BLUE Crabs SPR Situationer & proposed methodology
Species‐specific assessment and trial for Spawning Potential Ratio
Method for Blue Swimming Crab in the Danajon Reef
30 March 2014
Situationer and proposed
methodology
Nygiel B. Armada
Fisheries and Coastal Resource
Management Advisor
ECOFISH
Outline
Blue crabs fisheries in the Danajon Reef
Selection of sampling stations
Proposed methodologies
What to collect and how
Sampling schedule
Opportunities
Blue crabs fisheries in the Danajon reef
Primary blue crab fishing opera4ons
Crab pots
Crab gillnet
Others (blue crabs as bycatch):
Fish corral
Beach seine
Bo6om trawl
Bo6om‐set gillnet
Trammel net
Diving for crabs
Crab liftnets
Blue crabs fisheries in the Danajon reef
Inventory of primary blue crab fishing opera4ons
Municipality
(# of par@cipa@ng
brgys.)
Buenavista (3)
Clarin (3)
Getafe (10)
Inabanga (10)
Tubigon (6)
Grand Total
Diving
for crabs
36
36
Gears and Opera@ons
Crab gillnet Crab liG net Crab pot
8
13
83
80
50
234
23
17
40
70
29
32
131
Total
8
13
212
126
82
441
Blue crabs fisheries in the Danajon reef
Catch trends
Municipality
Buenavista
Getafe
Inabanga
Tubigon
Landing site
Asinan
Pandanon Is.
Hambongan Is.
Lawis
Bagongbanwa Is.
Crab gillnet Crab pot Diving
2.11
2.24
1.28
2.53
1.91
4.02
* Based on 217 records, preliminary data sets from 2013 catch monitoring survey
Blue crabs fisheries in the Danajon reef
Size frequency
20.0
19.0
18.0
17.0
16.0
15.0
14.0
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
20.0
19.0
18.0
17.0
16.0
15.0
14.0
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Crab gillnet,
Ave. 13.8 cm
0
50
100
150
Crab pot,
Ave. 12.1 cm
0
5
10
15
Spawning potential ratio (SPR)
• An analytical reference point for age-structured models in fisheries assessment
• Also “spawning stock biomass-per-recruit” (Shepherd 1982), “percentage
spawning-per-recruit” (Mace and Sissenwine 1993)
Annual egg production under harvest
SPR =
Annual egg production unfished
Conventionally:
• Data requirements for population model:
• Size at maturity
• Size‐at‐age
• Fecundity estimates, with size
• Mortality and recruitment
Not practical when
applied to data‐poor
fisheries
Spawning potential ratio (SPR)
New approach (Prince et al, 2011):
• Underlying principle: SPR% level to avoid recruitment overfishing (Clark,
1991, 1993, 2002; Mace 1994) » Replacement Level
• Generally, replacement level of SPR is around 20-25% of the unfished
level of spawning for various species
Prince (November 2012)
Spawning potential ratio (SPR)
New approach (Prince et al, 2011):
• Correlated SPR to Beverton-Holt Life History Invariants (BH-LHI)
A – BH‐LHI curve using Jensen (1996)
M/k = 1.5;
Lm/L∞= 0.66;
M x Agem = 1.65
Type I M/k >0.8 ‐ green
‐ Indeterminate growth
B ‐ M/k = 0.8 Type II M/k
Method for Blue Swimming Crab in the Danajon Reef
30 March 2014
Situationer and proposed
methodology
Nygiel B. Armada
Fisheries and Coastal Resource
Management Advisor
ECOFISH
Outline
Blue crabs fisheries in the Danajon Reef
Selection of sampling stations
Proposed methodologies
What to collect and how
Sampling schedule
Opportunities
Blue crabs fisheries in the Danajon reef
Primary blue crab fishing opera4ons
Crab pots
Crab gillnet
Others (blue crabs as bycatch):
Fish corral
Beach seine
Bo6om trawl
Bo6om‐set gillnet
Trammel net
Diving for crabs
Crab liftnets
Blue crabs fisheries in the Danajon reef
Inventory of primary blue crab fishing opera4ons
Municipality
(# of par@cipa@ng
brgys.)
Buenavista (3)
Clarin (3)
Getafe (10)
Inabanga (10)
Tubigon (6)
Grand Total
Diving
for crabs
36
36
Gears and Opera@ons
Crab gillnet Crab liG net Crab pot
8
13
83
80
50
234
23
17
40
70
29
32
131
Total
8
13
212
126
82
441
Blue crabs fisheries in the Danajon reef
Catch trends
Municipality
Buenavista
Getafe
Inabanga
Tubigon
Landing site
Asinan
Pandanon Is.
Hambongan Is.
Lawis
Bagongbanwa Is.
Crab gillnet Crab pot Diving
2.11
2.24
1.28
2.53
1.91
4.02
* Based on 217 records, preliminary data sets from 2013 catch monitoring survey
Blue crabs fisheries in the Danajon reef
Size frequency
20.0
19.0
18.0
17.0
16.0
15.0
14.0
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
20.0
19.0
18.0
17.0
16.0
15.0
14.0
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Crab gillnet,
Ave. 13.8 cm
0
50
100
150
Crab pot,
Ave. 12.1 cm
0
5
10
15
Spawning potential ratio (SPR)
• An analytical reference point for age-structured models in fisheries assessment
• Also “spawning stock biomass-per-recruit” (Shepherd 1982), “percentage
spawning-per-recruit” (Mace and Sissenwine 1993)
Annual egg production under harvest
SPR =
Annual egg production unfished
Conventionally:
• Data requirements for population model:
• Size at maturity
• Size‐at‐age
• Fecundity estimates, with size
• Mortality and recruitment
Not practical when
applied to data‐poor
fisheries
Spawning potential ratio (SPR)
New approach (Prince et al, 2011):
• Underlying principle: SPR% level to avoid recruitment overfishing (Clark,
1991, 1993, 2002; Mace 1994) » Replacement Level
• Generally, replacement level of SPR is around 20-25% of the unfished
level of spawning for various species
Prince (November 2012)
Spawning potential ratio (SPR)
New approach (Prince et al, 2011):
• Correlated SPR to Beverton-Holt Life History Invariants (BH-LHI)
A – BH‐LHI curve using Jensen (1996)
M/k = 1.5;
Lm/L∞= 0.66;
M x Agem = 1.65
Type I M/k >0.8 ‐ green
‐ Indeterminate growth
B ‐ M/k = 0.8 Type II M/k