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Silver carp ( Hypophthalmichthys molitrix ), bighead carp ( Aristichthys nobilis ), grass carp ( Ctenopharyngodon idella ), and black carp ( Mylopharyngodon piceus ) are the four major Chinese carps and are commercially important aquaculture species in China. Reproduction of these carp has declined since the construction of the Three Gorges Dam (TGD) due to an altered water fl ow and thermal regime in the Changjiang (Yangtze) River. However, details of the changes in reproduction of the four species are not well understood. To assess the impact of the TGD on reproduction of the four carp, we investigated their eggs and larvae at Yidu City, which is 80 km below the TGD, during 2005-2012. We examined diff erences in larval abundance of the four species in the Jianli section (350 km downstream of the TGD) before (1997)(1998)(1999)(2000)(2001)(2002) and after (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) construction of the TGD. Based on these observations, the fi rst spawning date of the four species was delayed a mean of about 25 days after the dam was constructed. Mean egg abundance in the Yidu section of the river was 249 million and mean larval abundance was 464 million, which were signifi cant decreases since the 1980s. Moreover, larval abundance in the Jianli section after the dam was constructed was signifi cantly lower than that before construction (ANCOVA, P <0.05). The observed larval abundance accounted for only 24.66% of the predicted value in 2003 when the dam was fi rst inundated. The present spawning grounds between the TGD and Yidu section of the river are very similar to those described in the 1980s, and some spawning grounds exist upstream of the TGD. Large free-fl owing stretches upstream of the TGD and the creation of artifi cially fl ooded downstream reaches are needed to stimulate spawning and eff ectively conserve these four major Chinese carps species.

Chinese sturgeon ( Acipenser sinensis ) is the fl agship species of the Changjiang River. The migration route of this species is blocked by the fi rst dam, the Gezhou Dam, and its reproduction is aff ected by the Three Gorges Dam (TGD), one of the largest dams in the world. We studied the impact of the impoundment of the Three Gorges Reservoir (TGR) since 2003 on the spawning stock and the natural reproduction of the Chinese sturgeon by using our monitoring data from 1997 to 2013. Results indicate that TGR impoundment has delayed the fi rst spawning dates of the fi sh from middle-late October to late November, decreased the amount of spawning activities from twice to only once each year, and signifi cantly reduced egg production. In particular, the fi sh did not demonstrate any spawning activities in 2013. Therefore, TGR impoundment signifi cantly aff ects the natural reproduction of the fi sh downstream of the TGD. The spawning stock size of the fi sh is also predicted to further decrease in the future, which will lead to a risk of population extinction. Ecological regulations must be imposed on decreasing the water temperature to 20°C before mid-October and increasing water discharge downstream of the TGD in October to induce spawning of the Chinese sturgeon.

SummaryIn order to understand the downstream hydrological and water chemical status after impoundment of the Three Gorges Reservoir (TGR) and to assess the impact of changes on the spawning of Chinese Sturgeon, we assessed hydrological factors (water temperature, water level, water discharge and sediment concentration), and some water chemical factors (dissolved oxygen and ammonia-N) at the Yichang spawning reach during pre-and post-impoundment periods. In addition, hydro-acoustic survey on the occurrence and distribution of Chinese sturgeon were undertaken and investigations on sturgeon-egg-eating predatory fishes were conducted to evaluate the spawning occurrence date of the Chinese sturgeon during autumn between 1997 and 2008. The

Summary The present study investigated the presence of Chinese sturgeon Acipenser sinensis on its only remaining spawning ground (below the Gezhauba Dam), and monitored the behaviour under different environmental conditions from 24 December 2015 to 23 January 2016. A fixed ARIS (Adaptive Resolution Imaging Sonar) system was used and a total of 72 Chinese sturgeon were detected during nine observations. Detections initially recorded a few A. sinensis in the early days of late‐December 2015, with an increase in recordings, leading to a peak in early‐January 2016 and declining thereafter. Water temperature slowly decreased during the study period from 18.1 to 15.7°C. During the middle of this temperature decline the sturgeon observations peaked, suggesting that Chinese sturgeon could have an optimal temperature range. The sturgeon Detections Per Unit Effort (DPUE) was higher in the night hours, peaking before dawn, suggesting a circadian behaviour rhythm. Sturgeon spawning was not observed during the investigation period. A delay in the decrease in water temperature caused by the Three Gorges Reservoir and the few numbers of reproductively mature individuals are suspected to have contributed to the failure in natural breeding.

