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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)
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)
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.