| Northern bluefin tuna （Thunnus thynnus） belongs to the pelagic of highly migratory fish, for itwith the highest economic value the Northern bluefin tuna fishery has been in a state of overfishing.Monaco consider that the East and Mediterranean bluefin tuna stock is on the verge of extinction, itis proposed to require implementation of the international trade ban on northern bluefin tuna. Basedon the data of fork length of northern bluefin tuna caught in Atlantic Ocean from1960to2009andlongline observers survey data, the biomass of Norhern bluefin tuna resources in the Atlantic Oceanwas evaluated by Length based Cohort Analysis （LCA） method and its Biological and catch ratewere analyzed The main results of the study were as follows:1. Species composition and catch rate of Northern bluefin tuna by tuna longline fishery in thenorth Atlantic OceanLongline fishery caught8species include tuna and likely tuna2species, chondrichthyes2species, Billfish1specie and other fish3species in the north Atlantic Ocean. Altogether513individuals of fish are captured. Main species by catch rate from high to low are as follows: blueshark, northern bluefin tuna （Thunnus thynnus）, albacore, Tapertail ribbonfish, Ocean sunfish,Shortfin mako, Swordfish, Escoler. And the dominant species is blue shark and northern bluefintuna. Average catch rate of northern bluefin tuna is1.76ind/1000hooks（s. d=1.47n=38）, Averagecatch rate of blue shark is4.62ind/1000hooks（s. d=2.30n=38）. Significant correlation betweenCatch rate of blue shark and northern bluefin tuna. No Significant correlation is found betweenSST and catch of blue shark and northern bluefin tuna.2. Biological analysis on northern bluefin tuna, Thunnus thynnus, in the north Atlantic Ocean The biological characteristics of northern bluefin tuna （Thunnus thynnus）were analyzedusing data collected by scientific observers onboard a tuna longline vessel in the south of Icelandfrom October to December2010. The fork length （L F） ranged from154to230cm, withpredominant175-190cm （67%） and mean188cm. The relationships between fork length andweight can be expressed asW3104L2.4907F（R20.7698） for females,W=2×10-4LF2.5204,（R2=0.8335） for males, andW=3×10-4LF2.4907,（R2=0.7698） forcombined sexes. About86%of the sampled females were mature, compared with51.3%of themales. The feeding stages were dominated by stages0and1（about72.2%）. No significantcorrelation between feeding stage and maturity stage was found.3. According to the LCA （Length based Cohort Analysis, LCA） of length generationto study resources dynamic in the Atlantic oceanAccording to the LCA （Length based Cohort Analysis, LCA） of length generationto study resources dynamic in the Atlantic ocean, the results are as follows: Natural mortalitycoefficient of bluefin tuna in the eastern group of Atlantic is0.28（M=0.28）; Natural mortalitycoefficient of bluefin tuna in the western group of Atlantic is0.28（M=0.28）; Fishing mortalitycoefficient is relatively high within the40-50cm range in each fork length group of the easternAtlantic group in1960-1970; each fork length group fishing mortality coefficient does not changesignificantly in1971-1995, all of it are at a relatively low level; and fishing mortality coefficient ofeach fork length group are substantially upward trend in1996-2009. Fishing mortality coefficientgroup is at a relatively high level in each fork length group of the western Atlantic group in1960-1977; each fork length group fishing mortality coefficient is at a relatively low level in1978-2002;each fork length of fishing mortality coefficient group are substantially upward trend in2003-2009.The resources and resource mantissa are at a rising trend from1960to1990in Easternthe Atlantic group resource dynamic, the amount of resources and resources mantissa fallssubstantially from1990to2009, the resources and resources mantissa is at minimum level in2009.The Atlantic West Group resources and resources are at the highest level in1963, the amount ofresources and resources mantissa fall substantially from1964to1982, the amount of resources and resources mantissa are in a smooth trend from1983to2009,but are at the lowest level. The Atlanticbluefin tuna resources is in a serious recession. |
