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The premise of catch-and-release angling is that most fish survive fisheries interactions. Therefore, it is common for anglers, management agencies, and other organizations to share information on handling practices and other strategies that are believed to improve fish welfare and survival. Recent media coverage has sensationalized the use of carbonated beverages to treat bleeding fish, an intervention that is purported to stop bleeding but has yet to be validated scientifically. We captured Northern Pike (Esox lucius) via hook and line, experimentally injured their gills in a standardized manner, and treated them with either Mountain Dew, Coca Cola, or carbonated lake water and observed the duration and intensity of bleeding, as well as overall blood loss (using gill colour as a proxy) while the fish was held in a lake water bath. As a control, we had a group of experimentally injured fish that did not have liquid poured over their gills before the observation period. All treatments and the control were conducted at two different water temperatures (11-18 °C and 24-27 °C) to determine if the effects of pouring carbonated beverages over injured gills is temperature dependent. When compared to the control, we found that the duration and intensity of bleeding increased regardless of the type of carbonated beverages used in this study, and there was no effect of water temperature. Use of chilled versus ambient temperature beverages similarly had no influence on outcomes. As such, there is no scientific evidence to support the use of carbonated beverages for reducing or stopping blood loss for fish that have had their gills injured during recreational angling based on the context studied here. This study reinforced the need to scientifically test angler anecdotes and theories when it comes to best practices for catch-and-release fishing.

Minimum length limits (MLLs) combined with reduced bag limits are frequently used by fisheries managers to improve size-structure in Northern Pike Esox lucius populations. We evaluated the effectiveness of a relatively moderate 660-mm MLL and a two-fish-daily bag limit (hereafter, “moderate limit”) and a relatively conservative 813 mm MLL and one-fish-daily bag limit (hereafter, “conservative limit”) on size structure of Northern Pike in Wisconsin lakes. We used a before–after-control–impact design on a series of treatment and reference lakes to test the efficacy of each regulation. Across seven moderate-limit lake pairs, mean and mean maximum total length (i.e., mean of the 10 longest fish) in treatment lakes did not differ relative to reference lakes, where there was no MLL and a five-fish-daily bag limit (relatively liberal; hereafter, “liberal limit”). Across five conservative treatment lakes, there was a significant reduction in mean size relative to references, but mean maximum size increase...

Inundated floodplains, backwaters, and wetlands are important spawning habitats for many freshwater fish. In Midwestern North America and areas of northern Europe, the Common Carp Cyprinus carpio and Northern Pike Esox lucius inhabit many of the same watersheds and perform migrations to interconnected wetlands during the spring to spawn. In this study, the movement patterns of adult Northern Pike and Common Carp from lakes into adjoining wetlands were assessed in Minnesota to determine how and when these species moved, and if Common Carp might be blocked or trapped without disrupting the Northern Pike. Adult Northern Pike migrated over an extended several-week period starting early each March, when temperatures were greater than 4oC and when the fish were fully sexually mature (i.e., females were ovulated and running with eggs, and males were spermiating). In contrast, adult Common Carp migrated over relatively short time periods that lasted just a few days between April and June, and whose specif...

An important component of effective fisheries management is estimating fish ages. Age estimates can be used to estimate recruitment, relative abundance of age-groups, total mortality, and growth. Because of difficulty in estimating Northern Pike Esox lucius ages using scales and whole cleithra, we compared precision and bias of age estimates from whole cleithra, sectioned cleithra, metapterygoid bones, otoliths, and scales. Metapterygoid bones and sectioned cleithra represent two novel structures for estimating ages in North America, and the assessment of otoliths is limited. Complete agreement and consensus agreement rates were greatest for otoliths, sectioned cleithra, and metapterygoid bones. Otoliths provided the most precise age estimates and whole cleithra were the least precise. Consensus age estimates for sectioned cleithra were lower than whole cleithrum estimates. Consensus age estimates from sectioned otoliths were lower than mean age estimates from scales, sectioned cleithra, and whole...

Establishment of nonnative Northern Pike Esox lucius in Pactola Reservoir, South Dakota, has prompted concern among biologists about the influence of this species on the lake’s intensively managed salmonid fisheries. Ancedotal information suggests that catch rates of Rainbow Trout Oncorhynchus mykiss have declined while mean size and abundance of Northern Pike has increased, although quantitative information on diet and growth of the Northern Pike population is lacking. To address potential interactions between Northern Pike and Rainbow Trout, we assessed size-dependent predation by Northern Pike on Rainbow Trout and determined the relative energetic contribution of stocked Rainbow Trout to Northern Pike growth using bioenergetics modeling. Stable isotopes combined with traditional diet analyses revealed that smaller Northern Pike (

Age estimates based on calcified structures are central to the analysis and management of fish populations. A variety of structures have been used in studies of Northern Pike Esox lucius despite limited data on whether the structures provide comparable results. We quantified precision and bias of ages estimated from cleithra, otoliths, anal fin rays, and scales of Northern Pike sampled in tributaries of Green Bay, Lake Michigan. For three independent readers, the precision (CV) of age estimates did not significantly differ among otoliths, cleithra, and anal fin rays but was significantly lower for scales than for the other structures. Similarly, partial agreement among readers was greater than 90% for ages estimated from otoliths, cleithra, and anal fin rays, whereas partial agreement was 76% for scale-based ages. We discuss the tradeoffs associated with precision and bias for each structure in the context of reader experience, fish age, and management goals. We recommend that when fish mortality ...

