This report not to be cited without prior reference to the authors
International Couneil for
the Exploration ofthe Sea
ICES C.M. 1995/J:7
Baltic Fish Committee
ACOUSTIC IDENTIFICATION OF O-GROUP COD IN THE BALTIC SEA
.by
K.M. Lehmann and J.R. Nielsen
*
Danish Institute for Fisheries Research, Department ofFish Biology,
North Sea Centre, P.O. Box 101, DK-9850 Hirtshals, Denmark
ABSTRACT
Combined acoustic, oceanographic and trawl surveys have been conducted during 1993 and 1994
to determine the distribution for young of the year (YOY) Baltic cod in the Bomholm Basin
(ICES Subdivision 25, Baltic Sea). During these cruises acoustic signals were obtained at some
sites which were analysed to see wether they were indicative of the presence of YOY cod.
Sampling was performed at these sites with 'GOV' and 'IYGPT' trawls resulting in the catch of
YOY cod. Coneurrent with trawl sampling, vertieal profiles were taken for salinity, temperature
and oxygen. Current veloeities were performed (ADCP). The methodology of acoustic for
deseribing the vertieal and horizontal distribution ofjuvenile eod is discussed based on the limited
data on YOY cod obtained during the RJV Dana survey September/Oetober 1994 in the Bornholm
Basin and adjoining waters. Further, the utility of existing TS-functions are discussed related to
YOY cod. On that basis design offuture investigations are proposed.
Key Words: Acoustie target identifieation, YOY Baltic Cod, CTD, ADCP, ICES Subdivision 25.
* Authorship equaI.
•
Introduction
Several combined hydroacoustic and trawl surveys have been carried out by RIV Dana in the
Bornholm Basin and adjoining waters related to the AIR Program "Mechanisms influencing long
term trends in reproductive success and recruitment of Baltic cod: implications for fisheries
management" (AIR2-CT94-1226). Two pilot surveys were performed in August 1993 (DS0793)
and August 1994 (DS0894) with the purposes of localizing young ofthe year (YOY) cod and get
a fishery independent spawning stock biomass estimate, respectively. A later survey was carried
out in October 1994 to eontinue the seareh for the YOY eod. To loealize different stages and size
groups of YOY eod (eggs, larvae, 0- and l-group juveniles) and measure environmental
parameters oftheir habitats a variety of equipment and several eatch gears have been used during
these surveys which include hydroacoustic equipment, ADCP, CTD, Particle Counter, BONGO,
small meshed pelagic ringtrawl (MIK), small meshed pelagic young fish trawl (IYGPT) and large
demersal and pelagic trawls with small mesh sizes (GOV, EXPO). A major purpose of the AIR2
project is to loealize and map the pelagic and horizontal distribution ofjuvenile O-group Baltic eod
and estimate their relative densities. The present work aims to contribute to the establishment of
an acoustic identification eatalogue with acoustic patterns of small eod in the central Baltic Sea
and to develop methods to distinguish different acoustic patterns for YOY cod related to physical
and biological eonditions. Based on 38 kHz acoustic split beam measurements ofsingle fish echo
refleetions, which are related to catch in concurrent performed trawl fishery to detect aeoustic
patterns and distribution patterns ofjuvenile O-group eod, the present preliminary results will be
the first limited material in this eatalogue. Further investigations based on combined acoustic and
trawl surveys with both RN Dana and RN Havfisken using both 38kHz and 120 kHz split beam
echosounders are performed in 1995 to supplement with more extensive information to this
catalogue and hopefully to establish an empirical TS algorithm of small YOY eod based on 120
kHz single fish echo reflections.
:l\1aterials and methods
Data were collected during the RIV Dana survey DS 1094 from 27 September to 6 Oetober 1994
where the Bornholm Basin and adjacent waters was surveyed with a combination ofhydroacoustic
measurements and demersal and pelagic trawl sampling.
