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Ecosystem surveys are carried out annually in the Barents Sea by Russia and Norway to monitor the spatial distribution of ecosystem components and to study population dynamics. One component of the survey is mapping the upper pelagic zone using a trawl towed at several depths. However, the current technique with a single codend does not provide fine-scale spatial data needed to directly study species overlaps. An in-trawl camera system, Deep Vision, was mounted in front of the codend in order to acquire continuous images of all organisms passing. It was possible to identify and quantify of most young-of-the-year fish (e.g. Gadus morhua, Boreogadus saida and Reinhardtius hippoglossoides) and zooplankton, including Ctenophora, which are usually damaged in the codend. The system showed potential for measuring the length of small organisms and also recorded the vertical and horizontal positions where individuals were imaged. Young-of-the-year fish were difficult to identify when passing the camera at maximum range and to quantify during high densities. In addition, a large number of fish with damaged opercula were observed passing the Deep Vision camera during heaving; suggesting individuals had become entangled in meshes farther forward in the trawl. This indicates that unknown numbers of fish are probably lost in forward sections of the trawl and that the heaving procedure may influence the number of fish entering the codend, with implications for abundance indices and understanding population dynamics. This study suggests modifications to the Deep Vision and the trawl to increase our understanding of the population dynamics.

Energy metabolism was assessed in red blood cells (RBCs) from Atlantic cod and short-horned sculpin, two species that have markedly different levels of blood glucose. The objective was to determine whether the level of extracellular glucose has an impact on rates of glucose metabolism. The blood glucose level was 2.5 mmol l(-1) in Atlantic cod and 0.2 mmol l(-1) in short-horned sculpin, respectively. Oxygen consumption, lactate production and glucose utilization were measured in whole blood and related to grams of RBCs. Glucose utilization was assessed by measuring both glucose disappearance and the production of (3)H2O from [2-(3)H]-glucose. RBCs from both species have an aerobic-based metabolism. In Atlantic cod, extracellular glucose is sufficient to provide the sum of glucosyl equivalents to support both oxidative metabolism and lactate production. In contrast, extracellular glucose can account for only 10% of the metabolic rate in short-horned sculpin RBCs. In both species, about 70% of glucose enters the RBCs via facilitated transport. The difference in rates of extracellular glucose utilization is related to the extremely low levels of blood glucose in short-horned sculpin. In this species energy metabolism by RBCs must be supported by alternative fuels., (© 2014. Published by The Company of Biologists Ltd.)

To estimate the impact of accidental oil-spills on cod fisheries a model framework is developed in which a Dynamic Energy Budget (DEB) model is applied to assess mortality caused by petroleum substances in early life stages. In this paper we report on a literature search and DEB analyses, aiming for cod specific DEB-parameters. Furthermore, we explored the relevance of Fathead minnow DEB-parameters as surrogate by comparing LC50 values calculated from DEB-parameters with literature. Cod specific DEB-parameters could not be estimated based on available literature. LC50 values calculated from Fathead minnow DEB-parameters were higher than literature LC50 for early life stages of fish. Applying an extrapolation factor of 50 to the DEB-parameters resulted in LC50 values that were below literature irrespective of life stage. Therefore, we propose to use the last as an estimate for early life stages in cod and recommend relevant experiments with individual petroleum substances on cod., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The notion that the circadian rhythm is exclusively regulated by a central clock has been challenged by the discovery of peripheral oscillators. These peripheral clocks are known to have a direct influence on the biological processes in a tissue or cell. In fish, several peripheral clocks respond directly to light, thus raising the hypothesis of autonomous regulation. Several clock genes are expressed with daily rhythmicity in Atlantic cod (Gadus morhua) fast skeletal muscle. In the present study, myosatellite cell culture and short-term cultured fast skeletal muscle explant models were developed and characterized, in order to investigate the autonomy of the clock system in skeletal muscle of Atlantic cod. Myosatellite cells proliferated and differentiated in vitro, as shown by the changes in cellular and myogenic gene markers. The high expression of myogenic differentiation 1 during the early days post-isolation implied the commitment to myogenic lineage and the increasing mRNA levels of proliferating cell nuclear antigen (pcna) indicated the proliferation of the cells in vitro. Transcript levels of myogenic marker genes such as pcna and myogenin increased during 5 days in culture of skeletal muscle explants, indicating that the muscle cells were proliferating and differentiating under ex vivo conditions. Transcript levels of the clock gene aryl hydrocarbon receptor nuclear translocator-like 2 (arntl2) in myosatellite cells showed no daily oscillation regardless of photoperiod manipulation. On the other hand, mRNA levels of the clock gene circadian locomotor output cycles kaput (clock) showed circadian rhythmicity in 5-day-old skeletal muscle explant under different photoperiod regimes. The expression of arntl2, cryptochrome2 (cry2), period 2a (per2a) and nuclear receptor subfamily 1, group D, member 1 was not rhythmic in muscle explants but photoperiod manipulation had a significant effect on mRNA levels of cry2 and per2a. Taken together, the lack of rhythmicity of molecular clocks in vitro and ex vivo indicate that the putative peripheral clock in Atlantic cod fast skeletal muscle is not likely to be autonomous.

The spatial and temporal movement patterns of sympatric juvenile Atlantic cod Gadus morhua and Greenland cod Gadus ogac were studied using high-resolution radio-acoustic positioning in a coastal area of Newfoundland during the summers of 2009 and 2010. A total of 20 fish (10 G. ogac and 10 G. morhua) were equipped with acoustic transmitters and monitored for periods up to 23 days. Most fishes showed high site fidelity with mean residence times of 12·4 (G. morhua) and 14·4 days (G. ogac). A few individuals showed a transient use of the study area, ranging distances up to c. 4 km. Mean daily home ranges [95% kernel utilization distributions (KUDs)] and core activity areas were significantly larger for G. morhua (3·8 and 0·5 ha) than for G. ogac (2·7 and 0·3 ha). Home ranges were not related to total length (LT ) for G. morhua but showed a weak positive relationship for G. ogac. Gadus morhua occupied larger areas during the day while G. ogac occupied slightly larger areas at night. Mean rates of movement for G. ogac and G. morhua ranged from 0·83 to 1·24 and 0·76 to 1·76 LT s(-1) , respectively, and were highest during crepuscular periods. Overall, G. morhua were wider ranging, moved at faster rates and were active throughout the diel cycle compared to G. ogac of the same size. It is suggested that differential use of space and activity periods plays an important role in the successful coexistence of these two species., (© 2014 The Fisheries Society of the British Isles.)

