Sturgeon Fishery Research Articles

Lake Sturgeon population trends in the St. Clair–Detroit River system, 2001–2019

AbstractObjectiveThe Lake Sturgeon Acipenser fulvescens is listed as threatened or endangered in 15 states or provinces within the species' native range. Accordingly, investments in habitat and population restoration for this species have increased throughout the Great Lakes. To aid in the evaluation of restoration efficacy, robust population parameters are needed to inform management decisions. The St. Clair–Detroit River system (SCDRS) contains one of the largest self‐sustaining Lake Sturgeon populations in the Great Lakes; however, recent estimates of population abundance and growth parameters have not been assessed.MethodsOur study used baited setline and mark–recapture data collected between 2001 and 2019 to estimate whether the number of Lake Sturgeon captured varied annually and/or with water temperature and whether population abundance and the population growth rate (λ) varied among three subpopulations located in the SCDRS.ResultTrends in the number of Lake Sturgeon captured on setlines varied among subpopulations and by life stage. Annual trends in the number of Lake Sturgeon captured remained consistent over time in the upper St. Clair River, decreased for adults and increased for subadults in the lower St. Clair River, and increased in the Detroit River. With subpopulation abundances of 20,184 (95% confidence interval [CI] = 12,533–27,816) in the upper St. Clair River/southern Lake Huron, 6523 (95% CI = 5720–7327) in the lower St. Clair River, and 6416 (95% CI = 4065–8767) in the Detroit River, our study confirms that the SCDRS contains the largest Lake Sturgeon population with unimpeded access to the Great Lakes. The geometric mean λ for all subpopulations indicated stable populations and ranged from 1.00 to 1.16.ConclusionOur study provides an updated assessment of Lake Sturgeon population parameters that serve as a baseline to evaluate habitat restoration efforts and to inform management of the SCDRS recreational Lake Sturgeon fishery.

Investigating fishing strategies and habitat differences in late Holocene Oregon Coast sturgeon (Acipenser spp.) through coupled genetic and isotope analyses

Understanding the habitats people were fishing in the past is central to evaluating the relationship between coastal environmental change and human behavior. Researchers often use zooarchaeological identification of fishes and modern ecological data to infer the habitats people fished in the past. However, these inferences assume stable environmental conditions through time and can be hindered by precision issues in identification of archaeological specimens (species vs. genus or family). Here, we integrate genetic and bulk tissue stable isotope data to investigate a late Holocene sturgeon fishery in northern Oregon. Ancient DNA analysis indicated that people were fishing for both green and white sturgeon (Acipenser medirostris and Acipenser transmontanus) in comparable numbers. Stable isotope analyses of these same bones documented distinct isotope values for each species, correlating with species-specific habitat preferences. These findings highlight the value of paired isotope and genetic data to elucidate human fishing strategies and environmental change and provide baseline ecological data for modern fisheries.

Stock Composition of the Historical New York Bight Atlantic Sturgeon Fishery Revealed through Microsatellite Analysis of Archived Spines

AbstractA targeted commercial fishery for Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus once operated in the New York Bight, where it was assumed that most harvested Atlantic Sturgeon were natal to the Hudson River population. However, more recent evidence suggests that the fishery may have been targeting a mixed‐stock aggregation, in which case harvested Atlantic Sturgeon could have been comprised of individuals from multiple populations throughout the species’ range. Although there is now a moratorium on Atlantic Sturgeon harvest in the New York Bight, modern molecular approaches provide an opportunity to use archived tissues to perform a retrospective mixed‐stock analysis on the fishery. Genomic DNA extracted from archived fin spines from 80 Atlantic Sturgeon collected nearly 30 years ago suggests that the fishery primarily harvested individuals from the Hudson River population. However, based on individual‐based assignment tests, our results indicate that the fishery also harvested individuals from at least eight other populations located throughout the species’ range. This study highlights how archival hard parts that were previously used for age and growth analyses can be employed for retrospective genetic analyses. Further, because the New York Bight harbors relatively high concentrations of Atlantic Sturgeon, the study shows how localized management decisions can influence Atlantic Sturgeon conservation at rangewide scales. When integrated with more recent knowledge of species ecology, these analyses can be used to evaluate the efficacy of previous management strategies and understand the effects of historical processes on contemporary demography.

