Papers by Wouthuyzen Sam
The limited scientific information and lack of attention from stakeholders on the status of mangr... more The limited scientific information and lack of attention from stakeholders on the status of mangroves in Kembung River functioned as a basis of this study. Four series of Landsat data recorded in 1996, 2002, 2010, and 2013 were used to map mangrove land cover and changes detection. Hybrid classification technique, a combination of the object-based and random forest classifications, were applied in this study. The result showed that based on hybrid classification, mangrove coverage was detected within 82.6-88.4% overall accuracy. Change detection analyses showed that the mangrove area of Kembung River was relatively stable. For nearly two decades, we found mangrove loss about 197.2 ha, gain of 251.1 ha, and unchanged of 2904.9 ha. Changes in mangrove were generally caused by anthropogenic factors such as mangrove replanting, logging, changes over the function of mangroves into the road, embankment, settlement, shrimp farms, and natural growth. Serious attention from various parties a...
Procedia Environmental Sciences, 2015
The objective of this research was to evaluate the accuracy of random forest classification rule ... more The objective of this research was to evaluate the accuracy of random forest classification rule using object based image analysis (OBIA) application (eCognition Developer) and the results were compared with common pixel-based classification algorithm (maximum likelihood/ML) for mangrove land cover mapping in Kembung River, Bengkalis Island, Indonesia. Seven data input model derived from Landsat 5TM bands, ALOS PALSAR FBD, and spectral transformations (NDVI, NDWI, NDBI) were examined by both classifiers. Feature objects statistical parameters were selected and implemented on random forest classifier. Overall accuracy (OA) as well as user and producer accuracies and Kappa statistic were used to compare classification results. Our results showed that the more data model used produced higher overall accuracy and kappa statistics for RF classifier. For each data input model, random forest classifier has higher overall accuracy than maximum likelihood. The best mangrove discrimination in RF classifier was achieved when the combination of Landsat 5 TM, SAR, and spectral transformation were used, while in ML classifier, the best mangrove discrimination was achieved when the combination of Landsat 5 TM and ALOS PALSAR was used. The overall accuracy achieved by RF classifier was 81.1% and 0.76 for Kappa statistic. Meanwhile, for ML classifier, the overall accuracy achieved was 77.7% and 0.71 for Kappa statistic.
Jurnal Ilmu Dan Teknologi Kelautan Tropis, Feb 6, 2015
Minimnya informasi ilmiah dan kurangnya perhatian terhadap status mangrove di kawasan sungai Kemb... more Minimnya informasi ilmiah dan kurangnya perhatian terhadap status mangrove di kawasan sungai Kembung membuat penelitian ini penting dilakukan. Empat seri data Landsat, perekaman tahun 1996, 2002, 2010, dan 2013 digunakan untuk memetakan mangrove dan mendeteksi perubahannya. Teknik klasifikasi hibrida, yang merupakan gabungan klasifikasi berbasis obyek dengan algoritma klasifikasi random forest, digunakan dalam analisis perubahan tutupan mangrove. Hasil menunjukkan bahwa berdasarkan klasifikasi hibrida, tutupan lahan mangrove dapat dideteksi dengan memuaskan pada tingkat akurasi 82,6-88,4%. Analisis perubahan tutupan lahan menyatakan bahwa luas mangrove di Sungai Kembung relatif stabil dan dalam jangka waktu pengamatan tersebut, mangrove yang berubah menjadi penutup lahan lainnya sebesar 197,2 hektar, bertambah seluas 251,1 hektar dan yang tidak mengalami perubahan seluas 2904,9 hektar. Perubahan mangrove umumnya diakibatkan oleh faktor antropogenik seperti penanaman mangrove, penebangan, perubahan alih fungsi mangrove menjadi jalan, tanggul, permukiman, tambak udang dan pertumbuhan alami. Diperlukan perhatian yang serius dari berbagai pihak untuk mempertahankan keberadaan ekosistem mangrove di Sungai Kembung.
