Large-scale removal of discarded fishing gear and other plastic debris from the waters of Northwestern Hawaii meaningfully reduced entanglement rates of endangered Hawaiian monk seals, according to a new study. The findings, which are drawn from more than four decades of data, offer promising evidence that marine debris cleanup programs are successful and that reducing plastic inputs and scaling up removal efforts could maximize conservation outcomes across marine ecosystems worldwide. Plastic pollution severely threatens marine ecosystems, with derelict fishing gear being particularly harmful. Since the 1970s, abandoned, lost, or otherwise discarded plastic fishing gear has become widespread, continuing to trap and kill marine life even after being lost or discarded. For example, despite being remote and protected within the Papahānaumokuākea Marine National Monument, the Northwestern Hawaiian Islands are far from pristine due to the ever-present accumulation of plastic marine debris, which includes over 50 metric tons of abandoned fishing gear annually. Entanglement in this debris represents a significant threat to the region's population of endangered Hawaiian monk seals – one of the rarest pinnipeds in the world. To mitigate this harm, many cleanup efforts have been established to remove plastic debris from marine environments worldwide; in the Northwestern Hawaiian Islands, these have been ongoing since the 1980s. However, evaluation of the efficacy of these cleanup initiatives and their associated ecosystem and conservation benefits has been lacking. Jason Baker and colleagues analyzed more than 40 years of Hawaiian monk seal debris entanglement records, detailed monk seal monitoring data, and spatial and temporal data on plastic debris removal and found that large-scale cleanup efforts significantly reduced entanglement risks. Baker et al. discovered that the effectiveness of such programs is influenced by the initial entanglement rates, the amount of debris removed, and the timing of removal efforts. Locations like Lisianski Island, which had the largest baseline amounts of plastic debris and entanglement risks, saw the greatest impact from cleanup efforts. According to the authors, the observed reduction in monk seal entanglement is a proxy for broader ecological benefits, suggesting that other species and ecosystem functions also benefit from debris removal. Although the findings underscore the benefits of marine plastic removal, Baker et al. argue that preventing plastic pollution at its source, particularly from regulated and illegal fisheries, is a more effective long-term solution than merely mitigating damage after it occurs.
Thea Johanos, a study co-author, has worked for the monk seal program since the early 1980s and is largely the architect of the field data collection protocols that have been used for decades, notes Jason Baker.