Hydroacoustic data were obtained a10ng parallel transects covering the basin with an intertransect
distance of 10 nrn and on the cruise route offthe basin. Hanö Bay, Södra Midsjö Bank and the
area between Rönne Bank and Oder Bank were only covered with one transect each. A 38 kHz
Simrad scientific split beam echosounder system eonnected to an EchoAnn eehoanalyzer (Degnbol
et al.. 1990) was used for data colleetion. The basic settings were high power, pulselength 1 ms
. and receiver bandwidth 1 kHz. The hull mounted transducer was ofthe type 38-29/25. The system
was calibrated using the standard eopper sphere technique (Foote et aI. 1986, Degnbol et aI.
1990). The SL + VR ofthe system was 132.5 dB.
Species and size composition were sampled by trawling with a standard GOV bottom trawl
(mesh size in codend 16 mm stretched) and a mid-water IYGPT trawl (mesh size in eodend 16
mm stretched). The main log infonnation oftrawl stations are given on Tab. I, together with CTD
and ADep data. Speeies composition and abundanee ofstation 41 and 43 are given on Tab. 2 and
size distribution of eod, herring and sprat are showed on Figs. I to 4.
2
The length distribution of eod, herring and sprat were ealeulated to TS distributions using the
estimated empirieal TS function for Gadoids and Clupeoids used in the Baltic (Götze et al. 1994):
Gadoids (Bcised on large eod):
Clupeoids:
TS=20 log L (ern) - 67.5 dB (Foote et al. 1986)
. TS=20 log L (ern) - 70.8 dB (Lassen & Staehr, 1985)
The resulting TS values are showed on Figs. 1 to 4.
The single target values from the 38 kHz split beam echo sounder system \vere sampled du~ing
trawliryg ori stno. 41 and 43, startingjust before shooting the first trawl, aod endingjust after the
seeorid trawl was on deck. The reeorded single target values were pooled by dB size groiJps for
the two stations, respectively, and the eaIculated TS frequency distributions are given 00 Fig. 5.
Vertical profiles oftemperature, salinity and oxygen from station 41 and 43 were reeorded by a
CTD probe and sho\ved on Fig. 6.
Results
During the Dana surveys DS0793, DS0894 and DSI094 eovering the whole eentral Bomholm
basin, the basin edges and surrounding waters, signifieant numbers of sma1l, juvenile, O-group eod
have been fouod only on two loealities during the DS 1094 survey in the area between Oder Bank
and Rönne Bank (st. 41 and 43; Tabs. 1 & 2). These two stations covers a shallow water area, i.e.
10-20 m bottom depth (st. 43 and surrouridirig areas), and a more deep area with bottom depths
from 35-40 m (around st. 41), respeetively~ (Tabs. 1 & 2). Both areas are eharaetefized by slow
water currents below 0.3 knot at a1l depths eoming from shifting direetions and low salinities
below 7-8 %0 in the whole water eoluriui. The water temperature on both stations are about 1213°C in a1l vertieal layers exeept forthe near bottom water layer on station 41 \vhere the
temperature drops down to about 6°C. At this site the near bottom oxygen saturation is also lower
(app. 60%) compared to the oxygen saturation in all öther layers in the rest ofthe area being at
a level between 80-90 % saturation.
The eateh in the GOV trawl on st. 41 is by weight dominated by eod, while eod and flounder are
domimiting in the GOV eateh on st. 43. The IYGPT trawl eateh on st. 41 is by weight dominated
by sprat, while eod, floimder and herring are domioating in the IYGPT eateh ori st. 43. Largest
oeeurrenees ofsmall eod (TTL<=12 em) are in the GOV eatehes 00 böth stations, however, the
GOVeatches do not eontain eod smaller than 6 em, while eod down to 3-5 em length oeeur in the
IYGPT eateh.
. Tra~ling with the demersal GOV trawl is performed on bottom, however, the fishirig ami eateh
ofthe trawl during shooting and during heaving is not kOown, whieh makes pelagic eatehes ofthis
trawl very possible. The IYGPT trawl is hauled in ci pelagic zig-zag movement eovering the whole
. water column, i.e. from surfaee to bottom to surfaee again. This means that the vertieal
distribution ofthe single fish species aod size groups on thestations is not krtown based 00 ihe
preseot trawl catehes, in general. The eehograms (Fig. 7) show that large herring or/and sprat
shoals oeeur in the pelagic layers of the water eolurims on. the trawl stations. These shoals give
high, thin arid very distinet signals. However single fish echoes of small eod eari nöt Visually be
identified among the residual signals. (Fig. 7).
