Lake Trout Salvelinus Namaycush Research Articles

Don't count your eggs before they resorb: Early collection of ovarian follicles influences estimates of Lake Trout fecundity in Yellowstone Lake

AbstractObjectiveUnderstanding recruitment dynamics is necessary to predict population‐level responses to exploitation, management actions, or anthropogenic influences. Fecundity is commonly used as a metric of recruitment dynamics and can guide successful management of fisheries. However, an individual female's fecundity is not constant over time; females resorb ovarian follicles to regulate fecundity as they approach spawning. This suggests that sampling for fecundity too early may produce inaccurate estimates of relative fecundity. In Yellowstone National Park, suppression of invasive Lake Trout Salvelinus namaycush reduced the abundance of mature fish by 92% between 2012 and 2022. The continued efficacy of this suppression effort requires accurate assessments of reproductive potential of the population that remains.MethodsWe sought to determine whether the timing of ovarian follicle collection affected estimates of mean relative fecundity. We collected ovarian follicles from female Lake Trout, which are autumn spawners, between mid‐August and early October in 2021 and 2022. The number of ovarian follicles per sample was counted to obtain estimates of relative fecundity for each female.ResultWe observed a 13% decline in estimated mean relative fecundity between individuals that were sampled before mid‐September and those that were sampled after mid‐September.ConclusionOur data support strategic timing of fecundity sampling to best capture the true reproductive capability of a population, which is a key metric used in models that guide adaptive management of fishes.

Synthesis of recent research and attributes of recovered lean Lake Trout populations in Lake Superior, 1993–2022

AbstractObjectiveThis purpose of this paper is to describe the characteristics of recovered Lake Trout Salvelinus namaycush populations in Lake Superior by describing its population dynamics, ecology, and recent research and management activities since 1993, when Lake Trout were declared rehabilitated.MethodsData from commercial fisheries, recreational fisheries, agency stocking reports, and natural resource agency fishery‐independent survey data along with published research findings on lean Lake Trout in Lake Superior between 1993 and 2022 were synthesized and reported.ResultCurrently, Lake Trout populations are self‐sustaining and lightly exploited with only a few areas with elevated total mortality rates. The total annual mortality has been far below the target maximum range of 42–45%. Furthermore, stocking of hatchery Lake Trout is no longer necessary.ConclusionWe have learned from research and management experience that the regulatory role of Lake Trout in the Great Lakes is critical to proper ecosystem function. Thus, continued commitment from natural resource agencies to cooperate and implement effective management actions is required to preserve the accomplishments of lakewide recovery of Lake Trout populations.

Angling party persistence and visitation in a recreational Lake Trout fishery: Relative influence of travel distance and fuel costs

AbstractObjectiveCormack–Joly–Seber (CJS) mark–recapture analysis was used to estimate the effect of travel distance and fuel costs on angling party persistence (i.e., survival = probability of remaining in the Lake Trout Salvelinus namaycush fishery from year‐to‐year) and visitation (i.e., detection = probability of detection at the access point) over a 14‐year period (2006–2019) for the Lake Trout recreational fishery in Lake Opeongo, Ontario, Canada.MethodsBoat identification numbers, positioned near the bow and present by law, were used as “tags” in the CJS analysis. Complete trip creel interviews at the sole access point provided information on trip characteristics.ResultThe long‐term mark–recapture analysis of individual angling parties showed travel distance had a significant negative effect on party persistence among years and visitation within years. The distance effect was strongest for visitation, with visitation having a more negative relationship with distance than persistence. Persistence in the Lake Trout fishery was insensitive to fuel costs while the fuel cost covariate had a small though significant and negative effect on visitation. Time‐varying CJS models were ranked low with little model weight indicating the distance effect estimated for Lake Opeongo was a general phenomenon and not year dependent.ConclusionCormack–Joly–Seber mark–recapture analysis cleanly separated effects of travel distance and fuel cost between visitation versus persistence for Lake Trout angling parties. Prior to this analysis, travel costs were typically associated with visiting a recreational fishery, while here we have shown that travel costs can be associated with persisting as anglers in a fishery independent of visitation patterns. Long‐term monitoring of angling parties provides unique insights into angling patterns that can aid in travel cost estimation.

