Influence of water flow rate in mold on hooks and inclusions at the subsurface of ultra low carbon Al-killed continuous casting slabs

The influence of water flow rate on the surface cleanliness of slabs was investigated through the hook reveal and inclusion detection. The numerical simulation was performed to calculate the shell thickness with different water flow rate. With the decrease of the water flow rate from 99 to 88 L/s, the hook depth reduced at most of positions, and the number of > 5 μm inclusions decreased. The contour was calculated to provide guidance for adjustment of the water flow rate.

Hook evolution and inclusion entrapment during initial solidification process of continuous casting slab

A two-dimensional numerical model was established to describe the mechanism of hook formation and evolution during the initial solidification process of continuous casting slab. Melting, coarsening, growing, and burying stages were observed to follow hook formation at the meniscus. The coordinates at which the hook was finally buried into the shell were determined for different casting speeds and pouring temperatures. The final hook depth was predicted to be approximately 1.8–2.9 mm, which was confirmed by metallographic experiments. A physical model was established based on the calculated shell shape, and the process by which the inclusions were entrapped by the hook structure was investigated. The results indicated that the floating inclusions were most likely entrapped under the nascent hook, and the inclusions gathering near the meniscus were easily captured by the upper part of the nascent hook when overflow of the molten steel occurred. The hook-like structure increased the area of the shell inner face, which resulted in swirling flow of the molten steel near the shell and increased the probability of the inclusions being captured.

Pelagic longline fishery for albacore tuna (Thunnus alalunga) yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) in the high seas of eastern Pacific ocean.

This study highlighted the occurrence of a pelagic long line fishery targeting albacore tuna, yellowfin tuna and bigeye tuna in the high seas of eastern Pacific Ocean. Species selectivity of the fishing method was assessed. Hook depth, statistics of at-vessel survival rate grouped by hooks number, length frequency, weight frequency, length weight relationship, relative condition factor and Fulton’s condition factor were estimated for the target species. This fishing method proved highly selective for albacore tuna, where catches accounted for about 85% of catches, while other resources such as yellowfin tuna amounted to 4.8% and big eye tuna accounted for 9.70%. The results showed that, fish size increased with deeper depths. Hook No. 8 located at a critical depth indicated that fork lengths of tuna registered above this depth were significantly smaller than that those captured below it. Logistic regression model suggested a significant effect of hook depth on the catch efficiency. The highest density of catch efficiency was located at the depth of 167.57 m. An alternative strategy showed that hooks deployed at the depths ranging from 124 to 211 m will result in a more considerable fishing efficiency. The analyses also showed that the relative condition factors (Krel) of the three fish species were greater than (1) implying that they were in good physiological condition at the time of capture.

Pelagic longline fishery for albacore tuna (Thunnus alalunga) yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) in the high seas of eastern Pacific ocean.

This study highlighted the occurrence of a pelagic long line fishery targeting albacore tuna, yellowfin tuna and bigeye tuna in the high seas of eastern Pacific Ocean. Species selectivity of the fishing method was assessed. Hook depth, statistics of at-vessel survival rate grouped by hooks number, length frequency, weight frequency, length weight relationship, relative condition factor and Fulton’s condition factor were estimated for the target species. This fishing method proved highly selective for albacore tuna, where catches accounted for about 85% of catches, while other resources such as yellowfin tuna amounted to 4.8% and big eye tuna accounted for 9.70%. The results showed that, fish size increased with deeper depths. Hook No. 8 located at a critical depth indicated that fork lengths of tuna registered above this depth were significantly smaller than that those captured below it. Logistic regression model suggested a significant effect of hook depth on the catch efficiency. The highest density of catch efficiency was located at the depth of 167.57 m. An alternative strategy showed that hooks deployed at the depths ranging from 124 to 211 m will result in a more considerable fishing efficiency. The analyses also showed that the relative condition factors (Krel) of the three fish species were greater than (1) implying that they were in good physiological condition at the time of capture.

