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.     

Ecoacoustic monitoring of lake sturgeon (Acipenser fulvescens) spawning and its relation to anthropogenic noise

Lake sturgeon (Acipenser fulvescens) are endangered in the Laurentian Great Lakes with increasing binational efforts to establish spawning grounds to aid restoration. While SCUBA surveys can document spawning activity, these are labour-intensive and may disrupt spawning. We used passive acoustic monitoring to quantify spawning sounds of lake sturgeon as a first step to developing remote sensing of sturgeon spawning grounds. Acipenser sp. are known to make a variety of sounds including, “thunders” (aka drums), which have been documented in A. fulvescens during spawning. We quantified drums from a known spawning bed. We recorded 5 different potential sturgeon sounds but only quantified drums as a marker for spawning activity. Drums were low frequency with average frequency peaks at 40 and 92 Hz and a rapid drop-off thereafter. There was no relationship between calling activity and water temperature but calling activity increased as the summer progressed. Call production was most active from 0600 to 1500 h with little calling activity during nighttime recordings. The presence of low frequency boat sounds did correlate with a reduction in maximum calling rate so it is possible that commercial shipping may disrupt sturgeon communication, but more research is necessary to separate correlational from causative effects. These recordings represent a promising approach to map sturgeon spawning activity and show the potential effect of human activity on communication in this threatened species.     

Inheritance of microsatellite loci in the polyploid lake sturgeon (Acipenser fulvescens).

Inheritance in the expression of amplicons for four microsatellite primer pairs was determined using 10 families created from gametes of wild lake sturgeon (Acipenser fulvescens). Loci Afu34 and Afu68 expressed a maximum of two even-intensity bands per individual and had progeny genotype ratios that fit disomic inheritance (P > 0.05). Some variation exhibited at Afu34 and Afu68 was attributable to a null allele. Genotype expression at both loci also indicated that one female parent had transmitted unreduced gametes. Primer Afu39 amplified products that exhibited four gene doses, where genotype counts fit expected ratios for disomic inheritance (P > 0.05) indicating amplification of products from two disomic loci that share alleles. Meiotic drive was evident at the Afu39 loci based on a test for random segregation (P < 0.05). Only the expression of Afu19 gave evidence of tetrasomic inheritance based on a single progeny potentially produced by a double reduction gamete. No evidence for proposed octoploid inheritance was observed.     

Spawning lake sturgeon (Acipenser fulvescens Rafinesque, 1817) and their habitat characteristics in Rainy River,Ontario and Minnesota

Lake Sturgeon (Acipenser fulvescens) spawning habitat in the Rainy River was studied in light of the ongoing review of the rules governing water levels upstream that affect discharge rates through the International Falls dam. The objectives of this study were to assess the current status of spawning Lake Sturgeon below the dam by: (i) evaluating weight–length relationships, condition, age and growth; (ii) identifying spawning locations and characterizing its physical attributes; and, (iii) evaluating the effects of water surface elevation on the availability of spawning habitat. Spawning was confirmed with use of egg mats, and targeted sampling of spawning individuals was completed using gillnets and electrofishing. Physical attributes of spawning locations, including temperature, depth and water velocity were collected at a range of water levels using an Acoustic Doppler Current Profiler and representative sediment sampling. Biological characteristics and timing of spawning events were consistent with those previously reported for Lake Sturgeon. However, a wider range of depths (0.3–10.5 m) and velocities (0.01–1.9 m³/s) than reported in most single site studies was found here, with the ranges encompassing what is reported in the literature as a whole. Lake Sturgeon were found to prefer coarse spawning substrates dominated by bedrock, boulder or cobble. The availability of preferred spawning habitat varied significantly with the changing water levels observed during the study and was eventually limited at higher water levels by river channel form. Because of the implications for dewatering of nest sites, keeping flows constant during spawning is critical to Rainy River Lake Sturgeon spawning success.     

Digestive secretions of lake sturgeon, Acipenser fulvescens, during early development

Digestive secretions of lake sturgeon were analysed for 60 days post-hatch. Three developmental phases were observed. During the yolk-sac stage (days 1–16) the digestive system differentiated and digestive enzyme concentrations were low. Initiation of gastric secretion was concurrent with establishment of active feeding (days 14–18). Peptic and tryptic activities continued to increase thereafter. Amylolytic and lipolytic activities were highest during the larval feeding phase and then declined following metamorphosis of the larvae to juveniles (days 24–30). Changes in the digestive enzyme complement were age related, not dietarily induced, and appeared to correspond with the different feeding habits and, possibly, nutritional requirements of the distinct life history stages.     

Effect of temperature on early development of white and lake sturgeon,Acipenser transmontanus and A. fulvescens

Synopsis The effect of constant incubation temperatures (between 10°C and 26°C) on the developmental rates was found to fit a similar exponential relationship in both the lake and white sturgeon embryos and larvae. Although the lake sturgeon had an overall slower rate of development than the white sturgeon, no statistically significant difference was detected in the slopes of the exponential equations describing the effect of temperature on developmental rate. The effect of these incubation temperatures on embryonic survival also did not differ between these two species. Both species exhibited optimal survival between 14–17° C and incipient mortalities occurred at 20°C. Temperatures above 20°C were lethal for white sturgeon embryos. No effect of low incubation temperature on survival was evident from this study. A comparison of these North American species with Eurasian acipenserids suggests that all the sturgeon that have been examined exhibit a similar influence of incubation temperature on developmental rate.     

