A synopsis of lake sturgeon management in Alberta, Canada

The lake sturgeon ( Acipenser fulvescens ) is resident in the North and South Saskatchewan rivers of Alberta. Because of their confined distribution, low abundance, and vulnerability to anthropogenic impacts, lake sturgeon in Alberta have been the focus of specific management actions for nearly 60 years.
Lake sturgeon harvest was prohibited in Alberta from 1940 to 1968, after which a limited harvest was again permitted, but only as a hook-and-line sport fishery. After being reopened the fishery was primarily managed as a "trophy" fishery. Sport fishery harvest statistics have been compiled annually since 1968, through mail-out questionnaires sent to all holders of sturgeon angling licenses.
Few research studies have been undertaken on the life history or habitat requirements of lake sturgeon in the province, and biologists have relied primarily on anglers to provide information for management decisions. Preliminary population information for the South Saskatchewan River, from mark-recapture data, suggests a population size of about 3700 fish. Recent studies in the North Saskatchewan River indicate a population of about 1300 fish. Studies indicate that a portion of the population in both rivers is trans-boundary, moving between the waters of the adjoining provinces of Alberta and Saskatchewan, and creating concerns because of differences in angling regulations. During recent decades, major consumptive uses of water have also contributed to depletion of lake sturgeon habitat in the province.
After reviewing past management strategies and actions, Alberta Environmental Protection implemented a number of regulatory changes in 1987 to further protect lake sturgeon populations in the province while continuing to provide angling opportunities and maintaining a controlled harvest.     

Recovery plan for Kootenai River white sturgeon (Acipenser transmontanus)

The white sturgeon ( Acipenser transmontanus ) of the Kootenai River was listed as endangered on September 6, 1994 by the United States Fish and Wildlife Service. This transboundary population, residing in Kootenay Lake and Kootenay River in Canada, and the Kootenai River in the US, has been in general decline since the mid-1960's. There has been very little recruitment to this population in the last 20 years.
This population became isolated from other white sturgeon populations of the Columbia River basin during the last ice age of approximately 10,000 years ago. The population adapted to the pre-development conditions of the Kootenai system, with a high spring freshet and extensive side channel and low-lying delta marshlands. Modification of the Kootenai River by human activities, such as industrial developments, floodplain dyking, and dam construction has changed the hydrograph of the Kootenai River, altering sturgeon spawning, incubation and rearing habitats and reducing overall biological productivity.
A Kootenai River white sturgeon draft recovery plan was prepared by the US Fish and Wildlife Service in cooperation with other agencies in the US and Canada. The plan was peer reviewed and there was a parallel public consultation process, where public commentary was invited from both sides of the international border. The short-term recovery objectives of the recovery plan are to prevent extinction and re-establish successful natural recruitment. The identified long-term objectives are the re-establishment of a self sustaining population and the restoration of productive habitat, in order to downlist to threatened status and subsequently delist this population when recovery is well established. Specific actions needed for recovery include spring flow augmentation during the reproduction period; a conservation aquaculture program to prevent near-term extinction; habitat restoration, and research and monitoring programs to evaluate recovery progress.     

Ecology and biology of the lake sturgeon: a synthesis of current knowledge of a threatened North American <Emphasis Type="Italic">Acipenseridae</Emphasis>

The lake sturgeon is one of the largest North American freshwater fish and was once common in most inland rivers and lakes of the US and Canadian Midwest. World demand for caviar and sturgeon meat led to a dramatic decline of lake sturgeon populations throughout much of its range. Along with overfishing, lake sturgeon populations have been negatively affected by habitat degradation. Recruitment factors and early life history are poorly understood. Today, renewed interest in lake sturgeon restoration has led to numerous state and federally-funded research activities. Research has focused on identifying and assessing the size structure of remnant stocks, the availability of spawning habitat, and factors affecting reproductive success. Additional studies are needed to improve hatchery techniques, to better understand recruitment mechanisms, and how genetic diversity among and within meta-populations may affect long-term recovery of depleted populations.     

