According to a study published on Marine Pollution Bulletin plastic ingestions affects around 94% of Cory's shearwaters on the Catalan coast. Jacob González Solís, from the Department of Animal Biology and the Biodiversity Research Institute (IRBio) of the University of Barcelona (UB), heads the research group that carried out the study. In the case of Yelkouan shearwaters and Balearic shearwaters, conclusions state that 70% of studied birds were affected by plastic ingestion.
The paper is also authored by Marina Codina García, Teresa Militão and Javier Moreno, researchers at IRBio.
Plastic pollution is known to be a threat for marine ecosystems around the world, but it has not been much studied yet. Jacob González Solís explains that "this is the first assessment of plastic ingestion in Mediterranean seabirds. The Mediterranean Sea has been recognized as a singularly sensitive ecosystem because its coast is very industrialized, shipping activity is intense and it contains high density floating plastic areas."
Endangered Mediterranean seabirds
The scientific study is based on the analysis of 171 birds accidentally caught by longliners in the Catalan coast from 2003 to 2010. The UB research group studied plastic ingestion in nine particularly endangered seabird species: Cory's shearwater (Calonectris diomedea), Yelkouan shearwater (Puffinus yelkouan), Balearic shearwater (Puffinus mauretanicus), gannet (Morus bassanus); Audouin's gull (Ichthyaetus audouinii), Mediterranean gull (Ichthyaetus melanocephalus), yellow-legged gull (Larus michahellis), black-legged kittiwake (Rissa tridactyla) and great skua (Catharacta skua).
From civilization to seabirds' stomach
Floating plastic debris can produce entanglement, ulcers, infections and death to marine animals. They usually ingest them by mistake because plastic fragments resemble their natural food items (direct ingestion), but in other cases plastic comes from eating prey with plastic in the stomach (indirect ingestion). Ingested fragments are filaments, plastic spheres, laminar plastic and industrial pellets.
Results showed that 66% of seabirds had at least one piece of plastic in their stomachs. Cory's shearwaters were worst affected, with 94% of these birds containing plastic fragments (15 on average). In the case Balearic shearwaters and Yelkouan shearwaters, 70% contained plastic fragments.
"Results are alarming," emphasizes Gónzalez Solís. "All three of the worst affected are of conservation concern, particularly the Balearic shearwater, which is listed as critically endangered by the International Union for Conservation of Nature (IUCN). It is a Balearic endemic species; there are only around 3,000 breeding pairs in the world. We do not know its impact but it is necessary to study if it affects populations in a negative way."
Chicks, the most vulnerable
Seabird chicks are the most vulnerable to plastic ingestion as they cannot regurgitate as adults do. The lower occurrence of plastics in gulls probably results from their greater ability to regurgitate any hard remain. The study proves that plastic trash -- most of it from recreational activities -- enters oceans' food chain and may become a new threat for seabirds and marine ecosystems. Seabirds are among the most affected animals by plastic contamination, so they have been suggested as good as bioindicator species of the trends in plastic contamination at sea.
Sea isn't a rubbish bin
Accidental plastic ingestion is a global problem that affects as different species as the Laysan Albatros (Phoebastria immutabilis) in the Hawaiian Islands and the Northern Fulmar (Fulmarus glacialis rogdgersii).
"Plastic floats and is difficult to degrade," points out González Solís. "Eventually, all pollutants which are not destroyed on land arrive to the sea. The sea is not a rubbish bin. The control over plastic production and transportation at industrial level has probably improved, but there is an urgent need to develop stricter controls on waste dumping and prohibit ships' discharge into the sea."
González Solís is co-author of a study -- recently published on the journal PLOS ONE -- about the distribution of flavivirus -- viruses responsible for several infectious diseases that affect humans and other species -- among Western Mediterranean seabird populations. The study shows that yellow-legged gulls (Larus michahellis), widely distributed along the Mediterranean coast, may be potential reservoirs for these pathogens. Therefore, it is necessary to promote health surveillance on these seabird populations.
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