S11 8352

Damage of the tsunami to the Asari clam fisheries
in east Hokkaido
Hokkaido, Japan and the problems in its
recovery process

Natsuki Hasegawa & Toshihiro Onitsuka

87Deptth (m)Hokkaido

Tsunami in East Hokkaido

654
10‐Mar11‐Mar12‐Mar13‐Mar14‐MarAkkeshi area in East Hokkaido
・Pacific oyster culturing (200 ton yr‐1)
・Asari clam fisheryy (900(ton yyr‐1)(Ruditapes philippinarum)

Akkeshi‐ko estuary(ave depth: 1.5 m)
Akkeshi bay(‐35 m)
5 km

Clam fishing grounds

by K. Watanabe (Hokkaido Univ.)

Tsunami damage
Clam fishing ground

Oyster culture
BeforeBefore

After
After
After
Rearing facilities were destroyed &lost.
S diSedimentst withith clamslwere either
ith
washed out or locally re‐arranged.

In Akkeshi‐ko estuary,ymonitoring the clams & the environmental conditions
before the tsunami in the projects.
p j
Clam

Environments

Through continuous monitoring after the tsunami ,finding out the type and degree of the damage to Asariclam fishery and the problems encountered in therecovery process.

Coonditionn factorr

20
1816

Damaged 201114

Undamaged 201112✦

Carbohyydrate
Cmg ggDW‐1

10200
150

Damaged 2010

100D
Damagedd 2011*****50MAMJJASOND✦ Decline of condition factor at one month after tsunami* Low carbohydrate contents during summer 2011

Effects of tsunami in clam reproduction?

spent(reabsorp)
spawning
ripe
late developing
early developing
immatured

Matured male

June July June July2010
2011

Reabsorption((cancel of ggamete pproduction))

One month after tsunami, a massive clam die‐off washhappened(coincidingd( i idi theh ddecrease off condition
di i ffactor))

Any remaining clams could not dig themselves into grounds
without enough sedimentvarious stresses

Expansion of damage by clam rescue work?

Active individuals may have been harmed unintentionallythrough the aggravation of the benthic environment when
fishermen re‐buried
re buried the dying clams
clams.

Even in summer,

Anoxic condition
DDamagedd Undamaged
U dd• High density of clam
• Unsuitable condition in sediments
Remaining clams were negatively affected even in summer.

Recovery from the tsunami damage

それまでの調査

Sand capping for reconstruction of the fishing grounds••

Personal sand capping from MayLarge‐scale sand capping in winter (supported enterprise)Fear of effect of water quality in recovery

Nov 2011

Tu
urbidityy(ppm)

100

10

1

Apr2011

MayJunJul

Aug

Sep

Oct

Sand capping by each fisherman

High turbidity with sand capping was observed.

NovAfterf tsunamii(July 2011)

Turbidity((ppm)

Beforeftsunami(July 2010)
100

100

1010

1

1st15th

31th

1

1st15thHighg turbidityy with sand cappingpp g
was more frequent after the tsunami.

31th

by K. WatanabeUniv )(Hokkaido Univ.)

High turbidity might be affect the estuarine
ecosystems, particular seagrass beds, which is theecosystem engineer and modify the estuarine
ecosystems

Sanndrem
mainedSand cappingin summmerummmer

5San
nd capping
in w
winterumm
mer

×1
104 ind m‐‐2100

DamagedggroundUndamaged
ggroundDense population of juveniles in spring 2012 (spawnedafter tsunami).

Use of “Local” juveniles
for avoiding the need to transplant clams from other areas,
with an invasion of alien organisms and diseases.
Predatorex. Euspira fortunei

Diseaseex. Perkinsosis

P. marinus

from Guideline for improvement of productivity
in tidal flats by Fisheries Agency

Monitoring of the clams and the environmental conditions
b f
beforeandd after
f tsunamii revealed,l d• Tsunami
Tiddamagedd theth clamlfi
fishery,hdi
directly
tl & indirectly.
i di tl
Indirect damage might be mitigate ?
• SandS d capping
i was required,
i d butb t turbidity
t bidit were increased.
id
Its effects to the estuarine ecosystem are not clear,althoughlthh thi
this estuaryt
iis hheavily
il usedd iin llocall fifisheries.
h i• Beyond catastrophic damage of tsunami and theproblems
blin
i recovery activities,
ti iti jjuvenile
il clams
lwasdensely recruited.
Speed is required for recovery,b t care mustt bebutb ttakenk tot sustaint i theth fishery,fi hbecause fishery is supported by the ecosystems.

Acknowledgements• Akkeshi Fisherman: Mr. Y. Negishi, Mr. M. Suzuki• Akkeshi Fisheries Association• Guidance office for fisheries in Kushiro area, Hokkaido• Akkeshi Marine Station, Hokkaido Univ.
• Mr. H. Abe, Mr. K. Watanabe (Hokkaido Univ.)A catastrophic tsunami on March 11, 2011 damaged the Asari clam fishery inAkkeshi‐ko estuary, located on the Pacific coast of Hokkaido, Japan (N43º02',E144º52')). Sediments with clams from the fishing grounds were either
E144º52
washed out or locally re‐arranged by the tsunami. We monitored the clams
and their environmental conditions before and after the tsunami to find out
the type and degree of the damage to Asari clam fishery and the problems
encountered in the recovery process. The condition of the clams deteriorated
after the tsunami and their numbers reached a minimum one month after thetsunami when a massive clam die‐off occurred. Immediatelyy after thetsunami, it was thought that any remaining clams could not dig themselves
into the fishing grounds without enough sediment, and so might be subject tovarious stresses. Moreover, active individuals may have been harmed
unintentionally through the aggravation of the benthic environment when
fishermen buried the dying clams. The condition of the clams recovered aftera few months but some individuals showed abnormal tissue in their gonads
during the summer spawning season. Environmental monitoring showed thathigh turbidity with sand capping caused by reconstruction of the fishinggrounds, which might affect the estuary ecosystem, was more frequent after
theh tsunamii thanh b
beforeftheh tsunami.i Al
Althoughhh thereh
was catastrophichi
damage to Asari clam population and fishery, a dense population of juvenile
clams was observed in spring 2012, which is important for the reconstruction
off fifisheryhiin ththe llong tterm. ThisThi will
ill avoid
id th
the needd tto ttransplantl t clamslfromfother areas, which could possibly lead to an invasion of alien organisms anddiseases. Speed is required for recovery, but care must be taken to sustain thefishery