Analysis For Spatial-temporal Variation And Resources Status Of Albacore(Thunnus Alalunga) In The South Pacific Ocean

Tuna fisheries are well-known due to their high commercial values in the Chinese distant-water fisheries. The tuna species mainly consist of the tropical species-skipjack(Katsuwonus pelamis), yellowfin tuna(Thunnus albacares), bigeye tuna(Thunnus obesus) and temperature species, albacore tuna(Thunnus alalunga, here after ALB) etc. In term of catch compsiton and economic values, it is noted that ALB is an important tuna species, whose catch contribute to the one-third of the total annual longline catch in the Pacific Ocean. As the biomass of bigeye tuna stock declined seriously and the biomass of yellowfin tuna stock reduced, some longline fleets shifted to targeted species ALB, which is relatively a healthy stock during recently in the Pacific Ocean. ALB is an important pelagic species, which it was widely distributed between approximately 50°Nand 40°S and mostly high abundance occurred in the mid-latitude areas. They were also an important target species with high economic value in the Chinese tuna longliner. More and more scientific research for the species biology, ecology and stock assessment are focused. The relationship between environmental factors and inhabitating depths of ALB was significant and the vertical depth was different in various water area. It is noted that spatial-temporal variation of habitat depth of ALB was developed, and further the relationship between the vertical distribution and marine environmental factors were established, which shall surely facilitate the conservation and management strategy of ALB. It also benefits the longline fishing operation and mitigates the bycatch and promote the sustainable development of longline tuna fisheries. Based on fishery data and environment data collected by China longline fishery obsevers in two trips during the time from September, 2013 to January, 2014 and from March, 2014 to August, 2014 respectively, the biological composition of ALB and sea environment data was measured. In this thesis, the factors affecting fishing ground CPUE(catch per unit effort, CPUE) variation was researched and the relationship between habitat depth and environmental factors was studied, and spatialtemporal variation of habitat depth was analyzed. The main results are listed as following:(1)The biological composition of ALB and factors affecting fishing ground CPUE variation:In this paper, the focus was on analyzing the individual biology and the factors affecting fishing ground CPUE variation of ALB based on the data collected from Chinese tuna longline fishing-vessels in the South Pacific Ocean. The data include catch species, biological parameter, fishing gear information and the sea environment data. The results of the biological characteristic showed that:The relationship between FL and WW can be expressed as:WW = 3×10-5×FL2.9099(Male and female, R2 = 0.9153)The relationship between FL and TL was:TL = 1.0336 FL + 2.555(R2 = 0.9614),The relationship between FL and LD1D2 was:LD1D2= 0.2485 FL + 1.2381(R2 = 0.8151)(FL means fork length, cm; WW means boby weigth, kg; TL means total length, cm; LD1D2 means two dorsal fin length, cm.). The general additive model was used to analyze how spatial-temporal factors and environmental factors affect the CPUE of ALB, and the results showed that the most significant factor was longitude, which it contribute to the variance of 3.25%. It is noted that factors such as the latitude, salinity at 150 m water depth layer, temperature at 150 m water depth layer, time(season), temperature at 200 m water depth layer had significant effects of the CPUE which they contribute to the variance of 3.06%, 1.71%, 1.51%, 1.43%, 1.41%, respectively.(2) Relationship between vertical distribution of ALB and sea environment factorsBased on the data of ALB catch and sea temperature& salinity from observers, the CPUE of ALB at all layers were analyzed and researched as the significant evidence to speculate the suitable water depths and related environmental factors.The results indicated that ALB moved mostly between 150 m and 270 m in depth, the temperature value ranged from 16℃ to 22℃, salinity from 35.0 to35.6, and the stock most appeared between 190 m and 230 m in depth, while temperature is 18-20℃ and the salinity 35.2-35.4. The results could provide a basis research for the vertical distribution study and conservation of ALB in the South Pacific Ocean. For fishing vessels, they should set fishing gear legitimately and fishing in suitable seasons and waters. Thus it could obtain high commercial values and reduce bycatch rate to promote the sustainable development of tuna fisheries.(3) Spatio-temporal change of habitat depth for ALB.In this study, the focus was on analyzing the spatial-temporal variation of habitat depth of ALB based on the information collected by the scientific observers from two trips. Firstly, the hook shoaling was calculated according to longline-hook actual depth and captured hook position measured by the scientific observers using catenary curve method and longline shoaling rate method. Then the inhabitating depths of ALB in temperate and tropical waters were estimated according to the hook shoaling, respectively. Furthermore, the optimal habitat depth for ALB in the two waters were determined based on the analysis of the relationship between CPUE and hook depth. And the spatio-temporal variation of the optimal habitat depths was compared with statistical test. The result showed that it appeared high CPUE of ALB occurred in the survey area. The hook shoaling rates were 14.39% and 13.60% in the tropical waters and the temperate waters, respectively. The optimal habitat depth range of ALB was160-190 m in the tropical waters, and it was shallower in temperate waters with the optimal habitat depth range of 190-220 m. The mean habitat depth of ALB were significantly different(P<0.01) in different seasons, as the maximum and minimum depth appeared in the second quarter of the year with 218.0m and 197.0m by 95% confidence interval, respectively. So for fisheries, it should take full account of the vertical behavior of ALB in actual operation, then it will improve the catch rate of the target species and reduce the bycatch rate so that we can protect ecosystem, repectively.