Female Pike Research Articles

Examining the effects of authentic C&R on the reproductive potential of Northern pike

The practice within recreational fisheries to release captured fish back to the wild, known as catch-and-release (C&R), is an increasingly important strategy to protect fish stocks from overexploitation. However, C&R is a stressor and since animal reproduction is particularly sensitive to stress there is reason to suspect that such a practice induces sublethal fitness consequences. Here, we investigated whether and how C&R fishing influenced the reproductive potential in an anadromous population of Northern pike (Esox lucius). First, female pike were exposed to authentic C&R using rod-and-reel fishing in a coastal foraging habitat prior to the spawning period. Next, we observed the migration to the freshwater spawning habitat and compared both the timing of arrival and maturity stage between C&R-treated and control individuals. Finally, to evaluate effects on the quality and viability of eggs we stripped captured control and recaptured C&R-treated females, measured egg dry mass to assess nutrient content, conducted artificial fertilisations and incubated eggs in a controlled laboratory experiment. We found no evidence of C&R causing alterations in either arrival time, maturity stage, or the quality and viability of fertilised eggs. In combination, our results suggest that long-term effects of C&R-induced stress on key reproductive traits of pike, if any, are minor.

Environmental exposure to a major urban wastewater effluent: Effects on the energy metabolism of northern pike

Municipal wastewater effluents (MWWEs) consist of dynamic and complex mixtures of chemical and biological compounds that can alter the health of exposed aquatic organisms. Disturbance of energy metabolism has been reported in fish exposed to MWWEs. However, there is a scarcity of knowledge on the physiological events leading to perturbation of energy balance and thyroid regulation, and associated lipid metabolism. The objective of the present study was to use a set of biomarkers, from gene transcription to body condition, to investigate the effects of a chronic environmental exposure to a major primary MWWE on fatty acid metabolism and thyroid hormone levels in northern pike (Esox lucius) collected from the St. Lawrence River near Montreal (QC, Canada). The exposure of pike to MWWE was examined through determination of a suite of persistent and bioaccumulative halogenated flame retardants in liver as this effluent is a known regional source for these chemicals. Greater hepatic concentrations of polybrominated diphenyl ethers (PBDEs, range: 29.6–465ng/g w.w. and 88.8–823ng/g w.w. in females and males, respectively) and other halogenated flame retardants (e.g., dechlorane-related compounds) were determined in fish collected downstream of the MWWE’s point of discharge relative to the upstream site. This exposure in male pike was associated with decreased acyl-coA oxidase (acox1) and fatty acid synthase (fasn) mRNA levels as well as a decreased acyl-coA oxidase (ACOX) activity in liver. In female pike, MWWE exposure was associated with lower circulating free and total triiodothyronine (T3) levels and a tendency for greater total lipid percentages in liver. Present findings provide evidence that chronic exposure of a top predator fish to MWWE can be related to gender-specific effects on fatty acid metabolism and thyroid hormone homeostasis, and highlight the need for further investigation.

Repetition without Reproduction: Esko Männikkö’s The Female Pike

Esko Männikkö’s The Female Pike (1990–1995) depicts lonely, middle-aged men at their homes in the economically depressed, depopulated rural regions of northern Finland. Initially, the photographic series seems to share the goal that the photographer Bert Teunissen establishes for his ongoing Domestic Landscapes project: to salvage the remnants of cultural particularity before they are obliterated by the homogenizing effects of globalization. However, rather than reproducing or preserving national identity, Männikkö’s repetition of a rural iconography weighted with cultural significance in Finland has the effect of hollowing it out, opening a space to rethink it in his subsequent series Organized Freedom, Edition 2 (2001).

Intensive fishing can mediate stronger size-dependent maternal effect in pike (Esox lucius)

In pike E. lucius L., evidence on maternal effect on reproductive output is mixed. We studied whether older and larger pike females produce eggs and larvae of higher quality (weight, starvation resistance) in three forest lakes in southern Finland. Later, the study lakes were subjected to intensive experimental pike fishing, which we assumed would increase resource availability and lead to higher maternal investment (larger egg size). Length of female pike was positively correlated with the dry weight of eggs and larvae but this relation was dependent on female age. In old females, the effect of female length on egg weight was lower or even negative. Survival analysis showed a positive effect of female length on larval survival time indicating that larvae from larger females are less vulnerable to starvation during the early stage of life. After the intensive pike fishing, the positive effect of female length on egg weight was stronger in all age classes probably due to the released resources. Based on the high quality and amount of reproductive products in large (but not very old) females, they are important for the reproduction of pike populations. This should be considered in fisheries management.

