Marine Debris: Killers in our oceans

By DAVID ROE, HarbourKeepers and CoastKeepers Coordinator - this article first appeared in the National Parks Journal Vol 51 No. 6 Dec 2007 - Jan 2008

Photo coutesy of Melbourne Zoo

The little Green Sea Turtle starved to death. The autopsy found 76 pieces of plastic and fishing line blocking its stomach. The Bryde's whale died after beaching itself. Its stomach was completely congested with a massive six square metres of plastic bags. The Giant Petrel was granted a last minute reprieve when rescuers pulled 30cm of ribbon from its stomach through its mouth. Attached to the end of the ribbon was a party balloon.

Marine debris is having a devastating affect on marine wildlife. Every year six million tonnes of debris enters the world's oceans and every square kilometre of ocean is estimated to contain 18,000 pieces of floating plastic.

Globally it is estimated that one million sea birds and 100,000 marine mammals and turtles are killed every year by plastics that have been thrown or blown into the water.

Australia shares this global problem. In South Australia marine debris is the cause of death for around 370 sea lions and fur seals every year and more than 10% of the pelicans along the NSW coast have fishing line caught on their bodies that can lead to infection, limb loss and death.

A scientific committee established under the Act found that many threatened species in NSW have ingested marine debris or become entangled. This list includes, but is not limited to, three species of marine turtle, Wandering Albatross, Southern Giant Petrels, Australian Fur-seals, Humpback Whales, Sperm Whales and the Little Penguin population in Manly.

Most debris enters the marine environment by being blown from the land or washed through stormwater drains. Stormwater drains discharge directly into creeks, streams, rivers and oceans and in most instances do not have a structure to filter out items of rubbish before they enter the water. When gross pollutant traps are installed they are unlikely to trap smaller items such as plastic lids and cigarette butts.

A 2006 study by the Department of Environment and Climate Change found the greatest littered item by volume to be beverage-related, including plastic and glass bottles, plastic caps, drinking straws and tetra boxes. However the most common item of litter is cigarette-related, including cigarette butts, packets and tobacco.

Plastics are the most damaging of marine debris and the longest lasting in marine environments; plastic bottles will take 450 years to break down. To compound the problem plastics are 'serial killers'. Animals that die from ingesting plastic or becoming entangled in plastics such as a drink collar decompose or are eaten by other animals. In this process the plastic is released back into the marine environment and is free to kill again. This cycle can be repeated many times before the plastic finally breaks down.

Plastic bags pose one of the most disturbing threats to wildlife, especially considering the number of bags released in the environment and the ease with which they find their way into the oceans.

Nearly four billion plastic bags are used in Australia every year and over 3.7 billion will be dumped in landfill sites. However this is not the end of the journey for many plastic bags as 47% of items blown from landfill sites are plastic, predominantly plastic bags. These bags can be carried hundreds of miles before settling. Added to these landfill escapees are the 50 million plastic bags littered in Australia every year.

Once a plastic bag enters the water it drifts with the currents and its capacity to kill is fully realised. Plastic bags, with their pale colouration and gently undulating form, fool turtles and seals into mistaking them for jellyfish and making the fatal error of eating them. Once plastic bags are swallowed they cannot be digested and cause a slow and painful death.

Cigarette butts are the most commonly found item of litter and are easily washed through stormwater drains into the marine environment. Dropping a cigarette butt may seem innocuous to smokers who wish to rid themselves of the evidence of their habit, but cigarettes contain thousands of chemicals, including cadmium, arsenic and lead that leach into the waterways.

It may seem improbable that a few cigarette butts can pollute the ocean until the scale of the problem is considered. A staggering 4.5 trillion cigarette butts are littered worldwide each year and seven billion are littered in Australia alone.

Cigarette butts take five years to break down in seawater and in that time add their toxic chemicals to the 'pollution soup' that our waterways are becoming. Cigarette butts also pose a direct health threat to marine wildlife as marine turtles, birds and other marine animals have been found with them in their stomachs having mistaken them for food. It's true that smoking kills, but the death toll is not restricted to smokers.

The definition of marine debris used by the scientific committee included fishing gear as commercial and recreational fishing gear has a tendency to keep on fishing, and killing, after being discarded into the environment.

Ghost nets are fishing nets that have been accidentally lost or purposefully abandoned at sea and are having a devastating impact on marine wildlife worldwide. Ghost nets drift on ocean currents held upright by floats and indiscriminately catch fish, turtles, dolphins, dugongs and any other animal unfortunate enough to get too close.

Eventually the weight of dead animals will cause a net to sink. But as the animals decompose, buoyancy is restored and the nets continue their grisly journey. Ghost nets found in the Gulf of Carpentaria have been measured at four kilometres long.

Discarded recreational fishing line also poses a threat to marine animals. Sea birds become entangled in fishing line when foraging along the shoreline. Land birds use discarded fishing line for nesting materials with disastrous results for hatching chicks that become entangled before they leave the nest. And contrary to popular belief fishing hooks do not rust away after a few days but last for a year in seawater.

However not all seabird injuries come from discarded fishing line. A 2004 study by Australian Seabird Rescue found that the majority of injuries to pelicans are due to entanglement with fishing line currently in use. The ASB have worked extensively with recreational fishers to address this problem.

Marine debris is having a devastating effect on marine species worldwide. It is placing an even greater strain on marine ecosystems already stressed by overfishing, coastal developments and land-based pollutant run off. We can help reduce the toll by carefully disposing of our rubbish, tying knots in plastic bags before disposing, joining clean up events and stopping to think of the one million sea birds and 100,000 marine mammals and turtles that die every year whenever we see plastics on the ground - and pick them up.
References

1. Australian Seabird Rescue www.seabirdrescue.org
2. Carpentaria Ghost Nets Program www.ghostnets.com.au
3. Clean Up Australia www.cleanup.org.au
4. Global Litter Information Gateway www.unep.org/regionalseas/marinelitter/
5. NSW Litter Report 2006, Dept Environment and Climate Change