Patterns of movement of adult northern pike (Esox lucius L.) in a regulated river

Abstract –  We performed a tagging study on one of the spawning populations of northern pike ( Esox lucius L.) of the River Kajaaninjoki in Finland. Northern pike is the main predator in many lakes and rivers in the northern hemisphere. Previous tagging studies have shown a general tendency to sedentary behaviour by pike. Whether individuals in a fish population adapt a sedentary or moving strategy may affect population persistence. To study if the spawning population consists of sedentary or moving individuals and the pattern of movements, we tagged 40 pike with radio transmitters and followed them from May 2002 to June 2003. Pike were caught and tagged during the spawning season in the mouth of the River Kajaaninjoki which flows into one of the largest lakes in Finland, Lake Oulujärvi. Our results suggest that the pike spawning population consisted of sedentary pike ( N  = 16) dwelling the whole year in the river, and moving pike ( N  = 24) which moved to Lake Oulujärvi after the spawning period. Pike exhibited homing behaviour, as most of the migrating pike returned to the same spawning area in the following year. Large pike had a higher movement rate than small pike during the summer and seasonally the movement rate was lowest during the spring and highest during the summer.     

The effects of mechanically reducing northern pike density on the sport fish community of West Long Lake, Nebraska, USA

Abstract  Removal of piscivores may affect population size structure, abundance and growth rates of the remaining fish community. A total of 572 northern pike, Esox lucius L., was removed from 25-ha West Long Lake, Nebraska from 2003 to 2006. The northern pike population was reduced from 36 fish ha⁻¹ and 22 kg ha⁻¹ in 2002 to 20 fish ha⁻¹ and 9 kg ha⁻¹ in 2006. The northern pike population shifted to dominance by smaller individuals. Relative abundance increased for bluegill, Lepomis macrochirus Rafinesque, but remained similar between years for largemouth bass, Micropterus salmoides (Lacepède), and yellow perch, Perca flavescens (Mitchill). Bluegill and yellow perch size structure increased probably because of reduced predation by northern pike. The effects of reduced northern pike density on largemouth bass were less evident. The largemouth bass population may be returning to higher density with smaller size structure observed before pike were introduced. The sport fish community responded positively to the removal of northern pike in this small lake.     

Behavior of pike (Esox lucius L.) >50 cm in a turbid reservoir and in a clearwater lake

Abstract – Pike from two different waters were radio-tagged and released immediately upon recovery. In Bygholm Reservoir 19 pike (52–72 cm) and in Lake Ring 15 pike (53–77 cm) were tagged in late February and early March. Bygholm (58 ha) is a shallow eutrophic reservoir and Ring (22 ha) is a natural mesotrophic lake. The positions of the tagged fish were recorded through weekly trackings and a number of 3-day tracking sessions during a 9-month period. Diel activity patterns, home range sizes and habitat utilization by pike was compared between the reservoir and the lake. The pike in the lake occupied larger areas than the pike in the reservoir and were less associated with vegetation. In both waters pike were found more often in, or close to, vegetation during summer than during winter. No difference in average movement of pike was seen between the waters, but pike were more stationary in the reservoir than in the lake. There was no difference in the level of movement between different times of the day, but the diel rhythm of the pike changed significantly over the year. There were large behavioral differences between pike in the lake and in the reservoir and even more variation between individuals within each population.     

中国和匈牙利白斑狗鱼群体遗传变异的微卫星标记分析

本研究应用18个微卫星分子标记,对白斑狗鱼(Esox lucius L.)3个中国新疆群体(乌伦古湖、吉力湖和6号湖)和1个匈牙利巴拉顿湖群体的遗传结构进行了分析.结果表明,3个中国白斑狗鱼群体的平均等位基因丰富度(AR)、平均观测杂合度(Ho)和平均期望杂合度(HE)均显著低于匈牙利巴拉顿湖群体(P＜0.05),而匈牙利群体的平均近交系数(FIS)高于中国群体;经SMM和TPM模型检测,匈牙利白斑狗鱼群体存在显著的遗传瓶颈信号(P＜0.001);AMOVA和群体两两比较的FST值表明,中国与匈牙利白斑狗鱼的遗传分化十分显著(P＜0.01);NJ树、主成分分析(PCA)进一步证实中国白斑狗鱼与匈牙利白斑狗鱼群体间存在显著的遗传差异和分化.此外,贝叶斯遗传聚类结果表明,中国新疆6号湖白斑狗鱼群体极可能来源于乌伦古湖,而非吉力湖.     

