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At least 307 records · Page 17Linked to original sources
USGS2020

Trends and biological effects of environmental contaminants in lamprey

Environmental contamination is of global concern. Lamprey are scientifically, ecologically, culturally, and economically important fishes. Our study represents the first synthesis ever on environmental contamination in lamprey. Objectives of this study include: (1) evaluate lethal and sublethal effects of environmental contaminants on lamprey, thereby providing insight into the potential for environmental contaminants to affect lamprey abundance, (2) highlight the unique characteristics of contaminant accumulation in lamprey, (3) determine whether spatial and temporal trends observed in contaminant concentrations of other top predators of aquatic food webs are reflected in the spatial and temporal trends of contaminant concentrations of lamprey, (4) identify key environmental contaminants affecting consumption advisories for people eating lamprey, and (5) identify important gaps in our knowledge of environmental contamination in lamprey. The geographic scope of this synthesis is worldwide. We conclude that, in general, the environmental contaminant concentrations that have been experienced by lamprey in the wild appear to be nonlethal to lamprey. However, environmental contaminants exert sublethal effects on lamprey. Sea lamprey ( Petromyzon marinus ) and Pacific lamprey ( Entosphenus tridentatus ) are relatively high in total mercury (Hg) concentration compared with other fishes. Compared with other top predators, lamprey are relatively low in polychlorinated biphenyl (PCB) concentration and concentrations of organochlorine pesticides. We also conclude that regulations on the use of PCBs, beginning in the 1970s, were effective in dramatically reducing PCB concentration in lamprey since the 1970s. Emerging contaminants, such as pharmaceuticals, microplastics, and per- and polyfluorinated alkyl substances (PFAS), have yet to be studied in lamprey.

Journal of Great Lakes Research↗
USGS2020

Managing native and non-native sea lamprey ( Petromyzon marinus ) through anthropogenic change: A prospective assessment of key threats and uncertainties

Sea lamprey ( Petromyzon marinus ) is a species of conservation concern in their native range of the Atlantic coasts of Europe (Near Threatened to Critically Endangered) and North America (Secure to Critically Imperiled), and an invasive species of great economic and ecological concern in the Laurentian Great Lakes. Despite differences in life history strategy (anadromous natives vs adfluvial non-natives), the biology of sea lamprey is sufficiently similar to expect comparable responses to large-scale environmental change. We take a prospective look at the future (50 to 100 years) of sea lamprey management in an era of considerable environmental disturbance, and consider biological responses, management actions, and the future status of populations across the native and non-native ranges. Based on facilitated discussion by a diverse group of international experts, two major but poorly characterized classes of threats to sea lamprey were identified: climate change and socio-political issues. We discuss how climate induced changes affect growth, bioenergetics, and phenology of sea lamprey, and associated effects on control tactics (pesticides and barriers) and conservation. We consider tensions surrounding improving connectivity in the Great Lakes while controlling invasive sea lamprey, and discuss supplements and alternatives to pesticides and their wider effect, as well as the effects of new invasive species. To prevent the extirpation of native sea lamprey populations, or the re-expansion of non-native populations, we conclude with a call for new and ongoing dialogue and collaboration among all sea lamprey biologists and managers across the native and non-native range.

Journal of Great Lakes Research↗
USGS2020

Determining habitat limitations of Maumee River walleye production to western Lake Erie fish stocks: Documenting a spawning ground barrier

Tributaries provide spawning habitat for three of four major sub-stocks of Lake Erie walleye ( Sander vitreus ). Despite anthropogenic degradation and the extirpation of other potamodromous species, the Maumee River, Ohio, USA continues to support one of the largest fish migrations in the Laurentian Great Lakes. To determine if spawning habitat availability and quality could limit production of Maumee River walleye, two habitat suitability models were created for the lower 51 km of the Maumee River and the distribution and numbers of walleye eggs deposited in a 25 km stretch of river were assessed. Walleye eggs were collected using a diaphragm pump at 7 and 10 sites from March/April to May 2014 and 2015. The habitat suitability models showed that <3% of the river yielded ‘good’ walleye spawning habitat and 11–38% yielded ‘moderate’ walleye spawning habitat, depending on the model. However, a large set of rapids at river kilometer 28 and more than five river kilometers of less suitable habitat separated areas of ‘good’ habitat. The rapids may present a migratory barrier for many spawning walleye, as modeled water velocities exceed maximum estimated walleye swim speeds 71–100% of days during pre-spawn migration and spawning during the study period. In both study years, there was a sharp decline in mean egg numbers from spawning sites downstream of the rapids (439.7 eggs/2 min tow ± 990.6 SD) to upstream sites (5.9 eggs/2 min tow ± 19.4 SD). Physical barriers like rapids may reduce spawning habitat connectivity and could limit walleye production in the Maumee River.

