大西洋中部金枪鱼延绳钓渔场大眼金枪鱼(Thunnus obesus)叉长与原条鱼重、净重的关系及原条鱼重与净重的关系

THE RELATIONSHIPS AMONG FORK LENGTH, ROUND WEIGHT AND DRESSED WEIGHT OF BIGEYE TUNA (THUNNUS OBESUS) IN TUNA LONGLINING GROUND IN CENTRAL ATLANTIC OCEAN

根据2001年6—10月在大西洋中部金枪鱼延绳钓渔场现场调查所得到的大眼金枪鱼的叉长、原条鱼重和净重的数据,应用回归的方法分别对大眼金枪鱼的叉长与净重的关系、叉长与原条鱼重的关系、原条鱼重与净重的关系进行了研究。结果表明(1)不分性别、雄性、雌性的大眼金枪鱼净重(DW,DWM,DWF,kg)与叉长(FL,FLM,FLF,cm)的关系分别为DW=1.5286×10-5FL3.0192、DWM=1.6102×10-5FLM3.0098和DWF=1.4998×10-5FLF3.0205;(2)不分性别、雄性、雌性的大眼金枪鱼原条鱼重(RW,RWM,RWF,kg)与叉长的关系分别为RW=2.6472×10-5FL2.9400、RWM=2.8164×10-5FLM2.9275和RWF=2.2590×10-5FLF2.9724。在叉长相同的情况下,用本文中的RW-FL换算公式所得出的RW要比用Parks1981年的适用于整个大西洋的换算公式1)所得出RW略轻;(3)不分性别、雄性、雌性的大眼金枪鱼原条鱼重与净重的关系分别为RW=1.1623DW、RWM=1.1546DWM和RWF=1.1840DWF。本文中得出的RW与DW的换算系数要比ICCAT建议使用的系数略大。

This is a part of Chinese first tuna fishing project of observation and investigation in Atlantic high sea fishing ground as per the technical standard of international fishery organization. From 18 Jun. to 27 Oct. 2001, three large-scale tuna longliners were operated in the area of 12°50′N-04°11′S, 41°22′W-15°30′W, and bigeye tuna were randomly sampled and later were analyzed. The deep freezer longliners, about 740 GRT （gross register tonnage） and 56m LOA （length over all） were used to target bigeye tuna （Thunnus obesus）, along with other by-catch such as yellowfin tuna （ T. albacares）, swordfish （Xiphias gladius）, albocore （T. alalunga） and billfish （Istiophoridae）. In total, 253 individuals were sampled. Among them, 172 individuals were male and 82 individuals were female. For each sampled individual fish, fork length （FL） , round weight （RW）, dressed weight （DW） were measured. The length was measured by tape measure at precision of 0. 1cm, and the weight was measured by platform scale at precision of 0. 1kg. Based on the data measured for bigeye tuna （mixed, male and female）, their FL-DW, FL-RW relationships by power regression method, and RW-DW relationship by linear regression were analyzed. The fish sample coverage （individuals） was 19.3%. Our results of statistical relations for the fish in the order of the mixed, male and female are： on FL-DW by DW 1.5286 ×10^-5FL^3.0192 DWM= 1.6102 ×10^-5FLM^3.0098, DWF 1.4998 × 10^-5FLF^3.0205; on FL-RW by RW = 2. 6472 × 10^-5FL^2.9400, RWM = 2. 8164 × 10^-5 FLM^2.9275 , RWF = 2. 2590 × 10^-5 FLF^2.9724 Establishing the FL-RW relationship separately for male and female is benefcial for resource evaluation. FL-DW（or-RW） relationship reported in this paper can be referred to a preliminary estimation on FL-RW （or-DW） relationship of the tuna. At a given FL value, RW of the mixed bigeye tuna is little smaller calculated by the formula in this paper than that by Parks＇s formula. The RW-DW relationships for the mixed, male and female were RW = 1. 1623DW, RWM = 1. 1546DWM, RWF = 1. 1840DWF, respectively. The conversion factor （ mixed sex） from DW to RW was 1. 1623, slightly greater than 1.13 that recommended by the ICCAT used in the Atlantic Ocean. It is suggested by the way that the dressed weight of the fish processed by deep-freezer caught by longliners and sold onto Japanese market should be converted to round weight at a conversion factor of 1. 1623.