Geology topics

Thomas M. Evans

Publications and source records attributed to Thomas M. Evans.

6 recordsLinked to original sources

USGS2026

Availability of dark daytime refuge may limit mysid abundance in the Laurentian Great Lakes

The zooplankton Mysis diluviana is a major component of the Laurentian Great Lakes food web and has recently declined in abundance in both lakes Michigan and Huron. Drivers of these declines are not well understood. Here, we explore the hypothesis that recent increases in water clarity have contributed to the decline of M. diluviana (mysids) by limiting the availability of daytime dark refuge from visual predators. Using Secchi depth data from 1996 to 2021, we estimate that dark refuge has decreased substantially in lakes Michigan and Huron where mysids have declined, but dark refuge has remained more stable in lakes Ontario and Superior where mysid populations did not decline. Results from a 2021 uncrewed surface vessel hydroacoustic survey and lake-wide, net-based sampling in lakes Michigan and Huron revealed significantly more mysids in areas with dark refuge, such as Lake Michigan’s northern basin. Conversely, Lake Huron contains sparse dark refuge consistent with low mysid densities in that lake. Higher water clarity leading to increased predation may be a primary driver of mysid declines in the Great Lakes.

Laurentian Great Lakes↗

USGS2026

Evaluating the use of uncrewed surface vessels to enhance Lake Erie acoustic prey-fish surveys

Incorporation of autonomous uncrewed surface vessels (USVs) into large-scale acoustic surveys may enhance spatiotemporal extent and quality of fish density estimates. Lake Erie is currently surveyed by three motorized research vessels (RVs), which annually collect acoustic data and estimate prey-fish abundances. To evaluate the feasibility of incorporating a USV into the existing survey to increase spatial coverage, we compared paired acoustic measurements of target strength (TS), area backscattering coefficient (ABC), and areal fish density from four motorized RVs (three currently and one historically used) and one USV (Saildrone Explorer). Acoustic data were collected along 2-km transects during five sampling events distributed throughout Lake Erie. Despite observing event-specific differences that were likely impacted by sampling conditions, survey-level estimates of areal density between RVs and the USV were comparable (i.e., RV 6% lower than USV). RVs and the USV appear to react differently (speed and stability) to variable environmental conditions (wind and waves), which impacted data quality and must be mitigated in future applications. However, similar to previous comparisons in marine and freshwater environments, incorporating a USV into an acoustic survey could enhance annual fish density estimates by increasing effort, spatial coverage, logistical flexibility, and biological data collection opportunities from RVs.

Michigan, New York, Ohio, Pennsylvania↗

USGS2024

Peering into the eye of the sea lamprey: What can stable isotopes in lamprey eye lenses reveal about their life history?

The Atlantic sea lamprey ( Petromyzon marinus ) is an anadromous species which is a detritivore for years in freshwater, before metamorphosing into a juvenile and feeding parasitically at sea. However, their migratory patterns and marine ecology are poorly characterized. In other fishes, chemical analysis of calcified structures has aided in understanding their life history, but sea lamprey lacks these structures. Recent work using eye lenses suggests an alternate approach. Lenses are stable protein structures that accrue layers on their outer edge as they grow. We used stable isotope ratios (δ x Y) of hydrogen, carbon, nitrogen, and oxygen to explore lens layers and compare lenses to muscle. Returning adults were collected in May 2021 from the Penobscot (Maine), Connecticut (Massachusetts), and Susquehanna (Maryland) rivers. Lenses were dissected into three layers (surface, middle, core) and analyzed separately to investigate changes over time. We used mixed-effects models to assess differences in isotope ratios among lens layers. Isotope ratios changed from the core to the surface layer and δ 13 C were suggestive of a change from terrestrial to marine sources and δ 15 N showed an increase in trophic level as individuals grew, as would be expected when transitioning from detrital sources to marine prey. However, the isotope ratios of the outer lens layer generally did not correspond with the muscle, perhaps indicating a different temporal interval. These data suggest temporal accretion of lens proteins provide a record to explore sea lamprey ecology.

