Uncovering the Effects of the Southwest Monsoon on Fishing Activity in the Indian Ocean with VIIRS Boat Detection Data - Juniper Publishers

 Oceanography & Fisheries - Juniper Publishers

Abstract

In 2015, the Earth Observation Group (EOG) created the VIIRS Boat Detection (VBD) product, which is now employed by various fishery agencies to oversee fishing activities and ensure compliance with closures. VBD data offer real-time insights into the movements of fishing vessels, aiding in the detection of illegal fishing practices within restricted areas and intrusions into exclusive economic zones (EEZs). The Indian Ocean, a critical hub for global fisheries contributes over 14% of the world’s wild-caught fish production. The fishing grounds in the Indian Ocean region are amorphous clusters, which depict cyclical patterns in the number of boat detections, corresponding to the monsoon season from June to September, and fishing restrictions imposed by the government. An exponential increase in boat detections was also observed since October 2016. Contrarily, the vessels detected at the anchorage are predominantly shipping vessels, and their temporal pattern shows less pronounced cyclical variation compared to fishing grounds. Employing the ‘Pelt’ algorithm to detect change points in monthly boat counts for the anchorage from 2012 to 2022 revealed a significant change in the average number of boat detections per month in October 2018. This study highlights the utility of VIIRS boat detection data in monitoring fishing activity and its response to seasonal and regulatory influences in the Indian Ocean, ultimately contributing to more effective fisheries management and conservation efforts.

Keywords: VBD; Fishing grounds; Anchorages; Monsoon; Indian Ocean

Abbreviations: EOG: Earth Observation Group; VBD: VIIRS Boat Detection; EEZs: Exclusive Economic Zones; DMSP: Defense Meteorological Satellite Program; OLS: Operational Linescan System; VIIRS: Visible Infrared Imaging Radiometer Suite; JPSS: Joint Polar Satellite System; USAID: United States Agency for International Development; VMS: Vessel Monitoring System; AIS: Automatic Identification System; VNF: VIIRS Night fire

Introduction

Since the 1970s, it has been established that fishing boats emitting strong light can be identified using nighttime visible low-light imaging data obtained by polar-orbiting meteorological sensors [1]. Among the sensors capable of low-light imaging, two notable ones are the U.S. Air Force Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) and the NASA/NOAA Visible Infrared Imaging Radiometer Suite (VIIRS). These sensors employ light enhancement techniques to enable the detection of moonlit clouds during the night, meeting the requirements of meteorologists for both daytime and nighttime visible and thermal cloud imagery.

The OLS digital archive spans from 1992 to the present, offering relatively coarse resolution (2.7km ground sample distance) global data. On the other hand, the VIIRS sensor, in operation since 2012, provides significant advancements in low-light imaging. It boasts finer pixel resolution (742m × 742m) and in-flight calibration to radiance units [2]. In 2015, the Earth Observation Group (EOG) developed the VIIRS boat detection (VBD) algorithm with support from NOAA’s Joint Polar Satellite System (JPSS) with aid from the United States Agency for International Development (USAID) [3]. VBD data are generated in near real-time, with nightly records available for Southeast Asia since April 2012, and globally from 2017 onwards. In addition to the nightly data, EOG also produces monthly and annual summary grids.

Numerous fishery agencies, including those in the Philippines, Indonesia, Thailand, Japan, and South Korea, rely on VIIRS boat detection (VBD) data for monitoring fishing activities and identifying vessels operating in restricted areas [4]. VBD provides valuable maritime domain awareness, especially when it comes to identifying locations of “dark” vessels which lack Vessel Monitoring System (VMS) or the Automatic Identification System (AIS) [5]. To delineate fishing grounds and assess usage patterns over time, the monthly and annual summary grids are very useful. Recently, a global long-term VBD cumulative detection grid, spanning 2012-2021 has been developed and the findings will be shared in this report.

Methods

Besides, the monthly and annual summary grids, all the nightly VBD data have been stored in a database designed for easy retrieval based on criteria specified by users. Each pixel in the VBD data is assigned a label based on its clarity and location, often referred to as quality flags or QF. To construct a multiyear cumulative detection grid, pixels labeled QF 1, 2, 3, 8, and 10, corresponding to strong boat detection, weak detection, blurry detection, recurring detection, weak and blurry detections have been selected [4,6].

The accumulations of these detections have been aggregated into a global grid with 15 arc-second grid cells, which are approximately half a kilometer on each side at the equator. These grids provide information on the number of detections, the count of valid VIIRS observations, and the average radiance for each grid cell. To account for differences in data availability over various time periods in Southeast Asia and other parts of the world, the percentage frequency of detection is calculated by dividing the number of detections by the count of valid observations. This normalization ensures a fair comparison between these regions.