Ohio↗
USGS2020

A review of an electric weir and fishway in a Great Lakes tributary from conception to termination

A successful management plan requires clear goals and a process for evaluation. Without them, managers risk operational shifts in which continuous changes disguised as improvements may have little beneficial effect. The conception, design, and operation of an electric barrier and fishway on the Pere Marquette River of Lake Michigan serve as an illustration. The Great Lakes Fishery Commission operated an electric weir to stop migration of adult sea lampreys ( Petromyzon marinus ) and a fishway to provide upstream passage of rainbow trout ( Oncorhynchus mykiss ) during 2000–2009. The weir and fishway were successful in blocking some of the annual spawning run of sea lampreys (trapped an annual average of 439 sea lampreys) and it allowed passage of rainbow trout (an annual average of 6,091). Even with success that yielded an estimated density of 0.03 adult female sea lampreys per 100 m 2 of larval habitat upstream of the weir, lampricide treatments continued because the weir still allowed establishment of substantial densities of larval sea lampreys. Our evaluation suggests that an in-stream barrier must approach 100% blockage of sea lampreys to eliminate large recruitment events. The failure of the weir to reduce lampricide treatments was due to an informally defined purpose and measures for success at the onset, the complexity of electric weir systems (and the operational problems created by such intricacy), and lack of recognition of the reduction in larval sea lamprey recruitment needed to succeed. Control of sea lampreys in the Pere Marquette River could have benefited from an adaptive management approach.

Michigan↗
USGS2021

A case study of sea lamprey (Petromyzon marinus) control and ecology in a microcosm of the Great Lakes

The Cheboygan River, Michigan, is the only tributary to the upper Great Lakes where sea lamprey ( Petromyzon marinus ) are known to complete their entire life cycle. The Upper and Lower reaches are separated by the Cheboygan Lock and Dam located about 2 km from Lake Huron. In the Upper River, the Pigeon, Sturgeon, and Maple Rivers provide nursery habitat for larval sea lamprey. Burt and Mullett Lakes provide feeding grounds for juvenile sea lamprey. Low levels of immigration from Lake Huron occur when adult sea lamprey bypass the lock and dam. Lampricide treatment in the Pigeon, Sturgeon, and Maple Rivers began in 1966 and 15 treatments have been conducted to date at a combined cost of $435,000 USD per treatment. Treatments may become more difficult due to recent dam removals in the Pigeon (2016) and Maple Rivers (2018) that expanded habitat available to valued fishes and sea lamprey. At present, the landlocked population is less than 200 spawning adults, and those adults are generally smaller and may spawn earlier in the spring than adult sea lamprey from Lake Huron. Frequency of sea lamprey-induced wounding on steelhead ( Oncorhynchus mykiss ) and northern pike ( Esox lucius ) in Mullett Lake is less than 5%. Given increasing challenges of lampricide treatment, efforts to test other means of control such as sterile male release technique is on-going. The Cheboygan River represents a microcosm of the Great Lakes and is useful for learning about sea lamprey ecology and testing controls that supplement lampricides and barriers.

