assessment of the japanese sardine (sardinops melanostictus

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