Trends and Effects of a Recreational Lake Sturgeon Fishery in the St. Clair System

AbstractOne frequently desired outcome of Lake Sturgeon Acipenser fulvescens rehabilitation is to create a recreational fishery for the species. However, few waterbodies offer a recreational fishery where anglers can catch Lake Sturgeon regularly. Lake St. Clair and the St. Clair River (hereafter, “St. Clair system”) contain large, stable populations of Lake Sturgeon, and a recreational fishery allowing harvest has been present since 1950. Over the last several decades, the Michigan Department of Natural Resources (MDNR) has monitored the recreational Lake Sturgeon fishery in the St. Clair system by using numerous methods to assess angler participation, harvest rates, and population effects of the fishery. Lake Sturgeon anglers in the St. Clair system are predominantly male (89%) and largely reside in the three nearest counties (72%), although the geographic footprint of Lake Sturgeon anglers appears to be increasing. Estimates of angler abundance, trends in angler recapture of tagged Lake Sturgeon, sturgeon harvest data, and reported capture of MDNR “Master Angler”‐sized Lake Sturgeon by anglers all indicated that angling effort in this Lake Sturgeon fishery has steadily increased since monitoring began. Despite increasing angler participation, the recreational fishery has had no detectable population‐level effect on Lake Sturgeon in the St. Clair system. Harvest rates of tagged Lake Sturgeon are low, with most anglers practicing catch and release. Recapture rates of angler‐caught fish in comparison to MDNR survey‐caught fish suggested that hooking mortality is low. Additionally, apparent survival estimates of Lake Sturgeon have been constant. Information gained from monitoring the recreational Lake Sturgeon fishery in the St. Clair system will be valuable to managers assessing whether to establish a sturgeon fishery in other systems.

Pêches des bélugas, des anguilles et des esturgeons noirs de l’estuaire du St-Laurent

Cet article dresse un portrait ethnographique de l’exploitation, de la mise en marche et de la conservation de trois especes emblematiques de l’estuaire du Saint-Laurent : le beluga, l’anguille et l’esturgeon noir. L’approche de la political ecology mobilisee permet dans un premier temps de retracer l’histoire de la peche au beluga ayant permis l’avenement des peches d’anguilles et d’esturgeons. Deuxiemement, le processus de degradation environnementale qui a mene a des politiques de gestion ayant marginalise les pecheurs est examine. La maniere dont ces peches sont desormais liees a un phenomene de patrimonialisation de la nature et a de nouveaux mecanismes de marchandisation est enfin exploree. Cette analyse permet d’interroger les consequences environnementales du developpement capitaliste et des politiques de gestion de la nature pour les pecheurs et leur environnement et d’eclairer le processus de precarisation de ces peches.

Timely Events in Their Interrelation to Paddlefish and Sturgeon Harvest from 1945-2010

Abstract Due to the high amounts of harvest of natural fish populations, overexploitation can occur and subsequently lead to depleted fisheries. This is especially true for commercially exploited roe-bearing species that exhibit late age at maturation and intermittent spawning. Overexploitation can create an imbalance in natural ecosystem function and in turn jeopardize the livelihood of commercial fishers. Despite the problems created by overexploitation, trends of commercial harvest on large inland river roe-bearing populations have received minimal attention. As such, we evaluated trends in commercial fishing data from 1945-2010 for two roe-bearing species (paddlefish Polyodon spathula and shovelnose sturgeon Scaphirhynchus platorynchus) from two of the largest inland rivers in North America (Mississippi River and Missouri River) adjacent to Missouri. Commercial sturgeon and paddlefish catch has varied from ∼160 to 35,150 kg over the course of the 55-year duration. Abnormally high catches corresponded to initiation of worldwide caviar markets, onset of extensive regulations on the Missouri and Mississippi rivers, and the Caspian Sea fishery collapse; respectively. Further, our results suggest that the harvest of sturgeon and paddlefish have increased since 1945 and may be influenced by local, regional, and international events. Despite the increase in harvest and the possibility of overharvest, commercial fishing regulations have not been thoroughly evaluated for effectiveness. Further evaluation of current management and regulations of these paddlefish and sturgeon fisheries is suggested, especially considering these fisheries may be influenced by local, regional, and international events. Taking potentially influential events into consideration when evaluating and implementing regulations and authorizing commercial harvest permits are vital in sustaining a long term commercial fishery and protecting the livelihood of commercial fishers.

