Solar and lunar influences on the spawning activity of Pacific bluefin tuna (Thunnus orientalis) in the south‐western North Pacific spawning ground

Pacific bluefin tuna (Thunnus orientalis) migrate to the south‐western North Pacific spawning grounds (area off Taiwan and the Ryukyu Islands) from mid‐April to early July. Reproductive traits of the species in this area have been studied for some time; however, temporal changes in spawning activity...

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Bibliographic Details
Published in:Fisheries oceanography 2018-01, Vol.27 (1), p.76-84
Main Authors: Shimose, Tamaki, Aonuma, Yoshimasa, Tanabe, Toshiyuki, Suzuki, Nobuaki, Kanaiwa, Minoru
Format: Article
Language:English
Subjects:
Area
Biology
Eggs
Females
Fish
Fishing
Follicles
generalized linear model
Generalized linear models
Interspecific relationships
Larvae
Marine fishes
Migration
Moon
moon phase
Ovaries
Predation
reproduction
Resource evaluation
Seasons
Spawning
Spawning grounds
spawning interval
Statistical models
Temporal variations
Thunnus orientalis
Tuna
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Summary:Pacific bluefin tuna (Thunnus orientalis) migrate to the south‐western North Pacific spawning grounds (area off Taiwan and the Ryukyu Islands) from mid‐April to early July. Reproductive traits of the species in this area have been studied for some time; however, temporal changes in spawning activity during this season are not well understood. In this study, the spawning fraction (proportion of females with post‐ovulatory follicles to total mature females) in relation to solar calendar date and lunar day was investigated using a generalized linear model. Sampling was conducted almost every day throughout the fishing season at Ishigaki Fishing Port (24°21′N, 124°09′E), southern Japan between 2012 and 2014, and a total of 212 ovaries were histologically observed. Spawning fraction continued to increase from the beginning to the end of the season. This indicates that the peak season of occurrence in the area and the peak of spawning activity did not co‐occur. Spawning fraction also changed with the lunar day and significantly increased around the new moon. Eggs and early larvae hatched around the new moon may have reduced the predation risk during night‐time. These findings improve the current knowledge of reproductive biology and resource evaluation of Pacific bluefin tuna and indicate that spawning activity is not constant, and has two or three peaks in each season.
ISSN:1054-6006
1365-2419
DOI:10.1111/fog.12235