Michigan↗
USGS2020

Evidence of spawning by lake trout Salvelinus namaycush on substrates at the base of large boulders in northern Lake Huron

Identification of lake trout spawning sites has focused on cobble substrates associated with bathymetric relief (e.g., ‘contour’ or ‘slope’ along reefs), but this ‘model’ may be narrow in scope. Previous telemetry work conducted near Drummond Island, USA, Lake Huron, identified egg presence in substrates at the base of large boulders (>1 m diameter); however, the extent of this phenomenon was unknown. Telemetry data paired with multi-beam bathymetry identified a 0.63 km 2 area used by lake trout characterized by low bathymetric relief and numerous (~269) large boulders (>1 m diameter) with small-diameter substrates at their bases. Diver surveys revealed egg presence at all 40 boulders surveyed, exclusively associated with clean gravel-cobble (0.6–42 cm) substrates in undercut areas beneath overhanging edges of boulders and in narrow spaces between adjacent boulders. Egg presence was not associated with boulder or substrate physical characteristics which highlighted the possible importance of interstitial currents. Successful incubation in these habitats was inferred by capture of free embryos and post-embryos the following spring using traps and an electrofishing ROV although at lower densities than at popular spawning habitats nearby (1–3 km away). Free embryos and post-embryos were also caught where eggs were not observed the previous fall including unexpectedly on top of boulders which suggested that post-hatch stages may move more than previously thought. Extensive use of boulder-associated habitats for spawning, egg incubation, and early growth suggested this undescribed habitat type may provide an unanticipated contribution to total available lake trout spawning habitat and recruitment in the Great Lakes.

Lake Huron↗
USGS2022

Condition of resident fish communities in the Eighteenmile Creek Area of Concern, New York

The lower 3.5 km of Eighteenmile Creek, a tributary to Lake Ontario in New York, was designated as an Area of Concern (AOC) in 1985 under the Great Lakes Water Quality Agreement due to extensive contamination of bed sediments by polychlorinated biphenyls (PCBs) and other toxicants. Five beneficial use impairments (BUIs) have been identified in this AOC, including degraded fish and wildlife populations. We surveyed fish communities in the Eighteenmile Creek AOC and in a comparable section of a nearby reference stream (Oak Orchard Creek) during June 2019 to infer whether legacy contaminants are currently impairing fish communities in the AOC to an extent that they differ from the regional reference condition. Estimates of community abundance, biomass, diversity, and fish condition from each system were compared using a noninferiority testing framework. Biomass, diversity, and fish condition in the Eighteenmile Creek AOC were similar or superior to that in Oak Orchard Creek, while abundance was 20% lower in the AOC. These findings and those of a 2007 sampling effort suggest that fish communities in the Eighteenmile Creek AOC are not impaired despite recent studies indicating that PCBs are bioaccumulating in fish tissues at 1–2 orders of magnitude above background levels. Future assessments in the Eighteenmile Creek AOC might focus on the condition of benthic macroinvertebrate communities and potential toxicity of local contaminants to piscivorous wildlife in order to fully address the remaining aspects of the fish and wildlife populations beneficial use impairment.

New York↗
USGS2021

Telemetry evaluation of carbon dioxide as a behavioral deterrent for invasive carps

Carbon dioxide (CO 2 ) mixed into water is being explored as a possible management strategy to deter the upstream movements of invasive carps through navigation locks and other migratory pinch-points. This study used two-dimensional acoustic telemetry to assess the effectiveness of dissolved CO 2 as a chemosensory deterrent to two carp species in a large U-shaped pond. Free-swimming movements of telemetered bighead carp ( Hypophthalmichthys nobilis ) and grass carp ( Ctenopharyngodon idella ) were documented 24 h before treatment and 24 h during treatments at 60, 121 and 213 mg/L CO 2 (mean concentrations in pond water). Several behavioral endpoints were then quantified and compared to evaluate deterrence efficacy. In general, results showed that both carp species responded similarly to CO 2 treatments. Carps consistently relocated into areas away from the injection site and made fewer attempts to re-enter CO 2 treated areas. On average, CO 2 treatments reduced mid-line crosses between untreated and treated sides of the pond by 58% at 121 mg/L CO 2 and 78% at 213 mg/L CO 2 relative to normal swimming movements recorded before treatment. Fish swim speeds increased significantly when inside the CO 2 plume during treatments during 213 mg/L CO 2 trials relative to swim speeds outside the plume, possibly indicative of active searching and avoidance responses. Overall, this study found that CO 2 altered the behavior of bighead carp and grass carp. Natural resource agencies could consider the CO 2 concentrations identified in this study to inform future applications to deter invasive carps from locations where they are at-risk to move upstream.