Status and management of white sturgeon in the Columbia River in British Columbia, Canada: an overview

White sturgeon ( Acipenser transmontanus ) in the Columbia River in Canada have recently been listed as Endangered/Critically Imperiled, based on a shift in size and age-class composition from a population dominated by juveniles in the early 1980s to one presently dominated by adults. This shift has been attributed to a poor survival of early life stages. To determine the causes for this poor survival, investigations conducted annually since 1990 have focussed on identifying white sturgeon movement patterns, population dynamics, reproductive biology, and critical habitats. The reasons for the low recruitment remain poorly understood but river regulation and reservoir formation due to dam construction and pollution from municipal and industrial effluent inputs are suspected as contributing factors.
The history of dam development on the Columbia River and implications to white sturgeon are discussed from a historical perspective. A synopsis of post-1990 study results is provided and discussed in the framework of management strategies that include: 1) angling regulations, 2) flow enhancement strategies during spawning, 3) development of a population stabilization plan, 4) investigations into the feasibility of artificial stock supplementation, and 5) proposed future study programs to identify factors limiting recruitment.     

Management of lake sturgeon on the Winnebago System - long term impacts of harvest and regulations on population structure

The Winnebago System, Wisconsin, supports one of the largest self sustaining stocks of lake sturgeon, Acipenser fulvescens , in North America. Winter spearing harvest of the Winnebago sturgeon population has been actively regulated since 1903 and actively assessed since the 1940's. While historic population assessments have shown a steady increase in sturgeon densities in the system, recent surveys indicated overexploitation of adult females. From 1991–97, 13714 sturgeon were assessed through harvest and spawning surveys to characterize the status of the current population, and historical data from DNR files were reassembled and analyzed to discern population trends over the last 40 years. A summary of management actions since 1903 was completed and reviewed in the context of long term population trends. 1991–97 annual harvests averaged 1337 sturgeon with adult females comprising 46% of the annual harvests from 1991–96 and 34% of the harvest in 1997 following a reduction in the minimum size limit. With the higher size limit, estimated annual exploitation of adult females was 2 to 3 times higher than that of adult males. Historic harvest and population trends showed the benefits of conservative bag limits and harvest season lengths combined with strict law enforcement, and habitat protection, which resulted in an estimated 58% reduction in the annual harvest between 1955 and 1965 and a four fold increase in legal stock densities from 1955 to 1990. The analyses of the historic data reinforced the necessity of standardized long term harvest and population assessments for effective management of sturgeon populations and fisheries. Public involvement is also identified as an integral component to effective sturgeon management.     

Experimental passage of adult male Gulf sturgeon around Jim Woodruff Lock and Dam on the Apalachicola River,Florida

Dams can impede access to habitats that are required for the completion of life history phases of many migratory fish species, including anadromous sturgeons. Various forms of fish passage have been developed to permit migratory fishes to move above dams, but many dams still lack such structures. Translocation of ripe, mature fish above dams has been used as a first step to determine the efficacy of potential fish passage systems. The anadromous Gulf sturgeon, Acipenser oxyrinchus desotoi, inhabits the Gulf of Mexico and coastal rivers from Florida to Louisiana, and requires upriver spawning habitats to complete its life cycle. Historic overfishing and other anthropogenic threats, including dam construction, led to species declines and subsequent listing as threatened under the Endangered Species Act. In the Apalachicola River, FL, the 1957 completion of Jim Woodruff Lock and Dam (JWLD) created Lake Seminole and blocked Gulf Sturgeon from accessing 78% of historic riverine habitat—including potential spawning habitat—in the Apalachicola-Chattahoochee-Flint River Basin. The objective of this pilot study was to determine the efficacy of passage around JWLD through the trap-and-transport of 10 male Gulf sturgeon from the Apalachicola River to the reservoir above the dam. Through the use of acoustic telemetry, we were able to assess the ability of these fish to navigate Lake Seminole, access potentially suitable spawning habitat in the Flint and River, and complete their seasonal outmigration to the Gulf of Mexico. In this study, 2 translocated sturgeon moved 69 km upstream into potential spawning habitat in the Flint River, but 6 fish fell back through the lock/spill gates at JWLD within days of translocation. Four sturgeon appeared to remain trapped in the reservoir, and their long-term survival was deemed unlikely. Given our low sample size, and examination of male fish only, we cannot conclude that a trap-and-transport program would ultimately fail to restore spawning above JWLD, but our findings suggest that the risk of adult mortality is nontrivial. Alternatively, we suggest future studies examine the population level trade-offs associated with translocation of adults or consider alternatives such as a head-start program to rear and release juvenile sturgeon above JWLD to study viability of their passage in addition to effects on overall recruitment in the population.     

