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Paddlefishes and Sturgeons of the Yangtze and Mississippi Rivers: Status, Biology, and Management.
... In addition to the previously mentioned fish species, the Chinese sturgeon and other endemic fish species were previously commercially harvested for food in the Yangtze River . For instance, the annual commercial harvested number of Chinese sturgeon from the Yangtze River was around 400 to 600 during 1972-1980, and then reached 1163 in 1981 when large numbers of Chinese sturgeon were not able to pass the Gezhouba Dam and gathered below the dam ( Fig. 2a; Phelps et al. 2016;Huang et al. 2017). Also, the pre-spawn population of Chinese sturgeon in the mainstem Yangtze River below Gezhouba Dam was about 2176 individuals in 1980, but was reduced to \ 1000 in 1989, and then to only around 20 in 2017 (Fig. 2a;Zhu et al. 2009;Huang 2013;CMEE 2017;CMOA 2019). ...
... Likewise, the population of Chinese paddlefish in the mainstem Yangtze River below Gezhouba Dam dramatically decreased from about 32 individuals in 1985 to functional extinction. That is, the total existing population became too low to support natural reproduction around 1995 ( Fig. 2b; Wei et al. 1997;Phelps et al. 2016;CMOA 2019). ...
... Data sources:Zhu et al. (2009) and CMEE(2017)Ó Royal Swedish Academy of Sciences 2019 www.kva.Total harvested number and pre-spawn of Chinese sturgeon Acipenser sinensis (the vertical line indicates the initial operation of the Gezhouba Dam in 1981) in the Yangtze River and b total estimated number of adult Chinese paddlefish Psephurus gladius below the Gezhouba Dam in the mainstem of the Yangtze River. Data sources:Wei et al. (1997),Zhu et al. (2009), Huang (2013,Phelps et al. (2016),Huang et al. (2017), CMEE (2017, and CMOA (2019) Total estimated number of Baiji or Yangtze river dolphin Lipotes vexillifer and Yangtze finless porpoise Neophocaena asiaeorientalis in the mainstem of the Yangtze River. Data sources:Chen and Hua (1985),Chen et al. (1993),Zhang et al. (1993Zhang et al. ( , 2003, Turvey et al. (2007), Mei et al. (2014), Chen et al. (2016), CMEE (2017), and CAS (2018) Royal Swedish Academy of Sciences 2019 www.kva.se/en ...
China has over 1320 freshwater fish species, 877 of which are endemic. In recent decades, over-exploitation and landscape pressures have threatened them and led to a severe aquatic biodiversity crisis. In response, large-scale fishing bans have been promulgated to protect freshwater biodiversity in major Chinese rivers since the early 1980s. Here, we present the historical background and current challenges to the fishing bans. Implementing large-scale fishing bans may help improve China’s current freshwater biological resources and biodiversity to some extent. But implementing fishing bans alone is not sufficient to solve the crisis because of shortcomings of the current bans and expanding human pressures in most river basins. Thus, we recommend regulating other anthropogenic pressures, expanding duration and extent of current fishing regulations, establishing a comprehensive monitoring program, and initiating basin-scale ecological rehabilitation. These programs are also needed in other developing countries facing similar biodiversity crises and human pressures.
... It was an anadromous species reaching lengths up to 7 m and historically lived in many large rivers flowing into the West Pacific . The species declined due to overexploitation, but especially the construction of migration barriers prevented it from completing its lifecycle (Phelps et al. 2016). ...
Animals need to move between different habitats to successfully complete their life cycle. Anthropogenic activities and infrastructure impact animal movement, especially in the aquatic realm, due to habitat alteration (including fragmentation), pollution, overexploitation, the spread of invasive alien species and climate change. Gaining knowledge on the complex phenomenon of fish movement is essential to understand the diverse ways in which anthropogenic activities may influence the spatial ecology of fish, which can inform management. The four main methods to study fish movement are through observation and interception, electronic tracking, otolith chemistry and environmental DNA. We discuss the strengths and shortcomings of these methods and suggest effective management can be aided by combining these and other methods. Often the weaknesses of one technique can be met by the strengths of the others. Also, cross-boundary collaboration is essential for the successful management of fish that move over jurisdictional boundaries to complete their life cycle. Data analyses on interdisciplinary datasets obtained at spatial scales relevant to the movement ecology of a given population can yield a more holistic understanding of fish movement. This knowledge may help for the appropriate selection of cost-efficient, evidence-based and effective management actions that balance the needs of fishes and human activities.
Graphical abstract
Dams have reduced longitudinal river connectivity (LRC) worldwide, impairing habitat and migration opportunities for many freshwater fish species. However, national assessments linking LRC and threatened inland fish species distributions are lacking. Here, we show the trends in the LRC in China over the past 60 years, and quantitatively analyse their implications for threatened inland fish species. The average LRC in China decreased from 93.5% in 1960 to 25.1% in 2018, and the significant deterioration in LRC occurred over the last 20 years. Water resource regions with a high number of threatened fish species are concentrated in southern China, and the degree of threat to inland fish species increases with a decreasing average LRC. A total of 125 inland fish species are threatened by habitat degradation and loss, which is mainly caused by the construction of dams. Intrinsic factors and pollution are two other key threats to fish species in addition to the reduction of LRC. The results of this study can help us better understand the trends in LRC in China and their implications for inland fishes. Meanwhile, this study provides guidance for river management to help preserve biological diversity, including enhancing management of natural reserve areas, establishing ecological compensation mechanisms, preventing biological invasion, and monitoring and evaluation of restoration efforts.
This paper reviews five of the eight species of acipenseriforms that occur in China, chiefly those of the Amur and Yangtze rivers. Kaluga Huso dauricus and Amur sturgeon Acipenserschrenckii are endemic to the Amur River. Both species still support fisheries, but stocks are declining due to overfishing. Acipenseriformes of the Yangtze River are primarily threatened by hydroelectric dams that block free passage to spawning and feeding areas. The Chinese paddlefish Psephurus gladius now is rare in the Yangtze River system, and its spawning activities were severely limited by completion of the Gezllouba Dam in 1981. Since 1988, only 3-10 adult paddlefishes per year have been found below the dam. Limited spawning still exists above the dam, but when the new Three Gorges Dam is complete, it will further threaten the paddlefish. Artificial propagation appears to be the only hope for preventing extinction of P. gladius, but it has yet to be successfully bred in captivity. Dabry's sturgeon A. dabryanus is a small, exclusively freshwater sturgeon found only in the Yangtze River system. It is concentrated today in reaches of the main stream above Gezhouba Dam. The fishery has been closed since 1983, but populations continue to decline. Acipenser dabryanus has been cultured since the 1970s, and holds promise for commercial aquaculture; availability of aquacultural methods offers hope for enhancing natural populations. The Chinese sturgeon A. sinensis occurs in the Yangtze and Pearl rivers and seas of east Asia. There is still disagreement about the taxonomy of the Pearl and Yangtze River populations. The Yangtze River population is anadromous. Adults begin spawning at about age 14 years (males) and 21 years (females), and adults spend over 15 months in the river for reproduction. Spawning sites of A. sinensis were found every year since 1982 below the Gezhouba Dam, but it seems that insufficient suitable ground is available for spawning. Since 1983, commercial fishing has been prohibited but more measures need to be taken such as establishing protected areas and characterizing critical spawning, summering and wintering habitats.