The aim of this study was to characterize concentration- and time-dependent responses in juvenile Atlantic cod (Gadus morhua) following exposure for one and three weeks to the water-soluble fraction (WAF) of three weathered oils: Arabian Light crude oil (ALC), North Sea crude oil (NSC) and ship-diesel. The sum of polycyclic aromatic hydrocarbons (PAH) in water was highest after one week of exposure and within environmentally relevant concentrations. PAH metabolites in bile confirmed exposure to and uptake of PAHs. Hepatic cytochrome P450 1A (CYP1A) gene expression (mRNA quantification) increased dramatically following exposure to all three oil types (fold-change up to 165) and there was a time lag between gene and protein expression. Hepatic CYP1A protein concentration and ethoxyresorufin-O-deethylase (EROD) activity were more variable among individuals and treatments than gene expression. EROD activity in liver and gills increased in fish exposed to WAF from the two crude oils, but not in fish exposed to WAF from diesel. Exposure to diesel appeared to induce oxidative stress to a greater extent than exposure to crude oils. Other biomarkers (glutathione S-transferases, acetylcholine esterase, vitellogenin) did not appear to respond to the exposure and hence did not discriminate among oils. Biomarker responses in cod after exposure to weathered crude oils and diesel suggested that the CYP1A system and oxidative stress markers have the highest potential for discriminating among different oil types and to monitor the environmental consequences of spills., (Copyright © 2014 Elsevier B.V. All rights reserved.)

To test the hypothesis that impaired mitochondrial respiration limits cardiac performance at warm temperatures, and examine if any effect(s) are sex-related, the consequences of high temperature on cardiac mitochondrial oxidative function were examined in 10°C acclimated, sexually immature, male and female Atlantic cod. Active (State 3) and uncoupled (States 2 and 4) respiration were measured in isolated ventricular mitochondria at 10, 16, 20, and 24°C using saturating concentrations of malate and pyruvate, but at a submaximal (physiological) level of ADP (200µM). In addition, citrate synthase (CS) activity was measured at these temperatures, and mitochondrial respiration and the efficiency of oxidative phosphorylation (P:O ratio) were determined at [ADP] ranging from 25-200µM at 10 and 20°C. Cardiac morphometrics and mitochondrial respiration at 10°C, and the thermal sensitivity of CS activity (Q10=1.51), were all similar between the sexes. State 3 respiration at 200µM ADP increased gradually in mitochondria from females between 10 and 24°C (Q10=1.48), but plateaued in males above 16°C, and this resulted in lower values in males vs. females at 20 and 24°C. At 10°C, State 4 was ~10% of State 3 values in both sexes [i.e. a respiratory control ratio (RCR) of ~10] and P:O ratios were approximately 1.5. Between 20 and 24°C, State 4 increased more than State 3 (by ~70 vs. 14%, respectively), and this decreased RCR to ~7.5. The P:O ratio was not affected by temperature at 200μM ADP. However, (1) the sensitivity of State 3 respiration to increasing [ADP] (from 25 to 200μM) was reduced at 20 vs. 10°C in both sexes (Km values 105±7 vs. 68±10μM, respectively); and (2) mitochondria from females had lower P:O values at 25 vs. 100μM ADP at 20°C, whereas males showed a similar effect at 10°C but a much more pronounced effect at 20°C (P:O 1.05 at 25μM ADP vs. 1.78 at 100μMADP). In summary, our results demonstrate several sex-related differences in ventricular mitochondrial function in Atlantic cod, and suggest that myocardial oxidative function and possibly phosphorylation efficiency may be limited at temperatures of 20°C or above, particularly in males. These observations could partially explain why cardiac function in Atlantic cod plateaus just below this species׳ critical thermal maximum (~22°C) and may contribute to yet unidentified sex differences in thermal tolerance and swimming performance., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In the present study, our aim was to compare physiological and behavioural responses to different noxious stimuli to those of a standardized innocuous stimulus, to possibly identify aversive responses indicative of injury detection in a commercially important marine teleost fish, the Atlantic cod. Individual fish were administered with a noxious stimulus to the lip under short-term general anaesthesia (MS-222). The noxious treatments included injection of 0.1% or 2% acetic acid, 0.005% or 0.1% capsaicin, or piercing the lip with a commercial fishing hook. Counts of opercular beat rate (OBR) at 10, 30, 60, 90 and 120 min and observations of behaviour at 30 and 90 min post-treatment were compared with pre-treatment values and with control fish injected with physiological saline, an innocuous stimulus. Circulatory levels of physiological stress indicators were determined in all fish at 120 minutes post-treatment. All treatments evoked temporarily increased OBR that returned to pre-treatment levels at 60 minutes (saline, 0.005% capsaicin, hook), 90 minutes (0.1% acetic acid, 0.1% capsaicin), or 120 minutes (2% acetic acid), but with no significant differences from the control group at any time point. Fish treated with 0.1% and 2% acetic acid and 0.1% capsaicin displayed increased hovering close to the bottom of the aquaria and fish given 2% acetic acid and 0.1% capsaicin also displayed a reduced use of shelter. The only effect seen in hooked fish was brief episodes of lateral head shaking which were not seen pre-treatment or in the other groups, possibly reflecting a resiliency to tissue damage in the mouth area related to the tough nature of the Atlantic cod diet. There were no differences between groups in circulatory stress indicators two hours after treatment. This study provides novel data on behavioural indicators that could be used to assess potentially aversive events in Atlantic cod.

The classical notion of a centralized clock that governs circadian rhythmicity has been challenged with the discovery of peripheral oscillators that enable organisms to cope with daily changes in their environment. The present study aimed to identify the molecular clock components in Atlantic cod (Gadus morhua) and to investigate their daily gene expression in fast skeletal muscle. Atlantic cod clock genes were closely related to their orthologs in teleosts and tetrapods. Synteny was conserved to varying degrees in the majority of the 18 clock genes examined. In particular, aryl hydrocarbon receptor nuclear translocator-like 2 (arntl2), RAR-related orphan receptor A (rora) and timeless (tim) displayed high degrees of conservation. Expression profiling during the early ontogenesis revealed that some transcripts were maternally transferred, namely arntl2, cryptochrome 1b and 2 (cry1b and cry2), and period 2a and 2b (per2a and per2b). Most clock genes were ubiquitously expressed in various tissues, suggesting the possible existence of multiple peripheral clock systems in Atlantic cod. In particular, they were all detected in fast skeletal muscle, with the exception of neuronal PAS (Per-Arnt-Single-minded) domain-containing protein (npas1) and rora. Rhythmicity analysis revealed 8 clock genes with daily rhythmic expression, namely arntl2, circadian locomotor output cycles kaput (clock), npas2, cry2, cry3 per2a, nuclear receptor subfamily 1, group D, member 1 (nr1d1), and nr1d2a. Transcript levels of the myogenic genes myogenic factor 5 (myf5) and muscleblind-like 1 (mbnl1) strongly correlated with clock gene expression. This is the first study to unravel the molecular components of peripheral clocks in Atlantic cod. Taken together, our data suggest that the putative clock system in fast skeletal muscle of Atlantic cod has regulatory implications on muscle physiology, particularly in the expression of genes related to myogenesis.

