||Abstract of "Biology and stock assessment studies of tropical tunas for far seas fisheries":
1. "Stock Assessment of tropical tunas in the Atlantic and Pacific bluefin tuna" :
一、Biology and fishery of Pacific Bluefin tuna
Biology of Pacific bluefin tuna (Thunnus orientalis) was described including its external morphology, taxonomy, distribution, life history, growth, reproduction, migratory route of larvae and juveniles, and physiological ecology. Two spawning areas (Western North Pacific and the Sea of Japan) were investigated to reflect the problematic evaluation of stock status and issues of identification of birth place, the proportion of migration northward of juveniles from Nasei Shoto waters, the migratory routes of juveniles and the relationship to their environmental factors, the understanding of migration routes from eggs, larvae and juveniles of Pacific Bluefin tuna as occurrence of recruitment, introduction of numerical method to simulate the migratory routes, and evaluation of the separated proportion of juveniles migrated into either side of Pacific Ocean or the Sea of Japan by using the preference of their swimming direction. Pacific Bluefin tuna is harvested along the regime of Kuroshio Current, juveniles of small sized (about 1-3 cm SL) and medium sized (2-8 cm SL) is caught in the waters of western area of Okinawa main island and Amami Islands, respectively. Juveniles of Pacific bluefin tuna grow when they migrate northward along regime of Kuroshio Current. Besides, the mechanism of separation of juveniles into either the Sea of Japan or Pacific side was not known. The report was also dealing with the description of Pacific bluefin tuna fishery and evaluation outlook of stock status assessed recently.
二、Trial estimation of standardized catch per unit effort of yellowfin tuna by Taiwanese longline fishery in the tropical waters of Atlantic OceanThe trial standardized catch per unit effort (CPUE) of Atlantic yellowfin tuna caught by Taiwanese longline fishery was estimated by delta general linear models. For the manipulation, several factors were used including year, quarter, subarea, vessel category and the two-way interactions. Before estimating CPUE, historical catch and effort data were selected and re-examined by spatial and temporal distribution; then the 1990-2011 catch and effort data within the tropical area (15oN – 20oS) were selected and stratified into 5 subareas to make the nominal CPUE homogeneous as possible among subareas. The GLM and Delta-GLM were used to standardize yellowfin tuna CPUE for Taiwanese longline fishery in the Atlantic tropical waters from 1990 to 2011. The results obtained are very similar trend but the displacement of peaks in the series; and different trends were occurred between Japanese longline CPUE series and anyone of the Taiwanese 3 series.
2. "The impact of different target proxies on CPUE standardization of Indian Bigeye and Yellowfin tuna based on Taiwanese longline fishery data" :
The nominal bigeye CPUE was ranged between 4 no./ 1000 hooks and 9 no./ 1000 hooks in the tropical and whole Indian Ocean. As for the standardized CPUE series, they showed very similar trend with the nominal CPUE except after 2005 in the whole Indian Ocean. In 2012, the CPUE increased to the peak since lots of fishing activities occurred in the Somalia area. Before 2007, the nominal yellowfin CPUE was ranged between 2 no./ 1000 hooks and 5 no./ 1000 hooks in the tropical and whole Indian Ocean. After that, the nominal yellowfin CPUE continually dropped to the historical lowest CPUE of 1 no. / 1000 hooks. And then came back to the level of 2 no. / 1000 hooks in 2012. As for the standardized yellowifin CPUE series, they showed very similar trend with the nominal CPUE except before 1986. The treatment of target species proxy is considered as a crucial part in CPUE standardization. The information of number of hooks per basket seems not to be a proper target species proxy since there is a clear proportional relationship between the number of hooks per basket and the theoretical depth based on the observer data which collect from 2002.
3. "Comparisons of effects from different CPUE standardization models on WCPO yellowfin tuna for Taiwanese longline fishery" :
Taiwan is a member of the three organizations in the Pacific Ocean (WCPFC, IATTC, ISC) which impose the responsibility of enhancement of researches on Taiwanese tuna fisheries. This project is to review and screen the historical Taiwanese yellowfin catch data to reveal the data feature.; then to apply different CPUE standardization models to the data and discuss the appropriateness of each model. The models to be examined include GLM, GLMM, GAM and ZINB.