Oceanographic factors affecting interannual recruitment variability of Pacific saury (Cololabis saira) in the central and western North Pacific

Abstract

Pacific saury (Cololabis saira) has a short life span of 2 years and tends to exhibit marked population fluctuations. To examine the importance of sea surface temperature (SST) and mixed layer depth (MLD) as oceanographic factors for interannual variability of saury recruitment in early life history, we analyzed the relationship between abundance index (survey CPUE (catch per unit of effort)) of age‐1 fish and the oceanographic factors in the spawning and nursery grounds of the previous year when they were born, for the period of 1979–2006, in the central and western North Pacific. Applying the mixture of two linear regression models, the variability in the survey CPUE was positively correlated with previous year's winter SST in the Kuroshio Recirculation region (KR) throughout the survey period except 1994–2002. In contrast, the survey CPUE was positively correlated with the previous year's spring MLD (a proxy of spring chlorophyll a (Chl‐a) concentration) in the Kuroshio‐Oyashio Transition and Kuroshio Extension (TKE) during 1994–2002. This period is characterized by unusually deep spring MLD during 1994–1997 and anomalous climate conditions during 1998–2002. We suggest that saury recruitment variability was generally driven by the winter SST in the KR (winter spawning/nursery ground), or by the spring Chl‐a concentration (a proxy of prey for saury larvae) in the TKE (spring spawning/nursery ground). These oceanographic factors could be potentially useful to predict abundance trends of age‐1 saury in the future if the conditions leading to the switch between SST and MLD as the key input variable are elucidated further.

Review of population dynamics and management of small pelagic fishes around the Japanese Archipelago

“…1; partly overlapping with KESA), which is a winter spawning and nursery ground of saury, or by spring chlorophyll-a concentration (a proxy of prey for saury larvae) in the KOTZ and Kuroshio Extension (spring spawning and nursery grounds). The correlations between the survey-based CPUE and both winter SST and spring chlorophyll-a concentration were positive (Ichii et al 2018). The former correlation is consistent with that reported by Yasuda and Watanabe (2007) and partially consistent with that reported by Yatsu and Watanabe (2017).…”

“…The NPGO and sardine recruitment showed generally negative effects, and the relationship between the CPUE and February KESA SST anomaly was dome-shaped with a peak CPUE skewed positive toward the SST anomaly. Although a Rossby wave excited by NPGO propagates from the Central North Pacific to the Kuroshio area with a lag of 2-3 years (Di Lorenzo et al 2013), this lack of lag is consistent with the observed similarity in trajectories of CPUE and those of the relative abundance of Pacific saury estimated by a survey with drift nets in the Central North Pacific Ocean at longitudes of 170°E, 175°E, and 180°E, during June and July of 1979(Ichii et al 2018; hereafter called survey-based CPUE). These situations suggest that saury migrate from the Central North Pacific Ocean toward Hokkaido Island during summer, which is consistent with the summer migration patterns assumed by Suyama et al (2016).…”

“…These situations suggest that saury migrate from the Central North Pacific Ocean toward Hokkaido Island during summer, which is consistent with the summer migration patterns assumed by Suyama et al (2016). On the basis of statistical analyses of year-to-year variability of the surveybased CPUE during 1979, Ichii et al (2018 suggested that saury recruitment variability was generally driven by winter SST in the Kuroshio Recirculation area ( Fig. 1; partly overlapping with KESA), which is a winter spawning and nursery ground of saury, or by spring chlorophyll-a concentration (a proxy of prey for saury larvae) in the KOTZ and Kuroshio Extension (spring spawning and nursery grounds).…”

“…N.B. : Standardized CPUE (ton per fishing operation) was used for Pacific saury as a proxy of biomass differences in the optimum warmer winter SST in the Kuroshio Recirculation area for saury and cooler February KESA SST for sardine (Noto and Yasuda 1999;Yasuda and Watanabe 2007;Ichii et al 2018;Nishikawa 2018). However, the underlying mechanism of a generally negative effect of sardine recruitment and generally positive effects of NPGO on Pacific saury CPUE (Yatsu and Watanabe 2017) remains unknown.…”

Clarifying the effects of environmental factors and fishing on abundance variability of Pacific saury (Cololabis saira) in the western North Pacific Ocean during 1982–2018

“…Pacific saury ( Cololabis saira , saury hereafter) is an oceanic species and one of the most important fishery stocks in the western North Pacific Ocean, characterized by the interannual and decadal‐scale variability of stock abundance (Figures 1 and 2; Anonymous, 2019 March; Ichii et al., 2018; Tian et al., 2004; Watanabe, 2009). The distribution of saury extends to the coastal areas of the North America, where saury has been incidentally caught (Anonymous, 2019 March).…”