Combining ecology,human demands,and philosophy into the management of northern pike in Michigan

Northern pike (Esox lucius Linnaeus) are a common sportfish native to most waters in Michigan. Early use of northern pike was unregulated consumptive harvest. Pike anglers today vary from those interested in intense harvest, to winter spear fisheries, to those interested in catching trophy fish. Michigan pike are now managed within three ecological groupings: 1. High density and slow growing populations, managed to increase harvest and reduce density (managed with a daily bag limit of 5 fish and no size limit). 2. Moderate density populations with normal growth (most populations, managed with a 61-cm (24-in) size limit and creel of 2 fish per day). 3. Low density and rapid growing populations (managed for trophy fisheries with a 76-cm (30-in) size limit and restricted take). Recent management challenges also include loss of wetland-spawning habitat, driving a need for stocking to supplement natural reproduction. Michigan has managed spawning marshes and other habitat to produce northern pike from natural waters, and recent demand has led to hatchery production of fry. Technology for hatchery production has moved from extensively growing pike and stocking at a small size to the current system using pelleted feed, growing fish to a larger size at a lower density. Future plans for pike management in Michigan are even more focused on using ecology as a means to manage lakes and streams, but will require much more research to be feasible. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

The impact of catch-and-release angling on short-term behaviour and habitat choice of northern pike (<Emphasis Type="Italic">Esox lucius</Emphasis> L<Emphasis Type="Italic">.</Emphasis>)

In the northern hemisphere, pike (Esox lucius Linnaeus) is one of the most important recreational fisheries resources, and regulatory or voluntary catch-and-release angling is common. No information is available about the potential sublethal impacts on pike that catch-and-release fishing may cause, such as behavioural alterations and changes in habitat choice after release. Radio telemetry with N = 20 pike was used to test the hypothesis that fish modify behaviour by reducing movement as a reaction to a catch-and-release event in a previously unfished, slightly eutrophic lake, having an area of 25 ha and located in northeastern Germany. During a 7-month tracking period, activity of pike was monitored for consecutive 24 h every week. Minimum displacement per hour (m) and distance to shore (m) were significantly lower upon the first post release tracking compared to tracking before the capture. Two tracking events after capture, both movement and distance to shore were similar to those measured during pre-angling. There were no significant relations between the change in movement and distance to shore and size of pike. In terms of habitat choice, pike significantly selected for reed and avoided the pelagic area over the whole study period that was not influenced by catch-and-release angling. The results indicated that catch-and-release induces short-term behavioural alterations in pike, probably explained by physiological disturbances and facilitated by evolved anti-predation behaviours. Such alterations, however, seem to be of short duration and reversible suggesting sublethal catch-and-release impacts on pike behaviour are limited. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

The late Pleistocene desiccation of Lake Victoria and the origin of its endemic biota

A brief review is provided in some advances in understanding the ecology of pike Esox lucius Linnaeus over the last 10 years. Based on long-term studies and manipulative, often short-term experiments (laboratory, field and mesocosms) several established theories have been supported, as well as new concepts developed. Despite their wide distribution pike show low levels of polymorphism and divergence indicative of a recent common ancestral population. Recent genetic studies, however, indicate a single refugium in North America compared to several refugia in Europe. Pike are found in rivers, lakes and weakly saline waters. Variables such as growth and mortality are mainly affected by factors such as temperature, water transparency, productivity, availability of prey and density of pike and other predators. In choice of habitat pike have been shown to support the ideal free-distribution theory. The importance of macrophyte habitat in the life history of pike has been reconfirmed and pike have been shown to be flexible in response to water clarity. Pike are extremely ‘plastic’ in choice of prey types, prey size and in response to prey behaviour (e.g. they are unaffected by shoal size). Predation by pike not only affects abundance and biomass of prey (including younger and smaller pike through cannibalism which plays a major role in population dynamics, other fishes and invertebrates) but also evolution and adaptation of their morphology (in particular body shape) and behaviours. There appears to be no relationship between stock and recruitment. Recruitment is influenced by several abiotic factors in lakes and rivers. Pike play a major role in structuring freshwater communities and have been used in stocking programmes to improve water quality (biomanipulation). Many new concepts have been developed in pike behaviour in maximizing these stocking programmes both in biomanipulation and fisheries management. Despite many recent advances in understanding the ecology of pike, particularly at the individual level, developments in quantifying and modelling the role of pike as a top predator in large ecosystems have been limited, probably due to the difficulties of sampling natural populations. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

