从连续到偶发：中华鲟在葛洲坝下发生小规模自然繁殖

中华鲟(Acipenser sinensis Gray)为国家一级重点保护野生动物,典型的溯河洄游产卵鱼类。历史上,中华鲟在长江上游及金沙江下游产卵,由于葛洲坝修建阻隔了其洄游通道,1981年以后在葛洲坝下形成了比较稳定的产卵场,1982―2013年,每年均有自然繁殖发生。由于其栖息生境退化,每年洄游进入长江的中华鲟繁殖亲本逐年减少,2013―2015年连续3年在已知葛洲坝下中华鲟产卵场未监测到中华鲟自然繁殖活动。2016年11―12月的野外监测发现,中华鲟在宜昌葛洲坝下已知产卵场发生了自然繁殖。其中底层网具采集到中华鲟鱼卵(卵膜)67粒、仔鱼22尾;解剖食卵鱼发现,10尾食卵鱼类共摄食中华鲟卵454粒;水下视频观测到5处中华鲟卵黏附底质位点。根据采集到的鱼卵发育期及采集位点推算,产卵时间为2016年11月24日凌晨,产卵场位于葛洲坝大江电厂以下约300 m的江段内,产卵日水温为19.7℃,流量为6610 m3/s,水位为39.7 m。     

长江江苏溆浦段2015 年发现中华鲟野生幼鱼的形态和分子鉴定

在葛洲坝下中华鲟(Acipenser sinensis)产卵场连续两年未监测到自然繁殖的情况下,2015年6月在江苏溆浦段发现15尾疑似中华鲟幼鱼。本研究通过形态学和分子生物学方法对该15尾幼鲟进行鉴定。形态学度量结果显示,除1尾个体外,新发现的14尾幼鲟与历史记载的中华鲟野生幼鱼生物学性状完全一致,但其体长和体重低于历史同期出现在该区域的中华鲟。同时采用11个多态微卫星位点,对15尾幼鲟样本和分布于我国的3种鲟鱼,包括30尾中华鲟(A.sinensis)、39尾达氏鲟(A.dabryanus)和33尾施氏鲟(A.dabryanus)进行遗传分析,发现这15尾幼鲟与中华鲟的遗传距离最近(F_(st)=0.039,P0.05),其次为达氏鲟(F_(st)=0.108,P0.05),最远为施氏鲟(F_(st)=0.209,P0.05),从遗传和进化的角度判定该批幼鱼为中华鲟,该结果暗示中华鲟在葛洲坝下游极有可能找到了新的产卵场,为中华鲟的繁殖群体和幼鱼的种群监测提供了依据。遗传多样性分析显示,该批鱼的遗传多样性(SW=1.998)略低于野生中华鲟(SW=1.886),暗示中华鲟幼鱼遗传多样性水平降低,野生亲本的数量仍不容乐观。     

Factors affecting dam passage and upstream distribution of adult Pacific lamprey in the interior Columbia River basin

Low dam passage rates of adult Pacific lamprey (Entosphenus tridentatus) during upstream spawning migration have been implicated in the species' steep decline in the interior Columbia River basin. In this 2000–2010 study, we used radiotelemetry to evaluate potential predictors of lamprey passage success at McNary Dam, located ~469 river kilometres (rkm) from the Pacific Ocean. The tagged population included 276 lampreys collected at McNary Dam and 53 collected at Bonneville Dam (rkm 235) that migrated to McNary Dam. McNary Dam passage efficiency was similar for the two samples, with multiyear estimates of 0.65 and 0.75, respectively. Larger‐bodied lampreys and those with earlier migration timing were more likely to return to McNary Dam after release, to pass the dam and to be detected upstream from McNary reservoir. Far more lampreys entered the upper Columbia River than the Snake River, suggesting that environmental cues (e.g., water discharge, temperature) or conspecific cues (e.g., pheromone concentrations) affect lamprey distribution above this large confluence. Overall, results indicate that Pacific lamprey passage success at barriers depends on a combination of individual lamprey traits plus seasonal and site‐specific effects on behaviour.     