We designed the payment card questionnaires to survey the willingness to pay (WTP) of people using the contingent valuation method (CVM), in an attempt to evaluate the economic values of conserving the rare and endangered species influenced by the Three Gorges Project (TGP), including Lipotes vexillifer, Psephurus gladius, Acipenser dabryanus, Myxocyprinus asiaticus, Acipenser sinensis, Adiantum reniforme var. sinense, Myricaria laxiflora and Chuanminshen violaceum. The employees in the state-owned units andother companies from 31 provinces/autonomous regions were surveyed. A total of 1,036 valid surveys were collected in June 2008. The result indicated that 70.08% of the respondents were willing to pay for the conservation of the rare and endangered species. The average WTP bids of all the respondents were 127.82 RMB yuan per year. We also analyzed the correlation between the respondents’ characteristics and their WTP bids using the contingency table and the Chi-square test for independence. The results indicated that WTP bids were mainly affected by age, education level, profession, personal income, the awareness of TGP, the attention paid to TGP, and the knowledge of the influence of TGP on the rare and endangered species. In conclusion, the economic values of conserving the rare and endangered species affected by TGP is 82.19×108 RMB yuan per year. This study may provide basic information for the further policy-making of the conservation of the species in the Three Gorges area.
We observed a large adult Paddlefish entrained from the Mississippi River through the Bonnet Cane spillway, south Louisiana, which was injured and underweight. We captured, measured (23 metrics), and tagged the fish. After it had spent a week at large on the fioodway, we recaptured and released it back into the Mississippi River. The specimen was re-captured eight months later in northern Mississippi, 627 km upriver from where it was released. Distance traveled and water velocities in the river indicate that the fish was traveling at least 90-197 cm/s for prolonged periods, equivalent to gross speeds of 77-170 km/d. This incident suggests that a large entrained fish, trapped for several days in a hyperthermic and hypoxic habitat, can be viable when returned to the river. It also demonstrated that rescue efforts could reduce impacts of spillway operations to fish populations, and that comprehensive field assessment of fish morphology can be benign to fish.
The lower portion of the Sacramento River, California, has been highly engineered to protect low‐lying surrounding communities from annual flood events. While engineered floodplains have provided adequate protection for the surrounding communities, there remain unintended consequences to migratory fish that become stranded during high flow events. In April 2011, we rescued 24 threatened Green Sturgeon Acipenser medirostris that were stranded in two flood diversions along the Sacramento River. We tagged these 24 Green Sturgeon with acoustic tags and analyzed their survival and migration success to their spawning grounds. Additionally, we provided a population viability analysis to show the potential impacts of stranding and the benefits of conducting rescues at the population level. We found that 17 of these 24 individuals continued their upstream migration to the spawning grounds. Modeling suggests that recurrent stranding of a similar magnitude without rescue could affect the long‐term viability of Green Sturgeon in the Sacramento River. Population viability analyses of rescue predicted a 7% decrease below the population baseline model over 50 years as opposed to 33% without rescue. Despite the mitigated impact to the population with rescue, fish passage improvements should be considered as a long‐term goal for preventing population risks at flood control diversions.
Received May 4, 2012; accepted December 6, 2012
Mortality is a key parameter in understanding the dynamics of any fish population. We examined three methods to evaluate Shovelnose Sturgeon Scaphirhynchus platorynchus mortality (e.g., ratio of first year recruits to all recruits [Heincke's method], a linearized weighted catch curve, and an open system mark-recapture mortality approach). The Mississippi River was sampled in two distinct but connected geomorphic sections: upper Mississippi River (UMR; river kilometer 323-587) and the middle Mississippi River (MMR; river kilometer 0-322). All analyses were pooled across these areas due to potential emigration or immigration throughout both study reaches. Heincke's method estimated annual mortality at 16.9% for the full range of ages (9-23years) with generally increasing estimates with decreasing age ranges considered (10-23, 11-23, 12-23, and so on). A linearized weighted catch curve that considered increasing estimates of mortality for the shorter age ranges generated an annual mortality estimate of 29.0%.d Four mark-recapture models were considered using the program MARK. The model with the greatest support was the model that provided estimates of annual mortality for each year and a single recapture probability. The annual mortality estimates from this model varied from 2.7% to 70.7% after correcting for tag loss. The best fit model with a single estimate of annual mortality was the one that estimated annual recapture probabilities for each year and had a mortality estimate of 34.6% (after correcting for tag loss, but not for immigration, emigration, or sampling effort). The three methods provided varying results, and our data indicated that a single method to estimate Shovlenose Sturgeon mortality rate may not be appropriate. As such, biologists must recognize that disparities in Shovelnose Sturgeon mortality rates may exist using various methods and should use caution when choosing which method will be employed to estimate sturgeon mortality.
Two hundred of 295 shovelnose sturgeon Scaphirhynchus platorynchus captured in the Mississippi River near Rosedale and Vicksburg, Mississippi, were aged by examining sectioned pectoral fin rays. Ages ranged from 2 to 16 years, and the annual mortality was 20% for ages 7 and greater. The weight (W, g), to fork length (FL, mm) relation was W = 0.000001257 FL (R = 0.87). The von Bertalanffy growth equation for fork length was FL = 730(1 − e ); the equation for weight was W = 1,604(1 − e ). Mortality and mean length at age were less than has been reported for upper Mississippi River populations of shovelnose sturgeon. Knowledge of causes of mortality of shovelnose sturgeon may have applications in management of the sympatric pallid sturgeon Scaphirhynchus albus.
