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Benthic cover derived from 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 Hawaiian Islands from missions in 2018 and 2021

Metadata Updated: March 16, 2024

The benthic cover and fishing-net related data described in this dataset are derived from the GIS analysis of benthic orthophotos. The source imagery was collected by snorkelers using a Structure from Motion (SfM) approach during swim surveys in search of derelict fishing nets. Surveys were conducted by the NOAA Fisheries, Ecosystem Sciences Division (ESD) at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands (NWHI). Initial surveys occurred from September 24 - October 3, 2018 during an ESD-led marine debris removal mission aboard the NOAA Ship Oscar Elton Sette, and follow-up surveys occurred from September 13-14, 2021 on a joint mission with non-profit organization Papahanaumokuakea Marine Debris Project aboard the M/V IMUA.

During the 2018 mission, fishing nets were located during swim surveys and selected for SfM if the net was interacting with coral or hard substrate, the depth of the net was within ~1 - 4 m of the surface, and the area of the net fit within the 9 sq. meter SfM survey plot. During the SfM survey, a permanent 3 x 3 m plot was established around the center of the fishing net, and the net was photographed using a back and forth swim pattern ("before" photos) for later processing using a SfM approach. The net was then removed, the volume of net removed was estimated and recorded, and the same area was photographed again in the same way ("after" photos). A nearby (>50 m distant) paired control site was also photographed using the same method ("control" photos).

During the 2021 mission, we attempted to relocate all paired sites where "after" and "control" photos were taken in 2018 and if found, we reimaged the permanent 3 x 3m plot using the same SfM approach. Only a subset of 2018 sites were successfully relocated in 2021 (12 "after" sites, 8 "control" sites), and five new nearby "control" sites had to be established to fulfill our paired study design.

The photographs from each site were processed using Agisoft Metashape software to generate orthomosaic images that were analyzed in ArcGIS for benthic cover using a random point approach. In 2018, the number of points at net-impacted sites were constrained to the net coverage area and were scaled to the net area to ensure an equal point density among replicate net-impact sites. The same number of points were randomly assigned to the 3 by 3 m paired control site. In 2021, twenty random points were assigned to each orthophoto within the 2018 net polygon. Each point was classified into one of seven benthic categories: turf algae, macroalgae, sand, bare substrate, Porites compressa, sponge, or crustose coralline algae (CCA). In 2021, turf and macroalgae categories were merged into a single algae category and all coral species were assigned the coral category. The annotated points for each site were converted to percent cover for each benthic category. Fishing net size (sq. m) and degree of fouling were also calculated from the initial "before" orthophotos. Analyses were conducted to compare the benthic composition of net sites to control sites and to determine if fouling or net size contributed to these differences.

Access & Use Information

License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

Downloads & Resources

Dates

Metadata Date February 29, 2024
Metadata Created Date September 2, 2022
Metadata Updated Date March 16, 2024
Reference Date(s) March 30, 2020 (creation), April 20, 2022 (revision), 2022 (publication)
Frequency Of Update notPlanned

Metadata Source

Harvested from NMFS PIFSC

Additional Metadata

Resource Type Dataset
Metadata Date February 29, 2024
Metadata Created Date September 2, 2022
Metadata Updated Date March 16, 2024
Reference Date(s) March 30, 2020 (creation), April 20, 2022 (revision), 2022 (publication)
Responsible Party (Point of Contact, Custodian)
Contact Email
Guid gov.noaa.nmfs.inport:59172
Access Constraints Cite As: Pacific Islands Fisheries Science Center, [Date of Access]: Benthic cover derived from 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 Hawaiian Islands from missions in 2018 and 2021 [Data Date Range], https://www.fisheries.noaa.gov/inport/item/59172., Use Constraints: These marine debris survey data act as a proxy for area surveyed and have not been screened for accuracy based on environmental conditions or GPS accuracy. NOAA can not be held liable for use of these data in a manner other than for perusal of preliminary marine debris data for scientific research on coral reef ecosystems. When using this data, please credit the NOAA Fisheries, Ecosystem Sciences Division. Suggested citation: Pacific Islands Fisheries Science Center, 2022: Benthic cover derived from 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 Hawaiian Islands from missions in 2018 and 2021, https://www.fisheries.noaa.gov/inport/item/59172., Distribution Liability: While every effort has been made to ensure that these data are accurate and reliable within the limits of the current state of the art, NOAA cannot assume liability for any damages caused by errors or omissions in the data, nor as a result of the failure of the data to function on a particular system. NOAA makes no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty.
Bbox East Long -175.7880926
Bbox North Lat 27.89404863
Bbox South Lat 27.82745706
Bbox West Long -175.8211335
Coupled Resource
Frequency Of Update notPlanned
Harvest Object Id e7e244c5-bafa-40aa-b030-3c721cfb0be8
Harvest Source Id c0beac72-5f43-4455-8c33-1b345fbc2dfe
Harvest Source Title NMFS PIFSC
Licence NOAA provides no warranty, nor accepts any liability occurring from any incomplete, incorrect, or misleading data, or from any incorrect, incomplete, or misleading use of the data. It is the responsibility of the user to determine whether or not the data is suitable for the intended purpose.
Lineage Marine debris removal has been conducted by the Pacific Islands Fisheries Science Center's Ecosystem Sciences Division at the atolls, reefs and islands of Northwestern Hawaiian Islands since 1996. Standardized data collection has been implemented since 1999. Swim surveys are typically used in the comparatively high-relief and patchy lagoonal reef habitats. Survey areas are chosen based on regional reef morphology and past accumulation records. At each Structure from Motion (SfM) data collection site, a permanent 3 x 3 m plot was established around the center of the entangled fishing net in 2018. SfM images were taken underwater before and after net removal. The same method was also used at the paired control sites. Sites were relocated and reimaged in 2021. We used Agisoft Metashape software to generate orthomosaic images of each site from the photographs captured. Using 2018 orthomosaics, the planar net area (square meters) was calculated by delineating the net boundary in ArcGIS. In addition, the degree of fouling was estimated for each net based on the percent of the net surface area that was covered by fouling organisms. Using the orthomosaics from the "after" (impact) and "control" sites, benthic cover was assessed using a random point approach within the boundary of the net and at the paired control site. Each point was classified into an appropriate benthic category. The annotated points for each site were converted to percent cover. For both years, analyses were conducted to compare the benthic composition of net sites to control sites. In 2018, analyses were carried out to determine if fouling or net size contributed to these differences, and in 2021, analyses were conducted to track changes in benthic composition at net impacted sites three years after removal.
Metadata Language eng
Metadata Type geospatial
Old Spatial {"type": "Polygon", "coordinates": [[[-175.8211335, 27.82745706], [-175.7880926, 27.82745706], [-175.7880926, 27.89404863], [-175.8211335, 27.89404863], [-175.8211335, 27.82745706]]]}
Progress completed
Spatial Data Service Type
Spatial Reference System
Spatial Harvester True
Temporal Extent Begin 2018-09-24
Temporal Extent End 2018-10-03

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