Survival rate and population size of Indo‐Pacific humpback dolphins (Sousa chinensis) in Xiamen Bay, China

Abstract

The survival rate and population size of Indo-Pacific humpback dolphins (Sousa chinensis) in Xiamen, China, were estimated from vessel-based surveys during 2007-2010. Over the course of 202 d (881.1 observation hours), 76 groups were observed, and 52 dolphins were successfully identified. The Cormack-Jolly-Seber model estimated a constant apparent survival of 0.948 (95% CI: 0.922-0.966).Based on the open/POPAN model, the population size was estimated at 70 individuals (95% CI: 63-88). To explore the effect of uneven yearly survey effort, we pooled the data with seven sampling occasions with similar effort. This data set generated similar results of a constant survival of 0.957 (95% CI: 0.918-0.978) and population size of 72 (95% CI: 65-88). The small population size of the Xiamen humpback dolphins satisfies the Critically Endangered criterion of IUCN (D), and emphasizes urgency of the need for protection of the population. Improved monitoring efforts should be focused on enhancing our understanding of current status and evaluating impacts of all anthropogenic activities. A conservation plan for the population should also be drawn up.

Abundance and residency dynamics of the Indo‐Pacific humpback dolphin, Sousa chinensis, in the Dafengjiang River Estuary, China

“…In this study, we estimated the abundance of humpback dolphins exposed to the 3‐year survey ranged between 353 and 430 (mean = 389). This number cannot and should not be interpreted literally into a population size estimate, though POPAN modeling is frequently used to report population size (Chan & Karczmarski, ; Chen et al, , ; Xu et al, ). Chen et al () reported about 250 humpback dolphins in the Dafengjiang River Estuary, about 150 humpback dolphins in nearby Hepu Dugong Reserve habitat and, accordingly, concluded the population size is approximately 400 humpback dolphins in the northern Beibu Gulf.…”

“…Capture‐mark‐recapture exercises based on photo‐identification records were applied to understand residency pattern, emigration‐reimmigration dynamics, and abundance estimates (Chan & Karczmarski, ; Chen et al, ). Program SOCPROG (version 2.7; Whitehead, ) and program MARK (version 8.2; White & Burnham, ) were used to conduct the above analyses.…”

“…Accordingly, POPAN modeling in program MARK was used to estimate the humpback dolphin abundance () exposed to sampling during the entire study period (Chan & Karczmarski, ; Chen et al, ; Jutapruet et al, ; Schwarz & Arnason, ; Tyne et al, ; White & Burnham, ). A goodness‐of‐fit test by program RELEASE GOF in program MARK was applied to test the model suitability (Chen et al, ). Candidate models were built with effects on survival (ϕ) and capture ( p ) probabilities, including temporal dependency ( t ), group (age‐classes) variation ( g ), and constant over occasions (.).…”

Environmental models for predicting habitat of the Indo‐Pacific humpback dolphins in Fujian, China

“…The coastline extends up to 3,752 km, and consists of many bays, including the Port of Shacheng, Sanduao waters, Luoyuan Bay, the Minjiang River estuary, Fuqing Bay, Xinghua Bay, Meizhou Bay, Quanzhou Bay, Xiamen Bay and Dongshan Bay. Fujian province is known as an important habitat for humpback dolphins (Chen et al, , ; Liu & Huang, ), and has rich marine resources (Sun & Zhang, ).…”

“…at least 89.2 km 2 land was reclaimed between 1955 and 2000 in Xiamen (Liu & Huang, ). Currently, humpback dolphins have been found to mainly inhabit Xiamen (Chen et al, , ; Liu & Huang, ), and no more than 30 individuals in the Quanzhou, Dongshan and Ningde waters have been observed (Chen, Zheng, Wang, Xu, & Yang, ; Wu et al, ). However, dedicated surveys in Fujian are lacking in most of the areas except for Xiamen, meaning that the large‐scale distribution patterns of humpback dolphins are still poorly understood.…”