||Abstract of "Fisheries biological traits and stock assessment on temperate tuna resources in the three Oceans":
1. "Assessment on the Stock Conditions of Albacore Resource in the South Atlantic Ocean." :
This study will analyze the fishing logbook and observer data of Taiwanese tuna fishing vessels in South Atlantic Ocean. First transfer 1982-2001 Catch-at-size data into Catch-at-age to estimate age-structure and evaluate the recruitment of South Atlantic Albacore. And then use GLM to standardize CPUE trend, analyze the relation between Albacore catch and the marine environmental conditions. Finally, use Age Structured Production Model (ASPM) to assess the current stock status, find the optimal fishing strategy and implement risk analysis of South Atlantic albacore stock to provide crucial information of fishery management need. The results of this project will offer effective benefits for sustainably utilizing the South Atlantic albacore resources, ensuring the rights and interests of Taiwanese South Atlantic albacore fishery.
The results obtained as follows: (1) Based on the dominancy of albacore in their different oceanic habitats, summarized and pictorically shown their size distribution characters respectively, there are 3 subregions in the South Atlantic ocean: in which big-size in the subregion 1＆2,and small ones in the 3. And we found out there have been a circular fluctuations occurred in subregion 1 might imply some biological phenomena had arisen. (2) The most significantly related to sea surface temperature is average weights of albacore catch with a correlation coefficient 0.688,and to chlorophyll is the numbers of albacore catch with a correlation coefficient 0.707,however there is no significant relationship between salinity and all albacore catch factors.(3) According to the standardized CPUE trend ,we see a continuous decline from the beginning of Taiwanes longline fishery to 90s, then increase till the mid 90s, and leveled off since 2003 up to 2011.And factor “subregion” played the most important role in explanation of the model.(4) Evaluated by ASPM , with a the criteria 24,000mt as a constant TAC(Total allowable catch), we can assure that there appears a risk of smaller than 50% chance that the prospecting SSB/SSB2011 will reach the value always greater than 1 in-5years.
2. "Assessment on the Stock Conditions of Albacore Resource in the North Atlantic Ocean" :
The main tasks of this project are : (1) to use various methods to distinguish the fishing data targeted at albacore from targeted nonealbacore species and to use GLM model to standardize the Taiwanese distant long line fisheries effort statistics in the north Atlantic to obtain more correct CPUE trend; (2) to convert, based on age and growth equation, on Taiwanese CAS (catch at size) into CAA (catch in age) of Taiwanese albacore harvested in the North Atlantic; (3) to use ASPM to assess the albacore resource condition.
The results indicated (1) the effort distribution for hook per basket of Taiwanese logbook data indicated two modes, and the most effort was separately found in 9-10 and 16-17 hooks; the bigger catch rate of albacore was obtained by 6-13 hooks; (2) to remove the effect of target species, the Taiwanese long-line logbook data identified as albacore targeting (less than 16 hooks per basket) from 1999 to 2012 were used here and shown that the yearly-standardized CPUE continuously increased up to 2004, thereafter, it remained relative stable (2005-2009), and then further increased during 2010-2011; (3) the main age of Taiwanese catch of albacore got bigger from 1981 to 2010; the main age of Taiwanese catch was 5-8 from 1981 to 1997, the one was 6-10 from 1999 to 2006, and the one was 7-11 from 2007 to 2010 . In general, albacore caught in area 32 is bigger than caught from area 31. The majority of Taiwanese catch of albacore is greater than age 3 in area 31 and is greater than age 4 in area 32; (4) the averages of last five year results obtained from ASPM for MSY,、BCUR /BMSY and FCUR/FMSY are 34500 ton, 0.952 and 0.61, respectively, and we agree the conclusion for Stock Conditions of Albacore Resource in the North Atlantic Ocean from ICCAT (2013) that the stock is slightly overfished, but is no longer undergoing overfishing.
3. "Study on the stock conditions of albacore resource in the North Pacific Ocean" :
In order to gain a better knowledge of abundance index for the north Pacific albacore exploited by Taiwanese longliners, the generalized linear model (GLM) was applied to the daily logbook records of albacore-targeting fleets, which were defined based on their fishing activities and resultant catch compositions. In the GLM analyses, several sub-area segregations were adopted, and results showed that 2 sub-areas divided by 25oN Lat. can explain the highest proportion of variance either for the model or for the area factor itself. The GLM results revealed that the standardized CPUE fluctuated within a rather small range, suggesting that the north Pacific albacore population is currently under a reasonable exploitation, particularly since 2001.In this study, we also investigate the age compositions of north Pacific albacore based on length frequency data, given by OFDC, and growth equation reported by Wells et al. (2013). In the period 1995-2002, the albacore catch of Taiwanese longliners were mainly contributed by fish of age 2-4. Since 2003, significant proportion of the albacore catch was comprised of age 4-6 groups. Seasonal differences in the geographical distributions between age groups were observed. The CPUE gravity centers of albacore at age 5 and younger remained in the waters north of 25o N Lat. throughout the year, while those of fish older than 5 years tended to move down to the subtropical and tropical waters in June and July. Based on the monthly distribution of CPUE gravity center, those of fish older than 7 years likely move counter clockwise in the central north Pacific Ocean in the period of September-March.
4. "Studies on the resource condition of south Pacific albacore" :
5. "Age and growth study of South Pacific albacore and stock assessment of albacore in the Indian Ocean" :
The aims of this project include (1)studying on age and growth of albacore in South Pacific and (2) asses the Indian albacore stock. About the studying on age and growth of South Pacific albacore, the 1st dorsal spines and the last caudal vertebrae were used to study the age and growth of South Pacific albacore, by mean of character reading. A total of 373 spines and 135 caudal vertebrae were collected from 373 albacore specimens which were sampled by observers from Taiwanese distant water fishing boats operated in South Pacific, from June/2009 to February/2013. Since the central portion of the spines will become vascularized when fish gets older, the earlier rings will inevitably become obscured. Both spines and vertebrae collected from 135 individuals were used to calibrate the ring counts. From the results, the relationship between first ring of spine (R1) and the difference of ring counts on vertebra and spine (ΔCi = Vno - Sno) was obtained as ΔCi = -2.2523+2.9682 R1. All justified ring counts and fork length data set were then used to estimate the parameters of the von Bertalanffy growth equation by using non-linear regression method, and the results thus obtained were: L∞ = 142.9 (cm); k = 0.1371 (1/Yr); and t0 = - 1.40 (Yr). About the stock assessment, Age Structured Production Model (ASPM) with stochastic recruitment was applied to assess stock status of Indian albacore. For the selection of Base case, yields, indices of abundance and the needed biological parameters are made. A series of model fits related to different assumptions or parameters to examine the sensitivity of the results to these choices were also carried out. The status of Indian albacore resource and risk analysis were assessed by the best run of Base case and sensitivity tests.The results indicated that: (1)the annual yields were closed to or over MSY in recent years; (2)all the estimates of depletion are higher than 0.2, but decreased to the level of 0.4 about in recent years; (3)the fishing mortalities (F) were closed to the mortality at MSY (FMSY) in recent years, even was larger than FMSY in 2010; (4)though the mature biomass (Bmat )is still larger than the mature biomass at MSY (B mat MSY) in all the years, the value of Bmat 2011 was very closed to it. And the result of risk analysis indicated that only the yield decreased 20% thus could keep the fishing mortalities lower than F2011 and make the mature biomass (Bmat ) raised and closed to the mature biomass at MSY (Bmat MSY) in the further 14 years.