Mesopelagic fish, a large potential resource in the Arabian Sea

I019

MESOPELAGIC

FISH, A L A R G E P O T E N T I A L IN TIIE A R A B I A N SEA

Jakob University

of Bergen)

Department

of

HESOUI¢CE

Gj~saetei"

Fisheries

Biology,

Nordnesparken

2a)

N-5000

Bergen

ABSTRACT The m e s o p e l a g i c fish fauna in the A r a b i a n Sea was studied on cruises with R/V 'DR. F R I D T J O F NANSEN' c o n d u c t e d during the p e r i o d 1975-198]. A b u n d a n c e s were e s t i m a t e d using 38kHz echosounders and e l e c t r o n i c integrators. T h e e c h o r e c o r d i n g s were also used to study behaviour. S a m p l e s of the fish were c o l l e c t e d u s i n g c o m m e r c i a l sized pelagic trawls. D u r i n g daytime the m e s o p e l a g i c f i s h w e r e found in a layer between 2 5 0 - 3 5 0 m depth. In areas w i t h high c o n c e n t r a t i o n s of B e n t h o s e m a p t e r o t u m an a d d i t i o n a l very dense layer was u s u a l l y b o u n d at depths b e t w e e n 150-200m. D u r i n g n l g h t - t i m e , m o s t of the fish are found in the upper 100m) but usually some r e m a i n at d e e p w a t e r s (200-350m). The total a b u n d a n c e of m e s o p e l a g i c f i s h to be about i00.i0 6 tonnes. In the G u l f b i o m a s s ranged between 6 - 2 0 . 1 0 6 t o n n e s .

in the N o r t h e r n and Western A r a b i a n Sea is e s t i m a t e d of O m a n w h i c h was surveyed eight times, the e s t i m a t e d

U s i n g a trawl with an o p e n i n g of about 7 5 0 m 2 the m e a n catch rate in the s h a l l o w e s t d a y t i m e layer was about 5 t o n n e s . h -I . T h e h i g h e s t catch rate o b t a i n e d was about i00 t o n n e s . h -I The catch rates from the d e e p e r l a y e r s w e r e low. The most a b u n d a n t fish, about 6 months. At this

B. p t e r o t u m , has a fast g r o w t h rate and r e a c h e s stage t h e y s p a w n and m o s t f i s h p r o b a b l y die after

a length of spawning.

4cm

in

INTRODUCTION The A r a b i a n Sea is a h i g h l y p r o d u c t i v e area. However, only a minor part of the p r i m a r y prod u c t i o n goes to the fish s t o c k s c o n v e n t i o n a l l y harvested, w h e r e a s a larger part is c h a n n e l e d into the stocks of m e s o p e l a g i c fish, w h i c h c o n s i s t p r i m a r i l y of l a n t e r n f i s h e s ( M y c t o p h i d a e ) . The importance of l a n t e r n f i s h e s in this a r e a was i n d i c a t e d by studies on eggs and larvae c o l l e c t e d d u r i n g the I n t e r n a t i o n a l I n d i a n O c e a n E x p e d i t i o n 1 9 5 9 - 1 9 6 5 (Ahlstrom, 1968; Nellen, 1983) and later c o n f i r m e d by a c c o u s t i c a l m e t h o d s and t r a w l i n g by R/V 'DR. F R I D T J O F NANSEN' d u r i n g 1975-1976 (GJ~saeter, 1981b). S e v e r a l c r u i s e s w i t h R/V 'DR. F R I D T J O F NANSEN' have been c o n d u c t e d r e c e n t l y to p r o d u c e n e w e s t i m a t e s of the a b u n d a n c e of m e s o p e l a g i c flshes, to collect d a t a for f u r t h e r s t u d i e s on the e c o l o g y and llfe history of the species concerned, and to carry out e x p e r i m e n t a l f i s h i n g (Aglen, G j 6 s a e t e r , M y r s e t h and T i l s e t h 1982; G j ~ s a e t e r and Tilseth, 1983). The G u l f of O m a n is c o n s i d e r e d to be the area w i t h the g r e a t e s t potential for c o m m e r c i a l e x p l o i t a t i o n ( G j ~ s a e t e r , 1981c). As the bulk of the catches are c o m p o s e d of only a single species, this is a l s o the e a s i e s t a r e a to assess reliably. The aim of the present paper is to r e v i e w and a n a l y s e ment of l a n t e r n f i s h e s as a f i s h e r i e s r e s o u r c e .

some of the data r e l e v a n t

to the a s s e s s -

1020

J. Gj~saeter

MATERIAL

AND METHODS

All m a t e r i a l was c o l l e c t e d by the R/V 'DR. FRIDTJOF NANSEN', a 150 foot stern trawler with a 1500 hp m a i n e n g i n e (see Anon, 1978). The N o r t h w e s t A r a b i a n Sea was i n v e s t i g a t e d five times d u r i n g 1975-1976. The G u l f of Oman and the Gulf of Aden were covered again in 1979 and 1981 and the G u l f of Oman a l s o in 1983 (Fig.l). Information on cruise tracks and trawl s t a t i o n s are given by Kesteven, Nakken and Str~mme (]98]), Aglen e t a l . (1982} and G j ~ s a e t e r and T i l s e t h (1983).

~ C I

i Fig.l.

The a r e a i n v e s t i g a t e d i n d i c a t e the s u b a m e a s

[

6'o"

7o"

in the N o r t h - W e s t A r a b i a n r e f e r r e d to in the text.

Sea.

The letters

F i s h i n g was c a r r i e d out m a i n l y u s i n g a commercial pelagic trawl w i t h an e s t i m a t e d m o u t h area of 250m 2 . T h e m e s h size in the fox~waa'd part of the trawl was about 200mm (stretched) and d e c r e a s e d to 9mm in the cod end. In 1987 the t r a w l was e x t e n d e d by adding two new f r o n t p a r t s w i t h 800n~m and 1 6 0 0 m m m e s h to give m o u t h o p e n i n g s of about 500 and 800m 2 (Scharfe, 1983). The t r a w l i n g speed was u s u a l l y b e t w e e n 2 and 3 knots ( l - l . 5 m . ~ 1 ). On all c r u i s e s the m y c t o p h l d s w e r e sorted out and their volume was e i t h e r m e a s u r e d or estimated. I d e n t i f i c a t i o n and b i o l o g i c a l s t u d i e s of r a n d o m s u b - s a m p l e s w e r e c a r r i e d out onboard immedlarely after capture, and replicate s u b - s a m p l e s w e r e p r e s e r v e d in f o r m a l i n for further analysis in the l a b o r a t o r y . S t a n d a r d l e n g t h was m e a s u r e d to the n e a r e s t m i l l l m e t r e . Sex, stage of m a t u r i t y and s t o m a c h c o n t e n t s w e r e a l s o s t u d i e d in some samples. Samples for otolith studies w e r e p r e s e r v e d in 70~ alcohol. O t o l i t h s were A~cound down to thin s e c t i o n s to count p r i m a r y g r o w t h rings. The a c o u s t i c a l equipment o n b o a r d c o n s i s t e d of three sounders (120, 50 and 38kNz) and two echo i n t e g r a t o r s , each w i t h two channels. The ~SkHz sounder, w h i c h was used for integration, was c o u p l e d t o a c e r a m i c t r a n s d u c e r and a 2kw external t r a n s m i t t e r was applied. A 12OkHz echo s o u n d e r was u s e d to a c h i e v e better r e s o l u t i o n in the u p p e r 100m. The vessel was also e q u i p p e d w i t h a 24kHz sonar and a net sonde (5OkHz). In a d d i t i o n to the h u l l - m o u n t e d transducers, a towed body f i t t e d w i t h two t r a n s d u c e r s was used. D e t a i l s about the a c o u s t i c a l equipment, the s e t t i n g s used and the m e t h o d s a p p l i e d are given by Aglen e t a l . , (1982), and G j M s a e t e r (1981b). During d a y t i m e the e c h o r e c o r d i n g s were divided into three zones: l) upper iO0m; 2) Upper m e s o p e l a g i c - DI usually IO0-200m, most common and 3) D e e p m e s o p e l a g i c - DII - u s u a l l y below 200m.

