Northern Pike Esox Lucius Research Articles

Counting fish at night using artificial light: transect survey of common bream Abramis brama and northern pike Esox lucius abundance as an example

AbstractVisual transect counting of large‐bodied fish using artificial light at night in a shallow littoral zone (<1 m water depth) is introduced as a complementary survey method for fishes such as common bream Abramis brama and northern pike Esox lucius that are under‐represented in standard gillnet surveys. The results suggest that transect counting at night and applying necessary corrections for environmental variables could provide a simple and repeatable method to assess the presence and abundance of large‐bodied fishes in lakes with satisfactory water clarity.

Native and non-native species response to the colonization and subsequent suppression of northern pike Esox lucius.

The expansion of northern Pike Esox lucius outside its native range into the western states of North America is a growing problem due to their negative effects on fish communities. Illegally introduced E. lucius were first detected in Box Canyon Reservoir in northeast Washington in 2004. By 2010, the E. lucius population was estimated at more than 10,000 individuals. Between 2012 and 2019, a gillnet suppression programme was conducted, which reduced the E. lucius catch per unit effort in Box Canyon Reservoir by 97% and their biomass by 98%. Between 2004 and 2019, four standardized surveys were conducted to characterize changes in the Box Canyon Reservoir fish community. Even after E. lucius were effectively suppressed, native species showed no signs of recovery during the study. The relative abundance of all native species decreased 82% in total number and 56% in total biomass between 2004 and 2019. Conversely, the relative abundance of non-native species increased 26% in total number and 33% in total biomass over the same period. As an apex predator, E. lucius had a significant impact on the fish community in Box Canyon Reservoir over a relatively short period of time (7 years), and appeared to act as a catalyst to increase the rate of replacement of native species with non-native species, which likely increased the pace of taxonomic homogenization in the reservoir.

Individual variability in the movement ecology of Northern pike Esox lucius in a highly connected wetland system

Maintaining hydrological connectivity is important for sustaining freshwater fish populations as the high habitat connectivity supports large-scale fish movements, enabling individuals to express their natural behaviours and spatial ecology. Northern pike Esox lucius is a freshwater apex predator that requires access to a wide range of functional habitats across its lifecycle, including spatially discrete foraging and spawning areas. Here, pike movement ecology was assessed using acoustic telemetry and stable isotope analysis in the River Bure wetland system, eastern England, comprising of the Bure mainstem, the River Ant and Thurne tributaries, plus laterally connected lentic habitats, and a system of dykes and ditches. Of 44 tagged pike, 30 were tracked for over 100 days, with the majority of detections being in the laterally connected lentic habitats and dykes and ditches, but with similar numbers of pike detected across all macrohabitats. The movement metrics of these pike indicated high individual variability, with total ranges to over 26 km, total movements to over 1182 km and mean daily movements to over 2.9 km. Pike in the Thurne tributary were more vagile than those in the Ant and Bure, and with larger Thurne pike also having relatively high proportions of large-bodied and highly vagile common bream Abramis brama in their diet, suggesting the pike movements were potentially related to bream movements. These results indicate the high individual variability in pike movements, which was facilitated here by their access to a wide range of connected macrohabitats due to high hydrological connectivity.

Loss of genetic variation and ancestral sex determination system in North American northern pike characterized by whole-genome resequencing.

The northern pike Esox lucius is a freshwater fish with low genetic diversity but ecological success throughout the Northern Hemisphere. Here, we generate an annotated chromosome-level genome assembly of 941 Mbp in length with 25 chromosome-length scaffolds. We then genotype 47 northern pike from Alaska through New Jersey at a genome-wide scale and characterize a striking decrease in genetic diversity along the sampling range. Individuals west of the North American Continental Divide have substantially higher diversity than those to the east (e.g. Interior Alaska and St. Lawrence River have on average 181 and 64K heterozygous SNPs per individual, or a heterozygous SNP every 5.2 and 14.6 kbp, respectively). Individuals clustered within each population with strong support, with numerous private alleles observed within each population. Evidence for recent population expansion was observed for a Manitoba hatchery and the St. Lawrence population (Tajima's D = -1.07 and -1.30, respectively). Several chromosomes have large regions with elevated diversity, including LG24, which holds amhby, the ancestral sex determining gene. As expected amhby was largely male-specific in Alaska and the Yukon and absent southeast to these populations, but we document some amhby(-) males in Alaska and amhby(+) males in the Columbia River, providing evidence for a patchwork of presence of this system in the western region. These results support the theory that northern pike recolonized North America from refugia in Alaska and expanded following deglaciation from west to east, with probable founder effects resulting in loss of both neutral and functional diversity (e.g. amhby).