Bioaccumulation of organochlorine pollutants in the fish community in Lake Årungen, Norway

Organochlorine pollutants in the major fish species (pike Esox lucius, perch Perca fluviatilis, and roach Rutilus rutilus) of Lake Årungen, Norway, were investigated after an extensive removal of large pike in 2004. The organochlorine pollutants detected in fish liver samples in 2005 were dichlorodiphenyltrichloroethane (DDTs), polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), and heptachlor epoxide (HCE). DDTs were the dominant among all analyzed OCs. ΣPCB and HCB, detected in fish from two clearly distinct trophic levels (prey and predators), give an indication of biomagnification. All OC concentrations in female pike were significantly lower compared to males, which might be due to the removal of high concentrations of pollutants in roe during spawning.

Trait changes in a harvested population are driven by a dynamic tug-of-war between natural and harvest selection

Selective harvest of large individuals should alter natural adaptive landscapes and drive evolution toward reduced somatic growth and increased reproductive investment. However, few studies have simultaneously considered the relative importance of artificial and natural selection in driving trait changes in wild populations. Using 50 years of individual-based data on Windermere pike (Esox lucius), we show that trait changes tracked the adaptive peak, which moved in the direction imposed by the dominating selective force. Individual lifetime somatic growth decreased at the start of the time series because harvest selection was strong and natural selection was too weak to override the strength of harvest selection. However, natural selection favoring fast somatic growth strengthened across the time series in parallel with the increase in pike abundance and, presumably, cannibalism. Harvest selection was overridden by natural selection when the fishing effort dwindled, triggering a rapid increase in pike somatic growth. The two selective forces appear to have acted in concert during only one short period of prey collapse that favored slow-growing pike. Moreover, increased somatic growth occurred concurrently with a reduction in reproductive investment in young and small female pike, indicating a tradeoff between growth and reproduction. The age-specific amplitude of this change paralleled the age-specific strength of harvest pressure, suggesting that reduced investment was also a response to increased life expectancy. This is the first study to demonstrate that a consideration of both natural selection and artificial selection is needed to fully explain time-varying trait dynamics in harvested populations.

Biomarkers of Contaminant Exposure in Northern Pike (Esox lucius) from the Yukon River Basin, Alaska

As part of a larger investigation, northern pike (n = 158; Esox lucius) were collected from ten sites in the Yukon River Basin (YRB), Alaska, to document biomarkers and their correlations with organochlorine pesticide (total p,p'-DDT, total chlordane, dieldrin, and toxaphene), total polychlorinated biphenyls (PCBs), and elemental contaminant (arsenic, cadmium, copper, lead, total mercury, selenium, and zinc) concentrations. A suite of biomarkers including somatic indices, hepatic 7-ethoxyresorufin O-deethylase (EROD) activity, vitellogenin concentrations, steroid hormone (17B- ustradiol and 16-kebtestosteront) concentrations, splenic macrophage aggregates (MAs), oocyte atresia, and other microscopic anomalies in various tissues were documented in YRB pike. Mean condition factor (0.50 to 0.68), hepatosomatic index (1.00% to 3.56%), and splenosomatic index (0.09% to 0.18%) were not anomalous at any site nor correlated with any contaminant concentration. Mean EROD activity (0.71 to 17.51 pmol/min/mg protein) was similar to basal activity levels previously measured in pike and was positively correlated with selenium concentrations (r = 0.88, P < 0.01). Vitellogenin concentrations in female (0.09 to 5.32 mg/mL) and male (<0.0005 to 0.097 mg/mL) pike were not correlated with any contaminant, but vitellogenin concentrations >0.01 mg/mL in male pike from multiple sites indicated exposure to estrogenic compounds. Mean steroid hormone concentrations and percent oocyte atresia were not anomalous in pike from any YRB site. Few site differences were significant for mean MA density (1.86 to 6.42 MA/mm(2)), size (812 to 1481 microm(2)), and tissue occupied (MA-%; 0.24% to 0.75%). A linear regression between MA-% and total PCBs was significant, although PCB concentrations were generally low in YRB pike (< or =63 ng/g), and MA-% values in female pike (0.24% to 0.54%) were lower than in male pike (0.32% to 0.75%) at similar PCB concentrations. Greater numbers of MAs were found as zinc concentrations increased in YRB female pike, but it is unlikely that this is a causative relationship. Histological abnormalities observed in gill, liver, spleen, and kidney tissues were not likely a result of contaminant exposure but provide information on the general health of YRB pike. The most common histologic anomalies were parasitic infestations in various organs and developing nephrons and nephrocalcinosis in posterior kidney tissues. Overall, few biomarker responses in YRB pike were correlated with chemical contaminant concentrations, and YRB pike generally appeared to be healthy with no site having multiple anomalous biomarker responses.

