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This paper evaluates the outcome of the first release programme for Acipenser dabryanus rehabilitation in its natural habitat and focuses specifically on the growth rate of released juveniles, and on the dispersal of the fish after release. To conserve and restore natural recruitment, the conservation propagation programme has released hatchery-reared juveniles annually in the upper Yangtze River. This paper summarized the release activities and analysed post-release monitoring data. From 2010 to 2012, 7030 juveniles aged 1-3 years were released in the Shuifu and Yibin reaches of the upper Yangtze River. Incidental catches of 112 samples were recorded during the three-year observation period. Recapture sites were located between Yibin and Chongqing reaches (approximate range of 385 km), with 72.3% of the individuals recaptured within 20 km from the release site. Incidental catches were mainly in shallow water within 20 m of the riverbank. Body weight of the released sturgeon initially declined but this lost weight was soon regained. The low recaptured rate indicates that only a few of the released juveniles were able to survive and settle in the upper Yangtze River. The observed movement patterns suggest a potential additional downstream release site for future consideration to improve the performance of the released fish. [ABSTRACT FROM AUTHOR]

Swimming performance is one of the most important capacities for fish to cope with the harsh conditions in natural ecosystems and thus determines fitness of hatchery-reared fishes for stocking in the wild. Poor swimming capabilities of hatchery-reared fishes, including sturgeons, may be linked to the fact that the flow regimes in conventional culturing tanks are very often static and with very low currents, obviously differing from the natural environment. The objectives of the present studies were to: (i) learn about the swimming performance of the Dabry's sturgeon Acipenser dabryanus, one of the critically endangered species restricted to the Yangtze River, China; (ii) ascertain if it is possible to improve the swimming capacity of Dabry's sturgeon ( DS) by changing the current flow regime in conventional culturing tanks; (iii) determine the potential effects of such an environmental enrichment practice on the growth and survival of DS. Long-term culturing protocols with two culturing stages were conducted in a conventional tank with static water (Control, CT) as well as in a current-enriched tank with a step-controlled water velocity ( CET). Results showed after the first culturing stage, which began with 500 15-day-old post-hatch (dph) DS and ended with 40 dph DS, that the survival rates in CT (91.6%) were higher than that in the CET (84.4%). Total length, fork length and weight of DS in CET (n = 30) were higher than in CT (n = 30), but with no significant differences (P > 0.05). The Ucrit (13.2 ± 2.9 cm s−1, or 2.19 ± 0.48 FL s−1, n = 30) of the 40 dph DS in CET were significantly higher (10.2 ± 3.5 cm s−1, or 1.70 ± 0.59 FL s−1, n = 30) than in CT (P < 0.05) and the swimming endurance (101.6 ± 38.2 min, n = 15) of the 40 dph DS in CET at a velocity of 20 cm s−1 (representing 1.5-2.0 times Ucrit of 40 dph DS) is obviously longer (72.4 ± 38.2 min, n = 15) than in CT. The second culturing stage followed with 200 individuals of 40 dph DS coming from the first stage and ended with 80 dph DS. The survival rates during the second stage and the final growth parameters of 80 dph DS in CT and CET were not obviously different from each other (P > 0.05), whereas the Ucrit (48.5 ± 6.9 cm s−1, or 3.25 ± 0.46 FL s−1, n = 20) of the 80 dph DS in CET were also obviously higher (35.9 ± 8.5 cm s−1, or 2.41 ± 0.58 FL s−1, n = 20) in CT (P < 0.05). The results suggest a possible conservation culturing practice to improve the swimming capabilities of DS and will be foreseeably beneficial for hatchery-reared DS fitness when stocked in the wild, and will contribute to the effectiveness of future DS rehabilitation programmes. [ABSTRACT FROM AUTHOR]

This study was performed to determine the spatial structure and bottom characteristics of the only remaining spawning area of Chinese sturgeon ( Acipenser sinensis) located just downstream of the Gezhouba Dam. During the period 1996-2003, three methods were employed, including (i) the examination of the stomachs of opportunistic predatory fishes that feed on sturgeon eggs, (ii) tracking the mature sturgeons by ultrasonic tags and (iii) capturing eggs and yolk-sac larvae (ELS) at and near the river bottom by D-shaped bottom drift nets to monitor the spawning activities of A. sinensis. It was found that A. sinensis selected permanent locations to mate. There were two mating locations: an upstream mating area (UMA), in the tailrace of the Dajiang Hydroelectric Station and about 870 m far from the Gezhouba Dam (area, 0.1 km), and a downstream mating area (DMA), about 2500 m from Gezhouba Dam (area, 0.3 km). The DMA was the chief mating area and was used every year. The incubation area (for dispersal of fertilized eggs to incubate) was range from 870 m to 7 km from the dam. Generally, the total length of the spawning area was 5-7 km length (area 2.0-2.7 km) with the range slightly varied in different spawning activities. A relief map of the riverbed and a bottom hydroacoustic survey of the DMA found a deep depression and rocky substrate. These may be important characteristics of geomorphology for the spawning area of A. sinensis. [ABSTRACT FROM AUTHOR]