Lake Trout population dynamics in the Northern Refuge of Lake Michigan: Importance of stocking rate

AbstractObjectiveThe Northern Refuge of Lake Michigan was established under the auspices of the Great Lakes Fishery Commission in 1985 as an additional step toward restoring a self‐sustaining Lake Trout Salvelinus namaycush population to the lake. The overall goal of our study was to assess progress toward Lake Trout rehabilitation in the Northern Refuge through 2021.MethodsWe conducted annual (1992–2021) gill‐net surveys in the fall to assess the adult population and beam trawl surveys in the spring to assess naturally reproduced age‐0 Lake Trout.ResultSpawner abundance averaged 45 fish • 305 m of gill net−1 • day−1 during 1992–1999, just 4 fish • 305 m of gill net−1 • day−1 during 2000–2014, and then 67 fish • 305 m of gill net−1 • day−1 during 2018–2021. Sea Lamprey Petromyzon marinus wounding rate decreased by nearly 90% between the 2000–2014 and 2015–2021 periods. The average annual mortality rate of adult Lake Trout decreased from 43% during the 1990s and 2000s to 22% during 2015–2021. All of these population dynamics were partly driven by changes in Lake Trout stocking rates, which declined by roughly 50% during 1994–1996 but then increased roughly twofold during 2006–2010 and remained at this higher level during 2010–2018. In 2021, early signs of natural recruitment of Lake Trout became evident. Beam trawling during June 2021 yielded a wild age‐0 Lake Trout, the first ever caught since the surveys began in 1992. In addition, 15 (4% of total catch) of the Lake Trout caught in the fall 2021 gill‐net survey were unclipped (wild) fish. Estimated ages of these wild fish indicated that natural recruitment had begun sometime around 2015.ConclusionWith Alewife Alosa pseudoharengus abundance in Lake Michigan at record low levels, Sea Lamprey wounding rate greatly reduced, and Lake Trout spawner abundance at relatively high levels, the outlook for Lake Trout rehabilitation in the Northern Refuge holds promise.

Evaluation of the influence of correcting for gillnet selectivity on the estimation of population parameters.

Gill nets are a common sampling technique in inland and marine fisheries. However, gill nets are size selective and may result in bias estimates of population parameters. As such, selectivity is commonly assessed using indirect estimation techniques. Indirect estimates of gillnet selectivity have been suggested to improve estimates of important populations metrics (e.g., total annual mortality), but this assertion has not been assessed. In the current study, we simulated hypothetical populations of channel catfish Ictalurus punctatus, lake trout Salvelinus namaycush, walleye Sander vitreus, and white crappie Pomoxis annularis and sampled the populations based on published gillnet encounter and retention probabilities. Total annual mortality and von Bertalanffy parameters were then estimated using unadjusted (not "correcting" for selectivity processes) and adjusted ("correcting" for selectivity processes) age and(or) length data to evaluate the value of accounting for gillnet selectivity when estimating these metrics. Our results indicate that adjusting for retention and encounter probabilities rarely leads to improved estimates of total annual mortality, K, and L∞. For instance, estimates of annual mortality of lake trout based on age data adjusted for retention probability resulted in an overestimate of A by 14.4%. As such, we suggest that analysis of gillnet selectivity only be used when specific questions are being addressed (e.g., catch-at-age models) or in situation when all processes contributing to gillnet selectivity (e.g., contact probability, size-specific availability) are known.

Laboratory studies of fish entrainment sampling using a screw centrifugal impeller pump

AbstractObjectiveRegulatory legislation in both the United States and Canada requires water users with medium to high intake volumes to monitor entrainment losses to determine effects and to assess potential mitigation strategies to reduce harm to fish. Recent studies have recommended the use of both increased sampling frequency and sampling volume to characterize fish entrainment for large power plants on the Great Lakes. There is little doubt that increasing the flow rate and volume of water collected for sampling reduces the uncertainty in estimates of annual entrainment. Depending on the type of pump and the pumping flow rate used for entrainment sampling, considerable damage to fish larvae can occur. A screw‐type centrifugal pump has many qualities that make it ideal for entrainment sampling, but it has not yet been used as a sampling device for fish entrainment applications at power plants or other large industrial water users. The objective of this study was to determine mortality of entrainable fish eggs and larvae due to passage through a screw‐type centrifugal pump.MethodsIn a laboratory setting, Lake Trout Salvelinus namaycush eggs and larvae, Lake Whitefish Coregonus clupeaformis eggs, and Rainbow Trout Oncorhynchus mykiss juveniles were passed through a screw‐type centrifugal pump at three treatment flow rates: 39.5, 47.3, and 59.1 m3/h. Fish and eggs were monitored for mortality posttreatment and again at 24 and 48 h.ResultAcross treatments, very few mortalities were observed. Species specific moralities were four larval Lake Trout, one Lake Whitefish egg, and one juvenile Rainbow Trout. No mortality was observed for Lake Trout eggs.ConclusionThe present study identified high egg and larval survival (≥99%) after passage through a screw‐type centrifugal pump. High survival reduces error associated with identification and counting of entrained organisms, which provides more accurate estimates of annual entrainment losses.

