State-space Modeling Clarifies Productivity Regime Shifts of Japanese Flying Squid

Abstract

19 20 ABSTRACT (150-200 words) 21 Regime shifts of climatic and environmental conditions potentially affect productivity 22 of fisheries resources, posing challenging issues to stock management. The stocks of the 23 Japanese flying squid (Todarodes pacificus) are suspected to suffer from regime shifts, 24 but their detection is difficult and possibly doubtful because the nature of short-lived 25 species readily makes the effect of regime shifts confounded with observation errors. 26 Here we developed a new state-space assessment model to evaluate the influence of 27 regime shifts on spawner-recruitment relationship of the Japanese flying squid. The 28 model simultaneously estimates the population dynamics of multiple stocks that could 29share some life history parameters, making parameter inference stable. We demonstrate 30 that two-time regime shifts of productivity around 1991 and 2015 caused two-to 31 three-fold changes of maximum sustinabile yields. The model with regime shifts 32 clarifies the relationship between fishing pressure and spawner abudance that is difficult 33to detect in a model with no regime shift. The state-space approach will be a promising 34 tool to accurately assess stock status by separating recruitment process from observation 35 errors and contribute tothe management of marine biological resources sensitive to 36 regime shifts. 37 38 Keywords (up to 5) 39 Japanese common squid; MSY reference points; multistock modeling; state-space stock 40 assessment model (SAM) ; template model builder (TMB) 41Although these international circumstances require the estimation of MSY worldwide 62 (Costello et al. 2012;Martell and Froese 2013; Punt et al. 2014;Ichinokawa et al. 2017), 63 the existence of regime shifts makes the calculation of MSY challenging, because 64 regime shifts are likely to generate multiple stock-recruitment relationships and thus 65 multiple MSY-based reference points. It is suggested that although management advice A possible solution to estimation difficulty and unstability is joint modeling of 108 multispecies or multistocks rather than per-stock analysis (Thorson et al. 2013). 109Dynamics of multiple species and stocks could be partially correlated if they share 110 environmental conditions (Thorson and Minto 2015;). The 111 assumption on a species having the same life history paramter between different stocks 112 could be valid and enable parsimonious and stably predictive modeling. Fortunately, 113 there are two different stocks of the Japanese flying squid (autumn-spawning stock and 114 winter-spawning stock) that have been independently assessed (Kaga et al. 2019; 115 Kubota et al. 2019), but may have correlated dynamics (Hoshino et al. 2014). 116 In this article, we developed a new model for multistocks of annual life-span 117 species, called 'SAMUIKA' (State-space Assessment Model Used for IKA (squid in 118 Japanese)), to investigate whether and how regime shifts occur in productivity of the 119 Japanse flying squid. We firstly performed intensive model selecti...

Towards ecological, socioeconomic and cultural sustainability of marine ecosystem services

“…The next two papers (Nishijima et al, 2021; Shibata et al, 2021) focus on temporally variable biological parameters of specific fisheries stocks around Japan. Nishijima et al (2021) reveal regime shifts in the productivity of Japanese flying squid ( Todarodes pacificus ) stocks using a multi‐stock modeling approach.…”

“…The next two papers (Nishijima et al, 2021; Shibata et al, 2021) focus on temporally variable biological parameters of specific fisheries stocks around Japan. Nishijima et al (2021) reveal regime shifts in the productivity of Japanese flying squid ( Todarodes pacificus ) stocks using a multi‐stock modeling approach. Shibata et al (2021) infer that a recent increase in natural mortality of snow crab ( Chionoecetes opilio ) has drastically changed maximum sustainable yield.…”

“…In summary, this special feature introduces readers to current progress in marine ecosystem service studies. Population dynamic modeling is demonstrated to be useful for understanding fisheries productivity in a changing environment (Nishijima et al, 2021; Shibata et al, 2021). A large‐scale evaluation of biodiversity and ecosystem services will assist with the identification of hotspots and marine spatial planning (Sato et al, 2021).…”