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USGS2021

Remote ecological monitoring with smartphones and tasker

Researchers have increasingly used autonomous monitoring units to record animal sounds, track phenology with timed photographs, and snap images when triggered by motion. We piloted the use of smartphones to monitor wildlife in the Riverside East Solar Energy Zone (California) and at Indiana Dunes National Park (Indiana). For both efforts, we established remote autonomous monitoring stations in which we housed an Android smartphone in a weather-proof box mounted to a pole and powered by solar panels. We connected each smartphone to a Google account, and the smartphone received its recording/photo schedule daily via a Google Calendar connection when in data transmission mode. Phones were automated by Tasker, an Android application for automating cell phone tasks. We describe a simple approach that could be adopted by others who wish to use nonproprietary methods of data collection and analysis.

California, Indiana↗
USGS2021

Embracing ensemble species distribution models to inform at-risk species status assessments

Conservation planning depends on reliable information regarding the geographic distribution of species. However, our knowledge of species' distributions is often incomplete, especially when species are cryptic, difficult to survey, or rare. The use of species distribution models has increased in recent years and proven a valuable tool to evaluate habitat suitability for species. However, practitioners have yet to fully adopt the potential of species distribution models to inform conservation efforts for information-limited species. Here, we describe a species distribution modeling approach for at-risk species that could better inform U.S. Fish and Wildlife Service's species status assessments and help facilitate conservation decisions. We applied four modeling techniques (generalized additive, maximum entropy, generalized boosted, and weighted ensemble) to occurrence data for four at-risk species proposed for listing under the U.S. Endangered Species Act ( Papaipema eryngii, Macbridea caroliniana, Scutellaria ocmulgee, and Balduina atropurpurea ) in the Southeastern United States. The use of ensemble models reduced uncertainty caused by differences among modeling techniques, with a consequent improvement of predictive accuracy of fitted models. Incorporating an ensemble modeling approach into species status assessments and similar frameworks is likely to benefit survey efforts, inform recovery activities, and provide more robust status assessments for at-risk species. We emphasize that co-producing species distribution models in close collaboration with species experts has the potential to provide better calibration data and model refinements, which could ultimately improve reliance and use of model outputs.

Arkansas, Florida, Georgia, Missouri, North Caroli↗
USGS2021

Filling knowledge gaps for a threatened species: Age and growth of Green Sturgeon of the southern distinct population segment

The Green Sturgeon Acipenser medirostris is an anadromous, long-lived species that is distributed along the Pacific coast of North America. Green Sturgeon is vulnerable to global change because of its sensitive life history (e.g., delayed maturation) and few spawning locations. The persistence of Green Sturgeon is threatened by habitat modification, altered flows, and rising river temperatures. In 2006, because of persistent stressors, the U.S. Endangered Species Act listed the southern distinct population segment as threatened. Despite increased research efforts on this species after the listing, substantial gaps in basic population information for Green Sturgeon remain. We present the only published information on age structure and growth of a threatened population of Green Sturgeon. By analyzing archived fin rays collected from 1984 to 2016, we revealed highly variable growth among individuals. We detected several age classes from 0 to 26 y and found similar growth rates of southern distinct population segment Green Sturgeon compared with northern population Green Sturgeon. Although limited, this analysis is an important first step to understanding Green Sturgeon population dynamics and highlights critical research needs.

California, Oregon, Washington↗
USGS2021

Slow recovery of headwater-stream fishes following a catastrophic poisoning event

Accidental spills of chemicals and other pollutants can decimate populations of stream-dwelling species. Recovery from such accidents can be relatively fast and complete when the affected stream reaches can be recolonized from upstream and downstream sources. However, faunal recoveries from accidental spills that extirpate populations from entire headwater streams have not been extensively documented, and understanding resilience of headwater-stream biota is relevant for assessing threats to at-risk species. We assessed recovery of fish populations in a 5.7-km long headwater stream in the southeastern United States following a complete, or nearly complete, fish-kill caused by a chemical spill near the source of the stream. We sampled for fishes at five stream locations, two downstream and three upstream from a perched, culverted road-crossing located 2.4 km upstream from the stream mouth, over a period of 18.5 months following the poisoning event. We observed 11 fish species, representing <65% of the fish species expected based on occurrences in nearby tributary streams. In post-poisoning sampling, only three of these taxa were observed upstream of the culvert; all 11 species, including the federally threatened Cherokee Darter Etheostoma scotti, were found downstream of the culvert but were mostly represented by a few, large individuals. In contrast, dead individuals of at least eight taxa including the Cherokee Darter were observed upstream of the culvert at the time of the fish-kill. These observations provide evidence of slow recovery of a headwater fish fauna, and especially upstream of a barrier to fish movement, where the recolonization sources are primarily downstream. Additional case studies may reveal whether this result applies generally to headwater streams. Slow recovery could make species that primarily inhabit or maintain greatest abundances in headwaters, including multiple at-risk fishes, particularly vulnerable to the threat of accidental spills that result in local population extirpation.

