Intensive Fishing Effort and Market Controls as Management Tools for Invasive Aquatic Species: A Review

Invasive aquatic species may disrupt ecosystems and cause socioeconomic damage. Biosecurity protocols were developed to prevent transport and unintended introductions of invasive species, but less attention has been paid to management once they become established. The use of classical fisheries stock assessment to determine levels at which selectively targeted fisheries elicit recruitment overfishing is discussed. Case studies of several species of invasive aquatic organisms, including lionfish Pterois spp. two species of mytilids and three species of crayfish, including Faxonius rusticus (Girard, 1852), are discussed as examples. Fecundity as measured by egg production rate (EPR) is a key factor determining how the various species react to fishing pressure. Ecosystem modelling of predatorprey relations between indigenous and invasive aquatic species suggests that restricting fishing effort on indigenous predators of invasive prey may be as effective in managing invasive species in lieu of directly increasing fishing effort on the targeted species itself. Invasive mytilids Dreissena polymorpha (Pallas, 1771) and Mytella strigata (Hanley, 1843) may not be effectively controlled by intensive fishing effort due to high EPR values. However, crayfish that brood offspring and exhibit much lower EPR values may be ideal candidates for stock assessment and setting fishing effort targets to promote recruitment overfishing. Recommendations for managing invasive aquatic species include: collecting data on population dynamics of the invasive species; assessing predator populations; developing fisheries that target the invasive species; and collecting socioeconomic data to understand the human dimensions of the impacts of the invasive species and inform subsequent policy development.

DISTRIBUSI SPASIAL DAN TEMPORAL IKAN ENDEMIK RAINBOW SELEBENSIS (Telmatherina celebensis Boulenger) DI DANAU TOWUTI, SULAWESI SELATAN

Rainbow selebensis (Telmatherina celebensis) adalah salah satu jenis ikan endemik di Danau Towuti. Ikan tersebut memiliki warna tubuh yang indah dan berpotensi sebagai ikan hias air tawar yang bernilai ekonomis. Dikhawatirkan akan terjadi penurunan populasi ikan tersebut di alam akibat perubahan lingkungan dan penangkapan ikan yang intensif. Penurunan kualitas lingkungan tersebut secara tidak langsung berkaitan dengan penebangan hutan. Penelitian ini bertujuan untuk mengetahui distribusi spasial dan temporal ikan Rainbow Selebensis. Penelitian dilakukan di perairan Danau Towuti dari bulan Maret 2002 sampai dengan April 2003. Ikan ditangkap menggunakan jaring insang eksperimental (experimental gill net) dengan 4 ukuran mata jaring yaitu ¾, 1, 1¼, dan 1½ inci di 4 stasiun. Hasil penelitian menunjukkan bahwa ikan Rainbow selebensis berdistribusi luas di perairan Danau Towuti mulai dari wilayah litoral sampai dengan ke tengah danau. Jumlah ikan yang diperoleh lebih banyak dan ukuran ikan juga lebih bervariasi di stasiun yang terdapat tanaman air (stasiun I dan IV) dibandingkan di stasiun yang tidak terdapat tanaman air (stasiun II dan III). Distribusi ikan secara spasial dipengaruhi oleh kedalaman air dan tanaman air, sedangkan secara temporal dipengaruhi oleh ketinggian muka air, oksigen terlarut, dan pH. Puncak kelimpahan ikan ini ditemukan pada bulan Nopember. Rainbow selebensis (Telmatherina celebensis) is an endemic species in Lake Towuti. This species has excellent body color, which is commercialized as ornamental fishes. Concerning will be decress fish population due to change of environment and intensive fishing. Degradation of the environmental quality indirectly related the deforestation. The aim of this research is to obtain information on spatial and temporal distribution of Rainbow Selebensis in Lake Towuti on March 2002 until April 2003. The fish was captured with experimental gill net mesh size 0.75; 1; 1.25; and 1.5 inches at four stations. The result shows that Rainbow Celebensis has wide distribution in Lake Towuti from litoral zone until the middle of lake. At station where there are aquatic plant (station I and IV), the number and size of the fish were high and various compared to station where there were aquatic plant (station II and III). Spatial distribution of Rainbow selebensis was influenced by depth of water and existence of aquatic plant, while temporal distribution was influenced by water level, dissolved oxygen, and pH. The peak season abundance of the fish was in November.

HUBUNGAN PANJANG- BERAT, KEBIASAANMAKAN DAN KEMATANGANGONAD IKAN BILIH (Mystaecoleucus padangensis) DI DANAUTOBA, SUMATERAUTARA