Parasites of lake sturgeon, Acipenser fulvescens (Chondrostei: Acipenseridae), from central Canada

Nineteen species of parasites were recovered from lake sturgeon, Acipenser fulvescens, from four major waterways of Central Canada; the Saskatchewan, Nelson, Winnipeg and Rainy River systems, Twelve of these are new host records. Host specific parasites, Crepidostomum auriculatum , Diclybothrium armatum , Spinitectus acipenseri and Truttaedacnitis clitellarius , forming the core parasite species, were recovered with the highest prevalence (≥70%) and were most widely distributed. Polypodium hydriforme was recovered from only stage IV sturgeon oocytes. With the exception of Pomphorhynchus bulbocolli , prevalence and intensity of endohelminth infections were not correlated with sex or age of host but the distribution of non host-specific parasites among sampling sites was determined by the type and relative abundance of food items consumed. The parasites of lake sturgeon are closely correlated to its diet and the species of parasites recovered are more similar to those of freshwater sturgeon in Eurasia than to other species of Acipenser in North America. The present parasite community of lake sturgeon appears to have been shaped by three major factors; the presence of core parasite species which predates geographic isolation, a benthic freshwater diet which has reshaped the parasite community to one comprising freshwater species and a long association with freshwater habitats which is reflected in the reproductive isolation of the lake sturgeon and lastly, the establishment of a host-specific parasite, Spinitectus acipenseri .     

Discovery and evaluation of candidate sex-determining genes and xenobiotics in the gonads of lake sturgeon (Acipenser fulvescens)

Modern pyrosequencing has the potential to uncover many interesting aspects of genome evolution, even in lineages where genomic resources are scarce. In particular, 454 pyrosequencing of nonmodel species has been used to characterize expressed sequence tags, xenobiotics, gene ontologies, and relative levels of gene expression. Herein, we use pyrosequencing to study the evolution of genes expressed in the gonads of a polyploid fish, the lake sturgeon (Acipenser fulvescens). Using 454 pyrosequencing of transcribed genes, we produced more than 125 MB of sequence data from 473,577 high-quality sequencing reads. Sequences that passed stringent quality control thresholds were assembled into 12,791 male contigs and 32,629 female contigs. Average depth of coverage was 4.2 × for the male assembly and 5.5× for the female assembly. Analytical rarefaction indicates that our assemblies include most of the genes expressed in lake sturgeon gonads. Over 86,700 sequencing reads were assigned gene ontologies, many to general housekeeping genes like protein, RNA, and ion binding genes. We searched specifically for sex determining genes and documented significant sex differences in the expression of two genes involved in animal sex determination, DMRT1 and TRA-1. DMRT1 is the master sex determining gene in birds and in medaka (Oryzias latipes) whereas TRA-1 helps direct sexual differentiation in nematodes. We also searched the lake sturgeon assembly for evidence of xenobiotic organisms that may exist as endosymbionts. Our results suggest that exogenous parasites (trematodes) and pathogens (protozoans) apparently have infected lake sturgeon gonads, and the trematodes have horizontally transferred some genes to the lake sturgeon genome.     

The lake sturgeon,Acipenser fulvescens,in the Menominee River,Wisconsin-Michigan

Synopsis The Menominee River is the boundary between the Upper Peninsula of Michigan and northeastern Wisconsin. It contains one of the few fishable lake sturgeon populations remaining in either state. Two sections of the river harbor naturally reproducing sturgeon stocks. Dams at either end of these sections curtail upstream movement of fish; however, some sturgeon move downstream over the dams. Surveys conducted in 1969 and 1970 and again in 1978 and 1979 intensively studied the sturgeons in a 42 km stretch of the river. Mark and recapture estimates of the number of sturgeon longer than 25 cm in this section ranged from 1884 to 2865. The number of fish longer than 107 cm ranged from 185 to 243. An estimate of 2834 sturgeon between 25 and 165 cm was made on a different 34 km stretch in 1979. Censuses on the hook and line fishery in 1969 and 1970 estimated sturgeon harvests of 59 and 48 fish, respectively. In 1974, the size limit was raised from 107 to 127 cm. Harvests of these larger fish were estimated at 19 and 41 in 1981 and 1982, respectively. Some other characteristics of the sturgeons and the fishery on the Menominee are also included.     

Polypodium sp. (Coelenterata) from lake sturgeon (Acipenser fulvescens rafinesque) in the prairie region of Canada.

Polypodium sp. is reported for the first time from Canadian waters. It occurred in lake sturgeon (Acipenser fulvescens) eggs, from the Nelson River, Manitoba, and from Cumberland House, Saskatchewan. The prevalence of this parasite was 100% in females with eggs of 3.0 mm diameter or more. One, 4, 25, and 179 infected eggs were collected in gonads with eggs of this size class, but infected eggs were not apparent in individuals with smaller eggs. This is the northernmost occurrence of this parasite reported in North America.     