Assessment of the sturgeon catches and seal bycatches in an IUU fishery in the Caspian Sea

The paper presents a quantitative assessment of sturgeon catches and related Caspian Seals’ by-catches of the illegal sturgeon fishery in the region of Dagestan and the Volga River Delta in Russia. The study uses semi structured interviews, direct observations and informal conversations to collect data and estimates that about 10,491kg of sturgeons were caught with 788 seals of by-catch during 35 trips conducted by 15 boats in the period of 2013–2016. The results show that both IUU sturgeon catch and the rate of bycatch seals have not demonstrated significant change since 2013. However, the rates of seals by-catch have increased since the studies in 2008 – 2009 and may be recognized as the one of the biggest entanglements of pinnipeds as by-catch.

Status of Lake Sturgeon (Acipenser fulvescensRafinesque 1817) in North America

Summary Lake Sturgeon is a potamodromous, fluvial-dependent species from the family Acipenseridae, and one of the largest freshwater fishes within its North American range extending to the Great lakes, Mississippi River, and Hudson Bay drainages. Like almost all other sturgeon species, Lake Sturgeon populations throughout its range suffered mass declines or extirpation in the late 1800s into the early 1900s, due to extensive overexploitation and habitat loss and alteration. However, Lake Sturgeon are still present in low to high densities throughout their native range due primarily to factors including: the species long life span and resiliency, the remote location of many northern populations, long-term pro-active management programs effectively controlling exploitation, improved habitat and water-quality conditions, and recovery programs that have been in effect since the late 1970s. Recovery programs initiated in the late 1970s are now just beginning to show signs of natural recruitment from populations re-built with stocked fish. Large sustainable recreational Lake Sturgeon fisheries with annual harvests of up to 45 000 kg and a commercial fishery with an annual harvest of up to 80 000 kg still exist and are maintained for Lake Sturgeon due primarily to rigid regulations, harvest controls, enforcement, and user involvement. The prognosis for the species is generally good, although habitat loss and maintaining public interest in the species management and recovery continue to be the greatest threats to local and regional populations. Hydropower development, especially in the northern part of the species’ range, is especially challenging due to the potential negative impact this type of development can have on a long migrating fish like Lake Sturgeon. Advances in understanding Lake Sturgeon life history, habitat requirements, and distribution within and among water systems has strongly indicated that dams and Lake Sturgeon can co-exist, if the correct planning and necessary mitigative techniques are employed at each site on a case-by-case basis.

Fish and fisheries in the Lower Rhine 1550–1950: A historical-ecological perspective

