Long‐term changes in recruitment of age‐0 Pacific bluefin tuna (Thunnus orientalis) and environmental conditions around Japan

Abstract

Recruitment of age-0 Pacific bluefin tuna (Thunnus orientalis) from 1952 to 2014 was examined by a sequential regime shift detection method. The regime shifts in recruitment were detected in 1957, 1972, 1980, 1994 and 2009

Long‐term variability in the fish assemblage around Japan over the last century and early warning signals of regime shifts

“…The sudden recoveries in recruitment and productivity of Japanese sardines in the KC‐KE region were associated with favourable regional SST anomalies that were enhanced under the favourable PDO regime after the mid‐1970s regime shift (Yatsu & Kawabata, 2017). The recruitment time series of Pacific bluefin tuna showed negative relationship with the PDO (Ishida et al, 2018). Catch and biomass of flying squid were high (low) during positive (negative) PDO period (Yatsu et al, 2013).…”

Occurrence of Pacific bluefin tuna Thunnus orientalis larvae off the Pacific coast of Tohoku area, northeastern Japan: Possibility of the discovery of the third spawning ground

“…PBF larval survey should be annually carried out off Tohoku and Kuroshio–Oyashio transition area to elucidate the ecological characteristics such as environmental factors, food availability, feeding, and growth of PBF larvae hatched in the area, comparing to those of the spawning grounds in the Nansei Islands area and Sea of Japan. Although it has been reported that interannual variability of the recruitment of age 0 fish is very high (Ishida et al, ; Yamada et al, ), information on the early life ecology and survival of PBF in the three spawning grounds will contribute to understanding the mechanism of recruitment variability and the stock structure.…”

“…Mortality during the egg, larval, and juvenile stages is considered to be the main cause of interannual variability in recruitment in many species (Bailey & Houde, ). In the case of PBF, interannual variability of the recruitment is very high (Ishida et al, ; Muhling, Tommasi, Ohshimo, Alexander, & DiNardo, ; Yamada, Takagi, & Nishimura, ), and there is no relationship between the spawning stock biomass and recruitment of PBF during both periods of high and low levels of PBF stock (ISC, ). Recently, several studies have revealed that the survival and consequent recruitment success of larval PBF depends largely on their growth during the larval stage in the two well‐known spawning grounds (Ishihara, Watai, Ohshimo, & Abe, ; Tanaka, Satoh, Iwahashi, & Yamada, ; Watai et al, ; Watai, Ishihara, Abe, Ohshimo, & Strüssmann, ).…”