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An environmental study of pike Esox lucius recorded their presence in 522 Irish lakes and that they coexisted with brown trout Salmo trutta in 97 of these. Statistical models, accounting for spatial non‐independence among lakes, suggested that lakes with greater area, maximum depth and stream connectivity show a higher probability of coexistence. Introductions of E. lucius are likely to have negative effects on S. trutta stocks in small isolated lakes, but coexistence may be possible in larger systems. [ABSTRACT FROM AUTHOR]

Intraspecific genetic admixture occurs when previously separated populations within a species start interbreeding, and it can have either positive, negative, or neutral effects on reproductive performance. As there currently is no reliable predictor for the outcome of admixture, an increased knowledge about admixture effects in different species and populations is important to increase the understanding about what determines the response to admixture. We tested for effects of admixture on F1 offspring quality in three subpopulations of pike (Esox lucius). Gametes were collected in the field, and eggs from each female were experimentally fertilized with milt from a male from each population (one "pure" and two "admixed" treatments). Three offspring quality measures (hatching success, fry survival, and fry length) were determined and compared between (a) pure and admixed population combinations and (b) the sex‐specific treatments within each admixed population combination (based on the origin of the male and female, respectively). The results suggested that although there were no overall effects of admixture on offspring quality, the consequences for a given population combination could be sex‐specific and thus differ depending on which of the parents originated from one or the other population. All offspring quality traits were influenced by both maternal ID and paternal ID. Sex‐ and individual‐specific effects can have implications for dispersal behavior and gene flow between natural populations, and are important to consider in conservation efforts. We tested for effects of genetic admixture on offspring quality in three natural subpopulations of pike (Esox lucius) in an artificial fertilization experiment with a common garden setup. The results revealed that although there were no overall effects on offspring quality on the population level, the effects for a given combination of populations could differ depending on which of the parents originated from one or the other population. Such sex‐specific effects have implications for dispersal behavior and gene flow between natural populations, and are important to consider in conservation efforts. [ABSTRACT FROM AUTHOR]

Variation in movement between individuals can have important ecological effects on populations and ecosystems, yet the factors driving differences in movement and their consequences remain poorly understood. Here, individual variability in the movements of juvenile (age 0 + and 1 + year) pike Esox lucius was assessed using passive integrated transponder ( PIT) telemetry in off-channel nursery areas over a 26- month period. Differences in the movement patterns of individuals were tested against their body sizes, ages, growth rates and trophic positions using data collected through a combination of catch-and-release sampling and stable isotope analyses. Results revealed that variation in movement between individuals was affected by age, with 1 + individuals moving more than individuals of age 0 + , but not length. Individuals whose TP was low on their initial capture event moved significantly less than those with a higher initial TP. Individuals that moved more grew faster and achieved a higher final TP. These results suggest that higher activity (i.e., increased movement) increases resource acquisition that enhances growth rates, which could ultimately maximise individual performances. [ABSTRACT FROM AUTHOR]

Accelerometer technology was used to evaluate behaviours in the teleost ambush predator pike Esox lucius foraging on crucian carp Carassius carassius. Automated rule-based estimates of prey-size determined handling time were obtained and are compared with video-recorded behaviours. Solutions to tag attachment and the limitations imposed by battery-time and data-logging capacities are evaluated. [ABSTRACT FROM AUTHOR]

This study tested for links among behaviour, state and life-history variables as predicted by the pace-of-life hypothesis in adult pike Esox lucius. First, a standardized open-field behavioural assay was developed to assess individual behaviour of wild-captured adult E. lucius. Behaviour within the standardized assay predicted swimming behaviour in the lake, providing an ecological validation of the assay. There was no relationship between standardized behaviour and any of the life-history and state variables, including metabolism, body condition, juvenile growth rate and adult growth rate in contrast to predictions from the pace-of-life hypothesis. This study demonstrates that it is possible to assess ecologically relevant behavioural variation in a large-bodied top predator using a standard open-field assay, but it is noteworthy that this standardized behaviour is not systematically related to standard metabolism or growth. [ABSTRACT FROM AUTHOR]

Half a century after introducing the final host Northern pike (Esox lucius L. 1758) into Lake Grundlsee in Austria, a sudden massive infection with the pike tapeworm Triaenophorus crassus Forel 1868 was noticed in the population of the intermediate host Arctic charr (Salvelinus umbla (L. 1758)) and led to the closure of this famous fishery. In an effort to contain the epidemic, a total of 1163 pike were removed over a period of three years (2008-2010). The efficiencies of gill and fyke netting as well as electro and spear fishing were assessed. All four methodswere costlywithEUR37-371 to catch a single fish. During intensive fishing, catch per unit effortandfishlengthsof pikedeclined. Fyke netting coupled with electro fishing turnedout to be the most practicable strategy to reduce the pike stock. After another three years, prevalence of T. crassus in Arctic charr could be reduced by 40% in 2013. However, it will be impossible to completely eradicate pike and its parasite in the lake. [ABSTRACT FROM AUTHOR]

