5 Rapp. P.-v. Réun. Cons. int. Explor. Mer, 170: 5-6. Février 1977. F O R E W O R D A. R. M a r g e t t s Symposium Convenor and Volume Editor After World War 2 echo-sounders and sonar were It was to provide a forum for the exchange of new developed rapidly and widely to become standard research results, experience and ideas in this field fishing vessel equipment for finding fish. Fisheries between scientists from all parts of the world; speci­ scientists, particularly in northern Europe, were soon fically it did not include consideration either of the looking into methods of using echo-sounders not only use and application of acoustic instruments in com­ to find fish but to estimate the quantities of fish in mercial fishing or of bioacoustics. FAO and the an area. Their ideas and methods were developed very International Commission for the Northwest Atlantic rapidly in the 1960s, so m uch so that by 1968 echo Fisheries (ICNAF) collaborated with ICES in this surveying with automated quantification of received Symposium and financially supported this publication. fish echoes was in use as a method of fish abundance Mr A. R. Margetts (Lowestoft, England), was con­ estimation. The methods were new, highly promising, venor for the Symposium. He was assisted in the but fraught with many sources of error. Scientific Planning Group by Mr L. A. Midttun (Ber­ Progress was reported regularly to the Gear and gen, Norway), Mr B. B. Parrish (Aberdeen, Scot­ Behaviour Committee of the International Council for land), Dr D. F. S. Raitt (FAO, Rome), Mr K. A. the Exploration of the Sea (ICES) at its annual Smith (Woods Hole, USA) and Mr H. Tambs-Lyche Statutory Meetings. Through ICES and FAO, in (ICES). March 1969 an Acoustic Training Course was held Authors were invited to submit to the Symposium at Svolvaer in Norway, at which also the apparatus papers on acoustic methods applied to the topics set and methods developed separately in Norway, Eng­ out as follows: land, Scotland and the Netherlands were demonstrated 1 Fishing gear and topographical studies and compared on research vessels at sea. The Svolvaer 2 Fish behaviour studies course was reported as FAO Fisheries Report No 78, 3 Fish abundance estimation 1969. 4 Identification and sizing of echo targets FAO Manuals in Fisheries Science No 5, Manual 5 Novel instrumentation. o f methods fo r fisheries resource survey and appraisal. Part 2. The use o f acoustic instruments fo r fish detection and abun­ The Symposium was attended by 125 experts from dance estimation, (Ed. Forbes, S. T. and Nakken, O.), 25 different countries throughout the world. An published in 1972, was a revision of the preliminary opening address was appropriately (because Norway manual of 1969 (FAO Tech. Pap. 83). was the host country and her scientists and technicians Acoustic assessment of fish stocks was just one, were amongst the pioneers of echo-sounder develop­ albeit then the outstandingly important one, of a ment) and kindly given by Mr K. Sunnanaa, Director wide range of uses of underwater acoustics being General of Fisheries for Norway. He and all partici­ researched and developed at widely separated centres pants were welcomed by the President of ICES, M. R. not only to improve detection of fish but also to Letaconnoux. Wherever possible, which, happily, was provide new tools for research scientists. Their use was in the great majority of cases, papers were presented making possible new methods for assessing abundance by their authors. Considerable and profitable discus­ of both adult and pre-recruit fish, for estimating the sion followed the presentation of papers, either indi­ sizes of individual fish, for studying fish migrations and vidually or grouped according to topics. Altogether behaviour, and for investigating the performance of 50 papers were presented. fishing gear and reactions of fish to gear. The first two programme sections, covering studies ICES initiated, convened and organised a Sympo­ of fishing gear, topography, fish behaviour and sium on Acoustic Methods in Fisheries Research, held in migrations, illustrated the wide range of novel uses Bergen at the invitation of Norway, 19-22 June 1973. of underwater acoustic apparatus. High-resolution 6 A. R. Margetts: Foreword sector scanning sonar had produced very impressive of readings were taken to reduce variance. One major results in both fish behaviour and fishing gear in­ source of error in acoustic assessment lies with the vestigations, particularly those concerning individual shoaling patterns and packing density within the fish in the open sea while, in contrast, very long range shoals of fish; much consideration was given to this low-frequency sonar provided a means of plotting fish and a number of ways of dealing with the problem, shoals at a distance of many miles. A combination of some very promising, were being developed though two