Epipelagic -- usua]]~ in the Gulf of ()man.

Mesopelagic

At n i g h t , two zones could and 2) Deep m e s o p e l a g i c g i v e n in Fig.2.

be recoKnised: NII below

2 ,

•

~, ,

,

8

6 J

Fish

in the A r a b i a n Sea

102]

1) U p p e r m i x e d l a y e r - NI, epipelagic - u p p e r lOOm; 20Ore. h s c h e m a t i c p r e s e n t a t i o n of these layers is

TIME 10

12

Iz.

15

18

20

,

50

:... --.'. .:.:...I

tO0

x

...

ISO

. . . .

.

$ : :

•,:

:. - - . . . . : :~,. ~'..:

•

.

°

..-:~

200

•

v

250

300

Fig.2.

S c h e m a t i c d r a w i n g of the SSLs in an area w h e r e B. p t e r o t u m dominates. 1 s c a t t e r e d , 2 d e n s e and 3 very dense r e c o r d i n g s .

In c o a s t a l w a t e r s small p e l a g i c fish, large p e l a g i c fish and d e m e r s a l fish were also o b s e r v e d , but u s u a l l y c o u l d be e a s i l y s e g r e g a t e d from the m e s o p e l a g i c fish. To e s t i m a t e the amount of m e s o p e l a g i c fish in the u p p e r m i x e d layer, the r e c o r d i n g s of p l a n k t o n d u r i n g d a y t i m e in the same or in a n e a r b y a r e a w e r e s u b t r a c t e d f r o m the total r e c o r d i n g s in this layer. To e s t i m a t e the abundance of mesopelagic fish, the mean echo integrator reading for each of the areas shown in Figure 1 was calculated, and a mean length of the fish caught was calculated. These lengths could then he approximately weighted by t h e n u m e r i c a l abundance in the layers concerned. The

integrated echo B

=

was c o n v e r t e d to e s t i m a t e s

f MC A

of fish h i o m a s s u s i n g the

formula:

~CA

w h e r e B is b i o m a s s of the s c a t t e r i n g o r g a n i s m s , M is i n t e g r a t e d echo i n t e n s i t y (mm per nautical m i l e ) , A is the c o r r e s p o n d i n g area. The c o n v e r s i o n f a c t o r is s e a l e d a c c o r d i n g to the m e a n l e n g t h of the fish: C

=

C'L

w h e r e L is fish l e n g t h and C' is c o n s t a n t d e p e n d i n g on the p e r f o r m a n c e of the a c o u s t i c a l e q u i p m e n t a n d of the f i s h s p e c i e s c o n c e r n e d . As no r e l i a b l e e s t i m a t e s of the a p p r o p r i a t e c o n v e r s i o n f a c t o r for l a n t e r n f i s h is known, a C' e s t i m a t e d for other small p e l a g i c fishes, c o r r e s p o n d i n g to a t a r g e t s t r e n g t h of - i0 log L = 22 dB ref. 1 kg.m -2 was used. In the deep layers (DII and Nil) fishes without a swim-bladder (e.g. Chauliodus sp.) were sometimes numerous. T h e s e g i v e a m u c h w e a k e r echo than a fish with s w i m b l a d d e r , but this was not c o m p e n s a t e d for; the b i o m a s s in these layers may be u n d e r e s t i m a t e d in some areas.

1022

J.

GjMsaeter

RESULTS Species

distribution

and b e h a v i o u r

L a n t e r n f i s h were found throughout the area studied w h e r e v e r the d e p t h was greater' than about 150m, and they were always the most abundant fish group in the Sound S c a t t e r i n g Layers (SSL). In the G u l f of O m a n and off Pakistan the dominant species was always B e n t h o s e m a pterotum. In the Gulf of Aden the a b u n d a n c e of B. pterotum was o c c a s i o n a l l y s u r p a s s e d b y B. fibulatum, S y m b o l o p h o r u s e v e r m a n n i , M y c t o p h u m s p ! n o s u m or Diaphus spp. O f f the s o u t h e a s t coast of 0man and off the e a s t e r n coast of S o m a l i a conditions were variable, but u s u a l l y either B. f i b u l a t u m or D i a p h u s spp. w e r e the d o m i n a n t species. In areas w h e r e B. p t ¢ r o t u m was abundant the SSL showed a p a t t e r n that was clearly d i s t ~ n g u i s h able from that found in other areas. The following d e s c r i p t i o n is based on o b s e r v a t i o n s in the G u l f of Oman, but it a l s o applies to other areas w h e r e B. p t e r o t u m dominated. During daytime usually two SSLs and a weak plankton layer in the s u r f a c e were usually observed. The upper SSL (DI) u s u a l l y o c c u r r e d at 150-200m depth o v e r a v e r t i c a l extent of 20-~Om (Table I, Fig.2), and it c o n s i s t e d both of small schools and of dense c o n c e n t r a t l o n s . In d e e p e r water, u s u a l l y c e n t e r e d at about 250m depth, a n o t h e r SSL (DII) appeared. This u s u a l l y had a v e r t i c a l e x t e n t of 70-100m, but a l t h o u g h it s o m e t i m e s g a v e very h i g h echo recordings, it had a more d i f f u s e a p p e a r a n c e on the e c h o g r a m s than DI.