Status and management of Atlantic sturgeon, Acipenser oxyrinchus, in North America

The Atlantic sturgeon, Acipenser oxyrinchus, consists of two subspecies distributed along the Atlantic coast of North America from Labrador to the east coast of Florida (Atlantic sturgeon subspecies – A. o. oxyrinchus) and along the Gulf of Mexico from Florida Bay, Florida to the mouth of the Mississippi River (Gulf sturgeon subspecies – A. o. desotoi). The species has been exploited throughout its range with landings peaking around the turn of the 20th century followed by drastic declines shortly thereafter. During recent years, landings in Canadian waters have increased substantially (approximately 129 metric tons in 1993) while in the United States landings are more controlled or prohibited (approximately 22–24 metric tons in 1993). Recently, the Atlantic States Marine Fisheries Commission developed a Fishery management plan for Atlantic sturgeon, and the United States Fish & Wildlife Service and Gulf States Marine Fisheries Commission drafted a Gulf Sturgeon Recovery/Management Plan. Fishery managers in Canada are in the process of establishing more stringent fishery regulations for sturgeon. Thus, the impact on populations due to harvesting should be substantially reduced. Current research focus includes: life history and population status studies, stock delineation, and development of culture and stock enhancement techniques. Implementation of the findings of such studies may be helpful in the restoration of depleted stocks.     

The fishery,biology, and management of Atlantic sturgeon,Acipenser oxyrhynchus,in North America

Synopsis The Atlantic sturgeon supported major fisheries along the entire Atlantic coast of North America. These fisheries peaked about 1890 and then suffered almost total collapse by 1905. The Atlantic sturgeon is anadromous and highly susceptible to capture during spawning migrations. Further, this species biological characteristics makes it very vulnerable to man-induced changes in natural habitat and slow to recover. Atlantic sturgeon mature at an advanced age (7–27 year for females, depending on latitude), exhibit a long interspawning period (2–5 year), and require suitable riverine, estuarine, and coastal environments for successful completion of their life cycle. Today, only remnant stocks exist in areas of former abundance. Management regulations vary considerably from state to state and range from full protection to no protection. Biological data are needed to: identify and characterize specific spawning and nursery areas; delineate migratory patterns and recruitment to various stocks; establish stock abundance; and, assess effects of various management strategies. In order to protect remaining stocks, the imposition of a total harvesting moratorium is recommended.     

Characterization of Pallid Sturgeon (Scaphirhynchus albus) Spawning Habitat in the Lower Missouri River

