Researchers reveal presence of microplastics in large pelagic fish in the Mediterranean

A research study co-led by the University of Barcelona and the Institute of Marine Sciences (ICM, CSIC), together with the Spanish Institute of Oceanography (IEO, CSIC), has revealed the worrying presence of microplastics in the stomachs of swordfish (Xiphias gladius) in the western Mediterranean.

The study, published in the journal Marine Pollution Bulletin, confirms the widespread presence of these pollutants in pelagic species. It also underlines the urgent need to reduce plastic pollution in the ocean to preserve the health of marine ecosystems, and thus also human health, through the food chain.

Marine pollution, and in particular plastic pollution, is emerging as a major concern for the health of marine ecosystems worldwide. Recent data indicate that the global production of plastics has reached extremely high levels, due to widespread use, low cost and durability, such that 6.3 billion metric tons of plastics have been produced recently. In the marine environment, these plastics degrade into smaller particles known as “microplastics,” which can act as vectors for chemical pollutants and pathogens.

In this study, the team analyzed the stomach contents of swordfish caught in the Western Mediterranean during two different periods: 2011–2012 and 2017–2019. The results reveal the presence of microplastics in 80% of the stomachs, the most detected polymer being polyethylene terephthalate (PET), which is used to make bags, films or bottles, among others.

“This study establishes a baseline for monitoring the ingestion of microplastics by swordfish in the western Mediterranean, a species that has recently undergone dietary changes, which could lead to changes in microplastic intake in the future,” say researchers Joan Navarro (ICM, CSIC) and Joan Giménez (IEO, CSIC).

Researcher Odei Garcia-Garin, from the UB’s Faculty of Biology and the Institute for Research on Biodiversity (IRBio), notes that “the results of the work are crucial for carrying out actions aimed at the management and conservation of swordfish in the Mediterranean, and establish a basis for monitoring the microplastics ingested by swordfish in the western area.”

To date, microplastics were known to be present in many marine ecosystems and could be ingested by various marine species. However, very little information was available on the presence of microplastics in large pelagic predators, such as swordfish in the western Mediterranean.

Based on their generalist and opportunistic feeding behavior, these fish are considered good indicators of ecosystem changes in the area. Although the Mediterranean population represents less than 10% of the global population, catch levels in this area are relatively high and comparable with larger ones, such as the North Atlantic.

For future research studies, the team will focus on assessing the physiological and toxic effects of microplastics on swordfish and other species. The researchers also want to further investigate the transfer of microplastics through the food chain and develop mitigation strategies to reduce plastic pollution, while assessing their long-term effectiveness.