TABLE

1

T y p i c a l depth d i s t r i b u t i o n of the sand s c a t t e r i n g by mesopelagic flsh in the Gulf of Oman.

layers

Depth m

Layer

caused

Vertical extent m

D I

150

D II

250

(140-200)

80

20

N I

20

70

NII

220

70

A b o u t one h o u r b e f o r e sunset the D I layer started to a s c e n d slowly. About half an hour b e f o r e sunset D I u s u a l l y r e a c h e d about 100m, at w h i c h t i m e b o t h this layer and parts of DII m o v e d r a p i d l y towards the surface and fused w i t h the e p i p e l a g l c layer, if present. The h i g h e s t speed of u p w a r d m i g r a t i o n was usually r e c o r d e d f r o m about i00 up to 10m, where an a v e r a g e of 1.7 m . m i n -I ( c o r r e s p o n d i n g to % 0 . 8 fish l e n g t h s . s -1 ) was often o b s e r v e d (T~ble 2). Parts of the D II r e m a i n e d in deeper waters during n i g h t time and became the N II layer. The night layers were usually m o r e diffuse than the d a y t i m e layers, and f r e q u e n t l y s c a t t e r e d echos o c c u r r e d over a wide depth range. The descent was u s u a l l y f a s t e r than the upward m i g ration, r e a c h i n g speeds of 3 m . m i n -l ( % 1 . 4 fish l e n g t h s . s -I) f r o m I0 to IOOm depth. The NI layer u s u a l l y c o n c e n t r a t e d n e a r the surface at early dawn b e f o r e starting the d o w n w a r d migration. TABLE

2

Migration

speed

Depth

Downward

Upward

Range

of DI layer during

the diel

vertical

migration

m

No. of observations

Speed m . m i n -I mean range

10 - i 0 0

i0

3.0

0.9

- 4.o

I00

-

]50

2

i.I

0.5

-

1.7

t50

-

200

2

1.9

1.3

-

2.'~

100

-

10

a

1.7

1.3

~

1.~{

I

0.8

150 - 10o

cycle

Mesopelagic

Fish

in

Arabian

the

1023

Sea

S o m e t i m e s the D[ layer or parts of it d e s c e n d e d and mixed with the DII layer some hours after s u n r i s e only to r e a p p e a r in the afternoon. On other occasions all the fish a p p e a r e d to be in the DI layer and no DII layer was ebserved. C a t c h e s from the DI layer usually c o n s i s t e d exclusively of t~. pterotum , a l t h o u K h sometimes s a l p s or j e l l y f i s h were included. In o t h e r layers although B. p t c r o t u m usu;{]ly dominated, o t h e r fishes, shrimps, e u p h a u s i i d s , squids, .~;a]ps and jellyfish were often present (Table 3). In 198] and 1983 sa]ps and j e l l y f i s h made up a significant portion of the catches, hut probably c o n t r i b u t e d little to the sound reflection from the SSLs (Aglen et al. 1982). In areas w h e r e B_. p t e r o t u m was absent tile DI layer was also absent.

TABLE

3

Layer Year B.

pterotum

C o m p o s i t i o n (percentage sound s c a t t e r i n g layers than 1% in weight).

1979

D I 1981

1983

1979

D II 1981

1983

1979

N I 1981

1983

1979

NII 1981

1983

99

96

iOO

73

45

81

95

47

83

45

55

21

+

+

4

4

3

9

3

+

8

37

75

1

1

1

Harpadontidae Cubiceps Other

6

sp

fish

+

1 1

+

+

+

+

Shrimps/krill Salps/jellyfish

4 +

Squid

of weight) of trawl catches in each of the in the Gulf of Oman (+ present, but less

+

1

2

6

6

11

1

1

9

21

1

+

+

4

25

7

2

48

2

1

1

1

2

33

1

16

The s p e c i e s c o m p o s i t i o n o b s e r v e d d u r i n g the cruises fits well w i t h previous o b s e r v a t i o n s (e.g. N a f p a k t i t i s and N a f p a k t i t i s 1969, Kotthaus 1972, Nafpaktitis 1978). The depth d i s t r i b u t i o n is, however, very d i f f e r e n t from that o b s e r v e d in most other areas. Several authors h a v e p o i n t e d out the r e l a t i o n s h i p b e t w e e n organic production and the depth of the SSL (e.g. K a m p a 1971, D i c k s o n 1972), and p r o b a b l y the very high production in the N o r t h - e a s t A r a b i a n S e a (Wooster, S c h a e f e r a n d Robinson, 1967) is the m a i n reason for the s h a l l o w d i s t r i b u t i o n of the $SLs. The h y d r o g r a p h l c a l s i t u a t i o n as d e s c r i b e d by Sandven (1979) does not seem to o f f e r any e x p l a n a t i o n to the depth d i s t r i b u t i o n . Previous observations on d e p t h d i s t r i b u t i o n of B e n t h o s e m a p t e r o t u m are few. K u b o t a (1982) f o u n d it b e l o w 400m by day off Japan, and Kinzer (1977) r e c o r d e d it at 300-500m in the A r a b i a n Sea. O f f Central A m e r i c a A l v e r s o n (1961) o b s e r v e d schools of the closely r e l a t e d B. p a n a m e n s e n e a r the surface in d a y t i m e , but a similar o b s e r v a t i o n has not been made in other areas. B. p t e r o t u m was o b s e r v e d d u r i n g this study to form two layers by day w i t h d i f f e r e n t s t r u c t u r e s a d e e p e r layer w h i c h h a d the d i f f u s e s t r u c t u r e commonly seen in SSLs, and an upper one with a s t r u c t u r e r e m i n i s c e n t of the layer of C e r a t o s c o p e l u s m a d e r e n s i s o b s e r v e d by Backus, C r a d d o c k H a e d r l c h , Shores, Teal, WinE, M e a d and Clarke, (1968) in w e s t e r n North Atlantic.

REACTION

TO L I G H T

Several experiments were conducted to study the reaction of B. p t e r o t u m to light usually u s l n g three .1000W h l g h - p r e s s u r e s o d i u m lamps as a light source. These showed that the fish w e r e r e p e l l e d by the light (Fig.3) and they subsequently c o n c e n t r a t e d deeper down. To get a quantitative idea of this c o n c e n t r a t i o n , echo integration was c a r r i e d out at a s t a t i o n in the G u l f of O m a n in F e b r u a r y 1983. A l t h o u g h the ship was stationary, a s i m u l a t e d speed of I0 knots was used for the i n t e g r a t i o n (see Table 4).

1024

J.

Gj~saeter

"'

i

''

r~ UJ

10@

Fig.3.

!