Acipenseriformes (sturgeons and paddlefish) globally have declined throughout their range due to river fragmentation, habitat loss, overfishing, and degradation of water quality. In North America, pallid sturgeon (Scaphirhynchus albus) populations have experienced poor to no recruitment, or substantial levels of hybridization with the closely related shovelnose sturgeon (S. platorynchus). The Lower Missouri River is the only portion of the species’ range where successful reproduction and recruitment of genetically pure pallid sturgeon have been documented. This paper documents spawning habitat and behavior on the Lower Missouri River, which comprises over 1,300 km of unfragmented river habitat. The objective of this study was to determine spawning locations and describe habitat characteristics and environmental conditions (depth, water velocity, substrate, discharge, temperature, and turbidity) on the Lower Missouri River. We measured habitat characteristics for spawning events of ten telemetry-tagged female pallid sturgeon from 2008–2013 that occurred in discrete reaches distributed over hundreds of kilometers. These results show pallid sturgeon select deep and fast areas in or near the navigation channel along outside revetted banks for spawning. These habitats are deeper and faster than nearby river habitats within the surrounding river reach. Spawning patches have a mean depth of 6.6 m and a mean depth-averaged water-column velocity of 1.4 m per second. Substrates in spawning patches consist of coarse bank revetment, gravel, sand, and bedrock. Results indicate habitat used by pallid sturgeon for spawning is more common and widespread in the present-day channelized Lower Missouri River relative to the sparse and disperse coarse substrates available prior to channelization. Understanding the spawning habitats currently utilized on the Lower Missouri River and if they are functioning properly is important for improving habitat remediation measures aimed at increasing reproductive success. Recovery efforts for pallid sturgeon on the Missouri River, if successful, can provide guidance to sturgeon recovery on other river systems; particularly large, regulated, and channelized rivers.     

Assessing the influence of habitat quality on movements of the endangered shortnose sturgeon

Movements of the endangered shortnose sturgeon Acipenser brevirostrum in the Ogeechee River (Georgia, USA) may be limited by unsuitable habitat conditions during June–September. The research objective was to determine if habitat quality is likely to impede movements and spawning of shortnose sturgeon in this system. We inserted ultrasonic transmitters in 18 adult shortnose sturgeon to monitor their monthly in-stream movements. Water quality data were collected at discrete locations along the Ogeechee River. We used geostatistical models based on Weighted Asymmetric Hydrologic Distance, in place of Euclidean distance, to predict water quality variables along the Ogeechee River, avoiding problems associated with linear distance metrics in a river network. Using ArcGIS, we constructed habitat quality models based on physiological tolerance to water temperature, dissolved oxygen, and salinity. During the summer months, tagged fish remained congregated above the fresh-saltwater interface. However, individuals appeared to move in response to changing water quality conditions. Seasonal habitat availability in other southern rivers should be similarly analyzed to assess potential relationships between the habitat and sturgeon movements. Although further laboratory and field studies are needed to better understand latitudinal variation in life history and environmental tolerances of shortnose sturgeon, the results of our study suggest that temporal and spatial variability in water quality affect habitat availability of southern populations of shortnose sturgeon.     

Population Status of North American Green Sturgeon, Acipenser medirostris

North American green sturgeon, Acipenser medirostris, was petitioned for listing under the Endangered Species Act (ESA). The two questions that need to be answered when considering an ESA listing are; (1) Is the entity a species under the ESA and if so (2) is the “species” in danger of extinction or likely to become an endangered species in the foreseeable future throughout all or a significant portion of its range? Green sturgeon genetic analyses showed strong differentiation between northern and southern populations, and therefore, the species was divided into Northern and Southern Distinct Population Segments (DPSs). The Northern DPS includes populations in the Rogue, Klamath-Trinity, and Eel rivers, while the Southern DPS only includes a single population in the Sacramento River. The principal risk factors for green sturgeon include loss of spawning habitat, harvest, and entrainment. The Northern DPS is not considered to be in danger of extinction or likely to become an endangered species in the foreseeable future. The loss of spawning habitat is not large enough to threaten this DPS, although the Eel River has been severely impacted by sedimentation due to poor land use practices and floods. The two main spawning populations in the Rogue and Klamath-Trinity rivers occupy separate basins reducing the potential for loss of the DPS through catastrophic events. Harvest has been substantially reduced and green sturgeon in this DPS do not face substantial entrainment loss. However there are significant concerns due to lack of information, flow and temperature issues, and habitat degradation. The Southern DPS is considered likely to become an endangered species in the foreseeable future. Green sturgeon in this DPS are concentrated into one spawning area outside of their natural habitat in the Sacramento River, making them vulnerable to catastrophic extinction. Green sturgeon spawning areas have been lost from the area above Shasta Dam on the Sacramento River and Oroville Dam on the Feather River. Entrainment of individuals into water diversion projects is an additional source of risk, and the large decline in numbers of green sturgeon entrained since 1986 causes additional concern.     

