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Mackerel fish (Rastrelliger kanagurta) is a fishery commodity in high demand by the community which is caught in the Malacca Strait. The number of mackerel catches tends to fluctuate every month because it is influenced by different mackerel fishing grounds. Determination of fishing ground tends to use traditional methods such as seeing ripples and a flock of birds flying above the water surface. This study aims to determine the effect of sea surface temperature and chlorophyll-a concentration on mackerel catches and determine the value of primary productivity of the VGPM model every month and also to determine the potential fishing ground to catch mackerel fish based on the sea surface temperature (SST) and chlorophyll-a concentration and Aqua MODIS satellite image data (SST and Chlorophyll-a) were downloaded from oceancolour.gfc.nasa.gov while the catch data were obtained from the Belawan Ocean Fishery Port, the data was taken from 2016 to 2020. The influence of SST and Chlorophyll-a concentration was analyzed and visualized on a map. It was found that every month the potential fishing ground for catching mackerel fish has a different location due to the influence of sea surface temperature and fluctuating chlorophyll-a caused by seasonal changes that occur in Indonesia, where the average SST ranged from 30.01 to 31.34°C and the concentration of chlorophyll-a ranged from 1.48 – 2.28 mg/m3 from 2016 – 2020 with a high net primary productivity ranged from 802.12 – 1.341.59 mgC/m2/day from 2016 to 2020. The potential area for catching mackerel (Rastrelliger kanagurta) caught using purse seines in the Malacca Strait is in the coordinates range of 980 10"51.6” – 1000 19"4.8” (longitude) and 30 28" 48” – 4 0 56"34.8” (latitude) and perpendicular horizontally to the Langkat Regency to Asahan Regency shoreline with a distance under 12 miles to 50 miles. Information on potential areas for catching mackerel can help fishermen in fishing activities so that they are more efficient and catch maximum results.

Leidong river flow is deriving from the Kualuh river basin as the largest river in Labuhanbatu District. The Leidong stream is possibly a water space with changed human exercises which has the potential to cause contamination and disturbance of oceanic biota. The purposes of this study were to figure out fish abundances and the growth of tarpon fish (Megalops cyprinoides) in the Leidong River, North Labuhanbatu District. The highest fish abundance was at station one which was 6 ind/m2, followed by stations 3 and 2 which were 5 and 4 ind/m2. The length and weight estimation of the catched angle at each station demonstrated the development of the tarpon fish with the esteem of b> 3 which is a positive allometric and the value of the condition factor of each K> 1, where this indicates that the condition of the fish in the estuary of the Leidong river morphologically can be said to have good plumpness.

Siombak Lake is one of Indonesia’s tropical tidal lakes located in Medan City, North Sumatra Province. This lake is very dynamic because the lake water level is fluctuating according to the Belawan waters’ tidal (Malacca Strait). This study aims to determine the distribution of sediments in Siombak Lake. The research was conducted from December 2018 - August 2019. The observation locations were taken at 8 points representing all depth layers. The technique used was the filtering analysis using the wet sieve method with stratified sediment filters in different diameters (4.75 mm, 1.7 mm, 250 μm, 850 μm, 150 μm). The data analyzed were weight percentage, texture type, C-organic, the content of nitrogen and phosphorus. The results of the analysis of sediment samples show that there are 3 sediment textures, namely loam, silt loam, and sandy loam. The C- Organic content in the sediments of Siombak Lake ranges from 1.73 - 5.10% at high tide and 1.91-4.40% at low tide. Nitrogen levels in the sediments range from 0.15 - 2.40% at high tide and 0.14-2.35% at low tide. Meanwhile, phosphorus levels in the sediments range between 5.95 - 19.86 ppm at high tide and 1.27-16.35 ppm at low tide.

This study aims to determine the carbon stock in seagrass communities in Central Tapanuli, North Sumatera, Indonesia. The research was conducted from July to August 2020 in the coastal areas of Hajoran and Jago Jago. The parameters measured in this study were density, coverage, biomass, carbon content, and carbon stock in seagrass. Biomass analysis and carbon measurement are divided into the top (above-ground biomass) and the bottom substrate (below-ground biomass). Carbon measurements are conducted using the loss on ignition (LOI) approach. The results showed that the seagrass ecosystem on the coast of Central Tapanuli Regency, which was covered by monospecies Enhalus acoroides, was in a less healthy condition with a cover percentage of 30.3-33.3% and a density of 59-67 shoots/m2. Above-ground and below-ground seagrass biomass reached 140.19-188.72 g/m2 and 368.13-423.69 g/m2 respectively, while carbon stock reached 70.57-94.86 g Corg/m2 and 18731-19603 g Corg/m2 and total standing stock range 257.87-290.90 g Corg/m2. The data obtained from this research can be used as a database to see the potential of seagrass beds as storage of CO2 and as an effort to mitigate and adapt to climate change.

