MACROSOUNDING AS A NEW CONCEPT IN THE STUDY OF MARINE ECOSYSTEMS

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MACROSOUNDING AS A NEW CONCEPT IN THE STUDY OF MARINE ECOSYSTEMS

A. Orlowski

To cite this version:

A. Orlowski. MACROSOUNDING AS A NEW CONCEPT IN THE STUDY OF MARINE ECOSYS- TEMS. Journal de Physique Colloques, 1990, 51 (C2), pp.C2-69-C2-72. �10.1051/jphyscol:1990217�.

�jpa-00230473�

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MACROSOUNDING AS A NEW CONCEPT IN THE STUDY OF MARINE ECOSYSTEMS

Sea Fisheries Institute, A l . Zjednoczenia 1, PL-81-345 Gdynia, Poland RBsumd

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Malgrd una longue phiode d'utilisation des methodes acoustiques dans les recherches halieutiques, leur application pratique se limitait en general d dvaluer des ressources halieutiques

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E n rdalitd, les m6thodes acoust iques pourraient contribuyer an devdloppement considerable du moddle empirique multifactoriel d 'dcosystdmes marins.

La dissertation prdsente 18un des nouveaux comcepts de traitement de donndes acoustiques recueillies pendant des examens de routine. Tra- dicionnellement les rdsultats de sondages sont prdsentds sous la forme d'dcogrammes od l'information sur la distribution de ressources halieutiques est dispersde sur des mdtres entiers de papier d'enregis- trement. Dans la mdthode proposde, n o m d e macrosondage l8image gra- phique verticale de densit4 de distribution de stocks halieutiques est produite par un ordinateur conformement aux dchelles choisies en fonction de la corrdlation spatiale et temporelle des phdnomBnea observds. L'image peut 8tre enrichie d'antres facteurs, tels que les isothermes et les isohalines avec l'utilisation de matrices multidi- mensionnelles de donnee8 environnementales, biologiques et acoustiques de la zone examinde. Una belle presentation dtant plus facile 4

interprkter pour les ocdanographes, donne des posibilitss plus lar es dOanalyse multiiactorielle de traits caracteristiquea d'un ecosystbe et permet de determiner des relations importantes.

E n tant qu'illustration de la methode de mdcrosondage, on prdsente l a premidre"photo"~historique de concentration de fraf dans la mer Baltique et des profils choisis de m6crosondage complexe.

Abstract

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Besides a long period of using acoustic methods in fishery research, their practical application was mostly limited to fish stock assessment. In reality, the acoustic methods could be applied for a significant development of the multi-factor empirical model of the marine ecosystem.

The paper presents one of new concepts of treatment of acoustic data collected during routine surveys. Traditionally, the results of sound- ing are presented in the form of echograms, where the information on fish distribution is dispersed over many meters of recording paper.

I n the method proposed, called macrosounding, a graphic picture of vertical fish density distribution is generated by a computerl accord-

ing to different scales chosen in relation to a spatial and tlme co- rrelation of the observed phenomena. The picture can be enriched by other factors, such as isotherms or isohalines, with the use of a multi-dimensional matrix of environmental, biological, and acoustic data from the surveyed area. Such a presentation, being easier to interpret for all marine scientists, gives wider possibilities of a multi-factor analysis of ecosystem features and allows to determine

important relationships.

As an illustration of the method of macrosounding, the first histo- rical "photo" of a sprat spawning concentration in the Baltic Sea and chosen complex macrosounding transects are shown.

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INTRODUCTION

Ecosystem characteristics is expressed by description of relationships, appearing between biological and environmental factors. A good example

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990217

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C2-70 COLLOQUE DE PHYSIQUE

of s u c h r e l a t i o n s h i p s is a dependence of f i s h d i s t r i b u t i o n i n r e l a t i o n t o most i m p o r t a n t e n v i r o n m e n t a l conditions.

Beatides a l o n g p e r i o d of u s i n g a c o u s t i c methods i n f i s h e r y r e s e a r c h , t h e i r p r a c t i c a l a p p l i c a t i o n wes m o s t l y l i m i t e d t o f i s h s t o c k a s s e s s m e n t . I n r e a l i t y , t h e a c o u s t i c methods c o u l d be a p p l i e d f o r a s i g n i f i c a n t development of t h e m u l t i - f a c t o r e m p i r i c a l model of t h e marine ecosystem.

One of s u c h i d e a s was p r e s e n t e d by OrZowski i n / 2 / , a s a m u l t i c h a n n e l e c h o - i n t e g r a t i o n f o r w i d e r a n a l y s i s of f i s h d i s t r i b u t i o n i n r e l a t i o n t o e n v i r o n m e n t a l c o n d i t i o n s . I n /3/ f u r t h e r c o n c e p t s of p r a c t i c a l u s i n g of a c o u s t i c methods f o r r e s e a r c h of marine e c o s y s t e m s have been g i v e n . 2

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MACROSOUNDING METHOD

T r a d i t i o n a l l y , t h e r e s u l t s of a c o u s t i c s o u n d i n g a r e p r e s e n t e d i n t h e f o r m of echograms. But nobody is a b l e t o a n a l y s e e c o s y s t e m f e a t u r e s when t h e i n f o r m a t i o n on f i s h d i s t r i b u t i o n i s d i s p e r s e d o v e r s o many m e t e r s o f p a p e r r e c o r d i n g s . The a u t h o r of t h i s p a p e r p r o p o s e s a new method o f g r a p h i c a l p r e s e n t a t i o n of v e r t i c a l f i s h biomass d i s t r i b u t i o n a l o n g t h e t r a n s e c t . The method h a s been c a l l e d m a c r o s o u n d i n g . The macrosoullding i s b a s e d on g e n e r a t i o n of v e r t i c a l f i s h d i s t r i b u t i o n by a computer, a c c o r d i n g t o a s c a l e chosen i n r e l a t i o n t o a s p a t i a l and t e m p o r a l c o r r e l a t i o n of t h e o b s e r v e d phenomena.

