| 中文摘要 |
本研究利用觀察員在太平洋所得的鯊魚混獲資料來進行單位努力漁獲量之標準化，以修正歷史漁獲資料，並回推鋸峰齒鮫（blue shark）及灰鯖鮫（shortfin mako shark）的混獲數量。根據2012年ISC鯊魚工作小組會議之建議，將北太平洋水域區分為A、B二個區域，其中A區域係30度N以北的水域，B區域是0度N－30度N的水域；而南太平洋則依據觀察員回報之鯊魚努力量分布，劃分為0度－20度S的低緯度水域（C區）及20度S以南的水域（D區）。由於鯊魚在鮪延繩釣的作業中是屬於混獲性魚種，常常會有零漁獲（Zero Catch）的情形產生，因此本研究利用Delta-lognormal GLM進行CPUE之標準化，避免過多無漁獲資料可能產生的標準化問題。結果顯示北太平洋大釣船歷年鋸峰齒鮫之總漁獲量約在0 – 1,151噸間變動，南太平洋則在100-3,600噸之間。小釣船則約在8,847 – 16,081噸間。北太平洋大釣船歷年灰鯖鮫之總漁獲量約在0 – 120噸間變動，南太平洋則在40-1,300噸左右。本研究進行了太平洋水域主要混獲鯊魚歷年CPUE變動情形的分析，結果顯示鋸峰齒鮫CPUE仍能維持一定水平，並未發現有明顯下降的趨勢，再加上該種類漁獲體長資料顯示，所漁獲的個體多為成熟的較大個體，因此目前針對該種類資源狀態的判斷仍持較樂觀的看法。灰鯖鮫則由於資料不足所限，導致CPUE無法估計的情形產生，本研究將嘗試其它方法來估算太平洋灰鯖鮫之歷年CPUE。此部份為本研究初步之結果，未來仍需持續進行分析。 |
| 英文摘要 |
The catch and CPUE of the blue shark and shortfin mako shark were estimated based on the observers’ records of Taiwanese tuna longline fishing vessels operating in the Pacific Ocean from 1971-2012. Based on the suggestion of the ISC shark working group in 2012, two areas namely, A (north of 30ºN), and B (0º-30ºN), were categorized in the North Pacific Ocean. According to the distribution of observed shark catch and effort, the South Pacific was divided into C (0º-20ºS) and B (south of 20ºS) areas in this study. The shark catch data reported by observers were used for CPUE standardization to adjust the historical shark catch in Task I and to estimate blue shark and mako shark catches for Taiwanese large scale longline fishery in the Pacific Ocean. Due to high zero catch records for both of blue and mako sharks, the CPUE was standardized using the delta-lognormal approach where one model is used to estimate the proportion of positive catches and a separate model the positive catch rate. All main effects tested were significant and included in the final model. Blue shark bycatch in weight were estimated about 0-1,151 tons in North Pacific Ocean and 100-3,600 tons in South Pacific Ocean between 1971 and 2012. The estimated shortfin mako shark catch in weight were 0-120 tons in North Pacific and 40-1,300 tons in South Pacific. Estimated annual catch of blue sharks by Taiwanese small-scale longline fisheries ranged from 8,847 to 16,081 tons in 2001-2011. Standardized CPUE series of the blue sharks caught by Taiwanese longline fishery showed a stable trend. The stable trend suggested that the blue shark stock in the North Pacific Ocean seems at the level of optimum utilization. However, the shortfin mako shark CPUE could not be estimated due to data limitations. The different methods will be tried to estimate the shortfin mako CPUE in Pacific Ocean. The results in present study are preliminary and further investigation is needed. |