In western North America, nonnative Brook Trout Salvelinus fontinalis in alpine lakes threaten the persistence of native trout and often offer limited sport fishing opportunity as they are prone to stunting. Stocking tiger muskellunge (Northern Pike Esox lucius × Muskellunge E. masquinongy), which are reproductively sterile, may be an option to eradicate Brook Trout in some alpine lakes. We used floating gill nets to survey 17 alpine lake Brook Trout populations, then stocked 13 lakes with tiger muskellunge, with four additional lakes serving as controls. Tiger muskellunge were stocked at a mean TL of 317 mm and a density of 40 fish/ha. Brook Trout were resampled for 4 or 5 years after stocking to evaluate changes in Brook Trout TL and CPUE (fish/net-night). Declines in CPUE were substantial for both treatment and control lakes but were significantly greater in treatment lakes. Mean Brook Trout CPUE in treatment lakes declined from 23.1 fish/net-night to 2.3 fish/net-night 5 years after stocking t...

In May 2007, viral hemorrhagic septicemia virus genotype IVb (VHSV IVb) was isolated from several fish species in Budd Lake, a 71-ha inland lake in central Michigan. Because of the virulence and pathogenicity of VHSV IVb, follow-up testing was conducted between 2007 and 2010. This testing found no further evidence of VHSV IVb presence. Similar patterns (i.e., initial mortality events followed by no evidence of additional infections) have been observed in other waterbodies, which leads to questions regarding the implications that these patterns could have for fisheries management (e.g., could stocking naive fish lead to additional epizootic occurrences?). This study was conducted to determine whether VHSV IVb was still present in Budd Lake by intensively sampling across multiple seasons, locations, and size-groups of Muskellunge Esox masquinongy, Northern Pike Esox lucius, and Largemouth Bass Micropterus salmoides. Individuals were tested for both active VHSV IVb infection and antibody production. ...

Westslope Cutthroat Trout Oncorhynchus clarkii lewisi in Coeur d’Alene Lake, Idaho, have declined in recent years; predation by Northern Pike Esox lucius, a nonnative sport fish, is thought to be a causative mechanism. The goal of this study was to describe the seasonal food habits of Northern Pike and determine their influence on Westslope Cutthroat Trout in Coeur d’Alene Lake by using a bioenergetics modeling approach. Fish were sampled monthly from March 2012 to May 2013 using pulsed-DC electrofishing and experimental gillnetting in four bays. Northern Pike catch rates from electrofishing were generally low but increased slightly each season and were highest in the southern portion of the lake; catch rates from gillnetting were approximately 50% higher during the two spring sampling periods compared with the summer and fall. Seasonal growth and food habits of 695 Northern Pike (TL = 16.2–108.0 cm; weight = 24–9,628 g) were analyzed. Diets primarily consisted of kokanee O. nerka, Westslope Cutth...

Oxytetracycline (OTC) immersion treatments were evaluated at the Waterville State Fish Hatchery (Waterville, Minnesota) for producing fluorescent marks on larval Northern Pike Esox lucius otoliths. A pilot marking trial conducted with 7-d-posthatch (dph) larvae resulted in poor mark efficacy and prompted further investigation on the treatment of younger larvae and modification of the treatment by use of osmotic induction to promote better mark formation. Northern Pike treated within 24 h post-hatch had significantly higher mark efficacies and marked otolith intensities than did Northern Pike treated at later life stages. Similar to the pilot marking trial, immersion of 7-dph fry in OTC solution resulted in poor mark efficacy, in which only 38% of the inspected fry possessed visible marks and most of the marks that were visible appeared faint. Simple immersion of newly hatched fry in OTC solution resulted in 91% marking success, and 65% of the visible marks appeared either clear or intense. The poo...

In order to project fishing effort and demand of individuals targeting Northern Pike Esox lucius in Minnesota, it is important to understand the catch orientations, management preferences, and site choice preferences of those individuals. Northern Pike are specifically targeted by about 35% of the approximately 1.5 million licensed anglers in Minnesota and by approximately 14,000–15,000 dark house spearers. Dark house spearing is a traditional method of harvesting fish through the ice in winter. Mail surveys were distributed to three research strata: anglers targeting Northern Pike, dark house spearing license holders spearing Northern Pike, and dark house spearing license holders angling for Northern Pike. Dark house spearers, whether spearing or angling, reported a stronger orientation toward keeping Northern Pike than did anglers. Anglers reported a stronger orientation toward catching large Northern Pike than did dark house spearers when spearing or angling. Northern Pike regulations were the ...