The first comprehensive investigation of pike Esox lucius trophic ecology in a region (Ireland) where they have long been thought to be a non-native species is presented. Diet was investigated across habitat types (lake, river and canal) through the combined methods of stable-isotope and stomach content analyses. Variations in niche size, specialization and the timing of the ontogenetic dietary switch were examined, revealing pronounced opportunism and feeding plasticity in E. lucius, along with a high occurrence of invertivory (up to 60 cm fork length, LF) and a concomitant delayed switch to piscivory. Furthermore, E. lucius were found to primarily prey upon the highly available non-native roach Rutilus rutilus, which may alleviate predation pressure on brown trout Salmo trutta, highlighting the complexity of dynamic systems and the essential role of research in informing effective management. [ABSTRACT FROM AUTHOR]

A recent publication (Pedreschi et al., 2014, Journal of Biogeography, 41, 548-560) casts doubt over the status of pike (Esox lucius) as a non-native species in Ireland by reporting two distinct genetic groups of pike present: one a human introduction in the Middle Ages, the other hypothesized to result from natural colonization after the Last Glacial Maximum (LGM). While the existence of two groups is not disputed, the hypothesized natural colonization scenario conflicts with the sequence in which the islands of Britain and Ireland became isolated from Europe after the LGM. An alternative natural colonization scenario raised herein was rejected, leaving an earlier, two-phase, human introduction of pike from Britain or Europe to Ireland as a realistic alternative hypothesis explaining the results of Pedreschi et al. (2014). This leaves the debates on human introduction versus natural colonization, introduced versus native species status, and pike management in Ireland wide open. [ABSTRACT FROM AUTHOR]

Large numbers of microsatellite loci for many species are increasingly made available from public data bases or through de novo isolation with next generation sequencing methods. However, the challenge remains to identify the subset of loci with suitable polymorphism for the populations of interest. This normally requires genotyping individuals in a representative subset of populations., Here, we present an approach that does not require individual genotypes, but instead uses the presence and absence of alleles in pooled DNA samples to estimate within-population variation ( WPV, i.e. polymorphism) and among-population variability ( APV, i.e. rare alleles). From these, we developed a scoring procedure to rank individual loci and thereby identify those most suitable for individual genotyping., We used multiplex PCR of 20 pooled individuals from each of 12 populations to screen a total of 80 published and unpublished microsatellite loci in the Northern pike Esox lucius, a species known to exhibit low genetic variability, thus predisposing it as a model species to test our approach. The screening of pooled samples revealed extremely different levels of microsatellite variability, ranging from 1·0 to 27·5 alleles per microsatellite ( WPV) and from 1·4 to 12 populations per allele ( APV). Scoring placed microsatellites with high WPV and medium APV at the highest ranks., We validated this outcome by genotyping individuals of two pike populations from geographically close areas. A strong differentiation potential (measured as Weir's & Cockerham's FST) as well as a better resolving power of higher over lower-ranked microsatellites (measured as Nei′s DA and probability of identity) proved that the method presented here is suitable for rapid and inexpensive identification of appropriate microsatellites without a priori knowledge of genotypes., Our scoring procedure is generally applicable to all population genetic studies based on microsatellites and is particularly recommended, if species with low genetic variability are to be investigated. [ABSTRACT FROM AUTHOR]

For circumpolar species, little is known on how somatic growth rates can vary at large, transcontinental spatial scales. In this study, a meta-analysis of growth rates was conducted for northern pike ( Esox lucius) across North America and Eurasia. Growth rates of northern pike did not differ between North American and 'coastal Eurasian' pike (e.g., UK, Ireland, Sweden), while growth rates for both of these groups were significantly higher compared to 'inland Eurasian' pike (mainly in Russia). There was no difference in growth between lentic and lotic habitats on either continent. In North America, pike growth was positively correlated with temperature, but in Eurasia, pike growth correlated poorly with most climatic variables. Similarly, maximum longevity in pike populations was significantly predicted by latitude in North America, but not in Eurasia. After standardising annual pike growth by the thermal opportunity for growth, a highly significant countergradient growth relationship was found for North American pike, while a significant, but considerably less predictive countergradient growth relationship was found for Eurasian pike. This study provides novel insights into the ecology of a circumpolar species and how populations function at extraordinarily large spatial scales. First, pike appear to be cosmopolitan across hydrologic habitats having fast or slow growth in either lentic or lotic environments. Secondly, continental-scale differences in pike growth rates are suggestive of major genetic and life-history differences. Finally, variable climate-growth relationships and countergradient growth patterns indicate that global climate change is likely to affect circumpolar fishes like pike in complex, nonlinear ways. [ABSTRACT FROM AUTHOR]

- Temperate lakes can be ice covered for several months each year, yet little is known about the behaviour and activity of the fish during the cold season. As northern pike represents the top of the food web in many northern temperate lakes and may structure the ecosystem both directly and indirectly, a detailed understanding of the behaviour of this species during winter is important. We continuously monitored the activity of adult northern pike ( Esox lucius) in a small temperate lake from late summer to winter for two consecutive years using an automatic acoustic positional telemetry system. Four subsample periods representing different temperature regimes from each year were chosen for further investigation. The results revealed that pike activity was similar between seasons. In all periods, a distinct diel pattern, showing increased activity during day as compared to night, was evident. Our findings indicate that the fish component of temperate lentic ecosystems can be more active during the cold season than previously assumed. This may have implications for the structuring effect of pike on the lower trophic levels. [ABSTRACT FROM AUTHOR]

