Effect of rainfall on water condition and catch results of eel (Anguilla spp.) in Cicatih River, Sukabumi, West Java

Indonesia is one of the countries with the largest eel catches in the world and is very vulnerable to climate change, especially with rainfall. Rainfall affects fishing activities and the surrounding aquatic environment. Fish resources in the Cicatih River are quite diverse, one of which is high economic fish, namely eel. This study aims to provide information about rainfall’s effect on eel catch results in Cicatih Rives, Sukabumi Regency. Sampling was conducted for six months, from August 2021 to January 2022. The method I use in this research is water condition and relationship analysis for water quality using APHA 2017 and analysis of the relationship between rainfall and fish catches. The result shows that the water quality of the Cicatih River is still in the optimal range for eel life. Still, there are water chemistry parameters that exceed the quality standard, and total nitrogen levels exceed 10mg/l. Most of the large eels in the Cicatih River were caught in the rainy season. Rainfall also affects the duration when fishing, and it is negatively correlated. High rainfall affects the time of fishing, which in turn affects the number of eel catches.


Introduction
Many countries feel the impact of extreme weather, especially in the tropics.Indonesia is a tropical country that is vulnerable to severe weather, especially rainfall.As an archipelagic country in the tropics, Indonesia has a wealth of natural resources, especially fisheries.One of the only fishery commodities in Indonesia is eel (Anguilla spp.).
Sukabumi is one of the regencies in Indonesia that has eel fishery resources.Eels have a unique behavior, which has a catadromous migration pattern.It goes to the river to grow and then to the sea to lay eggs [1].Eel has a life phase in three stages: the phase in the ocean, estuaries, and rivers [2].This fish is a high economic commodity and one of Indonesia's export commodities.Climate variability, especially rainfall, makes the habitat of these fish experience changes in conditions that impact their ability.The climate in Sukabumi is divided into two regional zones.Salak mountain and Gede Pangrango mountain influence the northern region, which is relatively humid and cool.At the same time, the southern part is controlled by the coastal climate with dry temperatures [3].These differences make the rainfall in the two regions different, coupled with extreme weather.Signs of changes in water quality in streams need to be identified to minimize problems with managing eel habitat.Efforts to manage eels in the Cicatih River require information regarding the characteristics of their natural habitat and fishermen's habits of catching eels.So this study aims to see the effect of rainfall on eel catches in the Cicatih River, Sukabumi Regency.

Materials and method
The study was conducted for six months, from August 2021 to January 2022, with data collection locations on the Cicatih River, Sukabumi Regency, West Java (Figure 1).Data were collected at three different stations, taken from the river's upstream, middle, and downstream segments.Data analysis was carried out at the Laboratory of Physiology of Aquatic Animals, Department of Aquatic Resources Management, Faculty of Fisheries and Marine Sciences, IPB University.Methods used in situ and ex situ.In situ data is in the form of water quality data, while ex-situ data is the monthly average rainfall and data of catch eels.

Rainfall
The collection of data on the average rainfall of the research area is used to describe the general condition of the average rainfall at the study site.Rainfall data was taken on the Climate Hazards Group InfraRed Rainfall (CHIRPS) website with the scope of the Cicatih watershed area.The data was taken from August 2021 to January 2022 and compared with the average rainfall from 2013.

Water condition
Water condition observations of Cicatih River water were carried out three times.Sampling was carried out during the transitional season between the dry season and the rainy season, so that it can represent all seasons in Indonesia.The collection of water condition data is used to determine the habitat characteristics of changes in water quality in the research location.The procedure for analyzing water condition parameters is presented in (Table 1).Physical parameters include temperature, conductivity, total suspended solids (TSS), and current velocity.Chemical parameters taken include dissolved oxygen (DO), acidity (pH), total nitrogen (TN), and total phosphate (TP).The data collection and analysis the standard method from [4].The assessment of the water condition data was carried out by comparing the measurement data with water quality standards based on the optimum value of water quality for the life of eel from various studies results.

Eel cathes
The collection of eel data was obtained from data from the catch of fishermen or communities within the Sukabumi Regency which was collected by the Sukabumi District Fisheries and Marine Service.
The eel catch data is sorted by the study period, August 2021 to January 2021.The eel data is processed using the Microsoft Excel 2019 statistical application.