Smallmouth Bass and Walleye predation on stocked age‐0 Walleye in Lake Oahe, South Dakota

AbstractObjectiveWalleye Sander vitreus are important sport fish that are commonly stocked to supplement populations. Increases in Smallmouth Bass Micropterus dolomieu abundance have prompted concerns regarding potential predation by these and other piscivores on stocked Walleye. Our objectives were to assess the timing and duration of predation on stocked Walleye, the frequency of occurrence and percent composition of Walleye in predator diets, and the percentage of stocked Walleye consumed.MethodsWe collected Smallmouth Bass, adult Walleye, Largemouth Bass M. nigricans, and Northern Pike Esox lucius diets in May (prestocking) and June–September (poststocking) 2019 and 2021 from three bays in Lake Oahe, South Dakota. We stocked two bays with Walleye (30–32 mm; 255–1649 Walleye/ha), whereas one bay was unstocked and served as a reference. We estimated Smallmouth Bass population abundance using Schnabel capture–recapture models, and we used bioenergetics to estimate the percentage of stocked age‐0 Walleye consumed.ResultWe found age‐0 Walleye in up to 11.4% of Smallmouth Bass diets and 14.6% of adult Walleye diets during the poststocking period. A single Largemouth Bass consumed one Walleye at 3 days poststocking (DPS), whereas we did not identify Walleye in Northern Pike diets. Daily mean percent composition by weight (±95% confidence interval) of age‐0 Walleye in diets peaked at 43.2 ± 35.1% at 3 DPS for Smallmouth Bass and 49.8 ± 97.7% at 14 DPS for adult Walleye. Following the peaks, age‐0 Walleye percent composition by weight rapidly declined and was generally 0% after 25 DPS. Smallmouth Bass abundance was 0.4–5.6 fish/ha, whereas recaptures of other predator species were insufficient for reliable population estimates. We estimated that Smallmouth Bass consumed 29,930 age‐0 Walleye in 2019 and 12,535 age‐0 Walleye in 2021 (up to 14.7 ± 4.7% of stocked fish), potentially representing an important source of stocking mortality.ConclusionOur research provides insights into the effects of poststocking predation on age‐0 Walleye by Smallmouth Bass and, to a lesser extent, Walleye, Largemouth Bass, and Northern Pike. Managers should consider predation on stocked fingerling Walleye from resident predators and should contemplate alternative stocking locations or timing to reduce potential predation.

Movements and habitat use of native and invasive piscivorous fishes in a temperate and channelized lowland river

AbstractLowland temperate rivers provide important habitats for piscivorous fishes, but with their year-round spatial and temporal habitat use is often poorly understood, including their use of off-channel habitats. Here, the movements and habitat use of the piscivorous native Northern pike Esox lucius and invasive pikeperch Sander lucioperca were investigated using acoustic telemetry in the highly regulated (through impoundment) lower River Severn, Western England over a 12-month period, where off-channel habitat availability was limited to a single boat marina. The movements of both species varied with season and temperature, with both species moving greater distances in spring. Increasing water temperatures up to 15 °C resulted in a higher frequency of movements of both species, but movements then decreased at temperatures higher than this. Northern pike detections in the river increased in periods of lower river discharge and warmer temperatures, with the off-channel refuge providing an important habitat all year round (78% of detections occurred there). While 63% of pikeperch detections also occurred in the marina, 89% of these detections occurred between December and April. These results thus emphasise the importance of this limited off-channel habitat as potential spawning locations for invasive pikeperch and foraging areas for native Northern pike.