Pike Esox lucius in the absence of prey and conspecifics were shown to have the highest habitat-change activity during dusk and to decrease preference for complex habitats in turbid water. As the behaviours indicate routine responses in the absence of behavioural interactions, E. lucius spatio-temporal distributions should be directly affected and thereby more easily assessed and avoided by prey, with potential consequences for encounter rates. [ABSTRACT FROM AUTHOR]

This study investigated the movement patterns of Baltic Sea pike Esox lucius in Matsalu Bay, Estonia, using otolith microchemistry. Migration patterns of E. lucius were remarkably diverse, but distinct groups were evident. Of the E. lucius analysed ( n = 28), 82% hatched in fresh water and 74% of them left this biotope during the first growth season. [ABSTRACT FROM AUTHOR]

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 longer compared with the reference populations. Lakes with 30-in minimum length limits had increased percentages of northern pike 20 in and longer, but the improvements did not carry over to fish 30 in and longer. A mix of slot length limits produced results that are more difficult to interpret but generally improved size structure. A metaanalysis incorporating all of the length regulations indicated that the changes in northern pike size structure in regulated lakes were very large for an ecological experiment. Length limits protected large northern pike, with the expectation that lower yields were an acceptable trade-off for producing larger fish for recreational fisheries. This study reveals the range and magnitude of responses we can reasonably expect from length limits as well as the substantial value of conserving large fish when the goal is improved population size structure. [ABSTRACT FROM AUTHOR]

Fisheries professionals charged with managing muskellunge Esox masquinongy frequently seek population information that requires the ability to identify cohorts as well as individuals; hence, reliable tagging methods are needed. Our approach was to simultaneously assess multiple marking techniques on different life stages of muskellunge over short and long time scales. We evaluated the short-term detection of visible implant elastomer (VIE) and passive integrated transponder (PIT) tags in muskellunge fingerlings in experimental ponds. We compared survival (relative to that of control fish) and tag retention for two PIT tagging locations (the cheek and dorsal musculature) and one VIE location (the jaw). Overwinter survival did not differ between tagged and untagged fish (84-98%), but overwinter PIT tag retention was lower for the cheek (92%) than the dorsal musculature (100%). We also fin-clipped and VIE-tagged (jaw) 1,651 muskellunge fingerlings from 1997 to 2002 to evaluate long-term tag retention in a broodstock lake. In addition, 125 adult muskellunge were captured and PIT-tagged from 2003 to 2006. Muskellunge were sampled annually with trap nets and electrofishing during spring and fall. Only 2 VIE tags were detected in adults marked as fingerlings. The proportion of PIT-tagged adults recaptured ranged from 52% to 84% during the sampling period. Our results indicate that both VIE and PiT tags are viable short-term marks for muskellunge fingerlings, while PIT tags appear to be reliable long-term tags when implanted in the dorsal musculature of adults. [ABSTRACT FROM AUTHOR]

Methods for quantifying selection pressures on adaptive traits affected by size-selective fishing are still scarce, and none have as yet been developed for recreational fishing. We present an ecologically realistic age-structured model specifically tailored to recreational fishing that allows estimating selection differentials on adaptive life-history traits. The model accounts for multiple ecological feedbacks, which result in density-dependent and frequency-dependent selection. We study selection differentials on annual reproductive investment under size-selective exploitation in a highly demanded freshwater recreational fish species, northern pike ( Esox lucius L.). We find that recreational angling mortality exerts positive selection differentials on annual reproductive investment, in agreement with predictions from life-history theory. The strength of selection increases with the intensity of harvesting. We also find that selection on reproductive investment can be reduced by implementing simple harvest regulations such as minimum-size limits. The general, yet computationally simple, methods introduced here allow evaluating and comparing selection pressures on adaptive traits in other fish populations and species, and thus have the potential to become a tool for evolutionary impact assessment of harvesting. [ABSTRACT FROM AUTHOR]

Uranium mining and milling operations in northern Saskatchewan (Canada) release effluents with elevated levels of certain trace metals and metalloids, including selenium. The goal of the present study was to evaluate the presence of seleniuminduced deformities in northern pike (Esox lucius) and white sucker (Catostomus commersoni) larvae originating from adults collected downstream of a uranium mine. Eggs were fertilized in the field and incubated in the laboratory following a two-way (crossover) analysis-of-variance experimental design to discriminate effects from maternal transfer versus those from exposure to site water in the developing embryos. Selenium concentrations in northern pike and white sucker eggs (8.02 and 4.89 μg/g dry wt, respectively; mean ± standard error throughout) from the exposure site were approximately two- to threefold higher than reference (2.35 ± 0.20 and 1.94 ± 0.25 μg/g dry wt, respectively). Among all evaluated deformities (skeletal curvatures, craniofacial deformities, fin deformities, and edema), only edema in white sucker fry from the exposure site was slightly elevated (∼3%) compared to reference. The occurrence of edema, however, can be associated with factors other than selenium (e.g., other metals and organic compounds). Both fish species displayed strong linear relationships between the selenium concentrations in eggs and other tissues (muscle, liver, kidney, and bone), suggesting that selenium concentrations in eggs could be predicted from selenium concentrations in adult tissues. The lack of a clear, toxic response in the present study is in agreement with selenium thresholds for early life-stage deformities reported in other studies, with egg selenium concentrations in northern pike and white sucker collected at the exposure site being less than the 10 μg/g (dry wt) threshold associated with the presence of deformities. [ABSTRACT FROM AUTHOR]

