# Responses of Fish Zeta Diversity (ζ) to Human Pressure and Cumulative Effects: A Feasibility Study of Fishing Ban Measures in the Pearl River Basin, China

## TL;DR

This study uses fish diversity data to identify areas in China's Pearl River Basin needing conservation or restoration due to human pressures, offering a new method for managing freshwater ecosystems.

## Contribution

A novel cumulative effect indicator based on zeta diversity is introduced to guide conservation and restoration decisions in freshwater systems.

## Key findings

- Fish communities in low-elevation areas are more affected by human activities than those in mountainous regions.
- The cumulative effect indicator shows a negative correlation with community uniqueness, validating its use for restoration planning.
- Zeta diversity responds differently to human pressures depending on elevation and diversity aspects like nestedness or turnover.

## Abstract

This study analyzed nearly four decades of fish data from China’s Pearl and Yangtze Rivers to develop a new method for identifying areas that need conservation or restoration due to declining freshwater fish diversity. Researchers created a novel indicator that measures the combined impacts of human activities (fishing, agriculture, and urban development) on fish communities by examining how different species are distributed across the river basin and respond to various pressures. They found that fish communities in low-elevation areas are more severely affected by human activities than those in mountainous regions, with some areas maintaining unique fish communities that require immediate protection while others have become homogenized and need restoration efforts. This research provides a scientific framework for decision-makers to prioritize conservation areas, implement fishing restrictions where needed, and guide restoration efforts in degraded regions, offering an approach that can be applied to other river systems worldwide facing similar challenges from human development and declining fish populations.

Amid declining fish diversity and human pressures in freshwater ecosystems, robust basin-scale assessments are vital for effective fisheries management. This study collated nearly four decades of fishery yields from the Pearl and Yangtze Rivers to identify conservation priorities in the Pearl River Basin. It introduced a novel cumulative effect indicator based on zeta diversity—a biodiversity pattern metric—integrated with cumulative effects analysis for management decision-making. The research employed a multi-site generalized dissimilarity model to examine the non-linear relationships between fish species composition (ζn) and human pressures, environmental factors, and geospatial variations across elevation gradients. The cumulative effect indicator, reflecting responses to anthropogenic stress when assessing ζ2 (related to β diversity), helped evaluate basins for conservation or restoration needs based on their unique or homogenized biotic communities. The results suggest that ζ diversity in low-elevation sub-basins has a stronger filtering effect on ζ by human pressures than in mid- to high-elevation sub-basins, where community aggregation is more random. The impact varied with diversity aspects (nestedness vs. turnover) and zeta order. A negative correlation between cumulative effects and community uniqueness validated the novel cumulative effect indicator’s effectiveness for guiding restoration in the Pearl River Delta, potential fishing bans, and karst conservation. This approach offers a theoretical basis for prioritizing areas for freshwater fish diversity conservation and fishing restrictions in the Pearl River Basin.