Chinese paddlefish, Psephurus gladius, is an extremely rare species native to the Yangtze River. Its main spawning grounds
are located in the upper reaches of the Yangtze River whereas young sturgeons have been known to drift from the upper reaches
down to the river’s estuary. Due to the impact of Gezhouba hydraulic project construction, the paddlefish population has been
divided into two population groups — one in the middle and lower reaches and the other in the upper reaches of the river,
under the pressure of overfishing and environmental pollution, both of which are declining steadily. At present, the population
in the middle and lower reaches is critically endangered, and the population in the upper reaches has not been successfully
sighted in recent years. Since the 1980s, many protection measures have been implemented to protect the paddlefish, such as
fishing restrictions, artificial breeding and habitat protection. However, with the deterioration of the overall ecological
environment in the Yangtze River basin, it has proven difficult to reverse the decline in paddlefish population. Based on
over 20 years of experience in paddlefish conservation, it is pointed out that more attention should be paid to the characteristics
of the species as well as environmental protection in the whole basin. It is recommended that planning on the ecological rectification
and restoration of the river basin that is centered on the conservation of fish species and their habitats be conducted.
Of 458 paddlefish (Polyodon spathula) collected from the Missouri River (South Dakota-Nebraska) from June 1975 to August 1976, 165 (36%) bore scars and 46 (10%) had severed rostrums. Small fish and young fish were as likely to be scarred as large fish and old fish. Scarred fish had lower condition factors than unscarred fish. Scars originated primarily from injuries sustained as a result of collisions with powerboats, and from wounds associated with snag-fishing.
Chinese sturgeon ( Acipenser sinensis), was once widely dispersed in almost all watersheds draining towards the western coasts of the Pacific Ocean. Today, the species is one of the highly endangered fish species in China and can be found only in the Yangtze and Pearl rivers and their adjacent coastal and marine areas. Due to the construction of the Gezhouba Dam, spawning grounds for the fish were drastically restricted but fortunately remained in the Yangtze River at a small-scale site located just downstream along a short reach of the river closely to the dam. Since 1998 we have undertaken annual investigations in this area using hydroacoustic methods, in order to estimate the size of spawning cohort and the selection of habitats. Based on strength and sizes of echo signals, the mature individuals of Chinese sturgeon were discriminated from the other fish species and then numerated. Most of the fish were detected close to the bottom and preferred to distribute themselves in the areas with water depths less than 15 meters. Because of different bottom structures with homogeneous granular material, the distribution of the fish was mainly influenced by water depths and perhaps current patterns. Total amount of sturgeons in the entire reach were estimated by simply summing up the numbers according to the identified densities in areas of different depths. Usually, there were about two separate spawning activities of Chinese sturgeon which took place annually during the observation period, with the scale of spawning activity being much larger at the first time than during the following spawning events. Estimations on the sizes of spawning cohorts on the restricted spawning ground before the first wave of upstream migrants appeared, were about 400 and 200 individuals during the periods of 1998-1999 and 2002, respectively. It was demonstrated that: a) the space of the current spawning site is not sufficient to accommodate all mature individuals simultaneously, and b) a serious decline in spawning stocks size of Chinese sturgeon during the investigational period seems to be indicated when comparing the counts between 1998 and 2002. The decline is about 50% which is a highly alarming figure.
The swimming performance of hatchery-reared, juvenile shovelnose sturgeon Scaphirhynchus platorynchus and pallid sturgeon S. albus was studied in a laboratory swim tunnel at 20°C and 10°C. The mean 30-min critical swimming speed was not significantly different between species at either temperature (36.9 cm/s for shovelnose sturgeon and 35.9 cm/s for pallid sturgeon at 20°C, 19.4 cm/s for shovelnose sturgeon and 15.0 cm/s for pallid sturgeon at 10°C). Free swimming (swimming without contact with the substrate) was observed less than 18% of the time at speeds greater than 15 cm/s. As speed increased, pallid sturgeon swam significantly less in the water column at 20°C; however, speed had no effect on percent free swimming among shovelnose sturgeon at 20°C. The results of this study indicate that, over the temperature and size range tested, shovelnose sturgeon and pallid sturgeon probably do not segregate in rivers due to different swimming or station-holding abilities
The study objectives were to identify the horizontal and verti-cal distributions of adult Chinese sturgeon (Acipenser sinensis) in relation to the Habitat Suitability Index (HSI) in order to assess the utility of the only remaining spawning grounds by adults and to understand the effects of river alterations on habitat use. Twenty-five adults were surgically implanted with ultrasonic transmitters and located by mobile tracking and fixed monitoring stations during the 2006–2009 spawning sea-sons. Fish locations and depths along with water depth and bottom characteristics (topography, velocity, and embedded-ness) were measured during tracking and used to determine HSI curves for non-spawning and spawning adults. Most fish locations (91%) were on the spawning grounds (GZD to Miaozui reaches). Horizontal distribution differed before and after spawning, among years, and between the sexes. Adults used deeper depths during the day than at night (P < 0.001), while also preferring shallower depths on the day of spawning rather than the days before and after. Mature females used deeper water than other females (P < 0.001). Comparison of horizontal and vertical distributions before and after river alterations found fewer adults using the grounds impacted by a diversion dike which was built on the spawning grounds. Adults also used shallower depths after the Three Gorges Dam regulated river flow over the spawning grounds. The HSI model and the use of Weighed Usable Areas (WUA) for mature and immature adults indicated suitable habitat was available, but was reduced by the river alterations resulting in reduced spawning success and placing the population into a situation close to extirpation.
Summary When paddlefish, Polyodon spathula, eggs were fertilized with UV irradiated (863 μW cm−2) sperm of Amur sturgeon, Acipenser schrenckii, viable gynogenetic diploid progeny with approximately 120 chromosomes occurred due to spontaneous diploidization of the maternal set of chromosomes (SDM). Distant hybridization of P. spathula eggs by A. schrenckii sperm induced inviable gynogenetic haploid progeny with approximately 60 chromosomes. When eggs gynogenetically activated by heterospecific sperm were heat-shocked with 37°C for 2 min at 18 min post-fertilization, a small proportion (7.8%) of viable gynogenetic diploid progeny appeared. The female inheritance of these gynogenetic diploid progeny was verified by chromosome analyses and microsatellite genotyping.
