Variation of blubber thickness of the Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) in human care: Adaptation to environmental temperature

• Published in: Water Biology and Security Vol. 2; no. 4; p. 100200
• Main Authors: Tang, Bin, Hao, Yujiang, Wang, Chaoqun, Deng, Zhengyu, Shu, Guilin, Wang, Kexiong, Wang, Ding
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2023; KeAi Communications Co. Ltd
• Subjects: Blubber thickness; Food intake; Thermal adaptation; Water temperature; Yangtze finless porpoises; Yangtze finless porpoises; Thermal adaptation; Food intake; Water temperature; Blubber thickness
• ISSN: 2772-7351; 2772-7351
• DOI: 10.1016/j.watbs.2023.100200

Blubber thickness (BT) has a seasonal pattern in most small cetaceans in temperate and polar regions, which may be a crucial adaptive mechanism in response to environmental temperature changes. However, BT and environmental temperature correlations have never been tested experimentally in any cetacean species owing to logistical difficulties in the aquatic environment. The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis, YFP) is one of the smallest cetacean species worldwide, which exclusively inhabits the middle and lower regions of the Yangtze River in China. Here, we investigated BT variation patterns in YFPs and their relationship to environmental temperature changes using ultrasound imaging technology by longitudinally monitoring four YFPs in human care. We found that blubber was not evenly distributed in the skin of YFPs. BT increased along the craniocaudal axis from the head to the umbilical girth, and decreased towards the fluke, with relatively thicker blubber in the dorsal region than in the ventral and lateral regions. Significant negative correlations between BT and seasonal water temperature changes were observed in YFPs. However, different body regions display different sensitivities to seasonal temperature changes. The BT in the anal girth region exhibited noticeable seasonal changes. In contrast, the umbilical lateral and ventral regions showed relatively blunt seasonal changes, indicating different adaptive functions of the blubber in different regions. BT in the dorsal region decreased linearly with increasing water temperature. In the lateral and ventral regions, BT significantly changed with water temperature at a threshold of 18 ​°C. The YFPs had relatively thinner BT than similar-sized harbor porpoises that inhabit relatively high latitudes with much lower water temperatures. This further demonstrates the adaptive function of BT in response to environmental temperatures in small cetaceans. This study elucidates the seasonal pattern of BT variation in small cetaceans and provides insight into adaptation mechanisms of small cetaceans to temperature changes. •The blubber thickness (BT) in captive YFPs was monitored longitudinally using ultrasound imaging. Results showed regional variations: anal girth region exhibited relatively higher seasonal changes, while umbilical lateral and ventral regions showed relatively lower seasonal changes, suggesting diverse adaptive functions of blubber in these areas.•Captive YFPs showed negative correlations between BT and water temperature. Dorsal BT decreased linearly with higher water temperature, while lateral and ventral regions had a threshold at 18℃ for BT changes.•Similar to changes in BT, the food intake of YFPs also had a negative correlation with water temperature, which implies that there might be a mechanism of environmental temperature regulating BT of YFPs by changing the appetite or food intake of the animals.