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Objective: The Lake Superior Kiyi Coregonus kiyi is an understudied species being considered for reintroduction into Laurentian Great Lakes where it no longer occurs. Herein, we provide descriptions of Kiyi reproductive biology with the intention of guiding potential gamete collections for propagation. Methods: Data were collected on Kiyi spawning timing, spawning locations, spawning season catch rates, length at sexual maturity, sex ratios, fecundity, egg size, and larval occurrences in Lake Superior from 1996–2021. These data were compared to observations made a century prior in Lakes Michigan, Ontario, and Superior. Result: Contemporary Kiyi spawning occurred between late December and late January when surface water temperatures cooled to <4°C. Spawning Kiyi were caught almost exclusively in 38.1‐mm stretch mesh, as compared to larger meshes (50.8–76.2 mm). Capture depths for developing, ripe, running, and spent female Kiyi were similar and ranged from 82 to 221 m. Fifty percent of female and male Kiyi were classified as sexually mature at ~150 mm total length. Fecundity estimates ranged from 1,578 to 6,720 eggs/female. Mean diameter of unfertilized eggs was 1.7 mm. Recently hatched larval Kiyi were collected at the surface during May–July at 62 of the 113 locations sampled throughout the lake in 2019. Conclusion: Our work suggests that Kiyi gamete collection efforts from mid‐December through January using 38.1‐mm gill‐net panels set at bathymetric depths of at least 100 m would maximize the collection of spawning Kiyi and reduce the bycatch of other Coregonus species. Future research questions include the following: (1) "Do Kiyi form spawning aggregations at specific spawning areas, or do they spawn indiscriminately across the lake?"; (2) "Do Kiyi spawn near the bottom or up in the water column?"; (3) "What is the relationship between fall lake overturn and Kiyi spawn timing?"; and (4) "Could summer larval and age‐0 Kiyi collections provide an opportunity for establishing a captive broodstock?" Impact Statement: Kiyi historically occurred in Lakes Huron, Michigan, Ontario, and Superior. Today it occurs only in Lake Superior. This study provides contemporary information on Kiyi reproductive biology with respect to where, when, and how to collect spawning Kiyi in Lake Superior for potential use in propagation and reintroduction programs. [ABSTRACT FROM AUTHOR]

The restoration of the once abundant Cisco (Coregonus artedi) is a management interest across the Laurentian Great Lakes. To inform the restoration, we (1) described historical distributions of Cisco and (2) explored whether non-indigenous Rainbow Smelt (Osmerus mordax) and Alewife (Alosa pseudoharengus) played a role in the decline of Cisco populations across the upper Great Lakes (i.e., Lakes Superior, Michigan, and Huron). Our source data were collected from fishery-independent surveys conducted by the U.S. Fish and Wildlife Service's research vessel R/V Cisco in 1952–1962. By analyzing data collected by gill-net surveys, we confirmed the importance of embayment and shallow-water habitats to Cisco. We found that Cisco was abundant in Whitefish Bay and Keweenaw Bay, Lake Superior, and in Green Bay, Lake Michigan, but we also found a sign of Cisco extirpation in Saginaw Bay, Lake Huron. Our results also showed that Ciscoes generally stayed in waters <80 m in bottom depth throughout the year. However, a substantial number of Ciscoes stayed in very deep waters (>150 m in bottom depth) in summer and fall in Lake Michigan, although we cannot exclude the possibility that these Ciscoes had hybridized with the other Coregonus species. By comparing complementary data collected from bottom-trawl surveys, we concluded that the spatiotemporal overlap between Rainbow Smelt and Cisco likely occurred across the upper Great Lakes throughout 1952–1962. These data were consistent with the hypothesis that Rainbow Smelt played a role in the decline of Cisco populations across the upper Great Lakes in the period. We also found that the spatiotemporal overlap between Alewife and Cisco likely occurred only in Saginaw Bay in fall 1956 and in Lake Michigan after 1960. Thus, any potential recovery of Cisco after the 1950s could have been inhibited by Alewife in Lakes Michigan and Huron. [ABSTRACT FROM AUTHOR]

