Small Pelagics

Klorofil-a banyak ditemukan pada fitoplankton dan menjadi indikator kesuburan perairan. Keberadaan fitoplankton ditandai dengan kandungan klorofil-a yang tinggi dan diikuti oleh keberadaan zooplankton yang akhirnya mempengaruhi keberadaan organisme perairan lainnya seperti ikan pelagis kecil maupun ikan pelagis besar sebagai suatu rantai makanan. Interaksi antara konsentrasi klorofil-a terhadap keberadaan dan konsentrasi ikan pelagis di Laut Jawa belum banyak diketahui.  Penelitian ini dimaksudkan untuk mengetahui hubungan interaksi antara klorofil-a terhadap konsentrasi ikan pelagis. Penelitian dilakukan dengan mengumpulkan data runtun waktu hasil tangkapan beberapa jenis pelagis besar dan kecil yang didaratkan di PPI Pekalongan tahun 2007-2011 serta data runtun waktu konsentrasi klorofil-a dari perairan utara Jawa yang diperoleh dari informasi sekunder. Metode analisis korelasi linear sederhana (bivariate correlation) digunakan untuk mengetahui ada atau tidaknya pengaruh antar variabel klorofil-a dan konsentrasi ikan pelagis. Hasil penelitian menunjukkan bahwa ikan layang (Decapterus russelli) paling nyata mendapat pengaruh dari konsentrasi klorofil-a (P<0,05) dan berkorelasi positif terhadap konsentrasi klorofil-a dengan nilai koefisien korelasi ( r ) sebesar 0,56, sedangkan ikan pelagis lainnya berkorelasi negatif. Ikan tongkol (Euthynnus affinis) posisinya menempati rantai makanan paling tinggi sebagai pemangsa, mempunyai korelasi positif (r = 0,5) terhadap Rastrelliger kanagurta dan r = 0,56 terhadap Amblygaster sirm.
KATA KUNCI: Ikan pelagis, klorofil-a, Laut Jawa

Ikan pelagis kecil di Indonesia merupakan salah satu sumberdaya melimpah dan digemari. Ikan pelagis kecil menjadi sumberdaya yang paling banyak ditangkap untuk dijadikan konsumsi masyarakat dari berbagai kalangan. Informasi proporsi jenis dan produksi hasil tangkapan suatu alat tangkap dibutuhkan sebagai dasar penentuan sasaran pengelolaan perikanan berkelanjutan. Oleh karena itu, kajian ini bertujuan memberikan gambaran proporsi jenis tangkapan ikan pelagis kecil pada alat tangkap purse seine di Perairan Selat Makassar. Data produksi tangkapan dianalisis secara spasial dan temporal untuk mengetahui gambaran pergerakan dan produksi ikan tiap bulan sedangkan data proporsi jenis tangkapan dianalisis untuk mendapatkan gambaran proporsi tangkapan pada alat tangkap purse seine di Selat Makassar. Hasil kajian ini memperlihatkan bahwa terdapat beranekaragam jenis ikan dari 307 titik tangkapan ikan pelagis kecil di Selat Makassar. Jenis ikan yang tertangkap sebanyak 9 jenis yaitu lemuru, kembung lelaki, siro, layang deles, layang pectoral pendek, tembang, selar bentong, layang benggol dan tenggiri. Berat tangkapan tertinggi pada bulan Juli sebanyak 27.840 kg atau 25,63% dari total keseluruhan tangkapan. ABSTRACT Small pelagic fish in Indonesia is one of the most popular and abundant resources. Small pelagic fish are the most widely caught resource for consumption by various groups of people. Information on the diversity and production of the catch of fishing gear is needed as a basis for determining targets for sustainable fisheries management. Therefore, this study aims to provide an overview of the diversity of various small pelagic fish catches in purse seine fishing gear in Makassar Strait waters. Catch production data are analyzed spatially and temporally to describe the movement and production of fish each month, while data on the diversity of catch types are analyzed to obtain an overview of the variety of catches in purse seine fishing gear in the Makassar Strait. The results of this study showed that there were various types of fish from the 307 catching points for small pelagic fish in the Makassar Strait. There were nine types of fish caught, namely lemuru, kembung lelaki, siro, layang deles, layang short pectoral, tembang, selar bentong, layang benggol and tenggiri. The highest catch weight in July was 27,840 kg or 25.63% of the total catch.

