Stock assessment of small yellow croaker Stock assessment of small yellow croaker

considering the impact of yellow goosefish considering the impact of yellow goosefish

predation in the East China Sea predation in the East China Sea

Young Il Seo, Joo Il Kim, Taeg Yun Oh, Sun Kil Lee,

Chang Ik Zhang, Jae Bong Lee, and Jung Hwa Choi

FAO Fisheries Technical Paper 477

by Éva E. Plagányi (2007)

Anchovy

Pinkgray goby

Chefoo thryssa

Black throat sea perch

Spearnose grenadier

Yellow croaker

Hair tail

croaker

White croaker

Common hairfin anchovy

Vertical striped cardinalfish

Belenger’s jewfish

Bluefin sea robin

Yellow goosefish

Horse mackerel

Chub mackerel

Tanaka’s snailfish

Agassiz’s snailfish

Lizardfish

Butterfish

Other food

Prey of Yellow goosefishPrey of Yellow goosefish

From yellow goosefish stomach, 69 fish species were found.

Yellow goosefishYellow goosefish

Lophius litulon

Valuable groundfish

Max. size: 150 cm

High TL species in food web

as a predator with a BIG

MOUTH

Mainly feeds on small yellow

croaker (more than 45% of

its total diet composition)

Small Yellow croakerSmall Yellow croaker

Larimichthys polyactis

one of the most valuable fish

species and ecologically

important species in Korean

marine ecosystem

This fish stock has been

decreasing due to overfishing

and ecosystem impacts, such as

predation mortality

100 kg/㎢

100~1K

1K~2K

2K <

Distributions of Yellow goosefish (Spring)Distributions of Yellow goosefish (Spring)

100 kg/㎢

100~1K

1K~2K

2,000<

Distributions of Yellow goosefish (Summer)Distributions of Yellow goosefish (Summer)

100 kg/㎢

100~1K

1K~2K

2K <

Distributions of Yellow goosefish (Autumn)Distributions of Yellow goosefish (Autumn)

100 kg/㎢

100~1K

1K~2K

2K <

Distributions of Yellow goosefish (Winter)Distributions of Yellow goosefish (Winter) Small yellow croaker (Spring)Small yellow croaker (Spring)

< 10 MT

10 ~ 50

50 ~ 100

100~ 250

Small yellow croaker (Summer)Small yellow croaker (Summer)

< 10 MT

10 ~ 50

50 ~ 100

100~ 250

Small yellow croaker (Autumn)Small yellow croaker (Autumn)

< 10 MT

10 ~ 50

50 ~ 100

100~ 250

Small yellow croaker (Winter)Small yellow croaker (Winter)

< 10 MT

10 ~ 50

50 ~ 100

100~ 250

Stomach contents of Yellow goosefishStomach contents of Yellow goosefish

Dominant species of stomach contents are hakodate sand shrimp, anchovy and small size fishes in the coastal area.

Number

13%

9%

8%

7%

40%

3%3%3%4%

4%

6%haKodate sand shrimpanchovyunidentif ied f isheschinese ditch praw npinkgray gobychefoo thryssablack throat sea perchspearnose grenadierunidentif ied shrimpsmantis shrimpothers

Weight

7%

6%

6%

6%

5%

53%

3%3% 3%4%

4% bluefin sea robinunidentif ied f ishesblack throat sea perchyellow goosefishanchovyspearnose grenadierPleuronectidae sp.pinkgray gobyhorse mackerel/w hite croakerothers

South Coast (2004-2006)

Stomach contents of Yellow goosefishStomach contents of Yellow goosefish

Dominant species of stomach contents are anchovy and small yellow croaker in the EEZ of Korea.

Number2%

5%45%

20% 5%

14%

3%2%2%

1%

28%

1% unidentified fishesanchovyyellow croakerLiparidae sp.Crangonidae sp.unidentified shrimpshaKodate sand shrimparrow wormBelenger' s jewfishchinese ditch prawnothers

Weight9% 8%

6%

51%

11%25%

7%2%

2%

2%1%

1%

unidentified fishesyellow croakeranchovyLiparidae sp.Tanaka' s snaifishbutterfishlizardfishBelenger' s jewfishagassiz' snailfishchub mackerel others

EEZ (2004-2005)

Stomach contents of Yellow goosefishStomach contents of Yellow goosefish

Dominant species of stomach contents are small yellow croaker, anchovy and hairtail in the East China Sea.Measured age of prey

Number

5%

4%

5%

2%4%

19%

35%

10%4%

11%

34% 2%

yellow croakeranchovyhair tailCrustaceanscroakerwhite croakercommon hairfin anchovyCephalopodsunidentifiedvertical striped cardinalfishsouthern rough shrimp

Weight

4%

8% 3% 5%

5%

2%

22%

45%35%

3% 3%

yellow croakeranchovyhair tailCrustaceanscroakerwhite croakercommon hairfin anchovyCephalopodsunidentifiedmetallic lantern fish

ECS (1994-1997)

Fishery dataFishery data

Annual variations of catch of small yellow croaker showed a negative correlationship with that of yellow goosefish in Korean waters.