The fatty acid (FA) profiles of the white muscle and heart tissues of cod Gadus morhua from five locations, Faroe Bank, Faroe Plateau, North-West Iceland, Norway-Barents Sea and Denmark-Skagerrak, were population dependent. The interregional differences of FAs were significantly dissimilar (P < 0.01) in most cases. By way of a rapid and simple analytical method, the stock dependence and harvest location of individual G. morhua were chemometrically determined by multivariate principal component analysis. The difference among the stocks was correlated with the average water temperature at the harvest locations. It thus appears that the tissue FA profile is a phenotypic trait that is partly temperature driven., (© 2014 The Fisheries Society of the British Isles.)

Recovery of depleted populations is fundamentally important for conservation biology and sustainable resource harvesting. At low abundance, population growth rate, a primary determinant of population recovery, is generally assumed to be relatively fast because competition is low (i.e., negative density dependence). But population growth can be limited in small populations by an Allee effect. This is particularly relevant for collapsed populations or species that have not recovered despite large reductions in, or elimination of, threats. We investigated how an Allee effect can influence the dynamics of recovery. We used Atlantic cod (Gadus morhua) as the study organism and an empirically quantified Allee effect for the species to parameterize our simulations. We simulated recovery through an individual-based mechanistic simulation model and then compared recovery among scenarios incorporating an Allee effect, negative density dependence, and an intermediate scenario. Although an Allee effect significantly slowed recovery, such that population increase could be negligible even after 100 years or more, it also made the time required for biomass rebuilding much less predictable. Our finding that an Allee effect greatly increased the uncertainty in recovery time frames provides an empirically based explanation for why the removal of threat does not always result in the recovery of depleted populations or species., (© 2014 Society for Conservation Biology.)

Understanding the biophysical mechanisms that shape variability in fisheries recruitment is critical for estimating the effects of climate change on fisheries. In this study, we used an Earth System Model (ESM) and a mechanistic individual-based model (IBM) for larval fish to analyze how climate change may impact the growth and survival of larval cod in the North Atlantic. We focused our analysis on five regions that span the current geographical range of cod and are known to contain important spawning populations. Under the SRES A2 (high emissions) scenario, the ESM-projected surface ocean temperatures are expected to increase by >1 °C for 3 of the 5 regions, and stratification is expected to increase at all sites between 1950-1999 and 2050-2099. This enhanced stratification is projected to decrease large (>5 μm ESD) phytoplankton productivity and mesozooplankton biomass at all 5 sites. Higher temperatures are projected to increase larval metabolic costs, which combined with decreased food resources will reduce larval weight, increase the probability of larvae dying from starvation and increase larval exposure to visual and invertebrate predators at most sites. If current concentrations of piscivore and invertebrate predators are maintained, larval survival is projected to decrease at all five sites by 2050-2099. In contrast to past observed responses to climate variability in which warm anomalies led to better recruitment in cold-water stocks, our simulations indicated that reduced prey availability under climate change may cause a reduction in larval survival despite higher temperatures in these regions. In the lower prey environment projected under climate change, higher metabolic costs due to higher temperatures outweigh the advantages of higher growth potential, leading to negative effects on northern cod stocks. Our results provide an important first large-scale assessment of the impacts of climate change on larval cod in the North Atlantic., (© 2013 John Wiley & Sons Ltd.)

This study describes how three individual fish, Atlantic cod (Gadus morhua L.), developed a novel behaviour and learnt to use a dorsally attached external tag to activate a self-feeder. This behaviour was repeated up to several hundred times, and over time these fish fine-tuned the behaviour and made a series of goal-directed coordinated movements needed to attach the feeder's pull string to the tag and stretch the string until the feeder was activated. These observations demonstrate a capacity in cod to develop a novel behaviour utilizing an attached tag as a tool to achieve a goal. This may be seen as one of the very few observed examples of innovation and tool use in fish.

Fine-scale temporal patterning in grunt production and variation in grunt attributes in Atlantic cod Gadus morhua and pollack Pollachius pollachius was examined. Pollachius pollachius produced only a single sound type, the grunt, similar to that previously described for G. morhua. Sound production and egg production were correlated in P. pollachius but not in G. morhua. Only G. morhua displayed a strongly cyclical pattern, producing more grunts at night. Finer-scale temporal patterning in grunt production was observed in both species which produced significantly fewer grunts following a period of high grunt production. These quieter periods lasted up to 45 min for P. pollachius and up to 1 h in G. morhua. Grunts were not always produced in isolation but organized into bouts in both species. Longer bouts were more frequent during periods of increased sound activity and were linked with changes in grunt characteristics including increased grunt duration, pulse duration and repetition period of each pulse combined with decreased dominant frequency. This study provides the first evidence of acoustic signalling being used by spawning P. pollachius and presents the most detailed analysis of the complexity of gadoid sound production., (© 2014 The Fisheries Society of the British Isles.)

The North Sea cod (Gadus morhua, L.) stock has continuously declined over the past four decades linked with overfishing and climate change. Changes in stock structure due to overfishing have made the stock largely dependent on its recruitment success, which greatly relies on environmental conditions. Here we focus on the spatio-temporal variability of cod recruitment in an effort to detect changes during the critical early life stages. Using International Bottom Trawl Survey (IBTS) data from 1974 to 2011, a major spatio-temporal change in the distribution of cod recruits was identified in the late 1990s, characterized by a pronounced decrease in the central and southeastern North Sea stock. Other minor spatial changes were also recorded in the mid-1980s and early 1990s. We tested whether the observed changes in recruits distribution could be related with direct (i.e. temperature) and/or indirect (i.e. changes in the quantity and quality of zooplankton prey) effects of climate variability. The analyses were based on spatially-resolved time series, i.e. sea surface temperature (SST) from the Hadley Center and zooplankton records from the Continuous Plankton Recorder Survey. We showed that spring SST increase was the main driver for the most recent decrease in cod recruitment. The late 1990s were also characterized by relatively low total zooplankton biomass, particularly of energy-rich zooplankton such as the copepod Calanus finmarchicus, which have further contributed to the decline of North Sea cod recruitment. Long-term spatially-resolved observations were used to produce regional distribution models that could further be used to predict the abundance of North Sea cod recruits based on temperature and zooplankton food availability.