The hypothesis that vagility, or tendency to move, in pike Esox lucius can be predicted from individual home range was tested using telemetry. Independently of fish size, mean annual excursion distance was positively correlated to winter (0·02–0·95 ha) and spring (0·02–0·59 ha) home ranges but not summer and autumn home ranges. [ABSTRACT FROM AUTHOR]

The object of this study was to test site fidelity of female pike Esox lucius and to contrast the activity centre size in summer and winter in a 25 ha lake in north-eastern Germany using radio telemetry. Weekly 24 h tracking and two 96 h tracking exercises were conducted by boat from June to December 2005 and by walking on surface ice from January to February 2006. Positions of 12 E. lucius [total length ( LT) = 450–733 mm] were recorded every 3 h within a 24 h tracking cycle. Site fidelity to individual summer activity centres was tested by translocating eight E. lucius away from their activity centre. All translocated E. lucius returned to their summer activity centre within 6 days, which provided evidence of site fidelity of E. lucius. There was no relation between E. lucius LT or the translocation distance and return time to the activity centre after translocation. In winter, the activity centre size of E. lucius was significantly larger than in summer, but there was considerable overlap between the sites chosen in winter and those in summer. The seasonal variation in activity centre size possibly reflected changes in habitat structure ( e.g. collapse of structured vegetated habitats in winter) or prey fish distribution. [ABSTRACT FROM AUTHOR]

The influence of the invasive black bullhead Ameiurus melas on the predatory efficiency of the pike Esox lucius was investigated using an additive experimental design. Pike predatory success on 0+ years roach Rutilus rutilus was significantly reduced in the presence of black bullhead. Among the different hypotheses that may explain such a pattern, the hypothesis of direct competition between pike and black bullhead was not verified, as black bullhead hardly fed on roach. Similarly, pike predatory efficiency did not decrease with turbidity, rejecting therefore the hypothesis of an indirect effect through black bullhead-generated turbidity. Therefore, the reduced predatory efficiency of pike was probably related to behavioural interference between pike and black bullhead. These laboratory results confirm the potential negative impact of black bullhead on native European fauna, with a particular emphasis on pike, which is a top predator considered as vulnerable in some European regions. [ABSTRACT FROM AUTHOR]

The effect of pike Esox lucius predation on the mortality of newly stocked Atlantic salmon Salmo salar smolts was investigated in the Pyhäjoki River, Finland. The number of smolts eaten by pike was assessed by estimating the size of the pike population (mark–recapture experiment) and studying the stomach contents of pike. Before recapturing the pike, approximately 39,700 smolts were stocked upstream of the 2.5-km-long (89-ha) research area. The estimated size of the >40-cm pike population was 1507 (95% CL 1012–4731) individuals (17 pike and 29.8 kg·ha−1). Pike were estimated to eat 29% of the released smolts during 1 week. The diet of the pike in the research area consisted almost entirely of smolts, whereas in the reference area with no stocked smolts, the meal sizes were significantly smaller and the importance of smolts as prey was substantially lower. Pike <40 cm had not eaten any smolts, probably indicating a size refuge for the smolts, or alternatively fear of intraspecific interactions or cannibalism of pike. [ABSTRACT FROM AUTHOR]

1. The keystone piscivore northern pike Esox lucius can structure fish communities, and models predicting pike-focused connectivity will be important for management of many waters. 2. We explored the ability of pike to colonize upstream locations and modelled presence–absence in lakes based on landscape features derived from maps. An upstream connectivity model (UC model) was generated using data from 87 lakes. We validated the UC model with retrospective whole-lake experiments involving introductions ( n = 49) and extirpations (by rotenone) of pike ( n = 96), as well as with the natural distribution of pike in lakes ( n = 1365) within 26 drainage basin networks in northern Sweden. 3. The UC model predicted the incidence of pike in lakes with stream-connections with 95·4% accuracy, based mainly on a single variable, SV5max, that measures the minimum distance found between 5 m elevation intervals (= maximum stream slope) along watercourses from nearest downstream source of potential immigrants. Recolonizations of pike in rotenone lakes generated a near-identical classification tree, as in the UC model. The classification accuracy of pike presence in the external validation procedure ranged from 88·7 to 98·7% between different drainage basins. Predictions of pike absence were not as accurate, due possibly to undetected introductions, but still lead to 86·6% overall accuracy of the external validation. Most lakes lacking pike, but misclassified as having pike based on low SV5max, were isolated from downstream sources of pike by subsurface streamflow through bouldery areas (SSB). 4. Synthesis and applications. The variable SV5max provide managers with a tool for revealing the location and severity of natural dispersal barriers to pike (and logically also barriers to other species with equivalent or less dispersal capacity). Because presented models only require map-based information, and have high predictive power, they may have the potential to be of fundamental use in predicting distribution of freshwater fish. These predictions may provide the means for prioritizing in risk assessment and control programmes to combat pike invasions, as well as contribute to determining a reference state of species incidence in specific lakes. Our results also point towards a possibility that, even where stream slope is low, long-term effective barriers may be designed that mimic natural SSB. [ABSTRACT FROM AUTHOR]

