Marine Litter

The threat posed by marine litter is a very simple one that is often overlooked. Many concerns about marine litter pollution have been largely aesthetic. However, the issue of marine litter is a serious one that is potentially life threatening to Hebridean cetaceans and other marine life.

Threats posed by seaborne debris are mechanical in nature when cetaceans become entangled or ingest debris

Entanglement:

Many animals can become ensnared by litter. The litter can become embedded in the flesh as tissue grows around it. For cetaceans, getting trapped in discarded fishing nets is a major threat. Photographs taken by SeaLife Surveys and HWDT have shown that a number of minke whales have been found to have creel lines and plastic straps wrapped around their rostrums. One was observed with fishing net trapped over its whole head. Such entanglement can impair an animal’s ability to swim, breathe and find food. Between the years 1992 and 2000, 15 out of the 70 minke whales stranded in Scotland died due to entanglement. Entanglement may also cause injury and wounds as the animal tries to disentangle itself from netting or ropes, which can also subsequently lead to infections.

Ingestion:

Many cetaceans have been found to ingest litter, either accidentally but most likely because they look similar to prey species. Once inside, litter can block intestines preventing digestion leading to starvation. It can also accumulate in the stomach making the animal ‘full’ and reducing the instinct to feed, again leading to starvation. In February 2003, a rare Cuvier’s Beaked whale washed up on the western coast of Mull. An initial investigation of the contents of its stomach and intestines revealed that it contained a large proportion of shredded black plastic bags resembling household bin liners. It is almost certain that this contributed to its death. Many Cuvier’s Beaked whales that are stranded are found to have ingested large quantities of plastics and it is thought they mistake these plastics for squid, their usual prey. In a similar incident in 2002, the Marine Conservation Society reported a minke whale washed up in France with 800g of plastics found in its stomach – many of these were of English origin.

Anything that is found in the marine system which does not occur naturally is considered marine debris. Much of the marine litter found is of a very durable nature; an estimated 90% is some form of plastic. During our regular monitoring of Hebridean waters, HWDT notes down all the pieces of litter we observe. As detailed in the diagram below, 68% of what we have seen constitutes plastics. Although some other unusual objects such as freezers have also been spotted bobbing on the surface!

Plastic stuff = candy wrappings, little pieces of plastic, tubes, etc.

??? = not identified

Other = welly, football 2*, tag, oil drum 4*, balloons 4*, polystyrene boxes, pool. sheet, pol. lump, poly bag, freezer

During these surveys we have observed only what is floating on the surface and this is but a tiny proportion of the litter in the sea today. 70% of litter sinks to the seabed. Much of this seaborne debris is very persistent and does not breakdown easily and therefore presents a long term and cumulative risk to many marine mammals.

The marine litter that cause such problems comes from a wide variety of sources these include: Fishing boats, merchant shipping, ferries, sewage related debris, recreational vessels, offshore installations and fish farms.

HWDT works to reduce marine litter by:

• Organizing and carrying out community beach cleans on a regular basis
  
• Conducting beach cleans of remote inaccessible beaches during our research trips
  
• Picking up litter at sea where possible
  
• Publicising and raising awareness of problems caused by marine litter
  
• Member of the blue flag campaign

For more information about marine litter please click on the links below.