Chinese sturgeon, Acipenser sinensis, is a critically endangered anadromous fish species spawning in the Yangtze River of China during October and November. In this study, we analyzed the effects of hydrological factors, such as water temperature and discharge, on the natural reproduction time of the Chinese sturgeon and evaluated the impact of the impoundment of the Three Gorges Reservoir (TGR) based on our survey data from 1998 to 2011. The results showed that the first spawning dates were significantly (P < 0.05) correlated with the date of water temperature reaching 20°C (20°C WT dates), October mean discharge (Oct. discharge), and the discharge change from October to November (Oct-Nov Δdischarge). Regression analysis suggested that one day delay of 20°C WT dates could postpone the first spawning date by 0.673 days. A discharge increase of 1000 m(3)s(-1) in October could bring forward the first spawning date by two days. Our results also indicated that the impoundment of the TGR had delayed the first spawning time due to water temperature lag and flow regulation. We suggest the following ecological regulations in order to facilitate conservation of the Chinese sturgeon: to eliminate water temperature lag by regulating water temperature downstream of the Three Gorges Dam (TGD), to enhance water discharge downstream in October, and to complete impoundment before October.

SummaryFor effective conservation, it is important to explore the environmental cues initiating the spawning activities of a fish species. Based on monitoring data gathered between 1998 and 2011, the relationships between spawning activities of the Chinese sturgeon, Acipenser sinensis, and several environmental cues were analyzed using the rare events logistic regression 'Relogit' method, which indicated that water temperature, 1-day Δ-discharge, and atmospheric pressure were among the key spawning cues for A. sinensis (P < 0.05). It is suggested that Chinese sturgeon might have an optimal environment window of 17-20°C water temperature, high dayto-day discharge increase, and low atmospheric pressure for spawning. In support of Chinese sturgeon reproduction, suggested modifications to the operational procedures for the Three Gorges Reservoir (TGR) to trigger spawning are: lowering the downstream water temperature to below 20°C before mid-October and expanding the period with water temperatures of between 17 and 20°C; to create a day-to-day intermittent increase in the discharge to an optimal spawning water temperature; and to regulate flow at nights with a low atmospheric pressure. IntroductionEnvironmental cues related to spawning activities of fish species have received much attention (Jobling, 1995), and include photoperiod (Rubin et al., 2005), water temperature (Danilowicz, 1995;Yang et al., 2007), water discharge (Lake, 1967;Chen and Wu, 2009;Paragamian and Wakkinen, 2011;Zhang et al., 2012), velocity (Carl, 1982Zhang et al., 2007), dissolved oxygen (Taylor, 1984;Schiemer et al., 2002), and climate (Zhang et al., 2008; Str€ ussmann et al., 2010). Each species may have an 'optimal environmental window' for reproductive success and recruitment maximization (Cury and Roy, 1989;Roy et al., 1992;Baumgartner et al., 2008). For a fish population to persist, reproduction must be successful to provide new recruits (Mangel et al., 2010). Therefore, understanding the environmental cues of fish spawning is of major importance for fishery management (Bryan et al., 2006; Wright and Trippel, 2009).The Chinese sturgeon, Acipenser sinensis, normally matures at an age of 13-26 for females and 8-18 for males (Wei et al., 1997;Gao et al., 2009). Historically, the fish reproduced in the upper reaches of the Yangtze and Pearl rivers. Spawning stock of the Pearl River was small and almost extirpated within the last decades. In the Yangtze River, Chinese sturgeon spawned in the 600-800 km upper reaches from Xinshi to Fuling in October and November before the Gezhouba Dam (GD) was built in the middle reaches of the Yangtze River in 1981 (Anonymous, 1988) (Fig. 1). Since then, the Gezhouba Dam has blocked spawning migration and drastically reduced the size of the A. sinensis population to a site restricted to a 3 km reach downstream of the dam, representing <1% of the original spawning site (Gao et al. In general, the Chinese sturgeon had two spawning activities each year before the impoundment of the Three Gorges Reservoir (TGR) i...