Catsharks shift to plastic substrates for egg-laying in an increasingly degraded Mediterranean

The Institut de Ciències del Mar (ICM-CSIC), in collaboration with the University of Valencia (UV), the University of Barcelona (UB), and the Catsharks Association, has discovered that the small-spotted catshark (Scyliorhinus canicula), a species native to the Mediterranean with distinctive small spots, is increasingly using plastic waste—particularly ghost fishing nets—as a substrate for laying its eggs. The details of this behaviour, especially in areas where natural biological substrates have become scarce, are documented in a recent study published in the journal Science of the Total Environment.

This is the first study to document this behavioural shift in small-spotted catsharks, highlighting the concerning impact of plastic pollution and the degradation of marine habitats. 

“The implications of this change could be profound for the long-term survival of small-spotted catsharks,” explains Blanca Figuerola, researcher at ICM-CSIC and member of the Medrecover group.

As plastic pollution increases and habitat-forming species decrease, small-spotted catsharks rely more on artificial materials. While the full impact of this change is not yet fully understood, researchers warn that it could affect the species’ survival, fitness, and distribution. “At first glance, plastics might seem like a good place for embryos to develop, but these artificial substrates do not offer the same benefits as habitat-forming species, which provide shelter and food for both small-spotted catsharks and their preys,” notes Figuerola.

UB researcher Anna Sánchez-Vidal adds: 

“Our research suggests that environmental pressures, along with the growing presence of plastics in the oceans, are pushing some species to adapt in unexpected ways. This is a clear example of how human-induced changes are impacting marine life.”

The study also reveals that small-spotted catsharks prefer to lay their eggs on biological substrates such as hydrozoans and sponges in shallow waters. However, in deeper areas, they increasingly resort to tube-dwelling polychaetes and plastic waste as alternatives. 

“This trend is particularly noticeable on the continental slope, where natural habitats are severely affected by human activities such as fishing,” explains Claudio Barría, co-author of the study and member of Catsharks.

Given this scenario, the scientific team warns of the long-term consequences this behaviour could have. Although the immediate effects on small-spotted catshark populations are not yet fully understood, there is concern that eggs attached to plastic waste could be carried to areas with conditions unsuitable for embryo development. David Ruiz, principal co-author of the study and scientist at UV, cautions: 

“If the juveniles survive, this could lead to increased competition for resources and displacement of other species.”

This team had already anticipated that plastic waste could be used by small-spotted catsharks for egg-laying in a previous study. Since there were no prior investigations analysing this behaviour or the factors influencing substrate preference for egg-laying, the scientists decided to explore the topic further.

Overall, the study underscores the urgent need to preserve biological habitats and tackle plastic pollution at its source, especially in vulnerable areas such as the Mediterranean. “Without immediate action, we could see more species adopting similar behaviours, which could have potentially devastating consequences for marine ecosystems,” warns the research team.