In Northern Pike Esox lucius negligible effects of external tags on growth and survival have commonly been reported, but no studies exist for age-0 fish. We tested the impacts of fin clipping, PIT tags, and three external tags (T-bar anchor, opercular, and streamer tags) on age-0 Northern Pike in a pond. We also examined the impacts of surgically implanted transmitters on small adult Northern Pike in a natural lake. The loss of PIT tags was lowest among all tags and close to 0%. Of the external tags, T-bar anchor tags performed best. Loss of these tags was initially low (on average 5.7% after 195 d) increasing to about 20.0% by 520 d posttagging. Tagging-induced mortality of a few percent was present in all tags tested within the first 195 d posttagging in the pond environment but not present afterwards. The PIT tags, fin clips, and external tags did not affect the growth or condition of surviving fish. Surgically implanted transmitters reduced the growth of small adult Northern Pike with total le...

We developed a gillnetting protocol by sampling 17 nonwadeable rivers across northern Ontario over the course of four summers from 2005 to 2008. The rivers represented a range of habitats; however, all had a coolwater to warmwater fish community characterized by walleyes Sander vitreus, northern pike Esox lucius, white suckers Catostomus commersonii, yellow perch Perca flavescens, and smallmouth bass Micropterus dolomieu. During the study, three net designs were used. Each net had one to four configurations that varied in height, length, monofilament diameter, and sequence of the mesh sizes. We found that most fish (87%) were captured in the lower half of 1.8-m-high gill nets and that there was no difference in catch between gill nets with serial panels (i.e., sequentially increasing mesh sizes) and those with randomly organized panels. Net that were set perpendicular to shore or angled to shore caught approximately twice as many fish as nets that were set parallel to shore. Contrary to expectati...

The relationship between mercury (Hg) concentrations in fish muscle and fish growth rates was assessed for 54 walleye Sander vitreus, 52 northern pike Esox lucius, and 35 lake trout Salvelinus namaycush populations throughout the Province of Quebec, Canada. We used the von Bertalanffy growth model to estimate the ages of fish specimens for a given length, and Hg concentrations in fish specimens at standardized length were determined via a quadratic regression model. Measured values of Hg concentrations in walleyes, northern pike, and lake trout were then correlated to the estimated age at standardized length for each population (375, 675, and 550 mm, respectively). A model-II regression was performed to describe the existing relationships. Growth rates were positively related to Hg concentrations in walleyes and northern pike (when three outliers were excluded), whereas no correlation was observed for lake trout. Our findings demonstrate that slower-growing walleyes and northern pike have higher ...

The effects of maximum, minimum, and slot length limits on the sizes and relative abundance of northern pike Esox lucius were evaluated in 22 Minnesota lakes. The regulations were implemented in 1989–1998 and lasted 9–15 years. As preregulation information was available back to the 1970s, the evaluation periods covered 21–37 years. Comparisons were made with reference populations from 47 ecologically similar lakes during the same extended period. Although the regulations did not achieve management objectives in every lake, the broader-scale, statewide finding was that they improved the size structure of northern pike populations but produced no consistent trends in relative abundance. The improvements were detected against the backdrop of reference populations that initially appeared to have similar sizes and relative abundances. Maximum length limits protecting fish over 20, 22, and 24 in produced significant long-term increases in the percentages of northern pike 24 in and longer and 30 in and ...

Because of its relatively natural hydrograph, the Yampa River, Colorado, is considered the crown jewel of native fish habitat in the upper basin of the Colorado River and has supported a relatively intact native fish assemblage. Nonnative fishes are thought to pose the greatest threat to native fishes in this system. Removal programs for nonnative northern pike Esox lucius and channel catfish Ictalurus punctatus have highlighted managers' perception of the threat posed by each species. Recent expansion of nonnative smallmouth bass Micropterus dolomieu in the Yampa River attracted an avid angling clientele but also coincided with a precipitous decline in native fishes, necessitating a rigorous assessment of the relative impact of all three nonnative predators on the native fishes. We used abundance, growth, and diet estimates for each predator species to quantify consumptive demand using bioenergetics models. Despite a low abundance of small-bodied fishes and thus a low number of fish in the small...

Introductions of nonnative northern pike Esox lucius have created recreational fisheries in many waters in the United States and Canada, yet many studies have shown that introduced northern pike may alter the composition and structure of fish communities through predation. We estimated the abundance of nonnative northern pike (2002–2003) and applied food habits data (1999–2003) to estimate their annual consumption of native bull trout Salvelinus confluentus and westslope cutthroat trout Oncorhynchus clarkii lewisi juveniles in the upper Flathead River system, Montana. Population estimates were generally consistent among years and ranged from 1,200 to 1,300 individuals. Westslope cutthroat trout were present in the diet of younger (≤600 mm) and older (>600 mm) northern pike during all seasons and bull trout were found only in larger northern pike during all seasons but summer. Bioenergetics modeling estimated that the northern pike population annually consumed a total of 8.0 metric tons (mt) of fi...