Quantifying the effects of density-dependent and density-independent factors in demographic and dispersal processes remains a major challenge in population ecology. Based on unique long-term capture-mark-recapture (CMR) data (1949-2000) on pike (Esox lucius) from Windermere, United Kingdom, we provide estimates of density-dependent and density- independent effects, under the influence of individual size and sex, on natural survival, fishing mortality, and dispersal. Because survival is expected to be related to the individual growth process, we also explore the degree of parallelism between the two processes by applying the best-supported survival model structure to individual growth data. The CMR data were analyzed using sex- and age-structured multistate models (two lake basins: north and south) assuming no seasonal variation in survival and dispersal. Total survival and dispersal probabilities were insensitive to this assumption, and capture probability was shown to be robust to assumptions about intra-annual variation in survival and dispersal. The analyses revealed that large pike (>55 cm) displayed marked basin-specific differences in survival and dispersal responses to the abundance of conspecifics in which pike from the south basin show high density dependence in survival and a low degree of density dependence in dispersal, whereas the opposite was found for those of the north basin. Both large- and small-pike dispersals were found to be dependent upon the between-basin gradient in perch (Percafluviatilis, the main prey) abundance, but most so for north-to-south dispersal. The strength and pattern of density-dependent mortality in small pike was influenced by temperature in a peculiar way: at low summer temperatures survival was lowest at high small-pike abundances and low perch abundances; at low temperatures, survival was lowest at high small-pike abundances and high perch abundances. Analyses of individual small-pike growth trajectories showed a similar modulation of the positive perch abundance effect on growth rate when temperature increases. The growth analysis also indicated that cannibalism may be biased in favor of rapidly growing individuals or at least increased growth rate for the surviving individuals. Altogether, this study provides evidence of a complex interplay between density- dependent and density-independent factors affecting survival, dispersal, and individual growth of an aquatic top predator. [ABSTRACT FROM AUTHOR]

The short-term tolerances of northern pike, Esox lucius L., fry reared in a freshwater hatchery, to salinity were examined in the laboratory. Survival of two size groups of pike fry (mean length 21 ± 2 mm SD and 37 ± 4 mm SD) was examined over 72- to 96-h periods at 9–14 ppt salinity in combination with temperatures of 10, 14 and 18 °C. A parametric survival model found a significant correlation between survival of pike fry and temperature and salinity, respectively. LC50 values after 72 h were between 11.2 and 12.2 ppt, being lowest at 10 °C. Pike fry did not survive more than 13 ppt. Mortality at 12 ppt was significantly faster at 18 °C than 10 or 14 °C. Moreover, mortality was higher and faster for large than for small pike fry at 12 ppt and 14 °C. These results imply that pike raised in fresh water can survive stocking into brackish waters below 11 ppt at least for a short time. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The morphological response of two 1 year-old prey species, perch Perca fluviatilis and roach Rutilus rutilus to the presence of predatory pike Esox lucius, was tested in a 6 week aquarium experiment. The growth of perch was higher than that of roach but there was no difference in growth of prey between predator and control treatments. The presence of pike caused morphological changes in both perch and roach. Perch showed an increase in body depth during the experiment whereas the morphological response of roach to pike was more related to a displacement of the dorsal and pelvic fins and width of the anal fin. Differences in morphological responses of perch and roach to pike can be interpreted by their overall differences in antipredator strategies. [ABSTRACT FROM AUTHOR]

The genetic variability of 11 French pike Esox lucius populations from rivers or extensive aquaculture ponds was analysed using seven microsatellite markers. The fish stocking of eastern European pike in French rivers is widespread, so five supplementary populations from this region were also analysed. Genetic variability within the French population was small, and similar to that previously found in Europe for this species. French populations from stocked rivers and extensive farms formed a genetically homogeneous group, and did not diverge from most eastern European samples, which may reflect either ancestral polymorphism or a complete introgression of French populations by introduced stocks. Bayesian analysis of the admixture between populations enabled identification of the French populations that were likely to be affected by introduced stocks (of local or foreign origin). Three genetically distinct evolutionary branches were identified: continental Europe, Danube basin, and south-western France. The last is a new finding in the species which needs to be further explored by comparisons with wild populations at other sites. [ABSTRACT FROM AUTHOR]

During the myotomal myogenesis in pike ( Esox lucius) two phases of muscle differentiation can be distinguished. In the first phase, the somite cells-derived stock, the primary myoblasts (of mesodermal origin), fuse to form multinucleate myotubes. Participation of myotomal cells of mesodermal origin is insufficient for further muscle development. In the second stage mesenchymal cells migrate, via myosepts, into the myotome between myotubes. Immunocytochemical detection of proliferating cell nuclear antigen (marker of S phase of cell cycle) showed their mitotic activity. Transmission electron microscope analysis revealed that the differentiation of these cells depends on their position. Cells remaining in the myosepts develop into fibroblasts and produce collagen fibres, while those that have migrated into the myotomes transform into secondary myoblasts. Mesenchymal cells in the studied species are believed to participate in hypertrophy and hyperplasy of muscle fibres. Thus the muscle fibres in pike ( E. lucius) are of mesodermal-mesenchymal origin. [ABSTRACT FROM AUTHOR]

