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Survevs of fisheries resources
JOURNAL OF EXPERIMENTAL GAMINE BIOLOGY AND ECOLOGY
ELSEVIER
J. Enp. Mar. Biol. Ecol. 178 (1994) 147-151
Book Reviews Srrrveys of Fisheries Resolarc~s, by D.R. Gunderson; John Wiley & Sons Inc., Chichester; 1993; 248 pp.; GBP 36.95; ISBN O-471-54735-2. One of the essential tools in fisheries management, as well as in marine ecological is the abundance survey. The aim of this is to quantify an animal stock in a specific geographic region at a given time, generally also with determination of size and age composition. While each survey of a particular fish stock presents its own problems, requiring a special solution, there are just a few generic surveys. These arc the subjects of Professor Gunderson’s book. The major survey types that are addressed are bottom trawl surveys, acoustic survcys, and egg and larval surveys. The traditional catch-per-unit-effort method of estimating abundance from commercial fisheries data is justifiably dismissed at the outset for being unworkable. Bottom tmzd surveys Otter trawls and beam trawls are both described in detail. The importance of bobbin gear to rough-bottom trawling is recognized, hence description of the eminently useful rockhopper gear. The importance of monitoring trawl pcrformante, to determine the nominal sampling volume, and of studying fish behaviour in relation to trawling, to determine the gear efficiency, is emphasized. Lack of attention to these matters must sabotage any attempt at consistent measurement of fish density by trawling. The twin topics of gear standardization and intercalibration are also addressed, as being essential for combining or interpreting data from different vessels. Detailed advice is given on sampling the catch, and recording and editing data. In a pattern repeated for each generic survey, examples of successful applications arc presented. ilc’ozrstit suuw_rs The basic elements of sound propagation, echo reception, and signal processing and display are described. The need for physical sampling to establish the identity, or species, and size and age composition, of acoustically detected targets, is elaborated without, however, comment on new work using discriminant analysis that may contribute significantly to acoustic classification. Given the general nonrcpresentativity of trawl samples, the simplifying principle is stated that, if possible, acoustic surveys be timed so that the target species is the dominant one. Two particular acoustic survey methods are treated: echo counting and echo integration. The lack of rigor which the subject matter allows in other places deprives the student of at least tw.0 useful formulae. The first is that for the effective sampling volume, alluded to on pp. 8 and 94, which should be contrasted with the nominal sampling volume on p. 80. The second missing expression is the Vfundamental equation for echo integration, .T*,= c 4 5. studies.
Elsevier Science B V.. Amswdam SSDl 0 0 2 2 - 0 9 X 1( 9 4 ) E 0 1 8
0 -
7
where s., is the area back-scattering coefficient, iyAis the fish density as projected on a unit surface area, and 0 is the characteristic mean back-scattering cross section, as defined in the text on p. 112. Derivation of this, by integration of the volume backscattering coefficient over the water column, is elementary and heuristically valuable, while also describing the very operation performed in modern echo integrators. Egg md lwvcrl surveys These are introduced with reference to current fisheries oceanography projects that aim to understand the processes responsible for recruitment fluctuations in commercial fisheries, hence of the population dynamics of egg and larval stages. The Global Ocean Ecosystem Dynamics Program (GLOBEC) is immediately brought to mind. The wealth of detail given in this chapter does not limit its generality, witness the practical prescriptions for delimiting the survey area of a pelagic fish survey and for analysing resulting data by poststratification, also useful in other types of survey. Direct counting techniques Aerial, SCUBA, snorkeling, underwater-camera, mannedsubmersible, and remotely-operated-vehicle survey techniques, among other types, are described. The introductory advice on the methodology of direct counting surveys is quite general, as it also applies to the major survey types. Apropos of the so-called direct counting techniques, Gunderson leaves no doubt as to the particular shortcomings of most of these, which have generally ignored the problem of measurement error. In a striking example, a survey of widow rockfish (Sehasre,s e~rtomek~~s)is noted to have yielded an abundance estimate of 830 tonnes in an arca where catch-at-age analysis yielded a total biomass of 22000 tonnes. In each of the chapters devoted to survey methods, analysis of the measurement error is a primary concern. It is cogently argued that this be considered a concomitant of the survey itself. Errors that might arise in the statistical combination of density measurements to estimate abundance are of little concern; they are, according to Gunderson. avoided by the survey design. On the first page of the first chapter, on survey design, the conventional statistical approach to sampling is disclosed by the condition that sampling sites be both random and representative. Apparently, sampling fish distributed over an area by vessel-borne instruments or gear is akin to drawing numbered balls from an urn while blindfolded. At least occasional difficulties in “fit[tingJ survey data into classical sampling theory” are admitted. The reader should be informed, if necessary. that geostatistical or spatial sampling techniques arc well established in applications to mining, oil and gas exploration, agriculture, and forestry, among others, requiring basic estimation. Applications in fisheries research are increasing. The same techniques also yield estimates of variance from single surveys, assuming that the coverage is more or less uniform or in any case representative. Sequential or systematic sampling is viewed by geostatistics as an advantage to be exploited, not a hazard to be avoided. Gunderson notes that, from logistical considerations, systematic surveys are often prefcrrcd and routinely followed. It is also noted that the few relevant studies on this subject “have shown that systematic designs are more accurate and/or precise than random designs in the case of trawl surveys . . .. sonar surveys .._, and phytoplankton surveys”. The issue of survey design is again addressed in the chapter on acoustic surveys. Here, as elsewhere, it does not seem to be appreciated that any departure from uniformity
Book Review
IIJ.
