Geology topics

Matthew A. Mensinger

Publications and source records attributed to Matthew A. Mensinger.

7 recordsLinked to original sources

USGS2025

Seasonal movements of nonnative White Catfish in the Penobscot River estuary

Objective White Catfish Ameiurus catus has been introduced to coastal watersheds across the United States. In the Penobscot River, Maine, this species has become increasingly common in upstream habitats that have been made accessible by recent dam removals. We characterized the movements of White Catfish to understand the temporal variation in their movement patterns and contextualize these findings within the recent changes in watershed connectivity. Methods We captured and tagged 10 adult White Catfish (mean fork length = 271 mm) with acoustic transmitters in the lower Penobscot River in July 2022. The movements of the tagged fish were monitored through April 2023 with a large network of stationary receivers. Results The tagged catfish were detected up to 6 km upstream and 31 km downstream from the release site. The total distance that was traveled by individuals ranged from 0 to 154 km during the study. Fall and spring movements were associated with changes in river flow and water temperature, but fish were relatively stationary from December through March, when at least five individuals were assumed to have overwintered in lower river tributaries. Conclusion Our results show that individual White Catfish may move considerable distances within large river systems and that these movements are potentially facilitated by changing river conditions. Collectively, this study fills a long-standing knowledge gap about the movement ecology of this species, adds context to help explain a recent increase in observations within their introduced range, and shows how changes in river conditions may be used to predict when and where these fish will move within a tidal system.

Maine↗

USGS2025

Smallmouth bass (Micropterus dolomieu) and chain pickerel (Esox niger) identified as Atlantic salmon (Salmo salar) smolt predators in a reservoir system

Reservoir predation has been identified as a leading mortality source for smolts migrating through impounded river systems. We investigated smolt predation risk for an endangered Atlantic salmon ( Salmo salar ) population in the Weldon Dam reservoir in the Penobscot River, Maine, USA. In spring 2022, we characterized the fates of 390 tethered smolts. Smolts were exclusively predated by two predator species not native to the study area: chain pickerel ( Esox niger , n = 43) and smallmouth bass ( Micropterus dolomieu , n = 42). Using Cox-proportional hazard analysis, we estimated that 23% (95% CI = 15%–29%) of tethered smolts were expected to be predated within a one-hour deployment. Water temperature was the primary driver of predation risk as predation probability increased from 10% to 33% when temperature increased from 5 to 15 °C. Smolts also incurred above-average predation risk when they were within 40 m of shore. We demonstrate that non-native fish predation may drive patterns of high impoundment mortality and that risk is spatially and temporally heterogeneous within these systems. Collectively, this study offers direct evidence of species-specific predation on Atlantic salmon smolts and illuminates potential strategies to mitigate predation risk during reservoir migration.

Maine↗

USGS2025

Spatial variation in landlocked Atlantic Salmon smolt survival associated with dam passage, avian predation, and stocking location

Objective We evaluated survival differences between upstream and downstream stocking for landlocked Atlantic Salmon Salmo salar smolts in a tributary to Lake Champlain. Methods We radio-tagged smolts and stocked them concurrently with 22,000 smolts at two release sites in 2 years. The downstream location (DS, river kilometer 16, no dam passage) was a historically used site in a dam tailrace, whereas the upstream site (US, river kilometer 27, two dams to pass) was in a side channel and stocked for the first time. We estimated survival, counted birds during stocking, and searched nesting colonies for transmitters. Results Within stocking reaches, survival per kilometer for the DS release group was markedly lower than that for the US group (US 2021 and 2022 = 0.98, 0.98, respectively; DS 2021 and 2022 = 0.82, 0.69, respectively). At the DS site, we documented a tenfold increase in avian predators following stocking, whereas no increase was detected at the US site. Passage was >96% at both dams, but postpassage survival (per kilometer) was much lower at the second dam (2021 = 0.78, 2022 = 0.82) compared to the first dam (2021 = 0.96, 2022 = 0.97). Surprisingly, cumulative survival to Lake Champlain was higher for fish that were released upstream in 2022 (US = 43%; DS = 32%) despite dam passage and additional migratory distance. At least 20% (2021) and 7% (2022) of successful migrants were later consumed by birds in the river delta or in Lake Champlain. Conclusions Upstream stocking did not consistently result in lower cumulative survival, likely due to predators habituated to annually reoccurring stocking in a dam tailrace that increased stocking-related mortality at the DS release site. We highlight the importance of evaluating historically used stocking sites, as substantial loss of smolts could be avoided by simple changes to stocking practices. Avian predation was a major source of mortality, necessitating further studies to understand and address survival issues within Lake Champlain.

Vermont↗

USGS2025

Evidence for size‐based predation risk during Atlantic salmon (Salmo salar) smolt migration.

