Marine debris found in 8.5% of whales and dolphins in Ireland

1st Nov 2017

Marine debris found in the stomachs and intestines of whales, dolphins and porpoise in Ireland in one of the largest studies of this kind undertaken

A new study just published in Environmental Pollution found marine debris in 8.5% of the dolphins and porpoise examined and microplastics in every individual examined. A total of 528 digestive tracts were examined, from 11 species making this one of the most comprehensive studies of the incidence of marine debris in whales and dolphins ever published.

Marine debris was classified into two categories, plastics, which occurred in 93% of individuals, and other items, which included a single metal fish hook and paint fragments. Macro-debris with a fisheries origin occurred in eight (35%) stomachs; four individuals (17%) contained other types of macro-debris. While the incidence of marine debris was much higher than that reported in other parts of the word this has been attributed to the larger scale of the current study. Surprisingly, deep-diving offshore species such as True’s and Cuvier’s beaked whales contained more plastics than coastal or pelagic individuals, especially plastic bags. Dr Simon Berrow a co-author on this study said “this study shows that while larger marine debris is widespread and consumed by nearly 10% of those individuals studied, the smaller fractions, known as microplastics are ubiquitous occurring in all whales, dolphins and porpoise examined”.  Examining only stranded individuals may bias the information as these individuals may have been sick or diseased and more likely to ingest marine debris. However the inclusion of known bycaught individuals in this study means the incidence of marine debris contamination reported does more likely reflect that found in the population.

 Harbour porpoise stranded in Kilkee, Co Clare. Photo Stephanie Levesque

Large plastic items were found in all compartments of the digestive tract but with plastics most had them in their stomachs. Plastic bags were the most frequently recorded item found in deep diving whales. A shotgun cartridge was found in one stranded True’s beaked whale, while ice cream wrapper and fragmented plastics were also found.

While larger marine debris has been shown to cause impaction of the gut and other complications which can lead to death, the impact of micro-plastic contamination is not known. It is thought it can act as a vehicle for persistent pollutants, which adhere to the large surface area resulting in a potential increase in contaminant burdens in marine mammals. All the individuals which were examined for microplastics which were found in all compartments of the digestive tracts. The number of particles per individual ranged from 1-88 with fibres being the most common. Nine different colours of micro-plastics were recorded. All yellow individuals came from one individual harbour porpoise. “We don’t know the consequences of this form of pollution but clearly microplastics are now ubiquitous in the marine environment”.

The study was a collaboration between research groups in two third level institutes, the Galway-Mayo Institute of Technology and University College, Cork together with the Irish Whale and Dolphin Group, an NGO and registered charity which co-ordinates a stranding scheme throughout Ireland and who sourced the stranded animals.

Reference: Lusher, A.L., et al. (2017)  Incidence of marine debris in cetaceans stranded and bycaught in Ireland: Recent findings and a review of historical knowledge, Environmental Pollution

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