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Annexes


Annex I. Participating scientific staff
Annex II. Records of fishing operations
Annex III. Results from length measurements
Annex IV. List of species
Annex V. Equipment and methods

Annex I. Participating scientific staff

From the Institute of Marine Research, Bergen:

Mr. T. Strømme (cruise leader)
Mr. H. Gjøsæter (biologist)
Mr. K. Strømsnes (research technichian)
Mr. H.P. Knutsen (instrument chief)
Mr. B. Kvinge (instrument technichian)
From CECAF, Dakar:
Mr. G. Everett (CECAF project leader), Nov 3-8
From the Republic of Cape Verde:
Miss V. Marques da Silva (biologist) Nov 5-6, Nov 16-27
Mrs. M.H. Vieira (biologist) Nov 28-Dec 1
From FAO/UNDP Cape Verde:
Mr. G. Beven (fishing master) Nov 5-6, Nov 16-Dec 1

Annex II. Records of fishing operations

Annex II. Records of fishing operations

Annex II. Records of fishing operations (cont. 1)

Annex III. Results from length measurements

FAMILY/SPECIES

STATION

LENGTHS IN SAMPLE



LOWEST

HIGHEST

MEAN ST.

DEV.

N

CAPROIDAE







Antigonia capros








379

11.0

16.0

14.2

.8

89


383

6.5

15.5

13.3

1.9

48

CARANGIDAE







Caranx crysos








374

41.0

64.0

51.9

6.4

18


375

43.0

63.0

52.7

6.8

8

Decapterus punctatus








355

11.5

21.5

18.2

1.8

147


358

12.5

19.0

14.0

1.0

117


360

9.0

17.0

11.5

1.3

119


369

12.5

19.0

14.3

1.1

115


371

12.0

19.5

15.6

1.5

126


372

17.5

23.5

21.3

1.1

107


377

15.0

22.0

17.4

1.1

134


380

18.0

21.0

19.4

.9

14


381

19.0

24.0

21.1

1.1

98


383

18.5

22.0

20.0

1.9

32


385

8.5

18.0

11.7

2.1

96


386

13.5

21.5

16.2

1.6

159


387

10.0

13.5

11.2

.9

100

Decapterus rhonchus








362

24.0

30.0

26.8

1.2

111


371

12.0

18.0

15.5

1.8

39


385

13.0

24.0

15.6

1.4

99

Decapterus macarellus








350

19.0

32.0

25.2

3.9

100


351

28.5

32.0

29.9

1.0

23


352

21.0

33.5

28.0

2.4

53


357

11.0

22.0

17.4

2.1

97


371

16.5

27.0

18.7

2.0

82


377

17.5

21.5

19.5

1.1

20


380

17.0

28.5

20.1

1.7

150

Selar crumenophthalmus








348

13.5

17.0

15.3

1.0

32


357

13.5

17.5

14.7

.9

32

CLUPEIDAE







Sardinella maderensis















357

12.0

17.0

14.5

1.2

23


371

16.0

25.0

20.2

3.0

11


385

17.5

26.0

22.4

1.7

35

LETRINIDAE







Lethrinus atlanticus








367

35.0

41.0

37.8

2.0

10

LUTJANIDAE







Lutjanidae indet.








378

41.0

48.0

45.3

2.3

8

MULLIDAE







Pseudupeneus prayensis








355

13.5

19.5

16.2

1.3

80


360

12.5

21.5

16.3

1.8

115


369

14.0

22.0

18.0

1.6

104


377

10.0

24.0

17.4

2.4

166


388

16.0

24.5

20.0

2.2

34

POMADASYIDAE







Paraphristipoma sp.








364

31.0

36.0

33.7

2.0

8

Pomadasys incisus








388

20.0

24.5

22.3

1.0

41

SERRANIDAE







Cephalopholis taenopsis








364

39.0

48.0

44.7

3.5

8

SHARKS







Rhizoprionodon acutus








367

81.0

92.0

87.4

3.7

8


368

66.0

85.0

80.0

6.7

7

Mustelus mustelus








363

66.0

97.0

84.7

5.8

35


367

80.0

96.0

86.4

5.6

16

SPARIDAE







Boops boops








369

14.0

16.5

15.3

.7

26


371

13.5

16.0

15.1

.6

26


379

22.5

27.5

25.1

1.2

70

Lithognathus mormyrus








355

21.0

30.0

25.8

2.9

14


388

23.5

29.5

26.5

1.4

55

Pagellus acarne








369

19.0

22.5

21.1

1.4

12


377

19.0

31.0

25.2

1.8

122

Spondyliosoma cantharus








351

36.0

46.0

40.3

5.1

3

Annex IV. List of species

List of species caught with R/V Dr. Fridtjof Nansen off Cape Verde Islands November 1981.