The largest population of endangered humpback chub Gila cypha inhabits the Colorado River below Glen Canyon Dam and the lower 14 km of the Little Colorado River (LCR), Arizona. Currently, adults from both rivers spawn and their progenies grow and recruit to adulthood primarily within the LCR, where we studied G. cypha's life history using hoop net capture data. Humpback chub undergo an ontogenesis from diurnally active, vulnerable, nearshore-reliant young-of-the-year (YOY; 30-90 mm total length) into nocturnally active, large-bodied adults ([greater than or equal to] 180 mm TL). During the day, adults primarily resided in deep midchannel pools; however, at night they dispersed inshore amongst the higher densities of YOY conspecifics. Many YOY G. cypha shifted to nocturnal habitats that provided greater cover, possibly, to avoid inshore invading adults. These findings mirror predator-prey scenarios described in other freshwater assemblages, but do not refute other plausible hypotheses. Gila cypha piscivorous activity may escalate in hoop nets, which can confine fish of disparate sizes together; adults were significantly associated with YOY conspecifics and small dead fish in hoop nets at night and eight G. cypha (156-372 mm TL) regurgitated and/or defecated other fish body parts during handling following capture. Gila cypha can definitely be piscivorous given the opportunity, but the magnitude of their piscivorous activity in the wild is debatable.

Historically, cisco Coregonus artedi Lesueur was the predominant prey fish and target of commercial fisheries throughout Lake Superior, but most spawning stocks collapsed by the mid‐1900s. Stocks partially recovered by the early 1990s, but contemporary abundance is considered to be below historical levels and driven by intermittent recruitment. Stochastic, age‐structured simulation models were used to determine whether historical (pre‐1955) cisco yield in Lake Superior was consistent with contemporary (1992–2015) abundance, life‐history characteristics and recruitment dynamics. When compared to contemporary stocks, the findings suggest historical stocks had: (1) similar recruits per spawner at low spawning stock sizes; (2) lower rates of compensatory density dependence; (3) similar or lower recruitment variation depending on the area and (4) higher median adult and age‐1 density. These findings are consistent with the hypothesis that eutrophication during the historical period supported greater recruitment and adult abundance and that re‐oligotrophication during the contemporary period may be limiting full recovery. [ABSTRACT FROM AUTHOR]

Fecundity of fish is influenced by several factors, including body length, condition, population density, and environmental conditions. It follows that fecundity of fish populations can exhibit spatiotemporal variability; thus, periodic quantification of length–fecundity relationships is important for management. We hypothesized that average fecundity of Cisco Coregonus artedi in the upper Laurentian Great Lakes would be lower in Lake Superior than in Lakes Huron and Michigan. The trophic status of these lakes recently converged, but Lakes Huron and Michigan currently support lower Cisco densities; thus, we expected that they would reach larger sizes and have greater fecundity owing to lower intraspecific competition. Ovaries were collected from prespawn Cisco during 2008–2010 to test this hypothesis. We also compared length–fecundity relationships for 2008–2010 to those of precollapse (1930s–1950s) populations to explore how relationships have changed. Average fecundity of Cisco during 2008–2010 was lower in Lake Superior compared to Lakes Huron and Michigan; length–fecundity relationships in the latter two lakes did not vary significantly, so they were combined. Body condition was highest in Lakes Huron and Michigan. We used otoliths to determine age and found that body condition was domed shaped with respect to age in Lakes Huron and Superior. There were no females older than age 5 in our samples from Lake Michigan because that population was just beginning to recover from very low levels. Females of intermediate age had the highest fecundities in both Lake Huron (ages 7–13) and Lake Superior (ages 8–18). We hypothesize that differences in body morphometry may also influence fecundity, with deeper‐bodied C. artedi albus, the predominant form in Lakes Michigan and Huron, having greater fecundity than shallower‐bodied C. artedi artedi in Lake Superior. Moreover, varying Cisco diets and seasonal movement patterns across lakes may have also contributed to differences. Females in Lakes Superior and Michigan are currently more fecund than their precollapse counterparts. [ABSTRACT FROM AUTHOR]