Population assessment and movement patterns of lake sturgeon (Acipenser fulvescens) in the Manistee River, Michigan, USA

Lake sturgeon (Acipenser fulvescens) population characteristics and migration patterns were evaluated in the Manistee River system, Michigan. Sturgeon (n = 102) were captured using gillnets, tagged and released in the system between 2001 and 2005. Biological data (weight, length, age, sex and spawning status) were collected to calculate length–weight relationships and relative condition factor (K_n), determine age structure, and estimate the annual spawning population size. Sturgeon were also implanted with radio and sonic transmitters, and migration patterns of 22 sturgeon were determined. The weight–length equation for sturgeon in the Manistee River system was log₁₀ W = 3.17log₁₀TL?5.52 and did not differ by sex. K_n equaled 0.72 and did not differ by sex or spawning status. Ages ranged from age 5 to age 54. Sexually mature male and female sturgeon were captured over the course of the study, and the size of the spawning population ranged from 21 to 66 spawners. Sturgeon migration movements up and down the Manistee River varied with date, water temperature, and discharge. The sturgeon appeared to use two different spawning sites in the Manistee River. The Manistee River system supports a remnant lake sturgeon population; the presence of a wide range of age classes and availability of a limited number of suitable spawning sites suggest continued recruitment to the population.     

Assessment of lake sturgeon (Acipenser fulvescens) recruitment in a regulated spawning tributary of Rainy Lake,Ontario

Continued study of the relationship between lake sturgeon (Acipenser fulvescens) recruitment and hydroelectric dams and operations, in a variety of river systems and habitat types is needed to improve the ability to predict and monitor impacts of the hydroelectric industry on this species. Herein, we present results of a juvenile lake sturgeon study aimed at addressing concerns over an inferred lack of recruitment resulting from spawning downstream of a hydroelectric generating station (HGS). Two years of sampling (2015 and 2016) were conducted in five sections of a 41 km long reach of the Seine River, Ontario, a lake sturgeon spawning tributary of Rainy Lake. Using an established gillnetting method, deepwater habitat was targeted to capture juvenile lake sturgeon to assess relative abundance, recruitment (cohort strength), and growth. Deepwater habitat, defined as water depths >6 m in this system, comprised only 2.1% of the wetted area in this study area. Within these habitats, a total of 331 lake sturgeon capture events were observed over the 2-years study period. The majority of the lake sturgeon catch (85%) was comprised of age-0 to age-5 individuals (both sampling years combined). Although inter-annual variation in cohort strength was apparent, each cohort between 2006 and 2016 was represented. The spatial distribution of cohorts varied among river reaches with younger individuals (age-0 and age-1) occupying reaches proximal to the Sturgeon Falls HGS, and larger, older individuals (age-2 to age-5) occupying reaches further downstream. The rarity of age-6+ individuals can likely be explained by ongoing downstream redistribution of juveniles over time, out of the Seine River and into Rainy Lake. Growth of juvenile lake sturgeon captured in the Seine River was above average relative to conspecifics from other rivers in the Hudson Bay drainage. Unfortunately, baseline data sets required to facilitate comparisons of contemporary (post-construction Sturgeon Falls HGS) versus historical (i.e. pre- Sturgeon Falls HGS) lake sturgeon recruitment, or to evaluate the influence of the Seine River Water Management Plan (2004) on lake sturgeon recruitment, are lacking. However, juvenile Lake Sturgeon are more abundant in this system than what had been surmised based on recent studies which implemented random sampling. Results indicate that juvenile lake sturgeon may reside in spawning tributaries for several years (age-0 to age-5) prior to seeking alternate habitats and highlights the value of targeted sampling (i.e. by depth) along the flow axis of rivers downstream of spawning areas when assessing lake sturgeon recruitment patterns.     

Habitat utilization of juvenile lake sturgeon, Acipenser fulvescens, in a large Canadian river

An increased understanding of the juvenile life history stage of the lake sturgeon, Acipenser fulvescens , has been recognized as a key requirement for improving conservation efforts for this once abundant species. The objectives of the current study were to develop an effective methodology for capturing juvenile lake sturgeon in a large riverine environment; to describe the physical habitat characteristics (depth, water velocity and substrate) associated with the areas where juvenile lake sturgeon were captured; and to determine basic population parameters (length, body mass and condition factor) for juvenile lake sturgeon captured in those areas. Gillnets (mesh sizes 25–108 mm) were used to sample the Winnipeg River, a large river in the northern extent of the species range, from 12 June to 6 November 2006. A total of 2154 juvenile (<530 mm FL) lake sturgeon were captured, which represented over 74% of the total fish catch. Moderate (51–108 mm) and small (25 mm) mesh gill nets were found to be efficient for sampling juvenile lake sturgeon, with the former capturing a wider range of sizes and the latter capturing fewer fish but resulting in decreased mortality. Juvenile lake sturgeon were captured at high densities in discrete areas characterized by water depths >13.7 m, detectable water velocities >0.20 m s⁻¹, and various substrate types.