Regulation and intensive use of most of the world's large rivers, has led to dramatic decline and even to extinction of riverine fish populations like salmon and sturgeon in the river Rhine. In general this decline is considered an unwelcome side-effect of the Industrial Revolution and large-scale river regulation (c. 1800), but the deterioration of stocks of some species may have started well before the 19th century. For the river Rhine, data on fish landings as proxies of abundance in the period 1550–1950 can be derived from historical market prices, fisheries taxation and fishery and fish auctions statistics, especially for commercially interesting species like Atlantic salmon, sturgeon, Allis shad and Twaite shad. Most data from which abundance of these species can be derived, however, appear to be missing in historical sources until decline of the investigated species sets in and the species become economically scarce goods. Atlantic salmon in the Rhine catchment appears to be already in decline during Early Modern Times (post 1500 AD) after which time river regulation, pollution and intensified fisheries finished off the remaining stocks in the 20th century. Salmon decline caused a cascade in the River Rhine ecosystem as fisheries shifted to, especially, Allis shad and Twaite shad, followed by (near-)extinction of these species. Dropping yields of salmon fishery did not lead to increased sturgeon fishery, although numbers of sturgeon also dwindled to extinction in the river Rhine. The onset of sturgeon decline appears to coincide with the period of the first large regulation works. It is shown that historical-ecological data on fish abundance can quantitatively underpin detrimental long-term processes in river ecosystems.

Commercial fishing gear modifications to reduce interactions between Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and the southern flounder (Paralichthys lethostigma) fishery in North Carolina (USA)

Bycatch of protected species in commercial fishing operations is a primary concern to fishery managers because it threatens the conservation, protection, and recovery of fragile species, such as the Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus). One potential solution to reduce the risk associated with commercial fishing operations is to design commercial fishing gear that is more selective in terms of interactions between Atlantic sturgeon and commercial fisheries. Given this conservation and management need, the overarching goal was to reduce Atlantic sturgeon fishery interactions and maintain southern flounder (Paralichthys lethostigma) catch in North Carolina. The specific objectives of this study were to design and evaluate the effectiveness of a modified gillnet. Overall, the results proved that lowering the profile and amount of webbing had a beneficial impact at reducing Atlantic sturgeon incidental encounters and bycatch. The modified gillnet reduced bycatch and Atlantic sturgeon encounters by 39.6% and 60.9%, respectively. Our design entangled 51.6% fewer southern flounder, which corresponded to a 48.9% reduction in total weight; the modified gear entangled slightly larger southern flounder than the control gear. Our findings showed the number of Atlantic sturgeon encounters was positively associated with mean water depth, with more Atlantic sturgeon encountered in deeper (5.1–6.3 m) than shallower waters; 75% were encountered at depths between 4.6 and 6.1 m. Most southern flounder (n = 518, 39.7%) were taken at a water depth between 3.76 and 5.0 m. This observation suggests that southern flounder prefer slightly shallower waters than Atlantic sturgeon.

A short history of sturgeon caviar production in Turkey

Compared to other countries, caviar production in Turkey has a short history, which began principally in the early 1950s, peaked during the 1960s, and began to decline towards the end of the 1970s. Sturgeon fishery was practiced in the estuaries of the rivers Kızılırmak, Yeşilırmak, Sakarya and Çoruh. Thus, processed caviar originated from the districts of Carsamba, Bafra (Samsun City) and Karasu (Sakarya City) and appeared mainly in the markets of Istanbul. Techniques used to capture mature fish were nets set at sea and with hooks (‘karmak’ in Turkish) at the mouth of a river. Two processing techniques were commonly used: (i) malossol/mongol caviar (lightly/highly salted) and (ii) pressed caviar. Landings were mainly recorded in the Istanbul Kumkapı fish hall, reaching 300 tonnes per year in the late 1960s; however, catches declined drastically in the 1970s to only about 30 tonnes. In 1962, caviar production from Acipenser sturio was between 1200 and 1300 kg in the Yeşilırmak River; 1000 to 1200 kg in the Kızılırmak River; and 50 to 80 kg in the Sakarya River. For A. nudiventris, the respective data were 300–400 kg from Yeşilırmak River; 500–600 kg from Kızılırmak River; and 200–250 kg from Sakarya River. The rapid decline in Black Sea sturgeon stocks led to catch restrictions in Turkish coastal areas beginning in 1971. Following the construction of several hydrodams on the main sturgeon rivers in the 1970s, the few sturgeon spawning grounds that remained were drastically affected. Further deterioration of riverine environments was caused by increased pollution in the 1970s–1990s. Sturgeon catches dropped rapidly to less than 10 tonnes after 1975, whereby the fishery collapsed with only a few fish recorded sporadically after 2000. Over the past five years, aquaculture farms began to rear sturgeons for caviar production, with anticipation of initial marketing in 2014–2015. The forecast for 2020 is on the order of 6–8 tonnes of caviar per year.