A specially designed net was used to study fish entrainment and injury through towboat propellers in 13 pools of the Upper Mississippi and Illinois rivers. The net was attached to the stern of a 48.8-m-long towboat with twin propellers (in Kort propulsion nozzles), and sampling typically took place while the towboat pushed 15 loaded barges upstream at a time. In total, 254 entrainment samples over 894 km of the 13 study pools were collected. The sampling efforts produced 16,005 fish representing 15 families and at least 44 species; fish ranged in total length from 3 to 123 cm, but only 12.5-cm or longer fish were analyzed because smaller fish could escape through the mesh of the trawl. Clupeidae (68% of total catch) and Sciaenidae (21%) were the dominant families. We detected no effects of towboat operation variables (speed and engine [i.e., propeller] revolutions per minute [RPM]) on entrainment rate (i.e., fish/km), but entrainment rate showed a wedge-shaped distribution relative to hydraulic and geomorphic characteristics of the channel. Entrainment rate was low (< 1 fish/km) in wide sections of the river, deep water, and swift current (or time periods characterized by faster flow); however, entrainment in narrow sections with shallow, slow water was highly variable and occasionally reached high levels (> 30 fish/km). Although total entrainment rate was not related to engine RPM, the probability of being struck by a propeller increased with fish length and engine RPM. Limits on engine RPM in narrow, shallow, and sluggish reaches could reduce entrainment impact, particularly for large-bodied fish.
The comparative osteology and phylogenetic relationships of fossil and living paddlefishes (Polyodontidae) are investigated in detail for the first time. This peculiar, poorly known group is of great significance to phylogenetic studies of primitive actinopterygians, because it is one of only two chondrostean families that have survived to the present. Consequently the group is frequently used as an outgroup for studies of the many fossil chondrostean groups and for higher-level studies of actinopterygian (and even osteichthyan) interrelationships.The family has a long but spotty fossil record dating back to the Upper Cretaceous, including species represented by relatively complete skeletons or at least skulls. These relatively complete fossils are extremely rare and belong to the species †Paleopsephurus wilsoni MacAlpin, 1947 from the Upper Cretaceous Hell Creek Formation of Montana (redescribed here); †Polyodon sp. nov. from the lower Paleocene Tullock Formation of Montana (described here); and †Crossopholis magnicaudatus Cope, 1883 from lower Eocene deposits of the Green River Formation in Wyoming (described in detail here for the first time based on much new material). Among the fossils, †Crossopholis is of particular interest, because it is now known by several nearly complete skeletons (reported and described here for the first time). †Paleopsephurus and †Polyodon sp. nov. are known from a single partial skull each, and some fragmentary postcranial material, but are well enough represented to include in our phylogenetic analysis. Other, more fragmentary, Upper Cretaceous and Paleocene material (some newly reported here) is placed in Polyodontidae incertae sedis.There are two extant species in the family, frequently referred to in the literature as “living fossils.” These two species are Polyodon spathula from the Mississippi River drainage of North America, and Psephurus gladius primarily from the upper Yangtze River drainage in China. The osteology of Psephurus gladius is described here in detail for the first time.Previous studies of Polyodontidae have been almost exclusively based on Polyodon spathula, because specimens of the other species are extremely rare and very poorly known. After accumulating and preparing material for several years, we were able to describe more fully all polyodontid species and examine the family phylogenetically. Our study reveals that Polyodon spathula is a highly derived member of the family, and generally not a good representative of the family when the family is used as an outgroup for higher-level phylogenetic studies of actinopterygians. The use of Polyodon spathula as the primitive polyodontid has previously led to several serious errors in the literature. We therefore also summarize certain primitive characters of Polyodontidae in this paper.Contrary to previous studies, we show that †Paleopsephurus has the stellate rostral bones unique to polyodontids (in addition to the long median rostral bones and extremely elongate snout also unique to the group). Also contrary to previous studies, Polyodontidae (at least primitively) does have ossifications of the quadratojugal, interclavicle and postcleithrum. We also report several other osteological features previously unknown from the family.Our study results in a phylogenetic hypothesis for paddlefishes that is radically different from the only other published cladogram (Gardiner, 1984b). We demonstrate that †Paleopsephurus clearly belongs in Polyodontidae, rather than Acipenseridae as proposed by Gardiner (1984b). †Paleopsephurus is the sistergroup to Polyodontinae, new subfamily (a group containing Psephurus, †Crossopholis, and two species of Polyodon). Psephurus is the sistergroup to Polyodontini, new tribe (a group containing †Crossopholis and Polyodon). Polyodon contains the extant Polyodon spathula as well as a new fossil species from early Paleocene freshwater deposits of Montana.A better understanding of polyodontid osteology also enables us to provide a phylogenetic hypothesis for Acipenseriformes (assuming monophyly of Acipenseridae) that differs from that of previous authors. In particular we find that †Chondrosteidae is the sistergroup to a group containing Acipenseridae plus Polyodontidae. Polyodontidae also provide evidence that the supraneurals in actinopterygians are the serial homologues of epurals, and not of fin radials.As has previously been apparent, Polyodontidae is one of several groups that indicate a transpacific biogeographic relationship for western North America (west of the continental divide) during the Early Tertiary.We also describe ontogenetic and intraspecific variation in paddlefish osteology. Based on the large amount of variation, we conclude that, in at least some fishes, it is important to examine large numbers of specimens, including extremely old individuals (i.e., “upper end ontogeny”) in the developmental series to more completely document the morphology. Normal-sized, reproductively active adult paddlefishes lack particular ossifications of the scapulocoracoid, vertebral column and neurocranium present in other osteichthyans; but as we show here, these elements eventually ossify in very large, older individuals. In this sense, paddlefishes appear to be the axolotls of the fish world, offering one of the best documented cases of paedomorphosis (or neoteny) known to date.
Based on the restoration efforts related to Acipenser dabryanus, a fairly comprehensive knowledge has been gathered on the environmental variations within the upper Yangtze River ecosystem. This study aims to assess the potential options to rehabilitate the A. dabryanus population in its native river. This paper reviews the restoration efforts for A. dabryanus (from the start of the fishing ban, to the construction of nature reserve and programmes for controlled release of cultured fish) since the year of 2000. Based on the results some pathways were tentatively proposed linking human activities to the species conservation needs (including considerations on food supply/rearing habitat, migration, reproduction/spawning habitat and survival/recruitment). The analysis on variations of its native river ecosystem (including abiotic and biotic factors as well as direct effects of human activities) indicated that the major adverse factors threatening survival of this species involves river fragmentation (e.g. dam construction, waterway regulation) as well as sand/gravel extraction, intensive fishing and water pollution. To conserve or further to rehabilitate wild population of this species, damming in the upper Yangtze River and its tributaries and potential counter actions or adequate compensation measures need to be seriously considered at first.
