Projected changes to freshwater fish habitats and stocks
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 CO 2 will promote growth of aquatic and riparian vegetation
Sea level • Barriers (waterfalls, weirs, culverts) may block retreat of freshwater habitats
Rainfall 2050 Source: Lough et al. (2011)
Effects of altered rainfall Source: Gehrke et al 2011
Projected habitat changes PICT Lower 2035 Upper Lower 2050 Upper Lower 2100 Upper Melanesia Fiji -5% 5% 5% 20% PNG -5% 5 -10% -5% 20% Solomon Islands -5% 5 -10% -5% 20% 5% 10% Vanuatu -5% 5 -10% -5% 5% 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 0 7. 5 0 12. 5 7. 5 100 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
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
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