Factors influencing egg thiamine concentrations of Lake Ontario lake trout: 2019–2020

In the Great Lakes region, thiamine deficiency is considered a recruitment bottleneck for lake trout Salvelinus namaycush and has been correlated with the consumption of non-native alewife Alosa pseudoharengus. While alewife, the most abundant forage fish in Lake Ontario, are the predominant prey for lake trout, they also consume benthic prey such as round goby Neogobius melanostomus. Because variation in the proportion of alewife in lake trout diets is linked to variation in egg thiamine concentrations, understanding how factors such as region of capture and hatchery-strain of lake trout influence diet, are key to understanding the patterns of variation in egg thiamine concentrations observed in this species. With recent increases in natural recruitment of lake trout being observed in the western region of the lake, understanding if egg thiamine is a potential driver is crucial to the rehabilitation of lake trout. In this study, we evaluated egg thiamine concentrations in lake trout during 2019–2020. We found no significant difference in egg thiamine concentrations among regions. However, a stocked Lake Superior deepwater morphotype (Superior Klondike Wild – SKW) showed significantly higher egg thiamine concentrations compared to the lean morphotype including Seneca (SEN) and Lake Champlain Domestic (LCD) strains. An analysis of fatty acid signatures of each hatchery-strain suggested that the SKW strain consumed a higher proportion of round goby than lean strains. Overall, these results suggest that morphotypic differences in the feeding ecology of lake trout can result in biochemical changes which may influence the effectiveness of restoration efforts.

Aerial Application of Organic Pellets Eliminates Lake Trout Recruitment from a Primary Spawning Reef in Yellowstone Lake

AbstractInvasive Lake Trout Salvelinus namaycush in the Yellowstone Lake ecosystem have been gillnetted since 1995 to suppress the population and allow for recovery of native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri. Although gillnetting is effective (Lake Trout population growth rate λ ≤ 0.6 during 2012–2022), the effort only targets free‐swimming, age‐2 and older Lake Trout. We developed a complementary suppression method using organic (soy and wheat) pellets to cause Lake Trout embryo mortality and reduce recruitment from spawning areas. The entire Carrington Island spawning reef (0.5 ha) was aerially treated with 3.56 and 3.00 kg/m2 of pellets in 2019 and 2020, respectively. Pellet decomposition caused dissolved oxygen concentrations to decline to lethal levels at 20 cm depth in the substrate, and pellets mostly dissipated from the reef within 12 d. Lake Trout fry trap CPUE was reduced to zero after ice‐off each spring after the treatments. Prior to the treatments, 71 fry were captured during 58 trap‐nights of effort in 2017–2019. After the treatments, no fry were captured during 273 trap‐nights in 2020 and 2021. Lake Trout CPUE in large‐mesh gill nets set near Carrington Island in September did not decline during 2017–2021 and fry were again trapped on the reef in spring 2022, suggesting that adults were not deterred from spawning there in the years after the pellet treatments. Complementary methods that increase mortality of prerecruits may allow for a reduction in gill‐netting effort and the long‐term costs of maintaining Lake Trout population suppression in Yellowstone Lake. Treatment of spawning areas may improve suppression efficiency for Lake Trout and invasive fish populations elsewhere because entire cohorts are targeted while immobile and temporarily concentrated in relatively small areas.