The northern Gulf of St. Lawrence (NGSL) stock of Atlantic cod (Gadus morhua), historically the second largest cod population in the Western Atlantic, has known a severe collapse during the early 1990 s and is currently considered as endangered by the Committee on the Status of Endangered Wildlife in Canada. As for many fish populations over the world which are currently being heavily exploited or overfished, urgent management actions in the form of recovery plans are needed for restoring this stock to sustainable levels. Stochastic projections based on a statistical population model incorporating predation were conducted over a period of 30 years (2010-2040) to assess the expected outcomes of alternative fishing strategies on the stock recovery under different scenarios of harp seal (Pagophilus groenlandicus) abundance and environmental conditions. This sensitivity study shows that water temperature is key in the rebuilding of the NGSL cod stock. Model projections suggest that maintaining the current management practice under cooler water temperatures is likely to maintain the species in an endangered status. Under current or warmer conditions in the Gulf of St. Lawrence, partial recovery might only be achieved by significant reductions in both fishing and predation pressure. In the medium-term, a management strategy that reduces catch could be favoured over a complete moratorium so as to minimize socio-economic impacts on the industry.

Aspects of peripheral and central nociception have previously been studied through recording of somatosensory evoked potentials (SEPs) to putative noxious stimuli in specific brain regions in a few freshwater fish species. In the present study, we describe a novel, minimally invasive method for recording SEPs from the central nervous system of the Atlantic cod (Gadus morhua). Cutaneous electric stimulation of the tail in 15 fish elicited SEPs at all stimulus intensities (2, 5, 10 and 20 mA) with quantitative properties corresponding to stimulus intensity. In contrast to previous fish studies, the methodological approach used in Atlantic cod in the current study uncovered a number of additional responses that could originate from multiple brain regions. Several of these responses were specific to stimulation at the highest stimulus intensities, possibly representing qualitative differences in central processing between somatosensory and nociceptive stimuli.

Atlantic cod (Gadus morhua) vertebrae from archaeological sites were used to study the history of the Icelandic Atlantic cod population in the time period of 1500-1990. Specifically, we used coalescence modelling to estimate population size and fluctuations from the sequence diversity at the cytochrome b (cytb) and Pantophysin I (PanI) loci. The models are consistent with an expanding population during the warm medieval period, large historical effective population size (NE), a marked bottleneck event at 1400-1500 and a decrease in NE in early modern times. The model results are corroborated by the reduction of haplotype and nucleotide variation over time and pairwise population distance as a significant portion of nucleotide variation partitioned across the 1550 time mark. The mean age of the historical fished stock is high in medieval times with a truncation in age in early modern times. The population size crash coincides with a period of known cooling in the North Atlantic, and we conclude that the collapse may be related to climate or climate-induced ecosystem change.

The construction of wind farms introduces artificial hard substrates in sandy sediments. As Atlantic cod (Gadus morhua) and pouting (Trisopterus luscus) tend to aggregate in order to feed around these reefs, energy profiling and trophic markers were applied to study their feeding ecology in a wind farm in the Belgian part of the North Sea. The proximate composition (carbohydrates, proteins and lipids) differed significantly between liver and muscle tissue but not between fish species or between their potential prey species. Atlantic cod showed to consume more energy than pouting. The latter had a higher overall energy reserve and can theoretically survive twice as long on the available energy than cod. In autumn, both fish species could survive longer on their energy than in spring. Polyunsaturated fatty acids were found in high concentrations in fish liver. The prey species Jassa and Pisidia were both rich in EPA while Jassa had a higher DHA content than Pisidia. Energy profiling supported the statement that wind farm artificial reefs are suitable feeding ground for both fish species. Sufficient energy levels were recorded and there is no indication of competition.

Melanin-concentrating hormone (MCH) is classically known for its role in regulating teleost fish skin color change for environmental adaptation. Recent evidence suggests that MCH also has appetite-stimulating properties. The gonadotropin-releasing hormone (GnRH) peptide family has dual roles in endocrine control of reproduction and energy status in fish. Atlantic cod (Gadus morhua) are a commercially important aquaculture species inhabiting the shores of Atlantic Canada. In this study, we examine MCH and GnRH transcript expression profiles during early development as well as in central and peripheral tissues and quantify juvenile Atlantic cod MCH and GnRH hypothalamic mRNA expressions following food deprivation. MCH and GnRH3 cDNAs are maternally deposited into cod eggs, while MCH has variable expression throughout early development. GnRH2 and GnRH3 mRNAs "turn-on" during mid-segmentation once the brain is fully developed. For both MCH and GnRH, highest expression appears during the exogenous feeding stages, perhaps supporting their functions as appetite regulators during early development. MCH and GnRH transcripts are found in brain regions related to appetite regulation (telencephalon/preoptic area, optic tectum/thalamus, hypothalamus), as well as the pituitary gland and the stomach, suggesting a peripheral function in food intake regulation. Atlantic cod MCH mRNA is upregulated during fasting, while GnRH2 and GnRH3 transcripts do not appear to be influenced by food deprivation. In conclusion, MCH might be involved in stimulating food intake in juvenile Atlantic cod, while GnRHs may play a more significant role in appetite regulation during early development., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Statistical properties of the site-frequency spectrum associated with Λ-coalescents are our objects of study. In particular, we derive recursions for the expected value, variance, and covariance of the spectrum, extending earlier results of Fu (1995) for the classical Kingman coalescent. Estimating coalescent parameters introduced by certain Λ-coalescents for data sets too large for full-likelihood methods is our focus. The recursions for the expected values we obtain can be used to find the parameter values that give the best fit to the observed frequency spectrum. The expected values are also used to approximate the probability a (derived) mutation arises on a branch subtending a given number of leaves (DNA sequences), allowing us to apply a pseudolikelihood inference to estimate coalescence parameters associated with certain subclasses of Λ-coalescents. The properties of the pseudolikelihood approach are investigated on simulated as well as real mtDNA data sets for the high-fecundity Atlantic cod (Gadus morhua). Our results for two subclasses of Λ-coalescents show that one can distinguish these subclasses from the Kingman coalescent, as well as between the Λ-subclasses, even for a moderate (maybe a few hundred) sample size.