物理栖息地模型在中华鲟自然繁殖生态流量决策中的应用

以国家一级保护物种中华鲟(Acipenser sinensis)为研究对象,探讨三峡大坝和葛洲坝水利工程在不同流量调度措施下对中华鲟产卵栖息地的影响。通过考虑中华鲟生境需求特性建立了中华鲟产卵场的物理栖息地模型,根据模型得出的适宜栖息地面积变化来量化不同的流量调度措施对其产卵场质量的影响,然后利用实测的中华鲟产卵量和资源量数据来验证和评价物理栖息地模型的可靠性和实用性,从而进行合理的生态流量决策。结果发现,年平均适宜栖息地面积的变化曲线与中华鲟的产卵量和资源量变化曲线有着相同的变化趋势,从而推断适宜栖息地面积可以反映中华鲟产卵栖息地的质量;并通过不同流量工况的计算,进行最佳生态流量决策。利用该物理栖息地模型可以有效地量化流量改变对目标物种栖息地质量的影响,为中华鲟产卵栖息地的生态水利调度提供评估和决策的方法。     

Larval lake sturgeon production and drift behaviour in the Menominee and Oconto Rivers,Wisconsin

Lake sturgeon (Acipenser fulvescens) have been negatively impacted by barriers to migration, pollution and overharvest. Biological data such as the timing of spawning activity and larval drift have provided a better understanding of larval production success or failure on a site-specific basis. However, many river systems that serve as reproductive locations for remnant lake sturgeon populations remain understudied. The objective of this study was to compare and contrast aspects of larval lake sturgeon drift within and between the Oconto and Menominee Rivers over multiple reproductive seasons. Differences in larval drift chronology, the size of drifting larvae during the season and the cross-sectional profile of drifting individuals as a function of river velocity were evaluated. D-frame drift nets were deployed at a single transect below spawning sites in the Menominee (2012, 2013 and 2014) and Oconto Rivers (2013, 2014 and 2015). A total of 4,442 larvae were captured across all seasons. Larvae exhibited nonrandom drift profiles related to water velocity, and larvae size was related to horizontal drift location. The seasonal increase in body size of drifting larvae also differed among drift events within and between years and across rivers. This information will provide a better understanding of lake sturgeon early life history and has practical management connections including spawning site protection/enhancement and river flow mitigation.     

Seasonal migrations of adult and sub‐adult redband trout in a high desert basin of Eastern Oregon,USA

Abstract – Redband trout (Oncorhynchus mykiss gairdneri) migrations were tracked between March 2007 and June 2009 in the Donner und Blitzen River, Oregon, USA, using radio telemetry and PIT tags. We investigated the upstream extent and timing of spawning migrations for two groups of trout, considered the factors that influenced the rate of trout migration and explored the seasonal patterns of redband trout migration related to temperature and flow conditions. We found that trout made long‐distance migrations (up to 91 km) to spawn. Spawning trout from the lower river and middle river migrated to the same reaches, but lower river trout reached spawning habitats later than individuals from the middle river. Migration rate had a positive relationship with fork length and mean river discharge. We also found that redband trout made upstream spring migrations as sub‐adults and as adults. Whereas adult trout migrated to spawn, immature individuals migrated to river segments with more favourable thermal conditions. In both cases, migrations occurred where seasonally appropriate or life‐stage‐specific habitat patches for growth, survival, or reproduction were spatially segregated.     

Estimating number of spawning white sturgeon adults from embryo relatedness

The goal for using genetic information derived from embryo samples is to gain insight into the reproductive biology of adult white sturgeon, Acipenser transmontanus Richardson. The relationship between egg development stages on the extraction of quality DNA was determined, and subsequent genotype data were used to infer contributing spawner numbers. White sturgeon DNA was present in extractions from all stages; however, pre‐gastrulation stage embryos generally failed to amplify sufficient genetic loci for analysis. Using experimentally created families, multivariate ANOVA and maximum‐likelihood sibship methods estimated the presence of 10 contributing parents from 11 actual adult spawners. It was observed that unidentified half‐sibling relationships (offspring sharing one parent) caused error for inferring parent numbers. Genetic methods estimated 13–40 parents potentially contributed to a collection of wild‐caught embryos, with variable numbers of parents inferred from separate spawning events (varying from 8 to 24). Egg source material provides a means to enhance the accuracy of annual spawning population size estimates, which is important for informing habitat restoration, harvest and water management decisions and recovery planning.     

