Evaluating the Presence of Marine Litter in Cetaceans Stranded in the Balearic Islands (Western Mediterranean Sea)

SIMPLE SUMMARY: The presence of plastic in oceans is extremely concerning as it poses a potential threat to marine organisms; for instance, they could become entangled in the plastic or they could ingest it. The objective of this work is to provide evidence, for the first time, of the impact that plastic debris has on stranded cetaceans in the Balearic Islands, in terms of ingestion and entanglement. We examined the occurrence of marine debris in the gastrointestinal tracts of 30 cetaceans, from five different species, that were found stranded around the Balearic Sea: Stenella coeruleoalba, Tursiops truncatus, Grampus griseus, Balaenoptera physalus, and Physeter macrocephalus. Three specimens (10% of the sample) were found to have ingested plastic items, including fishing nets, plastic bags, and strapping lines. The species affected were T. truncatus, and P. macrocephalus. Moreover, a total of seven cases of entanglement were recorded during the study, affecting four different species (S. coeruleoalba, T. truncatus, P. macrocephalus, and Megaptera novaeangliae), and all of them were entangled in discarded fishing nets. When possible, plastics were characterised by size, shape, colour, and polymer type. We concluded that the occurrence of marine debris observed in this work confirms the impact of plastic pollution on cetaceans in the Balearic Sea for the first time. ABSTRACT: The global distribution and presence of plastic, at all levels of the water column, has made plastic debris one of today’s greatest environmental challenges. The ingestion and entanglement of plastic-containing marine debris has been documented in more than 60% of all cetacean species. In light of the increasing pressure on cetaceans, and the diversity of factors that they face, the aim of this work is to provide evidence of the impact of plastic debris on stranded cetaceans, in terms of ingestion and entanglement, in the Balearic Islands for the first-time. Detailed examinations, necropsies, and plastic debris analysis were performed on 30 of the 108 cetaceans stranded between 2019 and 2022. Specimens belonging to five different species, Stenella coeruleoalba, Tursiops truncatus, Grampus griseus, Balaenoptera physalus, and Physeter macrocephalus, were evaluated. Ten percent of the cetaceans (N = 3) presented plastic debris in their stomach, with one case of obstruction and perforation. Fishery gear fragments (ropes and nets) were found in two adults of T. truncatus, whereas packaging debris (plastic bag, packing straps, and plastic sheets) were found in a juvenile P. macrocephalus. Plastic items analysed by Fourier transform infrared spectroscopy (FT-IR) reported three polymer types: polypropylene, polyamide, and high-density polypropylene. A total of seven cases of entanglement were recorded during the study, affecting four different species (S. coeruleoalba, T. truncatus, P. macrocephalus, and Megaptera novaeangliae). Only two individuals were freed from the nets, although one died after a week, whereas the rest were already found dead. In conclusion, data collected in the present study provided evidence of plastic ingestion and entanglement in cetaceans of the Balearic Islands for the first-time, thus highlighting the need for the regular examination of stranded cetaceans (as they are top predators) in future research to better understand the effects of these pollutants.