Geology topics

Patrick Kocovsky

Publications and source records attributed to Patrick Kocovsky.

34 records · Page 2Linked to original sources

USGS2018

Fish community responses to submerged aquatic vegetation in Maumee Bay, Western Lake Erie

Submerged aquatic vegetation (SAV) in clearwater systems simultaneously provides habitat for invertebrate prey and acts as refugia for small fishes. Many fishes in Lake Erie rely on shallow, heavily vegetated bays as spawning grounds and the loss or absence of which is known to reduce recruitment in other systems. The Maumee River and Maumee Bay, which once had abundant macrophyte beds, have experienced a decline of SAV and an increase in suspended solids (turbidity) over the last century due to numerous causes. To compare fish communities in open‐water (turbid) and in SAV (clearer water) habitats in this region, which is designated by the U.S. Environmental Protection Agency as an Area of Concern, and to indicate community changes that could occur with expansion of SAV habitat, we sampled a 300‐ha sector of northern Maumee Bay that contained both habitats. Using towed neuston nets through patches of each habitat, we determined that areas of SAV contained more species and a different species complex (based on the Jaccard index and the wetland fish index), than did the open‐water habitat (averaging 8.6 versus 5 species per net trawl). The SAV habitat was dominated by centrarchids, namely Largemouth Bass Micropterus salmoides, Bluegill Lepomis macrochirus, and Black Crappie Pomoxis nigromaculatus. Open‐water habitat was dominated by Spottail Shiner Notropis hudsonius, Gizzard Shad Dorosoma cepedianum, and White Perch Morone americana, an invasive species. These results indicate that restoration efforts aimed at decreasing turbidity and increasing the distribution of SAV could cause substantive shifts in the fish community and address important metrics for assessing the beneficial use impairments in this Area of Concern.

Michigan, Ohio↗

USGS2018

A spatially discrete, integral projection model and its application to invasive carp

Natural resource managers and ecologists often desire an understanding of spatial dynamics such as migration, dispersion, and meta-population dynamics. Network-node models can capture these salient features. Additionally, the state-variable used with many species may be appropriately modeled as a continuous variable (e.g., length) and management activities sometimes can only target individuals of certain sizes. Integral projection models (IPMs) can capture this life history characteristic and allow for the examination of size-specific management. We combined an IPM with a network-node model to capture both of these salient features. We then demonstrated how this model could be used to understand and manage populations of invasive species focusing on grass carp as an example. Grass carp disrupt ecosystems outside of their native range and have spread around much of the world, including North America. The impacts of grass carp include adversely changing aquatic plant communities, which in turn affect a wide range of endpoints ranging from water quality to waterfowl recruitment. We specifically examined two theoretical systems using parameters from the literature. First, we modeled a lake with two tributaries and examined how modified sterile males could be used as a control tool. We found that modified sterile males may be a feasible control tool to limit population growth. Second, we modeled a series of river pools and examined how harvest and deterrents could be used to decrease the risk of expanding grass carp's range within a river system. Within this system, we also compared the impacts of size specific harvest and uniform harvest across all sizes. We found that targeting the largest, spawning populations may be more important than targeting the populations close to the invasion front for reducing the risk of spreading grass carp. We also demonstrate that size of harvested fish was important for controlling populations.

Ecological Modelling↗

USGS2018

Inferred fish behavior its implications for hydroacoustic surveys in nearshore habitats

Population availability and vessel avoidance effects on hydroacoustic abundance estimates may be scale dependent; therefore, it is important to evaluate these biases across systems. We performed an inter-ship comparison survey to determine the effect of vessel size, day-night period, depth, and environmental gradients on walleye ( Sander vitreus ) density estimates in Lake Erie, an intermediate-scaled system. Consistent near-bottom depth distributions coupled with horizontal fish movements relative to vessel paths indicated avoidance behavior contributed to higher walleye densities from smaller vessels in shallow water (i.e., <15 m), although the difference decreased with increasing depth. Diel bank migrations in response to seasonally varying onshore-to-offshore environmental gradients likely contributed to day-night differences in densities between sampling locations and seasons. Spatial and unexplained variation accounted for a high proportion of total variation; however, increasing sampling intensity can mitigate effects on precision. Therefore, researchers should minimize systematic avoidance and availability related biases (i.e., vessel and day-night period) to improve population abundance estimates. Quantifying availability and avoidance behavior effects and partitioning sources of variation provides informed flexibility for designing future hydroacoustic surveys in shallow-water nearshore environments.

