Projected changes to freshwater fish habitats Presented by

Projected changes to freshwater fish habitats Presented by Peter Gehrke

Key messages • Freshwater fisheries are important in Fiji!!! • Increased rainfall will increase freshwater habitats in tropical regions, less in subtropics • Freshwater habitats in Fiji will increase 5 – 20% • Disturbed catchments degrade expanded habitats • Three adaptations to maximise positive outcomes and minimise negative effects on habitats

Diversity of freshwater habitats

Fijian freshwater habitats

Effects on freshwater are different! • Climate change will affect the quantity and variability of freshwater fish habitats • Changes in water quality and habitat quality will be secondary to changes in flow

Freshwater habitats

Fish migration and habitat connectivity

Rainfall 2050

Flow – the Maestro

Flow responses to rainfall Daily flow, Nabukavesi Creek, Fiji Episodic flow, Tontouta River, New Caledonia 65% of flow peaks are caused by cyclones 75% of cyclones cause overbank flooding Seasonal flow, Ba River, Fiji

Effects of altered rainfall

Temperature • Clearing bank vegetation will cause greater warming • Increasing CO 2 will promote growth of vegetation

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

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

Effects of disturbance on habitats Among highest suspended sediment and deposition rates in the world

Adaptation recommendations 1. Improve vegetation management to reduce habitat exposure and sensitivity to climate change

Adaptation recommendations 2. Build capacity of local communities to manage fish habitats and catchment vegetation

Adaptation recommendations 3. Map and monitor vegetation condition and water quality, and measure the success of management interventions

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) 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.