The mangrove ecosystem in Kunkun Village has been used as a tourist destination to be closer to nature. In addition, at this location there is also a river that is used as fishing tourism, as well as a mangrove forest that still has various fauna as one of the areas developed to be a mangrove ecotourism area. The aim of this study were to identify the suitability index of mangrove ecotourism and to determine the carrying capacity of the tourist area. This research was conducted using survey method with a sampling technique and determination of suitability based on weighting and scoring. The suitability index for mangrove tourism is included in the conditionally appropriate category with a percentage value of 55% to 75% which means that further management is needed so that the potential that exists in the mangrove ecosystem in this area can continue to be developed into an environmentally-based tourism area. While the carrying capacity of the area is 235 people/day which is divided into two groups of land and water tourism. However, the management of the ecotourism area is still lacking in terms of promotion of existing tourist spots. infrastructure in the ecotourism area is still less supportive and other facilities are not yet available.

South Labuhanbatu Regency has quite large water resources with the Barumun River which crosses Pasir Tuntung Village, Asamjawa Village, Kotapinang Village and Sisumut Village. This study aims to determine the factors that influence the income of fishermen in Asamjawa Village, South Labuhanbatu Regency. This research method is a descriptive method with a questionnaire tool and the data obtained were analyzed using SPSS software. The variables observed were fisherman’s income, fisherman’s education, length of time working as a fisherman, area of fishing location, daily working time, number of fishing gear and number of fisherman catches. The linear regression model of fishermen’s income in Asamjawa Village was obtained as follows: Y = -19.344,10 + 392.699,10 X1 - 5.024,53 X2 + 73.255,48 X3 + 16.349,29 X4 + 135.819,41 X5 + 12.465,72 X6. The regression analysis results obtained three variables that significantly affect the income of fishermen in Asamjawa Village, Torgamba District, South Labuhanbatu Regency. Where the variables that have a significant effect are the education variable, the number of catches, and daily working time.

Pelagic fishery business in Ternate Sea are mainly based on FADs fishing operations. Increase of intensive fishing activities will also increase the pressures on local pelagic fish resources of Ternate Sea in the future. So far, there has been limited scientific information related to the fish caught by local fishers. The aim of the study was to investigate length distribution, gonad maturity level (GML), and catchable size of fishes caught around FADs. The research was conducted in August 2020 in Ternate. The research method was a survey research by collecting samples of fish caught from gill nets and hand lines for total 30 fishing trips. The study results showed that the catch consisted of mackerel scads and yellow scads. The mackerel scads caught by gill nets were between 13-26 cm in size and dominated by the 19-20 cm size class, while fishes sizes caught by hand line were between 14-27 cm which were dominated by the 18-19 cm size class. Yellow scads caught with both gill nets and handlines showed the same length range of 12-23 cm, which was dominated by the size class of 18-19 cm. Mackerel scads caught with gill nets and handlines were dominated by fish in GML II (47%) followed by GML III (32%). GML of yellow scads caught with gill nets was dominated by GML III by 75%, while for fishes caught by hand line the percentage of GML III is 68%. The mackerel scads caught with gill nets and handlines were dominated by the non-catchable size category (100% for gill nets and 98.79% for handlines). On the other hand, all yellow scads caught with both gill nets and handlines are entirely (100%) of catchable size.

Poncan Gadang Island used by people for marine tourism, underwater and fisheries activities. These activities make the island’s area as a ship transportation route and feared the condition of the coral reef ecosystem will be damaged. This research aims to find out the condition of coral reef (life coral), the abundance of reef fish and the corellation between those two variables in Poncan Gadang Island. This research was conducted in June 2018 using Underwater Photo Transect (UPT) and Underwater Visual Cencus (UVC) methods. From the results of this research were found 14 species of reef fish that consists of 5 families and 161 individual fish with 23.96 % coral reef lifeform percentage (damaged category). The corellation between coral reef lifeform and abundance of reef fish is 29.5%, which means showing sufficient or moderate corellation.

Tapian Nauli Bay is along the coast of Sibolga Bay starting from the border of Sibolga City towards Barus, Tapanuli Tengah. In the Tapian Nauli Bay area there are plenty of fish biological resources and coral reef ecosystems. It is known that the reef fish community is a biotic component of the coral reef ecosystem that can be utilized as marine biological resources.This study aims to examine the diversity of reef fish. The method used in monitoring reef fish is a method Underwater Visual Census (UVC).The reef fishes observed were then grouped into 3 groups of fish, namely: target species, indicator species, and major species, then the structure of the reef fish community was calculated. The results showed that the composition of reef fish species in Sitardas Beach and Bakar island was dominated by major fish (97%), then followed by target fish (2%) and indicator fish (1%).And, overall the diversity of reef fish species in the Sitardas Beach and Bakar island waters shows a low level and shows a relatively unstable uniformity level.