Echo recordings s h o w i n g the r e a c t i o n of B. is t u r n e d on ( u p p e r ) a n d w h e n it is t u r n e d was l y i n g s t i l l d u r i n g the o b s e r v a t i o n s .

pterotum when off (lower).

the The

light ship

Mesopelagic

TABLE

4

Fish

in the Arabian

Sea

1025

Results of integration (mm deflection) at a s i m i l a t e d speed of I0 knots* at a light s t a t i o n in the G u l f of Oman, February 1983

Time

Note

1900

Boat

Integrator N I

deflection N II

stopped

1920

16

17

2045

71

43

2325

461

31

41

32

46

37

1930

Lights

2330

Lights

on

off

2335 2400

Boat

* 1 knot

at normal

speed

" 0.5m.s -I

The increase in echo a b u n d a n c e may p a r t i a l l y have r e s u l t e d from c o n c e n t r a t i o n of fish which h a d been too d i s p e r s e d for i n t e g r a t i o n before the light was turned on. It could also have r e s u l t e d from fish p r e v i o u s l y in the "blind zone" near the surface d e s c e n d i n g to depths where they could be detected. However, several e x p e r i m e n t s gave similar results. This effect was a l s o used to c o n c e n t r a t e fish during trawling. All a v a i l a b l e deck lights w e r e turned on, and a 1 0 0 0 W lamp was placed on each side of the w h e e l h o u s e and a third one was hung aft of the ship. T h e s e lights d e p r e s s e d the fish to 30m b e n e a t h the echo transducer, and a c c o r d i n g to the trawl sonde, the fish were tightly c o n c e n t r a t e d at 50m when the trawl r e a c h e d them at a speed of 2 knots. M o o n l i g h t gave r e s u l t s s i m i l a r to those o b t a i n e d by using lights above the water. At new m o o n the fish are found close to the surface, w h e r e a s at full moon they are deeper. Use of the towed t r a n s d u c e r l o o k i n g u p w a r d i n d i c a t e d that some fish were above the w o r k i n g level of the b o t t o m - m o u n t e d t r a n s d u c e r d u r i n g n e w moon, but not during full moon. Several studies have i n d i c a t e d that m o s t m e s o p e l a g i c fishes are r e p e l l e d by a r t i f i c i a l light (e.g. Blaxter and Cuttle, 1967). There are, however, also o b s e r v a t i o n s w h i c h indicate that some species are a t t r a c t e d by lights (e.g. N a k a m u r a 1970, Parin 1963). B. p t e r o t u m which was the d o m i n a n t species in this study is among those r e p e l l e d by light.

ABUNDANCE

ESTIMATION

The total a b u n d a n c e of m e s o p e l a g i c fish e s t i m a t e d on 5 cruises c o n d u c t e d d u r i n g 1975-1976 r a n g e d from about 6 0 - 1 5 0 . 1 0 6 tonnes (Table 5). Some areas w e r e r e - s u r v e y e d d u r i n g 19771983 and the r e s u l t s w e r e g e n e r a l l y of the same size order as the p r e v i o u s c r u i s e s (Table 5). The surveys w e r e taken o v e r a long time period, so it is d i f f i c u l t to isolate seasonal variation from other s o u r c e s of variation. It seems, however, that there is a h i g h e r biomass during w i n t e r and spring than d u r i n g summer and autumn. This p r o b a b l y is l i n k e d w i t h cycles in r e p r o d u c t i o n , w h i c h c o u l d he r e l a t e d to the m o n s o o n a l cycles. A l t h o u g h stock size is n o t e w o r t h y from a f i s h e r i e s point of view, stock d e n s i t y is m o r e important. Similarly, d e n s i t y in local areas may be more important than a v e r a g e density. Among the r e g i o n s s t u d i e d in 1975-1983, the m e a n density, m e a s u r e d in g . m -2 , was u s u a l l y highest in the Gulf of Omen, in the Gulf of A d e n and off Pakistan (Table 6). The highest average density, 220 g . m -2 was r e c o r d e d d u r i n g spring 1975 in the Gulf of O m a n w h e r e five out of eight cruises i n d i c a t e d d e n s i t i e s above l O O g . m -2 . For the Gulf of Aden 2 out of 7 cruises gave d e n s i t i e s h i g h e r than I00 g.m -2, w h e r e a s off the coast of P a k i s t a n only one of 6 cruises gave higher values than lO0g.m -2 .

1026

J.

TABLE 5

Gj~saeter

E s t i m a t e d abundance of m e s o v e l a g i e fish in the A r a b i a n Sea (106 tonnes). The areas r e f e r r e d to ace shown in Figure I.

Area

SIrlr~ 1975

Gulf of Oman

20

Auttmm Sp~ing 1975 1976 8

Strainer 1976

13

1]

Auttmm S~ming 1976 1977 15

Summer Winter 1979 1981 8

ii

Coast of P a k i s t a n

8

6

7

7

5

Arabian Peninsula, north

23

19

23

17

20

Arabian Peninsula, south

15

17

15

6

ii

Gulf of Aden, inner

12

22

5

2

3

3

9

Gulf of Aden, outer

28

16

II

4

4

2

8

~

Socotra area

26

20

6

20

Somalia, N o r t h

i0

5

5

1

3

Somalia, S o u t h

6

3

3

2

3

148

107

113

56

84

Total

TABLE 6

Winter 1983 f

I0

-

-

M e a n d e n s i t y of m e s o p e l a g l s fish in v a r i o u s parts of the Arabian Sea (g.m-2). The areas r e f e r r e d to are shown in Figure 1.

Area

Siring 1975

Gulf of Oman

Autumn 1975

S ~ 1976

220

88

143

~ 1976

Autumn 1976

121

165

S~ir~ 1977

Summer 1979

Winter 1981

87

120

Coast of P a k i s t a n

84

63

74

74

53

Arabian Peninsula, north

71

58

71

52

61

Arabian Peninsula, south

40

45

40

16

29

Gulf of Aden, "inner

120

120

50

20

30

25

90

Gulf of Aden, outer

187

107

73

27

27

I/

53

Socotra a r e a

85

~

19

65

Somalia,

North

79

47

39

8

24

Somalia,

South

60

~

~

20

30

I~

Wlnt~1983 77

103

In an analysis of the r e l a t i o n s h i p between m e a o p e l a g i c fish density and the distance from the shore (Gj~saeter 1981b) revealed no conslatant correlation. However, very high densities were sometimes o b s e r v e d along the shelfbreak, in a band e x t e n d i n g only a few kilometres offshore (Fig.4). In such areas the biomass could exceed 2000g.m -2.

Mesopelagic

Fish

in

the

Arabian

Sea

102"/

u~ ¢w tu uJ

Fig. 4.

Echo r e c o r d i n g s to the shelf.

showing

dense

concentrations

of B. p t e r o t u m

close

The d i s t r i b u t i o n of biomass in the d i f f e r e n t SSLs in the G u l f of Oman 1 9 8 1 - 1 9 8 3 is i l l u s t r a t e d in Fig.5. During d a y t i m e the m a j o r i t y of the b i o m a s s was usually found in DII, while at night the NI layer was m o s t dense. Figure 5 also i n d i c a t e s that the day r e c o r d i n g s were consistently h i g h e r than the night r e c o r d i n g s . However, during the surveys in 1975-1976, no such d a y / n i g h t d i f f e r e n c e s were found, w h e r e a s off P a k i s t a n in 1977 night r e c o r d i n g s were c o n s i s t e n t l y h i g h e r (Gjgsaeter and Tilseth, 1983).