Journal of Fish and Wildlife Management↗
USGS2021

Gonad size measured by ultrasound to assign stage of maturity in Burbot

We measured gonad size (diameter and circumference) by ultrasound and used it as a metric to assign stage of maturity in Burbot Lota lota from Lake Roosevelt, Washington. We collected paired gonad tissue and ultrasound measurements monthly from November 2017 to March 2018 and processed gonad tissue for histological analysis to confirm stage of maturity. We measured gonad diameter and circumference by ultrasound. We also measured excised gonad diameter (i.e., true gonad diameter) by digital calipers and excised gonad circumference (i.e., true gonad circumference) by a measuring tape. All late vitellogenic (stage 6) ovaries measured by ultrasound had a diameter greater than 3.90 cm, suggesting a value of 3.90 cm or greater may be used to characterize females capable of spawning in the current reproductive cycle. One mid-spermatogenic (stage 3) and all ripe (stage 4) testes were too large to be measured and were assigned a diameter of 5.11 cm, the maximum value capable of being measured by our ultrasound transducer. A value of 5.11 cm or greater may be used to characterize males capable of spawning in the current reproductive cycle. Testis circumference measured by ultrasound is not reported because some testes were wider than the ultrasound transducer and could not be measured. Measurements of testis diameter did not differ between measurement methods (ultrasound versus true), but ultrasound measurements of ovary diameter and circumference were higher than true measurements. We attributed the difference between measurement methods to flattening of the ovary while applying the ultrasound transducer. Gonad diameter and circumference measured by ultrasound were highly correlated with gonadosomatic index and ovarian follicle diameter, indicating gonad size measured by ultrasound is an appropriate index of gonad development in Burbot.

Washington↗
USGS2021

Selection of habitat-enhancing plants depends on predator-prey interactions

Shallow areas of drawdown reservoirs are often devoid of adequate fish habitat due to degradation associated with unnatural and relatively invariable cycles of exposure and flooding. One method of enhancing fish habitat in these areas is to sow exposed shorelines with agricultural plants to provide structure once flooded. It remains unclear if some plants may be more suitable than others to provide effective fish habitat. To determine the fish habitat potential of various crops, we performed a replicated tank experiment evaluating the selection of agricultural plants by prey and predator fishes with and without the presence of the other. We submerged diverse treatments of potted plants in outdoor mesocosms stocked with prey and/or predator fish and monitored selection of plant species, stem density, and stem height over 0.5-h trials. Prey fish selected the densest vegetation, and selection was accentuated when a predator was present. Predators selected the second highest stem density and were more active when prey were present. Prey schooling was increased by predation risk, suggesting that cover was insufficient to outweigh the advantages of increased group size. Our data indicate that the perception of cover quality is reciprocally context dependent on predator–prey interactions for both predator and prey. Applications of the two most selected plant treatments in this study could enhance structural habitat for both predator and prey fishes in reservoirs, adding to their already reliable functionality as supplemental forage crops for terrestrial wildlife.

Journal of Fish and Wildlife Management↗
USGS2021

Catch rates for sturgeon chubs and sicklefin chubs in the Upper Missouri River 2004–2016 and correlations with biotic and abiotic variables