Ikan bilih (Mystacoleucus padangensis Bleeker) diDanau Toba adalah jenis ikan introduksi dari Danau Singkarak, Sumatera Barat. Pada saat ini terdapat kecenderungan ukuran individu menurun, hal ini antara lain disebabkan oleh penangkapan yang intensif menggunakan alat tangkap bagan apung dengan ukuran mata jaring relatif kecil (< 1,25 inci). Penelitian ini bertujuan untuk melihat beberapa aspek biologi meliputi ukuran panjang dan bobot, kebiasaan makan, tingkat kematangan gonad dan fekunditasnya. Hasil penelitian diperoleh hubungan panjang dan bobot individu bersifat allometrik positif dengan panjang total rata-rata 12,6 cmdan bobot rata-rata 19,8 g/ekor. Dari analisa lambung ikan bilih pemakan detritus (78,2 – 92,9 %), fitoplankton dan zooplankton sebagai pakan tambahan (4,9 – 11,5 %) serta seresah tumbuhan sebagai pakan pelengkap (1,9 – 1,8 %). Hasil pengamatan ikan bilih yang matang gonaddiperoleh nilai fekunditasnya rata-rata berkisar antara 5.262 – 16.117 butir telur. Hasil pengamatan TKG dan jumlah telur menunjukkan ikan bilih dapat bertelur danmemijah sepanjang tahun dan berkembang dengan baik sehingga ikan ini tetap lestari walaupun adanya eksploitasi yang cukup intensif. Bilih (Mystacoleucus padangensis Bleeker) in Toba Lake was introduce from Singkarak Lake,West Sumatra. At present the growth was decreased, it caused by intensive fishing and the uses of lift net with small mesh size (under 1,25 inch). This research aims to know some biological aspects of bilih such as length - weight, relationship food habit, level of gonadal maturity, and fecundity. The results showed that growth pattern of bilih positive allometric with average length of about 12,6 cm and average weight of about 19,8 gr/each. Bilih detritus feeding (78,2 – 92,9%), phytoplankton and zooplankton as additional food (4,9 – 11,5%) and seresah tumbuhan as complement food (1,9 – 1,8%). Fecundity of ranged from 5.262 – 16.117. TKG observation and eggs gain showed that bilih could development and spawn in long years and growth well enough, so that bilih can stlll growth rapidly eventhough there is an exploitation.

Aspek biologi reproduksi ikan pari blentik Neotrygon kuhlii di perairan Selat Sunda

<p class="BasicParagraph"><strong>ABSTRACT</strong></p><p class="BasicParagraph"> </p><p class="BasicParagraph">Bluespotted stingray fish <em>Neotrygon kuhlii</em> is the important fish economically captured from Sunda Strait. Intensive fishing could decrease bluespotted stingray stock. This study was aimed to know the length-weight, and reproduction characteristic. The reproduction characteristic covered the size of first gonad maturity, the level and also index of gonad maturity of bluespotted stingray fish in Labuan Fishing Dock, Banten. The result showed the equilibrium of length-weight of female fish was about W=0.0007L2,1496. Meanwhile, the male fish was about W=0.0000L2.251. Male fish was better than female fish according their relatively condition factor. Decreasing of the factor condition was caused by feeding habit to grow the reproduction cells. The size of first gonad maturity for the female and male respectively were about 550–799 dan 550–760 mm. The highest level maturity even female or male was on IV achieved in June and Juli 2013. Increasing the index (IKG) was followed by the level of gonad maturity.</p><p class="BasicParagraph"> </p><p class="BasicParagraph">Kata kunci: bluespotted stingray, reproductive characteristic, condition factor, Sunda Strait<strong></strong></p><p class="BasicParagraph"><strong> </strong></p><p class="BasicParagraph"><strong> </strong></p><p class="BasicParagraph"><strong>ABSTRAK</strong></p><p class="BasicParagraph"><strong> </strong></p><p class="BasicParagraph">Ikan pari blentik <em>Neotrygon kuhlii</em> merupakan salah satu sumberdaya ikan ekonomis penting dan sebagai hasil penangkapan di Selat Sunda. Penangkapan yang intensif dapat mengakibatkan penurunan stok ikan pari blentik. Penelitian ini bertujuan untuk mengetahui panjang bobot, dan karakteristik reproduksi. Karaktersitik reproduksi itu sendiri meliputi ukaran pertama kali matang gonad, tingkat kematangan gonad dan indeks kematangan gonad ikan pari blentik di perairan Selat Sunda yang didaratkan di Pelabuhan Perikanan Pantai (PPP) Labuan, Banten. Berdasarkan hubungan panjang bobot ikan pari betina diperoleh persamaan hubungan panjang dan bobot untuk ikan pari blentik betina W=0,0007L2,1496. Sementara itu pada ikan jantan, persamaan hubungan panjang bobot W=0,0000L2,251. Ikan pari blentik jantan mempunyai faktor kondisi yang relatif lebih besar daripada ikan pari betina. Penurunan nilai faktor kondisi disebabkan bagian terbesar dari makanan yang dikonsumsi digunakan untuk perkembangan sel-sel reproduksinya. Kisaran ukuran pertama kali matang gonad ikan pari blentik betina 550–799, sedangkan untuk ikan pari jantan adalah dengan kisaran panjang total tubuh 550–760 mm. Tingkat kematangan gonad tertinggi ikan betina dan jantan (TKG IV) ditemukan pada bulan Juni dan Juli 2013. Indeks kematangan gonad (IKG) ikan pari semakin meningkat seiring dengan meningkatnya TKG.</p><p class="BasicParagraph"><strong> </strong></p><p>Keywords: ikan pari blentik, karakteristik reproduksi, faktor kondisi, Selat Sunda</p>