State‐space modeling clarifies productivity regime shifts of Japanese flying squid

Abstract

Regime shifts of climatic and environmental conditions potentially affect the productivity of fishery resources, posing challenges in stock management. The stocks of the Japanese flying squid (Todarodes pacificus) are suspected to suffer from regime shifts, but detecting the occurrence of regime shifts in this species is generally difficult and unreliable because the short‐lived nature of this species inherently confounds the effect of regime shifts with observation and process errors. Here we developed a new state‐space assessment model to evaluate the influence of regime shifts on the spawner‐recruit relationship of the Japanese flying squid. The model simultaneously estimates the population dynamics of multiple stocks that could share some life history parameters, thereby stabilizing parameter inference. We demonstrate that two regime shifts in productivity around 1991 and 2015 caused two‐ to threefold changes of maximum sustainable yields. The model with regime shifts clarifies the relationship between fishing pressure and spawner abundance that is difficult to detect in a model with no regime shift. The state‐space approach is a promising tool for accurately assessing stock status by separating the recruitment process from observation errors and is expected to contribute to the effective management of marine biological resources sensitive to regime shifts.

Modeling Pulse Dynamics of Juvenile Fish Enables the Short-term Forecasting of Population Dynamics in Japanese Pufferfish: A Latent Variable Approach

“…Accordingly, our random-effect model could efficiently avoid overfitting, reduce uncertainty in observation errors, and smooth yearly trends in abundance indices. The availability of random effect models is growing in fisheries science along with the development and wide application of TMB (Nielsen and Berg 2014;Thorson and Barnett 2017;Nishijima et al 2021). We demonstrate that a latent-variable model with random effects can provide an effective solution for CPUE standardization in data-poor situations.…”

“…In this paper, we develop a latent variable approach for CPUE standardization to accurately forecast short-term population dynamics of Japanese pufferfish based on survey data. Random effects models with latent variables are prevailing in recent fisheries science because they can robustly estimate a large number of parameters, which would cause overfitting or a failure to converge if using fixed effects (Nielsen and Berg 2014;Thorson and Barnett 2017;Nishijima et al 2021). Here, we aim to stably estimate appropriate positive values of expected CPUE, even for zero-catch samples, by using a random effects model.…”

Towards ecological, socioeconomic and cultural sustainability of marine ecosystem services

“…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).…”

“…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.…”