Rotenone induces mortality of invasive Lake Trout and Rainbow Trout embryos

AbstractObjectiveNonnative fish, including Lake Trout Salvelinus namaycush and Rainbow Trout Oncorhynchus mykiss, are actively invading lakes and streams and threatening Cutthroat Trout O. clarkii and other native species in the western United States. Programs have been implemented to suppress invasive trout using netting, trapping, electrofishing, angling, or other traditional capture methods. Because these methods are costly and primarily target older, free‐swimming life stages, development of new suppression methods that target embryos on spawning areas is desired to increase suppression efficacy and reduce long‐term costs.MethodsWe evaluated the capability of rotenone, N‐methylpyrrolidone, diethylene glycol ethyl ether, sodium chloride, calcium carbonate, and gelatin to induce mortality of Lake Trout and Rainbow Trout embryos in controlled laboratory experiments.ResultExposure to liquid and powdered rotenone formulations for 12 h at 4 mg/L caused 98% ± 0.7 (mean ± SE) and 99% ± 0.6 Lake Trout mortality, respectively. Exposure to liquid and powdered rotenone formulations for 12 h at 4 mg/L caused 62% ± 4.7 and 85% ± 3.2 Rainbow Trout mortality, respectively. N‐methylpyrrolidone, diethylene glycol ethyl ether, sodium chloride, calcium carbonate, and gelatin exposures were not effective at increasing embryo mortality of either species.ConclusionDeveloping embryos represent a vulnerable life history stage that can be exploited by targeted applications of rotenone. Incorporating novel suppression techniques that effectively increase mortality of embryos in an integrated pest management approach may enhance effective suppression of invasive fishes.

Combination of Acoustic Telemetry and Side‐Scan Sonar Advances Suppression Efforts for Invasive Lake Trout in a Submontane Lake

AbstractExpansion of an invasive Lake Trout Salvelinus namaycush population in Swan Lake, Montana, threatens a core area population of Bull Trout S. confluentus. Given the recent development of novel suppression methods, such as use of carcass analog pellets to cause high mortality of embryos, there was a need to quantify spawning season aggregation sites, site use, and spawning habitat for Lake Trout in Swan Lake. Acoustic tags were implanted in 85 Lake Trout during the summer in 2018 and 2019. Nightly tracking efforts during autumn in both years resulted in 1,744 relocations for 49 individual Lake Trout. Kernel density analysis was used to evaluate Lake Trout aggregation sites, identifying 10 distinct sites. All spawning sites were located in the littoral zone along areas of steep bathymetric relief, and these sites composed 48% of total relocations during both spawning seasons. In 2019, side‐scan sonar imaging was used to classify and quantify the total area of spawning substrate, which constituted 12.8% of the total surface area estimated for spawning sites 1, 6, and 9 and 11.4% of the total surface area for aggregation sites 2–5, 7, 8, and 10. Simultaneous treatment of all spawning sites would require 205,709 ± 86 kg of carcass analog pellet material, resulting in 370.4 ± 0.2 kg of phosphorus inputs and 7,487.9 ± 3.1 kg of nitrogen inputs to Swan Lake. Thus, pellet treatment would increase the Carlson's trophic state index (TSI) values from 20.8 to 27.7 for total phosphorus and from 22.1 to 26.2 for total nitrogen. Based on a TSI threshold of less than 40 for an oligotrophic lake, the use of carcass analog pellets could be feasible for supplementing the gill‐netting suppression of Lake Trout in Swan Lake.

Contemporary Growth and Survival of Stocked and Wild Lake Trout in Lake Champlain Evaluated Using Maxillary Age Estimates

AbstractThe population of Lake Trout Salvelinus namaycush in Lake Champlain has been sustained by stocking since 1973, but natural recruitment of wild fish has been observed since 2012. By 2020, continued recruitment and maturation of wild year‐classes indicated that updated population parameters were needed to assess and adjust management practices. Age estimation from historical methods (fin clips and scales) was undependable due to crowding of annuli in older fish and the inability to verify uncertain age estimates using a 5‐year fin clip rotation for older fish. We used maxillary bones to obtain precise and accurate age estimates for adult wild and stocked fish. In combination with preadult ages derived from fin clips and length–frequency analysis, we estimated the contemporary survival and growth of juvenile (age 2–3), early‐adult (age 3–4), and adult (age 5+) Lake Trout in Lake Champlain. The precision and accuracy of our maxillary age estimates were greater than or comparable to the precision and accuracy of otolith and maxillary age estimates of Lake Trout populations in the Great Lakes. Estimates of Lake Trout growth suggested that stocked and wild fish grew at different rates, with stocked fish having an early size advantage but ultimately reaching a similar maximum size. There were no significant differences in length–weight relationships between stocked and wild fish. Estimates of adult survival were slightly greater than range‐wide averages and well above recent estimates for stocked populations in the Great Lakes. Juvenile and early‐adult survival estimates were similar to each other and both far lower than adult estimates. Stocked and wild fish had similar survival rates in all age‐classes. Ultimately, the use of maxillary bones allowed us to make better estimates of contemporary population parameters necessary for informing management decisions.