Lake Erie↗

USGS2018

What it is to be established: policy and management implications for non-native and invasive species

Management of invasive species, whether prevention, population reduction, or eradication, requires assessment of the invasive species’ population status and an assessment of the probability of success of management options. Perceptions of a species’ permanence in an environment or lack thereof frequently drives how limited time, financial, and personnel resources are allocated to such efforts. Language we use to describe a non-native species’ status largely defines these perceptions and sets boundaries, real or perceived, to potential management actions. Here we discuss the use of a particular term – “established” – when confronting management decisions for invasive species. Our objective is to contribute to bridging the gap between the realms of conceptual development and management with respect to use of the term “established”. We find that although there are benefits of polysemy and synonymy to conceptual development they present an additional challenge to managers who must weigh the costs, benefits, and potential for success of particular management actions. We also examine how existing conceptual frameworks might be augmented to bridge the theoretical-practical gap, such as more precisely defining potential management actions and explicitly including assessment of risk.

Management of Biological Invasions↗

USGS2018

Fisheries research and monitoring activities of the Lake Erie Biological Station, 2017

This report presents biomass-based summaries of fish communities in western Lake Erie derived from USGS bottom trawl surveys from 2013 to 2017 during June and September. The survey design provided temporal and spatial coverage that does not exist in the interagency trawl database, and thus complemented the August Ohio-Ontario effort to reinforce stock assessments with more robust data. Analyses herein evaluated trends in: total biomass, abundance of dominant predator and forage species, non-native species composition, biodiversity and community structure. Data from this effort can be explored interactively online (https://lebs.shinyapps.io/western-basin/), and future analyses will be supported by public data and metadata records available on ScienceBase (https://doi.org/10.5066/F7KK9B1R).

Michigan, Ohio, Ontario, New York, Pennsyvania↗

USGS2017

Water guns affect abundance and behavior of bigheaded carp and native fish differently

Water guns have shown the potential to repel nuisance aquatic organisms. This study examines the effects of exposure to a 1966.4 cm 3 seismic water gun array (two guns) on the abundance and behavior of Bighead Carp Hypophthalmichthys nobilis , Silver Carp H. molitrix (collectively referred to as bigheaded carp) and native fishes (e.g., Smallmouth Buffalo Ictiobus bubalus ). Water guns were deployed in a channel that connects the Illinois River to backwater quarry pits that contained a large transient population of bigheaded carp. To evaluate the effect of water guns, mobile side-looking split-beam hydroacoustic surveys were conducted before, during and between replicated water gun firing periods. Water guns did not affect abundance of bigheaded carp, but abundance of native fish detected during the firing treatment was 43 and 34% lower than the control and water guns off treatments, respectively. The proximity of bigheaded carp to the water gun array was similar between the water guns on and water guns off treatments. In contrast, the closest detected native fish were detected farther from the water guns during the water guns on treatment (mean ± SE, 32.38 ± 3.32 m) than during the water guns off treatment (15.04 ± 1.59 m). The water gun array had a greater impact on native fish species than on bigheaded carp. Caution should be taken to the extrapolation of these results to other fish species and to fish exposed to water guns in different environments (e.g., reduced shoreline interaction) or exposure to a larger array of water guns, or for use of water guns for purposes other than a barrier.

Illinois↗

USGS2017

An integral projection model with YY-males and application to evaluating grass carp control

Invasive fish species disrupt ecosystems and cause economic damage. Several methods have been discussed to control populations of invasive fish including the release of YY-males. YY-males are fish that have 2 male chromosomes compared to a XY-male. When YY-males mate, they only produce male (XY) offspring. This decreases the female proportion of the population and can, in theory, eradicate local populations by biasing the sex-ratio. YY-males have been used as a population control tool for brook trout in montane streams and lakes in Idaho, USA. The YY-male control method has been discussed for grass carp in Lake Erie, North America. We developed and presented an integral projection model for grass carp to model the use of YY-males as a control method for populations in this lake. Using only the YY-male control method, we found that high levels of YY-males would need to be release annually to control the species. Specifically, these levels were the same order of magnitude as the baseline adult population (e.g., 1000 YY-males needed to be released annual for 20 years to control a baseline adult population of 2500 grass carp). These levels may not be reasonable or obtainable for fisheries managers given the impacts of YY-males on aquatic vegetation and other constraints of natural resource management.