0

10,000

20,000

30,000

40,000

50,000

60,000

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Cat

ch o

f SYC

(MT)

0

2000

4000

6000

8000

10000

12000

14000

Cat

ch o

f YG

F (M

T)

Small yellow croakerYellow goosefish

y = -0.0959x + 8893.6R2 = 0.1283, P<0.05

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

0 10,000 20,000 30,000 40,000 50,000 60,000

Yellow croaker (mt)

Yello

w g

oose

fish

(mt)

Multispecies Virtual Population Analysis Multispecies Virtual Population Analysis

Common input data included catch-at-age data (only landings), maturity-at-age, and weight-at-age

Input data of the MSVPA included stomach content data, prey (small yellow croaker, anchovy, hairtail) weight-at-age in the predator stomach contents, predator (yellow goosefish) annual ration, and natural mortality.

Stomach content data and estimates of weight-at-age in the stomach contents of predators from 1994 and 1997 were used because those years had most complete for MSVPA

Predation equationsPredation equations

S - suitability coefficient of prey p for predator iBS - suitable prey biomassR - annual ration of the predator iW - weight at age of prey pM2 - predation mortalityM – natural mortality, M1 – residual mortality, U - stomach content

- avg. predator population, - avg. prey population

∑∑=i a ji

jijiapjiap BS

NRSM

,

,,,,,,2

∑∑+=p a

apapapjiofjiji NWSSBS ,,,,,,,,

( )( )∑∑

=

p ajiapapjiap

jiapapjiapjiap WNU

WNUS

,,,,,,,

,,,,,,,,,, /

/

M2M1M +=

To estimate the stock size from catch at age data and stomach contents of predators, predation mortalities must be known

To calculate predation mortality, the stock size and the suitabilities must be known

Average suitability Average suitability

0 1 2 3 4 5 6

1

2

3

4

5

6

0

0.2

0 1 2 3 4 5 6

1

2

3

4

5

6

0

1

Age

of g

oose

fish

Age

of g

oose

fish

Age of small yellow croaker Age of hair tail

Larger yellow goosefish feed on older prey species.

Comparison of natural mortality Comparison of natural mortality

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1 2 3 4 5 6 7 8 9 10

Age

Nat

ural

Mor

talit

y MSVPAsingle species

Small yellow croaker

0.0

0.4

0.8

1.2

1.6

2.0

0 1 2 3 4 5 6 7 8 9 10 11 12Age

Nat

ural

Mor

talit

y

MSVPAsingle species

Hairtail

Predatory natural mortality of small yellow croaker was highest at age 3

and that of hairtail was at age 4-5.

Comparison of average abundance Comparison of average abundance

0

200000

400000

600000

800000

1000000

1200000

1400000

1600000

1800000

2000000

0 1 2 3 4 5 6

Age

Ave

rage

Pop

ulat

ion

Size

at A

ge

SSVPAMSVPA

Small yellow croaker

0

400000

800000

1200000

1600000

2000000

0 1 2 3 4 5 6Age

Ave

rage

Pop

ulat

ion

Size

at A

ge

SSVPAMSVPA

Hairtail

Average abundance estimates of prey species by MSVPA were higher than those by SSVPA.

The difference of small yellow croaker was high until age 2.

Temporal trend of prey stock sizeTemporal trend of prey stock size

0

2000000

4000000

6000000

8000000

10000000

1988 1991 1994 1997Year

Tota

l Pop

ulat

ion

Estim

ates

SSVPAMSVPA

Small yellow croaker

0

1000000

2000000

3000000

4000000

1988 1991 1994 1997Year

Tota

l Pop

ulat

ion

Estim

ates

SSVPAMSVPA

Hairtail

Total population estimates of prey species by MSVPA were higher than by SSVPA.

Temporal trends of predation mortalityTemporal trends of predation mortality

0.0

0.4

0.8

1.2

1.6

1988 1991 1994 1997Year

Pred

atio

n M

orta

lity

SYC age-3Avg. SYC age-3HTL age-4Avg. HTL age-4

Predation mortalities of prey species at age 3 showed a similar variation

pattern from 1988-1997.

Small yellow croaker consumed by Yellow goosefishSmall yellow croaker consumed by Yellow goosefish

0

500000

1000000

1500000

2000000

2500000

3000000

3500000

4000000

4500000

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Year

Num

ber o

f con

sum

ed(th

ousa

nd) Age-6

Age-5Age-4Age-3Age-2Age-1Age-0

0

200000

400000

600000

800000

1000000

1200000

0 1 2 3 4 5 6

Prey age

Sm

all y

ello

w c

roak

erco

nsum

ed(th

ousa

nds)

Age-0 small yellow croaker was the highest consumed by yellow goosefish.

Over 80% of small yellow croaker at ages 0-2 were predated by yellow goosefish.

Reference point of small yellow croaker considering yellow goosefish predation

Reference point of small yellow croaker considering yellow goosefish predation

0

5

10

15

20

25

30

35

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Fishing mortality

YPR

of S

YC, g

0

20

40

60

80

100

120

SPR

ratio

of S

YC, %

SSVPAYGF FcurYGF F30YGF F40SSVPAYGF FcurYGF F30YGF F40

Fcur= 1.11F40%= 0. 28~0.35

ConclusionsConclusions

Adult population sizes are comparable in single species and multispecies models.

Most predation mortality of SYC occurs in age 0 to 2.

Predation impact by yellow goosefish on small yellow croaker was considerable.

Two species management application can be applicable, although the fishing pressures to both species (SYC, YG) need to be reduced in the ECS.