A multiweek standardized sampling regime during 2004–2016 in a 60-km reach of the Upper Missouri River assessed reproduction and catch rates for Sturgeon Chub Macrhybopsis gelida and Sicklefin Chub Macrhybopsis meeki . We sampled age-0 Macrhybopsis (primarily Sturgeon Chubs, but potentially including Sicklefin Chubs) all years to indicate successful reproduction, but noted an inverse correlation of catch per unit area (CPUA) with year. There was an inverse correlation for CPUA of age-1+ Sturgeon Chubs with year. There was no correlation for CPUA of age-1+ Sicklefin Chubs with year, but we noted a depression in CPUA during 2010 and 2012. The study reach includes restoration directives for federally endangered Pallid Sturgeon Scaphirhynchus albus , with 245,000 hatchery-origin Pallid Sturgeon (HOPS) stocked since 1998 to supplement the declining wild stock. Pallid Sturgeon longer than 350 mm fork length transition to piscivory and are known to prey on Sturgeon Chubs and Sicklefin Chubs. We examined the hypothesis that mass additions of HOPS to the existing predator community could have population-level effects on the two chub species. Population modeling for the stocked HOPS through time yielded estimates of nearly 1,300 piscivore-sized HOPS in 2004, an increase to 26,000 HOPS in 2012, and decreasing numbers through 2016 (14,500). A negative correlation between HOPS abundance and age-0 Macrhybopsis CPUA had the best support among other candidate variables (discharge, water temperature, catch rates of Sauger Sander canadensis ). We found an inverse correlation for CPUA of age-1+ Sturgeon Chubs and estimated HOPS abundance, and there was also evidence of an inverse association between age-1+ Sicklefin Chub CPUA and HOPS in the study area. Results for a 60-km reach of the Upper Missouri River suggest declining CPUA for age-0 Macrhybopsis and Sturgeon Chubs during 2004–2016 and modest recovery of Sicklefin Chubs after 2012. Although causative factors driving CPUA changes through time are not known, correlative analyses suggest that large numbers of HOPS added to the Missouri River predator community potentially influence CPUA of Sturgeon Chubs and Sicklefin Chubs in the study area. Testing this hypothesis will require expanded quantification of chub populations and HOPS numbers through time.

Montana, North Dakota↗
USGS2021

Factors influencing the post-release movements of translocated fishers: Implications for translocation success

Long distance, post-release movements of translocated wildlife can be a key factor limiting translocation success. Yet, for many species, we have little or no understanding of factors that influence post-release movements. Translocations have been important for recovering fisher Pekania pennanti populations across the southern portion of their North American range. However, little is known about the post-release movements of translocated fishers and how these movements may be influenced by demographic or translocation-process factors. To restore fishers in Washington State, we moved 90 fishers from central British Columbia and released them at nine sites in the Olympic Fisher Recovery Area on the Olympic Peninsula of Washington from 2008 to 2010. We evaluated post-release movements of 48 fishers to determine both the distance and duration of movements prior to home range establishment. Fishers moved extensively following their release. Multi-model selection indicated a high level of support for the hypothesis that post-release movements differed by fisher sex and age; whereas, year of release had no apparent effect on movements, and release date had only a marginal influence on male movements. Mean distance (± 95% CI) from a release site to a home range was greater for adult males (62.0 ± 19.6 km) than for juvenile males (31.4 ± 16.0 km), adult females (30.9 ± 21.1 km), and juvenile females (29.0 ± 13.5 km). Mean number of days from release until home range establishment was similar for the sexes, however the variance in movement duration was greater for females. Twenty-six of 27 females established home ranges over an 11-month period (December-October), while 19 of 21 males did so within a 4-month period (April-July). Mean home range sizes differed between males (128.3 ± 21.1 km2) and females (63.5 ± 9.0 km2) and were among the largest reported for the species. A greater proportion of females (18 of 27; 67%) than males (8 of 21; 38%) established home ranges within or partially within the recovery area. Six females left a previously established home range during the breeding season, presumably to find breeding males. Given the large distances that fishers can move following release, translocation success could be furthered by releasing individuals at fewer sites in the interior of large reintroduction areas to facilitate greater exposure to a recovery area and greater opportunity to interact with conspecifics and potential mates.

Washington↗
USGS2022

Limited land base and competing land uses force societal tradeoffs when siting energy development

As human populations grow, decisions regarding use of the world's finite land base become increasingly complex. We adopted a land use–conflict scenario involving renewable energy to illustrate one potential cause of these conflicts and resulting tradeoff decisions. Renewable energy industries wishing to expand operations in the United States are limited by multijurisdictional regulations in finding developable land. Interest groups entreat industries to avoid land for various reasons, including avoidance of prime wildlife habitat in accordance with an “avoidance-first” mitigation strategy. By applying a uniform set of rules for renewable energy facilities to the Prairie Pothole Region and portions of the Northern Great Plains, we evaluated the effects of regulations and avoidance of prime wildlife habitat on the amount of land available for development. In our scenario, existing regulations excluded 39% of the project area from potential development, with human infrastructure accounting for 30% (10–66% among states), whereas federally protected species accounted for < 1% at project area and state levels. Unregulated lands accounted for 61% of the project area, with conservation areas predicted as high-quality sites for breeding grassland birds and waterfowl and for migrating whooping cranes Grus americana accounting for 19% within the project area (6–27% among states). This model demonstrated a limited land base available for new development when accounting for regulations and concerns of a subset of societal interest groups. Additional interest groups likely will have different and competing concerns, further emphasizing the complexity of future land-use decisions as the available land base for development diminishes.