Selective predation of threespine stickleback by rainbow trout

Abstract – Threespine stickleback (Gasterosteus aculeatus) with divergent pelvic phenotypes from Wallace Lake, Alaska, were exposed to rainbow trout (Oncorhynchus mykiss) to test for selective predation. Trout more often successfully preyed upon individuals with pelvic reduction, which supports the hypothesis that robust pelvic girdles are maintained in stickleback populations because of selection by fish predators. Stickleback with complete pelvic girdles experienced a higher incidence of wounds from unsuccessful predation attempts, although this finding was not statistically significant, possibly because of low frequencies of wounded individuals. Spines likely facilitate postcapture defence, although stickleback with spines may also be less targeted by trout. This study supports the hypothesis that stocked rainbow trout pose a conservation threat to pelvic‐reduced stickleback populations.     

Using otolith microchemical analysis to investigate the importance of brackish bays for pike (Esox lucius Linnaeus, 1758) reproduction in the southern Baltic Sea

The brackish Baltic Sea is inhabited by several primary freshwater fish species. The pike (Esox lucius) is the largest of these species and acts as the top predator in the marine food web of the Baltic Sea. Prior studies have shown the importance of brackish bays as spawning grounds for the Baltic Sea pike. To identify the spawning habitat of the pike population around the island of Rügen (southern Baltic Sea)—either freshwater streams flowing into the Baltic or brackish lagoons of the Baltic—we used the ICPMS method to quantify the strontium to calcium (Sr:Ca) ratios in sagittal otoliths of 79 adult pike. In total, only six per cent (n = 5) of the analysed Baltic Sea individuals were classified as being of freshwater origin. Ninety‐four per cent (n = 74) of analysed pike were classified as having hatched in brackish water. Compared to previous studies on Baltic Sea pike, our sample shows a high proportion of pike that is of brackish origin: this highlights the adaptive capacity of this species with regard to its ability to reproduce in different salinities. Our data highlight the importance of brackish bays for pike reproduction in the southern Baltic Sea, even if pike live on the upper limit of their salinity tolerance in this area. This is an important finding considering decreases in commercial catches in the last 30 years indicating a population decline supposedly related to recruitment failures.     

Reproductive costs, condition and carotenoid-based colour in natural populations of threespine stickleback (Gasterosteus aculeatus)

Abstract –  Male threespine stickleback, Gasterosteus aculeatus , display an orange/red throat during the breeding season, which is carotenoid-based colour. We examined the relationship between energy-based costs of reproduction and colour in three lacustrine populations of threespine stickleback: two benthic (Willow and Big Beaver) and one limnetic (Lynne) ecotypes. In two lakes (Willow and Big Beaver) where benthic males defend nests against cannibalistic groups, males paid higher energy costs than in the third lake (Lynne) where cannibalistic groups are absent. We then examined colour variation within each population. Males from Lynne Lake did not change colour during the parental stage, whereas males from Willow and Big Beaver lakes became more intensely coloured. In addition, colour was typically independent of condition within stages. We propose that energy-based reproductive costs could explain some of the observed variation in colour by altering the payoffs associated with signalling effort during current versus future reproduction.     

Pike predation on hatchery-reared Atlantic salmon smolts in a northern Baltic river

Abstract –  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.     