Ecological Modelling↗

USGS2017

Sparse targets in hydroacoustic surveys: Balancing quantity and quality of in situ target strength data

Hydroacoustic sampling of low-density fish in shallow water can lead to low sample sizes of naturally variable target strength (TS) estimates, resulting in both sparse and variable data. Increasing maximum beam compensation (BC) beyond conventional values (i.e., 3 dB beam width) can recover more targets during data analysis; however, data quality decreases near the acoustic beam edges. We identified the optimal balance between data quantity and quality with increasing BC using a standard sphere calibration, and we quantified the effect of BC on fish track variability, size structure, and density estimates of Lake Erie walleye ( Sander vitreus ). Standard sphere mean TS estimates were consistent with theoretical values (−39.6 dB) up to 18-dB BC, while estimates decreased at greater BC values. Natural sources (i.e., residual and mean TS) dominated total fish track variation, while contributions from measurement related error (i.e., number of single echo detections (SEDs) and BC) were proportionally low. Increasing BC led to more fish encounters and SEDs per fish, while stability in size structure and density were observed at intermediate values (e.g., 18 dB). Detection of medium to large fish (i.e., age-2+ walleye) benefited most from increasing BC, as proportional changes in size structure and density were greatest in these size categories. Therefore, when TS data are sparse and variable, increasing BC to an optimal value (here 18 dB) will maximize the TS data quantity while limiting lower-quality data near the beam edges.

Ohio↗

USGS2017

Evaluating factors driving population densities of mayfly nymphs in Western Lake Erie

Mayfly ( Hexagenia spp.) nymphs have been widely used as indicators of water and substrate quality in lakes. Thermal stratification and the subsequent formation of benthic hypoxia may result in nymph mortality. Our goal was to identify potential associations between recent increases in temperature and eutrophication, which exacerbate hypoxic events in lakes, and mayfly populations in Lake Erie. Nymphs were collected during April–May 1999–2014. We used wind and temperature data to calculate four measures of thermal stratification, which drives hypoxic events, during summers of 1998–2013. Bottom trawl data collected during August 1998–2013 were used to estimate annual biomass of fishes known to be predators of mayfly nymphs. We used Akaike's Information Criterion to identify the best one- and two-predictor regression models of annual population densities ( N /m 2 ) of age-1 and age-2 nymphs, in which candidate predictors included the four measures of stratification, predator fish biomass, competition, and population densities of age-2 (for age-1) and age-1 (for age-2) nymphs from the previous year. Densities of both age classes of nymphs declined over the time series. Population densities of age-1 and age-2 nymphs from the previous year best predicted annual population densities of nymphs of both age classes. However, hypoxic conditions (indicated by stratification) and predation both had negative effects on annual population density of mayflies. Compared with predation, hypoxia had an inconsistent effect on annual nymph density. The increases in temperature and eutrophication in Lake Erie, which exacerbate hypoxic events, may have drastic effects on the mayfly populations.

Journal of Great Lakes Research↗

USGS2017

Fisheries research and monitoring activities of the Lake Erie Biological Station, 2016

We conducted a biomass-based assessment of the Lake Erie Western Basin fish community using data collected from 2013-2016 Western Basin (spring and autumn) bottom trawl surveys. Biomass of total catch per hectare has decreased 75 percent since 2013. Declines were observed across all functional groups, but most notable was the decline of Emerald Shiner, which decreased from 25.3 kg/ha in spring 2013 to <0.01 kg/ha by autumn 2013. The four primary predator species – Walleye, Yellow Perch, White Perch, and White Bass – all decreased from 2013 to 2015. In 2016, White Bass and Yellow Perch (all lifestages combined) continued to decline, while Walleye and White Perch (all ages combined) increased slightly from 5.6 kg/ha and 3.4 kg/ha to 9.0 kg/ha and 5.0 kg/ha, respectively (autumn catches). Despite decreasing trends in biomass, there was little change in biodiversity. Declines in forage biomass, i.e. Emerald Shiner and age-0 White Perch, resulted in an increased mean trophic level of catches. Forage fish to piscivore ratios reflected marked shifts in species composition toward greater forage in 2014 and 2016.