Assessing the effect of Separation Levee Project on Chinese sturgeon (<Emphasis Type="Italic">Acipensor sinensis</Emphasis>) spawning habitat suitability in Yangtze River,China

Chinese sturgeon (Acipenser sinensis) is a protected anadromous fish species. The migration pattern of the fish has been blocked by the construction of Gezhouba Dam, reducing the natural spawning site length to less than 7 km along the Yangtze River. However, the fish has since established an alternative spawning ground in the narrow reach downstream of Gezhouba Dam. To enhance navigation, a Separation Levee Project (SLP) was implemented in the new-found spawning habitat of the fish. To therefore evaluate the effect of the SLP on Chinese sturgeon spawning habitat suitability, the conditions in the spawning habitat were simulated using River2D (a two-dimensional hydrodynamic model). Two main approaches (habitat kinetic energy and circulation metrics) were used in the simulation. The study showed that SLP only slightly changed the physical conditions in the spawning habitat. Using hydrodynamic simulation, the weighted usable area (WUA) before and after the SLP construction was also computed and habitat preference curve developed for water depth and velocity. On the average, SLP reduced WUA—a finding that was consistent with field-measured data. Based on WUA, the habitat conditions were more sensitive to SLP proximity than metrics based on velocity gradients. SLP posed detrimental impacts on the suitability of spawning habitats of Chinese sturgeon. The findings in this study provide further basis for the protection and restoration of Chinese sturgeon spawning habitats in especially the lower reach of Yangtze River.     

密西西比河干流大坝建设对鱼类的影响及保护措施

如何减轻大坝阻隔对鱼类等水生生物的影响以及制定有效的恢复措施一直是河流生态保护的主要内容。文章通过文献调研、资料收集等方式对美国密西西比河干流大坝建设状况及其对鱼类的影响进行梳理, 总结了当前美国所采取的相关保护措施和效果。统计结果显示, 密西西比河干流共建有梯级闸坝41座, 均分布在干流的上游, 多数大坝坝高不超过15 m, 库容小于0.3 km3。这些弱调蓄能力的低水头坝阻隔了密西西比河鱼类洄游, 但目前仍未修建过鱼设施。相关研究证实, 密西西比河洄游性鱼类可以利用泄水闸门完成上行和下行, 但过鱼效率随着大坝梯级的递增逐级下降, 尤其是鲟类, 仍难以抑制其种群的衰退。受长期蓄水影响, 密西西比河上游鱼类群落产生了空间分化, 但仍保持着较高的物种多样性。1986和2000年, 美国分别实施了上密西西比河生态系统环境管理计划(UMRS-EMP)和上密西西比河生态恢复和维持策略(UMRS-RMS), 采用渔业资源长期监测计划(LTRMP)及9项栖息地修复措施, 从生态系统层面保障了密西西比河鱼类资源的持续稳定。这种系统性修复方式可为我国筑坝河流鱼类资源保护与河流生态修复提供参考和示范。     

Spawning by lake sturgeon (Acipenser fulvescens) in the Detroit River

Overfishing and habitat destruction in the early 1900s devastated lake sturgeon (Acipenser fulvescens) populations in the Great Lakes. Although a comprehensive restoration strategy for this species was recently drafted by the Michigan Department of Natural Resources, a lack of current data on Great Lakes sturgeon stocks has hindered rehabilitation efforts. Historically, the Detroit River supported one of the largest lake sturgeon populations in the Great Lakes; however, little is known about the current population or its habitat use. The main objective of this study was to determine if lake sturgeon spawns in the Detroit River. As part of a larger study, baited setlines were used to capture lake sturgeon in the Detroit River in the spring and summer of 2000 and 2001. In each year of the study, ultrasonic transmitters were surgically implanted in 10 adult fish to track their movements, evaluate habitat use and identify possible spawning sites. Using telemetry and egg mats to verify spawning activity, one spawning site was located and verified in the Detroit River. Spawning was verified by recovering sturgeon eggs deposited on egg collection mats anchored at the site. Telemetry data suggested that several other possible spawning sites also may exist, however, spawning activity was not verified at these sites.     

