited (LUCL), work to develop a prototype deterrent unit, which could be deployed on tuna pair pelagic trawls 2 .

 Acoustic methods of reducing the bycatch of harbour porpoises, Phocoena phocoena, in bottom set gillnets have now been shown to be very effective, and regulations requiring the use of approved �pingers� in specific areas and fisheries have been introduced in the USA3 and in Denmark 4 , and may now be expected to be applied elsewhere. (Pingers are acoustic deterrent devices.)

 The causes of dolphin and other small cetacean bycatch in trawl fisheries appear to be very different from set gillnet captures, and the LU team demonstrated during the EC project CETASEL 5 that dolphins can be attracted to pelagic trawls and can spend significant periods interacting with them. It is believed that some of these animals have learned to enter the nets in order to predate on the fish as they accumulate in the mouth of such nets. The CETASEL study also revealed that these animals do not need to echolocate in order to find the net as the pelagic trawl proved to be a very noisy underwater sound source. Echolocation behaviour was detected when the animals were very close to their prey as analysis of the recorded sonar behaviour predominantly showed very short range inter-click time intervals. Without extensive sonar activity during their approach, it is unlikely that dolphins can acquire a clear image of the trawl net�s structure, and the evidence, from other studies, suggests that they may rely on retracing a �memory mapped� route when exiting the net in order to breath at the surface. The basic cause of multiple animal captures could therefore relate to sudden changes in net geometry which can cause the memorised exit route to be obstructed at a time when the animal may have little or no reserve of air to permit exploration. The age profile of the by-caught animals taken in pelagic trawls suggests this is an adult, knowledge-based, behaviour and quite different from the largely juvenile, 1 to 2 year old age profile, observed in gillnet captures 6 , which suggest a vulnerability due to lack of experience.

Figure 2. AQUAmark100/200 acoustic deterrent devices.

The alarm system developed will be used to explore the practicability of deterring dolphins from the near vicinity of pair pelagic trawls when cetacean by-catch risks are believed to be high. As stated, these risk periods appear to relate to net geometry changes which can occur during course changing manoeuvres and when hauling the net. The prototype unit to be deployed comprises a control unit in the wheelhouse of a vessel which will communicate via a through water acoustic link to an underwater pod. This pod will contain a battery power supply and a sound generator which, once triggered, will generate broad band �aversive� signals for a pre-set period chosen to match the vessel�s manoeuvring time � e.g. 5�10 minutes typically. The deterrent sounds generated by the underwater pods will be based on the wide band signals which were developed in previous research projects carried out by LU, which have been shown to be very effective at displacing harbour porpoises in the vicinity of gillnets.

 As an adjunct to this study, it is intended that trawls of other tuna vessels will be equipped with a small number (4�6) of the AQUAmark100�6 , developed originally for use in gillnet fisheries and the newly developed AQUAmark200� deterrents (Figure 2) with these pingers positioned in a ring around the �sharks teeth� of the trawl. The data reported in EC DGXIV 98/019 (ADEPT)7 and by Imbert 8 suggests that dolphins are repelled to a �safe� distance by these pingers, and that, when grouped together, they should act effectively to keep the animals just outside the hazard zone for typical pair pelagic gear. By using AQUAmark 100s on one trawl and AQUAmark 200s on another, sensible comparisons as to the relative effectiveness of each type of pinger can be made and, through constant monitoring throughout the entire tuna season, comparisons can be made between all three types of pingers.

Figure 3. Pair pelagic trawl operation � acoustic deterrent (red arrow) positioned to evict animals and deter entry to its sphere of influence.


References
  1. BIM 2000 � Diversification trials with alternative tuna fishing techniques including the use of remote sensing technology. Final report of EU Contract 98/010, Bord Iascaigh Mhara, Dun Laoaghaire.
  2. Consultancy Report EL/BIM/117 � Loughborough University Consultants Ltd.
  3. NOAA � NMFS Bulletin � Regulations and specification for pinger used in the sink gillnet fisheries in the Gulf of Maine.
  4. Danish Regulations for pingers to be used in the Wreck net fishery for cod (August 2000).
  5. Project DG XIV AIR 3-CT94-2423 CETASEL � Final Report.
  6. Project Epic EC DG XIV 97/0006 � Final Report.
  7. Project ADEPTs EC DG XIV 98/019 � Final Report.
  8. Imbert, G., et al., Prevention a l�aide de repulsivfs acoustiques des captures de dauphin par les thonailles. 10e Conference International sur les cetaces Mediterranee de la RIMMO, Juanles Pins, November 2001.
Contact: Goodson A.D., Loughborough University of
Technology, Loughborough LE 11 3TU, UK; Rihan D.,
Bord Iascaigh Mhara, PO Box 12 Crofton Road, Dun Laoghaire,
Co. Dublin;& Smerdon A., Aquatec Subsea Ltd, Hartley,
Wintney, Hampshire RG27 8NY, UK.