Marine Biology, 2006
A survey for leptocephali around Sulawesi Island in the central Indonesian Seas during May 2001 f... more A survey for leptocephali around Sulawesi Island in the central Indonesian Seas during May 2001 found that the leptocephali of the congrid eel, Ariosoma scheelei, were present in all seven areas that were sampled. A total of 551 leptocephali (22–166 mm TL) were collected, and A. scheelei was by far the most abundant species of leptocephali collected during the survey. The wide range of sizes in most areas indicated that spawning had occurred during a period of several months in many different areas, although the exact spawning locations were not determined. The larger size classes were more abundant in all areas except in Tomini Bay on the northeast side of Sulawesi Island. The highest catch rates were observed at the eastern edge of the Java Sea and to the north in the Celebes Sea near Makassar Strait. Premetamorphic leptocephali were also collected in surface samples at 11 stations (N=62), but metamorphosing leptocephali (N=86) were only caught in IKMT tows that fished from the surface to about 200 m. Metamorphosing leptocephali were collected primarily at two stations in the Java Sea and Makassar Strait where a surface layer of lower-salinity water was detected. Their total lengths (105.3–153.3 mm) and the largest premetamorphic individuals suggested that this species can reach maximum sizes of about 165 mm before beginning to metamorphose. It is hypothesized that this species may be abundant in the Indonesian Seas region and that it has ecological traits such as large size at recruitment and a small size at reproduction that have made it successful in many regions of the Indo-Pacific.
Naturwissenschaften, 2009
Remarkably little is known about the life histories of the many tropical anguillid eels distribut... more Remarkably little is known about the life histories of the many tropical anguillid eels distributed across the Indo-Pacific region, and since the Danish expedition to study eels in the region in 1928 and 1929, research on these eels has only begun again in recent years. Sampling for anguillid leptocephali in the Indonesian Seas has been carried out recently to learn about the spawning ecology and larval distributions of tropical eels there. The leptocephali of Anguilla marmorata, Anguilla bicolor pacifica, Anguilla borneensis, Anguilla interioris, and Anguilla celebesensis were collected around Sulawesi Island both in May 2001 and October of 2002. The development of genetic identification techniques has enabled these leptocephali to be identified to species, and their distributions and sizes during different seasons indicated that there are differing life history patterns among sympatric species in the region. A. celebesensis was found to have been spawning in Tomini Bay of northeastern Sulawesi Island in March and April 2001, but apparently, no spawning had occurred in the late summer and fall of 2002. Studies on anguillid glass eels have suggested that tropical anguillids may spawn throughout much of year, but our research on leptocephali in Tomini Bay and data on the downstream migration of tropical anguillids in the major tributary to Tomini Bay indicate that A. celebesensis may have a distinct seasonal pattern of spawning possibly related to the regional monsoon cycles. This is the first evidence of seasonality of spawning in tropical anguillid eels whose life histories are only just beginning to be revealed.
Marine Biology, 2008
Leptocephali of the widely distributed tropical marine eels of the genus Kaupichthys (family Chlo... more Leptocephali of the widely distributed tropical marine eels of the genus Kaupichthys (family Chlopsidae) were collected around Sulawesi Island during a sampling survey in the Indonesian Seas in late September and early October 2002, and the otolith microstructure of 24 of the 59 specimens captured was examined to learn about the larval growth rates and spawning times of these small sized eels. Leptocephali ranging in size from 25 to 60 mm were collected in Makassar Strait and the Celebes Sea, but they were most abundant in the semi-enclosed Tomini Bay of northeast Sulawesi Island. The Kaupichthys leptocephali examined had 39–161 otolith growth increments. Their back-calculated hatching dates indicated that five age groups were present and each group appeared to have been spawned around the full moon of previous months. Average growth rate estimates of the first two age groups were 0.65 and 0.54 mm/day for the 27.4–30.4 and 37.6–45.6 mm age classes. The growth rates of the oldest three age groups (52.0–60.8 mm) appeared to have slowed down after they reached their approximate maximum size. An increase in increment widths at the outer margin of the otoliths of those larger than 53 mm suggested that the process of metamorphosis had begun even though there were few external morphological changes indicating metamorphosis. It is hypothesized that chlopsid leptocephali have an unusually short gut that may not need to move forward during early metamorphosis. The presence of four age classes in Tomini Bay suggests that the Togian Islands region may be productive habitats for Kaupichthys juveniles and adults.
