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S11 8352
Damage of the tsunami to the Asari clam fisheries in east Hokkaido Japan and the problems in itsin east Hokkaido, Japan and the problems in its recovery process
Natsuki Hasegawa & Toshihiro OnitsukaNatsuki Hasegawa & Toshihiro Onitsuka
Tsunami in East HokkaidoHokkaido
7
8
6
th (m
)5D
ept
410‐Mar 11‐Mar 12‐Mar 13‐Mar 14‐Mar
Akkeshi area in East HokkaidoAkkeshi area in East Hokkaido・Pacific oyster culturing (200 ton yr‐1)・Asari clam fishery (900 ton yr‐1)y ( y )(Ruditapes philippinarum)
Akkeshi‐ko estuary (ave depth: 1.5 m)
Akkeshi bay(‐35 m)(‐35 m)
5 km
Clam fishing grounds
by K. Watanabe (Hokkaido Univ.)
Tsunami damage
Clam fishing ground
Before
Oyster culture
BeforeBefore
After
After
After
S di t ith l ith
Rearing facilities were destroyed & lost.
Sediments with clams were either 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 Asari clam fishery and the problems encountered in the recovery process.
20
r16
18
n factor
Damaged 2011
12
14
onditio
n Damaged 2011
Undamaged 2011
200 10
Co
Undamaged 2011
✦
150
ydrate
gDW
‐1 Damaged 2010
D d 2011
50
100
Carboh
ymg g Damaged 2011
*****M A M J J A S O N DC
✦ 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
June July
immatured
June JulyMatured maleReabsorption
(cancel of gamete production)
June July2010
June July2011
Matured male
( g p )
One month after tsunami, a massive clam die‐off was h d( i idi h d f di i f )happened(coinciding the decrease of condition factor)
Any remaining clams could not dig themselves into grounds without enough sediment various stresses
Expansion of damage by clam rescue work?
Active individuals may have been harmed unintentionallyActive individuals may have been harmed unintentionally through the aggravation of the benthic environment when fishermen re buried the dying clamsfishermen re‐buried the dying clams.
Even in summer,
D d U d d
Anoxic condition
Damaged Undamaged
• 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 May • Large‐scale sand capping in winter (supported enterprise)
Fear of effect of water quality in recoveryFear of effect of water quality in recovery
Nov 2011
100
y(pp
m) 100
urbidity 10
Tu
1
Apr May Jun Jul Aug Sep Oct Nov
Sand capping by each fisherman
2011
High turbidity with sand capping was observed.
f f iBefore tsunami(July 2010)
After tsunami(July 2011)
100100
(ppm
)
1010
rbidity
(
11Tu
1st 15th 31th 1st 15th 31th
High turbidity with sand capping g y pp gwas more frequent after the tsunami.
by K. Watanabe(Hokkaido Univ )(Hokkaido Univ.)
High turbidity might be affect the estuarine ecosystems, particular seagrass beds, which is the ecosystem engineer and modify the estuarine ecosystems
mer
‐2
10
mer capping
mmerum
m
nd
maine
d
104indm
‐
5
nd capping
winterumm
Sand
in su m
San
rem
×1
0
San
in w
Damaged Undamaged
Dense population of juveniles in spring 2012 (spawned
gground
gground
Dense population of juveniles in spring 2012 (spawned after tsunami).
Use of “Local” juvenilesfor avoiding the need to transplant clams from other areas,for avoiding the need to transplant clams from other areas, with an invasion of alien organisms and diseases.
Diseaseex. Perkinsosis
Predatorex. Euspira fortunei
P. marinus
from Guideline for improvement of productivityfrom Guideline for improvement of productivity in tidal flats by Fisheries Agency
Monitoring of the clams and the environmental conditions b f d f i l dbefore and after tsunami revealed,
T i d d th l fi h di tl & i di tl• Tsunami damaged the clam fishery, directly & indirectly.Indirect damage might be mitigate ? S d i i d b t t bidit i d• Sand capping was required, but turbidity were increased.Its effects to the estuarine ecosystem are not clear, lth h thi t i h il d i l l fi h ialthough this estuary is heavily used in local fisheries.
• Beyond catastrophic damage of tsunami and the bl i ti iti j il lproblems in recovery activities, juvenile clams was
densely recruited.
Speed is required for recovery, b t t b t k t t i th fi hbut care must be taken to sustain the fishery,
because 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 in Akkeshi‐ko estuary, located on the Pacific coast of Hokkaido, Japan (N43º02', E144º52') Sediments with clams from the fishing grounds were eitherE144º52 ). Sediments with clams from the fishing grounds were either 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 problemsthe 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 the tsunami when a massive clam die‐off occurred. Immediately after the ytsunami, it was thought that any remaining clams could not dig themselves into the fishing grounds without enough sediment, and so might be subject to various 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 after a few months but some individuals showed abnormal tissue in their gonads during the summer spawning season. Environmental monitoring showed that high turbidity with sand capping caused by reconstruction of the fishing grounds, which might affect the estuary ecosystem, was more frequent after h i h b f h i Al h h h hithe tsunami than before the tsunami. Although there was catastrophic damage to Asari clam population and fishery, a dense population of juvenile clams was observed in spring 2012, which is important for the reconstruction f fi h i th l t Thi ill id th d t t l t l fof fishery in the long term. This will avoid the need to transplant clams from
other areas, which could possibly lead to an invasion of alien organisms and diseases. Speed is required for recovery, but care must be taken to sustain the fishery