We examined the relationship between bait and lure size and type and body size, injury, and handling time for northern pike Esox lucius, an important recreational fisheries resource in much of North America and Europe. Bait type and size were significantly related to the size of fish captured and hooking location. Hooking in critical locations (i.e., gills, gullet) was more likely to occur with natural bait, soft plastic shads and jigs, and spoons than with spinners and wobblers (i.e., plugs). Small baits (

A generalized additive model was developed that described the effects of fingerling stocking density on the abundance of walleyes Sander vitreus in 551 lakes in Minnesota. Walleye abundance was measured as a catch per effort (CPE) from 1,511 standard Minnesota Department of Natural Resources gill-net assessments conducted during 1986–2004. In addition to fingerling stocking, the effects of lake morphometry, productivity, and fish community variables on walleye CPE were also described using a generalized additive model. Lake morphometry variables had sharply nonlinear effects on walleye abundance. Walleye abundance declined in lakes with areas less than 1,000 acres and increased rapidly in lakes with depths of less than 30 ft. The lake productivity variable, total alkalinity, was positively related to walleye abundance. Abundance of northern pike Esox lucius had a negative effect and abundance of yellow perch Perca flavescens a positive effect on walleye abundance. The response of walleye abundanc...

Variables associated with year-class formation in upper St. Lawrence River northern pike Esox lucius were examined to explore population trends. A partial least-squares (PLS) regression model (PLS 1) was used to relate a year-class strength index (YCSI; 1974–1997) to explanatory variables associated with spawning and nursery areas (seasonal water level and temperature and their variability, number of ice days, and last day of ice presence). A second model (PLS 2) incorporated four additional ecological variables: potential predators (abundance of double-crested cormorants Phalacrocorax auritus and yellow perch Perca flavescens), female northern pike biomass (as a measure of stock–recruitment effects), and total phosphorus (productivity). Trends in adult northern pike catch revealed a decline (1981–2005), and year-class strength was positively related to catch per unit effort (CPUE; R 2 = 0.58). The YCSI exceeded the 23-year mean in only 2 of the last 10 years. Cyclic patterns in the YCSI time ser...

New approaches are needed for sampling northern pike Esox lucius in the complex habitats they use as nursery areas. We evaluated the potential of Quatrefoil light traps to measure differences in density of larval and juvenile northern pike, and we monitored changes in capture probability as the fish grew in size and their swimming capabilities improved. In hatchery raceways, light traps were effective for collecting northern pike at densities that seemed most realistic relative to natural nursery habitat (4–20 fish/m2 surface area). Light-trap catch rates differentiated among different densities in raceways, but efficiency decreased as density increased. Light traps effectively caught all sizes of fish, ranging from the stage when larvae first became active (12–13 mm total length [TL]) until the fish became too large to fit through the trap entrance (>66 mm TL). We also tried to apply the technique for sampling managed wetlands that simulated a more natural environment than the raceways. Light-tr...

To assess the ecological consequences associated with the degradation of riparian wetlands that historically provided spawning and rearing habitat for northern pike Esox lucius, annual spawning migrations and genetic structure were used to examine this species' dependence on four specific spawning areas in the Thousand Islands region of the Saint Lawrence River. Tagging and recapture over three consecutive spawning seasons resulted in low return rates (ranging from 1.2% in bays to 8.3% in tributaries), and some exchange was observed between locations. Angler recaptures indicated that northern pike did not disperse widely; 72% were recaptured less than 2.5 km from their tagging location, though the remainder moved distances ranging from 2.5 to 18 km. Six microsatellite loci showed significant allele frequency differences and small but significant genetic differentiation (F ST) values among spawning sites in close proximity ( 20 km) were ...

We used a number of different data sets and four criteria to evaluate evidence of competition and predation between walleye Sander vitreus and northern pike Esox lucius, muskellunge E. masquinongy, smallmouth bass Micropterus dolomieu, and largemouth bass M. salmoides in northern Wisconsin lakes. The four criteria were as follows: (1) indices of population abundance were inversely related, (2) two species had shared resources or one species preyed on the other, (3) competition or predation was strong enough to produce a measurable effect, and (4) experimental manipulations produced results consistent with the hypothesis of competition or predation. Using these criteria, we identified which species interact most strongly with walleyes, determined the most likely mechanism for interaction (predation, competition, or both), and characterized the effects of walleye stocking on these species. Largemouth bass was the only species that strongly interacted with walleyes: (1) indices of largemouth bass an...

