Changes in the demersal fish communities of the sandy
beach in Sendai Bay after the disturbance by the tsunami
Yuji Okazaki1, Yutaka Kurita1 and Shinji Uehara2

1Tohoku National Fisheries Research Institute, FRA, 3-27-5 Shinhama-cho, Shiogama, Miyagi, 985-0001, Japan
2Japan Sea National Fisheries Research Institute, FRA, 1-5939-22 Suido-cho, Niigata, 951-8121, Japan

Introduction

Conclusion

The tsunami caused by the Great East Japan
Earthquake (11 March 2011) damaged
marine environments along the coastal area
in northeast Japan.

Fish community and abundance did not drastically change after thetsunami. But the abundance of dragonet (E. mirabilis) markedly
decreased in 2011.

Recently, it has been reported that coastal
habitats such as eelgrass beds and rocky
shores have been damaged after the tsunami
disaster.

Although effects of the tsunami were not negligible, decreasing indragonet abundance may be influenced by high salinity in the survey
area.

Sendai Bay has a long sandy beach, which
provides a favorable nursery ground for fish
such as flatfish. Since the tsunami reached
up to 6m in height in Sendai Bay, it wassupposed that the shore habitat in Sendai Bay
was also damaged.

The tsunami hit coastal area in Sendai Bay

Negative impacts of the tsunami disaster on the summer-autumn fish
community in sandy beach were little.
But…

Thus, to describe the effects of the tsunamion the fish community and its sandy beachenvironment, we compared demersal fish inSendai Bay before and after the tsunami.

Somewhere in Sendai BayJapan

NatoriRiver

Sampling
area

MiyagiPref.
SendaiBayAn example of samplings
Sledge net-7m

Abukuma
RiverSledgenetTSobservation

Sledge net

2004
2005
2006
2007
2008
2009
2010
2011

Annual changes of abundance of dominant species

The abundance of fishchanged annually before
the tsunami.

64
2

In 2011, the abundance ofdragonet was very low.

Results

2005

2006

2007

2008

2009

2010

(2004-2010)

100After

6
42

2004

2005

2006

2007

2008

21

2009

2010

3
2
10

2005

2006

2007

2008

2009

2010

2011

2004

2005

2006

2007

2008

2009

2010

Relationship between abundance andbottom temperature/salinity(2011)

OthersDensity(inds./100m2)

Anchovy (Engrauris japonicus)

Sample size:10～300mm SL
Developmental stage: mainly juvenile

Flounder (Paralichthys olivaceus)

Sample size:60～200mm SL
Developmental stage: mainly adult

Poacher (Occella iburia)

Sample size:20～280mm SL
Developmental stage: Juvenile and Adult

Sole (Cynoglossus joyneri)

Dragonet

Schematic view of fish distribution
on temperature and salinity

Flounder80

Percentgae in number (%)

Snailfish (Liparis tanakai)
Dragonet (Repomucenus ornatipinnis )Flounder (Kareius bicoloratus)
Croaker (Nibea mitsukurii)
Croaker (N. argentata)High temperature

1043

7.5

605
2.50×

High salinity

Low salinity

×2
10

Low temperature40
Poacher

Sole

Annual changes of bottom salinity

20Sample size:15～55mm SL
Developmental stage: mainly adult×Dragonet (Eleutherochir mirabilis)

410

3

7.5

2105
2.50×0The occurrence of dragonet was lower in 2011 than that of 2004 -2010.

2011

Flounder43

2004

Before82011

Poacher

40

Composition of fish

100
2004

We sampled fish from summer to autumn in Sendai Bay
from 2004 to 2010 (before the tsunami) and 2011 (afterthe tsunami) using a sledge net (net width:2m, net
height:0.2m, mesh size:6mm, time of towing:10min.).

Sole

1280

The sledge net was towed at three or four depth ranges
between 5m and 15m depth along the shore.

-12mDragonet

10Number (inds./100m2)

Sendai
Air Port

July Aug. Sep. Oct. Nov. Dec.
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Number (inds./100m2)

Summary of sampling year and month

Number (inds./100m2)

Map

Results

Number (inds./100m2)

Material & Methods

Since the abundance of demersal fish had annually changed in Sendai
Bay before the tsunami, we should be careful in interpreting changes in
the fish community and abundance. Long-term monitoring is needed.

Dragonet mainly distributed in low salinity water.
Bottom salinity was higher in 2011 than that of 2004-2010.

2011