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A short note on a euphausiid, Euphausia pacifica, an important food source to

demersal fishes in Uljin area, the eastern coast of Korea

Jinho Chae*1, Changhoon Han1, Jae Hac Lee2 and Jae Sang Hong3

1Korea Institute of Coastal Ecology, 205-1 Juan 1 dong, Nam-gu, 402-835 Incheon, South Korea2Marine Environment Research Department, Korea Ocean Research and Development Institute,

Ansan P.O. Box 29, Seoul 425-600, South Korea3Department of Oceanography, Inha University, 402-751 Incheon, South Korea

(Received: February 22, 2007; Revised received: December 27, 2007; Accepted: January 11, 2008)

Abstract: Gut contents of two species of demersal fishes, Pleurogrammus azonus and Dasycottus steiger were examined to understand the importance of

a euphausiid, Euphausia pacifica as prey of demersal fishes at coastal waters off Uljin, the eastern Korea where aggregations of large amounts of the

euphausiids were found. Euphausiids were significantly important food source to the species of fishes examined. All of the stomachs of P. azonus examined

contained euphausiids (% of a food item frequency occurred, F = 100%) in March and June 2003. Individual numbers of euphusiids in the guts ranged from

10 to 540 individuals per gut. Percents of individual number of food item were 99.60 and 99.96 for euphausiids in March and June 2003, respectively. The guts

of D. steiger also frequently contained euphausiids (F = 86.67 and 79.20% in October 2002 and June 2003, respectively), while amphipods (F = 36.67% and

16.17%,) and other fishes (F = 33.33% and 45.80%) were also often observed. Pleurogrammus azonus preferred larger euphausiids with size range

16.9 -28.4 mm, while the range of euphausiids distributed in the ambient water column was much broader (from eggs to adults).

Key words: Dermersal fishes, Dasycottus steiger, Pleurogrammus azonus, Gut contents, Euphausia pacifica

PDF of full length paper is available with author (*jinhochae@gmail.com)

Introduction

A large amount of euphausiids, Euphausia pacifica, has

been found in the eastern Korean water adjacent to Uljin in the

study using a scientific fishfinder w/ 200 kH transducer and multiple

horizontal-towing nets (Hwang et al., 2005). They often formed

near-bottom aggregation in the depth of 100-200 m approximately

during the day and performed diel vertical migration actively with

ontogenic changes in distributional area. High-density demersal

layers of euphausiids have been also detected in the submarine

canyons off Geoges Bank where high estimates of squid and

demersal fish production attributed to the ecosystem (Greene et al.,

1988). This study area off Uljin shows resemblance in bottom

topography with Geoges Bank in terms of submarine canyons

developed off the extension of Hupo Bank with 200 m in approximate

depth. The submarine canyons may cause a funneling effect that

would further concentrated the animals at the bottom (Greene et al.,

1988).

Euphausiids in general play an important role in pelagic

marine ecosystem, providing link in the food chain between lower

trophic level plankton and higher trophic level consumers such as

pelagic invertebrates, fishes, birds and mammals (Mauchline, 1980;

Greene et al., 1988). Although euphausiids are preferable food item

to commercially important fishes (Yang, 1996; 1999), little attention

has been paid to fish-euphausiid interaction in eastern Korean coast.

We examined gut contents of commercially important and

dominant demersal fishes in the water of Uljin, eastern Korea to

understand the role of euphausiids as prey in contribution to the

ecosystem.

Materials and Methods

Samples were captured near the area whereeuphausiids aggregations were observed with using anecosounder and nets, or nets in the previous study (Hwang etal., 2005, Fig. 1). Among the fishes commercially caught in fisherynets set close to the region of euphausiids aggregations, onlytwo fish species, Pleurogrammus azonus (arabesque greenlingor Okhostk atka mackerel) and Dasycottus steiger (spinyheadsculpin) were available with sufficient amounts for data in thecollection of October 2002 (only in D. steiger), March 2003(only in P. azonus) and June 2003, while other species capturedwith small amounts also often included euphausiids in their guts.We fixed dissected guts or only food items with 5% offormaldehyde solution from 30 and 68 individuals of P. azonusin 25 March and 7 June, 2003, and 30 and 25 individuals of D.steiger in 29 October, 2002 and 7 June, 2003, respectively,then counted the food items using a stereomicroscope (MZ 12.5,Leica, Germany). Because most o f t he food i t emswere Euphausia pacifica in P. azonus and D. steiger guts, weshow the data only as% of the occurrence frequency of a fooditem to all examined gut samples (F) and% of number ofindividuals of a food item to that of whole food items (Cn, Godonet al., 1985). Gut contents of some specimens of D. steigerwere digested in much progress, and data of Cn were notavailable.