3
Other abundant fish species in the catches are flatfish such as flounder, turbot and plaice, and also
sculpins. These species are cIosely connected to the seabed environment and is, thus, not believed
to have significant vertical distribution above the 1 m offset layer from the bottom used in the
acoustic measurements. These species are, therefore, not believed to be incIuded in the obtained
echo signals and gives no acoustic noise in the analysed single fish echo reflections.
The length distributions in the trawl catches of the three most abundant fish species in the pelagic
water layers in the area (cod, sprat and herring) are compared to calculated TS values for the
observed length groups. The calculations are based on existing empirical estimated TS functions,
which are species and size specific (see the materials and methods section). Small cod have, where
they occur in significant numbers, ie. in the GOV catches, a tendency to have abimodal TS
distribution (and length frequency) within the TS interval -50 dB to -45 dB with modes around
-46 dB and -48 - -49 dB, respectively (Figs. 1-4). Within that interval there is an overlap in the TS
distribution for small cod (5-15 cm in TTL corresponding to ealculated TS values between -50 dB
and -45 dB) and sprat (5-16 cm in TTL corresponding to calculated TS values between -52 to -47
dB). In general, the calculated TS mode spectrum for small cod are observed to overlap with the
ealculated speetrum for especially larger sprat observed in the eatches. Also the length
distributions and the TS value distributions for the smaller size groups of the caught herring
overiap with the distributions ofthe larger size groups ofthe small cod and with sprat (in the TS
value interval -47 dB to -44 dB) based on the resuits from the GOV trawl eatches on both stations
and in the IYGPT eatch on s1. 43. Further, very small herring caught in the IYGPT trawl on s1.
41 have overiapping TS values with the smallest group ofthe small eod in the TS interval around
-51 dB. Figs. 1-4.
Regarding the observed TS value distribution from the 38 kHz split beam echosounder it appears
from Fig. 5 that the highest number of single fish echo reflections on the deeper s1. 41 originates
from the 23-29 m depth layer. This can be related to the pelagic localization of the thermocline
and the more modest halocline at the dept~ around 29-30 m (Fig. 6). In the 23-29 m water layer
and, thus, in the resuiting TS distribution pattern for the whole s1. 41 the observed single target
TS value distribution have several modes. The major number of single fish reflections on s1. 41 is
observed within the TS value interval between -59 dB to -52 dB. Abimodal TS distribution
pattern is (also) observed on the more shallow water st. 43. On both stations there exist a major
TS mode around -58 dB to -53 dB with dispersions between -64 dB to -50 dB. This mode can not
directly be explained based on the ealculated TS values for small eod, small herring and sprat
oceurring in the trawl catches on both stations, which have higher calculated TS values in the
interval around -52 dB to -45 dB (Figs. 1-4). However, other modes in the observed TS value
distribution on both stations covers this TS value interval. At s1. 43 the largest mode is observed
. arou'nd -44 dB with a dispersion between -48 dB and -40 dB while a more modest mode in the
same TS value interval appears on s1. 41. Based on the used TS function TS values up to around
-32 dB have been calculated for the large cod in the trawl catches. However, the observed TS
values on especially s1. 41 succeeds this level where TS values up to -26 dB is observed. Even
though the calculated single fish TS values represents a convoluted TS distribution of about 5-6
dB the observed extreme TS values about -26 dB can not be explained based on the species and
size composition found in the trawl catches. Possibly, these values represents very large cod that
have either avoided or escaped from the trawls or have stayed in not covered (hauled) \vater layers
by the large GOV trawl.
4
•
•
Discussion
Based on the found overlaps in the ealculated TS value distributions of single target refleetions
between smaIl eod, sprat and smaIl herring it is not possible to isolate and identif)' speeifie
aeoustic patterns for smaIl eod from those of sprat and smaIl herring oeeurring in the trawl
catehes. Thus, further analyses on the aeoustic signals with respeet to geometrie angles between
single target reflections identified to species and size group with special erriphasis on smaIl eod
gives no meaning based on the existing limited material.