Journal of Great Lakes Research↗
USGS2021

Lake-wide annual status of Mysis diluviana population in Lake Michigan in 2015

Mysis diluviana is one of the most abundant zooplankton by biomass in the Laurentian Great Lakes of North America, a predator of other zooplankton and an important prey for fishes. Studies of long-term trends in Lake Michigan have shown 2005–2016 densities to be 50–80% lower than 1990s densities, but these observations have been based on annual monitoring that is either spatially or seasonally limited. We combined Lake Michigan Mysis data from three annual programs and the 2015 Cooperative Science and Monitoring Initiative to achieve broad spatial coverage during spring, summer, and fall of 2015 and broad depth coverage during spring 2016. Lake-wide, annual density and biomass were 82 (SE: 10) Mysis /m 2 and 200 (SE: 36) mg dry mass/m 2 . Density and biomass estimates were highest offshore, generally higher in the north basin, and seasonally highest in summer. Annual lake-wide averages for depths >30 m were better captured by seasonally-extensive annual programs than spatially-extensive annual programs, although spring sampling may bias annual values low. Mysis cohorts grew 0.026 mm/d (age-0) and 0.007 to 0.027 mm/d (age-1). Annual mortality was 81–98%. Reproduction was fall-spring and seasonal lake-wide estimates ranged from 0.6 to 19.1% females brooding, 13–20 embryos/brood, and 3–46 embryos/m 2 . Annual production (423 mg dry mass/m 2 /yr, SE: 31) was lower than all but one previous estimate from lakes Michigan, Huron, and Ontario. While Mysis tend to persist, low Mysis production may be a concern for prey fishes that feed on Mysis .

Lake Michigan↗
USGS2021

Seasonal movements of muskellunge in the St. Clair – Detroit River System: Implications for multi-jurisdictional fisheries management

The St. Clair-Detroit River System contains a world-class Great Lakes muskellunge ( Esox masquinongy ) fishery that has avoided the declines observed in many Great Lakes muskellunge populations. Muskellunge are an upper trophic level predator, and therefore a naturally low-density species. Limited fishery-independent data exist on which to base management decisions. To remedy this, we initiated an acoustic telemetry study in May of 2016, in collaboration with the Great Lakes Acoustic Telemetry Observation System. Our objective was to describe patterns of movement of muskellunge in this large and open system to better understand their spatial ecology. We acoustically tagged 133 muskellunge in the Detroit River and Lake St. Clair, and movements of 58 fish that passed our data quality control screens were analyzed. We utilized mixed modelling to assess the effects of sex, length, release location, and season on daily movement rates. We found that movement rates only differed among seasons, with highest movement rates occurring in the fall and lowest movement rates in the winter. Muskellunge tagged at different locations exhibited distinct residency patterns, and fish frequently crossed jurisdictional and waterbody boundaries. Ultimately our study highlights the scope and patterns of muskellunge movement in a large, unimpounded system and demonstrates that management of these fish would benefit from consideration of their full distribution covering multiple management jurisdictions.

Michigan, Ontario↗
USGS2021

Evidence of successful river spawning by lake trout (Salvelinus namaycush) in the lower Niagara River, Lake Ontario

Restoration of a wild-produced lake trout Salvelinus namaycush population in Lake Ontario has not been successful despite the adult population often meeting or exceeding restoration targets. Lack of high-quality spawning habitat in Lake Ontario is suggested as one impediment to recruitment of wild lake trout, although the quantity and location of spawning habitat is poorly understood. If high-quality spawning habitat is limited in Lake Ontario, lake trout may be using uncommon spawning locations such as rivers. Anecdotal angler accounts point to the Niagara River as a lake trout spawning location. To better understand the potential of the Niagara River as a spawning location, egg and juvenile fish collections were conducted 12–14 river kilometers from the mouth of the Niagara River from 2010 to 2012; and mature female lake trout with surgically implanted acoustic tags were monitored from 2015 to 2019. Genetic analyses confirmed 60% of collected eggs and 93% of collected post-hatch juvenile fish in the Niagara River were lake trout. Tagged female lake trout returned to the Niagara River over consecutive years during the spawning season. The short duration of lake trout presence in the river (mean = 56 days/year) suggests female lake trout use the Niagara River primarily for spawning. Diversity in spawning locations may provide lake trout population’s resilience against environmental variability through a portfolio effect. Improved identification of riverine spawning locations, including their overall contribution to wild recruitment, may be a useful tool for managers to restore a wild-produced population of lake trout in Lake Ontario.

