Age and growth estimates from three hard parts of the spotted catfish, Arius maculatus (Actinopterygii: Siluriformes: Ariidae), in Songkhla Lake, Thailand’s largest natural lake

The spotted catfish, Arius maculatus (Thunberg, 1792), is a euryhaline fish that is economically important in the Indo-West Pacific. Population dynamics studies and stock assessments of this species have focused on marine stocks, but not those from fresh water. In this study, the age and growth of A. maculatus were, therefore, investigated for the inland stock in Songkhla Lake, Thailand. A total of 213 individuals ranging between 35 and 238 mm TL were used. The length–weight relation indicated positive allometry of this population. Three hard parts (otolith, dorsal- and pectoral-fin spines) were used for aging. The marginal increment ratio confirmed that an annulus was deposited once a year in all three hard parts. All of the samples were aged between 0+ and 6+ years. Verification of age estimates from three readers showed that the otolith was the most suitable part for age estimation. Three growth models (von Bertalanffy, Gompertz, and logistic) were applied in the study. The von Bertalanffy model best described the growth of this fish in Songkhla Lake. The obtained asymptotic length was 290.87 mm TL and the relative growth rate parameter was 0.166 year–1. Our results will be applied as inputs for fish stock assessment models. The obtained growth parameters also can serve as a reference for A. maculatus stocks elsewhere.

Length-Based Stock Assessment of Smith's Barb, Puntioplites proctozystron (Bleeker, 1865) (Cyprinidae) and Asian Redtail Catfish, Hemibagrus nemurus, (Valenciennes, 1840), (Bagridae) in a Multipurpose Reservoir in Thailand

Catches from inland fisheries in Thailand are about 200,000 tonnes annually and plays an important role in food security and subsidiary income. However, fish stocks are seldom assessed because of the lack of catch and effort data. In this study, two fish stock assessment models, viz., relative yield per recruit and length-based spawning potential ratio, were used to evaluate the status of two species as well as to highlight their applications to datalimited situation in Thailand. The study was conducted at Kangkrajan Reservoir, Thailand, for two targeted species, viz., Smith's barb, Puntioplites proctozystron (Bleeker, 1865) and Asian redtail catfish, Hemibagrus nemurus (Valenciennes, 1840) using length frequency data. The data were collected throughout 2019. Both species showed isometric growth. Von Bertalanffy growth parameters were estimated. Asymptotic length, curvature parameter and theoretical age at length zero were 36.2 cm TL, 0.39 yr-1 and -0.28 yr for P. proctozystron, respectively, and 63.2 cm TL, 0.37 yr-1 and -0.32 yr for H. nemurus. The exploitation rates reveal that both species are slightly overfished. Sizes at 50 % maturity and 50 % selectivities were 17.8 and 23.5 cm TL for P. proctozystron, respectively, and 15.6 and 20.8 cm TL for H. nemurus. Considering both parameters, the size at first capture to sustain the fisheries of P. proctozystron and H. nemurus should be >18 cm and >30 cm, respectively, which can be achieved by mesh-size regulations.

Fish Stock Assessment for Data-Poor Fisheries, with a Case Study of Tropical Hilsa Shad (Tenualosa ilisha) in the Water of Bangladesh

The anadromous tropical Hilsa shad formed the largest single-species fishery in Bangladesh, making the highest contribution to the country’s total fish production (14%) and nearly 83% of the global Hilsa catch in 2018. However, increased fishing pressure made the fishery vulnerable, and hence, information on the stock condition and its response to the current degree of removal is essential to explore the future potential for sustainable exploitation. This study carried out a rigorous assessment based on three different methodological approaches (traditional length-frequency based stock assessment method for fishing mortality and exploitation, Froese’s length-based indicators for fishing sustainability, and a surplus production-based Monte Carlo method-CMSY, for fisheries reference points estimation) for the best possible estimates of the Hilsa stock status in the water of Bangladesh. The present findings revealed that the stock is likely to be overfished due to over-exploitation. Depending on the outputs, this study recommended a lower length limit for the catch (> 33 cm), distinguished a selectivity pattern (mesh size limit ≥ 8 cm), and proposed a yearly landing limit (within the range of 263,000–315,000 tons) for the sustainable management of the Hilsa fishery in Bangladesh.