•
~
..
•
The ealculated TS values around -50 dB to -45 dB for the small eod and small herring and sprat
are very high, and lower values for these size groups are expeeted. The unexpected high values
rrught be due to a major methodological problem by using an empirieal TS algorithm estimated for
large ead, Le. the present used TS value distribution for aIl eod size groups are based on a TS
aIgorithrri that is established on the basis ofempirical estirriates for only larger eod with an 38 kHz
split beam echosounder. The reason for using this function in the present work is that no empirical
estimated TS algorithrri for smaIl size groups of eod in the Baltic Sea exist. The used TS function
based on a relatively long wavelength from an 38 kHz echosounder is useful for larger cad as the
wavelength/swimbladder-size relationship (= Ä/L) is high (» 1) for these size groups. However,
this is not the case for smaIl cod where the Ä /L relationship is around 1 or even lower thari 1
when estimated with a 38 kHz split beam echosounder with relatively long wavelengths (3-4 cm
in sea \vater). First of all, when Ä/L lays in the range around 1 resonanee may oeeur giving too
large TS values for smaIl eod. Further, in the Ä /L area around 1 and lower values, eompletely
different physieal eharaeteristies exist for the echo refleetion from an air bubble in water (i.e. the
swimbladder) eompared to higher Ä /L-values, as the relationship between the aeoustic cross
seetion area and the physical (target) cross section area are different when Ä /L »1 compared to
when Ä/L<= 1. For that reason, lower TS values for the smaIler eod are expected. Possibly, the
TS values for smaIl eod eould be iri the interval between -64 dB to -52 dB, which is the TS value
intervaI where major modes between -58 dB to -53 dB with dispersions between -64 dB and -50
dB aetuaIly occurred for the single target reflections on both st. 41 arid st. 43.
Ariother problem related to the present exaet calculated TS values for single fish targets is, that
they represent a eorivoluted mean TS value which varies wiihin an rarige (dispersion) of maybe
5-6 dB deperiderit ofthe swirribladder directivity and fish behaviour ofthe actual measured single
target. The ealculated TS valtie per length group represents, thus, a convoluted mean over Ei TS
distribution, and this vaIue has not been empirical estimated for small eod in the BaIti6 Sea. Even
for larger size groups of eod this mean. value and its range (dispersiori around the mean) is not
thoroughly empirical measured. As the TS value, and thus the mean TS and range, is dependent
offi~h behaViour and swimbladder direetivity, species arid size specifie differenees are very likeIy.
To measure an useful empirical TS algorithm for smaIl eod it is necessary to measure echo
reflections from single fish targets within a braad target size range (length groups), within a broad
range of target swimbladder directivities, and within a broad target behavioral rarige with an high
frequency split beam echosounder, e.g. with an 120 kHz split beam echosoimder, in the natural
environment of small eod in the Baltie Sea. Thlls, future investigations should first of all
concentrate on estimating an useful TS algorithrri for small cod size groups. To do so, it is
neeessary, wheri performing eombined aeoustie and trawl surveys, to get abundant trawl eatches
of smäll eod with no or only limited oeeurrences of other fish species and size groups with
5
overlapping TS value distributions and, eoneurrently,' it is neeessary to sampie aeoustie data on
single target refleetions from an high frequeney eehosounder to ensure that the Ä IL relationship
for small eod are relatively high.
Investigations on the eoming Dana eruises in the Baltie Sea related to the AIR2 program will
based on previous experienee eoneentrate on aeoustic measurements with an 120 kHz split beam
echo sounder to establish an useful TS algorithm for small cod and try, based on repeated selective
trawl fishery on stations with relatively high abundances of small cod, to identify differences in the
vertical distribution patterns ofsmall cod, small herring and sprat (as the most important pelagic
species) in different vertieal water layers.