Using stable isotope data to quantify niche overlap and diets of muskellunge,northern pike and walleye in a deep Minnesota lake

Muskellunge (Esox masquinongy Mitchill), northern pike (Esox lucius L.) and walleye (Sander vitreus Mitchill) often coexist in lake communities, yet uncertainty exists about the potential for interspecific competition among these top predators. Stable isotope data were used to assess niche overlap and diets of these predators in Elk Lake (Minnesota, U.S.A). δ¹³C indicated primary production sources (e.g. pelagic v. littoral) and δ¹⁵N indicated trophic position; the bivariate distribution of these isotopes defined the species’ isotopic niche. Niche overlap probabilities were calculated and stable isotope mixing models were used to quantify diet proportions. Muskellunge and northern pike niches overlapped little (<10%), while walleye overlapped muskellunge (15%–60%) and northern pike (33%–53%) more extensively. Muskellunge diets focused (50%) on cisco (Coregonus artedi Lesueur), walleye primarily assimilated non-cisco prey fish (80%), and northern pike diets were dominated by non-cisco prey fish (45%) and invertebrates (40%). The presence of a cisco population and the flexibility of northern pike to use invertebrate resources may decrease potential competition among these predators. However, cisco are threatened by climate change and eutrophication, and our results suggest that extirpation of cisco may cause major changes in potential competitive interactions among these top predators. Moreover, cisco were unique among prey species in their ability to exploit pelagic energy, such that loss of cisco will likely alter energy flow in lake food webs where they currently exist.     

Increased population density of pike Esox lucius– a result of selective harvest of large individuals

Abstract – The effect of selective harvest of large pike on number of middle‐sized pike was tested in a small, eutrophic lake in SE Norway. The pike population was estimated using a mark–recapture method in two different periods: before (1980–1983) and during the manipulation of the pike population (2004–2006). After an extensive size selective harvest of large pike (≥65 cm) in 2004, the number of pike in length‐class 45–65 cm, mainly 3+ pike, increased significantly from 2004 to 2005. The number in this length‐class was even higher in 2006. Since 2+ pike was part of the diet of large pike, the increase in number of 3+ pike in 2005 and 2006 is probably due to reduced consumption of 2+ pike, following the substantial selective removal of large pike in 2004 and 2005. To maintain a high annual survival of young pike, a selective exploitation of large pike has to be carried out annually.     

Regulation of Biomasses of Small (<41 cm) Northern Pike (Esox Indus L.), with Special Reference to the Contribution of Individuals Stocked as Fingerlings (4–6cm)

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.     

Voluntary angler logbooks reveal long‐term changes in a lentic pike,Esox lucius,population

Sixty‐two years of voluntarily collected angling logbook data from a large natural Danish lake were used to study variation in pike, Esox lucius L., CPUE (catch per unit effort), expressed as no. of captured pike per boat trip, as an index of stock size. Pike CPUE was positively related to pike release rate by anglers and negatively affected by certain commercial fishers. The stocking of young‐of‐the‐year pike and a fishery‐dependent index of perch, Perca fluviatilis L., abundance (which may be pike prey or predator depending on size) did not correlate with pike CPUE. Analyses of the size distribution of pike, based on sizes of annual record trophy pike captured by anglers, confirmed the negative impact of commercial pike fishing and revealed a positive influence of air temperature. It is concluded that high‐quality angler logbooks that record effort and catch can be a cost‐effective tool to inform lake fisheries management by revealing long‐term population trends. Further, state space modelling, a statistical technique not yet seen in recreational fisheries science, is recommended as a tool to model proxies for population dynamics from angler logbook data.     

Potential reasons for the changes in the abundance of pike, Esox lucius, in the western Gulf of Finland, 1939–2007

Abstract  Pike, Esox lucius L., catch-per-unit-effort (CPUE) in rod and line fishing fluctuated considerably in the western Gulf of Finland between 1939 and 2007. Since the beginning of the 1980s, CPUE has been only 3–4% of the highest CPUE during the period, suggesting a drastic decrease in population size. The collapse of the population coincided with a rise in the nutrient level in the Baltic Sea and consequent changes in productivity, turbidity and vegetation. The differences in the food web that followed the environmental change may partly explain the variation both in CPUE and in the mean weight of pike caught. Long-term fluctuations in salinity and temperature, however, did not seem to affect the population size. The mean weight of pike fluctuated inversely with CPUE, indicating changes in the recruitment of pike to the study area.     

