The analysis of chlorophyll-a distribution in fishing areas of Aceh waters

The distribution and abundance of fish are strongly influenced by several oceanographic parameters, one of which is chlorophyll-a. Chlorophyll-a is one of the oceanographic parameters that play an important role in primary productivity in the sea. The distribution of chlorophyll-a contained in phytoplankton can be used as a measure of fertility in water. With advances in geographic information systems or remote sensing, the distribution of chlorophyll-a can be used to estimate fish catchment areas. This study aims to look at the distribution of chlorophyll-a in Aceh waters both spatially and temporally to predict fishing locations. This study used satellite imagery combined with a Geographic Information System (GIS) to detect chlorophyll-a’s distribution . The results of satellite image processing show that the average monthly value of chlorophyll-a in Aceh waters ranges from 2.71 – 23.54 mg/m 3 , areas with high chlorophyll-a are generally located in the western waters of Aceh to the southwestern waters of Aceh, while areas with The lowest chlorophyll-a is generally in areas far from the coast (towards the open sea) with a range of 0.04 – 0.5 mg/m 3 where the lowest average occurs in the east monsoon. However, in general, the potential locations for fishing grounds are more in the waters west of Aceh than in the waters north of Aceh, Aceh waters.


Introduction
Aceh Province is located at the western tip of Indonesia which has fishery resources, so the fishing business is very prospective to be developed.Fishery is one of the business fields that is expected to be able to improve the welfare of the people of Aceh.The geographical location of Aceh province is at coordinates 2 o to 6 o North Latitude and 95 o to 98 o East Longitude, the sea area of Aceh waters is 295,370 km 2 consisting of 56,563 km 2 of archipelagic waters and an Exclusive Economic Zone (EEZ) of 230,807 km 2 (Irham et al., 2018).
Aceh's northern waters are one area with large capture fisheries potential.This is because the northern waters of Aceh are located between the Indian Ocean and the Malacca Strait which are on the western tip of the island of Sumatra.The distinct oceanographic nature of the Indian Ocean and the Malacca Strait makes this region unique.However, little oceanographic data has been collected from these waters (Rizal et al., 2010).A common problem faced by fishermen in determining fishing grounds is the existence of dynamic fishing grounds (Adnan, 2010).
The existence of fish in waters is dynamic, always changing or moving following the movement of environmental conditions, which naturally these fish will choose a habitat that is more suitable for their living conditions (Gaol et al., 2004).The habitat is strongly influenced by oceanographic conditions or parameters in the waters such as sea surface temperature, salinity, chlorophyll-a concentration, weather, currents, and so on (Simbolon, 2009;Tangke et al., 2016).Therefore, to see this  Irham et.al. (2023) the use of satellite imagery is very possible to use.The use of remote sensing methods to detect oceanographic parameters including sea surface temperature, chlorophyll-a index, salinity, currents, and other oceanographic conditions is a very appropriate alternative.The use of sensing technology through Aqua-MODIS satellite imagery by looking at the concentration of chlorophyll-a can provide significant results in determining potential fishing areas (Tangke, 2016).
Previous research on the identification of fish potential areas by utilizing sea surface temperature data from Terra or Aqua Modis satellite images.This research only utilizes sea surface temperature in identifying potential fish areas or the location of fishing areas (Kurniawan et al., 2015).Research related to the analysis of the distribution of chlorophyll-a to determine the fishing area was carried out by utilizing the Geographic Information System (GIS), namely Aqua Modis satellite imagery.This study discusses how to predict the fish catchment zone based on the distribution of chlorophyll-a by utilizing Aqua Modis satellite imagery data with a higher level of imagery than previous studies (Kurniawati et al., 2015), more precisely this research will be carried out in water areas WPP 571, which focuses on the northern waters of Aceh and in the waters of WPP 572, which focuses on the western waters of Aceh.
Analysis of the distribution of chlorophyll-a for determining fishing grounds in the Aceh region was also carried out by Samsul Bahri from January to August 2015.This study showed the range of chlorophyll-a ranged from 0.02-3.47mg/m³ with an average of 0.13-0.32mg/m 3 .In the northern and southern parts of Aceh Province, the chlorophyll-a content is relatively higher compared to the waters of the western part of Aceh (Bahri et al., 2017).However, the research that has been done has not looked specifically at the distribution of chlorophylla based on the district autonomy area and also the distribution over the last five years.Therefore, it is necessary to carry out the latest research to determine the distribution of chlorophyll-a in the northern and western waters of Aceh so that it can be used as a reference for information on fishing areas in the future.