F i g . 1

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Example of macrosounding: an a r t i f i c i a l l y - g e n e r a t e d f i s h d i s t r i - b u t i o n a l o n g t h e t r a n s e c t . F i s h d e n s i t y i s e x p r e s s e d by S v , which l i n e a r l y changes from -80 dB a t t h e b o r d e r s up t o -50 dB i n t h e middle of t h e

t r a n s e c t f o r l a y e r 1 0

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50 m.

F i g u r e 1 p r e s e n t s , a s an example, an a r t i f i c i a l l y g e n e r a t e d l a y e r o f f i s h , d i s p e r s e d between 1 0 and 55 m d e p t h s , w h i l e t h e median of biomass d e p t h d i s t r i b u t i o n is 50 m. I n t h e u p p e r l a y e r 10-50 m f i s h d e n s i t y , e x p r e s s e d by volume b a c k s c a t t e r i n g s t r e n g t h S,, i s c l o s e d between -80 dB and -50 dB.

The a l g o r i t h m k e e p s t h e mean d i s t a n c e , D , between n e i g h b o u r i n g d o t s as a randomly modulated v a r i a b l e w i t h t h e mean v a l u e r e l a t e d t o t h e mean biomass d e n s i t y of a c r o s s - s e c t i o n , e x p r e s s e d by Sv. If we a s s u m e / l / t h a t t a r g e t s d i s t r i b u t i o n i s d e s c r i b e d by t h e t h r e e - d i m e n s i o n a l P o i s s o n p r o b a b i l i t y l a w

( w i t h p a r a m e t e r p ) , t h e d i s t a n c e , D, between t a r g e t s i s p r o p o r t i o n a l t o p-1/3. The manner of f i l l i n g t h e v e r t i c a l l i n e s i n macrosounding v i s u a l i s a - t i o n a l g o r i t h m i s t o be matched t o t h e dynamic r a n g e of extreme v a l u e s of S v , a p p e a r i n g i n a n a l y s e d d a t a b a s e .

The macrosounding i n p r a c t i c e i s a k i n d of t r a n s f o r m a t i o n of s i n g l e f i s h and s h o a l s p i c t u r e s i n t o e q u i v a l e n t biomass u e r t i c a l d i s t r i b u t i o n

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F i g . 2

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P r a c t i c a l use of macrosounding. Real "photo" of spawning concen- t r a t i o n of s p r a t i n t h e B a l t i c S e a , East of Bornholm i n Nay 1985. Length of t r a n s e c t

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100 n a u t i c a l miles.

spawning c o n c e n t r a t i o n i n t h e B a l t i c Sea, E a s t of Bornholm is shown i n F i g . 2. A v e r t i c a l s c a l e corresponds t o depth i n meters

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a h o r i z o n t a l

s c a l e ( a b s c i s s a )

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t o n a u t i c a l m i l e s i n 5 Nm i n t e r v a l s . It means t h a t t h e s p r a t spawning c o n c e n t r a t i o n shown i n Fig. 2 i s observed along 100 n a u t i c a l miles.

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COMPLEX TRANSECT

The next s t e p of a p p l i c a t i o n of macrosounding v i s u a l i s a t i o n i s a s y n t h e s i s of such p i c t u r e and a g r a p h i c a l e x p r e s s i o n of isotherms and i s o h a l i n e s

( o r o t h e r c h a r a c t e r i s t i c s ) , u s e f u l f o r wider ecosystem a n a l y s i s . Such s y n t h e s i s i s c a l l e d t h e method of complex t r a n s e c t . The designation of com- p l e x t r a n s e c t parameters is p o s s i b l e if m u l t i-dimensional m a t r i x ( ai jk) of geographical d i s t r i b u t i o n of analysed f a c t o r s i n a surveyed a r e a i s calcu- l a t e d .

0

m

⁰⁴ ^{- -}

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^d

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F i g . 3

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Example of complex t r a n s e c t . Comparison of f i s h d i s t r i b u t i o n p a t - t e r n with isotherms [A] and i s o h a l i n e s [B] i n August 1983 f o r t h e main t r a n s e c t of P o l i s h f i s h e r y zone.

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C2-72 COLLOQUE DE PHYSIQUE

As an example of complex transect method the fish distribution pattern along the west- east transect of the Polish fishery zone in the Baltic Sea in summer 1983 is shown in Fig. 3, with correlated isotherms and isohalines.

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CONCLUSSION

The paper shows, how new concepts of treatment of acoustic data collected during routine surveys can enrich possibilities of wider analysis of ecosystem characteristics, thanks to a considerable progress in the field of data acquisition and processimg systems. Presented new forms of visua- lisation of acoustic data should enable a significant progress in deter- miming and interpretation of ecosystem characteristics by researchers.

REFERENCES

/1/ Lozow, J.B., J.B. Suomala, Jr. The application of hydroacoustic methods for aquatic biomass measurements, The Charles Stark Draper Lab. Final Report, Cambridge, Mass. (1971)

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/2/ OrZowski A. Multichannel echo integration and its application for determining of relationships between fish distribution and env iron- ment conditions. ICES C &.,I (1984)/B: 36.

/3/ Orbowski A. Zastosowanie akustycznych metod do bad& rozmieszczenia ryb i warstw rozpraszajqcych na tle Brodowiska morskiego. (Application of acoustic methods for research on distribution of fish and scattering layers in relation to environmental conditions). St. i Mat. Morak.

mst. ~ y b . B, 51 (1989)

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134 p.