Emigration of hatchery‐reared Pallid Sturgeon,Scaphirhynchus albus (Forbes and Richardson), through a Missouri River dam

The middle Missouri River (MMR; Fort Randall Dam, SD to Gavins Point Dam, NE‐SD) is stocked with hatchery‐reared pallid sturgeon, Scaphirhynchus albus (Forbes and Richardson), from upper Missouri River broodstock to aid recovery of this federally endangered species. Emigration of these fish through Gavins Point Dam restores genetic connectivity that likely existed pre‐impoundment but could lead to outbreeding depression in the future. Recapture data of hatchery‐reared pallid sturgeon stocked in the MMR were evaluated to improve understanding of pallid sturgeon emigration. From 2004 to 2015, 219 emigrants were caught: 4 stocked at age ≥2 years and 215 stocked at age ≤1 year. Emigration of the 2001‐2007 year classes stocked at age 1 was a consistent phenomenon and appeared higher than emigration of year classes stocked at ages 2–3. Little evidence suggested emigration was associated with an unusually high‐water event in 2011. The annual emigration probability of individuals stocked at age 1 estimated from multi‐state mark–recapture models was 0.05 [95% confidence interval = 0.04–0.06] for fish ages ≥1 year. This study suggests that alterations to stocking practices (e.g. stocking age) may affect emigration rates and, therefore, connectivity among pallid sturgeon populations.     

Restoration of sturgeons: lessons from the Caspian Sea Sturgeon Ranching Programme

Depletion of sturgeon stocks world-wide has increased interest in aquaculture-based restoration programmes. The Caspian Sea Sturgeon Ranching Programme (SRP) of the former Soviet Union represents a unique opportunity to evaluate expense, benefits and potential ecological and genetic effects of such restoration programmes. The SRP was initiated in the 1950s to compensate for lost spawning habitat in the Volga River and elsewhere. After its completion in 1962, the Volgograd Dam reduced spawning grounds in the Volga River system, the principal spawning tributary of the Caspian Sea, by ∼80%. For two of the three commercial sturgeon species (Russian sturgeon, Acipenser güldenstädti , and stellate sturgeon, A. stellatus ), yields improved after the imposition of the 1962 moratorium on sturgeon harvests in the Caspian Sea. Volga River fisheries were managed for spawning escapement. Although imprecisely known, the contribution of the millions of stocked Russian and stellate juveniles during 1962–91 was most likely important to sustaining fisheries, although less so (contributing to <30% of the adult stock) than natural recruitment. Apparently, reduced spawning grounds, supplemented with artificial spawning reefs were sufficient to support reproduction and large fishery yields of Russian and stellate sturgeons. For beluga sturgeon, Huso huso , harvests in the Volga River were nearly all dependent upon hatchery stocking. Beluga sturgeon spawning grounds were mostly eliminated with the construction of the Volgograd Dam. Without the hatchery programme, beluga sturgeon in the Volga River and Caspian Sea would in all likelihood have been extirpated. Currently, sturgeons are severely depleted in the Volga River and Caspian Sea due to poaching and lack of co-operation between countries exploiting the species. Aquaculture-based restoration in Russia is now viewed a chief means of rebuilding stocks of Caspian Sea sturgeons.     

Preliminary data on the induction of ovulation in white sturgeon (Acipenser transmontanus Richardson)

Forty-six white sturgeon females captured prior to their spawning migration in the San Francisco Bay and during their spawning run in the Sacramento River were induced to ovulate with three different hormonal substances: white sturgeon and common carp crude pituitary extracts, and [D-Ala⁶] GnRH analogue. All three inducing agents were potent at the respective doses of 2.5 mg, 4.0 mg and 0.1 mg dry matter per kilogram of female body weight. The best ovulatory responses and egg fertilities were observed in fish administered hormonal treatment during the months of March and April. Fish captured prior to and during their spawning migration exhibited similar spawning success.     