Vector polygons of ‘fishing grounds’ and ‘anchorages’ were drawn on the percentage frequency VBD grid. The anchorages have definite shapes, like a square or rectangle, whereas fishing grounds are closer to those anchorages and structureless. Some of the fishing grounds also coincide with ‘upstream’ gas flare locations detected in the VIIRS Night fire (VNF) dataset which have been eliminated before extracting temporal profiles [6]. EOG has developed methods for extracting temporal profiles from the database for specific spatial features identified in the summary grids.

Results

The Indian Ocean hosts some of the world’s most significant fisheries, contributing to more than 14% of the global catch of wild-caught fish [6]. Fishery agencies have the potential to depend on VIIRS boat detection (VBD) data to enforce regulations and implement management measures effectively. VBD data can offer real-time insights into the actions of fishing vessels, including signs of unlawful fishing practices within restricted zones and intrusions into exclusive economic zones (EEZs) [7]. Figure 1 shows the percent frequency of VBD detection in the northern Indian Ocean. The fishing grounds show up as large light gray features. The fishing grounds in the Indian Ocean seems to be in amorphous clusters [8]. Although fishing grounds encompass the largest expanse with VBD detections, the percentage of detection for an individual half-kilometer grid cell within these fishing grounds is quite low, seldom surpassing 1%. However, there are concentrated groups of non-fishing VBD features, primarily located near the shoreline, which exhibit higher percentage frequencies of detection, typically ranging from 1% to 3%. These non-fishing features comprise anchorages, platforms, and aquaculture sites. Figure 2 shows the temporal profile of fishing ground seen in figure 1.

The equation of the exponential curve shown in Figure 2 is:

y = 4E −15e0.0009x

The temporal profile of the fishing ground clearly demonstrates a cyclical seasonal pattern and a steady increase of fishing activity since October 2016. The decline in VBD in the fishing grounds during the monsoons (June -September) is not simply the effects of cloud obscuration but aversion of the fishing boats to the inclement weather and rough seas. Besides, fishing communities cease their fishing operations in concordance with government regulations, which ban commercial fishing during the monsoons to allow breeding and restoration of fishing stock [9-11]. The monsoon is the spawning season for fish and the ban helps in replenishing the fish stock and protect the fishermen from the rough sea. It is interesting to see the differences in the temporal profiles of the fishing ground in Figure 2 and the anchorage in Figure 3. The boats detected from the largest anchorage (Figure 3) are shipping vessels - not fishing boats. The anchorage’s temporal profile indicates that shipping activities are not heavily impacted by the monsoon. The cyclical pattern, although apparent, is not as distinct as it is for the temporal profile of the fishing ground.

To identify potential variations in the average number of anchored boats, a kernel-based offline multiple change point detection algorithm known as ‘Pelt’ was employed, which stands for “Pruned Exact Linear Time” [12]. By applying the ‘Pelt’ algorithm to the time series data of monthly boat counts for the anchorage from 2012 to 2022, only one significant change in the average number of boats was detected. This change occurred in October 2018, where the average number of boats per month shifted from 66 to 111. The average line for 66 is shown in red, and the average line for 111 is shown in green.

Conclusion

At night, the ocean presents itself as an extensive, dark canvas where any form of illumination becomes easily detectable by the VIIRS day/night band. However, the VIIRS boat detection data, despite being generated on a nightly basis, do not provide any indication of these sharply defined structures. The true nature of these structures becomes apparent when we examine them over a longer timeframe, accumulating detections across multiple years. In the Indian Ocean, due to south-west monsoon we see seasonal variations in fishing grounds, but the anchorages do not indicate the same. Moreover, the ban on fishing activity during the monsoons also has a significant effect and thus a distinct cyclical pattern of detections are noticed for the fishing grounds. Also, an exponential growth of fishing activity was noticed since October 2016. As for the profile of the largest anchorage, a rise in the average number of fishing boats was noticed in October 2018. It will be interesting to compare and study fishing grounds around the world which show similar rhythms.

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Impact Long Term Winter Season 2017/2018 Over Indonesia Maritime Continent Area - Juniper Publishers

 Recent Advances in Petrochemical Science - Juniper Publishers

Opinion

The winter season 2017/2018 could be one of the unusual condition with increasing the winter storm activities over Northern Hemisphere to affect aerodrome closed for certain airports in big city of the United States of America and Canada in Northern America Continent, it could be over European Countries and North Asaian Continent. The freezing water Niagara for the first time during last 50 years could be additional condition from coolest than normal and it might longer than usual based upon public information and collecting the global climatic chart from National Climate Centers under coordination from the World Meteorological Organization. If the condition winter season 2017/2018 compared with previous condition especially in the 17 years or it could be more than that period, the winter season 2017/2018 could be worst condition and situation especially with winter storm occurrences over most northern hemisphere. Reversal condition over southern hemisphere with summer season with few day occurrences of the heat wave over Australia continent last January 2018.

