Stock Assessment of Western Visayan Sea

Mesa, Sheryll V.1; Drusila Esther E. Bayate2; May R. Guanco1 1 Bureau of Fisheries and Aquatic Resources- National Stock Assessment Program,

Regional Field Office 6, Iloilo City 2 Bureau of Fisheries and Aquatic Resources- Central Office, Diliman Quezon City

Paper presented during the Training on Effective Technical Report Writing & Proper Oral Presentation of the NSAP, Eurotel, Baguio City, 16May 2014

Outline • Introduction • Materials & Methods • Results & Discussion - crab gear inventory - estimated harvest & CPUE - species composition - monthly seasonality - MSY - reproductive biology - population parameters • Conclusion • Recommendation

Order: Decapoda (ten appendages)

Infraorder: Brachyura (true crab)

Family: Portunidae (swimming crab)

blue swimming crab, flower crab, manna crab or sand crab

kasag, alimasag, lambay or masag.

I. Introduction

I. 1. Stock Profile

1. Lingayen Gulf

2. Tayabas Bay

3. Ragay Gulf

4. San Miguel Bay

5. Sorsogon Bay

6. Samar Sea

7. Carigara Bay

8. Visayan Sea

9. Guimaras Strait

10. Taytay Bay

11. Malampaya Sound

12. Honda Bay

13. Panguil Bay

14. Tawi-tawi

Philippine Blue Crab Major Fishing Grounds

(Ingles, 1996)

I. 2. Crab Fishing Gears

Crab Pot/Panggal

Crab Trap/ Bubo Pangasag

Bottomset gillnet/ Palugdang

Push net/ Hud-hud

Otter trawl

0

500

1,000

1,500

2,000

2,500

3,000

-

1,500

3,000

4,500

6,000

7,500

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

Mil

lion

of

Pes

os

Quan

tity

(M

T)

Year

Volume of Export (MT)

Value (Million of Pesos)

Production Trend (Ingles, 2004)

Export Trend (BAS Data)

National

I. 3. Framework for BSC Stock Conservation

Local Policies

• Negros Occidental:

- Provincial Ordinance No. 019: “An ordinance regulating the catching, selling, possessing or buying of gravid blue crabs and crablets in the Province of Negros Occidental”

- September 2003

• Iloilo:

- Provincial Ordinance No. 2012-093

- Catch size limit at 11cm; 50mesh size depth

- February 22, 2012

I.5. Objectives:

This study aims to provide scientific information on the biology of Portunus pelagicus caught in Western Visayan Sea.

Informations will serve as baseline in the implementation of the JAO 01-2014 as:

• fishing gear inventory

• harvest estimate and catch per unit of effort

• species relative abundance and monthly seasonality

• maximum sustainable yield

• reproductive biology

• population parameters

II. Materials & Methods:

Map of Visayan Sea showing the 10 monitoring stations of the Blue Swimming Crab Project

Premature FI Stage/Immature FII Stage/Developing

FIII Stage/Ripening FIV Stage/Spawning FV Stage/Spent

Five point scale of female gonadal maturity used for P. pelagicus (Sumpton et.al., 1994)

FIII Stage/Ripening

Data Analysis:

• Total Inventory of crab gears

• Estimated Harvest :

CPUE x Fishing days x Inventory

CPUE (computed in kg/d and kg/panel)

• MSY – Schaeffer & Fox Model

• FiSAT ver. 1.2.2 – population parameters

Reproductive Biology:

Sex Ratio = Fn/n

Sex Ratio (SR) = no. of male / no. of female

P = _________1_______ 1 + exp (S1+S2 x L)

P = proportion of mature individuals within a length class

S1 = intercept S2 = slope L = mid-length

W = aLb

GSI = GW/BW x 100

CY 2011 cpue

(kg/d) Fishing

days Vessel count by inventory

Harvest (MT)

Bottomset gillnet Crab pot Crab trap Modified danish seine (municipal) Fish coral Filter net Fish trap Manual push net Otter trawl Surface-set gillnet

3.26 4.61 4.00 0.38

10.00 3.08 0.83

16.89 7.77 3.59

248 246 229 25

36 4 8

70 42 6

325 479 36 131

195 32 49 21

111 21

262.92 542.93 32.94 1.26

70.20 0.39 0.33

24.83 36.22 0.45

TOTAL 972.47

Annual cpue, fishing days, and gear count of major crab fishing gears operating in Western Visayan Sea

III. Results & Discussion:

Annual cpue, fishing days, and gear count of major crab fishing gears operating in Western Visayan Sea

CY 2012 cpue

(kg/d) Fishing

days

Vessel count by inventory

Harvest (MT)

Bottomset gillnet Crab pot Crab trap Fish coral Fish trap Manual push net Otter trawl Surface-set gillnet

3.72 5.61 3.62 2.57 1.15

13.47 2.09 1.25

246 249 232 21 15 20

101 29

834 326 87 5 3

21 27 21

763.06 455.13 72.98 0.27 0.05 5.66 5.70 0.76

TOTAL 1,303.61

0

2

4

6

8

10

12

1992 1998 1999 2011 2012

CP

UE

(kg/

d)

0.00

0.20

0.40

0.60

0.80

1991 1992 1993 1994 1995 2011 2012

CP

UE

(kg/p

anel

)

CPUE (kg/d)

CPUE (kg/panel)

Ave. No. of Panels per Station

Negros Occidental

CPUE (kg/panel) per Station

0.54

0.57

0.57

0.59

0.66

0.75

0.81

0.86

0.98

1.00

1.08

1.27

1.51

1.59

1.90

2.66

3.76

4.46

18.73

45.93

- 10 20 30 40 50

Escualosa thoracata

Encrasicholina devisi

Photololigo edulis

Pricanthus tayenus

Sardinella sp.