We employed the work loop method to study the ability of ventricular and atrial trabeculae from Atlantic cod to sustain power production during repeated contractions at acclimation temperatures (10°C) and when acutely warmed (20°C). Oxygen tension (Po2) was lowered from 450 to 34% air saturation to augment the thermal stress. Preparations worked under conditions simulating either a large stroke volume (35 contractions/min rate, 8-12% muscle strain) or a high heart rate (70 contractions/min, 2-4% strain), with power initially equal under both conditions. The effect of declining Po2 on power was similar under both conditions but was temperature and tissue dependent. In ventricular trabeculae at 10°C (and atria at 20°C), shortening power declined across the full range of Po2 studied, whereas the power required to lengthen the muscle was unaffected. Conversely, in ventricular trabeculae at 20°C, there was no decline in shortening power but an increase in lengthening power when Po2 fell below 100% air saturation. Finally, when ventricular trabeculae were paced at rates of up to 115 contractions/min at 20°C (vs. the maximum of 70 contractions/min in vivo), they showed marked increases in both shortening and lengthening power. Our results suggest that although elevated heart rates may not impair ventricular power as they commonly do isometric force, limited atrial power and the increased work required to expand the ventricle during diastole may compromise ventricular filling and hence, stroke volume in Atlantic cod at warm temperatures. Neither large strains nor high contraction rates convey an apparent advantage in circumventing this.

To understand coastal dispersal dynamics of Atlantic cod (Gadus morhua), we examined spatiotemporal egg and larval abundance patterns in coastal Newfoundland. In recent decades, Smith Sound, Trinity Bay has supported the largest known overwintering spawning aggregation of Atlantic cod in the region. We estimated spawning and dispersal characteristics for the Smith Sound-Trinity Bay system by fitting ichthyoplankton abundance data to environmentally-driven, simplified box models. Results show protracted spawning, with sharply increased egg production in early July, and limited dispersal from the Sound. The model for the entire spawning season indicates egg export from Smith Sound is 13%•day(-1) with a net mortality of 27%•day(-1). Eggs and larvae are consistently found in western Trinity Bay with little advection from the system. These patterns mirror particle tracking models that suggest residence times of 10-20 days, and circulation models indicating local gyres in Trinity Bay that act in concert with upwelling dynamics to retain eggs and larvae. Our results are among the first quantitative dispersal estimates from Smith Sound, linking this spawning stock to the adjacent coastal waters. These results illustrate the biophysical interplay regulating dispersal and connectivity originating from inshore spawning of coastal northwest Atlantic.

Haemoglobin polymorphism in cod (Gadus morhua L) has been investigated throughout the last 50years. Field studies have shed light on the geographic distribution of the two common alleles (HbI(1) and HbI(2)), and laboratory studies have shown effects of genotype on physiological traits such as growth, reproduction and hypoxia tolerance. The geographic distribution of alleles shows a correlation with temperature, with increasing frequency of HbI(1) in warmer areas. This is likely due to temperature-related differences in oxygen affinity of the three genotypes. We provide a general ecological introduction to cod haemoglobin polymorphism and a detailed discussion of physiological studies, particularly laboratory growth studies. Although differences in oxygen uptake are almost certainly a contributory mechanism to observed differences in traits such as growth rate, many other environmental, behavioural and social factors may also contribute, making it difficult to quantify the effect of HbI either experimentally or in the field., (Copyright © 2013 Elsevier Inc. All rights reserved.)

With the construction of wind farms all across the North Sea, numerous artificial reefs are created. These windmill artificial reefs (WARs) harbour high abundances of fish species which can be attracted from elsewhere or can be the result of extra production induced by these wind farms. To resolve the attraction-production debate in suddenly altered ecosystems (cf. wind farms), the possible consequences of attraction should be assessed; thereby bearing in mind that ecological traps may arise. In this paper we investigated whether the wind farms in the Belgian part of the North Sea act as ecological traps for pouting and Atlantic cod. Length-at-age, condition and diet composition of fish present at the windmill artificial reefs was compared to local and regional sandy areas. Fish data from the period 2009-2012 were evaluated. Mainly I- and II-group Atlantic cod were present around the WARs; while the 0- and I-group dominated for pouting. For Atlantic cod, no differences in length were observed between sites, indicating that fitness was comparable at the WARs and in sandy areas. No significant differences in condition index were observed for pouting. At the WARs, they were slightly larger and stomach fullness was enhanced compared to the surrounding sandy areas. Also diet differed considerably among the sites. The outcome of the proxies indicate that fitness of pouting was slightly enhanced compared to the surrounding sandy areas. No evidence was obtained supporting the hypothesis that the WARs act as an ecological trap for Atlantic cod and pouting., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Synthesis and release of FSH and LH are differentially regulated by GnRH, but the mechanisms by which this regulation is achieved are not well understood. Teleost fish are powerful models for studying this differential regulation because they have distinct pituitary cells producing either FSH or LH. By using pituitary cultures from Atlantic cod (Gadus morhua), we were able to investigate and compare the electrophysiological properties of fshb- and lhb-expressing cells, identified by single-cell quantitative PCR after recording. Both cell types fired action potentials spontaneously. The relative number of excitable cells was dependent on reproductive season but varied in opposing directions according to season in the 2 cell types. Excitable and quiescent gonadotropes displayed different ion channel repertoires. The dynamics of outward currents and GnRH-induced membrane responses differed between fshb- and lhb-expressing cells, whereas GnRH-induced cytosolic Ca²⁺ responses were similar. Expression of Ca²⁺-activated K⁺ channels also differed with cell type and showed seasonal variation when measured in whole pituitary. The differential presence of these channels corresponds to the differences observed in membrane response to GnRH. We speculate that differences in ion channel expression levels may be involved in seasonal regulation of hormone secretion as well as the differential response to GnRH in LH- and FSH-producing gonadotropes, through differences in excitability and Ca²⁺ influx.