To asses the weather and climatic over the earth's surface that weather and climate development came from uneven solar radiation (solar activities) received by the earth's surface, it meant that solar radiation could consider as the main subject to asses/study the global circulation over lower atmosphere of the earth. Where we could consider solar radiation to have closed relation with solar activities in term of the sunspot and solar flare to investigate how much solar radiation/energy emits from the center of the solar system. In this case, the sunsput number counted every month could be used as the quantity and quality sun radiation/energy with high number of sunspot to represented large sun radiation received by the earth surface to the universe of the earth - sun system. It could also be with small number of sunspot with respect with the time especially daily, weekly, monthly, seasonally up to yearly basis to be represent less of the sun radition received by the earth surface. From further assesment and study of the sunspot number has a relation with the weather and climate condition over the earth surface especially formation of the global air circulation both north- south between equator- north and south poles and east-west direction over the equator. High or maximum number of the sunspot on the monthly basis for 6-12 months duration could encourage global phenomena of the El Nino (warming sea surface temperature over equator east Pacific Ocean) and small or minimum number of the sunpot could encourage reversal El Nino in term of the La Nina. Both of the global phenomena would affect certain weather and climatic condition globally arising unusual weather and climatic pattern over the earth's surface. Based on the sunspot number on the monthly basis could be arranged in term of the sunspot cycle to represent from minimum number toward maximum as the peak sunspot number then to be going down toward minimum number. Now, there 24 sunspot cycles with one cycle having duration at about 11 years. It means every sunspot cycle has period between 10-12 years. At this period 2017/2018, sunspot cycle number 24 would be toward small number of minimum of the sunspot or minimum sun's radiation receved by the earth surface. Such that La Nina episode would active starting middle of the year 2016 up to beginning 2018. Where La Nina episode has large contribution in the developing equatorial wave of the so called Madden Julian Oscillation (MJO) which create intra seasonal weather and climatic condition over the tropical area especially over Indian Ocean Indonesia Maritime Continent and West Pacific Ocean. During MJO passing over the consecutive areas Indian Ocean- West Pacific Ocean, array of the large tower of cumulonimbus cloud would be active to support the tropical cyclone formation and other local storm. Beside the global perspective, there would be regional perspective phenomena coincide with Asian winter monsoon activities in terms of the cold surge to form the Borneo Vortex mostly over west Indonesia Maritime Continent. With having long period and cooler condition during winter season 2017/2018, the Borneo Vortex frequently forms during lack MJO activities or when MJO move eastward toward East Pacific and Atlantic Ocean.

By the frequent MJO episode of occurrence over Indonesia Maritime Continent as part the global perspective from the dynamical meteortology and oceanoanography, there was two tropical cyclones formation closer with the Java island namely tropical cyclones " Cempaka” and “Dahlia” during period November 27^th, 2017- December 2^nd, 2017 . From the operational point of view, the formation tropical cyclone Cempaka on November 2017 was closer to the coastline of southern Java island causing flash flood, no storm surge over the coast line, land slide, flooding over some areas in central and eastern Java island. Then tropical cyclon Dahlia might cause low storm surge over Sunda Strait and some coastl area over southern west Java island and strong wind along northern coast of west and central Java island. The formation of the unusual Tropical cyclone would be in advance and generating over low latitudes approaching equator line. Then end of the year 2017 up to end January 2018, Indonesia Maritime Continent would suppress the cloud cover and rainfall due to the cooler than normal of the sea surface temperature Indian ocean west of Indonesia Maritme Continent. Unfortunately during February, activities of the cloud cover and rainfall would be increasing even MJO over Pacific-Otlantic Oceans. The Cold surge would not encourage the formation the Borneo Vortex, but the convergence zone of northerly and southerly would be part from the Inter Tropical Convergence frequently occurs with more active cloud cover and rainfall. The flooding areas and landside arose including Jakarta and adjoining area frequently occurs with additional condition coolest of the environment most over Java up to lesser of Sunda island. In the last that impact from long winter season over northern hemisphere would be in term frequently wet, cooled and windy weather and climate condition especially over southern area of Indonesia Maritime Continent to be interesting in further study.

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