Alternative restocking strategy could reverse declines of a critically endangered sturgeon

Demographic modelling can reveal options for improved conservation management, especially for rare or long-lived species not amenable to experimentation. Sturgeon (Acipenseridae) include many such species, endangered by demand for caviar, their unfertilized roe, and by dams blocking their migrations. Restocking of sturgeon populations with farm-raised individuals has probably prevented extinctions and widespread extirpations of some species, but it has rarely led to true recovery in Eurasia, given ongoing harvest. We used modified Leslie matrix models to test whether restocking with year-old juveniles instead of weeks-old fry could recover the critically endangered Amur sturgeon (Acipenser schrenckii), endemic to the Amur River basin along the Russia-China border. Without restocking, or even releasing an expert-recommended annual volume of young fry (10 million), we project that three of four Amur sturgeon populations will be nearly extirpated within 30 years. However, restocking with 5% as many (500 000) year-old juveniles annually could grow three populations (currently 0-425 mature females) and slow declines in another so that each has over 6400 mature females within 30 years. Retooling stocking efforts to use fewer juveniles that survive at higher rates than do small fry could buy time to reduce harvesting pressure on Amur sturgeon and for other related sturgeon species.