Situationer and proposed
methodology
Species‐specific assessment and trial for Spawning Potential Ratio
Method for Blue Swimming Crab in the Danajon Reef
30 March 2014
Outline
Blue crabs fisheries in the Danajon Reef
Selection of sampling stations
Proposed methodologies
What to collect and how
Sampling schedule
Blue crabs fisheries in the Danajon reef
Crab gillnet
Crab pots
Crab liftnets Diving for crabs
Primary blue crab fishing opera4ons
Others (blue crabs as bycatch): Fish corral
Beach seine Bo6om trawl
Blue crabs fisheries in the Danajon reef
Municipality
(# of par@cipa@ng brgys.)
Gears and Opera@ons Total
Diving for crabs
Crab gillnet Crab liG net Crab pot
Buenavista (3) 8 8
Clarin (3) 13 13
Getafe (10) 36 83 23 70 212
Inabanga (10) 80 17 29 126
Tubigon (6) 50 32 82
Blue crabs fisheries in the Danajon reef
Catch trends
Municipality
Landing site
Crab gillnet
Crab pot
Diving
Buenavista
Asinan
2.11
Getafe
Pandanon Is.
2.24
Inabanga
Hambongan Is.
1.28
2.53
Lawis
1.91
Tubigon
Bagongbanwa Is.
4.02
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)
SPR =
Annual egg production under harvest
Annual egg production unfished
• 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
Spawning potential ratio (SPR)
• Underlying principle: SPR% level to avoid recruitment overfishing (Clark, 1991, 1993, 2002; Mace 1994) » Replacement Level
New approach (Prince et al, 2011):
• Generally, replacement level of SPR is around 20-25% of the unfished level of spawning for various species
Spawning potential ratio (SPR)
New approach (Prince et al, 2011):
• Correlated SPR to Beverton-Holt Life History Invariants (BH-LHI)
M/k=4.0
Type I M/k >0.8 ‐ green
‐ Indeterminate growth
B ‐ M/k = 0.8 Type II M/k <0.8 ‐ blue
‐ Indeterminate growth
C ‐ Determinate Growth ‐ Type III ‐ red – marine mammals & some sharks
Lead to starting assumption: the relationship between SIZE and SPR
Spawning potential ratio (SPR)
New approach (Prince et al, 2011):
• Data requirements:
• Size at maturity: Collected only once
• Size composition of the population: Annual/seasonal, every assessment period
Applied to the assessment of blue crabs fishery in Danajon Reef:
SPR@Size Curves based on literature
(1) Assess current exploitation patterns using average size at capture data (2) Establish minimum size limits »
Generic SPR @ Size curve
Size Histogram from the Catch
Data
SPR Distribution by Size in Unfished Stock
(SPR=100%) SPR Distribution By Size In Fished Stock (SPR=?)
Current SPR=42%
Estimate of SPR & F/ M
Size of Maturity
Depletion (F/M ~ SPR)
Data collection: Sampling stations
Considerations:
Representativeness of
blue crabs fishing gears
and operations
Proposed methodologies: What to
collect and how
Primary information How Material needs
Catch per unit effort (CPUE)
Record total weight (g) of catch per gear
Weighing scale
Catch information
Blue crabs (M, F)
Others (by‐catch)
Record species name,
Size distribution of blue crabs in the catch,
segregated by sex
Record as carapace width (by 0.1 or 0.5 cm size class)
Calliper
Proposed methodologies: What to
collect and how
Other information to record:
Fishing gear descriptors :type of gear, # of units and material (crab pots and crab liftnets), # of panels, panel dimensions, mesh size (crab gillnets), bait, accessories
Number of fishers involved per operation
Date and time of operation
Fishing ground (based on standard grid map)
Landing site
Proposed methodologies: What to
collect and how
Standard forms, record sheets
Form A - Catch Data ECOFISH Project – Danajon MKBA
Date: Time: Reference No.: Fish Landing Site: Fishing ground: Vessel Type:
Fishing Gear: No. of Fishermen: Engine: Hp: Time of Fishing Gear Specifications
Start
End
Total Weight of Catch: Weight of Sample:
Species name (local, scientific) Sex
Sample Sub-Sample
Weight Number Weight Number
Portunus pelagicus M
F
Proposed methodologies: What to
collect and how
Standard forms, record sheets
Form B – Size (CW) & Female maturity stage information
ECOFISH Project - Danajon Bank
Date Time Reference No. Fish Landing Site Fishing ground Vessel Type
Hp
Fishing Gear Gear Specification
Proposed methodologies: Sampling
schedule
Oct‐14
Sun Mon Tue Wed Thu Fri Sat
1 2 3 4 5
Sun Mon Tue Wed Thu Fri Sat
1 2
Sun Mon Tue Wed Thu Fri Sat
1 2 3 4 5 6 7
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
