# Analysis of Relative Abundance Distribution and Environmental Differences for Blue Mackerel (Scomber australasicus) and Chub Mackerel (Scomber japonicus) on the High Seas of the North Pacific Ocean

## TL;DR

This study maps the distribution of two similar mackerel species in the North Pacific using fishing data and models, revealing how they respond to environmental changes and climate shifts.

## Contribution

The study introduces a new statistical model (ZOIBM) to accurately assess mixed mackerel catches and identifies environmental drivers of their distribution.

## Key findings

- Blue Mackerel prefer warmer southern waters, while Chub Mackerel favor cooler northern areas.
- Both species are shifting northward and eastward, likely due to climate change.
- Sea surface temperature is the key factor driving their distribution differences.

## Abstract

Blue Mackerel and Chub Mackerel are two economically important fish in the North Pacific Ocean that look very similar. Because they are difficult to tell apart, fishermen often report them together in catch records. This makes it hard for scientists to accurately assess the health of each species’ population. This study used fishing data from 2014 to 2023 and advanced computer models to distinguish between the two species in mixed catches. We successfully mapped where each species is most abundant. We found that Blue Mackerel prefer warmer, southern waters, while Chub Mackerel are more common in cooler, northern areas. Key environmental factors like sea surface temperature (SST) and Chlorophyll-a concentration (Chla) were found to drive these different distributions. Over the past decade, we observed that both species are moving northward and eastward, likely in response to climate change. As their habitats shift, their populations are overlapping more, which could lead to increased competition. Our findings provide a new method for accurately assessing these species and offer a scientific basis for better, more sustainable fishery management in the North Pacific.

The accurate assessment and management of Blue Mackerel (Scomber australasicus) and Chub Mackerel (Scomber japonicus) resources in the high seas of the Northwest Pacific are constrained by the persistent issue of data misreporting in catch records, which arises from their high morphological similarity. This study integrates fishery logbooks and field sampling data from Chinese purse seine fleets (2014–2023), along with key oceanographic factors—six of which were finally selected after correlation analysis. We introduce, for the first time, a Zero-One Inflated Beta Model (ZOIBM) to analyze the spatiotemporal distribution of the relative abundance of these two mackerel species. Furthermore, a Generalized Additive Model (GAM) was employed to reveal the environmental mechanisms driving their niche differentiation. The results show that the ZOIBM demonstrates excellent performance (R2 = 0.63, RMSE = 0.305), effectively quantifying the proportional composition of the two species in mixed catches. Spatially, high-abundance areas of Blue Mackerel were concentrated within 35–44° N, 145–160° E, with its proportion decreasing at higher latitudes. In contrast, Chub Mackerel exhibited an opposite latitudinal pattern, with its high-abundance areas covering a broader latitudinal range (35–47.5° N). The analysis of environmental drivers indicated that SST was the most critical factor for differentiation, while Chla and VO further amplified the divergence in resource utilization strategies between the species. From 2014 to 2023, the distribution centroids of both mackerel species showed significant northward and eastward shifts, and their spatial overlap has been continuously increasing. This research provides a methodological reference for the fine-scale assessment of co-occurring fish resources and offers a scientific basis for the sustainable management of the North Pacific mackerel fishery.