Deadly plastic oceans: entanglement and ingestion

One of the most shocking and saddening impacts of marine plastic debris is entanglement of and ingestion by marine species. Entanglement and ingestion is thought to have affected at least 267 different species. The range of species affected is huge including turtles, seabirds, whales and dolphins, penguins, seals and sea lions, sea otters, manatees, fish, and crustaceans. There is a vast amount of literature recording entanglement and ingestion. I have selected a few examples to illustrate how pervasive the problem is.

Entanglement

• Over a 23 year period Waluda and Staniland (2013) observed 1033 Antarctic fur seals entangled in marine debris at Bird Island, South Georgia. Plastic packaging bands were the most common cause of entanglement (43%), followed by synthetic fishing line (25%) and fishing net (17%). 44% of seals entanglement were juvenile males - who will have a lot of growing left to do. 
• Page et al. (2004) estimate that 1478 seals die from entanglement each year in Australia alone. Studying Australian sea lions and New Zealand fur seals at Kangaroo Island, Australia, Page et al. found that the rate of entanglement had not decreased in recent years, despite government and fishing industry efforts aimed to reduce the impact of fishing activities on non-target species. When lost or abandoned fishing gear 'catches' seals, fish or other species, this is known as 'ghost fishing' (Gregory, 2009). Australian sea lions and New Zealand fur seals have the 3rd and 4th highest entanglement rates for any seal species. 
• A northern gannet colony in Wales was studied for two weeks in October from 1996-1997 and 2005-2010. Votier et al. (2011) looked at 6 nests representative of the overall colony (in terms of individual nest size), and calculated that the average nest contained 469.91g of plastic, predominantly synthetic rope. The estimated colony total was 18.46 tonnes of plastic. On average this led to 63 birds entangled each year, or 525 individuals over the 8 study years. Votier et al. believe that this level of entanglement is unlikely to have population-level effects.
• Sightings of pods of endangered humpback whales showed at least 7 whales towing tangled rope or other debris (Gregory, 2009). 
• Sharks are often entangled in 'debris collars' (Gregory, 2009). 

Cartoon entanglement, from Happy Feet. Source.

Ingestion

• Several sea turtle species are seriously endangered from ingestion of plastic debris. Turtles often mistake floating plastic bags for jellyfish (Gregory, 2009). Analysing the stomach and oesophagus content of sea turtles in Southern Brazil, Bugoni et al. (2001) found that plastic bags were the most common form of debris ingestion, predominantly clear or white pieces, i.e. those most resembling jellyfish. 13.2% of green turtle deaths were accountable to the ingestion of anthropogenic debris. 
• There are over 100 species of bird known to ingest plastic (Gregory, 2009). These birds include albatrosses, of which Jimenez et al. (2015) studied 128 specimens of 7 different species. The amount of plastic fragments ingested varied significantly between species, indicating a difference in feeding and foraging patterns. Only 2% of mollymawk albatross (Thalassarche spp.) had ingested plastic, whereas 25.6% of great albatross (Diomedea spp.) had ingested plastic, with the highest being Diomedea sanford at 38.9%! 
• In the first study to examine plastic ingestion in common planktivorous fish, Boerger et al. (2010) found that approximately 35% of fish collected from surface waters of the North Pacific Central Gyre had ingested plastic, averaging 2.1 pieces of plastic per fish.

From these few examples it clear just how deadly the oceans have become for marine species, due to the anthropogenic input of plastic debris.