The marine food-web structure from the Pearl River Estuary (PRE) is especially vulnerable to climate change and other anthropogenic impacts, such as overfishing, which is directly linked to reductions in fish population sizes. As opportunistic feeders, Indo-Pacific humpback dolphins (Sousa chinensis) will likely respond to natural and anthropogenic changes by adjusting their diet. We expected that diet change had a significant impact on the population dynamics of the PRE humpback dolphins. Therefore, the relationship between diet composition and reproductive parameters in dolphins was investigated. Our results showed that the annual birth rate is 5.6%, and the survival rate of calf (surviving to three years old) is lower than 30%, which present a downward trend in recent years (2011-2018). Meanwhile, we examined spatiotemporal trends of diet compositions in 46 weaning humpback dolphins from 2004 to 2017 in the PRE based on blubber fatty acid signatures using quantitative fatty acid signature analysis (QFASA). Bombay duck was the predominant prey species, followed by Dussumier’s thryssa and mullet, whereas other prey species were present at considerably reduced proportions in diets. The proportion of larger fishes (Bombay duck and mullet) in the diet has exhibited a significant decreasing trend in recent years, whereas the smaller fish (Dussumier’s thryssa) steadily increased over the whole period, possibly due to the severe impacts of climate change and other human stressors on large fishes in estuarine waters. The proportions of Bombay duck in the diet were significantly and positively correlated with the population dynamics parameters. Our study provided solid evidence that diet shift and decrease of prey resources may have a further impact on the population size and structure of the dolphins.
 

Indo-Pacific humpback dolphins; reproductive parameters; diet; environmental change; fatty acids.