Annual bottom trawl surveys were initiated in the 1970s in Laurentian Great Lakes Superior, Huron, Michigan and Ontario and in 1990 in Erie to provide annual assessments of the status and trends of prey fish communities. Native Cisco Coregonus artedi and Bloater C. hoyi dominated the prey fish community of Lake Superior. Prey fish communities in lakes Huron and Michigan were dominated by nonnative Rainbow Smelt Osmerus mordax and Alewife Alosa pseudoharengus for much of 1978-2016, but Bloater was an important species during the 1980-1990s and more recently has become the dominant prey species in these lakes. Alewife dominated the prey fish community of Lake Ontario during all 1978-2016. While nonnatives dominated the prey fish community in Lake Erie, native Emerald Shiner Notropis atherinoides was an important species and occasionally the dominant prey fish after the establishment of Round Goby Neogobius melanostomus in the late 1990s. During the 1980s-1990s Bythotrephes cederstroemi, Dreissena polymorpha, and Dreissena bugensis caused profound changes in Laurentian Great Lakes ecosystems and likely contributed to declines in fish community biomass in lakes Michigan and Huron. The impacts of these invaders were more muted in lakes Erie and Ontario. Lake Superior stands out as the Laurentian Great Lakes success story: Lake Trout Salvelinus namaycush was restored, and native prey fishes dominate and support a viable fishery. Although the abundance of Bloater has increased recently in lakes Huron and Michigan, recovery of native prey fishes remains uncertain. The absence of native species among the principal prey fish in Lake Ontario indicates a lack of progress in native fish recovery. Recovery of native prey fishes remains unclear in Lake Erie. The ever-changing state of the Laurentian Great Lakes caused by the impacts of invasive species and ongoing climate and ecosystem change will continue to challenge restoration of native fish communities in the 21st Century. [ABSTRACT FROM AUTHOR]

Historically, the CiscoCoregonus artediwas abundant throughout the Great Lakes basin, but anthropogenic influences caused the collapse of stocks during the mid-1900s, and fishery managers are currently exploring options for restoration. To increase understanding of biotic and abiotic factors influencing Cisco recruitment dynamics throughout the Great Lakes, we used Ricker stock–recruitment models with rearing-habitat-weighted indices of recruitment and adult spawning stock size in Lake Superior to identify and quantify (1) the appropriate spatial scale for modeling age-1 recruitment dynamics and (2) the effects of biotic and abiotic factors on age-1 recruitment dynamics within the regions identified for modeling. Cisco recruitment variation in Lake Superior was best described by a regional model with separate stock–recruitment relationships for western, southern, eastern, and northern regions. The spatial scale for modeling was approximately 260 km. Age-1 recruitment was negatively correlated with adult spawning stock size in all four regions. Multifactor models suggested (1) a positive correlation between age-1 recruitment and the interaction between wind speed and air temperature on a lakewide scale and (2) a negative correlation between age-1 recruitment and the biomass of Rainbow SmeltOsmerus mordaxon a regional scale. Large-scale abiotic factors are beyond the control of fishery managers, so harvest of adult Ciscoes and potential predators and competitors should be carefully managed to achieve desired goals in Lake Superior. Although our study was limited to Cisco stocks in Lake Superior, we believe that our general findings can be more broadly applied (albeit with caution) to the restoration and management of remnant stocks throughout the Great Lakes basin. Received June 4, 2013; accepted August 16, 2013 [ABSTRACT FROM AUTHOR]