We sought to determine whether electrofishing catchability was density dependent and varied with physical and biological factors for walleyes Sander vitreus, largemouth bass Micropterus salmoides, smallmouth bass M. dolomieu, northern pike Esox lucius, and muskellunge E. masquinongy in Wisconsin lakes. Electrofishing catch rate (number of fish caught per shoreline mile) was linearly related to population density (number of fish per acre) in spring for largemouth bass, northern pike, and muskellunge and in fall for walleyes, largemouth bass, and smallmouth bass. In contrast, gear saturation caused the electrofishing catch rate to be nonlinearly related (hyperstable) to population density for walleyes and smallmouth bass during spring. Catchability was higher during spring than fall for walleyes, largemouth bass, and smallmouth bass. Catchability of walleyes during fall was positively related to the percentage of littoral zone, whereas catchability of largemouth bass, smallmouth bass, and muskellun...

Current guidelines with respect to the use of irrigation intakes limit Canadian operators to approach velocities (at the screen) of 3.8 cm/s; however, this value is based on relatively little data. To address this issue, I examined the ability of juvenile (2.3–7.4-cm fork length) northern pike Esox lucius to avoid impingement on irrigation intake screens under ambient environmental conditions in a swim tunnel (where water velocity was constant and uniform) and in a simulated intake where water velocity declined with distance from the test screen (as in real structures). The effects of impingement duration (in swim tunnel tests) and approach velocity (in both tests) on feeding and physical condition (abrasions, bruising, and scale loss) were also examined. Juvenile northern pike in the swim tunnel became impinged at speeds ranging from 10 to 28 cm/s. Injuries and mortalities from impingement up to 10 min in duration were nonexistent, although some short-term feeding disruptions were observed. Nort...

We investigated seasonal and 15-year trends in catch per unit effort (CPUE) and mean weight of black crappies Pomoxis nigromaculatus, ciscoes Coregonus artedi, northern pike Esox lucius, walleyes Sander vitreus (formerly Stizostedion vitreum), white suckers Catostomus commersoni, and yellow perch Perca flavescens captured in gill nets from 433 Minnesota lakes between 1983 and 1997. Seasonal trends were modeled using least-squares linear and polynomial regressions, and interannual trends were investigated with a linear mixed-effects model and an augmented serially alternating design. Four of the six species exhibited significant seasonal trends. Walleye CPUE increased linearly, whereas walleye and cisco mean weight and northern pike CPUE decreased linearly from spring through fall. Cisco CPUE and yellow perch mean weight exhibited curvilinear relationships, decreasing from spring through summer and then increasing from summer through fall. Two species exhibited significant 15-year trends across Mi...

I inserted radio transmitters into the oviducts of northern pike Esox lucius in an attempt to find their spawning grounds. Oviduct insertion of miniature radio transmitters was quick and easy. I hoped that transmitters would be expelled with the eggs to aid in identifying critical habitat used for egg deposition. Ten transmitters were implanted in the egg masses of female northern pike that were staging for spawning. Four of the transmitters were expelled during the spawning period, two in emergent shoreline vegetation and two in submerged vegetation. Northern pike that retained transmitters were smaller than fish that expelled them, indicating that expulsion was influenced by the size of the transmitter in relation to the fish's size. Although transmitters were not expelled by all study fish, advances in miniaturization and refinements in transmitter shape hold promise for future application of this technique.

Sustainable exploitation of Ontario's aquatic resources calls for a new management approach. This vast resource includes more than 250,000 lakes and offers angling opportunities for many popular species (e.g., walleye Sander vitreus (formerly Stizostedion vitreum), lake trout Salvelinus namaycush, brook trout S. fontinalis, northern pike Esox lucius, smallmouth bass Micropterus dolomieu, largemouth bass M. salmoides, and muskellunge E. masquinongy). In pioneer days, the “apparently inexhaustible abundance of resources” fostered an open-access policy promoting the recreational use of these resources for the benefit of the economy. After World War II, there was a rapid increase in angling effort and by the 1970s many lakes were being overexploited. Clearly, an unrestricted, open-access policy was no longer appropriate. The result has been a rapid proliferation of fishing regulations as exceptions to divisionwide regulations that were created to protect lakes where problems were detected. The growin...

Milltown Dam annually impedes the migration of 11 fish species, and data suggest that fish that migrate to the dam do not spawn once their migration is impeded. Densities of westslope cutthroat trout Oncorhynchus clarki lewisi and bull trout Salvelinus confluentus are low near Milltown Dam, but their annual presence at the dam suggests the potential to reestablish fluvial life history forms and enhance local or upriver populations. Operating a fish trap at Milltown Dam in 2000 and 2001, I captured westslope cutthroat trout and bull trout, implanted 42 with radio transmitters, and transported them upstream of Milltown Dam. I monitored the implanted fish to determine posttransport movements and spawning. Most of the fish captured continued upstream to spawn, and many migrations exceeded 100 km after transport. Several fish encountered pre- or postspawning problems, including entrainment in irrigation ditches, predation by nonnative northern pike Esox lucius, angler harvest, and fallback over Millto...

