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RESEARCH ARTICLE

Feeding habits of bigeye tuna (Thunnus obesus) in the North Pacific from 2011 to 2013

Seiji Ohshimo A C D , Yuko Hiraoka A , Takuya Sato A and Sayaka Nakatsuka A B
+ Author Affiliations
- Author Affiliations

A National Research Institute of Far Seas Fisheries, Fisheries Research Agency, 5-7-1, Orido, Shimizu-ku, Shizuoka-city, Shizuoka 424-8633, Japan.

B Tanaka Sanjiro Co. Ltd, 1562 Ogori, Fukuoka 838-0141, Japan.

C Seikai National Fisheries Research Institute, 1551-8 Taira-machi, Nagasaki City, Nagasaki 851-2213, Japan.

D Corresponding author. Email: oshimo@affrc.go.jp

Marine and Freshwater Research 69(4) 585-606 https://doi.org/10.1071/MF17058
Submitted: 28 February 2017  Accepted: 18 October 2017   Published: 19 January 2018

Abstract

In the present study, we analysed the stomach contents of 585 bigeye tuna (BET; Thunnus obesus) caught in the Kuroshio–Oyashio transition zone, a high-productivity region in the western North Pacific Ocean, to describe feeding habits and prey size. We identified 46 prey species belonging to 40 genera. Fish otoliths and squid beaks found in stomachs were used to calculate prey body length and weight from allometric relationships. The percentage index of relative importance (%IRI) was calculated from the mean percentage of occurrence, number and weight of each prey species. Squid and fish were the main prey of BET in the sampling area and the highest %IRI prey species during the survey was Eucleoteuthis luminosa (luminous flying squid; 7.6%), followed by Gonatopsis makko (mako armhook squid; 4.8%) and Magnisudis atlantica (duckbill barracudina; 2.3%). The %IRI of E. luminosa decreased and that of M. atlantica increased with increasing BET body length. The size of prey fish increased with increasing BET size, whereas the size of prey squid was similar across BET size. The results indicate ontogenetic shifts in the feeding habits of BET in the study area. These data provide fundamental information that will improve our understanding of oceanic food webs in the Kuroshio–Oyashio transition zone, an important foraging area for many pelagic species.

Additional keywords: diet, index of relative importance, predator–prey size relationship.


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