Spawning induction and seed production of Eastern little tuna,Euthynnus affinis (Cantor, 1849), in the post‐ and pre‐spawning seasons by hormonal treatment in a semi‐closed recirculation system with elevated temperature

We previously established a method for spawning induction in Eastern little tuna (ELT) Euthynnus affinis (Cantor, 1849) by administering a gonadotropin‐releasing hormone analog (GnRHa) during the natural spawning season in Japan (August–October). In order to establish seed production of ELT in the off‐spawning season, we first conducted three spawning induction trials by GnRHa administration from October 2011 to January 2012 using ELT broodstock (2 years old; three females and four males) maintained in a 10‐m³ tank with a semi‐closed recirculation system and static elevated temperature. Average water temperature and daily egg production in three trials lasting 11–15 days were 27.0 ± 0.09°C and 268 173 eggs (Trial 1), 27.0 ± 0.11°C and 277 9098 eggs (Trial 2), and 25.5 ± 0.39°C and 291 113 eggs (Trial 3) respectively. Mean fertilization rate and mean hatching rate were 70.4% and 60.5% (Trial 1), 83.9% and 79.6% (Trial 2), and 62.5% and 57.4% (Trial 3) respectively. We also succeeded in producing ELT larvae in the pre‐spawning season (April–July), although the quantity and quality of larvae produced were inferior to those produced in other calendar months. In trials involving periodic GnRHa administration during the off‐spawning seasons, hatched larvae were obtained in the 10‐m³ tank after six of nine administrations in the 2011–2012 off‐spawning season and in 16 of 19 administrations in the 2012–2013 off‐spawning season. The findings of this study demonstrated that hormonal treatment and thermal control could be used to extend the spawning period in ELT, potentially allowing larval production in the post‐ and pre‐spawning seasons.     

Potential for reintroduction of lake sturgeon in five northern Lake Michigan tributaries: a habitat suitability perspective

• 1. Conservation and rehabilitation efforts for lake sturgeon Acipenser fulvescens throughout the Great Lakes include the re‐establishment of self‐sustaining stocks in systems where they have been extirpated.
• 2. Information on the suitability of potential lake sturgeon habitat in tributaries is important for determining their capacity to support lake sturgeon stocking and to develop system‐specific rehabilitation strategies.
• 3. Geo‐referenced habitat information characterizing substrate composition, water depth, and stream gradient were applied to a life‐stage specific lake sturgeon habitat suitability index in a geographic information system to produce spatially explicit models of life‐stage specific habitat characteristics in five northern Lake Michigan tributaries from which lake sturgeon have been extirpated.
• 4. Habitat models indicated that high quality lake sturgeon spawning and staging habitat comprised 0 to 23% and 0 to 9% of the available habitat, respectively, whereas high quality juvenile lake sturgeon habitat was relatively ubiquitous throughout each river and comprised 39 to 99%.
• 5. Comparison of these data to lake sturgeon habitat availability in Lake Michigan tributaries currently supporting populations indicated that spawning and staging habitats may limit the ability of these systems to support spawning. Efforts to re‐establish lake sturgeon populations in these systems should consider the creation of spawning and staging habitat to increase reproductive and recruitment potential prior to the initiation of stocking efforts.

Copyright © 2007 John Wiley & Sons, Ltd.     

Threshold values of river discharge and temperature for anglers' catch of Atlantic salmon,Salmo salar L.

Abstract The catch by anglers of adult Atlantic salmon, Salmo salar L., was studied over a 5-year period in the River Gaula, Norway. Atlantic salmon were caught over a wide range (23–570 m³ s^?1) of the observed extent of river discharge (13–950 m³ s^?1) and throughout the range of temperature (4–23 °C), but both factors strongly affected catch rate. Significant correlations between the number of Atlantic salmon caught daily, and water temperature (r = 0.33) and river discharge (r = ?0.42) were found in 1987 and 1989, respectively. The highest daily catch occurred between 50 and 150 m³ s^?1, and at temperatures between 13 and 16 °C. Threshold values for water discharge and temperature were found to exist at 250 m³ s^?1 and 8 °C, with the highest catches below and above these values, respectively.     