Fatty acid composition of two small fish in the Gyda River (Kara Sea Basin, Northwestern Siberia, Russia)

The fatty acid composition of the flesh of rainbow smelt (RS, Osmerus mordax) and ruffe (RF, Gymnocephalus cernuus), two small fish species inhabiting the Gyda River (Siberia, Russia), was assayed using a gas-liquid chromatographic method with an ionization detection system and high efficiency capillary columns. RS was found to be richer in the total fatty acid content than RF (21.5 vs. 7.07 mg g–1). The proportion of saturated fatty acids (SFA) was similar in the fish studied (29.2 % in RS and 29.6 % in RF) whereas the flesh of RS contained a higher proportion of monounsaturated fatty acids, MUFA (42.2 vs. 13.9 %), and a lower proportion of polyunsaturated fatty acids, PUFA (28.6 vs. 56.5 %) than RF. RS is rich in essential n-3 PUFAs (2610 and 2390 μg g–1 for docosahexaenoic and eicosapentaenoic acids, respectively). In RF, the atherogenic index (0.39) and thrombogenic (0.20) index were lower than in RS (0.59 and 0.27, respectively). The fatty acid profile of RS in the study area differed from that reported for the flesh of this species from a Canadian estuary probably due to substantial differences in the diet of RS in these habitats. A comparison among fish species from the Gyda River indicated that in terms of nutrition indices, RS has the highest similarity with the muksun Coregonus muksun while RF is closely related to the northern pike Esox lucius. Based on the results from this study, both RF and RS can be recommended for human consumption. In particular, RS may be used as a replacement for muksun, an overfished species, in the traditional diet of indigenous peoples in northwestern Siberia.

Changes in Avian Top-Predator Diet in the 21st Century in Northeast (NE) Poland

The White-Tailed Eagle (WTE) Haliaeetus albicilla is a top avian predator that has rapidly increased in numbers and range in large parts of Europe in recent decades. In Poland, over the past 30 years, it has recolonized previously abandoned areas. In 1991, the first breeding pair in a large forest complex, the Augustów Forest (Northeast (NE) Poland), was recorded. In 2022, there were 13 breeding pairs. We analyzed changes in the diet composition of WTE in 2000–2023, divided into three periods: 2000–2005, 2009–2017, and 2018–2023. Throughout the 24 years of study, birds were the most frequently recorded food item, accounting for an average of 58% of food items, followed by fish (34%) and mammals (7%). During the study period, the most numerous food items were the Northern Pike Esox lucius, Coot Fulica atra, Common Bream Abramis brama, Mallard Anas platyrhynchos, and storks Ciconia sp. These species together accounted for 52% of food items. We recorded a long-term increasing share of Northern Pike, storks, and Great Crested Grebe Podiceps cristatus. Opposite changes, with declining frequency, were found for Coots and ducks. The share of the Coot, ducks, and Great Crested Grebe, as well as the total share of food connected with lakes in the WTE’s diet, increased along the growing area of lakes in the territory of the WTE. The proportion of fish in the food did not show a relationship with the increase in the area of lakes, while the most frequently eaten fish species changed. Observed changes in food composition appear related to the settlement of the habitat-diverse areas by individual breeding pairs and changes the availability of main food categories.

Biotic and abiotic factors that influence Walleye recruitment in stocked lakes in Michigan

AbstractObjectiveIn recent decades, widespread evidence of declining Walleye Sander vitreus recruitment in the Midwestern United States has raised concerns about diminishing ecological benefits and fishing opportunities, which in turn has resulted in natural resource agencies using stocking to supplement populations. Success of Walleye stocking events vary; thus, evaluating the external factors that influence recruitment success of Walleye resulting from stocking or natural production is critical for improved management.MethodsWe evaluated factors influencing the relative recruitment in 98 lakes stocked annually with Walleye by integrating 20 years of stocking data with fisheries assessment and abiotic data. We indexed recruitment as the relative abundance of Walleye cohorts from natural and stocked sources combined and used boosted regression tree modeling to identify variables that are associated with varying recruitment.ResultGrowing degree‐days at age 1, shoreline development index, mean depth, and degree‐days at age 2 were the most important variables. The boosted regression tree model explained 17% of observed variability in recruitment. A positive relationship between growing degree‐days and Walleye recruitment was observed, whereas shoreline development and lake depth had a negative relationship with recruitment. Secondarily important predictors were lake surface area, spring warming rate, Northern Pike Esox lucius abundance, and degree‐days at age 0. In general, Walleye recruitment was positively associated with these predictors, with the exceptions of spring warming rates >0.3°C/day and being exposed to >3500 degree‐days at age 0.ConclusionOur results indicate that thermal variables in addition to lake characteristics are important recruitment drivers in stocked waters and highlights the potential for resource managers to use this information to prioritize stocking efforts in temperate lakes.