High‐throughput SNP‐genotyping analysis of the relationships among Ponto‐Caspian sturgeon species

Legally certified sturgeon fisheries require population protection and conservation methods, including DNA tests to identify the source of valuable sturgeon roe. However, the available genetic data are insufficient to distinguish between different sturgeon populations, and are even unable to distinguish between some species. We performed high-throughput single-nucleotide polymorphism (SNP)-genotyping analysis on different populations of Russian (Acipenser gueldenstaedtii), Persian (A. persicus), and Siberian (A. baerii) sturgeon species from the Caspian Sea region (Volga and Ural Rivers), the Azov Sea, and two Siberian rivers. We found that Russian sturgeons from the Volga and Ural Rivers were essentially indistinguishable, but they differed from Russian sturgeons in the Azov Sea, and from Persian and Siberian sturgeons. We identified eight SNPs that were sufficient to distinguish these sturgeon populations with 80% confidence, and allowed the development of markers to distinguish sturgeon species. Finally, on the basis of our SNP data, we propose that the A. baerii-like mitochondrial DNA found in some Russian sturgeons from the Caspian Sea arose via an introgression event during the Pleistocene glaciation.In the present study, the high-throughput genotyping analysis of several sturgeon populations was performed. SNP markers for species identification were defined. The possible explanation of the baerii-like mitotype presence in some Russian sturgeons in the Caspian Sea was suggested.

Assessment of Caspian Seal By-Catch in an Illegal Fishery Using an Interview-Based Approach

The Caspian seal (Pusa caspica) has declined by more than 90% since 1900 and is listed as endangered by IUCN. We made the first quantitative assessment of Caspian seal by-catch mortality in fisheries in the north Caspian Sea by conducting semi-structured interviews in fishing communities along the coasts of Russia (Kalmykia, Dagestan), Kazakhstan and Turkmenistan. We recorded a documented minimum by-catch of 1,215 seals in the survey sample, for the 2008–2009 fishing season, 93% of which occurred in illegal sturgeon fisheries. Due to the illegal nature of the fishery, accurately quantifying total fishing effort is problematic and the survey sample could reflect less than 10% of poaching activity in the north Caspian Sea. Therefore total annual by-catch may be significantly greater than the minimum documented by the survey. The presence of high by-catch rates was supported independently by evidence of net entanglement from seal carcasses, during a mass stranding on the Kazakh coast in May 2009, where 30 of 312 carcasses were entangled in large mesh sturgeon net remnants. The documented minimum by-catch may account for 5 to 19% of annual pup production. Sturgeon poaching therefore not only represents a serious threat to Caspian sturgeon populations, but may also be having broader impacts on the Caspian Sea ecosystem by contributing to a decline in one of the ecosystem’s key predators. This study demonstrates the utility of interview-based approaches in providing rapid assessments of by-catch in illegal small-scale fisheries, which are not amenable to study by other methods.

Effects of IUU fishing and stock enhancement on and restoration strategies for the stellate sturgeon fishery in the Caspian Sea

Sturgeon is the most valuable fish species because of the high demand for their roe. The sturgeon fishery was historically the most important fishery in the Caspian Sea, but the major sturgeon species have now been classified as “critically endangered” by the International Union for Conservation of Nature. Considering commercial importance and data availability, we focus this study on stellate sturgeon. By applying a Depletion-Based Stock Reduction Analysis to model the population dynamics of the stellate sturgeon in the Caspian Sea, we estimate that the current stock is only 16% of the biomass (BMSY) that can produce the maximum sustainable yield (MSY). If all fish removals are stopped and no more stock enhancement takes place in the future, the stock would recover to BMSY by 2035 on average, with a 50% probability of it occurring between 2029 and 2058. If stock enhancement continues at the 2010 level, the rebuilding process will be 5 years faster, reaching BMSY by 2030. In contrast, if IUU fishing continues at the current level and only legal fishing is stopped, the stellate sturgeon will fail to recover and become extinct by 2042 without stock enhancement. Therefore, the priority of conserving the stellate sturgeon stock in the Caspian Sea is to eliminate IUU fishing. Practical rebuilding plans need also to include a combination of reducing fishing removals and restoring the spawning potential of the stock that has been lost by human interruptions in the ecosystem such as destruction of spawning grounds and overfishing.