The fish community of Lake Superior has undergone a spectacular cycle of decline and recovery over the past 60 years. A combination of Sea LampreyPetromyzon marinusdepredation and commercial overfishing resulted in severe declines in Lake TroutSalvelinus namaycush, which served as the primary top predator of the community. BurbotLota lotapopulations also declined as a result of Sea Lamprey depredation, largely owing to the loss of adult fish. After Sea Lamprey control measures were instituted in the early 1960s, Burbot populations rebounded rapidly but Lake Trout populations recovered more slowly and recovery was not fully evident until the mid-1980s. As Lake Trout populations recovered, Burbot populations began to decline, and predation on small Burbot was identified as the most likely cause. By 2000, Burbot densities had dropped below their nadir in the early 1960s and have continued to decline, with the densities of juveniles and small adults falling below that of large adults. Although Burbot populations are at record lows in Lake Superior, the density of large reproductive adults remains stable and a large reserve of adult Burbot is present in deep offshore waters. The combination of the Burbot's early maturation, long life span, and high fecundity provides the species with the resiliency to remain a viable member of the Lake Superior fish community into the foreseeable future. Received October 1, 2012; accepted July 9, 2013 [ABSTRACT FROM AUTHOR]

The cisco Coregonus artedi was once the most abundant fish species in the Great Lakes, but currently cisco populations are greatly reduced and management agencies are attempting to restore the species throughout the basin. To increase understanding of the spatial scale at which density-independent and density-dependent factors influence cisco recruitment dynamics in the Great Lakes, we used a Ricker stock–recruitment model to identify and quantify the appropriate spatial scale for modeling age-1 cisco recruitment dynamics in Lake Superior. We found that the recruitment variation of ciscoes in Lake Superior was best described by a five-parameter regional model with separate stock–recruitment relationships for the western, southern, eastern, and northern regions. The spatial scale for modeling was about 260 km (range = 230–290 km). We also found that the density-independent recruitment rate and the rate of compensatory density dependence varied among regions at different rates. The density-independent recruitment rate was constant among regions (3.6 age-1 recruits/spawner), whereas the rate of compensatory density dependence varied 16-fold among regions (range = −0.2 to −2.9/spawner). Finally, we found that peak recruitment and the spawning stock size that produced peak recruitment varied among regions. Both peak recruitment (0.5–7.1 age-1 recruits/ha) and the spawning stock size that produced peak recruitment (0.3–5.3 spawners/ha) varied 16-fold among regions. Our findings support the hypothesis that the factors driving cisco recruitment operate within four different regions of Lake Superior, suggest that large-scale abiotic factors are more important than small-scale biotic factors in influencing cisco recruitment, and suggest that fishery managers throughout Lake Superior and the entire Great Lakes basin should address cisco restoration and management efforts on a regional scale in each lake. Received March 5, 2011; accepted January 5, 2012 [ABSTRACT FROM AUTHOR]

We evaluated the energy density of bloaters Coregonus hoyi as a function of fish size across Lakes Michigan, Huron, and Superior in 2008–2009 and assessed how differences in energy density are related to factors such as biomass density of bloaters and availability of prey. Additional objectives were to compare energy density between sexes and to compare energy densities of bloaters in Lake Michigan between two time periods (1998–2001 and 2008–2009). For the cross-lake comparisons in 2008, energy density increased with fish total length (TL) only in Lake Michigan. Mean energy density adjusted for fish size was 8% higher in bloaters from Lake Superior than in bloaters from Lake Huron. Relative to fish in these two lakes, small (<125 mm TL) bloaters from Lake Michigan had lower energy density, whereas large (>175 mm TL) bloaters had higher energy density. In 2009, energy density increased with bloater size, and mean energy density adjusted for fish size was about 9% higher in Lake Michigan than in Lake Huron (Lake Superior was not sampled during 2009). Energy density of bloaters in Lake Huron was generally the lowest among lakes, reflecting the relatively low densities of opossum shrimp Mysis diluviana and the relatively high biomass of bloaters reported for that lake. Other factors, such as energy content of prey, growing season, or ontogenetic differences in energy use strategies, may also influence cross-lake variation in energy density. Mean energy density adjusted for length was 7% higher for female bloaters than for male bloaters in Lakes Michigan and Huron. In Lake Superior, energy density did not differ between males and females. Finally, energy density of bloaters in Lake Michigan was similar between the periods 2008–2009 and 1998–2001, possibly due to a low population abundance of bloaters, which could offset food availability changes linked to the loss of prey such as the amphipods Diporeia spp. Received July 20, 2011; accepted December 28, 2011 [ABSTRACT FROM AUTHOR]