Endocrine (sexual) disruption is not a prominent feature in the pike (Esox lucius), a top predator, living in english waters

The high incidence of intersex roach (Rutilus rutilus) in some United Kingdom rivers that has been associated with exposure to sewage treatment works (STWs) effluent led us to hypothesize that top predator fish also may be affected by estrogenic chemicals, because they are likely to bioaccumulate lipophilic compounds through a predator-prey relationship. To investigate this possibility, pike (Esox lucius) were sampled both upstream and downstream of STWs and then examined for total estrogenic activity of their bile, as measured using a yeast-based estrogen assay to determine the degree of recent exposure of the pike to estrogens and vitellogenin induction, and for possible disruption of sexual development, as measured using histological analysis of the gonads. No evidence of severe disruption was found in the sampled fish, which came from 16 sampling sites that were representative of English rivers. However, 14% of pike were intersex, of which 15 of 16 showed patches of male germ cells among predominantly female gonadal tissue. The incidence of masculinization was independent of whether the pike had been sampled upstream or downstream of STWs. Although pike are gonochoristic, it is not known if this masculinization of presumptive female pike is normal or, instead, indicative of endocrine disruption. Vitellogenin concentrations were not elevated in male pike at sites either upstream or downstream of STWs. The results suggest that sexual disruption is not common in pike, a fish at the top of the food chain in the freshwaters of England.

Behavioural interactions between prey (trout smolts) and predators (pike and pikeperch) in an impounded river

Movements of radio-tagged pike Esox lucius (L.), pikeperch Stizostedion lucioperca (L.) and outward migrating sea trout smolts Salmo trutta (L.) were studied in a shallow Danish reservoir to obtain information of predator–prey interactions between these species. Twenty pikeperch (55–74 cm) and 19 pike (52–72 cm) were tagged. Female pikeperch spent more time near the outlet sluice during the smolt run (May) than at other times of the year, apparently actively hunting the smolts delayed in this area. In contrast, male pikeperch did not seem to participate in the smolt predation but remained stationary during the smolt run, presumably guarding their nests. Most tagged pike were present at the spawning grounds during the peak of the smolt run, where they had little chance of smolt encounter. Twenty migrating trout smolts were radio-tagged in the river upstream of the reservoir. Ten of these were located in the vicinity of the outlet sluice at least once, but were unwilling or unable to find and enter the sub-surface outlet sluice. Only one tagged smolt left the reservoir. After 1–12 days in the reservoir, the remaining smolts were eaten by pikeperch or pike and the results indicate that female pikeperch and few female pike have adjusted their behaviour to predation on smolts during the smolt run. The smolt predation in this man-made reservoir is higher than in natural lakes, probably due to the changed physical environment and introduced predators, such as pikeperch. The outlet sluice practice and the temporal overlap between smolt run and predator-spawning may be key factors in smolt survival. Copyright © 2000 John Wiley & Sons, Ltd.

Seasonal changes in the neutral and polar lipid fatty acid content of female northern pike (Esox lucius L.)