New York, Ontario↗
USGS2021

Stationary hydroacoustics demonstrates vessel avoidance biases during mobile hydroacoustic surveys of alewife in Lake Ontario

Mobile hydroacoustic surveys are routinely used to estimate pelagic fish abundance . In the Great Lakes, alewife are commonly surveyed with mobile hydroacoustics, however, their behavior often has them associated with epilimnetic habitats which increases the potential for vessel avoidance to bias hydroacoustic observations. Abundance estimates from mobile hydroacoustic surveys are typically made using depth and size thresholds to classify targets to species. In hydroacoustic surveys, fish can appear to be smaller when oriented off horizontal axis, as is common with fish displaying vessel avoidance behaviour. This presents a problem where alewives that are diving may appear too small to be correctly classified. We compared alewife swimming behaviours and target strength distributions between stationary up-looking and mobile down-looking hydroacoustics to quantify how vessel avoidance may bias hydroacoustic observations. Alewives from the mobile survey were found to be diving away from the surface, moving faster and in more linear paths than the undisturbed fish from the stationary survey. In the mobile survey, alewives were observed at smaller target strength values than would be expected if boat avoidance was not occurring. Our results suggest that alewife behavioral changes associated with vessel avoidance affect the number and size of targets classified as alewife from mobile hydroacoustic surveys in Lake Ontario.

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↗
USGS2021

Implications of tagging effects for interpreting the performance of sea lamprey traps in a large river

Abundance estimates can be crucial for managing species of economic concern. The accuracy of these estimates can depend on the methods used to track animals and to estimate abundance from tracking data. We tested experimentally if disparate estimates of trapping efficiency calculated for sea lamprey ( Petromyzon marinus ) in the St. Marys River near Sault Ste. Marie, Canada could be explained by effects related to the invasiveness and handling involved in tagging or the tag size used in the marking procedures. Trapping is used to gauge adult abundance, trapping efficiency, and success of a binational sea lamprey control program in the Laurentian Great Lakes, North America. Our experiment compared nightly catches of sea lamprey marked with external fin clips, surgically-implanted passive integrated transponder tags (PIT-only), and surgically-implanted PIT and acoustic tags (PIT+acoustic). We found no evidence that the probability of being trapped was affected by the added invasiveness and handling of internal tagging. Nightly recaptures of PIT-only tagged sea lamprey, relative to fin-clipped sea lamprey, were not different from expectations based on the numbers of individuals released from each treatment group. Conversely, there was evidence of effects related to tag size. Nightly recaptures of PIT+acoustic tagged sea lamprey, relative to PIT-only tagged sea lamprey, were lower than expected based on numbers of individuals released from each treatment group. Effects related to tag size partially explain the disparate estimates in trapping efficiency observed for sea lamprey.

Ontario↗
USGS2021

Acoustic tag retention and tagging mortality of juvenile cisco Coregonus artedi

Release of hatchery-reared juvenile cisco ( Coregonus artedi ) is an important tool for recovering Great Lakes populations, but post-release survival is unknown. Telemetry using small acoustic tags provides opportunities to assess the efficacy of hatchery-reared fish releases. However, better understanding of the tolerance of juvenile cisco to acoustic tags is needed. Juvenile cisco mortality and tag retention as a function of tag size:body size (Relative Tag Weight, RTW) was observed for 30 d post tag implantation in the laboratory. Tag loss and mortality increased with RTW. A single mortality occurred for RTW ≤ 3% and tag retention and survival was <50% for RTW > 7.0%. Logistic regression predicted >95% survival and tag retention to 30 d for RTW < 2.5%, with full survival of study fish for RTW of ≤2%. Sedation and surgery times did not affect survival of tagged fish, but results of anesthesia-only and sham surgeries highlight the need to minimize handling effects for effective acoustic telemetry studies. Our findings clarify thresholds of RTW and indicate that juvenile cisco can receive acoustic tag implants. Observing these limitations can improve the effectiveness of acoustic telemetry to assess success of cultured juvenile fish releases for conservation or restoration of native forage fish populations. Evaluation of the effects of acoustic tags over longer time periods and under environmental conditions, like those at release sites, are needed to further validate this technology.