Evp. Mrrr. Bid.
Gol.
178 II9941
147-151
I-1’)
in coverage of a fish stock of unknown spatial distribution incurs the penalty of increased autocorrelation, hence less information for the available survey time. Certainlq prior information on a fish distribution can and should be exploited in survey design through the mechanism of stratification, which is recommended. Mention of two-phase designs is to bc especially noted for offering an adaptive means of stratifying a survey. Under discussions of data analysis, kriging is mentioned. This is but one of many techniques belonging to the general category of geostatistics. Other geostatistical tcchniques, such as that of intrinsic random functions of order k. can address the problem of non-stationarities for which ordinary kriging is inadequate. ,411in all, Professor Gunderson has delivered what he has promised in the introduction, namely an integrated presentation in a single volume of the basic fisheries survey methods. This may be the first instance of such a presentation; it has an easy reading style and uniformly excellent artwork. Much more has also been achieved. for some of the same methods may be applied, with minor adaptation, to other animals, for cxample, zooplankton and marine mammals. The general advice given on the need to study the sampling process critically is salutary. .S’~rr~e~:v of Ksheries Resources is already in use as a textbook at the Department of Fisheries and Marine Biology, University of Bergen. It is recommended for use in advanced undergraduate and postgraduate courses, if supplemented with material on acoustic measurements and statistics, including geostatistics. Specialists working in fisheries assessments will find this to bc a very useful reference. .4p~~1~is It is probably worth mentioning a few technical matters in the chapter on acoustic surveys. Rectification, in Figs. 3-5, changes negative-polarity portions of signals by inversion, not removal. The pressure used in the definition of intensity on p. 75 is the root-mean-square value. A transducer may be made up of several independent elements, as in the case of ceramic, piezoelectric materials, but may also be a single element, as in magnetostrictivc devices (p. 77). The intention, in any case, is to enable the pressure wave emanating from a distributed source to interfere, not interact (also p. 77). On p. 78, “self’ noise is more properly called “internal noise”, as self-noise more generally refers to own-ship noise. The frequency spectrum associated with a transmitted pulse is continuous, not discrete as described. The source intensity produced by the transducer is that of the farfield intensity, corrected for absorption losses and referred to a range of 1 m, not necessarily or generally measured at this distance. The oscilloscope or cathode ray tube may once have been commonly used in echo counting (pp. 82, 94, 121) but certainly automation is the rule today, follow ing R.B. Mitson’s pioneering development work first reported in 1961. In several places the distinction is not observed that attenuation refers to the sum of mechanisms that diminish the amplitude of a propagating wave. principally geometric spreading and absorption (see pp. 82-83). The integral expressions for the output of echo integrator systems lack the differential dR (p. 99). Use of the symbol r for the receiving sensitivity is exceedingly, unconventional. Correction of echo integrator outputs for noise ma! commonly be cffccted by thresholding (p. 100). but the correct practice is that of subtraction of the estimated reverberation noise level, done in the energy or intensity, domain. New echo sounders allow the sound speed profile to be user-specitied (p. 104). Source level (pp. 104, 105) is usually rcfcrred to 1 pPa at I-m range. abbrcviatcd
by the double solidus /i. In estimating target strength addition to volume, is a key ingredient.
for the swimbladder.
