Geology topics

Christine M Mayer

Publications and source records attributed to Christine M Mayer.

5 recordsLinked to original sources

USGS2025

Dead giveaway: Rising mortality rates suggest effectiveness of Lake Erie grass carp (Ctenopharyngodon idella) response

Grass carp ( Ctenopharyngodon idella ) are large, invasive fish that threaten Lake Erie’s economy and ecosystem. Incidental catches of grass carp have occurred since the 1980s in Lake Erie, while multi-day removal events were carried out in 2014 and 2017. To mitigate ecosystem impacts, a large-scale, multi-agency response to remove as many grass carp as possible from the Lake Erie basin (“strike teams”) began in 2018 and has increased every year. To date, total annual removals of fish has been the primary measure of progress; however, total annual removals do not indicate how efforts are affecting the grass carp population. Population vital rates, such as mortality rate, can indicate population demographic changes and may provide an alternative approach to measure how removals have impacted the grass carp population. We estimated annual mortality rates using 553 grass carp, representing 82.9 % of all grass carp removed in the Lake Erie basin, using a hierarchical catch-curve model and catch-at-age data from 2014 to 2022. Annual average mortality rates were initially low (4.3 %) and increased between 2017 and 2022 with the highest mortality (13.6 %) observed in 2021. Positive correlations between mortality and the number of fish harvested per year suggest that removals may be driving increases in the grass carp mortality rate. This increase in mortality rate shows promise for controlling the spread of grass carp within the Lake Erie ecosystem. This research supports the needs of fishery managers to better understand grass carp population dynamics and the adaptive management framework identified in the Lake Erie Grass Carp Adaptive Response Strategy.

Lake Erie↗

USGS2023

Food web changes reflected in age-0 piscivore diets and growth

Lake Erie walleye ( Stizostedion vitreum ) recruitment fluctuates annually and depends partially on their diet and growth during their first year of life. In recent decades, age-0 walleye diet and growth may be responding to food web changes in western Lake Erie. To determine how age-0 walleye have responded to changes in prey species and abundance, we compared diet between 2019, 2014 and 1994–1999. Larval walleye ate predominantly cyclopoids in 2019, compared to 1994–1999 when calanoids were the most consumed copepod. Juvenile walleye ate predominantly large cladocerans and benthic invertebrates in 2019, compared to 2014 and 1994 when fish was the most consumed prey. Additionally, in 2019 and 2014, age-0 walleye ate two of the current aquatic invasive species (AIS), Bythotrephes longimanu s and Neogobius melanostomus , and the historical AIS, Osmerus mordax . Age-0 walleye were smaller in 2019 than in 2014 and switched to consuming more AIS and less fish suggesting that more energetically favourable prey were not available. While age-0 walleye showed adaptation to new prey and conditions, they had a lower quality diet because they consumed less fish, but also because the invasive fish they now consume have a lower energy density than native species. However, lower quality diet and size may not result in reduced survival, if adequate alternative prey is available. Continued monitoring of age-0 walleye diet could provide confirmation that lower diet quality during the first year decreased walleye growth and aid to identify any effects changes in age-0 diets has on recruitment to the adult population.

Michigan, Ohio↗

USGS2020

Evaluating catchability in a large-scale gillnet survey using hydroacoustics: Making the case for coupled surveys

Abundance estimates facilitate successful fisheries management. Fisheries agencies often monitor abundance through fishery independent standardized protocols generating relative measures such as catch-per-unit-effort (CPUE), where CPUE is assumed proportional to true abundance. Unfortunately, this assumption is rarely met as fish behavior and environmental conditions influence catchability and sample gear efficiency. We used paired gillnet and hydroacoustic samples and a catchability equation ( U i = q N i β "> U i =qN i β ) to assess the correspondence between gillnet CPUE ( U i "> U i ) and hydroacoustic abundance estimates ( N i "> N i ). We found that gill nets were hyperstable (i.e., β < 1) and efficiency declined along environmental gradients. These gradients, such as increased depths, and decreased turbidity and water temperatures, likely influenced fish behavior, and encounter and gear saturation rates. As a result, catchability declined with increasing abundance qacross survey regions. Finally, simulations showed that catchability gradients and variable migratory patterns can contribute to annual variation in CPUE indices regardless of changes in abundance. Surveys plagued by varying catchability could benefit from coupling with hydroacoustics, a sample gear less subject to gear efficiency and catchability issues.