Usefulness of Otolith Weight for EstimatingAge‐BasedLife History Metrics of Lake Trout

AbstractTo determine if otolith weight can be used to accurately and precisely estimate age‐based life history metrics of Lake TroutSalvelinus namaycushpopulations, we quantified relationships between Lake Trout otolith age and weight sampled from a wide geographic and size range of North American lakes. Separate nonlinear age–weight models for each of 22 surveys (each year within each area or lake) described 82.8% of variation in the relationship between otolith age and weight, whereas separate age–weight models for each of 13 lakes or areas within lakes (years combined) described only 0.4% less variation. Over all surveys, age increased at an average rate of 1.13 years per milligram increase in otolith weight and the otolith weight–age relationship was significantly nonlinear. Age of individual fish could not be estimated accurately from otolith weight alone, although bias of mean age estimated from mean otolith weight was small, whether using survey‐specific or general otolith age–weight relationships. Age at maturity and survival derived from indirect otolith age–weight relationships were estimated with less bias than growth parameters. We conclude that a general model for estimating Lake Trout age from otolith weight may be more useful for maturity and survival analyses that are less susceptible to estimation error of individual (often old) fish than for growth analysis that can be susceptible to estimation error of individual (often old) fish.

Inferred Trophic Characteristics and Ecological Roles of Native and Nonnative Fishes in Odell Lake, Oregon

AbstractIntroduction and establishment of nonnative fishes can negatively affect native species and ecosystems through a variety of ecological interactions. For example, competition between species that occupy a similar trophic guild can result in extirpation or reduced abundance of native fishes. We used a combination of standard sampling methods and stable isotope analysis to evaluate relative abundance and isotopic niche overlap among native and nonnative species in Odell Lake, Oregon. Our primary focus was on interactions between native Bull Trout Salvelinus confluentus and nonnative Lake Trout Salvelinus namaycush; however, we also evaluated relative abundance and isotopic niche characteristics of other native and nonnative species. Overall, the relative abundance of nonnative fishes was greater than that of native fishes. For example, Lake Trout outnumbered Bull Trout 27:1, and the numerically most dominant species in our sample was nonnative Tui Chub Siphateles bicolor. We also observed isotopic niche overlap among a variety of native and nonnative fishes. Bull Trout and Lake Trout are both top‐level predators in Odell Lake and the probability that Bull Trout were within the isotopic niche of Lake Trout was 0.23. The probability that nonnative kokanee Oncorhynchus nerka and Tui Chub were within the isotopic niche of native Mountain Whitefish Prosopium williamsoni exceeded 0.95, and the probability that Tui Chub were within the isotopic niche of Rainbow Trout O. mykiss was 0.90. Based on data presented here and rangewide patterns for Bull Trout, we conclude that competition with Lake Trout is plausible and has the potential to influence the persistence of Bull Trout in Odell Lake. Further, we discuss ecological interactions potentially influencing the abundance of other native fishes in Odell Lake.

Egg Hatchability and Egg Thiamine Concentrations in Lake Trout from the Northern Refuge of Lake Michigan