shape, in
K.G. Foote Institute of Marine Research P.O. Box 1870 Nordnes N-5024 Bergen Norway
A Treatise on Limrzolog),. Vol. 4. The Zoohenthos, by G. Evelyn Hutchinson, edited by Yvette H. Edmondson; John Wiley & Sons, Inc., Chichester; 1993; 944 pp.; GBP 103.00: ISBN O-471-54294-6. This is the last volume of this four volume treatise on Limnology. The first volume described the geology, physics and chemistry of freshwater habitats, the second was an introduction to the biology of lakes and their plankton, the third dealt with limnological botany, and the present volume, the fourth, describes the zoobenthos. Sadly, G. Evelyn Hutchinson died at the age of 88. He had planned to produce this volume and, in addition, a fifth volume to encompass topics such as primary and secondary production, lake typology and lacustrine endemism. Maybe somebody else will attempt to complete his Treatise Yvette Edmondson took on the task of Editor of an incomplete manuscript of Volume 4. She describes some of the problems she had to deal with in her Foreword where she acknowledges the help and advice of many people. The result has been worth all the effort. Hutchinson, in his introduction to this volume, remarks that “The chief value of this treatise as compared with many other works on limnology now appearThe current volume attains this ing seems to be in the attempt to be comprehensive”. objcctivc for the areas of the subject that it discusses. The opening chapter (116 pp.) describes the protists, rotifers, sponges, coelenterates and Ectoprocta inhabiting freshwater. The families, genera and species of each group are defined; there are discussions of substrata, biology and ecology, often at the specific level. The chapter ends with an account of the lasiophil fauna, the protists, nematodcs, rotifers, oligochaetes, mites and microcrustaceans associated with the lasion. The lasion is the tangle of algae, millimetres to centimetres in thickness, often with associated detritus and, of course, bacteria, present on the bottom, often on hard surfaces. The interstices of the lasion are niches for small organisms. The second chapter (150 pp.) gives an account of the classification of the freshwater gastropods. Their capacity to live in this environment, low in calcium, and the problems they have with their shells are described. Respiratory physiology is reviewed in terms of the pulmonate lung, respiratory pigments, and effects of seasonally changing environmental temperature. Food and feeding methods, radular teeth, body growth as a function of diet are examined. Reproductive organs, spermatophores and eggs, brecding bchaviour and physiology are treated in some detail. An account of life histories, semel- and interoparity, population biology arc dealt with at a general and specific lcvcl.
ELSEVIER
J. Enp. Mar. Biol. Ecol. 178 (1994) 147-151
Book Reviews Srrrveys of Fisheries Resolarc~s, by D.R. Gunderson; John Wiley & Sons Inc., Chichester; 1993; 248 pp.; GBP 36.95; ISBN O-471-54735-2. One of the essential tools in fisheries management, as well as in marine ecological is the abundance survey. The aim of this is to quantify an animal stock in a specific geographic region at a given time, generally also with determination of size and age composition. While each survey of a particular fish stock presents its own problems, requiring a special solution, there are just a few generic surveys. These arc the subjects of Professor Gunderson’s book. The major survey types that are addressed are bottom trawl surveys, acoustic survcys, and egg and larval surveys. The traditional catch-per-unit-effort method of estimating abundance from commercial fisheries data is justifiably dismissed at the outset for being unworkable. Bottom tmzd surveys Otter trawls and beam trawls are both described in detail. The importance of bobbin gear to rough-bottom trawling is recognized, hence description of the eminently useful rockhopper gear. The importance of monitoring trawl pcrformante, to determine the nominal sampling volume, and of studying fish behaviour in relation to trawling, to determine the gear efficiency, is emphasized. Lack of attention to these matters must sabotage any attempt at consistent measurement of fish density by trawling. The twin topics of gear standardization and intercalibration are also addressed, as being essential for combining or interpreting data from different vessels. Detailed advice is given on sampling the catch, and recording and editing data. In a pattern repeated for each generic survey, examples of successful applications arc presented. ilc’ozrstit suuw_rs The basic elements of sound propagation, echo reception, and signal processing and display are described. The need for physical sampling to establish the identity, or species, and size and age composition, of acoustically detected targets, is elaborated without, however, comment on new work using discriminant analysis that may contribute significantly to acoustic classification. Given the general nonrcpresentativity of trawl samples, the simplifying principle is stated that, if possible, acoustic surveys be timed so that the target species is the dominant one. Two particular acoustic survey methods are treated: echo counting and echo integration. The lack of rigor which the subject matter allows in other places deprives the student of at least tw.0 useful formulae. The first is that for the effective sampling volume, alluded to on pp. 8 and 94, which should be contrasted with the nominal sampling volume on p. 80. The second missing expression is the Vfundamental equation for echo integration, .T*,= c 4 5. studies.