Growth and recruitment dynamics of young‐of‐year northern pike: Implications for habitat conservation and management

Maximising growth during the months after hatching is critical for fishes to surpass predator gape limits, make ontogenetic shifts in diet and increase overwinter survival. Constraints on growth during early life stages can have population and community‐level implications, yet are rarely addressed by habitat restoration or fishery management efforts. To assess environmental controls on larval growth rates, we sampled adult and young‐of‐year (YOY) northern pike (Esox lucius) emigrating from spawning grounds in six tributaries of Lake Michigan. We found that YOY growth rates differed significantly among natal streams, in parallel with variation in hatch date and water temperatures. Within each stream, individual growth rates were positively associated with trophic position, as measured by nitrogen isotope enrichment and gut contents. Earlier hatching individuals also grew faster, but the strength of this relationship varied with warming water temperatures (i.e., 21–27°C). Ageing of adult spawners indicated no differences among streams in average growth rates later in life. Our findings suggest that restoration efforts should replicate ecological conditions found in habitats producing large numbers of fast‐growing YOY. Key habitat attributes include adequate water level throughout the spring spawning season, and stable, warm water temperature conditions. Providing these environments during early life history could enhance the robustness of northern pike populations by boosting fitness from hatching to emigration to adult habitats.     

Recreational anglers as citizen scientists can provide data to estimate population size of pike,Esox lucius

Catch‐per‐unit‐effort is often used as an approximation of population size. However, for the management and conservation of populations, information about the number of individuals is fundamental. Pike, Esox lucius L., is a popular fish species for recreational anglers. In this study, data in the form of journal keeping by anglers were used: date; place; and photographs of the captured fish; pike were identified based on their natural markings in combination with length measurements. The data were analysed by spatial capture–recapture (SCR) models. Results showed that a small and densely vegetated lake (6.7 ha) in south‐eastern Sweden had a population size of 91 (±22 SE) pike ≥60 cm. On one occasion, 10 individuals were caught, that is 11.1% of the population, highlighting that angling may potentially have a substantial impact on the population size. Hopefully, this study can inspire angler–manager collaborations for conservation of fish stocks.     

Introduced northern pike predation on salmonids in southcentral Alaska

Northern pike (Esox lucius) are opportunistic predators that can switch to alternative prey species after preferred prey have declined. This trophic adaptability allows invasive pike to have negative effects on aquatic food webs. In Southcentral Alaska, invasive pike are a substantial concern because they have spread to important spawning and rearing habitat for salmonids and are hypothesised to be responsible for recent salmonid declines. We described the relative importance of salmonids and other prey species to pike diets in the Deshka River and Alexander Creek in Southcentral Alaska. Salmonids were once abundant in both rivers, but they are now rare in Alexander Creek. In the Deshka River, we found that juvenile Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) dominated pike diets and that small pike consumed more of these salmonids than large pike. In Alexander Creek, pike diets reflected the distribution of spawning salmonids, which decrease with distance upstream. Although salmonids dominated pike diets in the lowest reach of the stream, Arctic lamprey (Lampetra camtschatica) and slimy sculpin (Cottus cognatus) dominated pike diets in the middle and upper reaches. In both rivers, pike density did not influence diet and pike consumed smaller prey items than predicted by their gape‐width. Our data suggest that (1) juvenile salmonids are a dominant prey item for pike, (2) small pike are the primary consumers of juvenile salmonids and (3) pike consume other native fish species when juvenile salmonids are less abundant. Implications of this trophic adaptability are that invasive pike can continue to increase while driving multiple species to low abundance.     

Long-term variation in brown trout, Salmo trutta L., stocking success in a large lake: interplay between availability of suitable prey and size at release

Abstract –  Factors affecting long-term variation in brown trout, Salmo trutta L., stocking success were examined in a large lake, Lake Oulujärvi, in central Finland. Brown trout were stocked in spring (late May to early June) in 1974–1991 and in summer (late June to early July) in 1992–2001. The biomass of the vendace, Coregonus albula (L.), population (prey) at release time had the largest positive effect on stocking success within both periods: biomass of adult vendace in spring and both 0+ and adult vendace in summer. Increasing the size of stocked fish had a positive effect if the vendace available at release were only adults. The increasing trend of predator-catch-per-unit-effort (CPUE) [combined CPUE of northern pike Esox lucius L., burbot Lota lota (L.), and pike-perch Stizostedion lucioperca (L.)] through the study period and its negative effect on trout stocking success suggested an increasing effect of predation within the entire time series.     