Journal of Fish and Wildlife Management↗
USGS2022

Comparison of two detection methods of a declining rodent, the Allegheny woodrat, in Virginia

Allegheny woodrats Neotoma magister are an imperiled small mammal species most associated with emergent rock habitats in the central Appalachian Mountains and the Ohio River Valley. The monitoring of populations and their spatiotemporal distributions typically has relied on labor-intensive livetrapping. The use of remote-detecting cameras holds promise for being an equally or more effective method to determine species presence, although trap-based captures permit the estimation of other parameters (e.g., survival, population size, site fidelity). In 2017, 2018, and 2020 we compared standard livetrapping with paired cameras for determining site occupancy of Allegheny woodrats in the central Appalachian Mountains of western Virginia. We further examined the influence of baited vs. unbaited cameras at several sites of confirmed occupancy in 2019. We observed that the detection probability using cameras was approximately 1.7 times that of live traps. Also, detection probability at baited camera traps was 1.3–2.0 times that of unbaited camera traps. Estimates of occupancy ranged from 0.44 to 0.49. Our findings suggest that the use of baited remote-detecting cameras provides a more effective method than livetrapping for detecting Allegheny woodrats. Our study provides a framework for the development of a large-scale, long-term monitoring protocol of Allegheny woodrats with the goals of identifying changes in the distribution of the species and quantifying local extinction and colonization rates at emergent rock outcrops and caves throughout the species' known distribution.

Virginia↗
USGS2022

How effective is the Birdsbesafe® cat collar at reducing bird mortality by domestic cats?

The global decline of songbird populations is a well-recognized conservation issue. Domestic cats kill an estimated 2.4 billion birds each year in the United States alone—more than most other anthropogenic threats combined. As many pet owners are reluctant to keep their cats inside, collar-mounted antipredation devices for domestic cats may be an important conservation tool. We examined the effectiveness of the Birdsbesafe® collar cover (BCC), a sleeve of brightly patterned fabric worn over a typical breakaway collar. The BBC's designers intend for the collar's bright colors to alert potential prey to the cat's presence. By combining data from two studies in New York (2014 and 2019) and one in Florida (2019), all of which used similar methods, we tested the hypothesis that the BCC effectively reduces avian mortality caused by cats of different ages and sexes in different hunting environments. We tested 94 cats over a 12-wk period in New York in 2014 or 8-wk periods in Florida and New York in 2019 during the bird breeding seasons; cats alternated 2-wk periods with and without the collar. Across studies, we recovered 2.7 times fewer birds per cat with the BCC than without ( P = 0.006). The BCC was more effective at a temperate latitude than a subtropical one ( P = 0.047). There was no difference in the effectiveness of the BCC for cats of varying ages, sexes, or hunting environments. Our results suggest that the BCC could be one tool within a larger effort to decrease domestic cat predation of songbirds.

Florida, New York↗
USGS2022

Annual summer submersed macrophyte standing stocks estimated from long-term monitoring data in the Upper Mississippi River

System-scale restoration efforts within the Upper Mississippi River National Wildlife and Fish Refuge have included annual monitoring of submersed aquatic vegetation (SAV) since 1998 in four representative reaches spanning ∼ 440 river kilometers. We developed predictive models relating monitoring data (site-scale SAV abundance indices) to diver-harvested SAV biomass, used the models to back-estimate annual standing stock biomass between 1998 and 2018, and compared biomass estimates with previous abundance measures. We modeled two morphologically distinct groups of SAV with differing sampling efficiencies and estimated each separately: the first category included only wild celery Vallisneria americana, which has long, unbranched leaves and dominates lotic environments, while the second category included 17 branched morphology species (e.g., hornwort Ceratophyllum demersum and Canadian water weed Elodea canadensis ) and dominates lentic environments. Wild celery accounted for approximately half of total estimated total biomass in the four reaches, combined branched species accounted for half, and invasive species (Eurasian watermilfoil Myriophyllum spicatum and curly-leaf pondweed Potamogeton crispus ), a fraction of the branched species, accounted for < 1.5%. Site-scale SAV estimates ranged from 0 to 535 g·m −2 (dry mass). We observed increases in biomass in most areas between 1998 and 2009 and substantial increases (e.g., from < 10 g·m −2 to ∼ 125 g·m −2 ) in wild celery in extensive impounded areas between 2002 and 2007. Analyses also indicate a transitional period in 2007–2010 during which changes in biomass trajectories were evident in all reaches and included the start of a 9-y, ∼ 70% decrease in wild celery biomass in the southernmost impounded area. Biomass estimates provided new insights and illustrated scales of change that were not previously apparent using traditional metrics. The ability to estimate biomass from Long Term Resource Monitoring data improves conservation efforts through better understanding of changes in habitat and food resources for biota, improved goal setting for restoration projects and improved quantification of SAV-mediated structural effects such as anchoring of sediments and feedbacks with water quality.