Because offshore wind energy development is fast growing in Europe it is important to investigate the changes in the marine environment and how these may influence local biodiversity and ecosystem functioning. One of the species affected by these ecosystem changes is Atlantic cod (Gadus morhua), a heavily exploited, commercially important fish species. In this research we investigated the residency, site fidelity and habitat use of Atlantic cod on a temporal scale at windmill artificial reefs in the Belgian part of the North Sea. Acoustic telemetry was used and the Vemco VR2W position system was deployed to quantify the movement behaviour. In total, 22 Atlantic cod were tagged and monitored for up to one year. Many fish were present near the artificial reefs during summer and autumn, and demonstrated strong residency and high individual detection rates. When present within the study area, Atlantic cod also showed distinct habitat selectivity. We identified aggregation near the artificial hard substrates of the wind turbines. In addition, a clear seasonal pattern in presence was observed. The high number of fish present in summer and autumn alternated with a period of very low densities during the winter period., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Atlantic cod Gadus morhua experienced oxygen deficit ( D O 2 ) when exposed to oxygen levels below their critical level (c. 73% of pcrit ) and subsequent excess post-hypoxic oxygen consumption (CEPHO ) upon return to normoxic conditions, indicative of an oxygen debt. The mean ± s.e. CEPHO : D O 2 was 6·9 ± 1·5, suggesting that resorting to anaerobic energy production in severe hypoxia is energetically expensive., (© 2013 The Fisheries Society of the British Isles.)

Catastrophic collapses of top predators have revealed trophic cascades and community structuring by top-down control. When populations fail to recover after a collapse, this may indicate alternative stable states in the system. Overfishing has caused several of the most compelling cases of these dynamics, and in particular Atlantic cod stocks exemplify such lack of recovery. Often, competition between prey species and juvenile predators is hypothesized to explain the lack of recovery of predator populations. The predator is then considered to compete with its prey for one resource when small and to subsequently shift to piscivory. Yet predator life history is often more complex than that, including multiple ontogenetic diet shifts. Here we show that no alternative stable states occur when predators in an intermediate life stage feed on an additional resource (exclusive to the predator) before switching to piscivory, because predation and competition between prey and predator do not simultaneously structure community dynamics. We find top-down control by the predator only when there is no feedback from predator foraging on the additional resource. Otherwise, the predator population dynamics are governed by a bottleneck in individual growth occurring in the intermediate life stage. Therefore, additional resources for predators may be beneficial or detrimental for predator population growth and strongly influence the potential for top-down community control.

The response of age 0+ year juvenile Atlantic cod Gadus morhua to the presence of age 1+ and age 3+ year conspecifics was measured with and without cover available. Juveniles reacted by aggregating more closely and maintaining distance from older conspecifics in an experimental setting without cover but only to age 3+ year conspecifics when cover was available. The results indicate that prior residence of older juveniles can affect age 0+ year juveniles during benthic settlement and highlights the conservation value of structurally complex nursery habitats., (© 2013 The Authors. Journal of Fish Biology © 2013 The Fisheries Society of the British Isles.)

Natural resource management requires approaches to understand and handle sources of uncertainty in future responses of complex systems to human activities. Here we present one such approach, the "biological ensemble modeling approach," using the Eastern Baltic cod (Gadus morhua callarias) as an example. The core of the approach is to expose an ensemble of models with different ecological assumptions to climate forcing, using multiple realizations of each climate scenario. We simulated the long-term response of cod to future fishing and climate change in seven ecological models ranging from single-species to food web models. These models were analyzed using the "biological ensemble modeling approach" by which we (1) identified a key ecological mechanism explaining the differences in simulated cod responses between models, (2) disentangled the uncertainty caused by differences in ecological model assumptions from the statistical uncertainty of future climate, and (3) identified results common for the whole model ensemble. Species interactions greatly influenced the simulated response of cod to fishing and climate, as well as the degree to which the statistical uncertainty of climate trajectories carried through to uncertainty of cod responses. Models ignoring the feedback from prey on cod showed large interannual fluctuations in cod dynamics and were more sensitive to the underlying uncertainty of climate forcing than models accounting for such stabilizing predator-prey feedbacks. Yet in all models, intense fishing prevented recovery, and climate change further decreased the cod population. Our study demonstrates how the biological ensemble modeling approach makes it possible to evaluate the relative importance of different sources of uncertainty in future species responses, as well as to seek scientific conclusions and sustainable management solutions robust to uncertainty of food web processes in the face of climate change.

Photoperiod manipulation during early juvenile stages can influence growth in Atlantic cod. In the present study, one group of cod juveniles were reared under natural photoperiod conditions for Bodø (67° N, 14° E), whereas their counterparts were kept under continuous illumination. The mean weight of juvenile cod reared under continuous illumination was found to be 13% greater than those kept under natural photoperiod after 120days of light treatment. The molecular basis of this phenotypic plasticity is currently unknown but it is likely that DNA (cytosine-5)-methyltransferases (dnmts) are involved, since these genes play a crucial role in epigenetic regulation of gene expression. Phylogenetic analysis of Atlantic cod dnmt1, dnmt2 and dnmt3a revealed that within each group, the phylogeny follows the taxonomic relationship between the various species and comparative mapping of dnmt paralogues showed that these genes lie within regions of conserved synteny amongst teleosts. Of the three dnmt paralogues, dnmt3a had the highest expression in fast muscle of adult cod. In addition, dnmt1 and dnmt2 were differentially expressed between tissues but with prominent expression in gonads. Dnmt1 and dnmt3a transcript levels showed a significant increase in fast muscle of juvenile cod from the continuous light group at several time points. Remarkably, dnmt1 and dnmt3a transcript levels were 2-fold higher at 120days, by which point photoperiod conditions between the two light groups had become identical. Our data revealed that photoperiod can have an extended effect on expression of dnmt genes, which may be involved in the epigenetic regulation of muscle growth by photoperiod in Atlantic cod., (Copyright © 2013 Elsevier B.V. All rights reserved.)

In March 2012, fishermen operating in a fjord in Northern Norway reported catching Atlantic cod, a native fish forming an economically important marine fishery in this region, with unusual prey in their stomachs. It was speculated that these could be Atlantic salmon, which is not typical prey for cod at this time of the year in the coastal zone. These observations were therefore reported to the Norwegian Directorate of Fisheries as a suspected interaction between a local fish farm and this commercial fishery. Statistical analyses of genetic data from 17 microsatellite markers genotyped on 36 partially-degraded prey, samples of salmon from a local fish farm, and samples from the nearest wild population permitted the following conclusions: 1. The prey were Atlantic salmon, 2. These salmon did not originate from the local wild population, and 3. The local farm was the most probable source of these prey. Additional tests demonstrated that 21 of the 36 prey were infected with piscine reovirus. While the potential link between piscine reovirus and the disease heart and skeletal muscle inflammation is still under scientific debate, this disease had caused mortality of large numbers of salmon in the farm in the month prior to the fishermen's observations. These analyses provide new insights into interactions between domesticated and wild fish.

