Transcript 7th SPC HOF meeting

th
7
SPC HOF meeting
Vulnerability of Freshwater Fisheries
Peter Gehrke, Marcus Sheaves, James Terry, Joanna Ellison,
David Boseto, Boga Figa and Jacob Wani
Main freshwater fisheries species
Species
Characteristics
PICT
Kai
River herring
Carp
Migrate in freshwater only
Fiji
PNG
Macrobrachium
Gobies
Freshwater adults, juveniles migrate to
sea and return
Widespread
Barramundi
Mullet
Jungle perch
Adults migrate to sea to spawn,
juveniles return to freshwater
PNG, Vanuatu, Solomon Is, Fiji,
New Caledonia
Tropical snappers (black bass, spottail snappers, mangrove jack,
threadfin, trevallies)
Mostly marine visitors to freshwater
PNG, Solomon Is, Vanuatu
Rainbow trout*, snow trout*, mahseer*
High elevation cold-water species
PNG
Eel-tailed catfish, gudgeons
Substrate spawners
PNG
Fork-tailed catfish, saratoga, tilapia*
Mouth brooders
PNG (tilapia widespread)
Direct climate factors considered
Climate feature
2035
B1
2035
A2
2100
B1
2100
A2
Air Temperature
(˚C)
+0.5 – 1.0
+0.5 – 1.0
+1.0 – 1.5
+2.5 – 3.0
Rainfall
(river flow)
+5% - 20% in equatorial regions
5% - 10%
decrease in
subtropics
+10% - 20% in equatorial regions
5% - 20% decrease in subtropics
Extremes (wet years, dry years) become more extreme
Sea level (cm)
(salinisation)
Cyclones
El Niño
+8
+20 – 30
+8
+70 – 110
+18 – 38
+90 – 140
+23 – 51
+90 – 140
Increased intensity
Continuing feature but frequency & intensity uncertain
Effects of increasing temperature
Increasing CO2 will promote
growth of aquatic and riparian
vegetation
Effects of rising sea level
Barriers (waterfalls, cascades, weirs,
culverts) may block retreat of
freshwater habitats
Projected changes in rainfall
Effects of altered rainfall
Effects on fisheries habitats
Habitat
Temperature
Rainfall
Cyclone intensity
Sea level
Rivers
Warmer highland &
lower elevation
habitats
Greater flow
magnitude & duration
Increased area and
variability
Increased erosion
Increased habitat
damage, erosion,
sedimentation, snags
Increased salinity
downstream
Lakes
Increased stratification
& nutrient cycling
Improved water quality
Increased nutrient &
contaminant inputs
Increased sediment,
nutrient & contaminant
inputs
Increased connectivity
Salinisation of coastal
lakes
Increased marine
connectivity
Floodplains
Increased production
and decomposition
rates
Increased evaporation
and drying?
Increased area and
connectivity
Increase / decrease
vegetated habitats
Increased drying?
Increased connectivity
Increased erosion &
sedimentation
Vegetation disturbance
Salinisation of coastal
wetlands
Decline of freshwater
vegetation
Mangrove expansion
Estuaries
Inhibition of intertidal
primary production?
Increased connectivity
Reduced salinity
Increased connectivity
Increased erosion &
sedimentation
Vegetation disturbance
Inundation of intertidal
habitats
Increased connectivity
Increase / decrease area
Flow – maestro of freshwater habitats
• Flow (rainfall, runoff, groundwater) determines the
quantity of habitat available (depth, width, area, timing,
connectivity, duration, rate of change, predictability)
• Flow increase by 5% to > 20% in equatorial regions,
30% increase in Sepik-Ramu
• Temperature, sea level, flow and cyclones determine
the quality of available habitats
Flow responses to rainfall
Daily flow, Nabukavesi Creek, Fiji
Episodic flow, Tontouta River, New Caledonia
Seasonal flow, Ba River, Fiji
SE Queensland floods, January 2011
Murphy’s Creek before flood
Murphy’s Creek after flood
Projected habitat changes
PICT
Melanesia
Fiji
New Caledonia
PNG
Solomon Islands
Vanuatu
Micronesia
FSM
Guam
Palau
Polynesia
American Samoa
Cook Islands
French Polynesia
Samoa
Tonga
Likelihood
Confidence
2035 B1/A2
2100 B1
2100 A2
Lower
Upper
Lower
Upper
Lower
Upper
-5%
-5%
-5%
-5%
-5%
5%
5–10%
5–10%
5–10%
5–10%
-5%
-10%
-5%
-5%
-5%
5%
5%
20%
20%
5%
5%
-20%
-5%
5%
5%
20%
20%
20%
10%
10%
-5%
-5%
-5%
5%
5–10%
5%
-5%
-5%
-5%
5–10%
10%
5–10%
-5%
-5%
-5%
20%
20%
20%
-5%
-5%
-5%
-5%
-5%
5%
10%
10%
5%
5%
-5%
-5%
-5%
-5%
-5%
5%
10%
10%
5%
10%
-5%
-5%
-10%
-5%
-5%
10%
> 20%
> 20%
10%
> 20%
Unlikely
Somewhat likely
Likely
Very likely
Likelihood
0%
Very low
29%
Low
66%
Medium
90% 100%
High
Very high
Confidence
0% 5%
33%
66%
95% 100%
Interactions in disturbed catchments
• Removal of riparian vegetation causes increased warming (0.7 – 8.0˚C)
• Reduced catchment vegetation allows increased runoff and erosion
• Chronic exposure to contaminants reduces temperature tolerance (<5˚C)
• Erosion leads to increased turbidity and sedimentation of pool habitats
Effects on diversity
and abundance
Effects on diversity and abundance
Well-vegetated catchments
Disturbed catchments
Increased riverine habitat
High sediment deposition makes
availability from increased rainfall channels shallower and supports
supports more fish e.g.