Methods and Analysis Research Methodology
The primary data used is monthly Aqua-MODIS Chlorophyll-a imagery data throughout 2017-2018 with a resolution of 4 km x 4 km.Supporting data in the form of data on sea surface temperature and salinity.The research method used is a descriptive method with a quantitative analysis approach.
The descriptive method is a method used to obtain a description or description of an event studied at a certain time and place (Hadi, 1987).According to Sarwono (2006), research with a quantitative approach aims to test a theory, build facts, show relationships between variables, provide a statistical description, and predict.

Location and time of research
This research was carried out from July to December 2022.This research was carried out by processing satellite image data of chlorophyll-a content which took place at the GIS Laboratory at the Faculty of Marine Affairs and Fisheries, Syiah Kuala University.This research covers the northern waters of Aceh which belong to the waters area of WPP-RI 571 and the western waters of Aceh which belong to the waters area of WPP-RI 572 as shown in Figure 1.

Analysis of Chlorophyll-a and Sea Surface Temperature
The monthly images' chlorophyll-a and sea surface temperature data were downloaded from http://oceancolor.gsfc.nasa.gov.The data was processed using Sea Data Analysis System (SeaDAS) software, the reprojection stage was carried out, and the area masking was carried out according to the area of the research location.Data on chlorophyll-a and sea surface temperature were extracted in text form which was then processed in the Microsoft Excel program to find the average chlorophyll-a and temperature in 2 years and find its levels in monthly averages.
The average chlorophyll-a data and monthly temperature were then processed using ArcMap software.The temperature data in the form of  et.al. (2023) scattered points are interpolated using the IDW Spatial Analyst.Interpolation is the process of predicting the value at a point that is not a sample point, based on the values of the surrounding points that are sampled.The chlorophyll-a data was extracted using SeaDas (Sea Data Analysis System) software, then analyzed using ArcMap software to create maps of potential fishing areas spatially and temporally.
The Inverse Distance Weighted (IDW) method is a simple deterministic method by considering the surrounding points.This method assumes that the interpolation value will be more similar in sample data that is close than that which is farther away (Pramono, 2005).

Analysis of Wind Speed and Rainfall Data
Wind data is downloaded at data0nline.bmkg.go.id which is then processed using ArcGIS software.Wind data is in the form of total speed and total direction, which is processed using SeaDAS 7.4 software to extract the data into Microsoft Excel form and the u and v components can be identified and then wind speed is calculated using the equation: where V : total wind speed (m/s) u : wind in the longitude direction (m/s) v : wind in the latitude direction (m/s)

Results and Discussion Parameter Values Temporally
The highest average value of chlorophyll-a occurred in January ranging from 0.07 -82.46 mg/m 3 with an average of 23.54 mg/m 3 , which occurred in the west monsoon.Together with the variable value of the average SST which is relatively moderate, which ranges from 28.67 -37.09 0 C with an average of 31.01 0 C. The lowest average value of chlorophyll-a occurred in August, which ranged from 0.07 to 7.79 mg/m 3 with an average concentration of 2.47 mg/m 3 which occurred at the end of the eastern monsoon.Along with the relatively low average wind speed below 2.00 m/s which are in months of January and April.
From the results of the study of the average distribution of chlorophyll content in Aceh waters, it can be concluded that in January, April, July, September, October, November, and December there are several areas in Aceh waters with high potential as shown in Figure 2, Figure 3, Figure 4, and Figure 5 to serve as a potential fishing area zone.However, February, March, June, and August have relatively moderate concentrations of chlorophyll-a and tend to have little potential fishing area zones.A potential fishing area zone is an area of water that has a chlorophyll-a concentration content value of 0.5 -2.5 mg/m 3 and sea surface temperatures between 26 0C -29 0 C (Mursyidin, et.al., 2015).The Spatial Distribution of Chlorophyll-a The concentration of chlorophyll-a reached its highest average value with a concentration range of 0.07 -82.46 mg/m 3 , namely in the western season in January.The highest concentration values were found in the western waters of Aceh and the southwest waters of Aceh, to be precise, in the coastal waters of Aceh Jaya to West Aceh to Aceh Singkil waters, with chlorophyll-a concentrations ranging from 0.09 -82.46 mg/m 3 .The lowest concentration of chlorophyll-a was in May with concentrations ranging from 0.04 -7.1 mg/m 3 with the highest concentrations being on the east side of Aceh and Singkil waters.(2016), an increase in the concentration of chlorophyll-a in water has an effect and there is an increase in catches, and vice versa a decrease in the concentration of chlorophyll-a and there is a decrease in fish catches.

Bivariate Correlation between Parameters in the West Monsoon
The bivariate correlation of chlorophyll-a concentration in the west monsoon shows a very strong value and is inversely proportional to a wind speed of -0.832.The concentration of chlorophyll-a has a moderate correlation value and is directly proportional to the sea surface temperature of 0.243.The bivariate correlation of chlorophyll-a concentration shows a low value and is directly proportional to rainfall of 0.060.

