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Relationship between parent stock and juvenile recruitment In theory
Parent Stock
Juve
nile
Rec
ruitm
ent
Relationship between parent stock and juvenile recruitment In practice
Parent Stock
Juve
nile
Rec
ruitm
ent
Recruitment overfishing taking so many parents that there are not enough
juveniles to sustain the population
Parent Stock
Juve
nile
Rec
ruitm
ent
Options for fisheries management
1. Catch quotas or harvest limits
2. Spatial closures or marine reserves
3. Seasonal closures
4. Minimum legal size limit
Problem! we don’t know if the particular adults we protect are contributing to juvenile recruitment
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More and bigger coral trout in “green” zones but how important are “green’ zones as a source of juveniles?
Coral trout below 38cm are protected but how important are small adults as a source of juveniles?
ore and bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbiiiiiiiiiiiiiigger coral trout in
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Keppel Islands
Study location
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Where do larvae from green zones go?
Experimental Design: (A) Sample adults in 3 focal green zones (B) Sample juveniles across all green and blue zones Using parentage analysis we estimated:
(1) self-recruitment (2) dispersal green to blue (3) dispersal green to green
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Bar cheek coral trout Plectropomus maculatus 58 of 493 (12%) assigned to parents in 3 green zones...
Har
rison
et a
l 201
2 an
d in
pre
p
PPlleec o
ttto pa
0
10
20
30
40
50
60
Late ‘07 Mid ‘08 Late ‘08
No.
juve
nile
s
Sampled Assigned
A large number of juveniles were progeny of adults in reserves
Sampled 30% of adults in focal green zones Focal greens made up 50% of the green zone area
48 (83%) exported to fished (blue zone) reefs throughout Keppels
Egg Rock Clam Bay
Middle Is.
Do green zones export larvae to blue zones?
Har
rison
et a
l 201
2
2 Km
10 (17%) retained in natal green zones or exchanged among green zones
Middle Is.
Clam Bay
Egg Rock
Do green zones protect next generation in green zones?
Har
rison
et a
l 201
2
2 Km
Reserves can prevent recruitment overfishing
Blue zones: ~ 60%
of juveniles come from
green zones
Green zones: ~ 35%
of juveniles come from
green zones Scale for: Sampling only 30% adults Sampling only 50% of green zones H
arris
on e
t al 2
012
Big fish in reserves are the most valuable source of juveniles
0
10
20
30
40
0
10
20
30
% A
ssig
ned
vs
Sam
pled
% A
dults
Size class (mm)
Sampled (N = 466) Assigned (N = 58)
Minimum legal size (MLS)
However, all adults contribute including fish below minimum legal size
Har
rison
et a
l in
prep
Protecting the next generation
1 Reserves can prevent recruitment overfishing… they ensure of significant supply of juveniles to fished areas each generation.
2 Reserves can protect the next generation… significant numbers of juveniles return to protected areas.
3 Size limits work! Mature fish below the legal size limit contribute to juvenile recruitment.