Hatchery supplementation is frequently employed during the conservation and recovery of imperilled salmon populations. At the smolt stage, hatchery rearing practices often produce individuals that are larger than wild conspecifics. Under this ‘bigger is better’ strategy, it is assumed that larger fish are less susceptible to predation during migration. We tested this hypothesis on hatchery-reared Atlantic salmon ( Salmo salar ) smolts with fork lengths representative of those of natural and hatchery origins, allowing us to isolate the influence of size from rearing history. From May to June 2023 we characterized predation risk for acoustic-tagged ( n = 50) and tethered ( n = 192) smolts of various sizes through a mostly free-flowing section of the Penobscot River, Maine, USA. Across both methods, more than 50% of smolts were predated, with the majority of predation events being attributed to smallmouth bass ( Micropterus dolomieu ). Tethered smolts of all sizes experienced similar predation risk. In the acoustic telemetry component of this study, smaller, wild-sized smolts incurred greater overall mortality relative to standard hatchery sizes (95% vs. 75%), the majority of which occurred within 3 km of the release site. Collectively, these results allude to a strong predation influence imposed by smallmouth bass on smolts in freshwater sections of the Penobscot River and small-bodied migrants may incur greater predation risk, particularly near stocking sites.

Journal of Fish Biology↗

USGS2024

Dams facilitate predation during Atlantic salmon (Salmo salar) smolt migration

Diadromous fish populations have incurred precipitous declines across the globe. Among many stressors, these species are threatened by anthropogenic barriers that impede movement, alter riverine habitat, and augment predator communities. In this study, we used acoustic transmitters ( n = 220) with predation and temperature sensors to characterize Atlantic salmon ( Salmo salar ) smolt predation risk in the Penobscot River, Maine, USA. Across two seasons, we documented 79 predation events through a 170 km migratory pathway, which included three hydropower projects and a large estuary. We detected tagged smolts that were predated by fish ( n = 42), marine mammals ( n = 28), and birds ( n = 9). Using a multistate mark-recapture framework, we estimated that 46% of smolts were predated during downstream migration, which accounted for at least 55% of all mortality. Relative predation risk was greatest through impoundments and the lower estuary, where on average, predation rates were 4.8-fold and 9.0-fold greater than free-flowing reaches, respectively. These results suggest that predation pressure on Atlantic salmon smolts is exacerbated by hydropower projects and that predation in the lower estuary may be greater than expected.

Maine↗

USGS2021

American eel personality and body length influence passage success in an experimental fishway

Millions of dams impair watershed connectivity across the globe and have severely affected migratory fish populations. Fishways offer upstream passage opportunities, but artificial selection may be imposed by these structures. Using juvenile American eel Anguilla rostrata as a model species, we consider whether individual differences in behaviour (i.e. personality) and fish size can predict passage success. We evaluated the expression of bold and exploratory behaviours using open field and emergence assays in the laboratory. Then we assessed the propensity for individuals to volitionally climb through an experimental fishway to understand if personality and fish size could predict climbing success. We demonstrate personality in juvenile eels, and swimming speed in the open field was negatively associated with climbing propensity. Slower swimmers were up to 60% more likely to use the passage device suggesting that more exploratory eels incurred greater passage success. For successful climbers, climbing time was negatively associated with fish length. Synthesis and applications . Our results suggest fish may segregate at barriers based on personality and size. Preventing a subset of individuals from accessing upstream habitat is likely to have negative consequences for fish populations and aquatic ecosystems. Selection may be alleviated by increasing passage opportunities, maximizing fishway attraction and avoiding inefficient passage solutions.

Journal of Applied Ecology↗

USGS2021

The consequences of dam passage for downstream-migrating American eel in the Penobscot River, Maine

American eel ( Anguilla rostrata ) often pass hydropower dams during adult spawning migrations. We conducted a 4-year acoustic telemetry study that characterized passage risks through two dams (West Enfield and Milford) in the Penobscot River, Maine, USA. We released tagged fish ( n = 355) at two sites, estimated survival and delay under variable river conditions, and compared performance among dammed and free-flowing river sections. Survival rates (standardized per river kilometre, rkm) were lower at West Enfield (Φ rkm = 0.984 ± 0.006 SE) and Milford (Φ rkm = 0.966 ± 0.007 SE) compared with undammed River sections (Φ rkm = 0.998 ± 0.0003 SE). Cumulative mortality was 8.7% (4.4 km) and 14.2% (5.5 km) through dammed sections and 8.7% throughout the rest of the river (58.1 km). Fish that already passed an upstream dam incurred higher downstream mortality compared with individuals without passage experience. Additionally, fish endured long delays at dams, and >10% of fish were delayed >24 h. Low flows exacerbated the risk of mortality and delay. These results offer evidence for direct, latent, and sublethal consequences of dam passage for migrating eels.

Maine↗