The potential utility of pelvic fin rays as ageing structures was evaluated for southern US muskellunge Esox masquinongy Mitchill populations by comparing age estimates among three readers and against cleithrum estimates, and by comparing observed length changes of tagged fish with changes predicted from growth equations based on pelvic fin ray age estimates. Mean coefficient of variation in age estimates among all readers and between the two readers with prior ageing experience was 17.8% and 5.6%, respectively. Exact and within 1-year agreement rates between pelvic fin rays and cleithra were 76% and 100%, respectively. Mean (± 2 SE) estimated absolute error between observed and predicted length changes for 13 tagged muskellunge was 30 ± 14 mm. This evaluation indicated that pelvic fin rays may prove to be a useful, non-lethal method for ageing muskellunge in southern US waters. Validation studies are still needed to ensure that growth rings form consistently throughout fish's life span. [ABSTRACT FROM AUTHOR]

Using light microscopy the morphology, the mitotic index and levels of erythroid cell types were detected from 48 h pikeEsox luciusembryos before hatching to adult specimens. At the same developmental stages, the haemoglobins and globin chains expressed were electrophoretically characterized. The erythroid cells of the primitive generation were the most abundant from 48 h before hatching until 15–20 days after hatching, then their number decreased and only rare cells remained in the 3 month-old juvenile specimens. These cells divided and differentiated in the blood and were substituted by the definitive erythrocyte series. As in other vertebrates, the immature cells of the two generations differed in morphological properties and in the synthetized haemoglobin. The circulating erythroid cells of the definitive population cell lineage were, at all differentiation stages, smaller than those of the primitive generation. The definitive erythrocytes appeared in blood smears of 7 days post-hatching larvae, they increased rapidly and at 20 days they represented the predominant red blood cell population in the circulation of young pike. Electrophoretic analysis of haemolysates obtained from different developmental stages indicated the presence of distinct embryonic, larval and adult haemoglobins. The embryonic haemoglobins differed from those of the older larva and juvenile specimens and were detectable within the first week of post-hatching development when only primitive erythrocytes were present in the blood. [ABSTRACT FROM AUTHOR]

Vøllestad LA, Varreng K, Poléo ABS. Body depth variation in crucian carp Carassius carassius: an experimental individual-based study. Ecology of Freshwater Fish 2004: 13: 197–202. © Blackwell Munksgaard, 2004 Induced morphological defences, where individuals develop morphological structures as a response to signals from sympatric predators, are common among invertebrates. Such defences have also been reported in a freshwater fish, the crucian carp Carassius carassius. In crucian carp, the presence of piscivorous fish presumably induces the development of a deep body as a defence mechanism. We tested how the growth rate (in body depth, length and mass) of individually tagged crucian carp responds to pike Esox lucius odours and control water. In general, crucian carp exposed to pike odour grew better (both in length and mass) than control fish. The treatment crucian carp also developed deeper bodies than control crucian carp. Further, there was a strong positive relationship between individual growth rate and the rate of change in body depth and this relationship did not differ between control and treatment fish. [ABSTRACT FROM AUTHOR]

Circular whitish granular lesions, 5–12 mm in diameter, were observed on the skin and fins of a wild northern pike,Esox lucius, caught in a lake in the Republic of Ireland. Histological examination of the lesions revealed hypertrophied cells in the epidermis with deeply basophilic enlarged nuclei and dark-staining granular material in the cytoplasm. Transmission electron microscopy of these cells revealed naked hexagonal herpes-like virus nucleocapsids (97 ± 7 nm) in their nuclei while the cytoplasm contained multiple aggregates of enveloped viral particles. This is the first report of herpes-like virus particles in northern pike originating outside North America, where esocid herpesvirus-1 (EsHV-1) has previously been reported. Shared clinical, histological, morphological and epidemiological findings suggest that the observed particles in this report may also be EsHV-1. [ABSTRACT FROM AUTHOR]

The effect of school size on capture success in three different piscivores, perch Perca fluviatilis, pikeperch Stizostedion lucioperca and pike Esox lucius, was investigated. Roach Rutilus rutilus were used as prey in a pool experiment where individual predators were presented prey at densities of one, two, four, eight and 16 prey, respectively. Treatments were replicated seven times for each predator species. Perch was at first virtually unable to capture a prey from a school and suffered a significant confusion effect with increasing prey density. The effect, however, was limited in the long run, as the perch was a very effective predator in its hunting strategy where it singled out and repeatedly attacked single prey irrespective of prey density or school size. Pikeperch and pike were able to attack and capture prey at any prey density equally successfully and thus did not suffer from a confusion effect. Neither did these predators receive any apparent advantages from increasing prey density. [ABSTRACT FROM AUTHOR]

The threat-sensitive predator avoidance (TSPA) hypothesis was tested on hatchery-reared pike Esox lucius larvae. Larval swimming activity, food attacks upon zooplankton, escapes, immobility behaviour, vigilance, as well as time in vegetation under different predation risk were measured. Single larvae were video-filmed in aquaria allowing them to have visual contact with a small or a large perch Perca fluviatilis as predator. The odds of fleeing increased significantly if the larvae were exposed to a large predator instead of a small one. Swimming activity and foraging decreased significantly in the presence of a predator compared to the control. On the other hand, no significant effect was detected in time spent in the vegetation, and in vigilance of larvae, measured as time intervals between food attacks. The findings suggest that pike larvae primarily flee in the presence of a large predator, whereas they remain immobile, and forage, when possible, in the presence of a small predator. Sometimes a lack of response between the large and the small predator treatments was detected, which suggests that the antipredator response has a threshold, and when increasing the threat, the prey response does not increase. In the present paper it is demonstrated that hatchery-reared pike larvae respond to the level of threat, and thereby seem to be risk adjusting as predicted. [ABSTRACT FROM AUTHOR]