STRUKTUR UKURAN DAN TINGKAT PEMANFAATAN IKAN LENCAM (Lethrinus lentjan Lacepede, 1802) PERAIRAN ARAFURA DI PROBOLINGGO

AbstrakPenangkapan ikan di perairan Arafura banyak dilakukan oleh nelayan dari Pulau Jawa diantaranya Jakarta, Probolinggo, Pati, dan Indramayu. Nelayan dari Probolinggo yang menangkap ikan di perairan Arafura (WPP 718) menggunakan alat tangkap jaring dan pancing rawai dengan tujuan utama adalah ikan demersal, yaitu kakap (Lutjanus spp.), kerapu (Epeniphelus spp.), lencam (Lethrinus lentjan.), dan lainnya. Pemanfaatan ikan demersal terutama ikan lencam (Lethrinus lentjan) yang terus-menerus akan memicu terjadinya perubahan stok populasi ikan di perairan, sehingga diperlukan analisa ilmiah sebagai dasar pengelolaan perikanan. Tujuan dari analisa ilmiah ini untuk menjadi nilai kontrol dalam pengawasan jumlah eksploitasi ikan dan bahan pengkajian stok ikan lencam (Lethrinus lentjan). Penelitian dilakukan Februari hingga Desember 2017 di TPI Mayangan Probolinggo. Struktur ukuran ikan 23–65 cmFL dengan dominan pada ukuran 50 cmFL dengan ukuran pertama kali tertangkap (Lc) 44,5 cmFL. Laju pertumbuhan (K) 0,32 per tahun dengan panjang asimtotik 74 cmFL. Tingkat kematian karena penangkapan (F) lebih tinggi daripada tingkat kematian alami (M) dan tingkat eksploitasi E = 0,57%, yang berarti telah terjadi overfishing. Pengurangan eksploitasi sebesar 14%, dan penetapan ukuran layak tangkap serta ukuran legal diperdagangkan dapat menjadi upaya dalam dalam menjaga populasi ikan lencam.Abstract Fishing in Arafura waters is mostly done by fishermen from Java, including Jakarta, Probolinggo, Pati, and Indramayu. Fishermen from Probolinggo who catch fish in Arafura waters (FMA 718) use fishing nets and longline fishing with the main purpose being demersal fish, namely snapper (Lutjanus spp.), Groupers (Epeniphelus spp.), Lencam (Lethrinus lentjan) and others. Exploitation of demersal fish, especially lencam fish (Lethrinus lentjan) which will continually trigger changes in fish population stock in waters, so the scientific analysis is needed as a basis for fisheries management. The purpose of this scientific analysis is to become a control value in monitoring the amount of fish exploitation for fish stock assessment (Lethrinus lentjan). The study was conducted from February to December 2017 at TPI Mayangan Probolinggo. The size structure of fish 23–65 cmFL with a dominant size of 50 cmFL with the length at first capture (Lc) 44.5 cmFL. Growth rate (K) 0.32 per year with an asymptotic length of 74 cmFL. The fishing mortality (F) is higher than the natural mortality (M) and the exploitation level E = 0.57%, which means overfishing has occurred. The 14% reduction in exploitation and the determination of catch size and legal size of trade can be an effort in maintaining fish populations.

Maximum sustainable yield, maximum economic yield and sustainability in fisheries

A brief review of the concept of Maximum Sustainable Yield (MSY) used in fisheries management is discussed. The convenience of assessing the exploited stocks with the aid of simulation is advised, because implies the possibility to analyze the age structure of the fishery in more detail, as compared to the traditional methods of fish stock assessment. Emphasis is given to the use of the MSY as limit reference point because as long as the Fishing Mortality or fishing effort required for that point is kept at lower values, the fishery will have a good chance to be sustainable. A mention of the Maximum Economic Yield is made, proposing its use a target for the management, because it is reached in general with lower F values then that for the MSY, and this way keeping the fishery in a healthy condition.

Development Learning Models of Fish Stock Assessment Technique Subjects based E-Learning at Aquatic Resources Technology Management Program Study at the Jakarta Fisheries High School

The aim of the study in general is to develop a learning model fish stock assessment techniques based e-learning to meet competencies for program Students study of Aquatic Resources Management Technology in the Jakarta Fisheries University. This research uses research and development methods. Result of study: In the field trial, the value obtained from the results of the post-test is higher than the value of the Pre-test, the average value of the results of the pre-test 62 and the post-test average value of 86.79, so there is an increase of 24 , 79 points, the rate of increase is very significant, meaning that this figure shows that the model developed can improve student learning achievement in the Study Program of Aquatic Resources Management Technology. While the average percentage value obtained from field trials is 88.88%, this number is higher than the learning objectives specified in the specific instructional objectives of 80%..

Data for Fish Stock Assessment Obtained from the CMSY Algorithm for all Global FAO Datasets

Assessing the state of fish stocks requires the determination of descriptors. They correspond to the absolute and relative (to the carrying capacity of the habitat) fish biomasses in the ecosystem, and the absolute and relative (to the intrinsic growth rate of the population) fishing mortality resulting from catches. This allows, among other things, to compare the catch with the maximum sustainability yield. Some fish stocks are well described and monitored, but for many data-limited stocks, catch time series are remaining the only source of data. Recently, an algorithm (CMSY) has been proposed, allowing an estimation of stock assessment variables from catch and resilience. In this paper, we provide stock reference points for all global fisheries reported by Food and Agriculture Organization (FAO) major fishing area for almost 5000 fish stocks. These data come from the CMSY algorithm for 42% of the stock (75% of the global reported fish catch) and are estimated by aggregated values for the remaining 58%.