The results of the Laboratory of Nonlinear Dynamical Systems (2021)

According to voting at the Institute Scientific Council, the following result was recognized as the 2^nd most important one in the Institute in 2021

Lagrangian fronts as a predictor of locations for saury fishing

On the basis of the proposed concept of Lagrangian fronts and the database of the position of fishing boats in the Kuril Islands region, an analysis of the relationship between the locations of saury catches and fronts has been carried out. The locations of the fronts have been found every day during the 2004--2019 fishing seasons by calculating Lagrangian maps in the altimetric velocity field. Statistical analysis showed a strong correlation between the locations of catches and the positions of stable fronts with high values ​​of the finite-time Lyapunov exponent and its gradient (Fig. 1). In 2004 -2014, Lagrangian fronts with favorable conditions for fishing were formed around the quasi-stationary Hokkaido and Bussol anticyclones and at the boundaries of the 1st and 2nd branches of the Oyashio Current with an increased content of nutrients (Fig. 2). Calculating the Oyashio surface transport from 1993, we linked the catastrophic decline in catches from 2015 to a change in the flow of the 3rd Oyashio branch. Intensification of the 3rd branch and an increase in the Oyashio transport in 2015 - 2019 became favorable factors for the shift of fishing grounds from the traditional coastal areas of the southern Kuriles and Hokkaido to the east into the open ocean. A method is proposed for the operational forecast of favorable fishing grounds based on the daily calculation of Lagrangian fronts in real time. Recommendations are given to ichthyologists and fishermen on the trends of changes in the oceanographic situation in the fishing area in recent years.

Fig. 1. Cumulative distribution functions of the gradient of the finite-time Lyapunov exponent gradient in a 10 km buffer from the saury catch locations (dashed curve) and from randomly selected points over 1000 realizations. Averaging over a sample of 39,522 catch locations for the fishery seasons in 2004-2014.

Fig. 2. Positions of Lagrangian fronts of the quasi-stationary a) Hokkaido (center at 42.5 N, 147.5 E) and b) Bussol (center at 43.2 N, 153 E) anticyclones with superimposed catch locations in Sept.-Oct. 2004. The colors show the waters of the Soya (yellow) and Oyashio (blue) currents, the open ocean (green) and subtropical waters (red).

S.V. Prants, M.V. Budyansky, M.Yu. Uleysky, V.V. Kulik. Lagrangian fronts and saury catch locations in the Northwestern Pacific in 2004-2019. J. Marine Systems 2021, V. 222. Art. No. 103605 DOI: 10.1016/j.jmarsys.2021.103605 (1й квартиль WoS)