Fisheries Research↗

USGS2019

Effectiveness of shallow water habitat remediation for improving fish habitat in a large temperate river

Loss of shallow water riparian zones in the St. Clair River has reduced availability of nursery areas and refuge for fishes. To remediate habitat losses and provide fish nursery areas, five remediation projects were carried out along the river’s United States bank from 2012 to 2014, replacing seawalls with sloping banks and adding in-stream structure (e.g., root wads and boulders). Project evaluation is necessary to determine success, however there is no standard sampling protocol for shallow habitat in large rivers, especially when both adults and juvenile fishes should be targeted. Therefore, to assess remediation effectiveness and suggest appropriate sampling techniques for large river shorelines, we employed a multi-gear sampling strategy targeting multiple fish species and life history stages at five shoreline remediation and four control sites. We collected juvenile fishes with minnow traps and backpack electrofishing and adult fishes with gillnets. Poisson models were used to evaluate catch per unit effort (CPUE) differences between remediation and control sites for species of management priority (e.g., game fishes and rare species) and taxonomic groups. Model estimates were then used to calculate proportional abundances and compare species composition between site types. Results indicated that electrofishing CPUEs of Darters, mottled sculpin Cottus bairdi , rare threatened and endangered species, and juvenile and adult Centrarchidae were higher at remediation sites than at control sites. Additionally, juvenile Centrarchidae and mottled sculpin had a higher proportional abundance in electrofishing collections at remediation sites than at control sites. In contrast, CPUEs and proportional abundances were similar for all taxonomic and management priority groups of fish collected in minnow traps and gillnets. Electrofishing captured more species and more individuals and is therefore a valuable sampling technique for large river shorelines. Nevertheless, addition of minnow traps and gillnets allowed for a more comprehensive assessment of fish assemblages. Overall, this multi-faceted survey approach demonstrates that shoreline remediation projects were beneficial to recreational and ecologically important species in the St. Clair River.

Michigan, Ontario↗

USGS2019

Zooplankton dynamics in a Great Lakes connecting channel: Exploring the seasonal composition within the St. Clair-Detroit River System

The connecting channels linking the Laurentian Great Lakes provide important migration routes, spawning grounds, and nursery habitat for fish, but their role as conduits between lakes for zooplankton is less understood. To address this knowledge gap in the St. Clair–Detroit River System (SCDRS), a comprehensive survey of crustacean zooplankton was performed in both riverine and lacustrine habitats from spring to fall 2014, providing the first system-wide assessment of zooplankton in the SCDRS. Zooplankton density and biomass were greatest in northern reaches of the system (southern Lake Huron and the St. Clair River) and decreased downstream towards Lake Erie. The composition of zooplankton also changed moving downstream, transitioning from a community dominated by calanoid copepods, to more cyclopoids and cladocerans in the Detroit River, and to cladocerans dominant in western Lake Erie. Coincidentally, species richness increased as sampling progressed downstream, and we estimated that our single-year sampling regime identified ~88% of potential taxa. Other species assemblages have responded positively to recent water quality and habitat restoration efforts in the SCDRS, and this survey of the zooplankton community provides benchmark information necessary to assess its response to continued recovery. In addition, information regarding the lower trophic levels of the system is integral to understanding recruitment of ecologically and economically valuable fish species targeted for recovery in the SCDRS.

St. Clair-Detroit River System↗