Acknowledgements: We thank Poul Degnbol and Bo Lundgren, Danish Institute for Fisheries
Research, Fish Biological Institute, North Sea Centre, Denmark, for valuable diseussions.
References
Degnbol, P., T.F. Jensen, B. Lundgren and M. Vinther. Eehoann - an analyzer for echosounder
signals. ICES CM 19901B:I0
. Foote, K, AAglen, O. Nakken 1986. Measurement of fish target strength with a split-beam
echosounder. J. Acoust. Soc. Am. 80 (2): 612-621.
Lassen, H. and Staehr, K.-J., 1985. Target strength ofBaltic herring and sprat measured in-situ.
ICES C.M. 19851B:41.
6
•
Table 1.
Main logg information of RN DANA survey 10, September/October 1994, in the Bomholm Basin and adjoining waters.
A: Hanö Bay, B: Södre Mitsjö Bank, C: Between Rönne Bank and Oder Bank.
Stno.:
1
2
3
4
22
23
24
25
41
41
42
42
43
43
Gear
iygpt
lygpt
iygpt
iygpt
iygpt
Iygpt
iygpt
Iygpt
iygpt
gov
gov
;ygpt
iygpt
gov
Duration Locality
minuts
12
A
33
A
15
A
15
A
30
B
28
B
31
B
28
B
29
C
30
C
C
30
30
C
C
31
C
31
1
2
3
4
22
23
24
25
41
41
42
42
43
43
Gear
iygpl
iygpt
iygpt
Iygpt
iygpt
lygpt
Iygpt
Iygpt
iygpt
gov
gov
iygpt
iygpt
gov
Salinity
Oxygen saturation Codc=12
ADCP components bottom
Temperature 'C
Knob
Midwater Sottom
Midwate Sottom· Middwate Bottom numbers
N/S
E/W
31
32
0
35.1
0.69
10
9
60
60
3.6
-9.1
10.1
0.26
11
9
32
32
95
88
0
-10.7
0.41
13
0
11
29
33
18
60
-21.6
-9.5
0.46
12
10
7
93
85
0
7
0.6
-13.3
0.26
7
90
0
11
7
90
11
-0.2
2.6
0.05
12
12
7
90
7
90
3
90
0
11
11.3
0.25
11
7
7
90
5.9
0.09
12
4.2
2.1
12
7
7
90
90
0
-9.9
10.1
0.27
13
6
8
90
60
26
7
4.2
-9.2
0.20
13
6
8
90
60
306
7
-6.2
0.13
12
12
8
90
80
38
8
-2.9
-5.3
0.11
12
12
8
90
80
0
-1.6
8
12
-1.5
0.Q3
12
8
90
0.8
37
8
90
1.4
0.03
12
12
8
8
90
90
117
-0.2
Stno.:
UTe
Latitude
Longitude Date
Deptm
Depth m ADCP component Current
pos.- N
pos.- E YVMMDD HHMM Middwater Near bott N/S
E IW Knob
5554.4
1432.4
940930
1352
64
23.5
68.5
20
1.41
5550.6
1434.9
940930
511
40
20
11.6
-15.7
0.38
5548.2
1438.2
940930
814
20
-3.4
50
-3.2
0.09
5542.9
1442.9
940930
1145
10
16
-19.2
-11.3
0.43
5540.9
1657.9
941003
35
10
-10.3
20
-1.5
0.20
5542.4
5.3
1707.2
941003
600
10
22
0.2
0.10
5543.0
941003
1n5.1
924
12.9
0.27
10
4.8
18
1151
5544.6
1736.6
941003
20
15.3
0.32
38
5.6
5437.8
941005
1434.2
1018
-5.1
10
-9.5
0.21
28
5437.8
941005
1434.4
1146
10
28
-8.7
-10.6
0.27
5432.3
1427.8
941005
1545
2
6
-10
5
0.22
5432.4
1424.1
941005
1705
2
6
-5.2
3.5
0.12
5430.7
1419.6
941005
1946
2
6
-10.4
5.8
0.23
5430.8
1419.2
941005
2101
2
6
-11.3
8.9
0.28
-
Table 2. Calch per species in weight and numbers in GOV
and IYGPT trawl hauls on stations no. 41 and 43.
