Geology topics

Ashley H. Moerke

Publications and source records attributed to Ashley H. Moerke.

3 recordsLinked to original sources

USGS2025

Larval fish export in response to altered discharge in the St. Marys river rapids

The St. Marys River (SMR) forms the border between Michigan, USA, and Ontario, Canada, connecting lakes Superior and Huron. Discharge is controlled by a 16-gate water control structure upstream of the SMR rapids. The SMR rapids are a critical spawning habitat in the Great Lakes, yet the influence of regulated discharge on larval fish export remains poorly understood. From 2018 to 2021, larval fish were sampled across four locations to assess community composition and export dynamics under varying discharge releases. Rainbow smelt ( Osmerus mordax ) dominated catches (87.9 %), followed by species in the family Leuciscidae (i.e., native minnows) and burbot ( Lota lota ). Larval densities were strongly influenced by water temperature and, to a lesser extent, discharge. Bayesian state-space models estimated a total export of ∼ 41.3 million larvae from the rapids across 3 years, with the highest export in 2019. Rainbow smelt larvae exhibited peak densities at intermediate flows (300–600 m 3 s −1 ) and temperatures (∼18–19 °C), while non-rainbow smelt taxa showed species-specific, less consistent responses. Nighttime sampling consistently yielded higher larval densities. Export estimates varied by analysis but both manual and Bayesian approaches captured similar interannual and taxonomic trends. Despite past expectations, the larval community was largely composed of prey species, with limited representation of lake sturgeon ( Acipenser fulvescens ), lake whitefish ( Coregonus clupeaformis ), or walleye ( Sander vitreus ). These results suggest the SMR rapids currently support significant forage fish production and highlight the importance of discharge and temperature in structuring larval export.

St Mary's River rapids↗

USGS2025

Visioning and conceptual framework for coordinating Great Lakes connecting waters research and monitoring

The Laurentian Great Lakes are connected via naturally occurring straits and rivers: St. Marys River, Straits of Mackinac, St. Clair-Detroit River System, Niagara River, and the St. Lawrence River. Despite the historical ecological and economic importance of these waters, international agreements (e.g., Great Lakes Water Quality Agreement) only recently explicitly named the Great Lakes Connecting Waters (GLCWs), requiring governments to address the challenges of adequate restoration and protection from historical use and degradation. Standardized research and monitoring activities are needed; however, there is no established mechanism for coordination across the GLCWs. A three-day summit in 2023 convened experts to form the initial framework for a GLCWs Collaborative to increase standardizations and knowledge transfer. Participants drafted a governance structure and priorities following the principles of collective impact but allowed for place-based specificity for local connecting water organizations. Priorities and suggestions for success included: 1) co-development of the collaborative with all rights holders, stakeholders, and surrounding communities; 2) investment in research and technology specific to GLCWs; 3) investment in information transfer and training; 4) increased communication; and 5) better integration into existing Great Lakes research, monitoring, and funding programs. Expanding participation in all local GLCWs organizations with principles of inclusivity was identified as a larger collaborative goal. Next steps in the development of a GLCWs Collaborative include increased communication and formation of working groups and obtaining funding for a dedicated organization to begin supporting activities (communication, facilitation, logistics). By using a deliberate process for establishment, the potentially slower time frame for establishment may result in increased participation and success.

Laurentian Great Lakes↗

USGS2025

Food web structure of the Lake Superior fish community in 2021–2022

The trophic linkages and ecological requirements of the Lake Superior fish community have not been assessed on a whole lake scale in over a decade. Here, we investigated the trophic dynamics across multiple species and habitat zones of Lake Superior. From April to October of 2021 and 2022, a total of five piscivore, four planktivore, and six benthivore species were collected by region and length class during bottom-trawl, standard gillnet, commercial cisco gillnet, and recreational angler surveys. To assess trophic linkages, stomach contents were measured to estimate biomass consumed and a multivariate analysis was used to assess diet composition by species, length, and region. We found a high degree of interconnectedness in the Lake Superior food web, with Mysis as a critical diet item for most fishes. Native piscivore diets varied by region and with ontogeny. Lake charr were important habitat couplers in the lake, exhibiting a diverse diet and opportunistic foraging strategy. Conversely, Pacific salmon were more restricted in their foraging. Planktivores and benthivores primarily consumed Mysis , with less reliance on Diporeia compared to previous studies. Lake whitefish and cisco were the exception to this pattern, with broader bathymetric depth distributions represented in their diets. We found the food web to be supported by a predominantly native species assemblage, with redundancies at all trophic levels.

Lake Superior↗