Management approaches and aquaculture of sturgeons in the Lower Danube region countries

Summary This paper presents the status and trends in management of sturgeon species and the development of sturgeon aquaculture in the Lower Danube countries: Romania, Bulgaria, Serbia, Ukraine and Moldova. Sturgeon fishery moratoria and aquaculture development represent first steps in the Lower Danube countries to combat extirpation. Supportive stocking was used as a compensation for the impact of sturgeon fishery and dam construction, but these efforts unfortunately lacked adequate cooperation and coordination between and among region countries. Unsolved problems remain, such as the presence of illegal sturgeon fishery, water pollution, habitat destruction and fragmentation. Construction of fish passes and habitat restoration project developments are two key issues that have yet to be tackled in the Lower Danube region.

Caspian Sea sturgeon fishery: a historic overview

Summary The data on sturgeon fishery in the Caspian basin during last century as well as fishery management were analyzed. It was found that different factors influenced sturgeon stock in differrent time periods. The efficiency of various fishery management measures was demonstrated. Overall trend in the sturgeon fishery Prior to damming of the Volga River, fishing was the main factor influencing sturgeon populations. The total annual harvest amounted to 50 000 tonnes in the 17th century and varied around 32 000–37 000 tonnes in the 19th century. Sturgeon fishing in the Caspian Sea, along with river fishing, began in 1865 in its northern part, initially in coastal waters and then increasingly farther offshore. In the late 19th and early 20th century, it expanded to the central and southern parts of the sea. The total annual catches between 1901 and 1903 varied from 35 000 to 39 000 tonnes. However, excessive fishing in the sea resulted in a decline of sturgeon stocks, and catches in 1914–1915 decreased to only 27 700–28 700 tonnes per year, although the fishing fleet and effort remained practically unchanged (Korobochkina, 1964).

Current status and trends in shovelnose sturgeon (Scaphirhynchus platorynchus) management and conservation

Summary The objective of this study was to update information regarding the status of shovelnose sturgeon fisheries. Although a substantial amount of shovelnose sturgeon research has been conducted in the past decade, the study purpose was not to provide a comprehensive review of the literature; the primary interest was in the status, trends, and management of Scaphirhynchus platorynchus fisheries in North America. Biologists were surveyed in all 24 states within the native distribution of the species; results indicate that commercial harvest is currently permitted in eight states, recreational harvest is allowed in 13 states, and that regulations vary within rivers and jurisdictional boundaries. Although recreational exploitation of shovelnose sturgeon is thought to be low and not a significant threat to populations, commercial harvest is a major concern in states with a commercial fishery. In the last decade harvest has increased in all states with commercial shovelnose sturgeon fisheries, but recent implementation of regulations has decreased harvest in some states. Approximately half of the states with extant shovelnose sturgeon populations conduct routine monitoring of the species, and the understanding of shovelnose sturgeon populations is increasing.