Spawning Periodicity, Spawning Migration, and Size at Maturity of Green Sturgeon, Acipenser medirostris, in the Rogue River, Oregon

The Rogue River, Oregon represents one of three important spawning systems for green sturgeon, Acipenser medirostris, in North America. In this paper we describe the spawning migration, spawning periodicity, and size at maturity for green sturgeon caught in the Rogue River during 2000–2004. Green sturgeon were caught by gill net or angling; 103 individuals were tagged with radio or sonic transmitters (externally or internally). Green sturgeon caught by gill net and angling ranged from 145 cm to 225 cm total length. Histological and visual examinations of gonad tissues indicated that most green sturgeon were spawning or post-spawning adults that entered the Rogue River to spawn. Ripe individuals were caught when water temperature was 10–18°C. Specimens carrying transmitters migrated 17–105 km up river; reaches consisting of likely spawning sites were identified based on sturgeon migratory behavior. Most green sturgeon remained in the Rogue River until late fall or early winter when flows increased, after which they returned to the ocean. Eight green sturgeon (males and females) returned to the Rogue River 2–4 years after leaving, entering the river during March, April, and May when water temperatures ranged from 9°C to 16°C. None of the 103-tagged individuals entered the Rogue River during successive years. There appear to be few known natural threats to adult green sturgeon in the Rogue River. However, our data suggest that a high percentage of adults that spawn in the Rogue River (particularly males) were susceptible to harvest by commercial, Tribal, and sport fisheries after leaving the system because they were not adequately protected by maximum size limits during the period of this study. The implications of maximum size limits (or lack of size limits) to green sturgeon are discussed, and recent actions taken by Oregon and Washington Fish and Wildlife Commissions to manage green sturgeon more conservatively are presented.     

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

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.     

Genetic assessment of lake sturgeon (<Emphasis Type="Italic">Acipenser fulvescens</Emphasis>) population structure in the Ottawa River

Lake sturgeon (Acipenser fulvescens) are of conservation concern throughout their range. Many populations are dependent on fluvial habitats which have been increasingly impacted and fragmented by dams and human development. Although lake sturgeon were once abundant in the Ottawa River and its tributaries, historical commercial harvests and other anthropogenic factors caused severe declines and low contemporary numbers in lake sturgeon populations. Contemporary habitat fragmentation by dams may be increasing isolation among habitat patches and local rates of decline, raising concerns for persistence of local populations. We used microsatellite DNA markers to assess population structure and diversity of lake sturgeon in the Ottawa River, and analyzed samples from 10 sites that represent more than 500 km of riverine habitat. To test for evidence of anthropogenic fragmentation, patterns of genetic diversity and connectivity within and among river segments were tested for concordance with geographic location, separation by distance and obstacles to migration, considering both natural and artificial barriers as well as barrier age. Despite extensive habitat fragmentation throughout the Ottawa River, statistical analyses failed to refute panmixia of lake sturgeon in this system. Although the long generation time of lake sturgeon appears to have effectively guarded against the negative genetic impacts of habitat fragmentation and loss so far, evidence from demographic studies indicates that restoring connectivity among habitats is needed for the long-term conservation and management of this species throughout this river system.     

