After having found it in the stomachs of cetaceans, turtles, fish and even jellyfish, scientists studying this type of pollution in the Canary Islands have not been surprised that seabirds are not spared from the plastic plague either, although they did not expect some species to be so affected: 9 out of 10 shearwaters ingest it.
Seabirds suffer like few species from the punishment of the excesses of human development. In fact, it is estimated that their populations have decreased by 70% since 1950 and, currently, 28% of all their species are considered threatened.
Therefore, a team of researchers from the University of Las Palmas de Gran Canaria (ULPGC) has conducted a study on how the enormous amount of plastic dragged by the Canary Current (it is estimated that there are one million fragments per square kilometer, only on the surface) affects islands that represent a key point in the reproduction and migration of species such as the Atlantic shearwater, the yellow-legged gull or the Madeiran storm petrel.
The result is advanced this month in SSRN, the pre-publication platform of one of the most important scientific publishers, Elsevier, in an article whose first signatories are Alberto Navarro, from the Institute of Research in Sustainable Aquaculture and Marine Ecosystems (Ecoaqua), and Octavio Pérez, from the Institute of Biomedical and Health Research (IUIBS).
To reach their conclusions, they analyzed 88 birds of 14 different species that died from 2020 to 2021 at the Wildlife Recovery Center of Gran Canaria, either due to the problems they presented, or because they were sacrificed because they were considered unrecoverable and impossible to return to the natural environment.
In the study sample, three birds in particular were abundant: the Atlantic shearwater (Calonectris borealis, 45 specimens), the yellow-legged gull (Larus michaellis, 20) and the Madeiran storm petrel (Oceanodroma castro, 5). And they are precisely the three that have the highest proportion of specimens with plastic in their stomachs: 100% of the storm petrels, 88% of the shearwaters and 35% of the gulls.
The average number of plastic fragments in the digestive system of each affected shearwater (40 out of 45) was seven, mostly pieces of fishing line (73% of cases), with one specimen in whose stomach 23 plastics were recovered. Something similar was observed in the storm petrels, with an average of 5.6 plastics per specimen (in their case, 78% fragments) and one bird with 10 pieces of plastic in its body.
In the case of gulls, seven of the 20 specimens had eaten plastic. In their case, the average was 0.65 fragments per specimen studied, with maximum cases of four.
The authors emphasize that the birds could have ingested these fragments of plastic and fishing lines either by mistake, or by eating fish that had ingested them before.
The study also analyzes whether the birds had traces of chemical contaminants in their bodies that can be associated with plastic, either because they are among its components, or because the fragments absorbed them from the water while floating in the sea.
All the birds studied had traces of polychlorinated biphenyl number 153 (PCB 153), 95% had dichlorodiphenyldichloroethylene (d,p'-DDE); 94%, hexachlorobenzenes and PCB 138; 93%, naphthalene; and 92%, fluorene.
The authors emphasize that all these contaminants have been documented in plastic fragments in the sea, although in this case they cannot establish whether the birds ingested them by eating prey that had already accumulated them or by swallowing the synthetic waste they had in their stomachs.
In any case, they emphasize, it is necessary to investigate whether plastics are transferring chemical contaminants throughout the food chain, "since the ingestion of plastic occurs practically from the base."
And, in this regard, they recall the result of another recent study by the ULPGC: in some points of the waters surrounding Gran Canaria there is twice as much plastic, by weight, as zooplankton.
