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Comparison of daily- and annual- increment counts in otoliths of bigeye (Thunnus obesus), yellowfin (T. albacares), southern bluefin (T. maccoyii) and albacore (T. alalunga) tuna







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    Document
    National Report – Australia 2013
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    Pelagic longline and purse seine are the two main fishing methods used by Australian vessels to target tu and billfish in the Indian Ocean Tu Commission (IOTC) Area of Competence. In 2012, three Australian longliners from the Western Tu and Billfish Fishery and one longliner from the Eastern Tu and Billfish Fishery operated in the IOTC Area of Competence. They caught 13.1 t of albacore (Thunnus alalunga), 167.4 t of bigeye tu (Thunnus obesus), 23.0 t of yellowfin tu (Thunnus albacares), 209.3 t of swordfish (Xiphius gladius) and 2.5 t of striped marlin (Tetrapturus audax). These catches represent approximately 13 per cent of the peak catches taken by Australian vessels fishing in the IOTC Area of Competence in 2001, for these five species combined. In addition, Australian vessels using minor line methods took a small amount of catch. The number of active longliners and levels of fishing effort have declined substantially in recent years due to reduced profitability, primarily as a resu lt of lower fish prices and higher operating costs. The catch of southern bluefin tu (Thunnus maccoyii) in the purse seine fishery was 4503 t in 2012. A small amount of skipjack tu (Katsuwonus pelamis) was caught by purse seine fishing in 2012 (0.2 t). In 2012, less than 1 t of shark was landed by the Australian longline fleet operating in the IOTC Area of Competence and 11 371 sharks were discarded/released. In 2012, 17.8 per cent of all hooks set in WTBF longline operations were observed over three trips in the IOTC Area of Competence.
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    Meeting
    An overview of the bycatch landed by local and foreign tuna longliners in Mauritius for the period 2009 to 2012 2013
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    This paper presents by-catch estimates landed by tiol and foreign longliners fishing inside and outside the EEZ of Mauritius for the period 2009 to 2012. Some 100 licences are issued annually to foreign longliners to fish in the Exclusive economic zone (EEZ) of Mauritius. The average annual landing from these vessels during the period under report amounted to 3 102 tonnes of albacore tu which is the targeted species followed by 796 tonnes of yellowfin tu (Thunnus albacares), 360 tonnes of big-ey e tu (Thunnus obesus) and 1106 tons of by-catch comprising billfish, other tu-like species and sharks. A total of 21 196 tonnes of tu and tu-like species was transhipped in Port-Louis by non-licensed fishing vessels targeting albacore (Thunnus alalunga), from 2008 to 2012. The proportion of by-catch landed during this period varied between 28.9% and 39.4%. The total catch landed by non-licensed longliners targeting big-eye tu has increased over the years from 3495 tonnes in 2008 to 8125 tonnes i n 2012. The proportion of by-catch in the total catch seems to be the same (33.1%-47.0%) as compared to the level of by-catch of albacore-targeting fishing vessels (37.9%-39.4 %). The proportion of by-catch landed by longliners targeting swordfish (Xiphias gladius) varied between 37.2% to 49.6%. A comparison of shark landings by tu longliners and swordfish-targeting longliners was carried out: the levels of sharks in the total catch of longliners targeting big-eye tu are higher (7.9%-20.2%) than those targeting albacore (3.6%-8.03%). However, the catch of sharks was very significant in swordfish-targeting vessels varying between 24.3%-39.1% of the total catch in comparison to albacore-targeting fleets and big-eye targeting fleet. Sharks landed by swordfish-targeting vessels consisted mainly of blue shark (Prioce glauca) (74.2-84.2%) followed by moro (Isurus oxyrhinchus) (7.1-20.0%) and mako shark (Isurus paucus) (4.6-9.2%). Moreover, Mauritius has a small number of tiol boats targeting swordfish that operate in its EEZ. These boats also land a considerable amount of non-targeted tu and tu-like species including sharks. The by-catch levels for tiol boats targeting swordfish was higher (50.8%- 52.7% of the total catch) as compared to the FAD fishery whose by-catch varied between 27.9%- 42.9%.
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    Book (series)
    Historical trends of tuna catches in the world 2004
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    This paper reviews historical trends of the catches of the major commercial species (albacore, bigeye, bluefin, skipjack, and yellowfin) of tunas. The total world catch of these species has increased during the last 50 years (from 0.4 to 3.9 million MT), but the pattern of increase has varied among species, oceans and fishing gears. The causes of those variations are analyzed in this paper. In the world catch, the Pacific Ocean has been predominant throughout. In recent years catches from of the Indian Ocean have exceeded those of the Atlantic. Skipjack and yellowfin catches have shown a rapid increase. Bigeye catches also showed a constant increase, but at a lower level. The catches of albacore, bluefin and southern bluefin tunas have been stable or have decreased in recent years. The baitboat fishery took the greatest proportion of the total catches during the 1950s. However, the catch of the purse-seine fishery, became significant in the late 1950s, and became dominant by 1990. Lon gline catches started picking up in the late 1950s, increased until the 1990s and thereafter declined.

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