Heavy Metal Content in Fish of the Barguzin River (Eastern Cisbaikalia) and Assessment of Potential Risks to Human Health

In this paper, the levels of nine heavy metals in the organs and tissues of six commercially important fish species from the Barguzin River (Eastern Cisbaikalia, Russia), bream Abramis brama, roach Rutilus rutilus, crucian carp Carassius carassius, common carp Cyprinus carpio, perch Perca fluviatilis and northern pike Esox lucius, were investigated. The distribution of HMs in the fish organs and tissues was unequal and was determined by both their physiological functions and routes of entry. The study also characterized the environmental habitats, including water and sediments, and conducted an assessment of potential risks to human health associated with fish consumption. The results showed that the levels of Fe, Zn, Cu, Ni, Cd, Pb, Cr and Hg in the muscle tissue of fish from the Barguzin River were generally low and did not exceed the maximum allowable concentrations established in Russia and worldwide. However, Mn levels in a number of samples exceeded the corresponding maximum allowable concentrations, which may be attributed to its elevated presence in the habitat. The calculated fish condition factor K showed good health status of fish from the Barguzin River. The highest Metal Pollution Index values were recorded for northern pike scales (5.9), which, however, corresponded to a low level of contamination. The other metal pollution index values for fish organs and tissues were all below five, indicating either no or very low contamination. Risk to human health was assessed using target hazard quotients and hazard index. None of these indices, both for each fish species studied and for each of the nine heavy metals, exceeded one. This indicated that consumption of the fish species studied did not pose an excessive risk of non-carcinogenic health effects to humans. The data on the content of nine heavy metals in the main commercially caught fish species from the Barguzin River indicated a low level of tissue and organ contamination by heavy metals and the absence of health risks to humans associated with their consumption as food.

Evaluation of cannibalism during hatchery rearing of tiger muskellunge crosses

AbstractObjectiveJuvenile tiger muskellunge (Northern Pike Esox lucius × Muskellunge E. masquinongy) are cannibalistic, which can lead to a substantial reduction in yields within an intensive culture environment. Utah hatcheries have traditionally raised the female Northern Pike × male Muskellunge cross, and hatchery managers are reluctant to raise the female Muskellunge × male Northern Pike due to a perceived difference (increase) in cannibalism rates when rearing this cross.MethodsWe raised both crosses in replicated microcosms to evaluate the differential cannibalism between them. All rearing conditions were consistent among treatments and replicates. We evaluated weekly cannibalism using generalized linear regression models.ResultAfter 6 weeks, we found that the female Muskellunge × male Northern Pike cross offspring were significantly more cannibalistic than juveniles from the female Northern Pike × male Muskellunge cross, with total cannibalism across the 6‐week period estimated at 27% and 5.6%, respectively.ConclusionWe documented a previously unreported difference in tiger muskellunge cross cannibalism rates. Choosing the female Northern Pike × male Muskellunge cross could substantially increase survival of juvenile tiger muskellunge in aquaculture facilities.

Coarse woody habitat use by local fish species and structural integrity of enhancements over time in a shallow northern boreal lake assessed in a Bayesian modelling approach

Abstract The introduction of coarse woody habitat has been a widely adopted management practice for restoring and enhancing freshwater aquatic ecosystems. Although responses of aquatic fish and invertebrate communities have largely been documented for lotic systems, benefits for lentic ecosystems have been mostly unevaluated. We tested the responses of fish populations to coarse woody habitat structures through a Bayesian modelling approach in a northern boreal lake in Alberta, Canada by enhancing a stretch of littoral zone with low structural complexity through introduction of coarse wood bundles and whole tree structures. The study site was split into three treatments, a Spaced treatment (structures 30 m apart), a Clustered treatment (structures 15 m apart) and an unaltered area (Control). Catch per unit effort and catch per unit area data were collected over 2 years and posterior model predictions showed an increase in habitat use of the enhanced areas by spottail shiner—Notropis hudsonius; northern pike—Esox lucius; white sucker—Catostomus commersonii; brook stickleback—Culaea inconstans. No probable effect on overall fish condition, measured in Relative Weight, was linked to the enhancements. Across the 2‐year study, wood bundles degraded faster compared to the whole tree drops, coinciding with levelling off catch per unit effort and catch per unit area predictions near wood bundles, although catch predictions increased near the whole tree structures. Structural degradation set in as early as 1 week post‐construction for wood bundles and was mostly related to anchoring aspects. Results from our study provide evidence for the benefits provided by coarse woody habitat within northern boreal lake systems. They furthermore highlight the short‐lived nature of wood bundles built with biodegradable substances. Methodologically our results offer evidence on the feasibility and utility of predictive modelling frameworks in addressing pseudoreplication and providing informative value for ecological studies.