Stat-no
gear
CW-cod (\<g)
CNo-cod
CW-herring (kg)
CNo-herring
CW-sprat (kg)
CNo-sprat
CW-f1ounder (\<g)
CNo-f1ounder
CW-plaice (\<g)
CNo-plaice
CW-turbot (\<g)
CNo-turbot
CW-whiting (\<g)
CNo-whiting
CW-sculpin (\<g)
CNo-sculpin
CW-gobies (kg)
CNo-gobies
CW-eel
CNo-eel
41
iygpt
<0.50
26
5.24
951
124.30
33935
--.
.·
-·
·
---
41
gov
284.49
715
10.40
278
3.40
96
8.60
21
6.30
26
7.40
9
0.16
2
33.40
?
0.01
1
--
43
iygpt
18.38
81
12.80
108
3.32
818
28.40
153
0.60
4
3.30
14
.
-
3.10
?
0.72
1086
0.08
2
43
gov
64.42
351
4.50
110
0.74
113
147.30
486
3.10
22
17.20
61
--
10.20
86
5.68
19454
-
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_
59
I
rn
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Dana stno. 41: IYGPT-trawling, Cod length frequencies
t:;1l
W,
E
i
0
(")
co
I 1 I I 1 1 I I I I I I I I I I I I I I I I I I I
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"umbers
Herring length frequencies
I ~ LI'~"I"I-+-I
~
M
~
~
~
-+I~ " I- I" 'I
-+1-+-1
~ ~
....1-+-1-+1-+-1+1-1......1-11.....
1-11.....
1-+1-+-1-+1-+-1+1-1......1-11-+-1-11.....
1....1-+-1-+1-+-1+1-1......1-lIHI
~ ~ ~ ~
~ ~ ~ ~ ~ ~ ~
~ ~ ~
~
re
:
length croup cm
•
Sprat length frequencies
I~D
o
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J
o
I
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r
I
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....
J
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1 I
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,",,,,,,,,,,,,,,,,I
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length group cm
Dana stno. 41: IYGPT-trawling, Cod length convertet to TS values
i~ ~:: I~"-L+I-+I
0
I
I·
-+1-+1·-4-1-+-1I"'+-'IUyl>---II-....I -....I --+I--+I-+I-+I-+I-+I-+I-+1-+1-+1-+1-
~
~
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~
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~
~
~
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~
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q q
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ts values In dB ca/55
Herring length converted to TS values
III
~l!!
. : :1------=-1----1
~400
~ U20Q
~
0
~
-+1-+1-+1-+1-+-1-"'.-'1 yIJ·
.....I _-+I_+I_+I_+I_+-1-+-1-+-1-+-1-I>---ll>---II--II-....I --+I-+I-
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ .... ~ ~ ~ ~ ~ ~ ~
TS values dB class
Sprat length converted to TS values
lEI
E
0 ~
i
I
J
1-'
1
I
YI_....I --+I-+I-+I-+-I-+-I-I>---;I>--....I --+I-+I-+1-+-1-+-1-..--+-1-'.--
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~
q
~ ~ ~ ~ ~ ~ ~ ~ ~
TS values dB calss
Figure 2. Length frequencies of major species in catch and converted length distribution in catch
to species specific distribution of TS-values.
numbers In dB
class
0
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Dana stna. 43: IYGPT-trawling, cad length frequencies
j
'll1lliy,
lliJuIY'.
..,i.........4-I...,IH-'I.....'..·,H';,,,,,--;1,14-,-;,"'''''-+1_,.....1
~ ~ ;
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1....,&1,..,11+,...,,>-+,-+1-,,,,',;-;-;1>-+1-+,...,,"'.....
,'..,.,..,.',
~
~
~
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N
~ ~ ~ ~
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M
~
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I
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j ::1
o -r
I I ,
...
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J
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I
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I I
::
,' ,,'JJfuiliJ.,. .