Otolith-based analysis of survival and size‐selective mortality of stocked 0+ year pike related to time of stocking

The effect of time of stocking on the extent and source of mortality in 0+ year pike Esox lucius was investigated in a lake (20 ha) and a drainable pond (0·5 ha) using pike with alizarin marked otoliths. The results indicated that pike stocked late relative to the recruitment of native 0+ year pike fell victim to cannibalism from these larger individuals. This resulted in very low survival through the first growing season (<2%). Pike stocked early in the season exhibited significantly higher survival (>12%). Analyses of the size distribution of the alizarin marks from these fish revealed that the largest 0+ year pike exhibited by a factor of 3·3, higher survival than the average 0+ year pike in the lake. In order for large 0+ year pike to exhibit such high relative fitness a minimum of 69·7% of the original population must suffer size dependent mortality. In the pond the survival of the largest pike was by a factor of 4·2 higher than the average pike, and the corresponding size dependent mortality was 76·4%. The substantial size‐dependent mortality was most probably due to intra‐cohort cannibalism or habitat segregation between large and small 0+ year pike that exposes the small pike to predatory fishes in the open lake. Cannibalism exerts a major influence on the survival of 0+ year pike post‐stocking although the magnitude and origin differ in relation to stocking time.     

The evaluation of the stocking of pike fingerlings

Summary In order to evaluate the stocking of artificially propagated northern pike (Esox lucius L.) fingerlings (4–6 cm), of which 1–1,5 million/year are produced by the Organization for the Improvement of Inland Fisheries (O.V.B.), the composition and abundance of northern pike populations in four shallow waters were monitored during a 5–8 year period. The specimens stocked were marked by amputation of a ventral fin. At the end of their first growing season the numbers of these and of those that were naturally reproduced (O⁺ pike) as well as the abundance of larger specimens were estimated using mark-recapture methods. Sampling was executed by electrofishing, seining and (incidentally) trawling. The O⁺ pike was caught quantitively by electrofishing.Based on the distribution pattern observed during the sampling period, four age/length classes were distinguished. (1) O⁺ pike, caught almost without exeption within emerged or submerged vegetation; (2) O⁺<pike<41 cm (forklength) found within submerged, floating and ingrowing vegetation; (3) 41 cm<pike<54 cm caught within or in the vicinity of vegetated areas; (4) pike>54 cm, the majority of which — in two experimental waters — were found outside the vegetation. Within the length range of 0–54 cm, the biomass of O⁺ pike and of 0–41 cm pike appeared to be negatively correlated with those of larger pike. The standing stock<54 cm pike was found to be determined by the amount of aquatic vegetation. This phenomenon was still more pronounced when the different habitat preferences of the various length classes were taken into account (GRIMM, 1981).Based on the negative correlations it is concluded that the biomass of 0–41 cm pike/ha preferred habitat is determined by the biomass of larger northern pike and that the stocking of fingerlings does not influence this relationship.In one of the experimental waters a high mortality occurred due to the severe winter of 1978/–1979, causing a decline of at least 50% of the abundance of legal-sized (48 cm) northern pike. In the following year (1979) the numbers and biomass of the O⁺ class amounted to 10 and 5 times the previously recorded highest values, respectively. In 1980 the O⁺ class was virtually absent. As a result of these extreme values the negative correlation was found to be exponential, indicating a density-dependent relationship between smaller (0–41 cm) and larger (41–54 cm) pike. It was shown that, in the 3 years fingerlings were stocked, the abundance of 0–41 cm pike (kg/ha preferred habitat) relative to the abundance of larger pike, did not differ from that in the 4 years in which fingerlings were not introduced.In the two years that pike-fingerlings were introduced in the beginning of May in this water, the frequency of occurrence of O⁺ pike, originally stocked as fingerlings, amounted to ca. 80%. In the year stocking took place at the end of May, introduced pike constituted only ca. 6% of the O⁺ population. These high and low frequencies are explained by the fact that the first and last introduced specimens are either ahead of or behind the ecological time table: they are on the average larger or smaller then the naturally reproduced specimens.Intraspecific predation within the O-class can be a factor of importance (GRIMM, 1981). Therefore, it is supposed that the frequency of occurrence reflects the number of naturally reproduced pike that were replaced by the stocked ones.     