Illinois, Iowa, Minnesota, Wisconsin↗
USGS2022

Trace elements in blood of sea ducks from Dutch Harbor and Izembek Lagoon, Alaska

In 2001, we collected whole blood from sea ducks (Steller’s eider Polysticta stelleri, harlequin duck Histrionicus histrionicus, black scoter Melanitta nigra, and long-tailed duck Clangula hyemalis) wintering at Dutch Harbor, Alaska, and from Steller’s eiders molting at Izembek Lagoon on the Alaska Peninsula. Blood samples were analyzed for 19 trace elements, of which 17 were detected in one or more samples. In Steller’s eiders, mean concentrations of six trace elements (As, B, Fe, Hg, Se, Mo) were greater at Dutch Harbor and mean concentrations of four trace elements (Cr, Cu, Mg, Zn) were greater at Izembek Lagoon. Among sea ducks at Dutch Harbor, mean concentrations of five trace elements (Cu, Hg, Se, Zn, V) differed by species. Steller’s eiders had greater concentrations of Cu, Zn, and V in their blood, black scoters had the highest Se, and harlequin ducks had the highest Hg, with a mean concentration slightly above a threshold effect level. One Steller’s eider and one harlequin duck from Dutch Harbor had blood Pb levels above background concentrations. We have no observations to indicate that concentrations of these trace elements were associated with adverse effects.

Alaska↗
USGS2023

Natal contributions of Kokanee salmon to Flaming Gorge Reservoir, Wyoming–Utah: An evaluation using otolith microchemistry

In a system that uses supplemental stocking to enhance a fishery that serves a dual purpose, an understanding of the contributions from natural and hatchery-produced fish is important so that hatchery resources can be appropriately allocated. Kokanee Oncorhynchus nerka were first stocked in Flaming Gorge Reservoir (FGR), Wyoming–Utah, in 1963 and serve a dual purpose as a prey resource and sport fish. Although natural recruitment occurs in the reservoir, a supplemental stocking program was initiated in 1991. We sought to identify the natal origin (i.e., natural, hatchery) of kokanee in FGR using otolith microchemistry. We evaluated return to the creel, composition of spawning aggregates, and growth of kokanee in FGR and focused on differences associated with natal origin. We analyzed kokanee otoliths that we collected from hatcheries ( n = 60) and FGR ( n = 1,003) for the strontium isotope ratio, 87 Sr/ 86 Sr, using laser ablation and a multicollector inductively coupled plasma mass spectrometer. We conducted Kruskal–Wallis tests to compare the strontium isotope ratios from the otolith edge of kokanee that we sampled from hatcheries and FGR. Based on 87 Sr/ 86 Sr ratios, we could distinguish natural-origin kokanee from 11 of the 12 hatcheries ( P < 0.01); however, the Wigwam Hatchery was not significantly different from FGR ( P = 0.84). We used model-based discriminant function analysis to assign natal origins for kokanee caught in FGR. Hatchery contribution to the population at large varied from 21 to 50% among year classes from 2014 to 2018. The percentage of hatchery origin kokanee in the creel (18–50%) was similar to what we observed in the population. Hatchery-produced kokanee contributed a higher proportion to tributary-spawning aggregates (40–90%) than shoreline-spawning aggregates (19–58%) by sample year. Growth of natural and hatchery kokanee was similar, suggesting similar performance in the system. Results from this study identify that hatchery supplementation contributes to the population and recreational harvest of kokanee in FGR. This research also provides insight into the ecology of kokanee that is useful for better understanding kokanee population dynamics in reservoir systems.