East of SS"E

Oll 300

Nl I

Hll lO&

I0@

~0G

West ef 56"E

!-,:! 30@ X

100"

2~ - 2 8 JAN

28-31 JAN 1961

Fig.5.

g -I~ F E8

13- I~ FEB

I - 4 MARCH 19~3

Echo abundance of B. pterotum ( i n mm i n t e g r a t o r deflection) showing the relative importance of the 4 types of scattering layers. Recordings from the inner (W o f 5 8 " E ) a n d t h e o u t e r (E of 58"E) part of Gulf of Oman.

1028

GjMsaeter

J.

The highest d e n s i t y p e r m 3 was u s u a l l y found in the DI layers, because the g r e a t e r biomass o c c u r r i n g in the DII layer was m o r e v e r t i c a l l y spread. The average d e n s i t y of the DI layer in the G u l f of O m a n in 1981 and In 1983 ranged from 0 . 5 - 3 . S g . m -3 (see Fig.6). Locally, however, the values could be very m u c h higher. Out of 23 trawl hauls c o n d u c t e d in the DI layer in 1981, 8 were c a r r i e d out in areas where d e n s i t i e s were > 5g.m -3 and 5 in areas with >i0 g.m -3 In 1983 of the 33 trawl hauls, 11 were at densities > S g . m -3 and one at ~ density >1Og.m -3 Occasionally d e n s i t i e s as high as ]OOg.m -3 were o b s e r v e d locally near the edge of the shelves. Such a d e n s i t y was o b s e r v e d only once in 1983, but more commonly on the previous cruises.

3

ul v, 2,

o cQ

2

3

/.

6

1981

Fig.6

t

2

1983

E s t i m a t e d a b u n d a n c e of B. p t e r o t u m in the DI layer during six detail s u r v e y s in F e b r u a r y 1981 and two in F e b r u a r y 1983. Recordings from the s o u t h - w e s t e r n part of the Gulf of Oman.

The d e n s i t i e s of m e s o p e l a g i c fish o b s e r v e d i n ' t h e A r a b i a n Sea are h i g h e r than any o b s e r v e d anywhere else ( G J M s a e t e r and Kawaguchi, 1980). The h i g h primary p r o d u c t i o n in the area, coupled w i t h the r a t h e r low p r o d u c t i o n of other fish species (Kesteven, Nakken and Str~mme 1981), m a k e s this possible. W i t h our present k n o w l e d g e of the physical and biological environment it is not p o s s i b l e to e x p l a i n why such a large part of the total b i o l o g i c a l p r o d u c t i o n is c h a n n e l l e d t h r o u g h the m e s o l ~ l a g l c fishes, but the e x t e n s i v e oxygen m i n i m u m zone in the r e g i o n could well play an i m p o r t a n t role.

FISHING

TRIALS

During 1975 to 1976 to obtain samples. b r o a d e n e d to Include

t r a w l i n g was m a i n l y c a r r i e d Out to In 1979 and 1981 these aims were f i s h i n g trials.

identify the animals in the SSL8 and still important, but the goals Were

In the Gulf of O m a n 53 trawl s a m p l e s were taken from the m e s o p e l a g l c fish layers in 1979, and 75 in 1981. In 1979 t h e m e a n c a t c h rate was 2 0 O k g . h -I , 6~ of the samples gave catch rates > 5 0 0 k g . h -1 , and 2g > l O O O k g . h -1 (Table 7). In 1981 the m e a n catch rate was about 1000 kg.h-l; 44g and 36g of the samples gave catch rates of > 5 0 O k g . h - 1 and 1OOOkg.h -I r e s p e c t i v e l y Seven per cent gave m o r e than 6000 kg.h -1 (Table 7). Most of the very high catch rates were o b t a i n e d from the s h a l l o w day layer (DI), but nearly 20% of the nlght hauls in the surface layer (NI) r e s u l t e d in rates of > 1 O O O k g . h q . During these years most of the t r a w l i n g was c o n d u c t e d using a s m a l l - m e s h e d trawl with a mouth-size of about 250m 2.

Mesopelagic

TABLE

7.

in the A r a b i a n

Sea

1029

F r e q u e n c y d i s t r i b u t i o n of c a t c h r a t e s ( t o n n e s per h o u r ) f i s h i n g t r i a l s in the G u l f of O m a n in 1979 and 1981

Catch

Rate

1979

0 - 0.49

D II

N I

NII

15

II

21

3

- 0.9

I

1.0

-

l

1.9

0 - 0.49

during

D I

0.5

1981

Fish

I

i7

7

0.5

- 0.9

2

3

I

1.0

-

8

1

2.0

- 3.9

8

2

1.9

4

4.0 - 5.9

3

6.0

4

- 7.9

8.0 TOTAL

14

1

47

25

45

ii

In 1 9 8 3 m o r e specific f i s h i n g t r i a l s w e r e p e r f o r m e d by a s p e c i a l i s t in m i d w a t e r trawling ( S c h a r f e 1983) a n d l a r g e r t r a w l s w e r e used. The r e s u l t s , s u m m a r i s e d in T a b l e 8, s h o w t h a t the m e a n c a t c h r a t e for 47 h a u l s , m o s t of t h e m in the DI l a y e r , w a s 4.7 t o n n e s . h -I, a n d m o r e t h a n 80% g a v e c a t c h r a t e s h i g h e r t h a n 1 t o n n e . h -I, These figures are not directly comparable to t h o s e f r o m the p r e v i o u s y e a r s , not o n l y b e c a u s e the t r a w l w a s l a r g e r but a l s o b e c a u s e trawling was more specifically a i m e d at t a k i n g l a r g e c a t c h e s . Indeed, the e c h o - s o u n d i n g r e t u r n s s h o w the f i s h d e n s i t i e s in the DI l a y e r w e r e m u c h l o w e r t h a n d u r i n g the p r e v i o u s years (see F i g . 6 ) . T h e b e s t c a t c h r a t e s w e r e c o n s i s t e n t l y o b t a i n e d f r o m the DI l a y e r , but reasonably ~d c a t c h e s w e r e a l s o o b t a i n e d in NI l a y e r w h e n e v e r l i g h t s w e r e u s e d to c o n c e n t r a t e the f i s h .

TABLE

8.

Catch

F r e q u e n c y d i s t r i b u t i o n of c a t c h r a t e s ( t o n n e s f i s h i n g t r i a l s in the G u l f of O m a n 1983.