Potential effects of spawning habitat changes on the segregation of northern pike (<Emphasis Type="Italic">Esox lucius</Emphasis>) and muskellunge (<Emphasis Type="Italic">E</Emphasis>. <Emphasis Type="Italic">masquinongy</Emphasis>) in the Upper St. Lawrence River

Changes in spawning habitat of northern pike (Esox lucius) may affect their segregation from and coexistence with the closely related muskellunge (E. masquinongy). We estimated the areal coverage of robust and shallow emergent vegetation in three shared-spawning bays in the Upper St. Lawrence River from aerial photographs taken from 1948 to 2003. Robust emergent vegetation (e.g., cattail) increased in coverage by 155–241% while shallow emergents (sedges) decreased by 46–96%. The loss of sedges, an important northern pike-spawning habitat, may facilitate greater spawning overlap in offshore-submersed aquatic vegetation within bay habitats used by muskellunge. Development rates and characteristics of northern pike and muskellunge eggs and larvae were compared to better understand the implications of greater spawning overlap. Northern pike eggs developed faster than muskellunge eggs at temperatures of 4.7–19°C, and adhesive eggs and the presence of adhesive papillae were present in both species. Equations were used to predict degree-day requirements for hatching and swim-up in three habitats (shallow emergents, bay, and offshore shoal) along a temperature gradient. Northern pike required more estimated degree days to reach hatching in bay and offshore shoal habitat relative to shallow emergent habitat due to cooler temperatures. Significant spawning overlap is known to occur within bay habitats, but poor success of northern pike in deep bay habitats and overall reductions in abundance are hypothesized to currently buffer muskellunge from potential negative interactions between these species. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

Diet composition and prey selection of the pike,Esox lucius,in Çivril Lake,Turkey

Diet composition and prey selection of pike (Esox lucius) were studied in Çivril Lake, Turkey. The lake is eutrophic in character with a surface area of ca. 64 km^?2 and mean depth of 3 m. Stomach contents of 409 specimens were collected between October 2003 and April 2005. Pike diet included 10 prey fish species, two Crustaceae, four Insecta, one Hirudinae and one Amphibia. Feeding was homogeneous, with most pike specializing in prey fish and a few pike specializing on miscellaneous items. Feeding activity varied by season and ontogeny. Stomach fullness and the percentage of fish with prey were highest in spring and in small pike, while feeding intensity was lowest in winter and in large sized pike. Diet composition was dominated by fish, including Carasius gibelio, Chondrostoma meandrense, Esox lucius, Gambusia affinis, Gobio gobio, Hemigrammocapoeta kemali, Leuciscus cephalus, and Tinca tinca. Crustacea were also a significant component in spring and in small sized pike. The most important prey items were C. meandrense, Gammarus sp., H. kemali, and L. cephalus. Pike feeding in winter and summer was homogeneous, specializing mainly on fish as prey, while the diet in spring and autumn was heterogeneous with some pike specializing on Gammarus sp. Cannibalism at 8.7% was observed only in the large sized pike (>40 cm). Pike strongly preferred C. meandrense (Selectivity index V = 0.372; χ² = 27.739; P < 0.01), G. gobio (V = 0.192; χ² = 7.350; P < 0.01) and T. tinca (V = 0.146; χ² = 4.257; P < 0.05) despite their low abundance in the lake. Hemigrammocapoeta kemali was the most abundant prey fish in the environment; however, it was a negatively selected food item (V = ?0.358; χ² = 25.642; P < 0.01). Cyprinus carpio also inhabits the lake, but was not preferred by pike (V = ?0.056; χ² = 0.625; P > 0.05).     

