assessment of the japanese sardine (sardinops melanostictus
TRANSCRIPT
Assessment of the Japanese sardine (Sardinopsmelanostictus) stock in the northwestern Pacific
for Japanese management system
Hiroshi NISHIDA, Masayuki NOTO, Atsushi KAWABATA and Chikako WATANABE
National Research Institute of Fisheries ScienceYokohama, Japan
Sardinops melanostictus
(1) Current stock status (2) ABC(acceptable biological catch) setting(3) Suggestion for the stock recovery measure that promote
sustainable fishery
Egg
Juvenile
Wintering young
Stock biomass (VPA) and Fisheries catch
0
5000
10000
15000
20000
25000
1980 1985 1990 1995 2000 2005
Stoc
k bi
omas
s an
d Fi
sher
ies
catc
h in
wei
ght
(100
0 to
n)
Stock abundance decreased from ca.14-19 million ton during 1980’s to less than 1 million ton in late 1990’s.
10
100
1000
10000
1980 1985 1990 1995 2000 2005
Egg
abun
danc
e (1
012)
Egg abundance survey
Vertical towing from 150m depth (or near bottom) to the sea surface
Long Norpac net (0.335mm mesh size and 45cm mouth diameter) .
1988
2004
Egg abundance
Egg abundance (October-September, 1978-2006)
(2) ABC setting R/SSB・Age composition
16
17
18
19
1980 1985 1990 1995 2000 2005
Kuro
shio
Ext
ensi
on W
inte
r SS
T(℃
)
0
20
40
60
80
R/SS
B (in
ds./
kg)
0
5000
10000
15000
20000
25000
1995 2000 2005
Stoc
k in
num
ber (
106 )
5+43210
SSB and diversity in age composition is also the important step for sustainable fishery
From the historical perspective, the current stock status would not be in the conditions for rapid stock recovery.
02000400060008000
10000120001400016000
0 200 400 600Spawner in weight(103 ton)
Recr
uitm
ent i
n nu
mbe
r (
milli
on)
19992006
1996 1993
.Minimum spawning stock biomass at which good recruitments were produced in the past are defined as the limit biomass (Blimit). Blimit for Japanese sardine ( low stock level) = SSB1996(220000ton)
ABC for Japanese sardine = Catch limit corresponding to the fishing mortality preventing the total biomass from decreasing, and rebuilding the spawning biomass
SSB for preferable recruitment
Surface-midwater Trawl Survey
Hokuho-maru R/V Shunyo-maru
Juvenile Wintering young
Survey period: May-Jun. 1996-
3 stations during a night
Sub-surface trawl
Net opening: 25 x 25 m
Mesh aperture (cod end): 10 mm
Towing duration: 30 min.
Towing speed: 3.5 knot
Survey period: Jan-Feb. 2002-
3 stations during a day
Surface-midwater trawl
Net opening: 40 x 40 m
Mesh aperture (cod end): 17 mm
Towing duration: 60 min.
Towing speed: 5 knot
Geographical distribution and abundance of sardine juvenilesCircle size = No./net haul
1996
1997
1998
1999
2000
2001
2002
2003
Juvenile abundance index (standardized juvenile catch numbers by May SST in KOTZ and tow numbers) fairly agreed with recruitment numbers estimated from cohort analysis
050
100150200250300350400450
1996 1998 2000 2002 2004 2006
Juve
nile
Abu
ndan
ce In
dex
020406080100120140160
Recr
uits
sto
ck n
umbe
r (10
8 inds
.)
Juvenile abundanceindexrecruits stocknumber
Young (age-1)density survey in wintering area
計量魚探測線
4054.1
35
36
37
38
140 140.5 141 141.5 142 142.5 143
Sardine density(kg/ km^2)
<510100
1000
Transect linefor acousticsurvey
High density of young was associated to intrusion from Kuroshio-extension.
Surface-midwater trawl survey data is essentialfor the stock assessment in the years of poor
recruitment.
0
5000
10000
15000
20000
2002 2003 2004 2005 2006 2007
Biom
ass
(ton)
Coastal area(transect surveyarea)Offshore area (trawlsurvey area)
Tosa Bay is one of the spawning areas for Japanese sardine and plays an important role as protected area, because large scale purse seine fisheries are prohibited in Tosa Bay. →Ishida et al. S4-4190
(3)Suggestion for the stock recovery measure that promote sustainable fishery
Preservation of habitat (spawning area)
The reduction in spawning ground in time and space in recent years also indicates the reduction of biological diversity of sardine stock
Egg abundance >20*1012 around Boso region is needed for the favorable recruitment (Kuroda 2004)
BosoTosa bay
Spawning Biomass + Spawning Location (Diversity)→ stock rebuilding
Preservation of biodiversity(spawning area)
Summary
The stock size of Japanese sardine in the northwestern Pacific has shown a continuous decrease from 1987 to 2003 and the stock biomass estimate for 2003 was about 130 thousand tons.
From the historical perspective, the current stock status would not be in the conditions for rapid stock recovery.
The acceptable biological catch (ABC), that is the biological criterion for the TAC, is set to rebuild the SSB to the level ofminimum SSB at which good recruitments were produced in the past.
Preserving habitat and biodiversity is also the important step for sustainable fishery