Projected changes to freshwater fish habitats and stocks

Projected changes to freshwater fish habitats and stocks

Presented by Peter Gehrke

AuthorsThis 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 rainfallDaily flow, Nabukavesi Creek, Fiji

Seasonal flow, Ba River, Fiji

Episodic flow, Tontouta River, New Caledonia

Climate change effects

Climate feature 2035 2050 2100

Air Temperature (˚C) +0.5 – 1.0 +1.0 – 1.5 +2.5 – 3.0

Rainfall (river flow)

+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)

+8+20 – 30

+18 – 38 +70 – 110

+23 – 51 +90 – 140

Cyclones Increased intensity

El Niño Continuing feature but frequency & intensity uncertain

Temperature

• Increasing CO2 will promote growth of aquatic and riparian vegetation

Photo: David Boseto

Sea level

•Barriers (waterfalls, weirs, culverts) may block retreat of freshwater habitats

Rainfall2050

2050

Source: Lough et al. (2011)

Effects of altered rainfall

Source: Gehrke et al 2011

Projected habitat changes

PICT 2035Lower Upper

2050Lower Upper

2100Lower 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%

Polynesia

French Polynesia -5% 10% -5% 10% -10% >20%

Likelihood

Confidence

Interactions in disturbed catchments

Source: Google Earth

Effects on fisheries

Photo: Erin Michelle Smith

Projected fisheries changes

PICT Production (tonnes)

Average projected change (%)2035 2050 2100

MelanesiaFiji 4,146 0 0 12.5Papua New Guinea 17,500 2.5 7.5 7.5Solomon Islands 2,000 2.5 7.5 7.5Vanuatu 80 2.5 0 7.5PolynesiaFrench Polynesia 100 2.5 2.5 7.5

Adaptation recommendations

Photo: Joanna Ellison

• Maintain vegetation in catchments to avoid sediments and nutrients entering waterways

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 FigaPhoto: 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