MODEL PENEBARAN IKAN NILA DI WADUK MALAHAYU, BREBES, JAWA TENGAH

Waduk Malahayu merupakan salah satu waduk yang dimanfaatkan untuk perikanan. Kegiatan penangkapan di waduk ini telah lama dilakukan baik oleh nelayan sekitar maupun luar daerah. Saat ini telah terjadi indikasi adanya penurunan produksi sebagai akibat adanya degradasi sumber daya ikan dan lingkungan serta intensitas penangkapan yang tinggi. Diperlukan upaya pengelolaan untuk meningkatkan produksi ikan di Waduk Malahayu. Salah satu upaya tersebut adalah dengan melakukan penebaran ikan secara rutin baik oleh instansi pemerintah maupun nelayan setempat. Salah satu faktor keberhasilan penebaran ikan terhadap peningkatan produksi adalah jumlah padat tebar yang memadai. Akan tetapi, kajian mengenai jumlah padat tebar yang memadai melalui pendekatan model matematis belum banyak dilakukan. Model matematis mampu memperhitungkan aspek lain seperti penebaran kembali dan penangkapan ke dalam satu kajian model holistik dan analitik. Penelitian ini bertujuan untuk mengestimasi jumlah benih nila yang sebaiknya ditebar. Kondisi populasi ikan nila digambarkan dengan skenario laju pertumbuhan logistik, dengan pertimbangan adanya penebaran dan penangkapan. Hasil menunjukkan bahwa jumlah benih nila untuk ditebar sehingga dapat meningkatkan produksi adalah sekitar 8 ton/tahun atau setara dengan 533.333 ekor/tahun. Hasil dari kajian ini diharapkan bermanfaat bagi pengelolaan sumber daya ikan di Waduk Malahayu melalui pemulihan sumber daya. Fish stocking has been done as an effort to increase fish stock in Malahayu Reservoir. The need to fish stocking is due to the degradation of environment, fish resources and high exploitation either, lead to the decreasing of fish production on those reservoir. Fish stocking that intensively done by local government and community does not yet give an impact to the increasing of fish production. The amount of stocked seeds by using mathematical model approach has not done yet. Mathematical model approach is able to consider other aspects such as restocking activities and fishing into a holistic and analytical study. The current research aimed to estimate the amount of seed of Tilapia that properly stocked in Malahayu Reservoir. Population condition of Tilapia is described by logistic growth rate scenario, taking into account of stocking and fishing. In effort to increase the production, the amount of Tilapia should be stocked about 8 tonnes/year or 533.333 individuals/year. The results obtained in this research are expected to be beneficial for the management of fish resources in Malahayu Reservoir through stock enhancement.

Molluscan assemblages under the influence of peat-draining rivers off East Sumatra, Indonesia

<div><p>The central Indo-west Pacific biodiversity hotspot is of outstanding biological interest in terms of both taxonomy and ecology. However, the molluscan fauna of the region is poorly known. Here we present death assemblages of the subtidal (1–56 m) waters off Eastern Sumatra, Indonesia. Molluscan shells were sampled from a variety of settings from estuaries to coral reef-related carbonate environments. A total of 5064 shells was counted and 197 species were identified. Four shelly death assemblages which are defined by characteristic taxa are found in specific environments. A deposit-feeding community with low diversity and low abundances was recorded in settings with high amounts of terrigenous mud. Greater abundances and higher diversity were found farther offshore, especially in carbonate sediments in the vicinity of offshore islands where pteriomorphian bivalves are characteristic taxa. Protobranch bivalves, especially a species of <i>Nuculana</i>, appear to be best adapted to the organic-rich but food-limited, muddy substrate of the proximal marine environment influenced by peat-draining rivers. Thus, in addition to dominating deep-sea molluscan assemblages, some protobranch bivalves appear to be specialists in exploiting refractory organic materials of shelf environments.</p></div