Australia Yearbook - 2001

Chapter 14—Environment 599
Aquaculture is an emerging market for
supplementation of wild fisheries in response to
the global demand for seafood. The increase in
aquaculture production and value has more than
doubled in the past decade and was worth $602m
in 1998–99 (Chapter 16, Forestry and fishing).
Although the aquaculture industry is an emerging
market, supplying around a third of the value of
fisheries production in Australia, aquaculture is
heavily reliant on fishmeal as a protein feed for
farmed species. The high cost of protein feed to
aquaculture farms presently accounts for around
60% of grow-out production costs. Presently only
20–30% of protein in aquaculture feed is retained
by the fish; the rest is not eaten or is excreted.
This adds to increased nutrient loads in coastal
waterways. The development of alternative feed is
being trialed in Australia to reduce reliance on
fish meal and produce a better quality food
source with less wastage. Aquaculture can have a
positive influence on Australian fisheries by
providing restocking potential for wild stocks and
a reduction in fishing pressure. Negative
environmental impacts, however, include the
high demand for coastal foreshores, the
increased nutrient loads from farm waste,
depletion of wildstock fisheries for fishmeal
products and the introduction of diseases and
exotic species (Zann 1995). These impacts will
need to be addressed to ensure beneficial
environmental outcomes.
Marine pollution
Although Australia has a relatively clean image
compared to other marine environments around
the world, marine pollution is a serious threat to
marine biodiversity in Australian waters. Around
80% of contamination in our marine and
estuarine environments is thought to originate
from land based sources (SoE 1996). These
include point sources such as pipes and drains,
and diffuse sources from river and urban
catchments or from the atmosphere.
Hydrocarbons are a key pollutant, originating
from shipping, from accidents in offshore
petroleum exploration and from stormwater
run-off, stormwater being the most damaging and
the least adequately monitored. Table 14.29
summarises the main pollutants and their
sources.
Pollution impacts on Australia’s marine
environment in a variety of ways. Excess nutrients
released into estuaries and the sea are a major
threat to near-shore environments, with tropical
coral reefs and seagrasses highly sensitive to
nutrient inputs. Metals and pesticides released
into the environment can accumulate in marine
organisms or be magnified through the food
chain. High concentrations of these contaminants
in organisms can render them unfit for human
consumption, reducing stocks for commercial
and recreational fishing. Contaminants can also
lead to loss of wetland habitats, which are
important for fish nurseries, waterbirds and
plants, many endemic to Australia. The loss of
visual amenity can decrease economic returns
from tourism and recreational pursuits.
Rising sea temperatures
Carbon dioxide, a key player in global warming
from greenhouse gas emissions, is considered
partly responsible for the increase in global ocean
temperatures. Carbon dioxide absorbed into the
oceans, coupled with heat reaching ocean water
from the thinning of the atmosphere, has the
effect of increasing ocean water temperatures.
The Southern Ocean is considered an integral
part of the carbon cycle, absorbing as much as
20% of carbon released into the atmosphere.
14.29 MARINE POLLUTANTS IN AUSTRALIA’S ENVIRONMENT AND THEIR SOURCES
Pollutants
Sources
Nutrients
Soil erosion, fertiliser run-off, industrial and urban sewage discharge, animal
production
Suspended solids
Forest clearing, overgrazing, agriculture (soil erosion)
Organochlorines
Pesticides, herbicides, industrial chemicals
Organophosphates
Pesticides
Metals
Cu, Pb, Cd, Zn, Hg Discharge leachates, tailings, smelters, mining operations
Tributyltin (TBT)
Antifouling paints from ships
Pathogens
Stormwater, ballast water
Litter
Storm water, shipping, recreational and commercial fishing boats, ‘beach-goers’
Source: Derived from State of the Environment, Environment Australia 1996.