Four decades of Hawaiian monk seal entanglement data reveal the benefits of plastic debris removal.

Abandoned, lost, or otherwise discarded fishing gear causes harm to marine species and ecosystems. To mitigate the destruction wrought by this ocean plastic debris, various cleanup programs have been established, though to our knowledge the benefits of such efforts to marine species and ecosystems have not yet been empirically demonstrated. We examined more than 40 years of Hawaiian monk seal marine debris entanglement records before and after large-scale marine debris removal efforts were initiated in the Northwestern Hawaiian Islands, demonstrating a substantial reduction in entanglement rates where debris removal effort was most concentrated. Large-scale and sustained removal of abandoned, lost, or otherwise discarded fishing gear meaningfully benefits marine ecosystems and has the potential to be transformational in restoration efforts.

Coral cover remains suppressed three years after derelict net removal in a remote shallow water coral reef ecosystem.

The uninhabited Northwestern Hawaiian Islands (NWHI) contain 70 % of the shallow water coral reefs in the United States. An estimated 52 metric tons of derelict fishing nets accumulate here annually, becoming entangled in the reef structure and reducing coral cover. Here, we investigated the longevity of derelict net impacts on coral reef communities three years after net removal at Pearl and Hermes Atoll. Structure-from-Motion technology was used to resurvey net impact and control sites to determine whether coral cover rebounded at impact sites over time. Our results showed significantly lower coral cover at impact sites. Much of the bare substrate immediately exposed after net removal was also colonized by algae -not reef calcifiers. Continued monitoring of these sites will add clarity to the lasting nature of derelict nets on reefs, and supplementing net removal efforts with active restoration activities may assist in restoring the ecosystem function of impacted sites faster.

Movement and retention of derelict fishing nets in Northwestern Hawaiian Island reefs.

Derelict fishing nets pose hazards to marine systems as they travel through the ocean or become ensnared on coral reefs. Understanding of the movement of nets within shallow atolls can help to optimize operations to protect these shallow reefs. In 2018, six derelict fishing nets at Manawai (Pearl and Hermes Reef) in the Northwestern Hawaiian Islands were tagged with satellite-transmitting buoys and tracked for three years. This study reveals that nets that enter the atoll from the northeast travel southwest towards the center of the atoll, and nets in the center can remain ensnared on the same reef for at least three years. This study shows that satellite buoys are a successful approach to tracking derelict net movement, and can inform future debris removal missions.

Successful application of a novel technique to quantify negative impacts of derelict fishing nets on Northwestern Hawaiian Island reefs.

The remote and uninhabited Northwestern Hawaiian Islands (NWHI) contain 70% of the shallow water coral reefs in the United States and are regularly exposed to derelict fishing nets. These nets snag on the shallow reefs, damaging or killing benthic communities. However, no data exist to quantify this impact. Here we use a novel application of photogrammetry, Structure-from-Motion (SfM), to calculate benthic cover from mosaic images at net-impact and control sites. Net-impact sites had significantly higher cover of bare substrate, sand, and crustose coralline algae and significantly lower coral and macroalgae cover compared to control sites. These differences were unrelated to net size and fouling. Our study demonstrates the utility of using SfM to efficiently quantify impacts of derelict fishing nets. Revisiting these sites will be essential to document how the reef recovers to further our understanding of the lasting impacts of derelict fishing nets on coral reef habitats.