Lake Erie↗

USGS2015

Effects of freezing on white perch Morone americana (Gmelin, 1789): Implications for multivariate morphometrics

This study tested the hypothesis that duration of freezing differentially affects whole-body morphometrics of a derived teleost. Whole-body morphometrics are frequently analyzed to test hypotheses of different species, or stocks within a species, of fishes. Specimens used for morphometric analyses are typically fixed or preserved prior to analysis, yet little research has been done on how fixation or preservation methods or duration of preservation of specimens might affect outcomes of multivariate statistical analyses of differences in shape. To determine whether whole-body morphometrics changed as a result of freezing, 23 whole-body morphometrics of age-1 white perch ( Morone americana ) from western Lake Erie (n = 211) were analyzed immediately after capture, after being held on ice overnight, and after freezing for 100 or 200 days. Discriminant function analysis revealed that all four groups differed significantly from one another (P < 0.0001). The first canonical axis reflected long-axis morphometrics, where there was a clear pattern of positive translation along this axis with duration of preservation. Re-classification analysis demonstrated fish were typically assigned to their original preservation class except for fish frozen 100 days, which assigned mostly to frozen 200 days. Morphometric comparisons using frozen fish must be done on fish frozen for identical periods of time to avoid biases related to the length of time they were frozen. Similar experiments should be conducted on other species and also using formalin- and alcohol-preserved specimens.

Western Lake Erie↗

USGS2015

An examination of gender differences in the American Fisheries Society peer-review process

This study investigated the possibility of gender differences in outcomes throughout the peer review process of American Fisheries Society (AFS) journals. For each manuscript submitted to four AFS journals between January 2003 and December 2010, we collated information regarding the gender and nationality of authors, gender of associate editor, gender of reviewers, reviewer recommendations, associate editor's decision, and publication status of the manuscript. We used hierarchical linear modeling to test for differences in manuscript decision outcomes associated with author, reviewer, and associate editor gender. Gender differences were present at some but not every stage of the review process and were not equal among the four journals. Although there was a small gender difference in decision outcomes, we found no evidence of bias in editors’ and reviewers’ recommendations. Our results support the conclusion that the current single-blind review system does not result in bias against female authors within AFS journals.

Fisheries↗

USGS2014

Ecology and population status of trout-perch ( Percopsis omiscomaycus ) in western Lake Erie

Trout-perch Percopsis omiscomaycus is among the most abundant benthic species in Lake Erie, but comparatively little is known about its ecology. Although others have conducted extensive studies on trout-perch ecology, those efforts predated invasions of white perch Morone americana , Dreissena spp., Bythotrephes longimanus and round goby Neogobius melanostomus , suggesting the need to revisit past work. Trout-perch were sampled with bottom trawls at 56 sites during June and September 2010. We examined diets, fecundity, average annual mortality, sex ratio, and long-term population trends at sites sampled since 1961. Trout-perch abundance fluctuated periodically, with distinct shorter- (4-year) and longer-term (over period of 50 years) fluctuations. Males had higher average annual mortality than females. Both sexes were equally abundant at age 0, but females outnumbered males 4:1 by age 2. Diets of trout-perch were dominated by macroinvertebrates, particularly chironomids and Hexagenia sp. Size distributions of trout-perch eggs varied widely and exhibited multiple modes indicative of protracted batch spawning. A review of the few other studies of trout-perch revealed periodic fluctuations in sex ratio of adults, which in light of our evidence of periodicity in abundance suggests the potential for sex-ratio-mediated intrinsic population regulation. Despite the introduction of numerous invasive species in Lake Erie, trout-perch remain one of the most abundant benthic invertivores and the population is relatively stable.

