Currently, the California horn shark is listed as “data deficient” by the International Union for … [+]
Marine debris continues to be a pressing environmental issue worldwide, particularly plastic debris, which often comes from terrestrial sources and can break down into microplastics. While many types of litter contribute to marine pollution, cigarette butts are the most common form of plastic waste, and they pose unique threats to ocean ecosystems. These small but dangerous items, along with other forms of plastic, can contain harmful chemicals such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), which can have toxic effects on marine life. Species such as marine mammals, turtles and fish are known to ingest microplastics, which can lead to internal injuries, poisoning and even death. In addition to ingestion, large plastic items, including fishing gear and other debris, can entangle sea creatures, causing injury or even death. The consequences of plastic pollution are far-reaching, affecting both adult marine animals and vulnerable juveniles.
In Southern California, the city of Redondo Beach is home to a popular boardwalk known as the Esplanade, which stretches along the coastline and attracts a large number of visitors each year. This foot traffic results in significant accumulation of litter on the roads, much of which eventually washes into the ocean during rainfall or other extreme weather events. Despite regular street cleaning by the city, the constant flow of litter is difficult to manage and the impact on marine ecosystems remains a concern. While the Los Angeles County Department of Public Health monitors bacteria levels in beach waters, it does not track physical debris on the Esplanade, highlighting a gap in environmental monitoring. Given the potential for marine debris to enter the ocean and harm marine species, Dr. Evelyn Alvarez of California State University says it is essential to better understand how waste from this area can affect coastal ecosystems.
One species that can be significantly affected by marine debris is the California horn shark (Heterodontus francisci), a small, bottom-dwelling shark found along the Pacific coast. These sharks are known to ‘nest’ in crevices within rocky environments, laying spiral-shaped eggs that are vulnerable to environmental threats. Small horn sharks seek refuge on rocks, sand or algae, all of which can hold marine debris. The threat of entanglement or ingestion of waste materials is high—and with the species’ natural habitats threatened by both pollution and human activity on the rise, Alvarez believes it is essential to better understand the impacts of waste on horn sharks and behavior. their reproductive. While some studies have suggested that rising ocean temperatures due to climate change may also affect the energy expenditure and behavior of horn sharks, it remains unclear how marine debris specifically interferes with their habitat use.
In addition to environmental stressors such as habitat degradation and climate change, horn sharks face … [+]
Currently, the California horn shark is listed as “data deficient” by the International Union for Conservation of Nature, meaning there is not enough information to accurately assess its conservation status. In addition to environmental stressors such as habitat degradation and climate change, horn sharks face the threat of overexploitation, particularly in Mexico. This makes it even more urgent to collect more data on the species and investigate how factors such as marine debris may be contributing to its decline. An innovative tool that can help collect data is the Marine Debris Tracker, a smartphone app that allows citizen scientists to geotag and classify debris in their communities, providing valuable data on the types and amounts of debris found in specific area.
From June to July 2021, a group of citizen scientists used the marine debris tracker to monitor debris on the Esplanade at Redondo Beach. During the study, 1,556 wastes were recorded, with the dominant category being plastic (52%), followed by paper and wood (39%). In particular, cigarette butts and plastic food wrappers were the most frequently encountered waste, underscoring the prevalence of single-use plastics in the area. The collected data was geotagged and then uploaded to an open source database where it could be analyzed for trends and spatial patterns. Using tools like ArcGIS, the researchers created heat maps to visualize debris hotspots and examine how these areas might overlap with sightings of marine species, including those of the California horn shark.
Although the study did not observe many horn sharks during the debris tracking sessions, the data collected shows where marine debris is accumulating and how it may intersect with critical shark habitats. For example, some hot spots for egg guts were found near areas with high concentrations of waste, while others were located in areas without waste. This suggests that while marine debris may pose a risk to horn shark ‘nesting’, the full extent of its impact remains unknown and, Alvarez argues, requires further investigation.
Moving forward, Alvarez stresses that it is crucial to address the issue of cigarette butt pollution on the Esplanade, especially given its potential to introduce microplastics into the ocean. Simple interventions such as increasing the number of trash cans, providing designated cigarette butt disposal stations, and increasing public awareness through educational campaigns can help mitigate the impact of this pollution. She hopes her work will be the basis for ongoing monitoring and investigation of how marine debris affects local coastal ecosystems and species such as the California tip shark.