Due to the rarity of Chinese paddlefish (Psephurus gladius), very little information is available on this species. In order to save this critically endangered giant species, four large-range hydroacoustic surveys (using an echo sounder with a 199 kHz, 6.8° split-beam transducer) and capture surveys (by drift nets and setlines) were conducted in the upper Yangtze River during 2006–2008. According to the target strength (TS) study on Polyodon spathula (Hale et al., 2003) and Love’s formula about TS-fish length relationships (Love, 1971), the four acoustic surveys identified nine potential targets (TS > −26.29 dB) of P. gladius, two (TS > −22.40 dB) of them very probably the fish species sought. A total of 4762 setlines, 111 anchored setlines and 950 drift net catches were conducted in which 472 large fish specimens of various species were caught. However, no single P. gladius was caught directly. The gear used did not allow quantitative capture over rough ground with deep holes, perhaps allowing some large fish to effectively hide or escape; the hydroacoustic signals indicated this as likely. In any case, it is strongly suggested that P. gladius is on the verge of extinction and further rigid measures are proposed to save the very few remaining specimens.
SummaryA protocol for gynogenesis of P. spathula was developed in order to produce inbred lines and to develop a technique to preserve the endangered Chinese paddlefish (Psephurus gladius). Diploid gynogenesis was induced in P. spathula using ultraviolet (UV)-irradiated Amur sturgeon (Acipenser schrenckii) sperm for 4.5-min, 5-min or 5.5-min and subsequent heat shock treatment. UV irradiation of sperm for 5 min at a UV intensity (254 nm) of 863 μw cm−2 was the optimum dose to achieve diploid gynogenesis on the basis of observations on hatching rate of eggs. Three microsatellite loci were used to monitor exclusive maternal inheritance of gynogenetic progenies. The results showed all maternal genome among offspring with no paternal genome. The cytogenetic analysis showed that meiotic gynogenetic diploids possessed 120 chromosomes in metaphase plates, while haploid control groups N1–3 possessed 60 chromosomes.
This anthology is the first collection of primary science articles written by scientists working in America during the nineteenth century.
Aquatic organisms swim in a variety of ways, from jet propulsion to ciliary action: they swim at a wide range of speeds and span a vast size range, from bacteria to protists, to the largest whales. One of the most fascinating aspects of aquatic locomotion is the remarkable sets of adaptations that have been evolved for different purposes. This volume brings together research on a wide range of swimming organisms, with an emphasis on the biomechanics, physiology and hydrodynamics of swimming in or on water. Several chapters deal with different aspects of fish swimming, from the use of different 'gaits' to the operation of the locomotor muscles. All chapters are by recognized authorities in their different fields, and all are accessible to biologists interested in aquatic locomotion.
Growth, mortality, fecundity, egg diameter, and age at maturity were determined from samples of 270 paddlefish Polyodon spathula collected from the Atchafalaya River basin and Lake Pontchartrain, Louisiana, during a commercial harvest moratorium from 1987 to 1989. Early growth of paddlefish determined from back-calculation of annular measurements on dentary cross sections was high relative to paddlefish populations in the upper Mississippi River drainage; lengths of age-1 fish ranged from 411 to 455 mm in eye-fork length. Natural mortality of Louisiana paddlefish was high (26-48%), and data suggested a reduction in age at maturity (100% females mature at age 10), lower fecundity (average fecundity, 9, 500 eggs/kg body weight), and larger eggs (average diameter, 2.67 mm) relative to other paddlefish populations. Changes in reproductive life history characteristics may reflect rapid growth and high natural mortality rates. As the postmor-atorium commercial fishery for Louisiana paddlefish develops, conservative harvest regulations should be promulgated until the effects of harvest on paddlefish stock dynamics can be determined.
The pallid sturgeon (Scaphirhynchus albus Forbes and Richardson) was listed as an endangered species on September 6, 1990 (55 FR 36641) pursuant to the Endangered Species Act (Act) of 1973 (16 U.S.C. 1531 et seq.) as amended. The range of the pallid sturgeon overlays three U.S. Fish and Wildlife Service (Service) Regions: Region 3, Region 4, and Region 6, with Region 6 having been designated the lead Region for recovery (research functions are provided to all Service Regions by Region 8). Because of the wide range of the pallid sturgeon, its believed extreme rarity, numerous threats to species survival, and paucity of information on species life history and habitats, an eight-member, multi-disciplinary recovery team was established to develop this Pallid Sturgeon Recovery Plan (Recovery Plan). In development of the Recovery Plan, the recovery team utilized the expertise of other sturgeon researchers and managers and published literature. The Introduction section, Part I, of this Recovery Plan describes the distribution, status, life history, and habitat-association information that is known about the pallid sturgeon. Reasons for listing and threats to the species are also described. The Recovery section, Part II, provides the short- and long-term recovery objectives and actions needed to achieve recovery. Recovery tasks, which can be independently funded and carried out, are described for each action. The Implementation Schedule, Part III, of the Recovery Plan is essentially a summary table that indicates task priorities, task descriptions, duration of tasks, the agency or entity with the responsibility or administrative authority to fund or carry out the task, and lastly, estimated costs. All priority 1 tasks are listed first, followed by priority 2 and priority 3 tasks. Because of the immediacy for implementation of recovery actions to prevent extinction of the species, most tasks are assigned priority 1. This Recovery Plan is subject to modification as needed by new findings, changes in species status, and the completion of recovery tasks.
A novel electrosensory function is presented for the large, plankton-feeding, freshwater paddlefish, Polyodon spathula, along with a hypothesis which accounts for the distinctive, elongated rostrum of this unusual fish. Behavioural experiments conducted in the 'dark' (under infrared illumination), to eliminate vision, show that paddlefish efficiently capture planktonic prey to distances up to 80-90 mm. They make feeding strikes at dipole electrodes in response to weak low-frequency electrical currents. Fish also avoid metal obstacles placed in the water, again in the dark. Electrophysiological experiments confirm that the Lorenzinian ampullae of paddlefish are sensitive to weak, low-frequency electrical signals, and demonstrate unequivocally that they respond to the very small electrical signals generated by their natural zooplankton prey (Daphnia sp.). We propose that the rostrum constitutes the biological equivalent of an electrical antenna, enabling the fish to accurately detect and capture its planktonic food in turbid river environments where vision is severely limited. The electrical sensitivity of paddlefish to metallic substrates may interfere with their migrations through locks and dams.