Deep hooking,landing success and gear loss using inline and offset circle and J hooks when bait fishing for white sturgeon

The issue of deep hooking is of concern in white sturgeon, Acipenser transmontanus Richardson, fisheries because nearly all anglers use bait with a stationary presentation on the river bottom to catch them, and bait fishing is often associated with higher instances of deep hooking and hooking mortality. Deep hooking rates, landing success and catch rates were investigated for anglers bait fishing for white sturgeon using circle and J hooks with inline and offset alignments fished with both active and passive hook‐setting methods. Anglers hooked 578 white sturgeon and landed 508 fish, ranging in size from 60 to 316 cm total length (mean = 137 cm). Deep hooking rates averaged 0.6% and did not differ between hook types, hook alignments or hook‐setting methods. Landing success (the proportion of hooked sturgeon that were successfully landed) and catch rates were also equivalent between hook types, hook alignments and hook‐setting methods; landing success averaged 88% and catch rates averaged 0.27 fish/hr. Results of this study indicate that deep hooking is rare when angling for white sturgeon using standard bait‐fishing gear regardless of hook‐setting method or whether circle or J hooks were used; regulations restricting hook type in sturgeon bait fisheries are therefore unwarranted.     

A simple method for assessing minimum flows in regulated rivers: the case of sea lamprey reproduction

• 1. The sea lamprey (Petromyzon marinus) is an anadromous species that occurs in some large Iberian rivers, such as the Tagus, and their tributaries. The sea lamprey populations of the River Tagus are threatened by habitat loss and overexploitation, which means that conservation measures, including maintenance of the spawning grounds, are urgent. Habitat loss is mainly due to hydroelectric and flood‐control dams that have affected the migration and spawning habitats of anadromous species. The main objective of this study was to use a simple, cost‐effective method to assess a minimum instream flow for the regulated River Tagus. The method used was based on the wetted perimeter–discharge relationship, but accounted for the habitat requirements of spawning sea lampreys.
• 2. In 1998, a habitat survey was conducted along a 30 km segment of the River Tagus downstream from Belver Dam (the first impassable obstacle for fish movements), a stretch that includes potential habitats for spawning sea lampreys. Four spawning areas were identified, and in each one a representative reach was selected along which to collect elevation and geo‐positional data. For a range of flows from 0 to 50 m³ s^?1, hydraulic modelling and studies of spawning habitat availability were conducted, both for each reach and for the total wetted area of the four reaches.
• 3. The availability of spawning habitat was limited by flow. Results showed that the present minimum flow downstream from Belver Dam (8 m³ s^?1) is insufficient to ensure suitable habitat conditions in a significant part of the segment studied; gains in wetted usable area were more substantial with discharges of up to 20 m³ s^?1, and thus a minimum flow of 10–20 m³ s^?1 was recommended. Potential spawning habitat could be improved by increasing instream flow to at least 50 m³ s^?1. The impacts of the Belver release regime on anadromous species are discussed and a more ‘ecologically oriented’ form of water management is suggested

. Copyright © 2004 John Wiley & Sons, Ltd.     

Linking habitat characteristics with juvenile density to quantify Salmo salar and Salmo trutta smolt production in the river Sävarån,Sweden

Abstract Habitat mapping along 85 km of river was related to juvenile (15 years of electric fishing) and smolt (3 years of screw‐trapping) abundance data to estimate salmon, Salmo salar L., and sea trout, Salmo trutta L., smolt production in the River Sävarån, northern Sweden. Spawning site selection by radio‐tagged salmon (n = 12) and sea trout (n = 4) was also assessed. Fifty‐one hectares of potential spawning and nursery habitat was found in the main stem river, representing 25% of the total river area. These areas were estimated to yield 1300–7580 salmon and 630–3540 sea trout smolts based on juvenile densities, equating with 3 years of screw‐trap data (2990–5080 salmon and 680–2520 trout smolts, respectively). A hypothetical maximum production of about 19 900 salmon smolts was predicted for the river at a density of 40, 0+ salmon 100 m^?2. Tracking adults during the spawning period identified optimal and potential reproductive areas.     

Observations of ovarian involution in the Australian grayling (Prototroctes mareana)

Abstract  – A 2-year study of the threatened Australian grayling, Prototroctes mareana, was undertaken to investigate its reproductive strategy in relation to river flow. Monitoring of reproductive maturity in the Barwon River in south-eastern Australia indicated that no spawning occurred in the 2 years. In both years, ovarian involution was observed in a large proportion of the sampled population; flows during this period were less than the historical average. When coupled with the historical evidence, these observations suggest that spawning coincides with increased river discharge. River regulation may inhibit spawning.     