Maine↗

USGS2024

Paired comparisons with quiet surface drones show evidence of fish behavioral response to motorized vessels during acoustic surveys in Lake Superior

Acoustic surveys are important for fish stock assessments, but fish responses to survey vessels can bias acoustic estimates. We leveraged quiet uncrewed surface vessels (USVs) to characterize potential bias in acoustic surveys. Five conventional motorized ships overtook USVs from astern over 2 km transects at night in Lake Superior in 2022. We examined the difference in acoustic backscatter, average target depth, and average target strength (TS) between USV and motorized vessels. Although sound level measurements from the motorized vessels sometimes exceeded recommendations for scientific vessels, we did not detect differences in acoustic measures among survey vessels. However, the USVs recorded 2 dB higher acoustic backscatter and TS than motorized vessels, leading to ~15% higher fish densities with drones when using in situ TS and echo integration. Differences in fish density would increase to 30-60% if a standard TS value was applied. Target depth did not differ between USVs and motorized ships. These results are consistent with a change in orientation but not depth of insonified fish and limited horizontal avoidance of motorized survey vessels.

Lake Superior↗

USGS2022

Contemporary spatial extent and environmental drivers of larval coregonine distributions across Lake Ontario

Coregonine fishes are important to Laurentian Great Lakes food webs and fisheries and are central to basin-wide conservation initiatives. In Lake Ontario, binational management objectives include conserving and restoring spawning stocks of cisco ( Coregonus artedi ) and lake whitefish ( C. clupeaformis ), but the spatial extent of contemporary coregonine spawning habitat and the environmental factors regulating early life success are not well characterized. In Spring 2018, we conducted a binational ichthyoplankton assessment to describe the spatial extent of coregonine spawning habitat across Lake Ontario. We then quantified the relative importance of a suite of biophysical variables hypothesized to influence coregonine early life success using generalized additive mixed models and multimodel inference. Between April 10 and May 14, we conducted 1,092 ichthyoplankton tows and captured 2,350+ coregonine larvae across 17 sampling areas, predominantly within embayments. Although 95% of catches were in the eastern basin, coregonine larvae were also found in historical south shore spawning areas. Most coregonine larvae were cisco; <6% were lake whitefish. Observed catches of both species across sampling areas were strongly and similarly associated with ice cover duration, but the importance of site-specific characteristics varied, such as distance to shore and site depth for cisco and lake whitefish, respectively. These results suggest that regional-scale climatic drivers and local environmental habitat characteristics interact to regulate early life stage success. Furthermore, strong regional and cross-species variation in larval distributions emphasize the importance of lake-wide assessments for monitoring both the current eastern basin populations and potential expansions into western Lake Ontario habitats.

Lake Ontario↗

USGS2021

Before the first meal: The elusive pre-feeding juvenile stage of the sea lamprey

Although sea lamprey ( Petromyzon marinus ) in the Laurentian Great Lakes have been studied intensively for more than 70 years, many questions remain about their complex life cycle. One of the least understood portions is the post-metamorphic stage (hereafter pre-feeding juvenile, PFJ) that occurs prior to parasitic feeding. PFJ must emerge from stream sediments and migrate downstream into nearshore feeding areas. Key uncertainties include the internal and exogenous triggers that regulate the timing and duration of the migration, and the mechanisms the animal uses to navigate, avoid predators, and locate their first host. However, many of these factors may vary predictably among natal streams in response to stable geomorphological and hydraulic characteristics that regulate the timing of movements (e.g., flood phenology), energetic costs (e.g., stream length), and risk (e.g., predator density). An improved understanding of the PFJ stage presents two opportunities to improve the success of sea lamprey control: (1) identification of streams where natural mortality during the PFJ stage is high, allowing for the reallocation of larval control to streams more likely to produce successful parasites, and (2) removal or killing of PFJs in streams where natural mortality is low. Either approach represents an opportunity to limit parasitic damage to valuable fish stocks. Here, we review the state of knowledge of the PFJ stage and identify critical knowledge gaps that, if addressed, could facilitate sea lamprey assessment and control by exploiting the behavior of PFJ as they outmigrate from streams in search of their first meal.

Journal of Great Lakes Research↗