AbstractThe Northern Refuge of Lake Michigan was established in 1985 under the auspices of the Great Lakes Fishery Commission as part of an intensely managed effort to restore a self‐sustaining Lake Trout Salvelinus namaycush population to the lake. Despite the stocking of millions of Lake Trout into the refuge and survival of these stocked fish to adulthood, signs of natural recruitment by Lake Trout in the refuge have been very sparse. To ascertain whether low egg viability or poor fry survival could be limiting natural recruitment by Lake Trout in the refuge, hatching rates of eggs taken from Lake Trout caught in the Northern Refuge during October 2019 were determined in the laboratory. Moreover, survival rates of the hatched‐out fry were determined along with the thiamine concentrations in the fry. In addition, thiamine concentrations in eggs of ovulating Lake Trout caught in the Northern Refuge during 2019–2021 were determined. Egg hatching rate in the laboratory averaged 93%. Survival rate of Lake Trout fry up to 5 weeks after hatching averaged 97%. Mean (SE) thiamine concentrations in eggs of Lake Trout caught in 2019, 2020, and 2021 were 19.1 (3.6), 5.9 (1.3), and 6.2 (0.4) nmol/g, respectively; these levels are well above the threshold concentration of 2.3 nmol/g, above which the likelihood of experiencing mortality due to thiamine deficiency complex (TDC) is low. Thiamine concentrations in the Lake Trout fry at the end of the laboratory experiment averaged 11.2 nmol/g, and abnormal behavior in the fry was not observed. We conclude that TDC does not appear to represent a major impediment to Lake Trout rehabilitation in the Northern Refuge at present, although TDC may have contributed to the lack of detectable natural recruitment in the past.

A salt on your senses: influences of rearing environment on salinity preference and sensing in lake trout Salvelinus namaycush

A salt on your senses: influences of rearing environment on salinity preference and sensing in lake trout Salvelinus namaycush

Evaluation of post-stocking dispersal and mortality of juvenile lake trout Salvelinus namaycush in Lake Ontario using acoustic telemetry

Wild reproduction by stocked lake trout Salvelinus namaycush in Lake Ontario has yet to produce a self-sustaining population, requiring a reliance on stocking. Once released, age-1 juvenile lake trout are not typically surveyed until age-2, creating a gap in knowledge of fine-scale post-release behaviors. A method to track fine-scale movements and estimate mortality of juvenile lake trout could complement standard survey methods and benefit management decisions regarding stocking locations. We used acoustic telemetry to estimate post-stocking mortality and observe fine-scale spatial and temporal movements of 38 hatchery-reared, age-1 lake trout from an offshore stocking site in the eastern basin of Lake Ontario from 2017 to 2018. Cumulative post-stocking mortality was estimated at 5.3%, 10.5%, and 26.3% after one week, one month and one year, respectively. The majority of lake trout (68.4%) emigrated from the stocking location within two months and entered deep water (∼50 m) once warm-water incursions at the stocking site exceeded lake trout thermal preferences (15 °C). Lake trout made large movements (i.e., median 1.9 km, maximum 12.4 km straight-line distance) within the first hour post-release and had an average swimming speed of 1.64 km‧hr−1over the first day. There was no statistically significant relationship between total distance traveled and time of day, although distance traveled tended to be greater during crepuscular and dark periods compared to daylight. Our results provide a conservative estimate of post-release mortality and reveal behaviors of hatchery-reared juvenile lake trout that may be helpful when selecting stocking locations beneficial to restoration program goals.

First documentation of spawning by deepwater sculpins in the Great Lakes and potential impacts of round gobies

Deepwater sculpins Myoxocephalus thompsonii, formerly fourhorn sculpin M. quadricornis (marine form), inhabit all five Great Lakes. Deepwater sculpin is prey for lake trout Salvelinus namaycush and feeds on benthos. Populations have been declining with possible reasons being oligotrophication, quagga mussels (Dreissena bugensis), predation, and impacts of round goby Neogobius melanostomus competition or predation on eggs. Deepwater sculpins are thought to spawn during winter based on gravid females and appearance of larval fish in spring, but a male guarding a nest has not been documented. We used remotely operated vehicle technology during December 2015, March 2017, and March 2021 in 70–191 m in Grand Traverse Bay, Lake Michigan to identify the distribution of deepwater sculpins, round gobies, and nests with a guarding male. Round gobies were much more abundant (observations/hr = 139) in water < 125 m than were deepwater sculpins (11/hr), while in water > 166 m, deepwater sculpins were much more common (39/hr) than at shallow sites. At deep sites, round gobies were more abundant (51/hr) than deepwater sculpins (39/hr). On 16 March 2021 in 190 m of 1.9 C surface water we discovered several presumptive, unoccupied nests, but one nest in a depression next to a branch contained a deepwater sculpin and a clump of eggs. This is first evidence of where and how deepwater sculpins spawn. We also documented round gobies in the same area with one within 2 m of the nest, creating the possibility for consumption of eggs potentially affecting their long-term survival.