Spatially explicit model predicting the spawning habitat and early stage mortality of Northern pike (Esox lucius) in a large system: the St. Lawrence River between 1960 and 2000

Discharge fluctuations in the St. Lawrence River (Canada) affect reproduction habitat for Northern pike (Esox lucius Linnaeus). We developed a spatially explicit model for that large-scale river system to predict spawning habitat surfaces available for egg deposition and the potential mortality by dewatering occurring during the embryonic-larval stages. The spatial model used simulated current velocity, wetland type and water temperature at a high spatial resolution over the entire fluvial St. Lawrence River, Canada. Those three variables were integrated into a habitat suitability index (HSI) and weighted according to the literature. A new thermal preferendum curve, based on a field experiment, was included in the HSI, reflecting that the probability of observing pike spawners in a given area increased with temperature. The reproduction chronology was predicted every year with an original model based on air temperature in order to reconstitute the historic habitat surfaces for the period 1960–2000. The results revealed that discharge had a substantial effect on both suitable habitat for egg deposition and potential mortality following dewatering. The best and the largest spawning habitats were identified, as well as the most limiting regions in the river. The present findings have already been used to prepare a new discharge regulation plan for the Lake Ontario–St. Lawrence River system. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

Habitat utilisation by pike Esox lucius L. during winter floods in a southern English chalk river

Seven pike Esox lucius L., implanted with radio-transmitters, were tracked throughout autumn and winter in the River Frome, a southern English chalk river. During the first flood events of the year, pike remained within the main river channel but during subsequent flood events, pike could also be found in flooded fields, in drainage ditches or in a millstream. Eighty percent of the fixes over flooded land occurred within 10 m of the riverbank, although distances of up to 89 m from the bank were recorded. In ditches, pike could be found over 250 m from the main river. For pike in ditches and flooded fields, distance from the main river channel was positively correlated with discharge. There was individual variation amongst pike for the habitat types selected, with some pike utilising flooded field or ditch habitat more often than others. The proportion of time spent out of the main river channel does not appear to be related to the size of the pike. It is hypothesised that pike are leaving the main river channel to exploit feeding opportunities in the flooded fields and drainage ditches, rather than using these areas as refugia from high flow conditions.     

Effect of boat noise and angling on lake fish behaviour

The effects of disturbances from recreational activities on the swimming speed and habitat use of roach Rutilus rutilus, perch Perca fluviatilis and pike Esox lucius were explored. Disturbances were applied for 4 h as (1) boating in short intervals with a small outboard internal combustion engine or (2) boating in short intervals combined with angling with artificial lures between engine runs. The response of the fish species was evaluated by high‐resolution tracking using an automatic acoustic telemetry system and transmitters with sub‐minute burst rates. Rutilus rutilus swimming speed was significantly higher during disturbances [both (1) and (2)] with an immediate reaction shortly after the engine started. Perca fluviatilis displayed increased swimming activity during the first hour of disturbance but not during the following hours. Swimming activity of E. lucius was not significantly different between disturbance periods and the same periods on days without disturbance (control). Rutilus rutilus increased their use of the central part of the lake during disturbances, whereas no habitat change was observed in P. fluviatilis and E. lucius. No difference in fish response was detected between the two types of disturbances (boating with and without angling), indicating that boating was the primary source of disturbance. This study highlights species‐specific responses to recreational boating and may have implications for management of human recreational activities in lakes.     

Growth of pike Esox lucius L. in Lake Rubikiai (Lithuania)

The aim of the study was to determine the growth rate and growth parameters of pike Esox lucius L. in the mesotrophic Lake Rubikiai and to evaluate species growth in light of environmental conditions in Lithuanian lakes of different limnologic types. A total of 204 pike specimens were caught in two subsequent years, April 2005 and April 2006, in Lake Rubikiai. Six age classes (2–7 years of age) for males and 10 age classes (3–12 years of age) for females were identified by scale readings; 2‐ to 4‐year‐old males and 4‐ to 7‐year‐old females prevailed. Total length of pike ranged from 26.5 to 107 cm and weight from 106 to 7600 g. There were no statistically significant differences (Student’s t‐test, P > 0.1) between mean lengths and weights of males and females of the same age. Von Bertalanffy growth parameters for the entire population were: L_∞ = 131.7 cm, k = 0.1530 year^?1, t_o = ?0.0398 year. Calculated overall growth performance index ?′ was 3.42. The length‐weight relationship was described by the equation . The growth rate of pike in Lake Rubikiai was higher than in most other investigated Lithuanian lakes. Pike from Lake Rubikiai are characterized by average growth, compared to other populations from various geographical locations. No significant differences were established between the growth of pike in mesotrophic and eutrophic lakes. Pike growth rate did not correlate with lake surface area, maximum or mean depth, and negatively correlated with bogginess in mesotrophic lakes and limpidity and bogginess in eutrophic lakes (P < 0.05).     

