The demographics of the southern bluefin tuna (SBT) Thunnus maccoyii spawning stock were examined through a large-scale monitoring program of the Indonesian longline catch on the spawning ground between 1995 and 2012. The size and age structure of the spawning population has undergone significant changes since monitoring began. There has been a reduction in the relative abundance of larger/older SBT in the catch since the early 2000s, and a corresponding decrease in mean length and age, but there was no evidence of a significant truncation of the age distribution. Pulses of young SBT appear in the catches in the early- and mid-2000s and may be the first evidence of increased recruitment into the spawning stock since 1995. Fish in these two recruitment pulses were spawned around 1991 and 1997. Size-related variations in sex ratio were also observed with female bias for fish less than 170 cm FL and male bias for fish greater than 170 cm FL. This trend of increasing proportion of males with size above 170 cm FL is likely to be related to sexual dimorphism in growth rates as male length-at-age is greater than that for females after age 10 years. Mean length-at-age of fish aged 8–10 years was greater for both males and females on the spawning ground than off the spawning ground, suggesting that size may be the dominant factor determining timing of maturation in SBT. In addition to these direct results, the data and samples from this program have been central to the assessment and management of this internationally harvested stock.

Status stok merupakan salah satu dasar utama dalam merumuskan pengelolaan sumber daya ikan yang berkelanjutan di WPP NRI. Tulisan ini bertujuan untuk mengevaluasi status stok sumber daya ikan di WPP NRI dan alternatf pengelolaannya. Penelitian dilaksanakan pada tahun 2015-2016 dengan menggunakan metode holistik dan analitik. Hasil analisis menunjukkan potensi sumber daya ikan di perairan Indonesia (WPP NRI) adalah sebesar 12,54 juta ton per tahun dengan potensi tertinggi sebagai ikan pelagis kecil sebesar 4,88 juta ton/tahun (39 %) dan yang terendah adalah lobster sebesar 11.159 ton (1 %). Berdasarkan WPP NRI, potensi sumber daya ikan tertinggi sebesar 2,64 juta ton (21 %) terdapat di WPP NRI 718 (Laut Aru dan Laut Arafura) dan yang terendah sebesar 425.444 ton di perairan WPP NRI 571 (Selat Malaka dan Laut Andaman). Tingkat pemanfaatan ikan di WPP NRI secara keseluruhan didominasi status fully-exploited (indikator warna kuning) sekitar 44 %, diikuti status overfishing (indikator warna merah) sekitar 38% serta status moderat sekitar 18 %. Agar sumber daya ikan di perairan WPP NRI berada dalam tahapan yang berkelanjutan, maka harus dilakukan penataan upaya penangkapan dengan mengurangi jumlah upaya penangkapan sesuai acuan upaya optimal (f.opt) pada WPP yang mengalami kondisi overfishing dan meningkatkan upaya di WPP yang tingkat pemanfaatannya masih moderat dan fully-exploited. Stock status of fish resources were a basis advices to define an apropriate fisheries management towards sustainable fish resource. The purpose of this study was to evaluate the stock status of fish resources and its management alternative in FMAs. The study was conducted from 2015 to 2016 using a holistic and analytic method. Estimation of all fish potency in Indonesia marine waters was 12.54 million tons/year which the highest potency was small pelagic fish group about 4.88 million tons/year (39 %) and the lowest potency was spiny lobster group about 11,159 tons/year (1 %). Based on the FMAs, the highest potency was about 2.64 million tons/year (21 %) in FMA 718 (Aru sea and Arafura sea) and the lowest potency was about 425,444 tons/year (3 %) found in FMA 571 (Malacca strait and Andaman sea). Most of fish resources was in the condition of fully-exploited (44 % yellow color) followed by overfishing (34 % red color) and moderate (21 % green color). Fish groups which included in the highest overfishing by FMAs were squid group. Management alternatives in those prespective are suggested to decrease the fishing effort at the level of f.opt (fishing optimum) by fish groups on the FMAs experiencing overfishing accordingly and to increase an effort at the level of f opt for fish groups on the FMAs in the fully exploited and moderate condition

