| 中文摘要 |
一、 本研究計畫訓練科學觀察員於臺灣延繩釣漁船上採集南方黑鮪(Thunnus maccoyii)的耳石，並且判讀南方黑鮪耳石年齡與太平洋黑鮪(Thunnus orientalis)耳石年輪。觀察員在2013年於中印度洋(南緯30-36度，東經73-92度)採集223尾南方黑鮪的耳石，平均魚體尾叉長，體重與年齡分別為104.5 ± 13.5 cm，19.1 ± 9.2 kg與3.8 ± 2.5歲，於西南印度洋(南緯30-38度，東經23-32度)採集30尾南方黑鮪的耳石，平均魚體尾叉長，體重與年齡分別為109.7 ± 8.5 cm，21.2 ± 4.5 kg與4.6 ± 1.0歲，中印度洋的南方黑鮪尾叉長顯著小於西南印度洋的南方黑鮪尾叉長(t-test, t = -2.02, p = 0.02)，但體重與年齡則沒有顯著性差異，t-test統計值分別為 t = -1.14, -.150, p = 0.13, 0.07。 2013年觀察員所採集的太平洋黑鮪耳石樣本，總共進行年輪判讀的個體有246尾，其中135尾採集自屏東東港漁港，而111尾採集自南方澳漁港，所有魚體的平均尾叉長與體重分別為231.9 ± 22.3 cm與265.1 ± 73.1 kg，平均年齡為15.3 ± 5.1歲(範圍介於4-27歲)，採集自東港的樣本，其平均尾叉長(239.8 ± 13.3 cm)、體重(292.1 ± 48.1 kg)與年齡(17.5 ± 4.0歲)皆顯著大於南方澳樣本之平均尾叉長(222.6 ± 26.9 cm)、體重(232.3 ± 84.4 kg)與年齡(12.7 ± 5.1歲) (t-test, p ＜ 0.001)。比較歷年(2002-2013年)觀察員所量測的太平洋黑鮪尾叉長，發現魚體的平均長度由210 cm逐年遞增到235 cm，根據Age-Length Key所估算的平均年齡也由12-13歲逐漸遞增到15-16歲，造成此現象的可能是未成熟的幼魚入添減少為最主要原因。 |
| 英文摘要 |
一、 In this project, we trained the scientific observers to collect otoliths of southern bluefin tuna (SBT, Thunnus maccoyii) on Taiwanese longline vessels in the Indian Ocean. The otoliths collected from the SBT and Pacific bluefin tuna (PBF, Thunnus orientalis) were used for age estimation. In year 2013, 223 and 30 SBT individuals were sampled for otoliths in the central (30-36 °S; 73-92 °E) and southwestern (30-38 °S; 23-32 °E) Indian Ocean, respectively. The mean fork length, dressed weight and ages were 104.5 ± 13.5 cm, 19.1 ± 9.2 kg and 3.8 ± 2.5 years for the former and 109.7 ± 8.5 cm, 21.2 ± 4.5 kg and 4.6 ± 1.0 years for the later. The mean fork length was significantly smaller for the SBT collected in the central Indian Ocean than those in the southwestern Indian Ocean (t = -2.02, p = 0.02). However, the mean dressed weight and ages were not significantly different between these sampling locations (t-test, t = -1.14, -.150, p = 0.13, 0.07, respectively).In year 2013, 246 PBF were aged by reading otolith annuli. Among them, 135 otoliths were collected from the PBF landed in the Dong-Gang harbor and 111 otoliths were collected from the Nan-Fang-Ao harbor. The mean fork length and dressed weight of all samples were 231.9 ± 22.3 cm and 265.1 ± 73.1 kg, respectively. The estimated age for these PBF was 15.3 ± 5.1 years (range: 4-27 years). The mean fork length, dressed weight and age were all significantly larger for the samples collected from the Dong-Gang harbor (239.8 ± 13.3 cm, 292.1 ± 48.1 kg, 17.5 ± 4.0) than those from the Nan-Fang-Ao harbor (222.6 ± 26.9 cm, 232.3 ± 84.4 kg, 12.7 ± 5.1 years) (t-test, p ＜ 0.001). The mean fork length of the landed PBF measured by the observers showed gradually increase from approximately 210 cm at year 2002 to around 235 cm in recent years (2010-2013). The estimated mean age of the landed PBF also gradually increase from approximately 12-13 to 15-16 years. The decreasing recruitment of the immature PBF might be the main reason that cause the increasing trend of mean size and age of the PBF landed in Taiwan although other possibilities were carefully discussed in this report. |