Bivariate Correlation between Parameters in East Monsoon
The bivariate correlation of chlorophyll-a concentrations in the east monsoon shows a strong value and is directly proportional to a wind speed of 0.661.The concentration of chlorophyll-a has a low correlation value and is inversely proportional to the sea surface temperature of -0.141.The bivariate correlation of chlorophyll-a concentrations shows a moderate value and is inversely related to rainfall of -0.430.The relationship between Chlorophyll-a and Wind Speed Results The Pearson correlation between chlorophyll-a and wind speed is -0.832 (Table 2) in the west monsoon which has an inverse correlation with a very high degree of association, while 0.061 (Table 3) in the east monsoon which has a direct correlation with a high degree of association.As happened in July, the highest wind speed was 3.07 m/s (Table 1).At that time the concentration of chlorophyll-a was 10.26 mg/m 3 .The opposite condition occurred in August, namely, the value of chlorophyll-a concentration reached the lowest value of 2.47 mg/m 3 (Table 1).
The high concentration of chlorophyll-a in the west monsoon appears to be related to wind speed, high wind speed is thought to cause a strong mixing process that brings nutrients from the lower layers to the upper layers, supported by sufficient light intensity so that the growth of phytoplankton increases.The increase in phytoplankton can be seen from the increased chlorophyll-a value, this statement is reinforced by Thorpe (2007), who states that vertical fluid movement is influenced by the wind on the surface, causing nutrients to be lifted from the lower layers to the upper layers.This causes the mixing process to have a very important role in the life of phytoplankton to support the supply of nutrients that are needed to carry out the photosynthesis process.

The relationship between Chlorophyll-a and Sea Surface Temperature
The Pearson correlation between chlorophyll-a and sea surface temperature (SST) is 0.243 (Table 2) in the west monsoon and -0.141 (Table 3) in the eastern monsoon, which means that the SST correlation in the western monsoon is directly proportional to the moderate or sufficient level of association, while the SST correlation in the east monsoon is inversely proportional to the low level of association.This is presumably because the faster the wind speed, the faster the process of stirring the water mass so that the water mass in the lower layer which has a low temperature rises to the surface causing the surface temperature to be low.This is in accordance with the statement of Kunarso et al. (2011), that increasing the wind speed of the Southeast Monsoon will cause an increase in upwelling intensity which increases the flow of cold water from the lower layers to the surface.

The relationship between Chlorophyll-a and Rainfall
The high fertility of Aceh's waters to be precise in the west monsoon (November -February) is thought to occur due to runoff or surface runoff in river water based on the high rainfall in the west season with a range of 19.74 -40.73 mm/month (Table 1).Besides that, it is also strengthened based on the results of bivariate correlation analysis between chlorophyll-a and rainfall which shows a value of 0.060 mm (Table 2) in the west season and -0.430 mm (Table 3) in the east season.The existence of high river runoff also brings high nutrients from the land, this is the reason for the increase in water fertility which triggers the high development of primary productivity of waters.This statement is supported by a statement from Kunarso et al. (2019) which states that rainfall can cause an increase in the runoff of rivers that contain high concentrations of nutrients that are utilized for the growth of phytoplankton.Dahuri et al. (1996) further explained that the river acts as a water flow medium for the waste disposal process which will cause the carrying and accumulation of organic matter from the waste which is a contributor of nutrients to the waters.

Spatial Distribution of Chlorophyll-a
The results obtained show that concentrations tend to be high in the western waters of Aceh and the southwestern waters of Aceh, to be precise on the coasts of Aceh Jaya to West Aceh to Aceh Singkil waters, with chlorophyll-a concentrations ranging from 0.09 -82.46 mg/m 3 .Almost every west season (November -February), high concentrations of chlorophyll-a are found on the western side of Aceh's waters, namely from the coast of West Aceh waters to Nagan Raya and a few areas in Singkil waters.Then a high concentration of chlorophyll-a is also found in one part of the northern waters of Aceh, to be precise, on the coast of East Aceh waters (Figure 2, Figure 3, Figure 4, and Figure 5).
The low concentration of chlorophyll-a is found in areas far from the coast in almost every month and season, with a range of 0.04 -0.5 mg/m 3 (Figure 5).This is supported by the research results of Riyono et al. (2006) in Klabat Bay, namely the general pattern of distribution of chlorophyll-a, phytoplankton, and nutrients shows high values which are almost always found in waters that are relatively close to the coast

Figure 1 .
Figure 1.Map of research location (self-created in 2022)

Table 1 .
The Variability of Chlorophyll-a, SST, Wind Speed, and Rainfall

Table 2 .
Bivariate Correlation of Chlorophyll-a with Supporting Parameters in the West Monsoon

Table 3 .
Bivariate Correlation of Chlorophyll-a with Supporting Parameters in the East Monsoon