Migration and feeding habits of juvenile Chinese sturgeon (Acipenser sinensis Gray 1835) in the Yangtze Estuary: Implications for conservation

Spatial and temporal variation in migration and feeding ecology of juvenile Chinese sturgeon (Acipenser sinensis Gray 1835) is reported for waters around Chongming Island, Yangtze Estuary, between April and August 2015. A migration survey showed that juvenile Chinese sturgeon remained within the Yangtze Estuary for a period of time preceding their onward migration to the sea; upper estuarine reaches were an important transition habitat during April and May, while nearshore coastal areas were foraging habitat during June to August. Stable isotopic analysis revealed (1) significantly lower isotope values in smaller-sized Chinese sturgeon (<= 100 mm) than larger- sized fish (>100 mm), which indicated a dietary shift likely occurs at fork lengths greater than 100 mm; (2) the increase in values of delta C-13 and delta N-15 from May to August implied an ontogenetic dietary shift from lower to higher trophic-level prey items; and (3) slight changes in distributional range among different coastal sites implied that individuals fed on similar food items. Coastal shallows represent major foraging areas for juvenile Chinese sturgeon in the Yangtze Estuary. In addition to the conventional conservation measures at the nature reserve, we suggest additional conservation actions to better protect juvenile Chinese sturgeon residing in the estuary; namely: (1) expanding the protected area and adding a seasonal component, from April to August, to afford better protection of juvenile Chinese sturgeon in the whole estuary, but particularly just upstream of the estuary mouth and in nearshore waters; and (2) banning all fishing activities and extending protection to the food resources (such as zoobenthos and small-sized fishes) of juvenile Chinese sturgeon in coastal shallows.