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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