ACANTHURIDAE



Acanthurus monroviae

ANGUILLIFORMES


BALISTIDAE



Balistes capriscus

BELONIDAE



Ablennes hians

BRAMIDAE



Brama brama

CAPROIDAE



Antigonia capros


Capros aper

CARANGIDAE



Caranx crysos


Decapterus punctatus


Decapterus rhonchus


Decapterus macarellus


Selar crumenophthalmus


Seriola carpenteri


Seriola fasciata


Trachinotus ovatus


Trachurus trachurus


Uraspis secunda

CENTRACHANTIDAE



Spicara sp.

CLUPEIDAE



Sardinella maderensis

CONGRIDAE



Rhechias sp.

DACTYLOPTERIDAE



Dactylopterus volitans

FISTULARIIDAE



Fistularia petimba

GEMPYLIDAE



Gempylus serpens


Neolatus tripes


Promenthichthys prometheus

GERREIDAE



Eucinostomus melanopterus

GONOSTOMATIDAE



Vinciguerria sp.

HOLOCENTRIDAE



Adioryx hastatus

LABRIDAE



Bodianus speciosus


Xyrichtys novacula

LETRINIDAE



Lethrinus atlanticus

LUTJANIDAE


MACRORHAMPHOSIDAE



Macrohamphosus scolopax

MONACANTHIDAE



Aluterus sp.


Aluterus punctatus


Stefanolepis hispidus

MULLIDAE



Pseudupeneus prayensis


Lycodontis sp.

MYCTOPHIDAE


NOMEIDAE



Cubiceps sp.


Cubiceps gracilis


Psenes sp.

PARALEPIDIDAE



Lestidium sp.

POLYNEMIDAE



Galeoides decadactylus

POMADASYIDAE



Paraphristipoma sp.


Paraphristipoma octolineatum


Pomadasys incisus


Pomadasys peroteti

PRIACANTHIDAE



Priacanthus arenatus

SALPS


SCARIDAE



Sparisoma rubripinne

SCORPAENIDAE


SERRANIDAE



Cephalopholis taenopsis


Epinephelus guaza


Epinephelus alexandrinus

SHARKS



Rhizoprionodon acutus


Mustelus mustelus

SHRIMPS


SPARIDAE



Boops boops


Dentex sp.


Dentex macrophthalmus


Diplodus sp.


Diplodus bellottii


Diplodus fasciatus


Diplodus prayensis


Lithognathus mormyrus


Pagellus acarne


Pagellus bellottii


Spondyliosoma cantharus


Viridentex acromegalus

CEPHALOPODA


LOLIGINIDAE



Todaropsis sp.

SYNODONTIDAE



Synodus sp.


Synodus saurus


Synodus synodus

TETRAODONTIDAE



Lagocephalus laevigatus

TRACHINIDAE



Trachinus sp.


Trachinus draco

TRIGLIDAE



Chelodonichthys sp.


Chelodonichthys lastoviza

TRICHIURIDAE



Aphanophus sp.

ZEIDAE



Zeus faber

Annex V. Equipment and methods

The R/V DR. FRIDTJOF NANSEN is a 150 foot stern trawler with a main engine of 1500 horsepower. The vessel is equipped for acoustic surveying, bottom and midwater trawling, hydrography and plankton observations.

The bottom trawl was a 134 foot headline shrimp trawl adapted for demersal fish trawling. The foot rope was equipped with 0.5 m rubber bobbins. Bridles of 40 m gave it a horizontal distance between the wings of about 25 m. The effective vertical opening of the net was about 6 m. The pelagic trawl was of about 120 m circumference, and the vertical opening was normally 13 m. The pelagic trawl had an inner-net of mesh size 1 cm in the cod end. Pelagic trawl operations were usually monitored by aid of a 50 kHz acoustic net sonde.

Hydrographic observations were carried out with Nansen bottles with which temperature readings and samples for salinity and oxygen determinations were collected at standard depths. The salinity was determined with an inductive salinometer and dissolved oxygen by the Winkler method.