Special Issue - Marine Environmental Biology

Guest Editor - H.W. Shin, Korea

Journal of Environmental Biology July 2008, 29(4) 471-474 (2008)

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Chae et al.

We used a multiple set of closed-open-close nets (mesh

aperture 300 µm, mouth diameter 0.6 m) for collecting samples of

euphausiids in 4-5 June, 2003 and compared the body-lengths of

the Euphausia pacifica from the net collection with those of gut

contents of the Pleurogrammus azonus captured in 7 June, 2003.

The body length was measured from the anterior tip of the rostrum

(cephalothorax for calyptopis) to the distal end of the telson.

Results and Discussion

Euphausiids were significantly important food source to the

species of fishes examined (Fig. 2). All of the stomachs of

Pleurogrammus azonus examined contained euphausiids (F =

100%) in March and June 2003 (Table 1). Individual numbers of

euphusiids in the guts ranged from 10 to 540 ind / gut, probably

according to feeding rhythm of fish and/or different capturing time

which may have influence on progress of digestion. Squids were

the only alternative of food item found in P. azonus (Cn = 99.60 and

99.96 for euphausiids in March and June, 2003, respectively). The

guts of Dasycottus steiger also frequently contained euphausiids

(F = 86.67 and 79.20% in October 2002 and June 2003,

Fig. 1: Map showing area of collection of specimen. Solid line roughly

indicates fish capturing ground. Shaded area indicates krill aggregations are

detected with ecosounder and nets in separate study in October 2002,

March and June 2003

[ A ]

[ B ]

[ C ]

[ D ]

Fig. 2: A, A full stomach of the Pleurogrammus azonus before dissecting;

B, The gut contents mostly composed with a euphausiid, Euphausiid

pacifica; C, Bottled gut contents showing a large amount of euphausiids; D,

Undigested compound eyes of euphausiids among the remains in the gut of

Dasycottus setiger of which digestion progressed

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Euphausia pacifica as an important food source to demersal fish

respectively), while amphipods (F = 36.67% and 16.17%) and

other fishes (F = 33.33 % and 45.80%) were also often observed.

The fishes showed great preference to euphausiids, even

though they can feed on much larger squids (60mm - 80mm

approximately) or fishes. The most of fishes or some euphausiid

samples found in the gut of Dasycottus steiger were much digested

and not adequate to measure body lengths and even number of

individuals, while compound eyes or prey fish-bone were often

found (Fig. 2). Cannibalism of D. steiger was also observed in an

individual in June 2003. On the other hand, Pleurogrammus azonus

was preferred larger euphausiids which size range was 16.9 - 28.4 mm,

while the range of euphausiids distributed in the ambient water

column was much broader according to life stages from nauplius to

adults (Fig. 3).

Pleurogrammus azonus is distributed widely in Northwest

Pacific from Primorskii Krai in Russia, the Sea of Okhotsk, the Kuril

Islands to Ibaraki Prefecture and Tsushima in Japan to the Yellow

Sea (Yabe, 1983; Shinohara and Amaoka, 1994; Shinohara et al.,

1994; Sokolovskaya et al., 1998; Mecklenburg and Eschmeyer,

2003). The adults are benthic, while the fry often forms epipelagic

schools (Mel’nikov, 1996a,b). Even though it is very important

commercially in Korea and Japan, and may be an important food

source to other fishes such as chum salmon (and vice versa) and

seabird (Volkov et al., 1995; Nagasawa and Kaeriyama,1995;

Nagasawa, 1998; Takahashi et al., 2001), its role as predator is

little known in recent studies. Closely related species called as atka

mackerel, Pleurogrammus monopterygiu, is known to be planktivore

(Orlov, 1997). The populations distributed off Amchitca Island feed

on crustacean plankton such as hyperiid amphipods, calanoid

copepods, planktonic larvaceans (Simenstad et al., 1977), The

most important food source of the populations off Aleutian Islands

was euphausiids, while benthic crustaceans, chaetognaths, tunicates

were also found in the guts (Yang, 1996; 1999).