Elsevier Science B V.. Amswdam SSDl 0 0 2 2 - 0 9 X 1( 9 4 ) E 0 1 8
0 -
7
where s., is the area back-scattering coefficient, iyAis the fish density as projected on a unit surface area, and 0 is the characteristic mean back-scattering cross section, as defined in the text on p. 112. Derivation of this, by integration of the volume backscattering coefficient over the water column, is elementary and heuristically valuable, while also describing the very operation performed in modern echo integrators. Egg md lwvcrl surveys These are introduced with reference to current fisheries oceanography projects that aim to understand the processes responsible for recruitment fluctuations in commercial fisheries, hence of the population dynamics of egg and larval stages. The Global Ocean Ecosystem Dynamics Program (GLOBEC) is immediately brought to mind. The wealth of detail given in this chapter does not limit its generality, witness the practical prescriptions for delimiting the survey area of a pelagic fish survey and for analysing resulting data by poststratification, also useful in other types of survey. Direct counting techniques Aerial, SCUBA, snorkeling, underwater-camera, mannedsubmersible, and remotely-operated-vehicle survey techniques, among other types, are described. The introductory advice on the methodology of direct counting surveys is quite general, as it also applies to the major survey types. Apropos of the so-called direct counting techniques, Gunderson leaves no doubt as to the particular shortcomings of most of these, which have generally ignored the problem of measurement error. In a striking example, a survey of widow rockfish (Sehasre,s e~rtomek~~s)is noted to have yielded an abundance estimate of 830 tonnes in an arca where catch-at-age analysis yielded a total biomass of 22000 tonnes. In each of the chapters devoted to survey methods, analysis of the measurement error is a primary concern. It is cogently argued that this be considered a concomitant of the survey itself. Errors that might arise in the statistical combination of density measurements to estimate abundance are of little concern; they are, according to Gunderson. avoided by the survey design. On the first page of the first chapter, on survey design, the conventional statistical approach to sampling is disclosed by the condition that sampling sites be both random and representative. Apparently, sampling fish distributed over an area by vessel-borne instruments or gear is akin to drawing numbered balls from an urn while blindfolded. At least occasional difficulties in “fit[tingJ survey data into classical sampling theory” are admitted. The reader should be informed, if necessary. that geostatistical or spatial sampling techniques arc well established in applications to mining, oil and gas exploration, agriculture, and forestry, among others, requiring basic estimation. Applications in fisheries research are increasing. The same techniques also yield estimates of variance from single surveys, assuming that the coverage is more or less uniform or in any case representative. Sequential or systematic sampling is viewed by geostatistics as an advantage to be exploited, not a hazard to be avoided. Gunderson notes that, from logistical considerations, systematic surveys are often prefcrrcd and routinely followed. It is also noted that the few relevant studies on this subject “have shown that systematic designs are more accurate and/or precise than random designs in the case of trawl surveys . . .. sonar surveys .._, and phytoplankton surveys”. The issue of survey design is again addressed in the chapter on acoustic surveys. Here, as elsewhere, it does not seem to be appreciated that any departure from uniformity
Book Review
IIJ.
Evp. Mrrr. Bid.
Gol.