Conservation and collection efforts for the endangered Alabama sturgeon (Scaphirhynchus suttkusi)

The Alabama sturgeon (Scaphirhynchus suttkusi) is the rarest and most endangered sturgeon species in North America. Over an 8‐year period, the Alabama Division of Wildlife and Freshwater Fisheries, U.S. Army Corps of Engineers, and U.S. Fish and Wildlife Service cumulatively expended 2447 man‐days in efforts to collect Alabama sturgeon broodstock in an attempt to initiate a conservation propagation program. Out of nearly 29 000 fishes collected between March 1997 and May 2005, only five were Alabama sturgeon. Attempts to spawn and propagate these sturgeons were unsuccessful, and all have since died in captivity. In context with past collection efforts and anecdotal accounts, these results indicate that the Alabama sturgeon is becoming increasingly rare with the passage of time. Although there is evidence that some level of recruitment continued to occur in the Alabama River during the past decade, the increasing rarity of Alabama sturgeon suggests that mortality rates are exceeding recruitment.     

Effects of harvest and length limits on shovelnose sturgeon in the upper Wabash River, Indiana

Shovelnose sturgeon Scaphirhynchus platorynchus are one of the few sturgeon species that currently support sustainable commercial harvest. However, harvest closures for many Eurasian sturgeons have resulted in increased exploitation of this fishery, thereby raising concerns about the sustainability of shovelnose sturgeon resources. As a result, the maintenance of self‐sustaining shovelnose sturgeon populations will require the estimation of appropriate harvest levels. This study used an age‐structured population model to examine the effects of harvest (u = 0.15–0.75) and length restrictions on population abundance, mean length‐at‐harvest, biomass, yield, and reproductive potential of female shovelnose sturgeon in the upper Wabash River, Indiana. Model simulations for four hypothetical length‐restriction scenarios (610‐ to 813‐mm reverse slot limit, and a 610‐, 635‐, and 660‐mm minimum length limit) were compared to outputs with no restriction. All population parameters within each length‐restriction scenario declined with increases in harvest level. For each harvest level, all population parameters increased as length limits became more restrictive. The reverse slot limit and 610‐mm minimum length limit provided adequate protection to allow population parameters to increase through an annual harvest level of 0.55. However, these length restrictions were not sufficiently conservative to warrant implementation due to their similarity to length‐at‐maturity of female shovelnose sturgeon. The implementation of a 635‐mm minimum length limit would protect female shovelnose sturgeon from harvest rates >0.75, allow 92% of the females to remain available for harvest, and minimize short‐term (<30 years) declines in yield. Further, sensitivity and robustness analyses suggested that the 635‐mm minimum length limit would allow population parameters to increase even at the worst‐case scenario. As a result, the 635‐mm minimum length limit was recommended as the most appropriate regulation to promote conservation and sustainable harvest of shovelnose sturgeon in the upper Wabash River.     

Evaluating the efficacy of seasonal grazing and livestock exclusion as restoration tools for birds in riparian habitat of the Okanagan Valley,British Columbia,Canada

Riparian habitat supports the highest density and diversity of songbirds in Western North America despite covering less than 1% of the land area. Widespread destruction and degradation of riparian habitat, especially by livestock grazing, has led to habitat restoration efforts. In 2000, restoration activities in the form of permanent and seasonal exclusion of livestock from riparian areas were initiated to improve habitat for the endangered Western Yellow‐breasted Chat (Icteria virens auricollis) population, which is dependent on early successional shrub habitat for nesting, in the Okanagan Valley of British Columbia, Canada. We assessed the effectiveness of livestock exclusion by examining temporal changes in the abundance, richness, and breeding performance of birds in restoration and reference sites. The abundance of W. Yellow‐breasted Chats significantly increased between 2002 and 2013 in areas where restoration activities occurred. However, restoration did not have significant effects on the abundance, richness, or breeding performance of other riparian birds at the restoration sites independent of temporal changes that occurred at reference sites. Our results provide evidence that limiting livestock grazing in temperate riparian areas can lead to recovery of endangered riparian songbirds that rely on early successional shrub habitat but may have limited effects on common species that are not strictly reliant on this habitat.