Expulsion of miniature radio transmitters along with eggs of muskellunge and northern pike––a new method for locating critical spawning habitat

Identification and protection of critical spawning habitat for muskellunge Esox masquinongy and northern pike Esox lucius is important for preserving the reproductive potential of both species. In this study, we implanted miniature radio transmitters through the oviduct into the egg masses of female muskellunge and northern pike just prior to spawning. This non-surgical procedure was a novel approach for identifying spawning sites when transmitters were expelled with the eggs during egg deposition. Preliminary studies in three lakes showed that muskellunge and northern pike deposited many of the transmitters in likely spawning habitat. An inability to find eggs limited our validation of this method, but nevertheless, a relatively high proportion (70%) of northern pike larger than 690 mm (27.2 inches) expelled transmitters in a previously known spawning area in Willow Lake, Minnesota. Shoreline vegetation in that area consisted primarily of sedges Carex spp., and the adjacent water was shallow with substrate consisting of large mats of water bulrush Scirpus subterminalis. A lower proportion (50%) of muskellunge expelled transmitters in Elk Lake, Minnesota. Water depth at likely spawning sites averaged 1.1 m (3.6 feet) and vegetative cover was variable, but Chara spp. was common to most sites. In Moose Lake, Minnesota, containing sympatric populations of muskellunge and northern pike, 60% of muskellunge and 90% of pike expelled transmitters. Chara spp. beds were the predominant substrate where transmitters were expelled in Moose Lake, but the two species deposited transmitters on deepwater bars (3.7–5.2 m) in addition to shallow near-shore habitat. These results suggest more flexibility in depths used for spawning than typically reported for muskellunge and northern pike.     

Contribution of planktonic and detritic fractions to the natural diet of mesozooplankton in Bahía Blanca Estuary

The pike, Esox lucius Linnaeus, is a predatory fish that supports important fisheries and could substantially impact prey populations around the temperate northern hemisphere. Consumption of prey by pike is most readily estimated using the energy budget to calculate food intake indirectly using estimates of growth rate and metabolism. Resting metabolic rate, R _s, is a particularly important component of such calculations. Here, the available estimates of R _s are reviewed and compared. Scaling coefficients for variation with body mass are consistent between the two studies in which they have been derived (0.81, 0.82). However, the effect of temperature on R _s markedly varies among studies (Q ₁₀ from 1.73 to 4.80). There is substantial variation in R _s (twofold to fourfold) among studies when temperature and fish size are accounted for. This variation is shown to have a large effect on energy budget calculations of energy intake and to be sufficient to account for imbalances in published budgets. These effects depend on age of pike and season; in one energy budget model, a 50% reduction in R _s resulted in decrease of 19–42% in estimated energy intake of pike. Potential causes of among-study variation in R _s are discussed and it is recommended that standard techniques by applied in the future to differentiate between genuine biological variation among populations and experimental factors. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

Evaluating stocking of YOY pike Esox lucius as a tool in the restoration of shallow lakes