The stocking of newly hatched pike Esox lucius labelled with radioactive strontium (85Sr) and later electrofishing of the same area was found to be a workable tool in assessing the success of pike stockings. 85Sr-labelled individuals constituted 96% of the 0+year pike catch from late summer electrofishing in the stocked littoral areas of the heavily regulated Lokka Reservoir. The density of 0+year pike reached 2·1 individuals 100 m−2 in the stocked areas in comparison to 0·3 individuals 100 m−2 in the reference areas. In the three other stocked lakes the proportion of labelled pike in the catch ranged from 0 to 42% in late summer. The results suggest that pike stockings are profitable in filling empty or nearly empty 0+year pike habitats of regulated lakes or other waterbodies, where the natural reproduction of pike has declined due to human activities. [ABSTRACT FROM AUTHOR]

The hypothesis was tested that the daily increment width (IW) of the otolith comprises two components, one that correlates with basal metabolic rate (as has been demonstrated previously) and the other that correlates with apparent specific dynamic action ( Rsda)(the post-prandial elevation in metabolism). Simultaneous measurements of IW and metabolic rate before and after a meal were collected from individual pike Esox lucius. After feeding, IW and metabolic rate increased above basal levels for 5–6 days. There was no correlation between daily IW and Rsda, reflecting within-individual difference in the shapes of the post-prandial responses of the two variables. There was a significant relationship between the total changes of IW and metabolic rate integrated following meals. The magnitude of the post-prandial response as a proportion of the basal level was larger for metabolic rate than IW, mirroring the previously reported responses of these variables to acute temperature change. This study suggests that analysis of IW has the potential to provide a historic record of energy intake but only when integrated over a period equivalent to the digestion time. Consideration of energy budget theory indicates that IW is unlikely to provide a robust record of short-term somatic growth if activity metabolism is significant and variable. [ABSTRACT FROM AUTHOR]

Habitat use of 0+ year pike Esox lucius(mean 20–31 mm LT) 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. [ABSTRACT FROM AUTHOR]

Public opinion plays an important part in the successful development of a fisheries management plan. We used a mail questionnaire to survey 1,400 anglers who fish for muskellunge Esox masquinongy in Wisconsin. The survey included defined groups of muskellunge anglers separated by muskellunge club affiliation and geographic location and general anglers selected from a random sample of angler license sales. The survey questions were designed to obtain opinions regarding muskellunge fishery and trophy management in Wisconsin in terms of angling behaviors, regulation options, and perceived problems. All anglers generally preferred fishing with artificial lures and practiced the voluntary live release of legal-length muskellunge. Muskellunge anglers considered a trophy muskellunge to be at least 40 in long, with a preferred length of 50 in or longer. Muskellunge anglers also supported regulations for muskellunge that were based on a water's biological potential, along with increased restrictions on regulations such as minimum length limits. General anglers were less supportive of restrictive regulations and were more likely to keep a legal muskellunge for consumptive purposes. The greatest perceived problems with muskellunge fishing were Native American spearing and conflicts with users of speedboats and jet skis. Opinion surveys such as this can help in formulating management strategies that satisfy most anglers within biological limits. [ABSTRACT FROM AUTHOR]

Investigates the spatial distribution and social behavior of young-of-the year pike Esox lucius in early winter. Selection of reed beds in the early exploration phase; Increase in pool occupancy; Lack of evidence of territoriality; Preference for reed cover among juveniles; Habitat use.

An extremely limited haplotypic diversity within populations and a strikingly low divergence between European and Canadian haplotypes were found in pike Esox lucius. Certain haplotypes were associated with a particular geographical region in Europe: a widespread European and a restricted Hungarian-Norwegian type. The low haplotypic intraspecific divergence suggests a late Pleistocene expansion from an ancestral population. [ABSTRACT FROM AUTHOR]

Cites findings of a study conducted to evaluate the post-stocking survival of 0+ year pike Esox lucius in ponds as a function of water transparency, habitat complexity, prey availability and size heterogeneity. Impact of the initial size heterogeneity on cannibalism; Reasons for the difference in pike growth in varying water visibility; Implications of the study for fisheries management.

Between 1994 and 1997, 508 pike, Esox lucius L., were tagged in Lower Lough Erne (LLE), Northern Ireland. By August 2000, 79 of these fish were recaptured. Ten of 27 pike recaptured and released a second time were then captured a third time. Distance from tagging to recapture site ranged from 0 to 16 km, with most recaptures within 10 km. Pike dispersed widely after spawning, an observation supported by netting survey data, and tended to return to the same spawning sites year after year. The usefulness of designated sanctuary areas free of commercial fishing, intended to maintain a stock of pike reserved for angling was evaluated. To protect angling stocks of pike from commercial fishing, sanctuary areas should be somewhat larger than at present. [ABSTRACT FROM AUTHOR]