Rate

0 -0.9 1 -1.9

D I

4 - 5.9

iI

6 -7.9

1

8 -9.9

2

12

1

18

1

q. I00

Total

Other layers

4 ii

-

during

2

2 - 3.9

I0

N I with light

per h o u r )

1

34

5

8

1030

J. G j ~ o a e t e r

CATCH

RATES IN R E L A T I O N TO D E N S I T Y

E S T I M A T E S O B T A I N E D BY E C H O - I N T E G R A T I O N

D u r i n g t r a w l i n g echo i n t e g r a t i o n was run at a depth c o r r e s p o n d i n g to the vertical height of the trawl. From these values the a v e r a g e fish d e n s i t y (g.m -~) at the trawl opc.ninz was e s t i m a t e d and c o m p a r e d to the catch o b t a i n e d per m 3 sea w a t e r filtered. Data fro:,',, t h e DI layer obtained in 1983 are shown in Pigure 7. Table 9 shows the average "trawl et'fic[c~y" (the r a t i o b e t w e e n catch p e r m3 and o b s e r v e d fish d e n s i t y per m 3 ) for each layer. The a v e r a g e trawl e f f i c i e n c y was s i g n i f i c a n t l y h i g h e r in the DI layer than in ~ny of th{: . , t h e i r layers, but the d i f f e r e n c e s b e t w e e n the other layers (DII, NI and NII) were not SiKn[fi<,nlt There seems to have been no c o n s i s t e n t d i f f e r e n c e in catch e f f i c i e n c y between t h e small trawl used in 1979 and 1981 and the larger trawls u s e d in 1983. The a p p a r e n t l y low trawl e f f ~ c i e h c y in the NI, NII and DII layers give r e a s o n to s u s p e c t that the fish in these layers were mixed with plankton, w h i c h c o n t r i b u t e d s u b s t a n t i a l l y to the high i n t e g r a t o r values observed.

o

•

10

8,

•

O~ '~l~tf~ o

~

o

2 Fig.7.

~o

•

T 6"

4

6

8

10

12 14 16 DENS I I¥-IONNES

20

2;'

2&

26

R e l a t i o n b e t w e e n fish d e n s i t y in the track of the trawl e s t i m a t e d by echo i n t e g r a t i o n , and catch in the trawl.

T A B L E 9 A v e r a g e "trawl e f f i c i e n c y " , catch: e x p r e s s e d as g.m -3 for the v a r i o u s

Kind of layer Year

18

.

e s t i m a t e d d e n s i t y ratio each s o u n d s c a t t e r i n g layers

1979

D I 1981

1983

1979

1981

1979

1981

1979

198]

A v e r a g e trawl efficiency

0,51

o.77

o.57

0.II

0.05

0.07

0.17

0.6!

0.0;

Standard deviation

0.38

0.51

0.34

0.08

0.i0

0.05

0.20

0.6 i

0 . oG

23

33

16

ii

18

17

No. of stations

6

D II

N

NiI

I

9

,7

However, A g l e n et al. (1982) c o n c l u d e d that the echo c o n t r i b u t i o n from p l a n k t o n was small c o m p a r e d to the c o n t r i b u t i o n from fish in all layers. C o n s e q u e n t l y if the p l a n k t o n is ~ot r e s p o n s i b l e for the o b s e r v e d d i f f e r e n c e s in "trawl e f f i c i e n c y " , then there are real d i f f e r ~ ces in c a t c b a b i l i t y of the fish in the d i f f e r e n t layers. The d i f f e r e n c e in c a t c h a b l l t t y may be a r e s u l t of a d i f f e r e n c e in the a m b i e n t light levels in the layers, or possibly in the p h y s i o l o g i c a l state of the fish• In the DI layer where the a m b i e n t daylight will have been b r i g h t e r than in the other layers, it is likely that the fish can see the trawl . b:tt as a dark object. As the fish in this layer form s c h o o l s and dense a g g r e g a t i o n s , it l>J ,~} ~,~ p l a u s i b l e that they react in an o r g a n i s e d m a n n e r to avoid c o n t a c t with the oncomin~,~ wai }~ of the f o r e m o s t part of the trawl • Thus they could be h e r d e d to the centra} part <.~" :~ trawl and f i n a l l y caught by the finer m e s h e s in the cod end. Tile catch e f f i c i e n c y va[{,~:~ o b t a i n e d for the DI layer (0•5-0.3) s u g g e s t a s t r o n g t e n d e n c y to h a r d i n g. The a~:[ ircnt ::~[~i<~ ~

Mesopelagic

Fish

in the A r a b i a n

Sea

I031

trend in the data shown in figure 7 implies that the h e r d i n g may be reduced by the crowding, a s s u m e d to occur at very high densities. Fish in the other layers may not be able to see the trawl. L a n t e r n f i s h are known to have well d e v e l o p e d lateral line organs and ears (Marshall 1979), but these sense organs may give less d i r e c t i o n a l stimuli, and t h e r e f o r e result in a less o r d e r e d reaction, so that a large p r o p o r t i o n of the fish escape through the large m e s h e s in the front part of the trawl. Another alternative is that tbe a b ~ m d a n c c of biol u m i n e s c e n t plankton, such as the o s t r a c o d Cy~)ridina dentata, may light up the net so brightly that the fish responded, as they did to the artificial light above the surface, by swimming down. The a v e r a g e " t r a w l - e f f i c i e n c y " for the DII, NI and NII layers together is 0.13. For the shape and m e s h size of the trawl this seems to be r e a s o n a b l e value for small fishes which are u n a b l e to s u s t a i n rapid swimming, and which probably are rather passive at least during parts of the d i u r n a l cycle (e.g. Barham, 1971).

PRODUCTION Benthosema pterotum Bertalanffy's growth

has been equation

aged

by

counting

primary

growth

rings

in

the

otoliths.

Von

i t = L ~ (I - e -K (t - to) ) was f i t t e d to the a g e - l e n g t h data. The r e s u l t s v a r i e d w i t h the time and area where w e r e caught, ( L ~ r a n g i n g f r o m 58 to 76mm; K r a n g i n g from 1.56 to 2.46). For the G u l f It = 58mm

the fish

of Oman, (i - e -2"46

(t - 0.13))

was f o u n d to be the best fit (Gj~saeter, 1981c; G j M s a e t e r and Tilseth, 1983). Weight was c a l c u l a t e d a c c o r d i n g to the f o r m u l a W = 2.74 x 10 -5 12.83 . A typical length f r e q u e n c y d i s t r i b u t i o n and a g r o w t h curve of B. pterotum, based on m a t e r i a l from the Gulf of Oman, February 1983, are shown in F i g u r e s 8 and 9. H. G j ~ s a e t e r (1981a) e s t i m a t e d m o r t a l i t y using catch curves, and found that the i n s t a n t a n e o u s r a t e of n a t u r a l m o r t a l i t y (M) m a y be in the o r d e r of 6-15 per annum. S v ~ s a n d (1983) a n a l y s e d d a t a f r o m the Gulf of O m a n and found that v a l u e s of M = 2 b e f o r e s p a w n i n g and M = 12 after s p a w n i n g , g a v e a r e a s o n a b l e fit to the a v a i l a b l e data. T h e age of s p a w n i n g is h i g h l y v a r i a b l e but a m e a n of 7 m o n t h s seems to be a r e a s o n a b l e e s t i m a t e and it is probable that the fish o spawns o n l y once (Dalpadado, 1983; Svasand, 1983). U s i n g the e s t i m a t e d b i o m a s s "given in Table 5, the p a r a m e t e r s s p a w n i n g s t o c k was r e d u c e d by not m o r e t h a n 25~ of the v i r g i n f i t t e d a m o d i f i e d B e v e r t o n and Holt (1957) model. He f o u n d be o b t a i n e d by u s i n g a first age at capture, t e , of a b o u t 5 the y i e l d s h o u l d i n c r e a s e w i t h i n c r e a s i n g f i s h i n g m o r t a l i t y , considering the s t o c k in the G u l f of Oman, c o n c l u d e d that an is r e a l i s t i c f r o m a b i o l o g i c a l point of view. D a t a f r o m o t h e r parts of the A r a b i a n S e a we can do in these a r e a s is p r o b a b l y to use able yield.