178 II9941
147-151
I-1’)
in coverage of a fish stock of unknown spatial distribution incurs the penalty of increased autocorrelation, hence less information for the available survey time. Certainlq prior information on a fish distribution can and should be exploited in survey design through the mechanism of stratification, which is recommended. Mention of two-phase designs is to bc especially noted for offering an adaptive means of stratifying a survey. Under discussions of data analysis, kriging is mentioned. This is but one of many techniques belonging to the general category of geostatistics. Other geostatistical tcchniques, such as that of intrinsic random functions of order k. can address the problem of non-stationarities for which ordinary kriging is inadequate. ,411in all, Professor Gunderson has delivered what he has promised in the introduction, namely an integrated presentation in a single volume of the basic fisheries survey methods. This may be the first instance of such a presentation; it has an easy reading style and uniformly excellent artwork. Much more has also been achieved. for some of the same methods may be applied, with minor adaptation, to other animals, for cxample, zooplankton and marine mammals. The general advice given on the need to study the sampling process critically is salutary. .S’~rr~e~:v of Ksheries Resources is already in use as a textbook at the Department of Fisheries and Marine Biology, University of Bergen. It is recommended for use in advanced undergraduate and postgraduate courses, if supplemented with material on acoustic measurements and statistics, including geostatistics. Specialists working in fisheries assessments will find this to bc a very useful reference. .4p~~1~is It is probably worth mentioning a few technical matters in the chapter on acoustic surveys. Rectification, in Figs. 3-5, changes negative-polarity portions of signals by inversion, not removal. The pressure used in the definition of intensity on p. 75 is the root-mean-square value. A transducer may be made up of several independent elements, as in the case of ceramic, piezoelectric materials, but may also be a single element, as in magnetostrictivc devices (p. 77). The intention, in any case, is to enable the pressure wave emanating from a distributed source to interfere, not interact (also p. 77). On p. 78, “self’ noise is more properly called “internal noise”, as self-noise more generally refers to own-ship noise. The frequency spectrum associated with a transmitted pulse is continuous, not discrete as described. The source intensity produced by the transducer is that of the farfield intensity, corrected for absorption losses and referred to a range of 1 m, not necessarily or generally measured at this distance. The oscilloscope or cathode ray tube may once have been commonly used in echo counting (pp. 82, 94, 121) but certainly automation is the rule today, follow ing R.B. Mitson’s pioneering development work first reported in 1961. In several places the distinction is not observed that attenuation refers to the sum of mechanisms that diminish the amplitude of a propagating wave. principally geometric spreading and absorption (see pp. 82-83). The integral expressions for the output of echo integrator systems lack the differential dR (p. 99). Use of the symbol r for the receiving sensitivity is exceedingly, unconventional. Correction of echo integrator outputs for noise ma! commonly be cffccted by thresholding (p. 100). but the correct practice is that of subtraction of the estimated reverberation noise level, done in the energy or intensity, domain. New echo sounders allow the sound speed profile to be user-specitied (p. 104). Source level (pp. 104, 105) is usually rcfcrred to 1 pPa at I-m range. abbrcviatcd
by the double solidus /i. In estimating target strength addition to volume, is a key ingredient.
for the swimbladder.
shape, in
K.G. Foote Institute of Marine Research P.O. Box 1870 Nordnes N-5024 Bergen Norway
A Treatise on Limrzolog),. Vol. 4. The Zoohenthos, by G. Evelyn Hutchinson, edited by Yvette H. Edmondson; John Wiley & Sons, Inc., Chichester; 1993; 944 pp.; GBP 103.00: ISBN O-471-54294-6. This is the last volume of this four volume treatise on Limnology. The first volume described the geology, physics and chemistry of freshwater habitats, the second was an introduction to the biology of lakes and their plankton, the third dealt with limnological botany, and the present volume, the fourth, describes the zoobenthos. Sadly, G. Evelyn Hutchinson died at the age of 88. He had planned to produce this volume and, in addition, a fifth volume to encompass topics such as primary and secondary production, lake typology and lacustrine endemism. Maybe somebody else will attempt to complete his Treatise Yvette Edmondson took on the task of Editor of an incomplete manuscript of Volume 4. She describes some of the problems she had to deal with in her Foreword where she acknowledges the help and advice of many people. The result has been worth all the effort. Hutchinson, in his introduction to this volume, remarks that “The chief value of this treatise as compared with many other works on limnology now appearThe current volume attains this ing seems to be in the attempt to be comprehensive”. objcctivc for the areas of the subject that it discusses. The opening chapter (116 pp.) describes the protists, rotifers, sponges, coelenterates and Ectoprocta inhabiting freshwater. The families, genera and species of each group are defined; there are discussions of substrata, biology and ecology, often at the specific level. The chapter ends with an account of the lasiophil fauna, the protists, nematodcs, rotifers, oligochaetes, mites and microcrustaceans associated with the lasion. The lasion is the tangle of algae, millimetres to centimetres in thickness, often with associated detritus and, of course, bacteria, present on the bottom, often on hard surfaces. The interstices of the lasion are niches for small organisms. The second chapter (150 pp.) gives an account of the classification of the freshwater gastropods. Their capacity to live in this environment, low in calcium, and the problems they have with their shells are described. Respiratory physiology is reviewed in terms of the pulmonate lung, respiratory pigments, and effects of seasonally changing environmental temperature. Food and feeding methods, radular teeth, body growth as a function of diet are examined. Reproductive organs, spermatophores and eggs, brecding bchaviour and physiology are treated in some detail. An account of life histories, semel- and interoparity, population biology arc dealt with at a general and specific lcvcl.