Microsatellite polymorphism in Italian populations of northern pike (Esox lucius L.)

Northern pike (Esox lucius) is not considered an endangered species in Italy, but since recent studies indicate the decline of this population, conservation and management strategies based on the genetic differentiation of natural northern pike populations are needed. In this paper, genetic diversity was analysed in 10 Italian and 2 East European northern pike populations by means of seven microsatellite loci. Data indicated an appreciable genetic differentiation, in spite of a low genetic variation, and agreed with the low level of genetic polymorphism already observed for this species in North America and North Europe. Results of statistical tests revealed genetic peculiarities of the Italian populations, even though signals of recent contact between populations were found and discussed in relation to anthropic impacts, particularly to the stocking practice. This investigation represents the first approach to the knowledge of the genetic variability of Italian pike populations using microsatellite markers, and reported results could be of interest for future management and conservation programmes of this species in Italy.     

From regionally predictable to locally complex population structure in a freshwater top predator: river systems are not always the unit of connectivity in Northern Pike Esox lucius

Contemporary genetic diversity is the product of both historical and contemporary forces, such as climatic and geological processes affecting range distribution and continuously moulded by evolutionary forces selection, gene flow and genetic drift. Predatory freshwater fishes, such as Northern Pike Esox lucius, commonly exhibit small population sizes, and several local populations are considered endangered. Pike inhabit diverse habitat types, including lakes, rivers and brackish marine waters, thus spanning from small isolated patches to large open marine systems. However, pike population structure from local to regional scales is relatively poorly described, in spite of its significance to developing conservation measures. We analysed microsatellite variation in a total of 1185 North European pike from 46 samples collected across both local and regional scales, as well as over time, to address two overarching questions: Is pike population structure associated with local and/or regional connectivity patterns, and which factors likely have the main influence on the contemporary distribution of genetic diversity? To answer this, we combined estimators of population diversity and structure to assess evidence of whether populations within (i) habitats, (ii) drainage systems and (iii) geographical regions are closer related than among these ranges, and whether patterns are temporally stable. Contrasting previous predictions that genetic drift obscures signals of postglacial colonisation history, we identified clear regional differences in population genetic signatures, suggesting a major effect of drainage divides on colonisation history and connectivity. However, several populations deviated from the general pattern, showing that local processes may be complex and need to be examined case‐by‐case.     

Genetic population structure of pike (Esox lucius Linnaeus, 1758) in the brackish lagoons of the southern Baltic Sea

The Baltic Sea is a unique ecosystem and the largest body of brackish water in the world. It is inhabited by several originally freshwater fish species, one of them being pike (Esox lucius), which is adapted to the mesohaline conditions of the southern Baltic Sea and colonises its south‐western bays and lagoons. Using twelve microsatellite markers, we analysed the genetic structure of 407 Baltic Sea pike collected from ten locations in the coastal zone of the southern Baltic region and adjacent rivers and nearby lakes. We used traditional F‐statistics and a Bayesian approach implemented in STRUCTURE to investigate spatial structuring. Our results show an overall isolation by distance pattern with two distinct coastal clusters. The border area between the two clusters is characterised by a sharp salinity leap, indicating that the dispersal barrier is not physical, but physiological in nature. A third cluster was formed by three lake populations, presumably as a result of past stocking measures. Additional otolith microchemical studies demonstrate the brackish origin and residency of the majority of the pike from the coastal lagoons, supporting previous studies which suggest that the anadromous pike “ecotype” is scarce in this area of the Baltic Sea. Our results contribute to current knowledge on the population genetics of Baltic Sea pike in a previously unsampled area.