David N. MacLennan

Observation and extraction of three‐dimensional information on fish schools

The paper describes the performance calibration and use of a 90‐deg sector scanning sonar for the collection and extraction of information on the 3D structure of fish schools. The equipment, which consists of a 455‐kHz 60‐beam sector scanning sonar linked to a PC is described briefly. The specific calibration problems of a high‐frequency instrument with multiple beams is discussed and calibration data from on‐axis and beam shape measurements are presented. The deployment of the instrument for data collection at sea and the data collection methods are described. Examples of the data collected are given. A three‐dimensional data processing algorithm is presented along with results of reconstruction from selected schools. The statistical properties of within school data are discussed along with indications of the precision of internal structures that can be evaluated using the sonar. The development of this system is supported by the European research program, AIR.

Acoustics in Fisheries and Aquatic Ecology Part 1 Introduction

The ICES Symposium on Acoustics in Fisheries and Aquatic Ecology (SAFAE) was held in Montpellier, France, from 10 to 14 June 2002. There were 303 participants from 37 countries, emphasizing the strongly international character of the meeting. This Symposium was the fifth organized by ICES in a series concerned with acoustics in fisheries and related fields. The first two were held in Bergen (1973 and 1982), the third in Seattle (1987), and the fourth in Aberdeen (1995; ICES Journal of Marine Science, Vol. 53, no. 2). To complete the historical picture, two symposia on the special problems of shallow-water acoustics should be mentioned, one held in London (1997) and one in Seattle (1999; Aquatic Living Resources, Vol. 13, no. 5). By 2002, however, it was seen that shallowwater, marine, and freshwater acoustics required a joint approach to problem-solving and the sharing of experience. It was therefore decided that this ICES Symposium would encompass all these applications within the general theme of acoustical methods for the study of aquatic biota and their exploitation. Organized under ICES auspices, the primary sponsors of the meeting were the Institut de Recherche pour le Developpement (IRD) and the Institut Francais de Recherche pour l’Exploitation de la Mer (IFREMER); cosponsors were the Acoustical Society of America, the UK Institute of Acoustics, the US National Marine Fisheries Service, and the Societe Francaise d’Acoustique. The coconveners were Francois Gerlotto (IRD) and Jacques Masse (IFREMER). They were assisted by a Scientific Steering Committee comprising Pablo Carrera (Spain), David Farmer (Canada), Masahiko Furusawa (Japan), D. Van Holliday (USA), William Karp (USA), Ole Arve Misund (Norway), John Simmonds (UK), and Will Tesler (Russia). The conference secretariat was efficiently organized by Laurence Vicens from the Centre Halieutique of the IRD, which provided much logistical support, as did IFREMER, especially through the editorial work of Brigitte Milcendeau. The main objectives of the Symposium were: to bring together scientists with diverse interests in fisheries and aquatic acoustics, covering a broad range of environments; to present their research in this rapidly evolving field; to review what can be achieved with new technology and theoretical approaches; and to consider future directions of study. There was a big response to the call for papers. The 256 abstracts submitted were allocated among the following ten theme sessions:

Effects of variable mean target strength on estimates of abundance: the case of Atlantic mackerel (Scomber scombrus)

Atlantic mackerel Scomber scombrus is a small pelagic, migratory fish which supports commercial fisheries. These fish school and are detectable using echosounders, yet fishery-independent estimates of their abundance in the North East Atlantic do not consider acoustic data. Accurate estimates of mean target strength (TS) are presently limiting echo-integration surveys from providing useful estimates of Atlantic mackerel abundance and distribution. This study provides TS estimates for in situ mackerel from multi-frequency split-beam echosounder measurements. TS equals 52.79 dB at 18 kHz, 59.60 dB at 38 kHz, 55.63 dB at 120 kHz, and 53.58 dB at 200 kHz, for a mean mackerel total length¼33.3 cm. These values differ from those currently assumed for this the sensitivity of acoustically estimated mackerel biomass around the Shetland Islands, Scotland, in 2014, to various estimates of TS. Confidence limits were obtained using geostatistics accounting for coverage and spatial autocorrelation. Stock biomasses, estimated from 38 and 200 kHz data, differed by 10.5%, and stock distributions were similar to each other and to the estimates from an independent stock assessment. Because mackerel backscatter at 38 kHz is dominated by echoes from the flesh and may have similarities to echoes from fish with swimbladders, and backscatter at 200 kHz is dominated by relatively stable echoes from the backbone, we recommend using 200 kHz data for estimates of Atlantic mackerel biomass.

Effects of target strength variability on estimates of abundance: The case of Atlantic mackerel (Scomber scombrus)

Atlantic mackerel is a small pelagic, migratory fish which supports valuable commercial fisheries. Despite the fact that these fish school in massive numbers, and are readily detected using echosounders, fishery-independent estimates of the abundance of mackerel in the Northeast Atlantic do not yet consider acoustic data. Echo-integration surveys could provide annual estimates of abundance, with additional scope for studying mackerel distributions throughout the year. However, as in all acoustic surveys, this requires accurate estimates of target strength (TS). The present study provides in situ TS estimates for mackerel from measurements made at sea with a multi-frequency split-beam echosounder. Empirical results suggest mean TS of -51.22 dB at 18 kHz, -59.83 dB at 38 kHz, -55.51 dB at 120 kHz, and -53.43 dB at 200 kHz, for a mean fish length of 33.3 cm. These differ significantly from the values currently used in acoustic surveys. The sensitivity of mackerel abundance estimates to variations in TS estim...

Reflections on technology and science in fishery research

In the latter part of the 20th century, fishery research expanded from its original biological base to include new areas, notably investigations of fishing-gear performance and fish-detection by sonar. The past 50 years have seen huge advances in technology and the combination of physical and biological insights in fishery research. Fishing-gear investigations initially focussed on the economics of commercial fishing, but in the 1970s energy consumption in fishing became a major issue. Thereafter, the objectives changed to support for fishery management through gear innovations and research, giving a better understanding of exploitation patterns. During this period, fishery acoustics advanced from crude beginnings in the 1960s to the powerful stock-assessment tool it is today. Progress in these fields has depended on multidisciplinary research involving both the physical and biological sciences. There have been failures along the way, but there is now good understanding of how technology as well as science can make a positive contribution to fishery management. This essay describes these developments as seen from my personal involvement over the past half century. It concludes with some pointers to the future, and practical advice to young researchers considering a career in fishery research.

Fisheries and plankton acoustics: State of the art and beyond

Acoustical methods are well established as a means of remotely observing aquatic organisms. The range of applications reported in the literature is wide, from studies of isolated animals to populations extending over large areas. The geometric scale of target organisms is similarly huge, from microscopic plankton to the largest of marine mammals. The information required from acoustical investigations may be simple quantities like abundance estimates, or more descriptive output like species identification. In each case, there are different problems to be considered. The multi‐disciplinary nature of acoustical techniques is important. Success depends on a combined appreciation of scattering physics, animal physiology, statistics, and sonar technology to mention just some of the contributing fields. The historical context is explained, leading to a critical review of recent developments. To a large extent, the driving force has been new technology, especially the rapid growth of computing power. It is impor...