1. Stocking of piscivores in shallow, eutrophicated lakes to reduce cyprinid densities is a common approach in lake restorations. Young‐of‐the‐year (YOY) pike Esox lucius are frequently used to reduce cyprinid densities, but their effectiveness is equivocal. This study uses a simple model to assess the efficacy of pike stocking as a lake restoration tool. 2. The model evaluates YOY pike consumption in relation to different survival and growth patterns, timing of stocking, degree of piscivory of pike as well as YOY cyprinid growth patterns and productivity. The parameters used in the model are obtained from field surveys in eight study lakes stocked with YOY pike as well as from the literature. 3. Our model showed that all parameters studied were important for predicting the effects of pike stocking on cyprinids. In particular, body size at stocking, cyprinid production and pike survival were good predictors of biomanipulation success. 4. However, our model showed that only under very specific circumstances will stocking of YOY pike result in a reduction of YOY cyprinid densities large enough to affect water quality. 5. The findings of this study question the efficacy of pike stocking as an appropriate and reliable tool for restoration programmes in shallow lakes, and indicate that when used efforts should be made to optimize the timing of stocking in relation to YOY cyprinid production and to increase the stocking body size of the pike.     

The relationship between temperature and the size and age of larvae and peri‐metamorphic stages of Pleuronectes flesus

Habitat use of 0+ year pike Esox lucius (mean 20–31 mm L _T) was evaluated in artificial ponds (surface area = 16 m²) in relation to water transparencies (low and high), habitat complexity (low and high), food availability (zooplankton) and cannibalism (mortality in the ponds). Pike could choose freely between a structured area, an open water area and a structure and open water interface area. Habitat use shifted towards the structured habitat type in the presence of high habitat complexity and low water transparency. Both findings could be explained as a consequence of territorial behaviour. When cannibalism was intense, the proportions of pike using the structures were reduced and the largest pike, and hence the potential cannibals, were found inside the structures. Since the smallest pike were constrained to the unsheltered, and hence probably more hazardous, habitat outside the structures, this study suggests that mortality due to intra‐cohort cannibalism may occur in an indirect as well as a direct way.     

Pike predation affects breeding success and habitat selection of ducks

1. Fish and ducks often belong to the same local food web, and several studies indicate that there is a general negative effect of fish on breeding ducks. This pattern has so far been addressed mainly within the framework of competition for common invertebrate prey, while predation by large fish as a force behind settlement and abundance patterns in ducks remains largely unknown. This is the first study to address the effect of fish predation on breeding ducks, isolated from that of competition, and the first experiment to explore the ability of ducks to identify and avoid lakes with high risk of fish predation. 2. We used a before–after control–impact design and 11 naturally fishless lakes. Waterfowl on the lakes were surveyed during the breeding season of 2005. Large adult pike (Esox lucius) were added to two lakes in early spring 2008, and waterfowl surveys were repeated on all 11 lakes. 3. Pike introduction did not affect the number of pairs on lakes during the nesting season in any of three focal duck species (mallard Anas platyrhynchos, teal Anas crecca, and goldeneye Bucephala clangula). During the brood‐rearing season, however, there was a decrease in duck days in teal and goldeneye in lakes with pike, with similar trends observed in mallard. The number of goldeneye ducklings was also significantly lower in lakes with pike. We were unable to determine whether the response was attributable to direct pike predation or to broods leaving experimental lakes, but in either case, our study demonstrates high fitness costs for ducks breeding on lakes with pike. 4. The apparent inability of nesting ducks to detect pike and the clear fitness implications may influence the annual recruitment of ducks on a larger scale as pike are both common and widespread. Vegetation complexity and food abundance are likely to be of overriding importance when breeding ducks are choosing a nesting site. As pike have a strong influence on breeding birds, relying on vegetation and cues of food abundance, while ignoring indicators of predation risk from fish, could lead to lakes with pike acting as an ecological trap.     

History of muskellunge management in Nebraska

Muskellunge, Esox masquinongy, were first introduced to Nebraska waters in 1958. By 1967 anglers had caught the first muskellunge from Nebraska waters. Hybrid muskellunge, Esox masquinongy × E. lucius, culture and stocking started in 1976. Harvest regulations for muskellunge and hybrid muskellunge were first established in 1977 with a daily bag limit of one muskellunge or hybrid muskellunge of at least 762 mm (30 inches) in length. In 2000 the minimum length limit for muskellunge and hybrid muskellunge was increased to 1016 mm (40 inches). Hybrid muskellunge have been phased out, none have been stocked in Nebraska waters since 2003. Since 1998 muskellunge fingerlings have been held in Nebraska hatcheries until age-1 before stocking. Yearling muskellunge are raised on minnows and other small fish in Nebraska hatcheries and stocking success apparently is very good. Management and research of Nebraska’s muskellunge and hybrid muskellunge fisheries has been limited to routine sampling that has documented the presence of those fish in waters where they were stocked. Fishable populations of muskellunge can now be found in nine Nebraska waters across the state, but most Nebraska anglers are relatively uneducated in fishing techniques for muskellunge, identification, and proper handling.     

