Structure from motion images collected during marine debris surveys at coral reef sites entangled with derelict fishing nets at Pearl and Hermes Atoll in the Northwestern Hawaii...

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Geographic extent of marine debris structure from motion surveys conducted at Pearl and Hermes Atoll.

Time frame of marine debris Structure from Motion (SfM) surveys conducted at Pearl and Hermes Atoll during the 2018 mission.

Time frame of marine debris Structure from Motion (SfM) surveys at Pearl and Hermes Atoll during the 2021 mission.

Metadata for benthic imagery collected using a Structure from Motion (SfM) approach during in-water marine debris swim surveys. Surveys were conducted by the NOAA Fisheries Ecosystem Sciences Division at net impact sites at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands in 2021, three years post net-removal.

Benthic imagery collected using a Structure from Motion (SfM) approach during in-water marine debris swim surveys. Surveys were conducted by the NOAA Fisheries Ecosystem Sciences Division at net-impact sites 3 years after derelict fishing nets were removed at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands in 2021. Photos are organized by site in the "Impact Images" folder. See Impact Images metadata file (SfM_MarineDebris_ImpactImagesMetadata_PHR_2021.csv) for site information.

Metadata for benthic imagery collected at using a Structure from Motion (SfM) approach during in-water marine debris swim surveys. Surveys were conducted by the NOAA Fisheries Ecosystem Sciences Division at control coral reef sites at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands in 2021.

Benthic imagery collected using a Structure from Motion (SfM) approach during in-water marine debris swim surveys at "control sites" near fishing net removal sites. Surveys were conducted by the NOAA Fisheries Ecosystem Sciences Division at coral reef sites entangled with derelict fishing nets at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands in 2021 Photos are organized by site in the "Control Images" folder. See Control Images metadata file (SfM_MarineDebris_ControlImagesMetadata_PHR_2021.csv) for site information.

Metadata for benthic imagery collected using a Structure from Motion (SfM) approach during in-water marine debris swim surveys "after" the fishing net was removed from the reef. Surveys were conducted by the NOAA Fisheries Ecosystem Sciences Division at coral reef sites entangled with derelict fishing nets at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands in 2018.

Benthic imagery collected using a Structure from Motion (SfM) approach during in-water marine debris swim surveys "after" the fishing net was removed from the reef. Surveys were conducted by the NOAA Fisheries Ecosystem Sciences Division at coral reef sites entangled with derelict fishing nets at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands in 2018. Photos are organized by site in the "After Images" folder. See After Images metadata file for site information.

Metadata for benthic imagery collected using a Structure from Motion (SfM) approach during in-water marine debris swim surveys "before" the fishing net was removed from the reef. Surveys were conducted by the NOAA Fisheries Ecosystem Sciences Division at coral reef sites entangled with derelict fishing nets at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands in 2018.

Benthic imagery collected using a Structure from Motion (SfM) approach during in-water marine debris swim surveys "before" the fishing net was removed from the reef. Surveys were conducted by the NOAA Fisheries Ecosystem Sciences Division at coral reef sites entangled with derelict fishing nets at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands in 2018. Photos are organized by site in the "Before Images" folder. See Before Images metadata file for site information.

Metadata for benthic imagery collected using a Structure from Motion (SfM) approach during in-water marine debris swim surveys at control sites near fishing net removal sites. Surveys were conducted by the NOAA Fisheries Ecosystem Sciences Division at coral reef sites entangled with derelict fishing nets at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands in 2018.

Benthic imagery collected using a Structure from Motion (SfM) approach during in-water marine debris swim surveys at "control sites" near fishing net removal sites. Surveys were conducted by the NOAA Fisheries Ecosystem Sciences Division at coral reef sites entangled with derelict fishing nets at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands in 2018. Photos are organized by site in the "Control Images" folder. See Control Images metadata file for site information.

Information about marine debris research and removal efforts in Northwestern Hawaiian Islands by Pacific Islands Fisheries Science Center

Story map about marine debris removal efforts in 2018 with images and captions describing work that was conducted.

The structural complexity of coral reefs plays a major role in the biodiversity, productivity, and overall functionality of reef ecosystems. Conventional metrics with 2-dimensional properties are inadequate for characterization of reef structural complexity. A 3-dimensional (3D) approach can better quantify topography, rugosity and other structural characteristics that play an important role in the ecology of coral reef communities. Structure from Motion (SfM) is an emerging low-cost photogrammetric method for high-resolution 3D topographic reconstruction. This study utilized SfM 3D reconstruction software tools to create textured mesh models of a reef at French Frigate Shoals, an atoll in the Northwestern Hawaiian Islands. The reconstructed orthophoto and digital elevation model were then integrated with geospatial software in order to quantify metrics pertaining to 3D complexity. The resulting data provided high-resolution physical properties of coral colonies that were then combined with live cover to accurately characterize the reef as a living structure. The 3D reconstruction of reef structure and complexity can be integrated with other physiological and ecological parameters in future research to develop reliable ecosystem models and improve capacity to monitor changes in the health and function of coral reef ecosystems.