Creel Survey Methods to Assess Catch, Loss, and Capture Frequency of White Sturgeon in the Snake River, Idaho

AbstractMandatory catch‐and‐release regulations for white sturgeon Acipenser transmontanus have been used to protect small populations from excessive fishing‐related mortality. However, these regulations only remain effective if the combined magnitude of capture and probability of mortality per capture remains at some unknown, relatively low level. We conducted a roving‐access creel survey supplemented with report cards to gather information as a first step in determining whether fishing‐related mortality rates are sustainable in one popular Idaho fishery. Survey objectives were to estimate effort, catch rate, loss rate, and to estimate total catch and loss over a 1‐year period on the C. J. Strike reach of the Snake River. During May 2007 through April 2008, angler counts indicated that 35,062 h were expended in this reach (89% by bank anglers; 11% by boat anglers). Catch rate for bank anglers averaged 0.048 ± 0.004 fish/h (mean ± 90% confidence interval), whereas loss rate averaged 0.064 ± 0.004 fish/h. Boat anglers had higher catch rates and were more efficient at landing hooked white sturgeon. The lack of difference in catch or loss rates computed from on‐site interviews, report cards, or follow‐up phone surveys suggested that there was no bias associated with methods used to collect completed trip information. Based on expansion of these estimates, we calculated that anglers hooked and fought white sturgeon 4,361 times, with 1,996 landings (46%) and 2,365 losses (54%). Using the most recent population estimate, on average, a white sturgeon in this reach was hooked 7.7 times during 1 year, including being landed 3.5 times and lost an additional 4.2 times. The use of supplementary report cards improved precision of catch and loss rate estimates by increasing sample size. Our observations suggest that this method was an unbiased, cost‐efficient method for acquiring completed trip information for a difficult‐to‐monitor white sturgeon fishery and may be useful for similar fisheries.

Maturation and Reproduction of Shovelnose Sturgeon in the Middle Mississippi River

AbstractShovelnose sturgeon Scaphirhynchus platorynchus in the middle Mississippi River provide one of the last commercially viable sturgeon fisheries in the world, yet their maturation and reproduction have not been linked. During 2005 and 2006, we sampled adult and age‐0 shovelnose sturgeon to link age at maturation, the timing and periodicity of spawning, age‐0 sturgeon production, and the resulting age‐0 growth rates. Age at maturity was later than previous estimates, the minimum age of first maturation being 8 years for males and 9 years for females. Total egg count was slightly lower than previously reported (mean = 29,573 per female; SE = 2,472). Males and females typically spawned every 2 and 3 years, respectively. Peaks in mature fish coincided with rising river stages and water temperatures at which shovelnose sturgeon probably spawn. Peaks in spent adults followed. Age‐0 shovelnose sturgeon occurred during June and July 2005 and May and June 2006, confirming successful spawning. Age‐0 sturgeon grew between 0.69 and 1.69 mm total length/d; four distinct weekly cohorts occurred each year. During fall 2006, females contained ripe eggs, males were milting, and a single age‐0 sturgeon (total length = 55 mm) was captured, suggesting that shovelnose sturgeon spawn during fall as well as spring. Management must consider the protracted nature of spawning within seasons as well as differences in spawning activity between seasons.

Effects of Commercial Harvest on Shovelnose Sturgeon Populations in the Upper Mississippi River

AbstractShovelnose sturgeon Scaphirhynchus platorynchus have become an increasingly important commercial species in the upper Mississippi River (UMR) because of the collapse of foreign sturgeon (family Acipenseridae) populations and bans on imported caviar. In response to concerns about the sustainability of the commercial shovelnose sturgeon fishery in the UMR, we undertook this study to describe the demographics of the shovelnose sturgeon population and evaluate the influence of commercial harvest on shovelnose sturgeon populations in the UMR. A total of 1,682 shovelnose sturgeon were collected from eight study pools in 2006 and 2007 (Pools 4, 7, 9, 11, 13, 14, 16, and 18). Shovelnose sturgeon from upstream pools generally had greater lengths, weights, and ages than those from downstream pools. Additionally, mortality estimates were lower in upstream pools (Pools 4, 7, 9, and 11) than in downstream pools (Pools 13, 14, 16, and 18). Linear regression suggested that the slower growth of shovelnose sturgeon is a consequence of commercial harvest in the UMR. Modeling of potential management scenarios suggested that a 685‐mm minimum length limit is necessary to prevent growth and recruitment overfishing of shovelnose sturgeon in the UMR.