Recent reviews have further documented the decline of the shortjaw cisco in Lake Superior. This fish was the most abundant deepwater cisco species in Lake Superior in the early 1920s but presently makes up less than 1% of all deepwater ciscoes (i.e., including shortjaw cisco, bloater , and kiyi ) captured in biological surveys. Directed overfishing of deepwater cisco species during the 1930s and again during the mid-1960s and 1970s has been suggested as the cause of the shortjaw cisco's demise. In this paper, we re-examined the overfishing hypothesis by using historical and recent survey data to estimate the proportion of the historical commercial fishery landings that comprised shortjaw ciscoes. We developed time series of estimated harvest and relative abundance for all statistical districts in Michigan waters of Lake Superior during 1929-1996, for which aggregate catch and effort data were available but not previously examined. The spatial distribution of the fishery and the relationships of catch to fishing effort were examined for evidence of overfishing. Our analysis suggested that directed overfishing was probably not the cause of shortjaw cisco demise, as this species appeared to be declining in all statistical districts regardless of the intensity of the fishery. A count-based population viability analysis indicated that quasi-extinction of the shortjaw cisco is highly probable in the near future. We propose an alternative hypothesis based on the decline of Lake Superior's keystone predator, the lake trout , which resulted in an expansion of the population of its principal prey, the cisco , due to release from predation pressure. Competitive or predation interactions between the cisco and shortjaw cisco may be more likely explanations for the demise of the latter species. [ABSTRACT FROM AUTHOR]

Brook trout Salvelinus fontinalis from Isle Royale, Michigan, three Minnesota tributaries of Lake Superior, and Lake Nipigon in Ontario were analyzed for genetic variation at 12 microsatellite DNA loci. Analysis of molecular variance, genetic distance measures, and cluster analysis were used to examine the diversity, gene flow, and relatedness among the samples. The diversity estimates for the samples from Isle Royale were similar to those for the samples collected from Minnesota tributaries of Lake Superior, and all estimates were lower than those reported in other studies of brook trout from eastern North America. Genetic differences were detected among the brook trout at Isle Royale. Lake Nipigon, and the Minnesota tributaries of Lake Superior. Further, the population in Tobin Harbor at the eastern end of Isle Royale was distinct from the populations from tributaries at the southwestern end of the island. The Minnesota tributary population formed a group that was genetically distinct from those from Isle Royale and Lake Nipigon. The Isle Royale population should be managed to preserve the genetic and phenotypic variation that distinguishes it from the other brook trout populations analyzed to date. [ABSTRACT FROM AUTHOR]

Based on data from our annual lakewide bottom trawl survey of Lake Michigan, we determined that density of ninespine sticklebacks increased from an average of 0.234 kg/ha during 1973-1995 to an average of 1.318 kg/ha during 1996-2007. This greater-than-fivefold increase in density coincided with the dreissenid mussel invasion of Lake Michigan. Intervention analysis revealed that ninespine stickleback density in Lake Michigan significantly increased between the two time periods. In contrast, based on data from our annual bottom trawl survey of U.S. waters of Lake Superior, ninespine stickleback density decreased from an average of 0.133 kg/ha during 1978-1999 to an average of only 0.026 kg/ha during 2000-2007. This greater-than-fivefold density decrease, which was found to be significant via intervention analysis, coincided with population recovery for both lean and fat morphotypes of lake trout in Lake Superior. In contrast to Lake Michigan, dreissenid mussels have not invaded Lake Superior on a lakewide basis. Thus, a comparison of these two lakes indicated that the increase in ninespine stickleback abundance in Lake Michigan was most likely attributable to the dreissenid mussel invasion. In addition, based on our correlation analysis, alewives did not have an adverse effect on ninespine stickleback abundance in Lake Michigan. Perhaps the recent increase in biomass of green algae spp. associated with the dreissenid mussel invasion improved spawning habitat quality for ninespine sticklebacks and led to their stepwise abundance increase in Lake Michigan beginning in 1996. [ABSTRACT FROM AUTHOR]