Estimating Esox lucius (Esocidae, Esociformes) density and population structure in a large European alluvial river: the Allier (France)

We developed a sampling protocol for pike (Esox lucius L., 1758) in large alluvial rivers in order to estimate adult population density and structure. This species is known as an indicator of lowland river biotic integrity in Europe evidencing the interest to determine population densities to a reliable degree of accuracy. A two occasion mark-recapture experiment based on a combination of net fishing and boat electro-fishing was specifically designed for monitoring of backwaters and channel sectors during the annual high flow level of an alluvial river, the Allier (France). Estimated densities calculated by using Chapman-Petersen and Loglinear models were weak, ranging from 0.68 (±0.16) fish.ha^?1 to 0.71 (±0.20) fish.ha^?1. However, when the densities are divided by the area of potential riverine habitats, pike abundance was calculated as being 15.3 (±3.7) fish.ha^?1 to 15.9 (±3.8) fish.ha^?1. Pike growth was high and 8 to 9 year-old females were captured. Age and sex distribution emerged as unbalanced, highlighting the precarious status of pike in the studied stretch of the river due to very limited recruitment. Pike were mainly captured in parapotamic side arms which underlines the importance of lateral habitats in semi regulated large alluvial rivers with wide riffle-pool-run sequences dominating geomorphological units.     

Post-stocking survival of 0+ year pike in ponds as a function of water transparency, habitat complexity, prey availability and size heterogeneity

Survival of 0+ year pike Esox lucius (20–31 mm L _T) was evaluated over the first week following stocking in ponds (16 m²) depending on water transparencies (low and high), habitat complexity (low and high) and food availability (zooplankton). A multiple regression analysis showed that survival, essentially as a result of cannibalism, decreased with increasing size heterogeneity of pike, and the decrease was steeper when no food was available. Survival was equal in clear water and water containing copper chlorophyllin (chlorophyll), and slightly higher in complex than in simple habitats, but only when alternative prey availability was low. Conversely, growth in water containing chlorophyll was slightly faster than in clear water. This suggests that initial size heterogeneity is the prevailing factor controlling mortality when stocking 0+ year pike almost irrespective of the stocking environment.     

Predation of Northern Pike (Esox lucius L.) Eggs: A Possible Cause of Regionally Poor Recruitment in the Baltic Sea

Northern pike (Esox lucius) spawning habitat and egg mortality were studied in three spawning areas in 2001 along the Swedish coast of the Baltic proper: the Blekinge Archipelago, Kalmar Sound and coastal freshwater streams. Spawning peaked during the last week of April in streams, at temperatures ranging from 7.7 to 8.9 °C and during the first week of May in brackish waters, at temperatures ranging from 8.9 to 13.8 °C. Spawning occurred in shallow waters, at depths between 0.2–1.5 m, but generally most of the spawn was found in the shallowest areas. In streams, eggs were mainly attached to emersed vegetation, while in brackish sites pike eggs were well scattered among flooded emersed plants, submersed plants and filamentous algae. Mean egg density varied between 469–1829 m^–2 with the lowest density observed in Kalmar Sound. The calculated egg loss occurring from approximately one day after spawning to one day before hatching ranged from 41±7% in coastal streams to 67±6% in the Blekinge Archipelago and 100% in Kalmar Sound. The significant removal of eggs from spawning sites in Kalmar Sound and Blekinge was most likely due to predation from several fish species. In situ observations and stomach analyses suggested that many pike eggs in Kalmar Sound were lost to the three-spined stickleback (Gasterosteus aculeatus), a species that presently dominate the littoral small fish community. This study therefore suggests that egg predation by sticklebacks and other fishes may be a possible cause of the reported poor recruitment of coastal pike populations in the Kalmar Sound region.