Bigeye tuna is an important fish resource in the Indian Ocean. This species like other tuna species needs to be managed properly in both national and international levels. Therefore some data and information on population structure and bioreproduction are required for management purpose. The current research was conducted to identify the population structure and bioreproduction of bigeye tuna (<em>Thunnus obesus</em>) in west off Sumatera and south off Java and Nusa Tenggara of Indian Ocean where tuna fishing spots are important. This research was based on catch landed by fishermen from the Indian Ocean during 2010. Analysis of population structure was done using DNA genetic analyses and bioreproduction by using histology technique. Results show that the population structure of the bigeye tuna in the Indian Ocean consisted of two different sub populations namely sub population of west off Sumatra and sub population of south of Java and Nusa Tenggara waters. Most of catch (about 39%) was categorized as immature fish (GI I). The immature fish was mostly found in west off Sumatera waters, meanwhile the catch in south off Java and Nusa Tenggara waters was mostly categorized as mature fish. This result may indicate that south off Java and Nusa Tenggara waters is a spawning ground of the bigeye tuna.

Ikan cakalang (Katsuwonus pelamis) tergolong jenis ikan tuna yang merupakan tangkapan utama di Samudera Hindia. Kajian dinamika populasi menjadi penting sebagai dasar pengelolaan perikanan, agar stok ikan dapat dimanfaatkan secara berkelanjutan. Penelitian ini bertujuan untuk menyediakan informasi tentang parameter populasi ikan cakalang di perairan Samudera Hindia Selatan Jawa. Pengambilan data dengan bantuan enumerator di pusat pendaratan ikan (Cilacap, Palabuhanratu, Tamperan-Pacitan, dan Sendang biru-Malang) selama periode Januari-Desember 2012 dengan jumlah sample total sebanyak 3.118 ekor. Data frekuensi panjang (cmFL) selanjutnya dianalisis menggunakan program FiSAT II untuk menduga parameter pertumbuhan, mortalitas, dan rekrutmen. Hasil penelitian parameter populasi adalah sebagai berikut: panjang asimptotik (L”) sebesar 80,85 cmFL dengan nilai K sebesar 1,1/tahun dan nilai t0 sebesar -0,110 tahun. Mortalitas alami (M) sebesar 1,44/ tahun, mortalitas total (Z) sebesar 2,99/tahun dan mortalitas karena penangkapan (F) sebesar 1,55/tahun. Pola rekrutmen ikan cakalang terjadi setiap tahun dengan puncaknya diduga pada bulanApril sampai dengan Agustus. Tingkat eksploitasi sebesar 0,52/tahun, menyebar pada level yang optimum.

Pertiwi NPD, Nugraha B, Kartika R, Sulistyaningsih RK, Jatmiko I, Sembiring A, Mahardini A, Cahyani NKD, Anggoro AW, Madduppa HH, Ambariyanto A, Barber PH, Mahardika GN. 2017. Short Communication: Lack of differentiation within the bigeye tuna population of Indonesia. Biodiversitas 18: 1406-1413. All highly migratory tuna and tuna-like species have vast feeding grounds and spawning grounds. Indonesia’s tuna catch is the largest in the world. However, genetic diversity in the population structure within particular tuna species in Indonesia is very limited. Here we provide genetic data for bigeye tuna (Thunnus obesus) covering fishing grounds and local fish markets throughout Indonesia. A fragment of mitochondrial DNA in the D-loop control region was amplified from samples collected across Indonesia in the biennium 2012-2013. The results showed high haplotype diversity and low nucleotide diversity in our samples. Little differentiation occured between the eleven diverse sampling locations, nor was any separation detected between general regions of Indonesia, nor between samples from fishing grounds and samples from fish markets.