The relationship rainfall and eel catch
Rainfall and eel catch data collected during the study period were analyzed for correlation and analysis between rainfall with eel catch and rainfall with fishing duration, then compared using a graph to determine the effect of rainfall on eel fishing activities to analyze the correlation between rainfall and eel catch.To ensure the accuracy of our findings, we used statistical methods such as regression analysis to control for potential confounding variables.

Characteristic of the Cicatih River
The characteristics of the Cicatih River in the upstream section of the vegetation are diverse, and the substrate is in the form of medium and large rocks, while in the downstream, it is characterized by minimal vegetation, high air turbidity, and small rocks at the bottom.The Rainfall in Sukabumi Regency is relatively high.Sukabumi Regency has a monsoon rainfall pattern, with June, July, and August as the dry season and December, January, and February as the rainy season [8].The average rainfall from 2013 to 2020 is quite different each month (Figure 2).

Water condition
The rainfall that occurs will generally affect the condition of the waters in the study area, where it is found that the physical and chemical quality of the Cicatih River water is still within the optimal range for the life of the eel.However, chemical water parameters exceed the quality standard, namely total nitrogen.Total nitrogen content that exceeds 10mg/l describes the occurrence of organic pollution from human activities, such as residential and agricultural activities [9].Rainfall affects the erosion of rock and soil around rivers, so that minerals containing nitrogen enter the waters.The average total nitrogen levels in the Cicatih River ranged from 17-68 mg/L.Total nitrogen levels that exceed 10mg/l explain the occurrence of anthropogenic pollution from human activities, such as residential and agricultural activities.According to [10], nitrogen are elements that affect biological productivity.Nitrogen from soil and rocks around the river dissolve in water, so that phytoplankton are used to develop which then affects the food chain and biological productivity for zooplankton and small fish.The small fish are then used by eels as food.Nitrogen in the waters must be considered, because the excess residual organic matter into the waters will cause an increase in fertility or eutrophication of the waters [11].
TSS was found to be higher when the rains were relatively lower (Table 2).This is related to the location, which is in an area that receives waste input from residential and agricultural activities and accumulation from the upstream flow of the river.The nitrogen value was also high when the rain was relatively lower.Based on the field observation documentation, all stations are always close to plantations and fields, which leave traces of organic matter, such as dry leaves, on the water.The station is also close to residential areas, which helps domestic channel waste into the water through nitrogen.

Relationshipof rainfall with number of catchs
The difference in catches during the dry and rainy seasons was not significantly different (p-value 0.002).However, rainfall influences ecological conditions and the desire of fishermen to do fishing.When rainfall increases and results in an increase in discharge along the Cicatih River (Figure 3).It is suspected that the high water volume allows the eels to swim more freely to live and forage in the upstream area, so they have a greater chance of being catch.The presence of rain causes organic matter on land to fall into the water, creating biological productivity, which is then used to feed the eels.This is also supported by the statement according to [12], the appearance of eel is mostly found at night when the moon is dark and is followed by rain and according to [13], eel activity will increase when rainfall increases.

Relationshipof rainfall with average fishing duration
During the rainy season, it will certainly affect the duration of fishermen in eel fishing activities (Figure 4).According to the fishermen, the eels will come out after the rain stops, because after that the fish will look for food.However, from the fishermen's point of view, this causes anxiety because during the rainy season, the rain that subsides will not necessarily stop completely.Rain is likely to come back and this will certainly make it difficult for fishermen to get to their fishing spots.In the graph of the relationship between fishing duration during the rainy season, it can be seen that during the rainy season fishermen reduce the duration of their fishing activities.This of course will affect the number of catches produced.

Conclusion
High rainfall in the Cicatih River area affects the duration of fishing which in turn affects the number of eel catches.Rainfall also affects the water condition which adds to the total nitrogen content and affects the behavior of eels.

Figure 2 .
Figure 2. Graph of the average daily rainfall per month 2013-2020.

Figure 3 .
Figure 3. Graph of the relationship of rainfall with the number of catches.

Figure 4 .
Figure 4. Graph of the relationship of rainfall with the average fishing duration.

Table 2 .
Water condition measurement result.