Analysis on stomach content of bigeye tuna ( Thunnus obesus) in the eastern-central Pacific Ocean

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1 South China Fisheries Science Vol. 11, No. 1 Feb., 2015 doi: / j. issn ,,,,,, (,,,, ) : ( Thunnus obesus), ,,, (, P < 0. 05),, 32. 7% 38. 4% 47. 5% 50. 7% 50. 7% ( K-S, P > 0. 05) (, P < 0. 05), 10, 1 : ; ; ; : S : A : ( 2015) Analysis on stomach content of bigeye tuna ( Thunnus obesus) in the eastern-central Pacific Ocean ZHENG Xiaochun, DAI Xiaojie, ZHU Jiangfeng, CHEN Yan, GAO Chunxia, WU Feng, ZHANG Yanbo ( College of Marine Sciences, Shanghai Ocean University; Key Lab. of Sustainable Exploitation of Oceanic Fisheries Resources, Ministry of Education; Scientific Observing and Experimental Station of Oceanic Fishery Resources, Ministry of Agriculture; National Distant-water Fisheries Engineering Research Center, Shanghai , China) Abstract: Bigeye tuna ( Thunnus obesus, BET) is one of the main target species by tuna longline. Analysis on stomach content of BET can improve understanding its feeding characteristics. Based on BET stomach samples collected from longline fishery in the eastern-central Pacific Ocean from September 2010 to January 2011, we analyzed the prey composition, diversity and feeding intensity ( i. e., stomach fullness) of BET. The results show that fishes, cephalopods and crustacean were main preys of BET, with dominant prey species groups of Ommastrephidae, Sternoptychidae and Gempylidae. The feeding intensity compositions of BET were significantly different among various fork-length samples as indicated by One-Way ANOVA ( P < 0. 05). The proportion of empty stomachs in BET samples which was high, increasing along with gonad maturity stages ( empty stomach percentages were 32. 7%, 38. 4%, 47. 5%, 50. 7% and 50. 7% for maturity stages I V, respectively). There was no significant difference in feeding intensity composition between males and females ( K-S test, P > 0. 05). Moreover, the feeding intensity composition differed monthly ( One-Way ANOVA, P < 0. 05), with the highest stomach fullness in October and the lowest in January. Key words: the eastern-central Pacific Ocean; bigeye tuna ( Thunnus obesus) ; stomach content; feeding characteristics : ; : : ( ) ; ( 08-54) : ( ),,, zhengxiaochun1234@ 163. com : ( ),,,, xjdai@ shou. edu. cn

2 76 11 ( Thunnus obesus) ( T. maccoyii),,,,, SABATI [ 1 ] M NARD [ 2 ] ( T. albacora), [ 4 ] ;,, 1, Fig. 1 Sampling sites for stomach content of bigeye tuna, t , Primer 6. 0 ( 1),, SPSS m, 8. 8 m, 735 kw 2, ( GB ) [ 5 ],, 5 ( ) ;, 5 ( 0 - ; 1 - ( 1), 50% ; 2-50% ; 3-48%,, 24% ; 4 - ) 10% % ( Sternoptyx diaphana), ( Alepisaurus ferox) ( Gemplus serpens) 1. 2 [ 6 ] 5, [ 7-9 ] [ ],,,,,,, cm ( Simpson s diversity index) - ( Shannon-Weiner index) [ 13] cm [ 14 ] Kolmogorov-Smirnov( K-S) ( ) ; [ 15 ] ; ;, -, ( 2)

3 1 : 77 Tab. 1 1 Stomach content composition of bigeye tuna fishes group Cephalopods Crustacean prey species percentage frequency Alepisaurus ferox Trachurus japonicus Cololnbis snira Gemplus serpens Abalistes stellatus Chanos chanos Scomber japonicus Sternoptyx diaphana Ommastrephidae Sepiidae Peneus setiferus Pycnogonida unidentified Fig Simpson s diversity index and Shannon-Weiner index for diet composition in different fork-length groups 2. 2, 46. 8% 48. 6% 1 ; 2 3, ( F = , P <0. 05) ; ( F = , P < 0. 05) 2. 3, ( 4) ( 0 ) Fig. 3 3 Percentage of feeding intensity for bigeye tuna with different fork lengths

4 Fig. 4 Change of feeding intensity composition along with gonad maturity stage for bigeye tuna Fig. 5 Clustering tree of Euclidean distant of bigeye tuna based on feeding intensity, 32. 7% 38. 4% 47. 5% 50. 7% 50. 7%, %, 4. 17%, 50% ; 1,, 2, ; 3 4 ALVERSON [ 16 ] 24. 4%, ( Katsuwonus pel- [ 17 ] K-S, amis) 56% ( n =1 535, P >0. 05) 2. 4 Primer ,, 5, 2 : , 92. 7% ; , 89. 4% 11 12, 90%,,,, ( F = , P < 0. 05), 10, 1 ( T. alalunga), % cm 52. 2%, 48. 6% ; 47. 7%, 46. 8%, BARD [ 18 ], SATO [ 19 ],,, % PERRIN ( SPRF- [ 2 0] 4 [ 8 ] MO),, 5% 15%,,

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