Using coupled fish behavior–hydrodynamic model to investigate spawning migration of Japanese anchovy,Engraulis japonicus,from the East China Sea to Taiwan

Adult Japanese anchovies (Engraulis japonicus) migrate from the East China Sea to the coastal region of Taiwan to spawn around late winter and early spring and, later, their larvae constitute important fisheries in Taiwan. However, their migration route and its mechanism remain unclear. To investigate their spawning migration, we used a coupled fish behavior–hydrodynamic modeling approach. The physical field is simulated by the Pacific Ocean adaptation of the TaIwan Multi‐scale Community Ocean Model (TIMCOM) and the fish migration by Lagrangian tracer tracking with the aid of approximation of fish swimming behavior. We investigated three fish behavioral scenarios: (i) passive tracking of the current, (ii) swimming along with the current, and (iii) swimming along with the current and then changing to swimming toward the optimal spawning temperature. The comparison with and without Changjiang discharge is used to investigate the impacts of discharge reduction due to the Three Gorges Dam. Our results suggest that spawning migration of Japanese anchovy from the East China Sea to Taiwan may be aided by the China Coastal Current and that adult anchovies cannot reach the spawning site by passive advection alone. Thus, the swimming behavior of anchovies is crucial during the spawning migration, as it provides extra velocity and the orientation to the favorable spawning grounds. In addition, the adult anchovy is unlikely to reach the coastal area of Taiwan without Changjiang discharge. Our findings indicate that a coupled fish behavior–hydrodynamic model can help understand the influences of physical environment on the migration of Japanese anchovies.     

基于年龄结构的中华鲟资源量估算方法

根据长江中的中华鲟亲鱼捕捞数据的年龄结构,推算不同年龄段中华鲟亲鱼进入长江参与繁殖的占比,首次将长江和海洋中的中华鲟同时纳入估算模型进行计算,构建了一套估算中华鲟资源量的新方法。稳态计算结果显示,在葛洲坝截流前,长江中每年有效补充量为1 882尾,长江和海洋中育龄(雌:13~34龄,雄:8~27龄)总资源量为32 260尾,其中雄鱼15 310尾,雌鱼16 950尾,每年在长江中参与繁殖的中华鲟新老股群之和(1 727尾)占总资源量的比例约5%。计算得出葛洲坝截流后长江中的中华鲟产卵繁殖容量仅为截流前的6.5%,1981年葛洲坝截留造成68%~80%的1980年老股群被阻隔在上游。结合葛洲坝截流后的捕捞数据推算了1981年后长江和海洋中的中华鲟资源量变迁过程。计算结果与捕捞数据反映的趋势一致,证明模型可靠有效。研究表明,葛洲坝截流后,随着捕捞量的减少,长江中的繁殖群体数量上升,1990年左右达到峰值(约2 200尾),随后迅速下降,2010年为170尾左右。葛洲坝截流后中华鲟产卵繁殖环境容量的大幅下降是近年来中华鲟资源量急剧下降的重要原因。     

Patterns of fish movement at a desert river confluence

Quantifying fish movements in river networks helps identify critical habitat needs and how they change with environmental conditions. Some of the challenges in tracking fish movements can be overcome with the use of passive integrated transponder (PIT) tagging and antennas. We used PIT technology to test predictions of movement behaviour for four fish species at a mainstem–tributary confluence zone in an arid‐land river system. Specifically, we focused on the McElmo Creek tributary confluence with the San Juan River in south‐western Utah, USA. We quantified variation in species occurrences at this confluence zone from May 2012 to December 2015 relative to temporal and environmental conditions. We considered occurrences among species relative to tagging origins (tributary versus mainstem), season and time of day. Generally, fishes tagged in the focal tributary were more likely to be detected compared to fish tagged in the mainstem river or other tributaries. Additionally, adults were most likely to be detected across multiple years compared to subadults. Based on a Random Forests model, the best performing environmental variables for predicting seasonal detections included mainstem discharge during run‐off season (razorback sucker Xyrauchen texanus), tributary discharge during monsoon season (Colorado pikeminnow Ptychocheilus lucius) and mainstem water temperature (flannelmouth sucker Catostomus latipinnis and channel catfish Ictalurus punctatus). The variable responses by endemic and introduced fishes indicate tributary habitats provide several key functions within a fish community including spawning, rearing, foraging and refuge.