Populations of cisco Coregonus artedi in the Laurentian Great Lakes supported large-scale commercial fisheries and were the primary forage of piscivores during the first half of the 20th century. However, by 1970 populations had collapsed in all of the lakes. Since then, ciscoes have staged a recovery in Lake Superior. In this synthesis, we describe the status of ciscoes in Lake Superior during 1970-2006 and provide a comprehensive review of their ecology. Better understanding of age estimation techniques, application of hydroacoustic and midwater trawl sampling, and compilation of long-term data sets have advanced our understanding of the species. Management agencies contemplating rehabilitation of cisco populations should recognize that (1) knowledge of cisco ecology and population dynamics is increasing; (2) ciscoes are long-lived; (3) Great Lakes populations are probably composed of both shallow-water and deepwater spawning forms; (4) large year-classes can be produced from small adult stocks; (5) large variation in year-class strength is probably intrinsic to Great Lakes populations; (6) despite the longevity and early maturity of ciscoes, stocks can be overfished because large year-classes are produced infrequently; (7) regional environmental factors appear to play a large role in reproductive success; and (8) rainbow smelt Osmerus mordax are likely to have a negative effect on cisco recruitment under certain conditions. A top-down approach for rehabilitating lake trout Salvelinus namaycush in Lake Superior probably benefited cisco recovery through lake trout predation on invasive rainbow smelt populations. We argue that managing for populations of exotic alewives Alosa pseudoharengus to support popular recreational fisheries of exotic Pacific salmonids in the other Great Lakes conflicts with stocking efforts to rehabilitate native lake trout in those lakes. If native fish rehabilitation is a serious and primary goal for management agencies in the Great Lakes basin, we propose that an ecosystem-based approach to modifying the environment for the benefit of native fish species (i.e., decimation or eradication of invasive species) is required. [ABSTRACT FROM AUTHOR]

We characterized the nearshore habitat and fish community composition of approximately 300 km of shoreline within and adjacent to the major embayments of Isle Royale, Lake Superior. Sampling yielded 17 species, of which 12 were widespread and represented a common element of the Lake Superior fish community, including cisco , lake whitefish , round whitefish , lake trout , rainbow smelt , lake chub , longnose sucker , white sucker , trout-perch , ninespine stickleback , burbot , and slimy sculpin . The presence of brook trout in an embayment was associated with the common species of the Isle Royale nearshore fish community, particularly cisco, longnose sucker, and round whitefish. However, brook trout were present in only five embayments and were common only in Tobin Harbor. Most Isle Royale embayments had broadly overlapping ranges of nearshore habitats. Within embayments, fish were distributed along a habitat gradient from less-protected rocky habitat near the mouth to highly protected habitat with mixed and finer substrates at the head. Embayments with brook trout had greater mean protection from the open lake, greater variation in depth, greater mean cover, and higher mean frequencies of large substrates (cobble, boulder, and bedrock). Within those embayments, brook trout were associated with habitat patches with higher mean frequencies of small substrates (particularly sand and coarse gravel). Within Tobin Harbor, brook trout were associated with midembayment habitat and species assemblages, especially those locations with a mixture of sand, gravel, and cobble substrates, an absence of bedrock, and the presence of round whitefish, white sucker, and trout-perch. Comparison of embayments with the model, Tobin Harbor, showed that six embayments without brook trout had very similar arrays of habitat. However, four embayments with brook trout had relatively different arrays of habitat from Tobin Harbor. These results suggest that there is potential for further recovery of brook trout populations across Isle Royale nearshore habitats. [ABSTRACT FROM AUTHOR]