Dasycottus steiger is epibiont to bathydemersal and widely

distributed in the coastal area of the North Pacific, the East Sea, the

Bering Sea, Aleutian chain, Strait of Georgia, Burrand Inlet, English

Bay, east coast of Vancouver Island, west coast of Graham Island

and southeast Pacific to Washington (Hart, 1973; Eschmeyer et al.,

1983; Lamb and Edgell, 1986; Allen and Smith, 1988; Shinohara et

al., 1994). Jewett et al. (1989) found crustaceans are the most

preferred prey among benthic invertebrates and fishes.

The results of this study that feeding of Pleurogrammus

azonus concentrated to Euphausia pacifica may lead to several

possible explanations. The investigated fishes were all

demersal, and may encounter the near-bottom aggregation of

euphausiids. However, we have no information about feeding

time and vertical diel movement of the fishes and the fish

captures were made from daytime to early morning of next

day. Thus, there is another possibility that P. azonus fed on the

euphausids in mesopelagic or epipelagic zone at night where

dense Deep Scattering Layers (DSLs) of ecosounder were

recorded by euphausiid population (Hwang et al., 2005).

Regardless whether the feeding occurred at near-bottom or

not, the euphausiids were the most preferable food item, and

their abundance may provide so enough amounts that other

food items were little chosen. Size preference of P. azonus

may be explained that euphausiid adults formed aggregation

more nearer to bottom than larvae, otherwise size-selective

Table - 1: Gut contents of two species of demersal fishes, Pleurogrammus azonus, Dasycottus steige. F is % of the occurrence frequency of a food item

to all examined gut samples and Cn is % of number of individuals of a food item to that of whole food items

Fish species Date of No. of Body length (cm) Food organisms

capturing individual Mean Range Euphausiids Cephalopods Amphipods Fish

examined F Cn F Cn F Cn F Cn

Pleurogrammus azonus 25 March, 2003 30 29.3 17.8-35.4 100.00 99.60 3.33 0.13 13.33 0.27 0.00 0.00

7 June, 2003 68 27.1 19.7-32.4 100.00 99.96 1.47 0.04 0.00 0.00 0.00 0.00

Dasycottus steiger 29 October, 2002 30 35.6 29.4-39.4 86.67 na 0.00 0.00 0.00 0.00 33.33 na

7 June, 2003 25 32.8 24.2-38.5 79.20 na 0.00 0.00 16.67 na 45.80 na

0

5

10

15

20

25

30

0.3-

0.5

0.7-

2.0

3-4

5-6

7-8

9-10

11-1

2

13-1

4

16-1

7

19-2

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21-2

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23-2

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27-2

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% o

f in

d in

fis

h g

ut

0

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0.7-

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Krill body length (mm)

% o

f in

d in

wate

r colu

mn

Furcilia

(Meta)nauplius

Caliptopis Juvenilesadults

Fig. 3: Size range of Euphausia pacifica in the gut of Pleurogrammus

azonus and ambient water column in June 2003

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Journal of Environmental Biology � July, 2008 �

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predation of the fish on euphausiid prey occurred for their

optimal energy usage, even though they could encounter prey

animals of broad range in size.

Acknowledgments

This study was supported by Nuclear R & D Program of

MoST (Ministry of Science and Technology), ‘Prevention of bio-

impingement against power plant intake (PN52700). We thank

Captain M. S. Yoon, the skipper of a fishing boat, Wonyoung-Ho,

and Mr J. S. Kim in Korea Institute of Coastal Ecology for their help

in sampling at sea. We also thank Dr J.G. Myoung for his

encouragement and comments on this publication.

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