We used creel surveys from 55 northern Wisconsin lakes during the period 1990–1999 to characterize the sport fishery for northern pike Esox lucius. The northern pike daily creel limit on all lakes was five fish of any size (no length limit). Creel surveys were conducted both during the open-water and ice fishing seasons. Directed effort (anglers specifically fishing for a certain species) for northern pike was 5.5 h/acre for open-water fishing and 3.9 h/acre for ice fishing. A greater percentage of all anglers directed effort toward northern pike during ice fishing (mean, 31%) than toward open-water fishing (mean, 11.9%). Directed catch rates for northern pike were highest during the open-water fishery. Open-water directed catch rates averaged 0.31 fish/h, compared with 0.20 fish/h for ice anglers. However, releases of living northern pike exceeded 80% during the open-water fishery but were less than 50% during the ice fishery, resulting in higher harvest rates for ice fishing. Ice fishing harves...

Northern pike Esox lucius were sampled in Nebraska's Sandhill lakes during 1998 and 1999 to determine population characteristics and their influence on the fish community in these shallow, warm lakes at the southwestern edge of this species' natural range. Density-dependent growth, size structure, and condition were not evident in the northern pike populations sampled. Relative abundance of largemouth bass Micropterus salmoides was positively related to size structure of yellow perch Perca flavescens and bluegills Lepomis macrochirus when northen pike were absent. When northern pike and largemouth bass populations were sympatric, these relationships were less evident. Population size structure of yellow perch was lower in lakes with northern pike, but decreased size structure was not evident for bluegills. Northern pike growth decreased with July bottom water temperature, which ranged from 20°C to 25°C. Recruitment patterns of northern pike in the Sandhill lakes appeared to be lake-specific, stro...

The density of northern pike Esox lucius was estimated using mark–recapture techniques and compared with measures of growth and population size structure among 12 north-central Minnesota lakes. The relationships between density and either proportional stock density (PSD, a length-frequency index) or mean back-calculated length were negative and nonlinear. Regression of loge density and PSD explained 63% of the variation in PSD, and regressions of loge density and mean back-calculated length by sex for ages 2–5 explained 47% to 67% of the variation in growth rates among lakes. The relationships remained consistent when data from 17 northern Wisconsin lakes were pooled with those from the 12 Minnesota lakes (although the R 2 was reduced). The fastest growth rates and highest PSDs were observed at northern pike densities of less than 12–14 fish/ha. Inclusion of variables related to the productivity of the lakes only marginally improved the predictive capabilities of the relationship between loge den...

Conserving genetic diversity within and among populations of northern pike Esox lucius is important for maintaining their short-term fitness and long-term evolutionary potential. Northern pike have consistently shown low within-population variation, as detected by allozymes, mitochondrial DNA, and randomly amplified polymorphic DNA. Microsatellite DNA loci reveal considerably greater variation in northern pike, yet microsatellite variation tends to be less than that in other fish species. Low genetic variation within populations may result from compounding factors of low effective population size and bottlenecks. Allozyme, randomly amplified polymorphic DNA, and microsatellite markers have revealed significant differentiation of populations located in different continents and major drainages, but only microsatellites have differentiated populations on finer geographic scales. Within the north-central United States, analyses with microsatellites have detected genetic differences among most populat...

Bog lakes provide a unique but common environment for northern pike Esox lucius within the native range of northern pike. The Minnesota Department of Natural Resources intensively removed nearly half of the population of age-2 and older northern pike from a 28.3-ha bog lake. The removal provided a unique opportunity to study the population dynamics, diet, and secondary production of northern pike. These northern pike formed a dense population with moderate growth rates and a relatively high total mortality rate. Estimated density for fish of ages 2 and older was 59.0 fish/ha, growth through age 4 for both sexes was comparable to an international growth standard, total annual mortality was 63%, and natural mortality was a critically large component of the total mortality. Yellow perch Perca flavescens prey sustained much of the growth and secondary production of northern pike. Estimated secondary production was 4.0 kg/ha/year for male northern pike and 4.8 kg/ha/year for females, with the bulk of ...

From July to October 1994 and 1995, the food habits of walleye Stizostedion vitreum, sauger S. canadense, northern pike Esox lucius, and channel catfish Ictalurus punctatus were studied in Lake Sakakawea, a Missouri River main-stem reservoir in North Dakota. In 1994, no paddlefish Polyodon spathula were found in stomachs of these predators. In 1995, 3% of the walleyes, 12% of the saugers, and 1% of the channel catfish with identifiable prey ate wild age-0 paddlefish. Walleyes ate paddlefish from August to October, with the highest proportions in September, whereas saugers ate paddlefish from July to October in equal proportions. Walleye and sauger stomachs contained wild age-0 paddlefish as large as 167 mm body length (BL; 305 mm total length, TL), and one channel catfish stomach contained a 142-mm-BL (269-mm-TL) paddlefish. Predators were also sampled after 8,000 hatchery-reared, age-0 paddlefish (mean BL = 189 mm) were released in White Earth Bay, Lake Sakakawea. Hatchery-reared paddlefish were...