Two Simrad EK Sounders, 120 kHz and 38 kHz, connected to QM integrators, were run continuously. Settings and performance of the two acoustic systems were:


120 kHz

38 kHz

Basic range

0 - 100 m

0 - 100 m or 0 - 250 m

Transmitter

1/1 (330 W)

Ext. (2500 W)

Transducer (ceramic)

10° (circular)

7.5° × 8°

SL + VR

116.7 dB

139 dB (13.9.81)

Bandwith and pulse length

3 kHz, 0.6 ms

3 kHz, 0.6 ms

TVG and gain

20 logR, -0 dB

20 logR, -20 dB

Recorder gain

4

7

Integrator threshold


0.5

Ingegrator gain


20 dB (×10)

Depth intervals


According to recordings


The 38 kHz system coupled to the integrator was used for abundance estimation of fish, while the 120 kHz system was used as an additional aid during the daily analysis of the echo recordings.

Sampling and processing of catch data

For each trawl catch the weight and number of each species were estimated by sampling. Species determination was mainly based on ANON (1981) and partly on BLANCHE et al. (1970). Length measurements were frequently taken, mainly on the commercially important species. The catches and their main composition are listed in Annex II and main results from the length measurements are given in Annex III.

The echo recordings and their interpretation

Assessment of the abundance of fish resources based on acoustic observations combined with experimental fishing is a method which especially lends itself to fish found in schools or other aggregations in midwater. But there are also notable exceptions, e.g. surface schooling tunas and tuna-like species and strictly bottom dwelling fish such as rays and flounders. Any fish found very close to the bottom (½-1 m) or in the very surface layer will escape echo sounder detection. For navigational reasons the work with the R/V DR. FRIDTJOF NANSEN is limited to waters deeper than 10 m. The extreme inshore waters could thus not be covered.

Because of differences in behaviour and size, different species or groups of fish species may give rise to various types of echo-recordings. Small-sized pelagic fish are, for instance, often found in well-defined schools, the recordings of which can be distinguished from those of the often looser aggregation in which semi-demersal larger fish are often found. Such classification of the echo recordings is of considerable assistance in interpreting the acoustic observations, but a positive identification by fishing operations is still indispensable and also provides the only means of sampling fish in this type of combined survey.

Based on previous experience and on identification by fishing, the echo recordings in the surveyed waters were classified as follows:

(i) Recordings of true larger schools or dense layer mostly in upper water. These will most often derive from pelagic schooling fish usually of smaller size, e.g. clupeids, scads.

(ii) All other fish recordings which especially comprised looser aggregations of smaller and larger fish near bottom. These are ascribed to demersal or semi-demersal fish such as grunts, seabreams, groupers, croakers, bigeyes etc.

(iii) Recordings of mesopelagic fish distributed in scattering layers.

Acoustic abundance estimation

Average integrator deflection per nautical mile was calculated each five nautical mile steamed. All echo traces were evaluated daily and together with the information from the trawl catches the readings from the integrator were split in categories small pelagic fish, demersal fish, mesopelagic fish and plankton. The integrator deflection was classified in two levels scattered (1-9 mm), and slightly gathered (11-20 mm), and contour lines were drawn to distinguish between areas of different density of fish. This forms the basis for the preparation of the charts of distributions of fish. For each of the areas the mean integrator value and the area of extention were calculated and their product gives an indice of abundance for that area. The conversion factor C from index of abundance to absolute abundance is linearity dependent upon the length of the fish, and we can correct for this by multiplying the index of abundance with a length-correcting factor f, where f = l/17 (l = fish length). After summing up all indices of abundance within a region the length corrected indices are converted into fish biomass by multiplying with the C value for the fish of standard length 17 cm. For the 38 kHz system with standard settings C17 = 13.6 tonnes/nm²/mm/nm.

Calculation of C-value

The relationship between target strength of 1 kg of small pelagic fish with swim bladder and the length of the fish can be written:

TSkg = -10 log 1 - 22 dB
Analytical relation between C value, the acoustic system performance constants and the target strength of 1 kg of fish can be written:
It can be seen from those two formulas that the C value expressed in tonnes/n.mile² mm is straightly related to the fish length in cm
C = a × l
where


A = integrator gain
For the actual performance data of the acoustic system of R/V DR. FRIDTJOF NANSEN:
C1 = -26.5 dB
A = 30 dB

C = 0.8 × L T/n.mile²/mm/nm (L in cm)


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