Chinese sturgeon, Acipenser sinensis Gray, an anadromous fish, mainly distributes in the mainstream of Yangtze River, the continental shelf of East China Sea and Yellow Sea. Historical spawning grounds of A. sinensis were in the upper Yangtze and the lower Jingsha River, covering a stretch of at least 600 km of river length. After the damming of Yangtze River by the Gezhouba Dam in January 1981, the spawning grounds for A. sinensis were no longer accessible and fish alternatively spawned within a 30 km section below the Gezhouba Dam. Moreover, only one regular spawning ground has been found in the downstream area of the Dam. It is in a narrow portion within a 7 km length, just below the dam. A minor spawning ground was also found at Huyatan, around 15 km below the dam. The present attempts to estimate stock size of A. sinensis suggest that the major source of recruitment from a complementary colony is still obtained through natural reproduction. A. sinensis requires a certain water temperature, moderate bottom velocity, and special riverbed topography to spawn successfully. Due to the restriction of experimental instruments and methods, the research on the topography of spawning grounds is a first attempt to tentatively characterize the area in terms of fine-scale bottom profile and structure. Based on measurements taken during five surveys between 1999 and 2006, we analyzed the river bed morphology by assessing the elevation, slopes, and the bottom "roughness" of the spawning grounds by ArcGIS 9.0. The terrain of the riverbed was simulated by Inverse Distance Weighted scheme with an 8.0 m of grid size. The results showed that the roughness in regularly used alternative spawning site directly at the dam and the minor spawning ground further downstream are 1.74 × 10-3 and 0.36 × 10-3, respectively. Moreover, the slope of area between Gezhouba Dam and Moji Hill is much bigger than that between the Linjiang Stream and Huyatan. The average and standard deviation of length of elevations at the upstream and downstream spawning sites are 32.35 ±2.18 m and 30.14 ±3.85 m, respectively. Taking the average water level for spawning between 1983 and 2002 as a standard, the average water depth on the upstream and downstream spawning sites were 11.66 m and 13.87 m, respectively. These depths may be the optimal water depth for A. sinensis to spawn under the given hydrodynamic regime in the Yangtze River. Four views are considered in this article. (1) The topographical characteristics of the spawning ground which locates in the reaches between the Gezhouba Dam and the Shilihong are very similar to those on the historical spawning grounds. The natural reproduction of A. sinensis rarely occurs in the reach between the Linjiang Stream and Huyatan, and it is postulated that the major reason is to be found in the unsuitable terrain, which makes the hydrological regime and hydraulic conditions not suitable to trigger spawning activity. (2) The topography of the spawning ground below the Gezhouba Dam has been changed drastically during recent decades because of the River Regime Regulating Work. The increased complexity of the topography may yield some benefit for A. sinensis to attract fish to inhabit before the natural reproduction stage is reached, but the destruction of slopes on the spawning grounds perhaps goes against the dispersion of fertilized eggs and embryonic development. (3) The results provide further support for the hypothesis of "Dividing Function of the Spawning Ground of A. sinensis" in the area below the Dam at the present time. The turning of riverway and adverse slope of riverbed may be the absolutely necessary requirement for a suitable spawning ground of A. sinensis. Although the data are limted for such a working hypothesis, further studies should combine the accurate terrain data from historical spawning grounds of A. sinensis with thos from the new grounds to verify this potentially valid hypothesis. (4) The substrate, hydrological and hydraulis conditions are affected by the topography of the riverbed to a certan extent. It is necessary to make further investigation on the influence of riverbed terrain on the natural reproduction of A. sinensis, especially when considering the changes that may be anticipated with the full functioning of the Three Gorges Dam which must have also an effect on the hydrodynamics downstream even beyond the Gezhouba Dam.
The shovelnose sturgeon, Scaphirhynchus platorynchus, is a freshwater sturgeon of the Mississippi and Missouri rivers and their tributaries. It is one of the smaller North American sturgeons, seldom weighing more than 2.5 kg over most of its range except in the upper Missouri River, where individuals of over 7 kg have been found. Spawning occurs in spring at temperatures between 17 and 21 °C over rock or gravel substrate downstream from dams, near rock structures, or in tributaries, most males reach sexual maturity at 5 years, most females at 7 years. Adults do not spawn every year. Shovelnose sturgeon are found in large, turbid rivers and frequently concentrate in areas downstream from dams or at the mouths of tributaries. Population densities range up to 2500 fish per km. They are commonly found in areas of current over sandy bottoms or near rocky points or bars, where they feed primarily on aquatic invertebrates. The shovelnose sturgeon is classified as a sport species in 12 of 24 states where it occurs. Commercial harvest is allowed in seven states, where fresh shovelnose sturgeon sell for 55 to 88 cents per kg, smoked shovelnose for about $5.75 per kg, and roe from 33 to 110 dollars per kg. About 25 tons of shovelnose sturgeon are harvested commercially each year. Shovelnose sturgeon are considered extirpated in three states, fully protected in four states, and rare, threatened, or of special concern in eight states. Populations are considered stable throughout most of the upper Mississippi, lower Missouri, Red, and Atchafalaya rivers. Three states, Wyoming, West Virginia, and New Mexico, have developed plans to reintroduce the species into rivers where it has been extirpated.
The sturgeons belong to the family Acipenseridae and to the order Acipenseriformes. The Polyodontidae or paddle fishes are also included in this order.
The status of paddlefi sh Polyodon spathula in the United States was first described in two surveys published in 1986 and 1997; in this paper, we report the results of a similar survey of state and federal agency personnel
that we conducted in 2006. From the 1970s through the 1990s, the status of paddlefi sh stocks was on a downward trend throughout much of the species’ range. The 2006 survey results suggest that the status of paddlefish stocks has improved since the fi rst survey was conducted; 17 of 26 states in 2006 reported that their paddlefi sh populations were stable or increasing, compared to only 14 states in 1983 and 1994. The number of states with closed fisheries (i.e., no commercial or sport harvest) increased to 12 in 2006 from 8 in 1983. The number of states reporting declining or stable/declining paddlefi sh populations dropped from seven states in 1983 to only three states in 2006. The two principal reasons cited for reported declines have remained the same for more than three decades: habitat loss and overfishing. Two states where paddlefi sh were listed as extirpated (New York and Pennsylvania) have begun restoration efforts that may one day allow the status
of paddlefi sh in those states to be changed. As long as the demand for caviar remains strong, pressure on paddlefi sh stocks will undoubtedly remain high in the seven states where they are commercially exploited. however, earlier fears of a basin-wide collapse in paddlefi sh stocks should continue to diminish if resource managers are successful in combating overfi shing and continued habitat destruction, which will always threaten the long-term viability of paddlefi sh stocks throughout the Mississippi River basin.
