Habitat use of adult Pacific bluefin tuna Thunnus orientalis during the spawning season in the Sea of Japan: evidence for a trade-off between thermal preference and reproductive activity

K Fujioka,A Aoki,T Kuwahara,Ee Estess,H Fukuda,T Kitagawa,N Suzuki,Y Takahara,Cj Farwell,S Ohshimo,M Kato,K Sasagawa,O Abe,J Kinoshita,K Komeyama,S Furukawa

doi:10.3354/meps13746

Abstract

To examine the habitat usage of adult Pacific bluefin tuna (PBF), electronic tagging was conducted in the Sea of Japan during May and June of 2012-2017. Archival tags were internally implanted and pop-up satellite archival transmitting tags were deployed; data on the horizontal movements and diving behaviours of 36 individual PBF were successfully retrieved. In the summer spawning season, the tagged PBF were concentrated near Sado Island and Oki Island in the Sea of Japan, and they were distributed widely to the southwest (near Tsushima Island) or northeast (near the Tsugaru Strait) in the autumn and winter. We obtained the first long-term tracking record (246 d) for adult PBF, and this individual exhibited residency in a known spawning region during the spawning season in the proximity of warm-core eddy features. This fish spent most of the daytime below the thermocline between 30 and 150 m depths where the surface ambient temperature was 26.0 ± 1.5°C, but at night it ventured into the warm surface layer. Its whole-body heat transfer coefficient increased when it experienced warm waters (≥24°C), which we suggest is a physiological response to avoid overheating. The mean peritoneal cavity temperature was only 1.8°C higher than the ambient temperature, compared with 6.9°C higher during the cooler autumn-winter period. Our hypothesis is that the warm surface temperatures found in the spawning grounds induce a physiology-reproduction trade-off in adult PBF, which must behaviourally and physiologically thermoregulate their body temperature to gain spatial and temporal access to oceanographic conditions that may promote larval survivorship and growth.

Highlights

Understanding the reproductive ecology of Pacific bluefin tuna Thunnus orientalis (PBF) is essential to revealing the population dynamics of this commercially and ecologically important species
We examined the horizontal movements and vertical distributions recorded by both tag types and conducted a detailed analysis of the PBF’s thermal physiology using fine-scale (5 s sampling rate) archival tag data
The duration of recorded data ranged from 7−246 d for the archival tags and 1−240 d for the pop-up satellite archival transmitting (PAT) tags (Table 1)

Summary

Introduction

Understanding the reproductive ecology of Pacific bluefin tuna Thunnus orientalis (PBF) is essential to revealing the population dynamics of this commercially and ecologically important species. Mar Ecol Prog Ser 668: 1–20, 2021 research on PBF gonadal development and larval distribution has advanced our understanding of the spatial and temporal patterns of spawning activity (Chen et al 2006, Tanaka et al 2007, Ashida et al 2015, Okochi et al 2016, Ohshimo et al 2017, 2018). Recent electronic tagging research and catch data have shown that mature PBF typically enter the Sea of Japan through the Tsugaru Strait from the Pacific Ocean and distribute southwards throughout the basin (Boustany et al 2010, Fujioka et al 2015, Tawa et al 2017). The spatial and temporal patterns of the swimming behaviour of adult PBF in the spawning area have not been examined

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Results