I
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I
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~
~
~
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N
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~
~
~
~
~
~
~
~
;
~
~
~
~
lenglh group cm
•
I
Sprat length frequencies
j
=!
o .
r I
.., '"
J
, h4-'-;I-+-'+1-+1-+-1+1-+,-+-,+'....,-+-,+'-+'--+-I+'....
,--+-,+'....,-+-,+I....,--+-'+'....'--+-I+'....'--+-I+1....1--+-1+1....1-+-1
N
M
M
;
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,-11
+i....,--+-,+1....
...
0>
~
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~
~
~
~
~
~
~
~
~
~
~
~
~
~
length group cm
Dana stna. 43: IYGPT trawling, cad length converted to TS va lues
TS values In dB class
Herring length converted to TS values
wlJ
i~$:l_-+--+-~-+--+--+-"'_-.- L·
0
e
u
10
-
I,
I
I
I-
I
........
I
.herring
I
I
-+1-+1-1-1_'-+--11---+-_'-11---
TS values In dB class
Sprat length converted to TS va lues
TS values In dB class
Figure 4. length frequencies of major species in catch and converted length distribution in catch
to species specific distribution of TS values.
I
Dana stno. 41: Frequencies of observed single target values,
water depth layer 3-23 m.
j ,;
~
j
0.5
o
J
I
j
I
I
I
I
1[JJ.,,,,DJ, ,,,,Lll,,,,I
~
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~
~
~
~
~
~
~
~
~
dB cla55
Water depth layer 23 to 29 m.
•
dB CI>55
Water depth layer 29 m to 1 m above the bottom (35 ·40 m)
3blLlJlU
2.5
2
,
'.5
0.5
o
.
~
~
I
l?
~
~
~
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I
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UUlkUILlJJ",J
~
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q ~
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dB class
Water depth layer 3 m to 1 m above bottom (35 ·40 m)
~l.'I'I,I,I,~'I,I"'I'I,.,ILI"'I'I'I,',I,.,
,
~
~
~
~
~
~
~
~
~
~
~
~
~
~
~
~
~
~
~
",,1
~
dB class
Dana 5tno. 43: Frequency of observed single target value in dB,
waterdepth 3 m to 1 m above bottom (10 ·16 m)
70
60
~
.x
~
50
40
30
20
10
0
.
"?
N
"?
~
:l!
:l!
.
"I
dB class
Figure S. Observed single target values (38 kHz split beam) from RN DANA survey in Bornholm Basin
and adjoining walers, Seplember/oclober 1994.
.......-
_.
-~
_._._-
.
TEMP.oC:
I
o
15
SALINITY o/c,o:
OXYGEN %:
10
5
-1.
I
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:
10
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TEl\IP.oC:
o
=
=
3 ..
T/5:
ST.NR:
41
DATO:
941885
G8811
TIn:
54388N
BRD:
LGD:
B14327E
32.8
CTD.D':t'BDE:
OP5AMLET:
111
.
8.9
I
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L///.W///////////.W/Il
.1
~LJ//J~;L/.L/. w////////////////////////////////////////////n
MIDLIHC'
•
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SALINITY .%0:
5
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11 L'I
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11 lli
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ST.NR:
43
DATO:
941885 .
TID:
G183B
BRD:
54312N
LGD:
B14173E
CTD.D':t'DDE:
1616
OP5AMLET:
.137
11
1
BUHD-DYBDE'
17.1 M
T/5:
Figure 6. erD profiles of temperature, salinity, oxygen and ßuou..escence from RN DANA survey 10,
September/October 1994 on stno.: 41 arid 43.
5."
'.1
A)
: I
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.
':
I' ~~";t~"~~*~'·~~·~'tGI~.j'~t
r..
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h'~'"~I,~'~j::i:j4::1~
,
"
"':I'o~.oJii""····'
"
B)
I' "10"'"•
Echograms from SIMRAD 38 kHz split beam echosounder from GOV and
IYGPT trawl stations 41 and 43. A) St. 41, GOY trawling; B) St. 41,
IYGPT trawling; C) St. 43, GOY trawling; D) St. 43, IYGPT trawling.
~
..
C)
?~_._~----
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Figure 7.
..
(Continued).
f'"
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