fewer fish
barramundi, river herring, mullet,
tropical snappers, fork-tailed
catfish, macrobrachium, kai
Cold-water habitats for e.g.
rainbow trout contract upstream
in PNG
Cold-water habitats contract
further upstream and support
fewer fish
Floodplains more extensive and
support more fish, e.g.
barramundi, river herring,
gudgeons
Floodplain wetlands shallower
with sediment, support fewer
fish, possibly more carp
Lakes larger, support more fish,
e.g. tilapia, milkfish, mullet
Lakes become shallower, turbid,
fewer species, possibly more
carp
Projected fisheries production
PICT
Melanesia
Fiji
New Caledonia
Papua New Guinea
Solomon Islands
Vanuatu
Micronesia
FSM
Guam
Palau
Polynesia
American Samoa
Cook Islands
French Polynesia
Samoa
Tonga
Est. recent
production
(tonnes)
Projected change (%)
2035
2100
B1
A2
B1
A2
4,146
10
17,500
2,000
80
0
2.5
0
0
0
0
0.0
2.5
2.5
2.5
0
-2.5
7.5
7.5
0
12.5
0
7.5
7.5
7.5
1
3
1
0
0
0
0
2.5
0
0
2.5
2.5
7.5
7.5
7.5
1
5
100
10
1
0
2.5
2.5
0
0
0
2.5
2.5
0
0
0
2.5
2.5
0
2.5
2.5
7.5
7.5
2.5
7.5
Unlikely
Somewhat likely
Likely
Very likely
Likelihood
0%
Very low
29%
Low
66%
Medium
90% 100%
High
Very high
Confidence
0% 5%
33%
66%
95% 100%
Putting climate change in
perspective
‘In tropical systems it is possible that the effects of global climate
change will be overshadowed by other, larger disturbances
such as deforestation and land-use changes.’
‘Currently, the magnitude of global climate change is such that
most of its effects on freshwater fisheries could be easily
masked by or attributed to other anthropogenic influences,
such as deforestation, overexploitation and land use change’
(Ficke et al. 2007)
Ficke AD, Myrick CA and Hansen LJ (2007) Potential impacts of global climate change on freshwater fisheries. Reviews in Fish
Biology and Fisheries 17, 581-613.
Adaptation recommendations
Improving habitat management to reduce exposure and sensitivity to climate
change
• Better knowledge of habitat use and fish responses to changes in habitat.
• Plan future development to maintain habitat quantity and quality.
• Modify barriers to allow fish and invertebrates to retreat upstream.
• Revegetate cleared catchments to reduce exposure to warming.
• Revegetate cleared land to reduce effects on temperature tolerances.
• Engage with industry sectors to rehabilitate disturbed areas.
Supporting actions for fisheries
management
Build capacity of local communities to manage habitats and fisheries resources
• Promote cross-sectoral approaches for villagers to manage fisheries and
protect habitats.
Adopt more efficient fishing methods and limit fishing effort
• Regulate fishing gear to avoid negative interactions between increasing
fishing pressure and climate change, and to reduce risk of over-exploitation.
• Adapt fishing practices to harvest species tolerant to climate change.
• Diversify fisheries for wider range of species and habitats e.g. river herring,
eels.
Supporting actions for fisheries
management
Manage threats from invasive species
• Investigate ways to manage low-value invasive alien species that may be
favoured by climate change, to reduce impacts on food species.
Improving post-harvest methods
• Promote simple post-harvest methods, such as smoke curing, to reduce
spoilage under higher temperatures.
Monitor catches and measuring the success of management interventions
• Implement simple systems for collecting basic information on catch and
effort to assess effectiveness of adaptation.
Thank you