Utah, Wyoming↗
USGS2022

Round Goby captured in a North American estuary: Status and implications in the Hudson River, New York

Round Goby Neogobius melanostomus , a nonnative fish species to North America, has been rapidly expanding through the connected waterways of the Laurentian Great Lakes. Herein, we document the eastward and southern expansion of Round Goby into the Hudson River, New York, an iconic coastal estuary that drains to Long Island Sound and the Atlantic seaboard. In summer and early fall 2021, routine fish monitoring conducted by the New York State Department of Environmental Conservation documented a population of Round Goby in the tidal portion of the Hudson River. Over the course of monitoring in 2021, personnel collected 112 Round Goby between Albany, New York, and Poughkeepsie, New York, with the southernmost collection occurring approximately 140 km downstream of invasion front as reported in 2020 within the New York State Canal System. Although Round Goby previously colonized large rivers and streams in the Great Lakes watershed, there is little information about the invasion success and ecological impacts of Round Goby in estuarine environments in North America. We discuss the distribution and biological characteristics of the Hudson River Round Goby population as well as the potential ecological implications and areas of future research and monitoring for this range expansion.

New York↗
USGS2023

Validating a non-lethal method of aging endangered juvenile Lost River and Shortnose Suckers

Populations of imperiled Lost River Deltistes luxatus and Shortnose Chasmistes brevirostris suckers in Upper Klamath Lake, Oregon, are experiencing long-term decreases in abundance due to limited recruitment of juvenile suckers into the adult populations. Researchers use estimated ages based on fin rays to study environmental factors affecting year-class formation, generate annual juvenile sucker survival indices, and study variations in early life history. Biased or imprecise age estimates can lead to erroneous conclusions and have implications for age-based survival estimates, indications of recruitment, and growth estimators. We examined fin rays collected from individual suckers captured on multiple occasions and determined that juvenile suckers deposit a translucent increment on fin rays annually. Size-at-age data for suckers first captured as young as age 0 corroborated our finding of annual increment formation and indicate that the first increments are formed at age 1. We used edge and marginal increment analysis conducted on fin rays to determine the timing of annual increment formation. Our results indicate that increment formation occurs on fin rays of juvenile suckers from October to May and peaks between February and April.

Oregon↗
USGS2024

Prioritizing imperiled native aquatic species for conservation propagation

Native aquatic species are in decline, and hatcheries can play an important role in stemming these losses until larger ecological issues are addressed. However, as more federal and state agencies face budget uncertainty and the number of imperiled species increases, it is necessary to develop a tool to prioritize species for conservation propagation. Our objective was to create prioritized lists of aquatic species that may benefit from conservation propagation for five states in the United States. Biologists developed an influence diagram and provided information for multiple attributes affecting prevalence of species. The influence diagram and information for each species was used in a Bayesian belief network to generate a score to prioritize propagation of a species and the feasibility of propagation. When all taxa were ranked together within a state, mussels, amphibians, and a crustacean were included among fishes in the top species that may benefit from propagation. We recognize that propagation is one tool for conservation of imperiled species and that additional factors will need to be addressed to ensure species persistence. Nevertheless, we contend our quantitative approach provides a useful framework for prioritizing conservation propagation.

Colorado, Kansas, North Dakota, South Dakota, Utah↗
USGS2024

Experimental assessment of egg mat gear retention and collection efficacy

Assessment of egg deposition is widely used to provide an index of spawning efforts for lithophilic spawning fishes. However, little is known about the collection efficacy and bias of fish egg collection methods. We conducted a two-phased study consisting of a simulated-river flume study (two-part design), and a field study (an egg drift comparison with capture on mats) to assess egg collection methods and evaluate egg retention and capture on egg mats. Lake whitefish Coregonus clupeaformis egg retention on seeded mats decreased with increasing velocity and walleye Sander vitreus egg retention was variable as velocity increased. Fewer lake whitefish eggs were collected on egg mats when limestone reef rock was present in the flume study during the simulated spawned trials, but the inverse was true for walleye. Similarly, during field collections more lake whitefish eggs were collected in benthic D-shaped frame (D-frame) drift nets set near a known spawning reef compared to egg mats set on the reef, indicating lake whitefish eggs were drifting downstream along the river bottom. In contrast, fewer walleye eggs were observed in D-frame drift nets compared to number of eggs captured on the egg mats. Therefore, egg mats are an informative tool for evaluating walleye egg deposition in an immediate area but may underestimate egg deposition of lake whitefish, especially in lotic systems. Compared to other egg collection methods in the current literature, our study indicates that egg mats are useful for assessing egg deposition by lithophilic spawning fishes, but that the collection and retention efficacy and bias of this gear may vary between species and habitat types.

Journal of Fish and Wildlife Management↗