This study examined the effects of prey exoskeleton characteristics on gastric evacuation patterns in Atlantic cod Gadus morhua. Three distinct stages were highlighted in the gastric evacuation of crustacean prey characterized by a robust exoskeleton. The experiments confirmed that the three shrimp species, Pandalus borealis, Pandalus montagui and Eualus macilentus, and the crab Chionoecetes opilio, were evacuated from the stomach at different rates. The duration of all stages increased with increasing ash (and carbonate) content of the fresh prey. Thickness, chemical composition and morphology of the prey exoskeleton all affected gastric evacuation: duration of initial delay, overall evacuation rate and a decreased evacuation rate at the end of the process. The power exponential function (PEF), with its shape parameter, described the course of evacuation for these prey types well, especially the initial delay. The PEF does not, however, allow describing evacuation by the current stomach content mass independent of meal size, which limits its usefulness in estimating consumption rates of wild G. morhua. To predict and describe gastric evacuation of prey with a robust exoskeleton, it is therefore suggested that the square-root function be expanded with an initial lag phase, coupled to the mechanistically based cylinder model of gastric evacuation., (© 2013 The Authors. Journal of Fish Biology © 2013 The Fisheries Society of the British Isles.)

In the Barents Sea, the limited data on biological relevant indicators and their responses to various anthropogenic stressors have hindered the development of a consistent scientific basis for selecting indicator species and developing practical procedures for environmental monitoring. Accordingly, the main aim of the present study was to develop a common set of baseline values for contaminants and biomarkers in three species, and to identify their strengths and limitations in monitoring of the Barents Sea. Blue mussel (Mytilus edulis), Icelandic scallop (Chlamys islandica) and Atlantic cod (Gadus morhua) were sampled from a north Norwegian fjord in March, June, September and December 2010. Digestive glands from the bivalve species and liver from Atlantic cod were analysed for biomarkers of oxidative stress (catalase [CAT], glutathione peroxidase [GPX], glutathione-S-transferase activities [GST], lipid peroxidation as thiobarbituric reactive substances [TBARS] and total oxyradical scavenging capacity [TOSC]), biotransformation (ethoxyresorufine-O-deethylase activity [EROD]) and general stress (lysosomal membrane stability [LMS]). Concentrations of polycyclic aromatic hydrocarbons (PAHs) and metals in the bivalves and PAH metabolites in fish bile were quantified. Finally, energy reserves (total lipids, proteins and carbohydrates) and electron transport system (ETS) activity in the digestive gland of the bivalves and liver of Atlantic cod provided background information for reproductive cycle and general physiological status of the organisms. Blue mussel and Icelandic scallop showed very similar trends in biological cycle, biomarker expression and seasonality. Biomarker baselines in Atlantic cod showed weaker seasonal variability. However, important biological events may have been undetected due to the large time intervals between sampling occasions. Physiological biomarkers such as energy reserves and ETS activity were recommended as complementary parameters to the commonly used stress biomarkers, as they provided valuable information on the physiological status of the studied organisms. Interpretation of the seasonality in oxidative stress biomarkers was in general difficult but TOSC and lipid peroxidation were preferred over the antioxidant enzyme activities. This study is the first reporting seasonal baseline in these three species in a sub-Arctic location. Overall, the Icelandic scallop was considered the most adequate organism for environmental monitoring in the Barents Sea due to the interpretability of the biomarker data as well as its abundance, ease to handle and wide distribution from the southern Barents Sea to Svalbard., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The biggest discharge from the offshore oil industry is produced water (PW). As new technologies emerge to remove oil from such discharges, the question remains as to the effect that the water soluble fraction of contaminants present in PW may have on the biota surrounding the areas of discharge. We investigated the effects of 8 weeks of intermittent exposure to environmentally relevant concentrations (100 or 1000mg/L) of the aqueous fraction of PW (AFPW) on growth parameters, food consumption, respiratory burst activity of head kidney leukocytes (RB), activity of antioxidant enzymes and mRNA expression of immune- and detoxification-related genes of Atlantic cod. No significant effects of AFPW were seen on growth parameters, food consumption and/or RB. Furthermore, the activity of antioxidant enzymes and the expression of CYP1A, GST and UGT were not impacted by AFPW treatment. The mRNA expression of some immune related genes was affected in a similar manner as what has been described in Atlantic cod exposed to full PW suggesting that short chain soluble compounds present in PW might be responsible for its immunomodulatory effect. Traditionally used biomarkers of toxicant exposure such as phase I (CYP1A) and phase II (GST, UGT) genes do not seem to be reliable indicators of exposure to AFPW. This study confirms the fact that some immune related genes are affected by soluble components of PW and that further investigation on potential increased disease susceptibility is warranted., (Crown Copyright © 2012. Published by Elsevier Inc. All rights reserved.)

The resting and maximum in situ cardiac performance of Newfoundland Atlantic cod (Gadus morhua) acclimated to 10, 4 and 0°C were measured at their respective acclimation temperatures, and when acutely exposed to temperature changes: i.e. hearts from 10°C fish cooled to 4°C, and hearts from 4°C fish measured at 10 and 0°C. Intrinsic heart rate (f(H)) decreased from 41 beats min(-1) at 10°C to 33 beats min(-1) at 4°C and 25 beats min(-1) at 0°C. However, this degree of thermal dependency was not reflected in maximal cardiac output (Q(max) values were ~44, ~37 and ~34 ml min(-1) kg(-1) at 10, 4 and 0°C, respectively). Further, cardiac scope showed a slight positive compensation between 4 and 0°C (Q(10)=1.7), and full, if not a slight over compensation between 10 and 4°C (Q(10)=0.9). The maximal performance of hearts exposed to an acute decrease in temperature (i.e. from 10 to 4°C and 4 to 0°C) was comparable to that measured for hearts from 4°C- and 0°C-acclimated fish, respectively. In contrast, 4°C-acclimated hearts significantly out-performed 10°C-acclimated hearts when tested at a common temperature of 10°C (in terms of both Q(max) and power output). Only minimal differences in cardiac function were seen between hearts stimulated with basal (5 nmol l(-1)) versus maximal (200 nmol l(-1)) levels of adrenaline, the effects of which were not temperature dependent. These results: (1) show that maximum performance of the isolated cod heart is not compromised by exposure to cold temperatures; and (2) support data from other studies, which show that, in contrast to salmonids, cod cardiac performance/myocardial contractility is not dependent upon humoral adrenergic stimulation.