An annual daytime bottom trawl survey of the Lake Superior fish community designed in 1978 does not adequately assess the entire community. Whereas recent studies have recommended that pelagic species be surveyed with a combination of acoustic and midwater trawling methods (AC-MT), we used bottom trawling to study the effects of depth, diel period, and season on biomass estimates and the sizes of bottom-oriented species. Day and night bottom trawl samples were collected within 48 h at three depths (30, 60, and 120 m) at a Lake Superior site during eight sampling periods that included two seasons each year (early summer and late summer to early fall) for 2 years (2004 and 2005). Depth significantly affected the biomass of seven of the eight species analyzed, while diel period affected the biomass of six species. For most species, average biomass levels were higher at night. The effect of season on biomass was comparatively low (three species were significantly affected). Depth significantly affected the sizes of six bottom-oriented species, as the average length of most species increased with depth. The effects of diel period (three species) and season (one species) on average length were comparatively small. By adding night bottom trawl samples to night AC-MT collections, the entire fish community of Lake Superior can be monitored with a single lakewide survey employing multiple gears. The establishment of offshore sampling (i.e., where depths exceed 80 m) will provide estimates of deepwater species that have been largely undersampled by the 1978-designed survey. We recommend that the present fish community survey be maintained, albeit at a reduced level, until a nighttime survey time series is well established (in 3-5 years). [ABSTRACT FROM AUTHOR]

Evaluation of the biases in sampling methodology is essential for understanding the limitations of abundance and biomass estimates of fish populations. Estimates from surveys that rely solely on bottom trawls may be particularly vulnerable to bias if pelagic fish are numerous. We evaluated the variability in the vertical distribution of fish biomass during the U.S. Geological Survey's annual spring bottom trawl survey of Lake Superior using concurrent hydroacoustic observations to (1) test the assumption that fish are generally demersal during the day and (2) evaluate the potential for predictive models to improve bottom trawl-determined biomass estimates. Our results indicate that the assumption that fish exhibit demersal behavior during the annual spring bottom trawl survey in Lake Superior is unfounded. Bottom trawl biomass (BBT) estimates (mean ± SE) for species known to exhibit pelagic behavior (cisco Coregonus artedi, bloater C. hoyi, kiyi C. kiyi, and rainbow smelt Osmerus mordax; 3.01 ± 0.73 kg/ha) were not significantly greater than mean acoustic pelagic zone biomass (BAPZ) estimates (6.39 ± 2.03 kg/ha). Mean BAPZ estimates were 1.6- to 4.8-fold greater than mean BBT estimates over 4 years of sampling. The relationship between concurrent BAPZ and BBT. estimates was marginally significant and highly variable. Predicted BAPZ estimates using cross-validation models were sensitive to adjustments for back-transforming from the logarithmic to the linear scale and poorly corresponded to observed BAPZ estimates. We conclude that statistical models to predict BAPZ from day BBT cannot be developed. We propose that night sampling with multiple gears will be necessary to generate better biomass estimates for management needs. [ABSTRACT FROM AUTHOR]

