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

Abstract

Pacific saury (Cololabis saira) has a 2‐year life span and age‐1 fish migrates from the central and western North Pacific to Japanese waters from summer to winter. To understand interannual abundance variability of Pacific saury in the North Pacific, we examined the extended Japanese standardized catch per unit effort (esCPUE) with generalized linear models (GLMs) during 1982–2018. Explanatory variables included proxies of total and non‐traditional fishing effort (Ettl and Ent) and environmental factors. Each environmental variable was averaged for years t ‐1 and t, corresponding to esCPUE in year t, as esCPUE represented two‐year classes. Ettl and Ent were averaged for years t ‐ 2 and t‐1, assuming fishing of year t affects biomass in year t + 1. We compared four GLMs with different explanatory variables: (a) environmental factors only, (b) fishing effort (without interactions) only, (c) environmental factors and fishing effort (without interactions) and (d) environmental factors and fishing effort (with interactions, i.e., time‐varying effects). Explanatory variables of the best GLM in terms of AICc included the following: Ent with different effects between 1982–2015 and 2016–2018, sea surface water temperature (SST) of the Kuroshio Recirculation Area (KRA) in winter, North Pacific Gyre Oscillation (NPGO) in winter, Southern Oscillation Index in winter, and the biomass of Japanese sardine. The NPGO, a proxy of zooplankton abundance, and KRA‐SST may affect the early growth and survival rates of Pacific saury. We hypothesized the abundance variability of Pacific saury was driven by environmental factors and fishing, the latter of which more adversely affected since 2016.

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

“…Recent studies demonstrated that rather than increased fishing effort, unfavourable conditions both in the spawning ground in Kuroshio waters and the nursery ground in Oyashio waters resulted in the large decline in the catch and biomass of Pacific saury (Liu et al, 2019; Xing et al, 2022). On the other hand, Yatsu et al (2020) hypothesized that abundance variability of Pacific saury during 1982–2018 was driven by environmental factors and fishing, with the latter exerting more adverse effect after 2016. The Japanese catch of Pacific herring depends primarily on the Hokkaido‐Sakhalin stock (Nagasawa, 2001) and this stock did not recover even in the cold period after the middle 1970s (Figure 1), but has recovered since 2015 (Ivshina, 2022).…”

Development of a bioenergetics and population dynamics coupled model: A case study of chub mackerel

“…high correlation with the decadal-scale stock fluctuations of dominant fish species, including the Pacific Decadal Oscillation (PDO) (Mantua et al, 1997;Chavez et al, 2003), North Pacific index in winter (NPI) (Trenberth and Hurrell, 1994;Yasunaka and Hanawa, 2002), North Pacific Gyre Oscillation index in winter (NPGO) (Di Lorenzo et al, 2008;Yatsu et al, 2021), and Arctic Oscillation index in winter (AO) (Thompson and Wallace, 1998;Ohshimo et al, 2009). Meanwhile, local oceanic environments, such as sea surface temperature (SST) in the Kuroshio Extension, have also been reported to influence the dynamics of stock fluctuations of commercial fish species (Noto and Yasuda, 1999).…”