The response of ichthyofauna to the extensive exploitation of walleyes Stizostedion vitreum was measured in Henderson Lake, north-central Ontario. During a period of negligible recruitment, 89% (3,226) of the adult walleye population (1980–1982) was removed with trap and gill nets. Subsequent attempts to estimate adult walleye abundance in 1988 and 1991 were unsuccessful, suggesting the population had collapsed beyond recovery. Additionally, in 1986 the numbers of northern pike Esox lucius and yellow perch Perca flavescens had increased. With the collapse of the walleye population, northern pike and yellow perch densities were expected to increase, with northern pike eventually becoming the sole top predator. However, two large year-classes of age-0 walleyes were produced during 1985–1986. Furthermore, population estimates in 1994, 1995, and 1997 indicated the adult walleye population had recovered to 33% (1,056 fish) of the preexploitation number. Conversely, by 1997 the number of northern pike ...

In 2001–2003, all of the 400,000 juvenile brown trout Salmo trutta to be stocked into the watercourse of Lake Inari, in northernmost Finland, will be coded-wire-tagged to indicate rearing hatchery, genetic strain, site of stocking, and age of fish. One of our future objectives will be studying the relative predation by northern pike Esox lucius on stocked brown trout with respect to the different groups, as identified by coded wire tags. However, successful sampling of northern pike and the subsequent diet analysis will require answers for the following questions: Do coded wire tags injected into the snouts of juvenile brown trout accumulate in the intestine of a northern pike? If not, what is the evacuation time of the tags? Does evacuation time depend on the size of northern pike and brown trout? In experimental feeding trials, we found that coded wire tags implanted into snouts of juvenile brown trout (weight range, 28–260 g) did not accumulate in the intestine of northern pike (weight range, ...

Methods to contain the spread of nuisance or otherwise undesirable fish species are relatively limited. I describe an unconventional method used to help restrict the movement of northern pike Esox lucius from a mountain reservoir into downstream waters. Reservoir managers designed, installed, and monitored steel structures (“graters”) that served to increase the likelihood that fish entrained in discharge from Lake Davis (Plumas County, California) would incur fatal trauma. Seven species of fish, cumulatively hundreds of individuals, were observed killed by the graters. Injuries induced included dismemberment, lacerations, abrasions, and contusions. No failures to induce fatal trauma to entrained fish were observed, though a few crayfish Pacifasticus spp. remained alive after only partial dismemberment. The graters were fabricated from commercially available steel and sized to fit over 10-in and 30-in discharge ports of the outlet works. Reservoir and fishery managers could adapt these designs fo...

A traditional form of harvest for northern pike Esox lucius during winter is darkhouse spearing through the ice. Using a comprehensive evaluation of creel surveys and license sales in Minnesota, we document a long-term decline in this unique sport fishery. The decline in recreational spear fishing effort cannot be blamed on catch rates because spearing catch rates have not changed perceptibly with time. Catch rates for spearing (mean = 0.175 fish/h) are similar to harvest rates by anglers that are targeting northern pike. Conflicts between spearers and anglers have led to questions about relative harvests by each group and their effects on northern pike populations. Creel survey data since 1980 show that summer and winter angling account for most of the northern pike harvest. Spearing accounted for 15% of the average yield of northern pike by number, but spearing is selective for the larger fish. In comparison with population estimates, spearing removes a small proportion of the total population ...

Five synthetic structure designs were compared to determine their relative value as management tools to improve sport fishing in two 25-ha warmwater impoundments on the Rocky Mountain Arsenal, near Denver, Colorado. Sonic telemetry and systematic angling were used to evaluate attraction of adult northern pike Esox lucius and largemouth bass Micropterus salmoides to artificial structures popularized by Arizona Game and Fish, Anglers United, and the Bureau of Land Management in Saguaro Lake, Arizona. These included “bass bungalows,” “crappie condos,” “magic mushrooms,” “Fish'n Trees,” and a mixture of structure types. Structures containing Fish'n Trees consistently attracted adult largemouth bass as measured by sonic telemetry and systematic angling. Only 40% of the synthetic structures contained Fish'n Trees, yet they accounted for two-thirds of the largemouth bass caught or located with telemetry. Northern pike were not attracted to the artificial structures in either lake according to either mon...

