Anticipating fluctuations of bigeye tuna in the Pacific Ocean from three-dimensional ocean biogeochemistry

1. Subseasonal to decadal ocean forecasting can make significant
contributions to achieving effective management of living marine resources
in a changing ocean. Most applications rely on indirect proxies, however,
often measured at the ocean surface and lacking a direct mechanistic link
to the dynamics of marine populations. 2. Here we take advantage of
three-dimensional, dynamical reconstructions and forecasts of ocean
biogeochemistry based on a global Earth System Model to hindcast and
assess the capacity to anticipate fluctuations in the dynamics of bigeye
tuna (Thunnus obesus Lowe) in the Pacific Ocean during the last six
decades. We reconstructed spatial patterns in catch per unit effort (CPUE)
through the combination of physiological indices capturing both habitat
preferences and physiological tolerance limits in bigeye tuna. 3. Our
analyses revealed a sequence of four distinct regimes characterized by
changes in the zonal distribution and average CPUE of bigeye tuna in the
Pacific Ocean. Habitat models accounting for basin-wide fluctuations in
the thermal structure and oxygen concentration throughout the water column
captured interannual fluctuations in CPUE and regime switches that models
based solely on surface information were unable to reproduce. Decade-long
forecast experiments further suggested that forecasts of three-dimensional
biogeochemical information might enable anticipation of fluctuations in
bigeye tuna several years ahead. 4. Synthesis and applications. Together,
our results reveal the impact of variability of biogeochemical conditions
in the ocean interior on the dynamics of bigeye tuna in the Pacific Ocean,
raising concerns about the future impact of ocean warming and
deoxygenation. The results also lend support to incorporating subsurface
biogeochemical information into ecological forecasts to implement
efficient dynamic management strategies and promote the sustainable use of
marine living resources.