given above and a s s u m i n g the stock biomass, S v ~ s a n d (1983) that the highest y i e l d would months. At this level of tc P (Fig.lO). S v ~ s a n d (1983), annual y i e l d of 10.106 tonnes

are i n s u f f i c i e n t for similar analyses. The best the f o r m u l a of G u l l a n d (1970) for m a x i m u m s u s t a i n -

MSY = 0.5 M B o (where M is i n s t a n t a n e o u s c o e f f i c i e n t of n a t u r a l m o r t a l i t y and B o is b i o m a s s of the unexp l o i t e d stock). A s s u m i n g M = 2, p r o b a b l y an u n d e r e s t i m a t i o n , the annual y i e l d could be of the same size order as the biomass. H o w e v e r , o v e r most of this a r e a the stock d e n s i t y is p r o b a b l y too low to w a r r a n t a commercial f i s h e r y w i t h the t e c h n o l o g y a v a i l a b l e today. E x c e p t i o n s could be the G u l f of Aden and off the coast of P a k i s t a n w h e r e p o t e n t i a l annual yields of 20 and 8.10 6 tonnes a y e a r r e s p e c t l v e l y can be p r e d i c t e d u s i n g the G u l l a n d formula. However, the e s t i m a t e d fish production seems to be h i g h e r than e x p e c t e d from the e s t i m a t e s of primary p r o d u c t i o n (Cushing, 1973). A similar

1032

J.

GjMsaetem

LENGTH FHEO. DISTRIBUTION - TOTAL ~"4693

o_

o

....

S

=, ~0

"-1 ....

~S

20

~

Z~

35

40

,

45

LENGTH FREO. D I STR t BUT I ON - N 4

LENGTH FREQ. DISTRIBUTIOIq - O(

N=855

I,;=30"I qO"

t.u u bJ o.

tO.

5"

. . . . I ' '~ " " I ~ ! ! ! 1 (0

S

IS

20

~

""' ~ " 1 " " ' ' I . . . . 30

35

40

45

I

SO

S

(0

15

20

2S

~

35

40

4S

SO

45

SO

LENGTH FREQ. DISTRIBUTION - N2

LEN6TH FREQ. DISTRIBUTION - D2

bp=~ N=492

~0

tO

bJ (.J nbJ o. S

5

S

(0

45

20

2S

30

35

40

45

5

~0

~5

20

~

30

35

40

LENGTH( H M )

Fig.8.

Length distribution F e b r u a r y 1983.

o f B. p t e r o t u m c a u g h t

in t h e G u l f o f Oman,

Mesopelagic

Fish

Sea

in the Arabian

1033

60

50

.iI lJ /,+ J ×

7~ *- 5 0 (_9 z uJ _J

xx

x

20

x

x

t0

,

0

l

50

'

t00

t50

200

i

I

I

250

500

550

AGE(DAYS)

Fig.9.

Growth of B. p t e r o t u m from the Gulf off Oman, February 1983. Age is e s t i m a t e d by c o u n t i n g primary growth rings in the otollths. The line shows a yon Bertalanffy growth curve fitted to the data.

tc

5 0.3

0.2 3 >-

O.l

O.C

2;o'

+o'

,0+''

F

Fig.10.

Yield per r e c r u i t of B. pterotum a s s u m i n g the f o l l o w i n g parameters. G r o w t h c o n s t a n t s K=2.5, L~= 58mm, to=0.13. Age of s p a w n i n g 7 months. Natural m o r t a l i t y before spawning, ZI=2 and after s p a w n i n g Z2=12. Age at first capture tc=5 , 4 and 3 for the three curves r e s p e c t i v e l y .

1034

J. Gj¢saeter

situation has been observed in other areas (e.g. Clark, 1973) and several explanations l~ave been offered. It could result from higher conversion efficiencle8 than usually assumed (~.g. Graze, 1970) or from significant production by bacterio-plankton (e.g. Vinogradov, 1971). More research is obviously needed both on production and on ecological efficiency within the ecosystem of these waters.

