ウナギ標識放流個体群の水産資源学的研究

夹鳍鳗种群的渔业生物学研究近年来，日本鳗鲡种群有减少的趋势。本研究旨在利用鳗鱼种群的生存、生长、分布和其他生态特征等种群过程的研究结果，探讨恢复鳗鱼种群的策略和对策。2000年5月，在日本高知县的莫北河放养了7977条（00组）月龄鳗鱼，剪去其右胸鳍。2001年5月，在同一河流中放养了7989条无左胸鳍鳗鱼（01组）。研究水域从河口到上游大坝长度为7公里。在6个地点分别设置了3个木制诱饵捕鳗器。采用河流渔民渔业统计数据对渔获数据进行分析。研究时间截止到2003年12月。2000年以来00组年渔获量（number）分别为94、46、19、21，占总渔获量（%）的比值分别为8.5、7.5、2.6、2.6。瞬时死亡率约为0.5。4年间，上水地区鳗鱼自然种群年总捕获量增加率从57.2上升到70.2。然而，仅放养鳗鱼的捕获百分比从31.6下降到514。黄鳝总长度2000年为28.9 ~ 40.5 cm， 2003年为36.4 ~ 51.3 cm。3年平均增长量为8.4厘米。条件因子的变化范围很广，但有逐年增加的趋势。身体呈黄色，颜色从2000年的15.7%下降到2003年的90.0。这意味着放养的鳗鱼可能已经在这条河里归化了。自2000年以来，女性的比例从5.3%上升到95.0%。01组在2003年只捕获了8条鱼。这导致渔具的限制取决于鳗鱼的长度。结果表明：养殖数月的鳗鱼可在河中生存至少4年。人们认为，养殖的鳗鱼中有一半可以吃天然食物，通过归化生长、变胖、变黄。预计通过放养幼鳗，鳗鱼的存量可能会增加。然而，在河流中恢复一些适合鳗鱼种群的栖息地必须保持较高的存活率和鳗鱼的生长速度。少

Fisheries biology of the stocked eel population with a fin clipped mark The eel stock in Japan has tendency of decrease recently. The purpose of this study is to discuss on strategies and counter plans to recover eel stocks using research results of population processes such as survival, growth, distribution and the other ecological characters of the stocked eel population.7977 fish (00 group) of some months cultured eel which were clipped off a right pectoral fin by scissors were stocked into the Monobe river, Kochi prefecture, Japan, in May, 2000. And 7989 eels (01 group) without a left pectoral fin were stocked into the same river, in May, 2001. The research water length was 7 km from a mouth of the river to an upper dam. Three wooden bait traps for, eels were set at 6 points respectively. Fishery statistics by river fishermen was used to analysis catch data. The research period was until December of 2003.Annual catch(number) of 00 group was 94,46,19,21 and the ratio to total catch … More (%) was 8.5,7.5,2.6,2.6 since 2000, respectively. The instantaneous mortality rate was about 0.5. Percent catch of annual total catch added a natural eel population in the upper water place was from 57.2 to 70.2 for four years. However the percent catch of only stocked eel was from 31.6 to 514. The range of total length of eel was 28.9 to 40.5 cm in 2000 and 36.4 to 51.3 cm in 2003. The average increment was 8.4 cm for three years. The condition factor showed very wide range, but had a tendency of increase year by year. Percent yellowish body, color was from 15.7 in 2000 to 90.0 in 2003. This means stocked eels may have naturalized in the river. Percent female was from 5.3 to 95.0 since 2000. 01 group was caught only 8 fish in 2003. This resulted limitation of fishing gear to depend on eel length.Some conclusions were as follows, Some months cultured eel could dwell and survive in a river at least for four years. It was considered that the half of stocked eels could eat natural foods, grow, become fat and make yellowish body by naturalization. It is expected that the eel stock might increase by stocking of young eels. However rehabilitation of some suitable habitats in a river for an eel population must be maintained higher survival rate and also growth rate for eels. Less