Metabolic rate, branchial morphology, and modes of gill ventilation were studied in young (2-10 g) North American paddlefish, Polyodon spathula, with anatomical, behavioral, and physiological methods. Polyodon lacks the oral and opercular valves that are typical for fishes that rely on a buccal pump system to ventilate the gills, and the jaw opening system of Polyodon is poorly suited for regular pumping movements. Unrestrained, undisturbed juvenile paddlefishes swim constantly at a mean speed of 1.1-1.5 body lengths · $s^{-1}$ (bls). The maximum speed sustainable for > 10 min is 1.6-1.8 bls. When forced to swim at slow speeds in flow tanks or water tunnels, ventilation of the gills by buccal pumping occurs at a frequency of 50-80 · $min^{-1}$ . As swimming speed increases, buccal ventilation becomes intermittent and continuous ram ventilation occurs above 0.6-0.8 bls, which means that Polyodon is essentially an obligate ram ventilator under normal conditions. Oxygen consumption ( $\dot{M}O_{2}$ ), carbon dioxide production ( $\dot{M}O_{2}$ ), and the gas exchange ratio (R) were determined as a function of inspired Po₂ during undisturbed swimming in still water at 25° C Oxygen consumption, buccal pressure, and swimming performance were also measured at set swimming speeds in a flow tank and small water tunnel. Oxygen consumption at the preferred swimming speed of 1.25 bls was 6-7 μmol O₂, · $g^{-1}$ · $h^{-1}$ . Carbon dioxide production was 3-4 μmol CO₂ · $g^{-1}$ · $h^{-1}$ , yielding an R of 0.5-1.0. Paddlefishes are O₂ regulators in mild hypoxia (150 down to 90 mmHg) but die quickly at Po₂ < 90 mmHg. During steady swimming in normoxia, paddlefishes normally maintain 70%-80% of the maximum sustainable speed. This results in a normal minimum metabolic rate that is about twice that of the minimum (resting) rate of other acipensiform fishes. From a phylogenetic standpoint, other acipenseriforms also use ram ventilation, leading to the hypothesis that the evolutionary origin of a reliance on ram ventilation in Polyodon probably predates the origin of the filter feeding habit. Constant swimming may be metabolically expensive, but it would appear to allow some energy to be conserved by ram ventilation. This may be particularly advantageous for species such as P. spathula that combine filter feeding and ram ventilation.
North American paddlefish Polyodon spathula historically occurred in the Mississippi, Saint Lawrence, and Alabama rivers, as well as several other Gulf of Mexico coastal drainages. Recent population declines in some locations and the local extirpations of others purportedly have been due to habitat loss, overharvest, and other biotic and abiotic changes to riverine ecosystems. Mitigation for these declines has emphasized hatchery production and supplemental stocking programs, which use a number of geographical sources for parental stock. To investigate phylogeographic relationships within and among several watersheds, we surveyed allozyme and mtDNA variation among 189 individuals collected from six regions of the Mississippi River drainage plus the Mobile Bay and Pearl River drainages. Paddlefish exhibited lower levels of allelic and haplotypic diversity than other freshwater species, a characteristic shared with other “primitive” fishes. Allozyme variation at 64 presumptive loci was segregated into two major groups: a Mobile Bay drainage group and a group from the Mississippi River and Pearl River drainages. More subtle population divergences were observed among major regional tributaries within the Mississippi River, although a clear and unambiguous level of geographical clustering was not delineated. Furthermore, several of the localities harbored “private,” but rare, polymorphisms. These results demonstrate that the populations are sufficiently divergent to warrant differential management considerations for any rehabilitation, restoration, or protection measures.
Dabry's sturgeon, Acipenser dabryanus, is a relatively small (130 cm, 16 kg) and now rare sturgeon restricted to the Yangtze River Basin. It behaves as a resident freshwater fish, does not undertake long distance migrations (except for spawning), and lives in a variety of habitats. It historically spawned in the upper Yangtze River, but the spawning sites are unknown. Acipenser dabryanus reaches maturity earlier than do other Chinese sturgeons, which gives the species aquaculture potential, and artificial spawning has been carried out. However, the native population in the Yangtze has sharply declined in the last two decades due to overfishing, pollution and habitat alteration and destruction, especially since the construction of the Gezhouba Dam, which was built in 1981 across the Yangtze River at Yichang, Hubei Province. Since 1981, Dabry's sturgeon rarely occurs below the Gezhouba Dam because downstream movements are blocked. Clearly, conservation of Dabry's sturgeon must be emphasized. Conservation methods may include protecting habitats, controlling capture and stock replenishment.
Paddlefish Polyodon spathula (n = 576) were collected from Kentucky Lake, Kentucky–Tennessee, with experimental gill nets in 2003–2004 to assess population characteristics and the potential for commercial overfishing. Additional data were collected from 1,039 paddlefish caught by commercial gillnetters in this impoundment. Since the most recent study in 1991, size and age structure have been reduced and annual mortality has tripled. In the 1991 study, 37% of the fish collected were older than the maximum age we observed (age 11), and in 2003 annual mortality for paddlefish age 7 and older was high (A = 68%). Natural mortality is presumably low (
Age at sexual maturity has not been described previously for the pallid sturgeon Scaphirhynchus albus, an endangered species. Age and reproductive development data were obtained for five male and nine female pallid sturgeons collected from 1983 to 1991. Spawning bands were observed in pectoral fin ray sections of age-25 and age-41 females. Males reached sexual maturity at ages 5–7. Females began egg development at ages 9–12 and first spawned at age 15. Eight of the specimens we examined were collected from the headwaters of the Atchafalaya River, where pallid sturgeons had not been previously reported.
Paddlefish fisheries in some states have become increasingly important, but in other states populations have declined severely and the species range has been reduced. Commercial paddlefish harvests today come mainly from the impounded Tennessee, Mississippi, and Arkansas Rivers. Sport fisheries have replaced commercial fisheries in some areas and even though they are extremely localized, they account for sizable harvests. Declining paddlefish populations reported in several states are a result of loss of spawning habitat. Recent studies in these and other states have increased our knowledge about the paddlefish and its management. Identification and protection of spawning areas is critical to the maintenance of the fisheries.