REFERENCES Aglen, S., J. Gj~saeter and S. Tilseth (1982). s~r.veys of me.sopelagic fish resources in t h e G u l f o f Oman a n d t h e G u l f o f A d e n J u l - A u ~ 1979 and Jan-Feb 1981. Reports on Surveys with the R/V 'DR. FRiDTJOF NANSEN'. Bergen 1982, 7Opp. Ahlstrom, E.H. (1968). Appraisal of the IIOE larval fish collection at IOBC, Cochin, India. UNESCO Informati0n Paperg, 137, I-I0. Alverson, F.G. (1961). Daylight surface occurrence of myctophid fishes off the coast of Central America. Pacific Science, 15, 483. Anon (1978). Final report survey results of R/V 'DR. FRIDTJOF NANSEN'. In: Repgrt of ~he gAS/Norway workshop on the f!sh@r~ resources of the North Arabian Sea, Vol.2, Papers. Development Report Indian Ocean Programme, PAO, 13-61. Backus, R.H., J.E. Craddock, R.L. Haedrich, D.L. Shores, T.M. Teal, A.S. Wing, G.W. Mead and W.D. Clarke (1968). Ceratoscopelus maderensis: peculiar sound-scattering layer identified with this myctophid fish. Science , 160, 9911993. Barham, E.G. (1971). Deep-sea fishes: lethargy and vertical orientation. Pp. 100-118 in Farquhar, G.B. ed. Proceedings of an International S~mposium on blolo~Ical sound-sc@tterin~ in the ocean. Washington, D.C., Maury Center for Ocean Science, Rep. Mc-OOJ. Beverton, R.J.H. and S.J. Holt (1957). O n the d y n ~ I c s of exploited fish populations. Fishery Investigations Ser. II, 26. Her Majesty's Stationery office, London, 533 PP. Blaxter, J.H.S. and R.I. Currie (1967). The effects of artificial lights on acoustic scattering layers in the ocean. In: Aspects of Ma~Ine Zoology, N.B. Marshal, ed. Symposia of the Zoological Society of London (19). Academic Press, London, 1-14. Clarke, T.A. (1973). Some aspects of the ecology of lantern-fishes (MFctophldae) in the Pacific Ocean near Hawaii. Fisher ~ Bgl%etiq , Seattle , 71, 401-434. Cushing, D.H. (1973). Production in the Indian Ocean and the transfer from the primary to the secondary level. In: The B i o l o ~ of th e Indian Ocean. Zeitzchel, B. ed., Springer Verlag, Berlin, 475-486. Dickson, R.R. (1972). On the relationship between ocean transparency and the depth of sonic scattering layers in the North Atlantic. Journal .du cons ell ~ Conse!l permanent international pour l'ex~loration d£.l@ met, 34, 416-422. Dalpadado, P. (1983). Aspect, of the biology of Benthgiema ' pterotum from the Indian Ocean__t M.Sc. thesis. University of Bergen Gj~saeter, H. (1981a). Da~sone!esnin ~ 8om me,ode i aldersstudler p~ fisk. Cand~real. thesis. University of Bergen, 172 pp (in Norwegian). Gj~saeter, J. (1981b) Abundance and production of lanternfish (Myctophidae) in the western and northern Arabian Sea. Fiskepidirektoratets skrifter s~rie HavundersMkelser, IZ, 215257. Gj6saeter, J. (1981c) Review of the mesopela~ic fish resources of the Arabian Sea. FAO/GCP/ INT/368(NOR), 1-32. Gj@saeter, J. and K. Kawaguchi (1980). A review of the world resources of mesopelagic fish. FAO fisheries technical paper No. 193. 1-151. GjMsaeter, J. and S. Tilseth (1983). Suryey on mesopelaglc [is h resources in the Gulf of 9m~n, Feb~uar~ 1983. Reports on Surveys with the R/V 'DR. PRIDT$OF NANSEN', NORAD/PAO/ UNDP project GLO/82/O01, 1-30. Graze, N.V. (1970). The biomass and production of different trophic levels in the pelagic communities of south seas. In: Matin 9 food chains, J.H. Steele, ed., University of California Press, Berkeley, 458-468. Gulland, J.A. (1970). The fish resources of the ocean. Fishin~ News (Books! Ltd. Surre_~y England, 255 pp. Kampa, E.M. (1971). Photoenvironment and sonic scattering. In: Proceedings of an inter~ national s~mposium on biological sgun d scattering in the sea, Farquhar, G.B., ed., Maury Center for Ocean Science, Washington. 51-58. Kesteven, G.L., O. Nakken and T. Stromme (1981). The small-pela~i ¢ and demersal fish z.esources of the NorthWest Arabian Sea. Surveys 1975-1976. Reports on surveys with the R/V 'DR. PRIDTJOF NANSEN'. Institute of Marine Research, Bergen, 55PP. Kinzer, K. (19?7). Observations on feeding habits of the mesopelagic fish Benthosema ilac:aJ<~. (Myctophidae) off northwest Africa. In: Oceanic Sound scatterin[~_~rediction, Anders~I~ N.R. and Zahuranec, B . , I . e d s , Plel~um P r e s s , New Y o r k , 3 8 1 - ~ 9 2 .

Mesol~elat~.ic

Vit, h i n

tile

Arabian

Sea

1035

Kotthaus, A. ( 1 9 7 2 ) . Pische des lndisch~m Ozeans. I'~rgebnisse der ichthyologischen Untersnchungen wiihrend der Expedition des Forscbungsschiffes 'METEOR' i n d e n I n d i s c h e n Ozean, Gel obey" 190 I1 b i s Mai 1 9 6 5 . A. S y s t c n l a t i s c l l e r Tell, 4. Iniomi (Nachtrag: Faro. M y c t o p h i d a e ) 'MI-TI'I;]OR' l : o r s c h u n g s e r g e b n i s s e |tt~ih~? . I ) . , 1 2 . 1 2 - ] 5 . Kubota, T. (1982). Food of lantel'nCtshcs in Suruga Bay, Central Japan. In: Proceedings of the North t'acific Aquaculture symposium, Me]tell, H.tt. and Mere, I~.A., eds., Alaska University, l:airbanks, 275-283. M a r s h a l l , N.t~. ( 1 9 7 9 ) . Developmt?nts i n I)ct~p-.qca b i o l o g y , l~landforl] I'ress, Poole, l)orset, r)lllJ [) . Nafpaktitis, I~.G. ( 1 9 7 8 1 . Systematics :~ml d i s t r ] b u t : i o n (if l a n t e r n - f i s h e s of tile genera l,obianchia and Diaphus (Nyctol)hidac) in t h e Indian Ocean. Natural History Museum L o s Angeles County Science Bulletin, 3o. 1-~_. Nafpaktitis, B . G . a n d M. N a f p a k t J t i s (19~#~). l,anternfishes (Family Myctophidae) collected dt~'ing c h a i s e s 3 a n d 6 o f t h e t t . V . 'ANTON BRUUN' i n t h e I n d i a n O c e a n . Natural History Museum I,os A n g e l e s C o u n t y S c i e n c e Bulletin,_ 55. 1-79. Nakamura, E.L. (1970). Observations on the biology of the myctophid, Diaphus garmani. Co p e i a , 1970(2). 374-377. Nellen, W. ( 1 9 7 3 ) . Kinds and abundance of fish larvae in the Arabian Sea and the Persian Gulf. In: The Biology of the Indian Ocean. Zeitzchel, B. e d . , Springer-Verlag, Berlin. 413-430. Parin, N.V. (1963). Results of a study of the pelagic fish fauna of the Pacific and Indian Ocean with the assistance of electric light. Trudy Institut okeanologia, Akademia Nauk SSSR 6 2 . Sandven, S. (1979). Coastal oceanography of the Arabian Sea. Data processing and interpretation. Thesis, University of Bergen. Part I. 39PP, Part II. Figs. Sch~rfe, J. (1983). Report on midwater trawling trials for lanternfish with B/v 'DR. FRIDTJOP NANSEN' in the Gulf of Oman 9 Peb to i March 1983. Repbrt to PA0. ~-n preparation,. Sv~sand, T. (1983). Populasjonsmodell for fisk med kort livssyklus med anvendelse p~ en tropisk myetophSdae. Cand. Scient. thesis, University of Bergen, 64 pp (in Norwegian). Vinogradov, M.E. (1971). Studies of the life activity of oceanic biological systems. In: Life activity of pelagic communities in the ocean tropics, Vinogradov, M.E. ed., Translated 1973. Israel Progr. Scient. Transl. Jerusalem. i-9. Wooster, W.S., M.K. Schaeffer and M.K. Robinson (1967). Atlas of the Arabian Sea for fishery oceanography. University of California. IMR Ref. 67-12. 1-35, 140 plates.