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Garbage
Summary of the potential impacts
of marine litter on the environment
Garbage enters the port and harbour
environment via numerous pathways, both from on
and offshore, one of which is through overboard
dumping from ships and boats. The International
Chamber of Shipping estimates that between 1.4 and
2.5 kg of wet garbage and 0.5-1.5kg of dry garbage
is produced per person, per day on medium sized
ships. Many vessels, especially passenger ships
have sophisticated onboard systems virtually to
eliminate this type of waste. Nevertheless many
ships and boats rely on adequate and convenient
reception facilities being available in ports and
harbours for the disposal of garbage. Inadequate
reception facilities may discourage users from disposing
of their litter responsibly ashore, and may lead
to garbage being disposed of overboard at sea. The
development and implementation of mandatory waste
management plans for ship generated waste in UK
ports and harbours under the Merchant Shipping (Port
Waste Reception Facilities) Regulations 1997 is
addressing this problem.
Shipping is estimated to contribute
between 10 and 20 % of the world's marine debris
(Sheavly 1995; Faris & Hart 1994). The Marine
Conservation Society’s (MCS) Beachwatch survey
in 1997 indicated that 14% (221 items/km) of the
litter items found in survey areas along the UK
coast were attributable to shipping. This made shipping
the second largest source of debris in the marine
environment in this study, after tourism (MCS 1998).
However, present methods of determining the sources
of litter wastes on beaches are far from scientifically
rigorous. Efforts are now being made to bring a
measure of standardisation to beach surveys and
to improve methods of determining the sources of
items of litter found on beaches (Earll 1998). The
OSPAR Convention on the protection of the marine
environment of the north-east Atlantic is undertaking
a pilot project to monitor beach litter, among the
objectives of which is to develop and test a harmonised
survey protocol. Using current information the MCS
revised its sourcing methodology and found that
in the 1998 Beachwatch survey under 3% of the litter
in the marine environment was attributable to shipping,
making it the fourth largest source of debris in
the UK (MCS 1999).
In most areas ships can safely
and legally dispose of biodegradable wastes, such
as ground paper and food wastes, overboard at least
three miles offshore where they may provide a food
source for marine animals, but within three miles
of the coast even biodegradable items should not
be thrown over board. However, the North Sea and
the English Channel are MARPOL Special Areas for
Garbage where the disposal of any garbage into the
sea is prohibited within 12 miles of land. It is
the disposal of non-biodegradable items, particularly
plastics, that poses a growing threat to marine
life. The strength and durability of plastics make
them very persistent, and they can be transported
by currents and winds, sometimes great distances,
to form accumulations of litter along certain beaches
and other sinks. The Marine Conservation Society
(MCS 1998) stress that the impact of litter on marine
species and habitats is difficult to assess because
of lack of research in this area.
The impacts of marine litter on
the environment are summarised below. A number of
reviews (MCS 1998; EA 1998) provide case studies
in the UK and abroad of damage and fatalities caused
to marine mammals and birds by plastics. It is estimated
that one million seabirds are killed annually world-wide
by ingesting marine litter and entanglement (Huggett
personal communication 1998). However, no examples
have been given of such impacts occurring to designated
marine mammals in SACs. In general, the effects
of ship generated litter on marine are likely to
be minimal and short-term in nature.
Summary of the
potential impacts of marine litter on the environment
(Laist 1997; MCS 1998; EA 1998; Fowler 1985; Westcott
et al 1994)
- Larger pieces of debris, such as sheets of plastic,
may cause smothering of benthic animals and plants
in intertidal and subtidal habitats and abrasion
of debris against hard sediment surfaces may cause
damage.
- Plastic litter, including litter from ships
such as plastic bags and strapping bands, can
have adverse affects on birds and marine mammals,
including dolphins and seals, as a result of entanglement
and ingestion. However, discarded fishing nets
and lines are the most common damaging items.
- Floating garbage items can also provide a means
of transport for harmful aquatic organisms.
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