THE EFFECT OF DEPTH OF HOOKS, SET AND SOAK TIME TO THE CATCH PER UNIT OF EFFORT OF TUNA IN THE EASTERN INDIAN OCEAN

Yellowfin (Thunnus albacares) and bigeye (T. obesus) tuna have been intensively exploited by longline fleets since 1980’s, however, a large proportion of zero catch per set of target species still accurred. Zero catch data contributed significantly to the low catch per unit of effort (CPUE) compared to other countries at the same fishing area. Therefore, understanding the factors contributed to the CPUE of tuna is essential, in order to improve longline fishing efficiency. A total of 2.115 set-by-set data were obtained from Indonesian Scientific Observer Program. The onboard observations were carried out at commercial tuna longline operated in Eastern Indian Ocean from August 2005 to December 2014. Several analytical approaches were conducted in this paper. First, General Linear Model (GLM) was applied in order to model the relationship between CPUE with all the variables involved. Second, boxplot diagram, polynomial and linear regression were applied to fit the relationship between CPUE with set time, soak time and depth (represented by hook position) respectively. The result showed that, there was no significant relationship between set time and CPUE of bigeye and yellowfin tuna. Soak time was positively related with CPUE of yellowfin and affect adversely on bigeye. Depth also have significant relationship with CPUE of tuna, where catch of yellowfin decreased linearly with hook depth, whereas catch of bigeye was performed the opposite. Improvement in tuna longline fishery in eastern Indian Ocean can be achieved through implementation of the specific soak time and hook depth for each target species, i.e. yellowfin and bigeye tuna.

PEMETAAN KARAKTER EKOSISTEM DAN SEBARAN DAERAH PENANGKAPAN IKAN MADIDIHANG (Thunnus albacores) DI PERAIRAN UTARA PAPUA (Ecosystem Character Mapping and Fishing Ground Spatial Distribution of Yellowfin Tuna (Thunnus albacores) in Northern Papua)

<p>ABSTRACT<br />The research was aimed to study the condition of the seasonal ecosystem characters (water temperature, salinity, flow and depth) and the seawater temperature data from MODIS satellite, TRITON Buoy temperature, salinity, currents and depth of the hook in northern waters of Papua which is associated with fish catches of yellowfin tuna (Thunus albacores). The research method was based on a survey with emphasis on water parameters, ecosystems character which have a great influence of the fishing ground. The ecosystem variables that effecting fishing ground of yellowfin i.e. temperature, salinity, current and depth. Results from this study showed that the value of north Papua sea surface temperatures were relatively high during January and February, with the highest temperature in January 30.33 oC and relatively low in April with a temperature of 29.9 oC. In January - March, the salinity of the waters of north Papua 34-35.4 for each month and in depth, the current ranged from 4.4 to 39.1 cm/sec. The depth for setting the hook to catch yellowfin in a large numbers was mostly in between 177 and 219 meters, where temperatures ranged between 19.7 and 23.6 oC. Yellowfin monthly production in June to August and December 2010 to February 2011 showed a positive relationship between yellowfin catches and depth of water temperature (r = 0.544), depth of the hook (r = 0.533), salinity (r = 0.403) and current (r = 0.537). The results of multiple regression analysis showed a strong relationship to each variable parameters of temperature, depth, salinity and current (r = 0.611) of the catch.<br />Key words: ecosystems, hook depth, mapping, temperature, yellowfin tuna</p><p>-------</p><p>ABSTRAK<br />Penelitian ini bertujuan untuk mengkaji kondisi musiman karakter ekosistem (suhu perairan, salinitas, arus dan kedalaman) hasil pengukuran satelit MODIS dan data TRITON buoy serta pola sebaran suhu perairan, salinitas, arus dan kedalaman mata pancing di perairan Utara Papua yang dikaitkan dengan hasil tangkapan ikan madidihang/yellowfin tuna (Thunus albacores). Metode penelitian adalah metode survei dengan penekanan pada nilai variabel parameter perairan/ karakter ekosistem yang sangat berpengaruh terhadap daerah penangkapan ikan (fishing ground) madidihang yaitu suhu, salinitas, arus dan kedalaman. Hasil evaluasi penilaian secara umum menunjukkan bahwa, nilai suhu permukaan laut di utara Papua relatif tinggi pada bulan Januari dan Februari, dengan nilai tertinggi 30,33 oC dan relatif rendah pada bulan April dengan nilai 29,9 oC. Pada bulan Januari hingga Maret, massa air dengan salinitas berkisar 34 – 35,4‰ untuk setiap bulan, dan di kedalaman di perairan utara Papua, kecepatan arus 4,4 - 39,1 cm/dt. Kedalaman mata pancing yang di-setting pada kedalaman 177 - 219 meter, dimana suhu berkisar antara 19,7 - 23,6 oC. Produksi bulanan madidihang pada Juni-Agustus dan Desember 2010-Februari 2011 menunjukkan hubungan positif antara hasil tangkapan madidihang dengan suhu perairan (r = 0,544), kedalaman mata pancing (r = 0,533), salinitas (r = 0,403) dan arus (r = 0,537). Hasil analisis regresi berganda menunjukkan hubungan yang kuat untuk setiap variabel parameter suhu, kedalaman, salinitas dan arus(r = 0,611) terhadap hasil tangkapan.<br />Kata kunci: ekosistem, kedalaman mata pancing, pemetaan, suhu, yellowfin tuna</p>