# The Spatio-Temporal Distribution and Population Dynamics of Chub Mackerel (Scomber japonicus) in the High Seas of the Northwest Pacific Ocean

## TL;DR

This study examines how climate change and fishing affect the distribution and population of chub mackerel in the Northwest Pacific Ocean.

## Contribution

The study provides new insights into the spatio-temporal dynamics and population health of chub mackerel under climate and fishing pressures.

## Key findings

- High catches of chub mackerel were concentrated near Japan and Russia's exclusive economic zones from 2016 to 2021.
- The fishing grounds' gravity center shifted northwest, with a yearly decline in catch per unit effort.
- The population remained healthy despite reduced CPUE, likely due to high resource biomass rather than overfishing.

## Abstract

Chub mackerel (Scomber japonicus) is the main fishing species in the high seas of North Pacific Ocean (NPO) fishery, bringing great ecological and economic values. In recent years, the catch of chub mackerel has changed somewhat in response to the warming climate, changes in fishing effort, and the implementation of management systems. To provide more useful information for fishery management, we studied the characteristics of the fishing grounds of chub mackerel and evaluated their status of growth and exploitation. We emphasized the importance of climate warming to the dynamics of the chub mackerel population. This study is of great significance to the formulation of management measures for chub mackerel in the high seas of the NPO.

Chub mackerel (Scomber japonicus) is a typical small pelagic fish in the high seas of the Northwest Pacific Ocean (NPO), with great ecological and economic values. It is crucial to understand the spatio-temporal distribution and the population dynamics of chub mackerel for commercial fishing and fishery management. In this study, we analyzed the population dynamics and stock status of chub mackerel based on commercial fishing data. Results showed that from 2016 to 2021, high catches of chub mackerel were concentrated along the outer edge of Japan or Russia’s exclusive economic zone line, and the gravity center of the fishing grounds moved to the northwest gradually, with a decrease in the average value of catch per unit effort (CPUE) year by year. The fishing pressure may not be the major reason for the decrease in chub mackerel as the resource biomass was at a high level. The body length structure was reasonable, and large individuals were still present. The study highlights the fact that the population status of chub mackerel was healthy in 2016–2021 according to our results. However, it has to be emphasized that resource exploitation and fishery management also need to take into account the influence of climatic conditions.