We quantified seasonal changes in the total fatty acid content and the content of major fatty acid classes (i.e., saturates, polyunsaturates, etc.) in the neutral lipids and polar lipids of ovaries, liver, white muscle, and adipopancreatic tissue of female northern pike in central Alberta. Concentrations (percent wet weight) of polar lipid fatty acids (PLFAs) increased during fall and winter in all the organs and tissues examined. As the ovaries were recrudescing between July and March, ovary PLFA content increased from 0.03 to 4.60 g and the combined PLFA content of the three somatic tissues increased from 1.87 to 2.68 g (quantities are expressed per kilogram carcass weight of pike). During this period the quantity of neutral lipid fatty acids (NLFAs) (per kilogram of carcass weight) in the ovary increased from 0.01 to 1.95 g and liver NLFA content decreased from 0.60 to 0.14 g. The NLFA content of adipopancreatic tissue was 3.5–5.5 g/kg carcass weight and that in muscle was 2–4 g/kg carcass weight, but neither showed significant seasonal variation. There were no significant seasonal changes in either the total fatty acid content or the content of any fatty acid class in the combined neutral lipids or combined total lipids (neutral lipids plus polar lipids) of the three somatic tissues. Thus, there do not appear to be large seasonal transfers of fatty acids from somatic to ovarian tissues or from neutral to polar lipids in female pike.

Spawning activity of male and female pike, Esox lucius L., determined by acoustic tracking

Two male and three female pike, Esox lucius L., were tracked by means of intraperitoneally implanted acoustic transmitters prior to and throughout the 1988 spawning season in Loch Davan, Scotland. Highly significant variations in activity occurred on a diel and seasonal basis. Fish were relatively inactive at night for the whole of the tracking period. Mean daily distance moved ranged between 0.43 and 0.44 km∙d−1 for females and between 0.24 and 0.38 km∙d−1 for males in the weeks preceding spawning (March 27 – April 16); increased to a peak of 1.13 km∙d−1 for females and 1.72 km∙d−1 for males in the week April 24–30; and subsequently decreased to prespawning levels, 0.29 km∙d−1 for females and 0.24 km∙d−1 for males, by the week May 8–14. Levels of visually observed pike spawning activity followed a similar pattern. Males were more active than females for most of the spawning period; no significant differences were found before and after spawning. Highest levels of activity coincided with elevated water levels and water temperatures of 8–10 °C.

The Food of the Pike, Esox lucius, in Heming Lake, Manitoba

The stomach contents of 29,477 northern pike (Esox lucius) captured mainly in gill nets at Heming Lake, Manitoba, between 1950 and 1962 were examined. The food consisted almost exclusively of fish: trout-perch (Percopsis omiscomaycus) and yellow perch (Perca flavescens). Other fish included common suckers (Catostomus commersoni), spottail shiners (Notropis hudsonius), sticklebacks (Eucalia inconstans and Pungitius pungitius), pike, burbot (Lota lota), whitefish (Coregonus clupeaformis), tullibee (Leucichthys sp.), yellow walleye (Stizostedion vitreum), cottid (Cottus cognatus), and darters (Etheostoma nigrum). Among invertebrates were crayfish, mayflies, dragonflies, caddisflies, and leeches. Ducks, small mammals, and frogs formed an insignificant part of the diet. Seasonal variation in food content and annual variation in the degree of feeding were evident. Trout-perch were important as food items in May and June, the spottail shiner in July, the yellow perch in August and September, and stickleback between October and March. Coregonine fishes, important in the life-cycle of Triaenophorus crassus but of minor importance as pike food, occurred in higher concentrations in October. There appeared to be annual differences in the degree of feeding, possibly related to differences in temperature. The frequency of empty stomachs from pike caught by angling and in gill nets was approximately the same. No obvious differences were noted in feeding habits of male and female pike, but there were some minor differences in the food of pike from shallow and deeper water habitats. Over an 11-year period of intensive fishing, there did not appear to be any unusual changes in the food habits of pike. The size of the prey is related to the size of the pike. There is a marked increase in the number of small perch, trout-perch, and spottail shiners consumed by pike of increasing size. The possible effects of the predator (pike) on other prey species is discussed. Relative abundance and seasonal availability appeared to determine the incidence of prey consumed. The reduction in the average size of the pike appears to have had some effect on the survival of other species of fish.