Projected impacts of climate changes on fishing and aquaculture

Climate change is already affecting Australian marine life and, consequently, Australian fisheries and aquaculture (Newton 2007). However, current climate change research, expertise and knowledge in the fisheries area are, at best, limited and patchy.

The impacts affecting aquatic systems and fisheries (both wild harvest and aquaculture), especially in estuarine and marine areas, are rising sea level, increasing acidity of marine waters, increasing global temperature, and changing rainfall patterns (amount and variability). These impacts have been analysed comprehensively (to the extent permitted by available data) in two recent reviews commissioned by the Australian Greenhouse Office (Hobday et al 2006, Hobday and Matear (eds) 2005); they are summarised in the table below.

In NSW, the predicted changes in the abovementioned variables will result in alteration of the ocean currents, due to increased frequency of El Niño-Southern Oscillation (ENSO) events, an increase in extreme event storm surges, and a decreasing flow of fresh water to estuaries, with a shift in nutrient supply to the nearshore coastal waters. These alterations will be manifest in significant estuarine and nearshore habitat change, change in trophic (food chain) relationships and shift in the recruitment patterns of aquatic plants and animals, including commercially and recreationally harvested fish and invertebrates. Shifts in the range and distribution of harvested species, the composition and interactions within aquatic communities and the structure and dynamics of communities are predicted to occur.

NSW DPI’s responsibilities under the Fisheries Management Act (FMA) extend beyond the sustainable management of fishing activity, to include conservation of a public resource for the people of NSW. Consequently, the impacts of climate change on natural habitats and biodiversity, threatened species, protected areas and introduced pests are considered alongside the effects on wild fish harvest and aquaculture. Within this range of responsibilities not all impacts are negative. There are various consequences for exotic species. The impact of species such as the freshwater fish carp may diminish because of reduced spawning opportunities on floodplains. For other exotics, such as the marine alga caulerpa, the distribution may increase, due to more-suitable conditions in estuaries.

Oyster farmers might be affected as the nutrient supply shifts from estuaries to nearshore coastal waters as a side-effect of climate change

Oyster farmers might be affected as the nutrient supply shifts away from estuaries to nearshore coastal waters as a side-effect of climate change

Impacts on NSW native biodiversity and threatened species will vary, and will be linked to predicted changes in the principal oceanographic driver on the east coast: the East Australian Current (EAC). Possible species range and distribution extensions of warmer water northern species and constriction in the range and distribution of the cooler water southern species is predicted as the EAC and associated anticyclonic warm core eddy systems move south.

The changing fresh water flow to estuaries and predicted upstream migration of salt water will alter aquatic habitats and change the distribution of wetland plants and aquatic animals. Consequently, the estuary areas suitable for oyster culture will change. The harvest of prawns will also change, as the juvenile stage of their life cycle relies on the upper estuarine wetlands, and migration into the offshore prawn fishery is related to fresh water discharge through the rivers and estuaries. Tidal wetlands lower in the estuaries (particularly saltmarsh), which are also an important nursery habitat, will become smaller, because there is rarely the capacity for them to expand landward as sea level rises.

In Australia, the management of wild harvest fisheries is structured within an ecosystem-based fisheries management (EBFM) framework. As a consequence, risk analysis and adaptive capacity for harvest strategy changes have been incorporated into the environmental impact assessments and fisheries management strategies (FMS) for NSW wild harvest fisheries. Harvest strategy is defined as the variety of fish and invertebrate species that can be taken, the fishing gear/methods permitted for use by licensed fishers, the geographic area in which fishing by an approved method can be carried out, and the statutory management controls and compliance rules that apply to the commercial and recreational fishing industries.

If economic viability is reduced as predicted for impacts resulting from climate change, fisheries resource harvest strategies will affect social wellbeing, often negatively. Harvest strategies change because of changes to the recruitment patterns for fish, crustaceans and molluscs, which occur due to changes in physical habitats and ecological processes in estuaries and the coastal environment. Structural adjustment and adaptive management of fisheries industries may be necessary.

 

Variable Impact
Sea level rise and storms
  • Rise in sea level due to thermal expansion of the ocean, glacial melt, and increased frequency or intensity of extreme storms, leading to higher risk of inundation and flooding.
  • Shoreline erosion and realignment, leading to loss of amenity or damage to assets (natural and human).
Warmer ocean temperatures
  • Increased frequency of coral bleaching events (present models project the Great Barrier Reef will warm by 2° to 5°C by 2100).
  • Potential impacts on biodiversity, through effects on the distribution and reproductive patterns of marine organisms and, consequently, food web dynamics (productivity).
Ocean acidification
  • Increased CO2 concentration in sea water is altering ocean chemistry, making it more difficult for calcitic organisms, such as coccolithophores, corals and molluscs, to grow and function. 
Decreased rainfall and drought
  • Warmer temperatures will cause greater evaporation, increasing the severity of drought for a given decrease in rainfall. 
Increased river temperatures
(freshwater)
  • Warmer temperatures will change species distributions (food web dynamics), as poikilothermic fish and invertebrates attempt to behaviourally thermo-regulate by migrating to cooler water in geographically constrained rivers and lakes.
  • Metabolic rates increase with the consequent need for more food to support this higher metabolism.

Run-off changes

  • Climate changes over land will cause changes in run-off reaching coastal and marine systems, and alter the availability and quality of fresh water – this has implications for productivity and ecosystem function of coastal and estuarine environments. 
  • Related changes in riverine flooding frequency and intensity will occur.
Ocean stability and currents
  • Changes to wind and water temperature affect water column stratification and stability, leading to changes in upwelling of nutrient-rich deeper waters and productivity of surface waters. 
  • Changes to ocean currents, notably the East Australian and Leeuwin currents, may affect dispersal and distribution patterns of marine organisms.
ENSO
  • Some models suggest global warming may lead to an increase in the frequency or intensity of El Niño events – if so, Australia may have more intense droughts and La Niña floods, particularly in the eastern part of the country.
Tropical cyclones and storm surges
  • Combined with higher sea levels, the projected increase in frequency and intensity of tropical cyclones would cause more frequent and intense coastal flooding. 
  • Tropical cyclones may occur further south than they do at present. 
  • There are likely to be shifts in prevailing wind and wave patterns.
Increased fire and wind
  • Increased frequency and/or intensity of aeolian dust and fire-borne particulates can affect coastal productivity and promote blooms.

Table: Some likely impacts of climate change on Australia’s oceans, coasts and rivers, as exemplified by biophysical change from climate drivers [Australian Greenhouse Office (Hobday and Matear (eds), 2005, Hobday et al., 2006 and Newton 2007), Bureau of Meteorology (2007), CSIRO (2007), Fisheries Research and Development Corporation (2007), Hennessy et al., (2007) and World Wildlife Fund (2007)].