Journal of Great Lakes Research↗
USGS2021

Spatial and temporal distributions of Dreissena spp. veligers in Lake Huron: Does calcium limit settling success?

The larval stage of invasive Dreissena spp. mussels (i.e., veligers) are understudied despite their seasonal numerical dominance among plankton. We report the spring and summer veliger densities and size structure across the main basin, North Channel, and Georgian Bay of Lake Huron, and seek to explain spatiotemporal variation. Monthly sampling was conducted at 9 transects and up to 3 sites per transect from spring through summer 2017. Veliger densities peaked in June and July, and we found comparable densities and biomasses of veligers between basins, despite differences in density of juvenile and adult mussels across these regions. Using a generalized additive model to explain variations in veliger density, we found that temperature, chlorophyll a , and nitrates/nitrites were most important. We generated an index of veliger attrition based on size distributions that revealed a higher rate of attrition in the North Channel than the rest of the lake. A logistic model indicated a threshold calcium concentration of around 22 mg/L was necessary for veligers to survive to larger sizes and recruit to their juvenile and benthic adult life stages. Improved understanding of factors that regulate the production and survival of Dreissena veligers could improve the ability of managers to assess future invasion threats as well as explore potential control options.

Lake Huron↗
USGS2021

Understanding sea lamprey populations in the Great Lakes prior to broad implementation of sea lamprey control

Control of invasive sea lamprey in the Great Lakes with a selective pesticide (lampricide) that targeted larval sea lamprey began in the late 1950's and continues to be one of the main methods for control. Although the Great Lakes Fishery Commission, which was formed with the mandate of controlling sea lamprey, often expresses the success of the sea lamprey control program in terms of percent reduction from lake-wide pre-lampricide control adult sea lamprey abundances, there remains a large amount of uncertainty surrounding these estimates. In this study, we gathered historical data on adult sea lamprey captures from trapping efforts from the mid-1950's through the late 1970's to better understand pre-control abundance. We used this information to estimate lake-wide population abundances of adult sea lamprey using a weighted linear regression that includes environmental and lampricide treatment predictor variables. We varied trapping efficiency for early trapping data to evaluate the uncertainty in abundance estimates. Pre-control adult sea lamprey abundances in all lakes were much greater than current population sizes, but estimates were quite sensitive to trapping efficiency. In Lake Superior, declines in abundance aligned with increases in control efforts, but in other lakes, declines were occurring prior to the onset of lampricide application, perhaps because of a loss of prey. We suggest that previous estimates of pre-control adult sea lamprey abundance may have been underestimated unless trapping efficiency was greater than what is currently achieved in the basin.

Great Lakes↗
USGS2021

Environmental factors influencing annual sucker (Catostomus sp.) migration into a Great Lakes tributary

Fish migration in rivers is a growing area of concern as mounting anthropogenic influences, particularly fragmentation from dams and barriers, constitute major threats to global river species diversity. Barriers can impede the movement of fishes between areas critical to the completion of their lifecycle, affecting both population and ecosystem viability. In response, fish passage solutions have been identified as a critical need to maintain fisheries viability in the Laurentian Great Lakes, and around the world. Pivotal to the success of these fish passage solutions is a more complete understanding of the movement phenology and environmental cues that instigate migration. We used a dual-frequency identification sonar (DIDSON) to evaluate environmental triggers of river entry during spring and summer for three size classes of migratory fishes in the Boardman River, a Lake Michigan tributary. Our results indicate that medium size fish (>30 cm and < 50 cm), primarily composed of white sucker Catostomus commersonii and longnose sucker Catostomus catostomus were 21% more likely to enter the river at sunset and 25% less likely at midnight in comparison to midday. Entry rates of medium fish increased 6% for every 1 °C increase in river temperature, 4% for every 1 m 3 /s increase in river discharge from the day prior, and were reduced by 1% for every 10 cm increase in lake level. Understanding these processes in the tributaries of the Great Lakes is important to inform the fish passage solutions currently being developed for the Boardman River, and to inform management regulations for Great Lakes migratory fishes.

Michigan↗