Environmental Biology of Fishes, 2007
A research cruise was conducted in the eastern Indian Ocean off west Sumatra, Indonesia, in June ... more A research cruise was conducted in the eastern Indian Ocean off west Sumatra, Indonesia, in June 2003 to learn about the spawning and larval ecology of the tropical freshwater eels of the genus Anguilla in the region. A total of 43 anguillid leptocephali were collected during the cruise and they were genetically identified as 41 Anguilla bicolor bicolor, 1 Anguilla marmorata, and 1 Anguilla interioris. A. bicolor bicolor leptocephali were 44.1–55.5 mm TL and most of them were at the fully grown stage. Reexamination of the historical data of Jespersen (1942) also suggested a relatively low abundance of small size leptocephali (<40 mm) of this species off west Sumatra. Although the study area has long been considered to be a spawning site of A. bicolor bicolor, the distributions of leptocephali from the two surveys and the patterns of ocean currents in the region suggest the possibility that the main spawning area of this species is located farther offshore.
Journal of Fish Biology, 2007
A sampling survey for leptocephali was conducted in the eastern Indian Ocean to the west of Sumat... more A sampling survey for leptocephali was conducted in the eastern Indian Ocean to the west of Sumatra from 5 to 20 June 2003 in an overlapping area with the historical survey in September to November 1929 during the Danish Round the World Expedition. The age and larval growth rate of 34 Anguilla bicolor bicolor collected in 2003 were estimated using their otolith microstructure to obtain new information about the early life history of this sub-species. The total lengths and ages of these leptocephali were 44·1–55·5 mm and 114–158 days, respectively. Their hatching dates ranged from 3 January to 20 February 2003. Combining these age data and the estimated age of leptocephali collected by others in the same area, this sub-species was estimated to have a wide range of spawning periods. Individual growth rates of the leptocephali in 2003 ranged from 0·32 to 0·39 mm day−1 with a mean ±s.d. of 0·35 ± 0·02 mm day−1. These values were lower than the growth rates of leptocephali of other tropical eels such as Anguilla celebesensis or Anguilla borneensis, suggesting that A. b. bicolor from the eastern Indian Ocean have a longer leptocephalus period of oceanic migration.
The freshwater eels have fascinated biologists because of their spectacular long-distance migrati... more The freshwater eels have fascinated biologists because of their spectacular long-distance migrations between their freshwater habitats and their spawning areas far out in the ocean . Recent progress on the molecular phylogeny of freshwater eels suggests that they originated in the tropics (4), and information on the reproductive ecology and recruitment of tropical species will provide new insight into the evolution of the spawning migration of the freshwater eels (5, 6). However, the larvae (leptocephali) of the many sympatric tropical species are morphologically similar , so they are impossible to identify, and their spawning areas are thus virtually unknown. Recently, however, we have collected small leptocephali from around Sulawesi, Indonesia, and have used species-specific genetic markers to identify them as larvae of Anguilla celebesensis and A. borneensis, which provides the first definitive information about the general spawning areas of these tropical eels. Moreover, the discovery of a spawning area of A. celebesensis in Tomini Bay and the presence of small specimens of two species in the Celebes Sea indicate that, in contrast to the long migrations made by temperate eels, tropical eels make much shorter migrations to spawn in areas near their freshwater habitats. This difference in migratory behavior may reflect an evolutionary cline among freshwater eels that extends from tropical to temperate regions.
Seasonal sea surface (SST) of the Omura Bay was estimated using 13 digital data of Landsat-5 TM t... more Seasonal sea surface (SST) of the Omura Bay was estimated using 13 digital data of Landsat-5 TM thermal infrared (TIR) band. These data consisted of 5 data collected in autumn, 3 in winter, 3 in spring and 2 in summer. The simple regression model between TIR and SST truth data of each season showed that each model is good for
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Papers by Wouthuyzen Sam
Conference Presentations by Wouthuyzen Sam