PosterPDF Available

Spatiotemporal Analysis of Illuminated Boats at Night

Authors:

Abstract

This poster documents the analysis of point detections of lighted boats off the Pacific Coast of the United States. The patterns observed in the 2016-2017 period are consistent with the boats being part of the light-induced squid fishery. We show variation in the distribution of boats through the year and in response to the weekend closure of the squid fishery. The boat distributions also show the effectiveness of established Marine Protected Areas in excluding this fishery from protected zones.
Spatiotemporal Analysis of Illuminated
Boats at Night
This project began with downloading individual tabular files produced by NOAA (Elvidge et al.
2015). The available data ranged from July 2016 to December 2017. These files contained
individual entries for potential boats, including location and associated brightness. These files were
compiled into one spreadsheet which was brought into ArcGIS Pro. We georeferenced the file in
ArcGIS Pro, resulting in a shapefile of point data. Datasets were then assigned to analysis groups
including seasons, days of the week, and weeknight/weekend. We ran point density analyses on
these groups to view the shifting spatial trends across different temporal scales. The point density
analysis used radiance as a factor, giving more weight to points with brighter values. Using the
output of the point density analysis for weeknight/weekend, we also created a raster file for the
average difference in radiance between weeknights and weekends. The point data was also used to
create space time cubes, which aggregates points based on location and time, showing some of the
temporal and spatial trends in one graphic.
Photos of squid boats fishing south of Anacapa (Channel
Islands). Bright lights used to lure squid produce high
levels of light pollution.
Photos: Ben Banet
Eliza Gutierrez-Dewar, Christopher D. Elvidge, Travis Longcore
Fall 2017 – Spring 2018
Elvidge, C. D., M. Zhizhin, K. Baugh, and F.-C. Hsu. 2015. Automatic boat identification system for VIIRS low light
imaging data. Remote Sensing 7:3020–3036.
Key Findings:
Channel Islands National Park and other islands are centers of squid fishing, with
activity close to and inside Marine Protected Areas.
Bright boat activity decreases visibly from weeknight to weekend.
The VIIRS satellite and NOAA algorithm pick up non-squid boat activity as seen
through consistent shipping routes from ports (i.e. Long Beach).
The presence of bright boats in common squid fishing locations on weekends strongly
indicates boats in violation of fishing regulation.
There are temporal trends in radiance density from season to season and week to week,
but perhaps not a large enough temporal scale to categorize these trends.
Average Weeknight vs. Weekend Comparison of Boat Brightness: Average weeknight radiance
and average weekend radiance, focused on the Channel Islands and showing activity out of
Long Beach, which persists on weekends.
(Left) Potential Boat Locations by Radiance: The complete dataset derived from tables downloaded from NOAAs
website containing over 28,000 points. (Right) Radiance by Season Surrounding Channel Islands: The average
nightly radiance by season surrounding the Channel Islands.
July 2016
December 2017
one cube =
one month {
one square =
100 km x 100 km
Space Time Cubes
Light pollution poses a threat to biological resources in
national parks and protected areas, including offshore
areas. One source of light pollution offshore are bright
lights used to attract squid to the surface to capture.
Little data is publicly available on squid boat
locations, so there has yet to be any exploration on the
ecological effects of the lights used on the boats. This
project uses nighttime upward radiance data measured
by the satellite based VIIRS day/night band to track
locations of squid boats based on the bright lights they
use to lure squid during fishing. This data was
processed using an algorithm created by the National
Oceanic and Atmospheric Administration (NOAA) to
filter out interference with the satellite, identify
potential point locations of boats, and record their brightness. We used these points and their
associated values to analyze the spatial and temporal trends of brightly illuminated boats off the
California Coast, specifically focusing on Channel Islands National Park. The temporal analysis
reveals shifts in fishing locations between seasons, on a daily level, and from weeknights to
weekends when take of squid is not permitted. The analysis provides new data that can be used to
analyze compliance with fishing guidelines, as well as a first step to assess the effects of light
pollution on sensitive species in surrounding areas.
Overall Activity Around the Channel
Islands: A map of the average
nightly radiance from July 2016 to
December 2017. Marine Protected
Areas included for reference of
activity near protected areas.
Change in Average Nightly Radiance from Weekend to Weeknight: The difference between
brightness-weighted boat density on weeknights and weekends. Areas red show where activity
increases significantly from weekend to weeknight.
Radiance Through Space Time Cubes: A map showing the density of bright lights along the coast by month.
Stacked bars are made of up of cubes which aggregate one month of data in a 100 sq. km area.
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