Accuracy and Precision of Otolith‐Derived Age Interpretations for Known‐Age Lake Trout

AbstractCatch‐at‐age data are used to inform important management decisions for recovering populations of Lake Trout Salvelinus namaycush. Age data for Lake Trout are commonly derived from interpretation of annual growth marks (annuli) on the fish’s otoliths. Due to the tendency for annuli to vary in appearance and the subjectivity that is inherent to any age interpretation method, it is important that the common sources of interpretation error be well understood for any aging method used to inform management plans. In this study, coded wire tags were used to establish true ages for 153 Lake Trout to measure the precision and accuracy of age interpretations made from transverse‐sectioned otoliths and to identify sources of potential age interpretation error that researchers and managers may encounter when using this method. Precision of age interpretations, as measured by average coefficient of variation, ranged from 7.9% to 9.2%. Accuracy of age interpretations varied among readers, with exact matches ranging from 41.8% to 53.6% and accuracy within ±1 year ranging from 81.0% to 83.0%. Age interpretation errors were more likely to be overestimates of true age for Lake Trout under age 7 and underestimates for Lake Trout over age 13. However, only reader 1 exhibited significant systematic bias in their age interpretations. Poor clarity of the first annuli, growth checks resembling annuli, and faintness of narrow annuli near otolith margins in older fish were identified as likely sources of interpretation error in this study. A digital reference collection of known‐age Lake Trout otoliths is provided as supplemental material in the online version of this article. This collection can be used for training new readers, measuring the accuracy of age interpretations, and monitoring for aging bias by anyone using otoliths to obtain age data for Lake Trout.

Quantifying the Spatial Structure of Invasive Lake Trout in Yellowstone Lake to Improve Suppression Efficacy

AbstractInvasive Lake Trout Salvelinus namaycush have altered the once‐pristine Yellowstone Lake ecosystem through top‐down effects by consuming Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri. To conserve Yellowstone Cutthroat Trout and restore the ecosystem, a Lake Trout gillnetting program was implemented to suppress the invasive population. We evaluated the spatial structure of Lake Trout in Yellowstone Lake with the intent of increasing suppression efficiency. Specifically, we addressed questions related to adult Lake Trout aggregation and movement during summer and autumn (spawning) periods and how Lake Trout used locations in the context of suppression efforts. We tracked 373 Lake Trout (&gt;500 mm TL) during the summer and autumn of 2016 and 2017. Based on kernel density estimates, Lake Trout were highly aggregated at 9 locations during summer and 22 locations during the spawning period. Using a novel metric, individual days (product of mean individuals per survey and mean length of stay), five summer locations and five spawning locations had at least 30 individual days. These locations are suggested as priority areas for targeting Lake Trout suppression. Lake Trout were less aggregated and moved less during the summer, making them less vulnerable to a passive gear in the summer than during the autumn spawning period. Lake Trout exhibited low spawning site fidelity compared to populations elsewhere, possibly due to decades of intensive gill netting at spawning locations. Given the aggregation and movement patterns observed in Yellowstone Lake, continuing to target adult Lake Trout during the spawning period is the most cost‐effective approach to Lake Trout suppression.

High prevalence of basin fidelity and homing by lake trout (Salvelinus namaycush) in a small northern lake

Identifying how habitat structure influences the spatiotemporal movements of fishes is important for conservation, population assessment, and management purposes. Here, we determined whether acoustically tagged lake trout (Salvelinus namaycush) from a 305 ha lake exhibited homing behaviour and lake basin fidelity over multiple seasons and years. The lake has two distinct deep basins (north and south) connected by a shallower centre basin. Fifteen lake trout captured during the spawning season from both deep basins were tagged and released in the south basin. All translocated north-basin fish quickly returned to the north basin (median = 1.85 days, range = 0.36–4.5 days), apart from one fish that returned 41 days post-release, while none from the south ventured into the north basin during this time. After translocated individuals returned, all fish demonstrated high basin fidelity among years, as &gt;90% of detections were from the same basin fish were captured, while &lt;0.7% (by three fish) were from the opposite deep basin and &lt;9% from the centre basin. The probability a fish was detected outside its basin of capture was highest in winter (15.9%) and fall (14.3%) and lowest in summer (0.41%).