such systems could be invaluable to fisheries none was yet entirely satisfactory. Again, the collection biologists. Acoustic transmitting and transponding of data at an enormous rate requires great attention tags were being used to follow fish movements and being paid to suitable computerisation. Throughout migrations, Doppler shift had been applied to the the discussions on this programme section it was study of the dynamics of fish shoals and, in enclosed repeatedly emphasised that an understanding of the waters, a laid out range with hydrophones was being biology of the fish in the sea area investigated was employed to track the detailed short-distance move­ fundamental; fish target echoes were not from ment of acoustically tagged fish and the positions of inanimate objects and allowance must be made for towed gear. Now that data are collected by these this between theory and practical results. methods at such an enormous rate, there is clearly a This volume has been edited by Mr A. R. Margetts requirement for computerised methods of processing with assistance from Mr J. E. Ehrenberg on several them: one computerized display of the direction and of the papers. While the authors themselves are speed of movement of both fish and fishing gear responsible for the technical content and presentation during a fishing operation was presented. of the papers, it is possible that, especially with papers The programme sections on fish abundance estim­ from USSR and Japan, some misrepresentation ation and on fish target strength measurement and arising from translation difficulties may still be in this sizing provided very clear examples of how carefully publication. Technical questions may be resolved di­ thought-out and planned surveys using correctly rectly with the authors. designed and calibrated apparatus can quickly and Of the 50 Symposium papers, several were either comprehensively describe not only the distribution but withdrawn from publication or omitted as being not also the quantity of pelagic fish in an area on a very properly within the stated scope of the Symposium. large scale. No other method of such instantaneous This volume contains 42 papers on subjects within the assessment is comparably effective. But, inherent in the programme framework outlined above. Of these, three method are many sources of error. Together the are concerned with fishing gear and topographic presented papers and ensuing discussion showed that studies, six with fish behaviour and migrations, 32 these were recognised and that various steps had with fish abundance, identification and sizing, and already been taken, with varying but encouraging one with very recent or future possible developments. degrees of success, to eliminate or minimize biasses and The papers are here arranged in an order broadly variances. The papers speak for themselves, but here conforming to the main topic headings as above. In it is to be noted firstly that, as yet, there is no acoustic two instances two papers presented separately to the method by which fish in the open sea or elsewhere Symposium have been combined as one paper. can be identified so fish from which echoes are The organizers of the Symposium herewith express recorded must be sampled by some method such as their gratitude to Norway for providing the venue and fishing or photography, and, secondly, that thorough excellent facilities for this Symposium at the Students and correct calibration of acoustic apparatus is of Centre, Bergen, and to the Director and staff of the paramount importance. Methods of calibration using Fiskeridirektoratets Havforskningsinstitutt, Bergen, live fish have proved reasonably successful ; an elabor­ for their invaluable assistance in staging it. Thanks ate experiment with simulated targets under large- are also recorded here to the Scientific Planning scale laboratory conditions showed particularly how Committee, to the Chairmen of the sessions at the many serious and difficult to interpret inaccuracies Symposium, to the Secretariat of ICES, to the authors can occur in an acoustic echo quantification system. of contributed papers and to the participants at the The best measurements of target strengths so far have Symposium; all of these together made for the ack­ been with free-swimming fish on which large numbers nowledged success of the Symposium. 45 Rapp. P.-v. Réun. Cons. int. Explor. Mer, 170: 45-51. Février 1977. THE EFFICIENCY OF THE GRANTON OTTER TRAWL DETERMINED BY SECTOR- SCANNING SONAR AND ACOUSTIC TRANSPONDING TAGS F. R. H a r d e n J o n e s, A . R. M a r g e t t s , M . G r e e r W a l k e r a n d G . P. A r n o l d Fisheries Laboratory, Lowestoft, Suffolk, United Kingdom The efficiency of a 24 m Granton otter trawl, rigged with bunt and midwing tickler chains, was de­ termined directly using sector-scanning sonar and plaice fitted with acoustic transponding tags.