size depenMortality during the early stages is a major cause of the natural variations in the size and recruitment strength of marine fish populations. In this study, the relation between the size-at-hatch and early survival was assessed using laboratory experiments and on field-caught larvae of the European sardine (Sardina pilchardus). Larval size-at-hatch was not related to the egg size but was significantly, positively related to the diameter of the otolith-at-hatch. Otolith diameter-at-hatch was also significantly correlated with survival-at-age in fed and unfed larvae in the laboratory. For sardine larvae collected in the Bay of Biscay during the spring of 2008, otolith radius-at-hatch was also significantly related to viability. Larval mortality has frequently been related to adverse environmental conditions and intrinsic factors affecting feeding ability and vulnerability to predators. Our study offers evidence indicating that a significant portion of fish mortality occurs during the endogenous (yolk) and mixed (yolk /prey) feeding period in the absence of predators, revealing that marine fish with high fecundity, such as small pelagics, can spawn a relatively large amount of eggs resulting in small larvae with no chances to survive. Our findings help to better understand the mass mortalities occurring at early stages of marine fish. It is commonly accepted that mortality occurring during the early stages of development of marine fish (eggs through to post-larvae) is a major cause of the natural variation in the abundance of marine fish populations 1–3. Recent findings suggest that the great majority of the mortality occurring at these early phases is selective, and that an individual's phenotype influences its probability to survive (review in 4). Moreover, selection greatly varies amongst cohorts, implying that selective mortality is an important source of variability in total mortality, and thus in the variability in recruitment strength 4. Therefore, understanding the phenotypic variability in selected traits is fundamental to understanding the dynamics of fish populations and anticipating which species/populations may be most affected by environmental change. The high mortality experienced during the larval phase of fishes is widely regarded to be size-dependent 5. In the growth-dependent mortality hypothesis, faster-growing individuals within a population have lower risks of mortality due to predation since i) larger larvae have stronger swimming

Sea surface temperature (SST), zooplankton biomass and chlorophyll a concentration, along with abundance of four cope- pod species: Acartia clausi, Acartia lilljeborgii, Paracalanus parvus and Calanus pacificus, and eggs and larvae of small pelagic fishes: Sardinops caeruleus, Scomber japonicus, Opisthonema spp. and Anchoa spp., were measured and estimated from May 1997 to December 1998 in Bahía Magdalena, Mexico. In order to study response of these species to seasonal environmental conditions and to the anomalous warming conditions driven by the 1997-98 El Niño event. Positive SST anomalies were present during 15 months with a maximum value of +4.4 °C recorded during summer of 1997. Zooplankton biomass was lower by half than the previous El Niño 1982-83, but the seasonal pattern was maintained. A chlorophyll concentration maximum of 9.2 mg/m 3 was observed in late spring to early summer, with a minimum of 0.2 mg/m 3 in winter. Copepod abundance changes and an increase of tropical s...

RESUMEN La temperatura superficial del mar (TSM), biomasa zooplanctónica, concentración de clorofila a y los cambios en la abundancia de cuatro especies de copépodos: Acartia clausi, Acartia lilljeborgii, Paracalanus parvus y Calanus pacificus, y huevos y larvas de: Sardinops caeruleus, Scomber japonicus, Opisthonema spp. y Anchoa spp., fueron medidos y estimados en Bahía Magdalena, México de mayo de 1997 a diciembre de 1998 para estudiar la respuesta de estas especies a los cambios estacionales y a las condiciones anómalas inducidas por El Niño 1997-98. Se registraron anomalías positivas de temperatura superficial del mar durante 15 meses alcanzándose valores de hasta +4.4 °C durante el verano de 1997. La biomasa zooplanctónica fue dos veces menor que durante el Niño 1982-83, pero el patrón estacional se mantuvo. La máxima concentración de clorofila se presentó a fines de primavera y principios de verano (9.2 mg/m 3), con un mínimo (0.2 mg/m 3) en invierno. Se registraron cambios importantes en la abundancia, así como un incremento de especies tropicales de copépodos, en la fase más intensa del calentamiento. La especie templada Calanus pacificus asociada con la influencia de la Corriente de California se registró con bajas abundancias en los meses con las temperaturas más bajas. La variabilidad en la abundancia estacional de las especies autóctonas mantuvo la distribución previamente registrada en esta bahía, pero su abundancia disminuyó cerca de un tercio en comparación con la de El Niño 1982-83. La abundancia de peces pelágicos menores templados y tropicales mostró importantes cambios relacionados con este efecto de calentamiento, las larvas de Sardinops caeruleus disminuyeron en un 50% con respecto al niño 1982-1983, en tanto que Opisthonema spp. incrementó, su abundancia en un factor de 10 durante 1997-98. ABSTRACT Sea surface temperature (SST), zooplankton biomass and chlorophyll a concentration, along with abundance of four cope-pod species: Acartia clausi, Acartia lilljeborgii, Paracalanus parvus and Calanus pacificus, and eggs and larvae of small pelagic fishes: Sardinops caeruleus, Scomber japonicus, Opisthonema spp. and Anchoa spp., were measured and estimated from May 1997 to December 1998 in Bahía Magdalena, Mexico. In order to study response of these species to seasonal environmental conditions and to the anomalous warming conditions driven by the 1997-98 El Niño event. Positive SST anomalies were present during 15 months with a maximum value of +4.4 °C recorded during summer of 1997. Zooplankton biomass was lower by half than the previous El Niño 1982-83, but the seasonal pattern was maintained. A chlorophyll concentration maximum of 9.2 mg/m 3 was observed in late spring to early summer, with a minimum of 0.2 mg/m 3 in winter. Copepod abundance changes and an increase of tropical species were registered during the most intense phase of the warming. The temperate copepod Calanus pacificus associated with the California Current, was recorded only during the cold period before the onset of El Niño. The seasonal abundance of autochtonous species followed the pattern previously recorded in the bay, but decreased by about one third, compared to El Niño 1982-83. The abundance of temperate and tropical small pelagic fishes showed important changes related to the intense warming effect, with half the abundance of previous reports for temperate Sardinops caeruleus while, tropical Opisthonema spp abundance increased by up to an order of magnitud in 1997-98.