Scolopsis taenioptera

Nemipterus virgatus

Sardinella gibbosa

Charybdis feriata

Aetobatus narinari

Pelates quadrilineatus

Gerres erythrourus

Sardinella fimbriata

Atule mate

Acetes sp.

Leiognathus splendens

Rastrelliger brachysoma

Rastrelliger kanagurta

Encrasicholina heteroloba

Portunus pelagicus

% Abundance

Dominant species of all fishing gears in the crabbing areas of Western Visayan Sea CY 2011-2012

Gear % 10 Dominant

Species

% Crab Species

% P. pelagicus

Bottomset gillnet Crab pot Crab trap Manual push net Otter trawl

88.43 99.99 99.86 99.96 60.81

51.97 100.00 94.09 3.74 7.22

51.11 93.49 87.37 3.57 2.09

Relative abundance of crab species identified per major crab fishing gears in

the Visayan Sea

0

2

4

6

8

J F M A M J J A S O N D

GSI

(%

)

0

5

10

15

20

25

J F M A M J J A S O N D

Rec

ruit

me

nt

(%)

0

50

100

150

200

J F M A M J J A S O N D

Cat

ch (

MT)

SEASONALITY

1991

1992

1993

1994

1995

1999

2011

2012

0

200

400

600

800

1000

1200

1400

1600

1800

0 10,000 20,000 30,000 40,000

Yie

ld (

MT

)

Effort (gillnet panels)

Fox Data

MSY and fMSY for the crab fishery of Western Visayas at different period using the Fox Models

Fox Model MSY - 1,365MT fMSY – 19,473

Species N Premature

(PM)

Female

(F)

Male

(M)

Ratio

PM: F: M

P. pelagicus 3,487 223 1,595 1,669 1:7:7

0.0

0.5

1.0

1.5

2.0

J F M A M J J A S O N D

Rat

io

F M

Observed sex ratio and monthly male and female distribution of P. pelagicus caught in Western Visayan Sea

0%

20%

40%

60%

80%

100%

J F M A M J J A S O N D

Fre

quen

cy

V

IV

III

II

I

PM

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

J F M A M J J A S O N D

GS

I (%

)

Monthly female gonadal frequency and GSI distribution of P. pelagicus caught in Western Visayan Sea

Computed length at first maturity (Lm) for P. pelagicus caught in Western Visayan Sea

Author/Year Lm (cm)

Ragay Gulf (Inlgles & Braum, 1989) Visayan Sea (Ingles, 1996) Danajon Bank (Armada, 2009) Visayan Sea (This study)

10.5

10.6

12.0

11.5

Lm = 11.5cm

Observed length frequency distribution of P. pelagicus caught in Western Visayan Sea by bottomset gillnet (BSGN), crab pot (CP),

and otter trawl (OT)

Author/Year Area L∞ k

Ingles & Braum, 1989

Germano et.al., 2006

Olaño et.al., 2009

Bayate et.al., 2011

Ingles, J., 1996

Romero, F., 2009

Mesa et.al., 2012

(this study)

Ragay Gulf, Philippines

Eastern Visayas, Philippines

Sorsogon Bay, Philippines

F

M

Guimaras Strait, Philippines

Visayan Sea, Philippines

Visayan Sea, Philippines

Visayan Sea, Philippines

18.00

8.95

21.09

19.39

21.77

22.50

19.95

19.10

1.58

1.23

1.58

1.58

1.40

0.70

1.40

1.55

-

-

-

-

2.84

-

-

2.75

Comparative growth parameter values for P. pelagicus in various fishing grounds of the Philippines

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Leyt

e G

ulf

,20

06

San

Ped

ro B

ay,2

006

Bili

ran

Str

ait,

20

06

Orm

oc

Bay

,20

06

Cam

ote

s Se

a,20

06

Vis

ayan

Sea

,20

09

Gu

imar

as S

trai

t,2

011

Vis

ayan

Sea

,20

12

E va

lue

s (y

ear-

1)

E E10

Threshold 0.5

Exploitation rate (E) values from mortalities and optimum exploitation rate (E10) from Beverton & Holt yield per recruit analysis in comparison to the threshold value of P. pelagicus from

various biological studies conducted

IV. Conclusion: P. pelagicus stocks in Western Visayan Sea is experiencing

overfishing based on the following results: - decreasing CPUE (kg/panel) - MSY with decreasing yield and increasing fMSY number of panels per boat - Growth overfishing with decreasing L and higher E values than E10

- Recruitment overfishing with high percentage of catch size prior to Lm of major crab gears

V. Recommendations:

• banning of otter trawl operation in the municipal waters (FAO 201)

• JAO 01-2014

• Effort reduction for bottomset gillnet or crab entangling net thru systematic licensing system

reduction of number of gillnet-panels or

reduction of fishing vessels operating

• JAO 01-2014

• Regulation of crab pots: • use of bamboo made materials • limit the number of pots used per operation • and increase the trap entrance diameter

• Catching size limit to 11.5cm carapace width (CW).

• Ban of catching berried crabs

• Possible closed season in the months of August to

September or January to February.