Growth, mortality, fecundity, egg diameter, and age at maturity were determined from samples of 270 paddlefish Polyodon spathula collected from the Atchafalaya River basin and Lake Pontchartrain, Louisiana, during a commercial harvest moratorium from 1987 to 1989. Early growth of paddlefish determined from back-calculation of annular measurements on dentary cross sections was high relative to paddlefish populations in the upper Mississippi River drainage; lengths of age-1 fish ranged from 411 to 455 mm in eye-fork length. Natural mortality of Louisiana paddlefish was high (26–48%), and data suggested a reduction in age at maturity (100% females mature at age 10), lower fecundity (average fecundity, 9,500 eggs/kg body weight), and larger eggs (average diameter, 2.67 mm) relative to other paddlefish populations. Changes in reproductive life history characteristics may reflect rapid growth and high natural mortality rates. As the postmoratorium commercial fishery for Louisiana paddlefish develops, conservative harvest regulations should be promulgated until the effects of harvest on paddlefish stock dynamics can be determined.
This study quantified the effects of temperature and fish mass on routine metabolism of the American paddlefish Polyodon spathula. Thermal sensitivity, as measured by Q10 value, was low in P. spathula. Mean Q10 was 1·78 while poikilotherms are generally expected to have Q10 values in the 2·00-2·50 range. Mass-specific metabolism did not decrease with increased fish size to the extent that this phenomenon is observed in teleosts, as evidenced by a mass exponent (β) value of 0·92 for P. spathula compared with 0·79 in a review of teleost species. Other Acipenseriformes have exhibited relatively high β values for mass-specific respiration. Overall P. spathula metabolism appears to be more dependent on body mass and less dependent on temperature than for many other fishes. An equation utilizing temperature and fish mass to estimate gross respiration for P. spathula was derived and this equation was applied to respiratory data from other Acipenseriformes to assess inter-species variation. Polyodon spathula respiration rates across water temperature and fish mass appear most similar to those of Atlantic sturgeon Acipenser naccarii and white sturgeon Acipenser transmontanus.
Gut contents of shovelnose and pallid sturgeon from the lower and middle Mississippi River were obtained by colonic flushing, a safe and easily implemented alternative to gastric lavage. Diets of both species were dominated numerically by immature Trichoptera, Ephemeroptera, and Diptera. Primary prey, based on volume, for shovelnose sturgeon were Trichoptera, and for pallid sturgeon were various fishes. Geographic and seasonal nuances in diet were observed for both species, but the general dichotomy of shovelnose sturgeon as browser on invertebrates and pallid sturgeon as predator on fishes did not change. Data indicate that both species require hard substrates for feeding. Data demonstrate that colonic flushing is an effective technique for describing diet and inferring ecological and behavioral information about sturgeon.
Microsatellite variation from 13 disomic loci is reported for a total of 208 individuals of the genus Scaphirhynchus. This includes 105 individuals of the pallid sturgeon (Scaphirhynchus albus) from the lower Mississippi River, 11 pallid sturgeon from the Upper Mississippi and Missouri rivers, 65 shovelnose sturgeon (S. platorynchus) from the lower Mississippi River, six Alabama sturgeon (S. suttkusi), and 21 individuals of sturgeon identified as intermediate between S. albus and S. platorynchus. Results indicate that all five of the above population/species units are significantly differentiated from one another based on pairwise FST estimates. Locus Spl-7 was diagnostic for the Alabama sturgeon and serves to further differentiate this allopatric species from other Scaphirhynchus. Classification of genotypes with and without a priori designations failed to clearly delineate the species and intermediates in the latter case but was successful for the species but not in the intermediates in the former case. The presence of six unique alleles in five of the 21 morphologically ‘intermediate’ sturgeon examined requires additional evaluation but suggests that these individuals are possibly not the result of hybridization. We hope that raising these important issues will bring all stakeholders to the table to establish a concerted effort needed for both morphological and molecular analyses to adequately address the question of hybridization and the origin of the morphological variation in these fishes.
Dabry's sturgeon, a large, long‐lived migratory fish is endemic to the Yangtze River. Over‐fishing and habitat destruction have caused large‐scale declines in natural stocks in the last two decades.
Examining patterns of genetic diversity has become an integral component of many management plans for endangered species. DNA fingerprinting was applied to detect genetic diversity in Dabry's sturgeon collected in 1958–1959, 1980–1981 and 1998–1999.
Studies on direct genetic parameters (genetic variability, hypervariable loci and heterozygosity) and indirect parameters (band‐sharing coefficient and allelic frequency) showed that the continuous decline in wild populations has caused the loss of genetic diversity in present‐day sturgeon.
The present‐day populations have the lowest genetic variability; thus, effective management is needed to preserve genetic diversity.
A conservation strategy is urgently required, comprising artificial rearing facilities coupled with breeding management plans.
Copyright © 2003 John Wiley & Sons, Ltd.
SummaryA multiyear study of pallid sturgeon distribution and relative abundance was conducted in the lower and middle Mississippi river (LMR and MMR, respectively). The LMR and MMR comprise the free-flowing Mississippi River extending 1857 river kilometers (rkm) from its mouth at the Gulf of Mexico upstream to the mouth of the Missouri River. A total of 219 pallid sturgeon and 6018 shovelnose sturgeon was collected during the periods 1996–1997 and 2000–2006. Trotlines baited with worms were the primary collecting gear. The smallest pallid sturgeon captured on trotlines was 405 mm FL and the largest was 995 mm FL. Mean size of pallid sturgeon was statistically smaller in the Mississippi River below the Atchafalaya River near Baton Rouge, LA (621 mm FL). Mean abundance (catch per trotline night) of pallid sturgeon was highest at water temperatures around 10°C. There was a latitudinal trend in mean abundance of pallid and shovelnose sturgeon, but the pattern differed between species. Pallid sturgeon abundance was statistically (P < 0.05) higher (0.3 fish per trotline night) in the lower reach between the Atchafalaya River and New Orleans (rkm 154–507), and at the Chain of Rocks (COR), a low water dam near the mouth of the Missouri River. Pallid sturgeon abundance between these two locations was statistically the same (0.12–0.23). Shovelnose sturgeon abundance increased going upstream, but was disproportionally higher at the COR (22 fish per line compared with <6 fish per line in other reaches). Overall, the ratio between pallid and shovelnose sturgeon varied from a high of 1 : 6 at the lower reach, and gradually decreased upstream to a low of 1 : 77 at the COR. Based on differences in sturgeon abundance, size and habitat characteristics, the free-flowing Mississippi River can be divided into two reaches in the MMR (i.e. COR is a separate location), and four reaches (i.e., including the Atchafalaya River) in the LMR where management goals may differ.