Recent predator demand and prey supply studies suggest that an annual daytime bottom trawl survey of Lake Superior underestimates prey fish biomass. A multiple-gear (acoustics, bottom trawl, and midwater trawl) nighttime survey has been recommended, but before abandoning a long-term daytime survey the effectiveness of night sampling of important prey species must be verified. We sampled three bottom depths (30, 60, and 120 m) at a Lake Superior site where the fish community included all commercially and ecologically important species. Day and night samples were collected within 48 h at all depths during eight different periods (one new and one full moon period during both early summer and late summer to early fall over 2 years). Biomass of demersal and benthic species was higher in night bottom trawl samples than in day bottom trawl samples. Night acoustic collections showed that pelagic fish typically occupied water cooler than 15°C and light levels less than 0.001 lx. Using biomass in night bottom trawls and acoustic biomass above the bottom trawl path, we calculated an index of acoustic detectability for each species. Ciscoes Coregonus artedi, kiyis C. kiyi, and rainbow smelt Osmerus mordax left the bottom at night, whereas bloaters C. hoyi stayed nearer the bottom. We compared the biomass of important prey species estimated with two survey types: day bottom trawls and night estimates of the entire water column (bottom trawl biomass plus acoustic biomass). The biomass of large ciscoes (>200 mm) was significantly greater when measured at night than when measured during daylight, but the differences for other sizes of important species did not vary significantly by survey type. Nighttime of late summer is a period when conditions for biomass estimation are largely invariant, and all important prey species can be sampled using a multiple-gear approach. [ABSTRACT FROM AUTHOR]

We developed methods for the cryopreservation of sperm of the endangered Colorado pikeminnow Ptychocheilus lucius. Sperm were collected from a captive broodstock population of Colorado pikeminnow reared and maintained at the Dexter National Fish Hatchery and Technology Center. Our objectives were to (1) evaluate the effects on sperm motility of 24-h storage in Hanks' balanced salt solution (HBSS); (2) characterize sperm motility and duration; (3) examine the relationship between sperm motility and osmotic pressure; (4) examine the effect of four cryoprotectants (dimethyl sulfoxide [DMSO], dimethyl acetamide [DMA], glycerol, and methanol [MeOH] at two concentrations [5% and 10%]) on postthaw motility; and (5) compare the effect of two cooling rates (40°C/min and 4°C/min) on postthaw motility. The sperm samples diluted with HBSS retained higher motility (mean ± SD, 77 ± 22%; n = 9) than did undiluted samples (12 ± 30%; n = 9) after 24 h of storage. When exposed to HBSS at 274 mosmols/kg or more, few sperm became motile (∼ 1%). Exposure to HBSS at 265 mosmols/kg elicited threshold activation (defined as 10% motility), and maximum motility (>95%) was observed at 93 mosmols/ kg. The maximum motility of sperm was observed within 10 s after activation with deionized water, and sperm remained motile for 57 s. The sperm that were cooled at a rate of 40°C/min and cryopreserved with 5% MeOH retained higher postthaw motility (56 ± 13%) than did sperm cryopreserved with DMSO, DMA, or glycerol (at 5% and 10%). When the sperm samples were cooled at a rate of 4°C/min, sperm cryopreserved with MeOH (5% or 10%) or DMSO (5% or 10%) retained the highest postthaw motilities (≤14%). The use of cryopreserved sperm can assist hatchery managers in the production of fish, provide for the long-term conservation of genetic resources, and assist in the recovery of endangered species such as the Colorado pikeminnow. [ABSTRACT FROM AUTHOR]

The largest population of endangered humpback chub Gila cypha inhabits the lower Little Colorado River (LCR) and the main-stem Colorado River near its confluence with the LCR in Grand Canyon, Arizona. At present, fish in both rivers spawn almost exclusively in the LCR. Flows in the main-stem Colorado River are regulated by Glen Canyon Dam, and water temperature approximates predam winter temperatures year-round. The LCR continues to provide a relatively natural hydrograph and seasonal warming patterns. Length-weight relationships among adult humpback chub from the lower Colorado River basin showed a seasonal pattern of declining condition during spring spawning season followed by recovery of condition during summer through early winter. Fish from the main stem recovered condition more rapidly after reproduction than did fish from the LCR and may have benefited from dam-mediated environmental changes. Grand Canyon Colorado River fish had the greatest weight at length of eight locations sampled in the upper and lower basins. Records since 1978 indicate a decline in condition of lower basin humpback chub coincident with a reported decline in population size in Grand Canyon. We recommend increased monitoring of all populations, including mark-recapture studies to provide population estimates during the spawning season and condition monitoring during October-November to determine more subtle changes in fish health. [ABSTRACT FROM AUTHOR]