The use of chemical anesthetics, such as tricaine (MS-222), on fish that might subsequently be consumed by humans or animals is currently banned in Canada and restricted in the United States. Although “nonchemical” substitutes such as sodium bicarbonate or clove oil preparations have been used, appropriate concentrations have not yet been determined for nonsalmonid species native to North America. In this study, we found that solutions of 2.66 g sodium bicarbonate/L or 60 mg clove oil/L were optimal as anesthetics for use on walleyes Stizostedion vitreum at 10°C. At these concentrations, complete immobilization required 7.0 ± 0.5 (SE) and 4.3 ± 0.4 min, respectively, and recovery occurred in 4.9 ± 0.5 and 10.9 ± 1.2 min, respectively, for sodium bicarbonate and clove oil. These concentrations were also found to be suitable for use on smallmouth bass Micropterus dolomieu, northern pike Esox lucius, and lake sturgeon Acipenser fulvescens. Clove oil is recommended over sodium bicarbonate for surgica...

Successful application of special regulations, such as slot length limits for northern pike Esox lucius, hinges upon angler compliance with the regulations. Yet, noncompliance was greater than expected under 508–762-mm (two lakes) or 559–762-mm (three lakes) protected slot length ranges in five north-central Minnesota lakes. Illegal fish averaged 13% of the harvested northern pike measured by creel clerks and 19% of the tag returns. Exploitation of similar-sized northern pike was greater in two reference lakes that had no size limits. In reference lakes, an average of 57% of creeled fish and 70% of tag returns were fish of sizes that would have been protected by slot length limits. In spite of extensive promotional efforts, the high (up to 29% on one lake) voluntary tag returns from illegal-size fish implies a simple lack of awareness of special regulations among anglers. Levels of noncompliance reported here show that individual lake management will require a fishing public that is more aware of...

Fish assemblages that include northern pike Esox lucius as a dominant predator were sampled in 19 small (

Larval northern pike Esox lucius were sampled in natural and artificial wetlands associated with Conesus Lake, New York, on 25 April, 8 May, and 26 May 1992. Larval northern pike population densities declined significantly between the first (25 April) and second (8 May) sampling periods, indicating mortality or emigration from the wetlands; only two northern pike were captured on 26 May. Larval northern pike population densities were higher in artificial wetlands on 25 April, but on 8 May no difference could be detected. Mean total length of larvae was greater in artificial wetlands on 25 April and 8 May. Larval northern pike began feeding at approximately 15 mm total length. No difference in number of food items eaten was detected between natural and artificial wetlands; however, percentage of copepods, the taxa most commonly eaten, was higher in northern pike stomachs from natural wetlands. Cannibalism was observed in 1 of the 76 stomachs examined and constituted the only vertebrate food item f...

The ruffe Gymnocephalus cernuus, an exotic Eurasian percid, recently became established in the St. Louis River estuary, Lake Superior, after accidental introduction. Management actions (catch regulations and stockings) were enacted in 1989 to increase the density of top-level predators in the estuary, and thus to increase predation on ruffe. We conducted a field and laboratory study to determine if, and to what extent, native piscivores consume ruffe. Stomachs of 3,669 predators were examined in 1989–1991. Ruffe occurred in 6.7% of burbot Lota lota, 5.8% of bullheads Ictalurus spp., 4.7% of smallmouth bass Micropterus dolomieu, 2.6% of northern pike Esox lucius, 2.6% of black crappies Pomoxis nigromaculatus, and 1.3% of yellow perch Perca flavescens (4.5% after 1989) captured during the 3-year study. No ruffe were found in 967 stomachs of walleyes Stizostedion vitreum examined. Ruffe were 22.7%, of the diet (by weight) of bullheads (during the only year bullheads were captured) and 0.1–17.9% of t...

We captured 702 northern pike Esox lucius in 416 gill-net sets on 17 monthly occasions from July 1991 to June 1993 to examine seasonal variation in sampling data in Lake Thompson, South Dakota. Mean catch per effort (CPE) of northern pike 35 cm or longer differed significantly among months during both years. Mean CPE was lowest in winter and peaked in spring of both years. Size structure estimates were lowest during early spring and summer when males dominated samples and were highest during winter when females dominated samples. Northern pike 86 cm or longer were caught primarily in winter during ice cover. Relative weight (Wr ) of male and female northern pike increased during fall, peaked in late winter, and declined during the spawning period. A similar pattern was found for the gonadosomatic index of female northern pike but not for males. Increases in the gonadosomatic index for males occurred entirely during fall. Gonadosomatic index and Wr were positively correlated for female northern pi...

Adult northern pike Esox lucius and largemouth bass Micropterus salmoides were monitored with ultrasonic transmitters in two 25-ha lakes in Colorado to evaluate the effect of water level drawdown on movement. Water levels in one lake were reduced from September through November, whereas an adjacent lake was held at full pool levels. Largemouth bass in the treatment lake moved greater distances and exhibited larger 24-h use areas during drawdown conditions. Increases in movement and use areas by northern pike associated with low water levels were not significantly different from those at full pool levels. Movement of largemouth bass and northern pike in the stable lake remained constant throughout the study. These results suggest that water level fluctuations may alter predator behavior.