Environmental abundances of the non-native round goby Neogobius melanostomus influence feeding of native fish predators.

The authors assessed the importance of the round goby Neogobius melanostomus as prey for three native predatory fish species, Atlantic cod Gadus morhua, European perch Perca fluviatilis and northern pike Esox lucius, in a northern and southern area of the Baltic Proper, using a combination of visual analysis and DNA metabarcoding of predator stomach contents. To explore the influence of environmental abundances of N. melanostomus on predation, they related the occurrence of N. melanostomus in predator diets to its abundance in survey fishing. Gadus morhua and E. lucius in the southern area showed the highest tendency to feed on N. melanostomus when it was abundant, as N. melanostomus occurred in up to 100% of stomachs and constituted up to 88% of the total diet volume proportion. The diet contribution of N. melanostomus was associated with N. melanostomus abundances for G. morhua and E. lucius, and when N. melanostomus was abundant, these predators exhibited lower prey richness and a higher degree of piscivory. G. morhua and P. fluviatilis also fed less on crustacean prey when N. melanostomus was abundant. The high importance of N. melanostomus in diets of native fish predators may modify indirect interactions between N. melanostomus and native prey species in invaded coastal communities.

Do angler catch and harvest rates differ between open water and ice anglers in Wisconsin?

Understanding seasonal differences in species-specific vulnerabilities to recreational angling can be important for informing sustainable fisheries management practices, like fishing seasons or season-specific regulations. However, comparisons of angler catch and harvest rates among seasons with disparate modes of fishing, like open water and ice angling in north-temperate lakes, are lacking. We used all available Wisconsin Department of Natural Resources point-intercept creel survey data during 1990–2020 to test for seasonal differences in the fisheries for five species targeted by open water and ice anglers in Wisconsin, USA, lakes (black crappie Pomoxis nigromaculatus, bluegill Lepomis macrochirus, northern pike Esox lucius, walleye Sander vitreus, yellow perch Perca flavescens). Specifically, we tested for: 1) species-specific differences in mean open water versus ice angling catch and harvest rates; 2) trends in species-specific mean open water versus ice angling catch and harvest rates during 1990–2020; and 3) monthly patterns in mean species-specific angler effort and catch rates. Mean angler catch rates of the five study species were significantly higher during the open water season and mostly temporally stable – only black crappie and bluegill open water catch rates and black crappie ice season catch rates significantly increased during 1990–2020. Mean angler harvest rates were significantly higher in the open water season for black crappie, bluegill, and walleye. Harvest rates were significantly higher during the ice season for northern pike and did not differ between seasons for yellow perch. Harvest rates were mostly temporally stable across species, although harvest rates declined for bluegill ice fishing and yellow perch in both seasons. Species-specific angler effort and catch rates mostly corresponded with seasonal (spring/early summer) vulnerabilities of our study species, although higher winter effort and catch rate patterns for northern pike and yellow perch may suggest unique harvest preferences for those species. Our results suggest that ice angling should not be assumed to have a negligible influence on fish populations in north-temperate lakes, fisheries-dependent and -independent monitoring data should be jointly considered when assessing fish population status, research on the human dimensions of ice fisheries is critically needed, and angler knowledge of seasonal fish vulnerabilities are generally coupled with higher fish catch rates.