Large amounts of derelict fishing gear accumulate and cause damage to shallow coral reefs of the Northwestern Hawaiian Islands (NWHI). To facilitate maintenance of reefs cleaned during 1996–2005 removal efforts, we identify likely high-density debris areas by assessing reef characteristics (depth, benthic habitat type, and energy regime) that influence sub-regional debris accumulation. Previously cleaned backreef and lagoonal reefs at two NWHI locations were resurveyed for accumulated debris using two survey methods. Accumulated debris densities and weights were found to be greater in lagoonal reef areas. Sample weight-based debris densities are extrapolated to similar habitats throughout the NWHI using a spatial ‘net habitat’ dataset created by generalizing IKONOS satellite derivatives for depth and habitat classification. Prediction accuracy for this dataset is tested using historical debris point data. Annual NWHI debris accumulation is estimated to be 52.0 metric tonnes. For planning purposes, individual NWHI atolls/reefs are allotted a proportion of this total.

NOAA technical memorandum NMFS PIFSC

This document provides detailed procedures for collecting and processing imagery using Structure-from-Motion techniques developed by Ecosystem Sciences Division (ESD) in collaboration with Scripps Institution of Oceanography and the University of Hawaii at Hilo. These procedures are designed to efficiently generate coral demographic and benthic community metrics across the broad spatial scale of the Pacific Rapid Assessment and Monitoring Program. This pipeline consists of four key steps: (1) Image collection by SCUBA divers, (2) Data management, post-processing, and QC, (3) Generating 3-D models and 2-D orthophotos in Agisoft Metashape, and (4) Extracting demographic data in ArcMap. This SOP is the result of comprehensive testing of different camera systems, collection techniques, and software. While the following procedures are designed to meet ESD needs, we primarily use commercially available cameras and software, making these methods adaptable based on programmatic capacity and needs.

Marine Pollution Bulletin is concerned with the rational use of maritime and marine resources in estuaries, the seas and oceans, as well as with documenting marine pollution and introducing new forms of measurement and analysis. A wide range of topics are discussed as news, comment, reviews and research reports, not only on effluent disposal and pollution control, but also on the management, economic aspects and protection of the marine environment in general.

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.

Booklet summarizing marine debris removal and research efforts in the Northwestern Hawaiian Islands in 2018 by Pacific Islands Fisheries Science Center

The Papahānaumokuākea Marine National Monument (PMNM) includes all of the Northwestern Hawaiian Islands (NWHI) and encompasses 1,508,870 km2 (582,578 mi2) of the Pacific Ocean. Within the boundaries of the monument lie coral reefs, atolls, shoals, and seamounts, including 70% of all shallow-water coral reef habitats (<200 m) in the United States. The PMNM was named a World Heritage site in 2010 by the 34th session of the World Heritage Committee in recognition of its cultural and natural values (World Heritage Committee 2010). The extensive coral reefs found in the PMNM are home to more than 7,000 marine species, one-quarter of which are found only in the Hawaiian Archipelago (PMNM Webmaster 2019). Many of the islands and shallow-water environments in the PMNM are important habitats for rare species, such as the green sea turtle (listed as threatened under the U.S. Endangered Species Act) and Hawaiian monk seal (listed as endangered under the International Union for Conservation of Nature Red List and as endangered under the U.S. Endangered Species Act). The PMNM contains only 15 km2 of emergent land, but 14 million seabirds representing 22 species use this land as breeding and nesting grounds (PMNM Webmaster 2019). Land areas provide a home for four species of birds found nowhere else in the world, including one of the world’s most endangered ducks—the Laysan duck (PMNM Webmaster 2019).

This step describes the initial site survey in 2018. The swim survey method was developed for surveys in lagoonal, reticulated reef areas. During swim surveys, two or more divers swim across reefs to search for debris while being directed by personnel in small boats to follow pre-planned routes and are coordinated for maximum visual area covered. Survey areas and routes are chosen based on regional reef morphology and past accumulation records. Based on this net prevalence information, five spatial zones were defined. A minimum of three nets in each of the five zones were surveyed using a Structure from Motion (SfM) approach if the net also fit within the additional selection criteria (≥ 75% hard substrate and within ~1-4 m depths).

At each impact site established in 2018, a permanent 3 x 3 m plot was established around the center of the net by securing zip ties to the reef at each corner of the plot and taking a GPS location at the center. Depth measurements were recorded at each corner of the plot. Only nets that fit within the plot were selected for this study to allow rapid data collection of the Structure from Motion (SfM) imagery. In 2018, SfM images were taken underwater before net removal to record the extent of the reef covered by net.

In both years, images were collected by snorkeling in a cross-hatch pattern over the plot at 1 m above the substrate to achieve image overlap of at least 60% (~580 images per site). JPEG images were collected using a Nikon SL2 digital camera in an underwater housing.

This step only occurred in 2018 when the net impact sites were established.

Fishing nets were disentangled from the reef by hand or carefully cut using knives to free the net from the benthos in order to minimize impacts to the underlying habitat.

A second series of "after" images were collected in the same manner as the first series of "before" images (i.e., before the fishing net was removed from the reef).

In 2018, a paired control site was selected for each net impacted site within the same zone (≥50 m away from net-impact site for independence). The same photogrammetry method was also used at the paired control sites (3 x 3 m plot).

In 2021, each paired control site was relocated and reimaged. When the old control site could not be found, a new paired control site was established using the same criteria and reimaged.