Projected changes to freshwater
fish habitats and stocks
Presented by
Peter Gehrke
Authors
This presentation is based on Chapter 7 ‘Vulnerability of
freshwater and estuarine fish habitats in the tropical Pacific to
climate change’ and Chapter 10 ‘Vulnerability of freshwater
and estuarine fisheries in the tropical Pacific to climate
change’ in the book Vulnerability of Tropical Pacific Fisheries
and Aquaculture to Climate Change, edited by JD Bell, JE
Johnson and AJ Hobday and published by SPC in 2011.
The authors of Chapter 7 are: Peter C Gehrke, Marcus J
Sheaves, James P Terry, David T Boseto, Joanna C Ellison, Boga
S Figa and Jacob Wani. The authors of Chapter 10 are: Peter C
Gehrke, Marcus J Sheaves, David T Boseto, Boga S Figa and
Jacob Wani.
Key messages
• Freshwater fisheries are important!!!
• Increased rainfall will increase freshwater habitats
in tropical regions, less in subtropics
• Freshwater fish production may increase by ~12%
• Disturbed catchments restrict production
• Five adaptations to maximise positive outcomes
and minimise negative effects
Importance of freshwater fisheries
• Catch 24,000 tonnes
per year
• 4% of GDP derived
from fisheries
• Consumption up to
100 kg per year
• Part of culture and
language
Photo Jacob Wani
Diversity of freshwater habitats
Flow – the Maestro
Effects on freshwater are different!
• Climate change will affect the quantity of
freshwater habitat available to fisheries
• Changes in water quality and habitat quality
will be secondary to changes in flow
Freshwater habitats
Photo Boga Figa
Fish migration and habitat
connectivity
Source: Gehrke et al 2011
Flow responses to rainfall
Daily flow, Nabukavesi Creek, Fiji
Episodic flow, Tontouta River, New Caledonia
Seasonal flow, Ba River, Fiji
Climate change effects
Climate feature
Air Temperature (˚C)
Rainfall
(river flow)
2035
2050
2100
+0.5 – 1.0
+1.0 – 1.5
+2.5 – 3.0
+5% - 20% in
equatorial
regions
+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
+18 – 38
+70 – 110
+23 – 51
+90 – 140
Increased intensity
Continuing feature but frequency & intensity uncertain
Temperature
Photo: David Boseto
•Increasing CO2 will promote
growth of aquatic and
riparian vegetation
Sea level
•Barriers (waterfalls,
weirs, culverts) may
block retreat of
freshwater habitats
Rainfall
2050
2050
Source: Lough et al. (2011)
Effects of altered rainfall
Source: Gehrke et al 2011
Projected habitat changes
PICT
2035
Lower
2050
Upper
Lower
2100
Upper
Lower
Upper
Melanesia
Fiji
-5%
5%
-5%
5%
5%
20%
PNG
-5%
5-10%
-5%
20%
-5%
20%
Solomon Islands
-5%
5-10%
-5%
20%
5%
10%
Vanuatu
-5%
5-10%
-5%
5%
5%
10%
-5%
10%
-5%
10%
-10%
>20%
Polynesia
French Polynesia
Likelihood
Confidence
Interactions in disturbed catchments
Source: Google Earth
Effects on fisheries
Photo: Erin Michelle Smith
Projected fisheries changes
PICT
Melanesia
Fiji
Papua New Guinea
Solomon Islands
Vanuatu
Polynesia
French Polynesia
Production
(tonnes)
Average projected change (%)
2035
2050
2100
4,146
17,500
2,000
80
0
2.5
2.5
2.5
0
7.5
7.5
0
12.5
7.5
7.5
7.5
100
2.5
2.5
7.5
Adaptation recommendations
• Maintain vegetation in catchments to avoid
sediments and nutrients entering waterways
Photo: Joanna Ellison
Adaptation recommendations
• Build capacity of local communities to manage
habitats and fisheries resources
Photo: Joanna Ellison
Adaptation recommendations
• Adopt more efficient fishing methods and limit
fishing effort
Photo: Boga Figa
Photo: Boga Figa
Adaptation recommendations
• Manage threats from invasive species
Photo: Boga Figa
Adaptation recommendations
• Monitor catches and
measure the success of
management interventions
Photo: Jacob Wani
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.’ (Ficke et al. 2007)
Photo: Jacob Wani