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Incidence of marine debris in cetaceans stranded and bycaught in Ireland: Recent findings and a review of historical knowledge
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This study examined stranded and bycaught cetaceans in Ireland and found plastic debris — including microplastics — in a substantial portion of the animals, with ingestion increasing over the sampling period. The findings highlight that marine mammals in Atlantic waters face growing exposure to plastic pollution.
Interactions between marine mammals and plastic debris have been the focus of studies for many years. Examples of interactions include entanglement in discarded fishing items or the presence of ingested debris in digestive tracts. Plastics, including microplastics, are a form of marine debris globally distributed in coastal areas, oceanic waters and deep seas. Cetaceans which strand along the coast present a unique opportunity to study interactions between animals with macro- and microplastics. A combination of novel techniques and a review of historical data was used to complete an extensive study of cetaceans interacting with marine debris within Irish waters. Of the 25 species of marine mammals reported in Irish waters, at least 19 species were reported stranded between 1990 and 2015 (n = 2934). Two hundred and forty-one of the stranded cetaceans presented signs of possible entanglement or interactions with fisheries. Of this number, 52.7% were positively identified as bycatch or as entangled in fisheries items, 26.6% were classified as mutilated and 20.7% could not be related to fisheries but showed signs of entanglement. In addition, 274 cetaceans were recorded as by-catch during observer programmes targeting albacore tuna. Post-mortem examinations were carried out on a total of 528 stranded and bycaught individuals and 45 (8.5%) had marine debris in their digestive tracts: 21 contained macrodebris, 21 contained microdebris and three had both macro- and microdebris. Forty percent of the ingested debris were fisheries related items. All 21 individuals investigated with the novel method for microplastics contained microplastics, composed of fibres (83.6%) and fragments (16.4%). Deep diving species presented more incidences of macrodebris ingestion but it was not possible to investigate this relationship to ecological habitat. More research on the plastic implications to higher trophic level organisms is required to understand the effects of these pollutants.
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Microplastics in marine mammals stranded around the British coast: ubiquitous but transitory?
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Researchers examined the entire digestive tracts of 50 stranded marine mammals from 10 species around the British coast and found microplastics in every single animal. However, the relatively low particle counts suggest that microplastics may pass through the gut rather than accumulate permanently. The findings indicate that microplastic ingestion is ubiquitous among marine mammals, though the long-term health consequences remain unclear.
Microplastics in marine mammals stranded around the British coast: ubiquitous but transitory?
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Researchers examined whole digestive tracts of 50 stranded marine mammals from 10 UK species and found microplastics in every animal (mean 5.5 particles). The low numbers and predominance in stomachs versus intestines suggest particles are largely transitory rather than accumulating permanently in marine mammal guts.
Evaluating the Presence of Marine Litter in Cetaceans Stranded in the Balearic Islands (Western Mediterranean Sea)
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Researchers performed necropsies on cetaceans stranded in the Balearic Islands of the western Mediterranean Sea, documenting for the first time the presence, types, and quantities of ingested and entangled plastic marine litter, contributing evidence on plastic debris impacts to cetacean populations in this region.
Microplastics in Cetaceans Stranded on the Portuguese Coast
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Researchers examined the intestines of 38 stranded cetaceans along the Portuguese coast and found microplastics in over 92% of the animals. Harbour porpoises had significantly more microplastics than common dolphins, likely due to differences in diet and feeding strategies. The study notes that while the quantities found were not expected to cause immediate harm, the potential for chemical bioaccumulation from plastic additives in cetacean tissues warrants further investigation.
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