Lake Erie↗

USGS2014

Fisheries research and monitoring activities of the Lake Erie Biological Station, 2013

In 2013, the U.S. Geological Survey’s Lake Erie Biological Station successfully completed large vessel surveys in all three of Lake Erie’s basins. Lake Erie Biological Station’s primary vessel surveys included the Western Basin Forage Fish Assessment and East Harbor Forage Fish Assessment as well as contributing to the cooperative multi-agency Central Basin Hydroacoustics Assessment and the Eastern Basin Coldwater Community Assessment (see Forage Task Group and Coldwater Task Group reports, respectively). Further large vessel sampling included individual research data collection as well as assisting with University (e.g., University of Toledo) and agency (e.g., USFWS, USEPA) large vessel sampling needs. Our 2013 vessel operations began on April 4th and concluded on November 21 with a total of 77 large vessel sampling days (83 total days). During this time, crews of the R/V Muskie and R/V Bowfin deployed 174 trawls covering 147 km of lake-bottom, over 13 km of gillnet, collected hydroacoustic data that extended over 250 km of the central and eastern basins, and approximately 180 collective zooplankton, benthos, and water samples. 2013 was the first complete sampling year using the R/V Muskie. Technologies available on the new platform provided opportunities for LEBS to improve data sampling methods and results. An investment was made in mensuration gear for the trawls. This gear is attached to the trawl’s headrope, footrope, and wings; thus, allowing measurement of the area swept and conversion of catches to densities. Another improvement included real-time output of water parameter sonde profiles (e.g., temperature, dissolved oxygen). The ability to view profile data on a tablet allowed quick identification of thermoclines as well as the presence (or absence) of hypoxia. Minor modifications were made to survey designs relative to last year (see 2013 report), and thus, collection of long-term data from the R/V Muskie has commenced. One minor change was that we are now indexing yellow perch maturation data during our fall trawl surveys in response to a request from the Lake Erie Yellow Perch Task Group. Within the following sections, we describe results from our 2013 sampling efforts in Lake Erie.

Report↗

USGS2009

Ages and lengths of yellow perch Perca flavescens , white perch Morone americana , and lake whitefish Coregonus clupeaformis in commercial trap nets in western Lake Erie

We collected samples of yellow perch (Perca flavescens) and white perch (Morone americana) in spring, and of lake whitefish (Coregonus clupeaformis) in autumn, from commercial trap nets set in western Lake Erie in 2008. The yellow perch sample (N = 153) was dominated (72%, of the total sample) by the 2003 year class, followed by the 2005 year class (12%). The white perch sample (N = 201) was dominated by the 2005 year class (39% of the total sample), followed by the 2003 year class (23%). The lake whitefish (N = 99) sample was dominated by the 2003 year class (75%) followed by the 2001 year class (10%). For yellow perch (both sexes in spring, analyzed separately) and lake whitefish (males in autumn), mean total length at age 5 was the same for the 2001 year class (calculated from historical data) and the 2003 year class.

Lake Erie↗

USGS2009

Surveillance and status of fish stocks in western Lake Erie, 2008

The Lake Erie Biological Station has conducted bottom trawl assessments of fish populations in western Lake Erie near East Harbor State Park, Ohio each summer and autumn since 1961. The catches of most age-0 forage fishes in 2008 were less than their 15-year means. Mean densities for five species exceeded the long term mean. Mean density of age-0 white perch Morone americana was more than double last year’s mean and the long-term mean. Densities of both yellow perch Perca flavescens and walleye Sander vitreus were at or above their long term mean. Catches of round goby Neogobius melanostomus (all ages combined) exceeded the previous five years, but were substantially below the species’ 13-year (1996-2008) mean. For five species, mean total lengths of age-0 individuals captured in 2008 were greater than their respective 20-year means. During 1988-2007, the frequency of occurrence for yellow perch diet items was highest for benthic invertebrates and zooplankton during the summer and benthic invertebrates in autumn. During summer zooplankton and benthic invertebrates were frequently consumed by white perch. Benthic prey for white perch occurred more frequently in the last 5-10 years.

Lake Erie↗