Assessing Antipredator Behavior and the Potential to Enhance It in a Species of Conservation Concern

AbstractAnimal behavior has the potential to guide the management of populations at risk of extirpation. This includes insights into how animals respond to novel predators and whether those responses can be enhanced to improve survival. Training hatchery‐reared fish to recognize predators has been proposed as a way to reduce postrelease mortalities in the wild. Identifying the presence of innate predator recognition and the capacity for learning to recognize predators in specific species or populations can inform conservation management practices. Here, antipredator behavior (time spent moving and distance from a predator) and the efficacy of predator training were assessed for three populations of a species of conservation concern, the Arkansas Darter Etheostoma cragini, which is vulnerable to predation by esocid predators like the introduced Northern Pike Esox lucius. Arkansas Darters demonstrated some innate ability to recognize and respond to a novel esocid predator and also responded to predator cues (training), although the direction of the response to cues was opposite our prediction. Populations differed in their response to the predator treatment, highlighting the value of managing populations separately. Although the fitness consequences of exposure to predator cues remain to be tested in Arkansas Darters, our results suggest that antipredator behavior is innate and that exposure to predator cues does affect behavior; however, whether or how those behavioral changes affect survival is unclear. This study demonstrates the importance of testing enrichment practices and incorporating behavioral observations into conservation programs to guide population‐specific management decisions.

Fatty Acid Composition of Northern Pike from an Arctic River (Northeastern Siberia, Russia)

We assayed the fatty acid composition of muscles of the northern pike Esox lucius Linnaeus, 1758 inhabiting the Gyda River, Siberia, Russia using gas-liquid chromatography. Of 43 fatty acids identified in the pike samples, 23 fatty acids accounted for 99.3% of the total content. The most abundant saturated fatty acids (SFA, 31.6%) were palmitic (C16:0, 20.0%) and stearic (C18:0, 7.3%) acids. Among monounsaturated fatty acids (MUFA, 15.1%), oleic acid (C18:1n9, 10.2%) and palmitoleic acid (C16:1, 4.1%) demonstrated the highest levels. The most represented polyunsaturated fatty acids (PUFA, 53.3%) were arachidonic acid (C20:4n-6, 7.6%), eicosapentaenoic acid (EPA, C20:5n-3, 7.3%), and docosahexaenoic acid (DHA, C22:6n-3, 26.3%). The fatty acid profile of specimens from the Gyda River was different in comparison to profiles found in other pike populations, most likely due to different diets. Pike flesh has good nutrition quality in terms of a low n-6/n-3 ratio (0.36), low atherogenic (0.39), and thrombogenic (0.22) indices, and a high ratio of hypocholesterolemic to hypercholesterolemic fatty acids (2.83), and this species can be recommended as a replacement or alternative to other fish sources in traditional diets.

Interannual variability in the trophic niche of young‐of‐year fish belonging to four piscivorous species coexisting in a natural lake

Abstract Predatory fish species play a key role in aquatic ecosystems by exerting top‐down control on the food web. Also, their intra‐guild trophic interactions (i.e. competition) are crucial for the stability of the community. However, most studies focus on adult stages, while juveniles remain poorly studied, although their recruitment is the basis for the maintenance of predator populations. We analysed carbon and nitrogen stable isotopes ratios of the young‐of‐year of four coexisting widespread predatory fish species (northern pike Esox lucius, European perch Perca fluviatilis, pikeperch Sander lucioperca, and European catfish Silurus glanis), sampled over 3 years in a shallow natural lake. We found that the hierarchy in trophic position between species was consistent across years and similar to that known for adults, but with large variations around a general pattern: pike and pikeperch tended to occupy the highest trophic positions while perch occupied the lowest, and catfish had very varying positions. Species partitioned their niches to decrease interspecific competition, but with some occasional overlaps, contributing to preserving their body condition. Depending on density, which was particularly impacted by harsh environmental conditions, niche overlap fluctuated across years, leading to niche enlargement of densely populated species, except for catfish. These mechanisms enabled species coexistence, allowing the co‐occurrence of alien and native predators within the same ecosystem. This work advocates for time‐integrated studies of trophic webs because they capture the variability of their dynamics better than a static picture. This is particularly true for juveniles whose survival strongly depends on their capacity to cope with competition. Information from trophic mid‐term studies of juveniles provides valuable guidance for optimised management of species.