The present study assessed differences in fecundity and egg quality from Atlantic cod Gadus morhua fed isoproteic diets containing 13% fat (low fat, LF) or 20% fat (high fat, HF) and either stressed or left unstressed as a control over the spawning season. Each diet was fed to triplicate groups of G. morhua from June 2009, through to first maturation and spawning. In January 2010 sub-groups of G. morhua were moved to land-based spawning tanks where the experimental trial was carried out. At the start of the experiment, G. morhua fed the high-fat diet were significantly larger than G. morhua fed low-fat diet. These differences were maintained through the spawning season, although with a loss of mass in both dietary groups. Relative fecundity through the season was significantly lower in stressed G. morhua fed LF compared to unstressed G. morhua fed the same diet. Stressed G. morhua had a higher variability in weekly amount of eggs spawned, spawning occurred more irregularly, and the spawning period lasted longer than in unstressed G. morhua. Several egg quality variables were also affected: eggs from G. morhua fed LF and exposed to stress had lower fertilization and hatching rates compared to the unstressed G. morhua fed the same diet as well as all G. morhua fed HF. Gadus morhua fed a low-fat diet appeared less tolerant to stress than fish fed a high-fat diet., (© 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.)

Common haematological [haematocrit (Hct)], primary (serum cortisol) and secondary (serum glucose and plasma lactate) analytes were utilized to compare blood biochemical status of Gadus morhua captured rapidly by jig with that of G. morhua captured by commercial demersal longline. In general, the physiological status of G. morhua, despite blind hook times, was significantly more disrupted (pronounced haemo-concentration and significantly elevated concentrations of cortisol, glucose and lactate) following longline capture relative to capture by jig, while no differences were detected among longline-caught fish as a function of dehooking method (or concomitant extent of overt physical trauma). Blood profiles from the more stressed G. morhua, a possible function of more extended longline hook times, were similar to the most stressed values reported for this species. The results also demonstrate that, although acute blood biochemical status is an effective gauge of relative stress, it does not reflect physical injury status, which has been shown to exert a strong influence on delayed mortality in previous studies in this species. Thus, acute blood chemical status alone may not be the most complete predictor of mortality. Future studies should evaluate physiological repercussions from capture-handling against physical trauma during more extended post-release periods for this species., (© 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.)

Homing behaviour and group cohesion in Atlantic cod Gadus morhua from the northern Gulf of St Lawrence were studied based on tagging-recapture data from two periods, the 1980s and a recent period from 1996 to 2008. Two or more tags from a single tagging experiment were frequently recovered together in subsequent years. The null hypothesis was tested that the frequency of matching tag recoveries occurred by chance only through random mixing of tagged G. morhua before their recapture by the commercial fishery. The alternative hypothesis was that non-random, positive association (group cohesion) existed among tagged individuals that persisted through time and during migrations. Results show that the G. morhua population exhibits a homing behaviour, with temporal stability across seasons and years: 50% of recaptured fish in the recent period were caught <34 km from their mark site, even 3 years after release. In the 1980s, G. morhua were located at <10 km from their release site 1 year after tagging during summer and at <16 km during spring and autumn combined. Despite the increasing distance between the mark and recapture sites over time, the difference was not significant. In addition, occurrences of two or more tagged fish from the same release event that were caught together indicated a non-random association among individual fish for periods of one to several years and through migrations over several hundred kilometres. Hence G. morhua showed group cohesion in addition to site fidelity. These two interacting behaviours may be fundamental for the rebuilding and conservation of depleted fish stocks., (© 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.)

Much of the inter-individual variation observed in animal behaviour is now attributed to the existence of behavioural phenotypes or animal personalities. Such phenotypes may be fundamental to fisheries and aquaculture, yet there have been few detailed studies of this phenomenon in exploited marine animals. We investigated the behavioural and neuroendocrine responses of Atlantic cod (Gadus morhua L.), to situations reflecting critical ecological challenges: predator attacks and territorial challenges. Both hatchery-reared and wild fish were tested and behavioural profiles were compared with baseline conditions. We then used an objective, multivariate approach, rather than assigning individuals along one-dimensional behavioural axes, to examine whether distinct behavioural phenotypes were present. Our results indicate that two distinct behavioural phenotypes were evident in fish from each background. In hatchery-reared fish, phenotypes displayed divergent locomotor activity, sheltering, brain monoamine concentrations and responses to competitive challenges. In wild fish, phenotypes were distinguished primarily by locomotor activity, sheltering and responsiveness to predator stimuli. Hatcheries presumably represent a more stressful social environment, and social behaviour and neuroendocrine responses were important in discerning behavioural phenotypes in hatchery fish, whereas antipredator responses were important in discerning phenotypes in wild fish that have previously encountered predators. In both fish types, behavioural and physiological traits that classified individuals into phenotypes were not the same as those that were correlated across situations. These results highlight the multidimensionality of animal personalities, and that the processes that regulate one suite of behavioural traits may be very different to the processes that regulate other behaviours., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Life-history theory suggests that animals may skip reproductive events after initial maturation to maximize lifetime fitness. In iteroparous teleosts, verifying past spawning history is particularly difficult; the degree of skipped spawning at the population level therefore remains unknown. We unequivocally show frequent skipped spawning in Northeast Arctic cod (NEAC) in a massive field and laboratory effort from 2006 to 2008. This was verified by postovulatory follicles in temporarily arrested ovaries close to the putative spawning period. At the population level, "skippers" were estimated to be approximately equally abundant as spawning females in 2008, constituting ∼24% of the females 60-100 cm. These females never truly started vitellogenesis and principally remained on the feeding grounds when spawners migrated southward, avoiding any migration costs. The proximate cause of skipping seems to be insufficient energy to initiate oocyte development, indicating that skipped spawning may partly be a density-dependent response important in population regulation. Our data also indicate more skipping among smaller females and potential tradeoffs between current and future reproductive effort. We propose that skipped spawning is an integral life-history component for NEAC, likely varying annually, and it could therefore be an underlying factor causing some of the currently unexplained large NEAC recruitment variation. The same may hold for other teleosts.