This study investigated the habitat use of 0+ pike (9-17cm) in relation to two different water transparency regimes (clear water/ chlorophyll water), two different light regimes (day/night)and the presence/absence of prey using 16m[SUP2] experimental ponds. Pike could freely Choose between two structured habitats (a simple structured and a complex structured), an interface habitat (between the structured habitats and open water)and an open water habitat. Foraging success of the pike in relation to water transparency was investigated by comparing mean condition (Fultons K) of the pike as well as the number of surviving prey fish. Habitat use was influenced by the presence/absence of prey and varied between waters with different transparency. The presence of prey intensified the use of structural habitats of 0+ pike in both clear and chlorophyll waters. A preference for complex habitats was found in clear water and was presumably related to foraging. The pike in chlorophyll water, in contrast, appeared more evenly distributed among all habitats, as illustrated by a more intensive use of open water in chlorophyll water compared to the clear water. No detectable impact of water transparency on the foraging success of 0+ pike was found. [ABSTRACT FROM AUTHOR]

Muskellunge Esox masquinongy eggs activated with UV-irradiated yellow perch Perca flavescens sperm were subjected to heat shock at 31±1° C for 6 min, 20 min after fertilization in three experiments. Survival at eyed stage was 1·7±1·6, 6·8±4·8 and 2·3±0·5% in experiments I, II and III, respectively. After rearing the gynogenetic muskellunge in troughs and then in ponds, the sex ratio of gynogens in experiment I did not significantly (P> 0·05) differ from the expected ratio 0 : 1 (male : female), however, one male and one intersex were observed. In experiments II and III, the sex ratio of gynogens differed significantly from expected (0 : 1). Three months after hatching, the growth of females did not significantly (P> 0·05) differ among control and gynogenetic groups, whereas male growth was significantly (P< 0·01) higher in the control v. gynogenetic group. The histological structures of the gynogenetic fish gonads in both sexes were similar to those described in the gonads of control muskellunge. After the overwintering period, signs of active spermatogenesis were observed in the testis of 1+ year old gynogenetic fish, whereas ovaries contained only oocytes at the perinucleolar stage. At this stage, plasma sex steroids testosterone (T) and oestradiol-17β (E2) cannot be used to discriminate the sex of gynogenetic muskellunge, as intersex, male and female fish had similar levels of T and E2. [Copyright &y& Elsevier]

In our recent study of the population genetics of pike (Esox lucius) in Ireland (Pedreschi et al., 2014, Journal of Biogeography, 41, 548-560), we reported the existence of two main demographic units and showed that these may correspond to two independent and temporally staggered colonization events, the first of which may have been too old to be caused or assisted by human translocations. Ensing (2015, Journal of Biogeography, doi:10.1111/jbi.12410) first used our genotypic data to explore alternative historical scenarios, then attempted to reconcile the 'two-wave' colonization process of Ireland by pike with translocation activities by humans in Neolithic/Bronze age times. Here we illustrate why the evidence base for Ensing's reconstruction is weak and we outline a realistic strategy to better understand the role of pike in Irish freshwater ecosystems. [ABSTRACT FROM AUTHOR]

The composition and abundance of four northern pike (Esox lucius L.) populations were monitored in the period 1974–82. The biomasses of 0+ pike, pike «35 cm and pike «41 cm were negatively correlated with those of larger individuals following an exponential relationship. It is argued that this density-dependent relation is the result of a regulation in which intraspecific predation may play a major role. The standing stock of pike «54 cm, if related to pike habitat available, was very similar both among sites within years and among years within sites. This stock is tied to a maximum per unit of vegetated area. Within this maximum the biomass of pike «41 cm is determined by the biomass of larger individuals. Therefore stocked pike did not contribute extra biomass to the population. [ABSTRACT FROM AUTHOR]

The markings of pike (Esox lucius L.) were found to be specific to individual fish. The subsequent recapture of pike after 2 years of growth, indicated that the markings could be used for the positive identification of specific pike. [ABSTRACT FROM AUTHOR]

Describes the characteristics of an atypical, pigment-producing form of Aeromonas salmonicida isolated from diseased pike, Esox lucius L. Bacterial growth; Biochemical comparison of pike isolates; Similarity of the pike isolates to the isolate from sea trout.

The article presents information on a disease called Leukaemic lymphosarcoma in a hatchery-reared rainbow trout. Lymphosarcoma, often described in mammals, also occurs in lower vertebrates. In teleosts, most of the cases reported are from fish of the order Salmoniformes, and occur with the greatest frequency in fish of the genus Esox. The population, from which the affected fish came originated in California, was imported as eggs, hatched in raceways and grown in indoor tanks until approximately 10-15 cm long.

The basic nuclear protein in the sperm of the Northern pike is a protamine, 32-residues long, which behaved as a single component during ion-exchange chromatography and gel electrophoresis. Amino acid analysis gave close to molar ratios for the eight different residues with no evidence of microheterogeneity. However, the presence of sequence variants was revealed following a combination of automated protein sequencing and cleavage of the protamine by CNBr, endoproteinase Lys-C and thermolysin. At position 28 there is an equal probability of having serine or glycine. At position 9 glycine is found more frequently than serine. The reciprocal nature of the substitutions results in glycine and serine contents which are close to a 4:2 ratio. Pike protamines are homologous to those of the trout but show less sequence variation between components. [ABSTRACT FROM AUTHOR]