Stock Discrimination of Northern Pike Esox lucius L., 1758 Inhabiting Lakes Simenlik and Ladik (Samsun-Turkey) Using Otolith Biometry and Shape Analysis

This study was carried out to investigate the relationships between total length and otolith dimensions and to detect the otolith shape index values of Northern pike (Esox lucius) which has high economic value, sampled from Ladik and Simenlik Lakes. A total of 140 specimens (Lake Ladik: 82 individuals, Lake Simenlik: 58 individuals) were sampled. Otolith height, length, perimeter, and area were determined by Imaging Software. Nonlinear and linear models were applied to estimate the relationships between the otolith measurements and total length. Form factor, circularity, roundness, rectangularity, aspect ratio, and ellipticity were used for otolith shape analyses. It was found that the relationship between the total length-otolith length was found to have the highest r2 value (Lake Ladik r2=0.949, Lake Simenlik r2=0.914) among the total length-otolith morphometrics at both localities. Otolith shape indices were calculated by using otolith measurements. As a result of comparing shape indices, it was found that there was a significant difference in two localities using roundness, ellipticity, and aspect ratio (P <0.05). The results indicated otolith shape indices could be used as a suitable tool to discriminate Northern pike populations.

Fish and Zooplankton Community Responses to the Cessation of Long-Term Invasive Eurasian Watermilfoil (Myriophyllum spicatum) Chemical Treatments in a North-Temperate, USA Lake

2,4-Dichlorophenoxyacetic acid (2,4-D) is commonly used to control invasive aquatic macrophytes, including Eurasian watermilfoil (Myriophyllum spicatum) (EWM). Potential influences of 2,4-D on non-target organisms are poorly understood; however, research has suggested the possibility of lethal effects on certain fish species. Lake Ellwood, Wisconsin was treated with 2,4-D to control EWM annually during 2003–2012. Fish surveys following treatment revealed natural recruitment failures of several regionally thriving species, including largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus). We hypothesized that these species had been negatively influenced by the chemical treatments. We monitored the post-chemical treatment fish community and aquatic ecosystem for responses during 2013–2019. Similar data were collected from Cosgrove (EWM absent) and Seidel lakes (EWM present, no chemical treatment) as reference systems. Limnological and submersed aquatic vegetation conditions did not change on Lake Ellwood post-chemical treatment. Total zooplankton density increased immediately post-chemical treatment on Lake Ellwood and then stabilized, whereas total zooplankton density did not change on the reference lakes over time. Analyses indicated immediate increases in recruitment post-chemical treatment for largemouth bass, smallmouth bass (Micropterus dolomieu), bluegill, and yellow perch (Perca flavescens). Back calculation of year class strength confirmed failures occurred during treatment for northern pike (Esox lucius), largemouth bass, bluegill, and black crappie (Pomoxis nigromaculatus). Our results provide evidence to suggest long-term 2,4-D treatments may negatively influence fish through lethal and sublethal mechanisms. Thus, there remains a critical need for directed research on whole-lake herbicide treatment side-effects.

Environmental Cues of Spawning Migration into a Confined Wetland by Northern Pike and Common Carp in Lake Erie: Identifying Fine‐Scale Patterns

AbstractRestoration of wetlands in the Laurentian Great Lakes is designed to improve numerous ecosystem services including nutrient sequestration, support recreational uses, augment waterfowl habitat, and provide spawning and nursery habitat for fish. These projects often use Northern Pike Esox lucius, as a sentinel species for assessing restoration success because of their obligate use of emergent and submergent vegetation by the early life stages. However, invasive species such as Common Carp Cyprinus carpio also utilize these habitats and can have negative effects. Thus, fostering the use of these wetlands by Northern Pike and limiting access by invasive carp is a common restoration management concern. Using a dual frequency sonar system to observe fish migration in a recently connected Lake Erie coastal wetland, we were able to identify fine‐scale environmental correlates to immigration by each species during early spring. Both species overwhelmingly migrated during daylight hours and against the flow of water that was generated through seiche‐driven water oscillations. However, Northern Pike predominantly immigrated during the initial increase in water temperature immediately after ice‐out; Common Carp also began to enter the wetland at low temperatures shortly after ice‐out, but immigration exhibited a slow exponentially increasing pattern, such that the primary immigration timing differed by almost 30 d. Thus, we demonstrate common fine‐scale spawning migration patterns (i.e., water oscillation effects and time of day) for both species and reinforce the temperature‐correlated differences in spawning migration. Using these results could enable managers of connected wetlands to more precisely and dynamically manage habitat accessibility for desired species like Northern Pike while better regulating invasive Common Carp spawning migration and use of these systems.