Rebuilding the critically endangered Yangtze finless porpoise population: Successful release from an ex situ conservation programme

Ex situ conservation and population reinforcements or reintroductions are vital strategies for protecting endangered species, yet efforts for cetaceans have been notably limited. Through post-release monitoring based on wearable radio tag and passive acoustic methods, we report the first successful release of a critically endangered small-toothed whale, the Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), into the wild. Our monitoring results indicate that, by the third day after release, the two porpoises from the ex-situ population had joined a local individual and gradually integrated into the core distribution area of the local population. Continuous monitoring by the Yangtze Cetacean Protection Network revealed no recorded deaths among the released porpoises. This successful release demonstrates the potential of this approach as a supplementary measure for the restoration of the Yangtze finless porpoise wild population., Animals and the release site
Two male YFPs (T21M42: 135.0 cm, 42.4 kg; T21M02: 127.0 cm, 33.2 kg), both from the ex-situ population in Tian-e-Zhou, were captured on April 28, 2021. Following health examinations and the implantation of identification chips, they were transferred to the Laowan branch for a two-year acclimatization period. On April 25, 2023, at 10:30 AM (UTC + 8), both porpoises were released into the upstream waters of the Middle branch, near the Laowan branch (Fig. 1). This release site was chosen due to its relatively low levels of human activity and the presence of abundant fish resources. It is not part of the main navigation channel, and during the dry season, it hosts a stable group of over ten local YFPs.
Tracking with wearable radio tags
The released porpoises were tracked using a wearable radio tag system. This system comprises a flexible vest-style miniature radio tag that transmits signals collected by base stations positioned around the release area (Fig. 2)...., , # Rebuilding the critically endangered Yangtze finless porpoise population: Successful release from an *ex situ* conservation programme

[https://doi.org/10.5061/dryad.k0p2ngfj5](https://doi.org/10.5061/dryad.k0p2ngfj5)

## Description of the data and file structure

The release of the Yangtze finless porpoise is part of a protective research programme and that the survival of the individuals included was ensured. We applied wearable radio tag to track the Yangtze finless porpoise after releasing. When the porpoises surface to breathe, the tag exposed to the air emits electromagnetic waves, which are collected by the base stations, allowing us to obtain spatiotemporal information on the tagged porpoises. Stationary passive acoustic monitoring (PAM) using automatic porpoise indentification device RPCD-A4 was applied to complement monitoring. Vessel-based visual surveys were conducted to monitor the distribution of wild porpoises post-release.

### Files and variables

#### File: Radio\_d...,