Peter Grønkjær

Aarhus University | AU · Department of Biology

Salmonids are well known for their natal homing behaviour, meaning they return to breed in the same area where they originated. However, not all individuals return to their natal breeding grounds—a behavioural trait known as straying. The prevalence of straying is difficult to explore and therefore quantitative estimates for straying are seldom rep...

Arctic char (Salvelinus alpinus) is a top predator and the most widespread fish in Arctic lakes. The presence of Arctic char affects the predator-prey dynamics of the key species in the food webs in these lakes. This study sought to elucidate the effects of habitat (littoral, pelagic, or profundal) and lake morphometry on the trophic position of th...

Recruitment to the Faroe Plateau cod (Gadus morhua) stock (62°N, 6.8°W) is highly variable between years, and availability of suitable prey during the early life stages may determine the year class strength. Here we first investigate interannual variability in recruitment (1983–2017) of cod based on survey data and data from stock assessments. Posi...

Large‐scale, climate‐induced synchrony in the productivity of fish populations is becoming more pronounced in the world's oceans. As synchrony increases, a population's “portfolio” of responses can be diminished, in turn reducing its resilience to strong perturbation. Here we argue that the costs and benefits of trait synchronization, such as the e...

Coexistence of ecotypes, genetically divergent population units, is a widespread phenomenon, potentially affecting ecosystem functioning and local food web stability. In coastal Skagerrak, Atlantic cod (Gadus morhua) occur as two such coexisting ecotypes. We applied a combination of acoustic telemetry, genotyping, and stable isotope analysis to 72...

Integrated otolith chemistry and muscle tissue stable isotope analyses were performed to allocate juvenile Diplodus puntazzo and Diplodus vulgaris to nurseries in the Adriatic Sea. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) was used to quantify the concentrations of chemical elements in the otoliths. Fish muscle samples...

Accurate age estimates are key life history parameters for understanding growth, reproduction and susceptibility to exploitation. Using a combination of fin spine growth increments and bomb radiocarbon dating, we provide minimum age estimates for the small Atlantic squaloid shark, black dogfish (Centroscyllium fabricii) sampled in Greenland waters....

The isotopic composition of inorganic carbon in otoliths (δ¹³Coto) can be a useful tracer of metabolic rates and a method to study ecophysiology in wild fish. We evaluated environmental and physiological sources of δ¹³Coto variation in Icelandic and Northeast Arctic (NEA) cod (Gadus morhua) over the years 1914–2013. Individual annual growth increme...

The relationship between physiology and temperature has a large influence on population‐level responses to climate change. In natural settings, direct thermal effects on metabolism may be exaggerated or offset by behavioural responses influencing individual energy balance. Drawing on a newly developed proxy, we provide the first estimates of the th...

Co-existence of sympatric populations of a fish species is a common phenomenon. In the fjords of southern Norway, 2 ecotypes of Atlantic cod Gadus morhua co-exist during their juvenile life stage. Cod of the North Sea ecotype are on average 2 cm larger than the fjord ecotype at the end of their first growing season in October, suggesting either dif...

Horizon scanning is an increasingly common strategy to identify key research needs and frame future agendas in science. Here, we present the results of the first such exercise for the field of sclerochronology, thereby providing an overview of persistent and emergent research questions that should be addressed by future studies. Through online corr...

Seasonal prey bursts are important for the life cycles and energy budgets of many predators. This study documents the diet and, especially, the importance of the ephemeral occurrence of capelin as prey for Atlantic cod (Gadus morhua) in Godthaabsfjord, west Greenland, over an annual cycle. The cod showed clear differences in diet composition on the...

Accurate and consistent age readings are cornerstones of age‐based assessment and management of exploited fish stocks. Otoliths are the preferred structure for age determination, often performed by counting the number of completed 001 zones. Uncertainty regarding the identification of the first translucent zone and the timing of translucent zone fo...

The availability of suitable prey during the early life of fish may determine recruitment to the adult population. Since larval and juvenile feeding can be highly selective, their preferences for certain prey species and sizes should be considered when estimating the availability of prey. In this study, diet composition (and prey preferences) of 49...

In this study, we examined whether late stages of small-spotted catshark (Scyliorhinus canicula) embryos exhibit a freeze response that stops ventilation, when exposed to electric stimuli. We document that the embryos exhibit a freeze response both when the electric stimuli is turned on and turned off.

Reconstruction of the trophic position of a fish can be performed by analysing stable nitrogen and carbon isotopes in otolith protein. However, ambient temperature may affect the tissue–diet isotopic spacing of stable isotopes from diet to predator tissue and bias estimates of trophic position. To test this, otolith protein, heart and muscle tissue...

The pelagic fishery of Lake Tanganyika, which is largely made up of the three species Lates stappersii, Limnothrissa miodon, and Stolothrissa tanganicae, has been in decline, and there is no clear understanding of the primary underlying causes. It has been suggested that climate change has altered the primary productivity of the system, but detaile...

By examining the maturity of 283 black dogfish Centroscyllium fabricii from Greenland waters, a shift in size‐at‐maturity in both sexes over the past 25 years is observed. Size‐at‐first maturity decreased approximately 10 cm in both sexes, and L50 and L95 shifted similarly in males, but not in females. It is argued that bycatch in the Greenland hal...

Current knowledge on the feeding ecology of the Greenland shark (Somniosus microcephalus), a potential top predator in arctic marine ecosystems, is based on small sample sizes as well as narrow size ranges of sharks. Therefore, potential size-related feeding patterns remain poorly documented. Using stomach content data (N=88) and stable isotope val...

Knowledge of metabolic costs associated with maintenance, foraging, activity and growth under natural conditions is important for understanding fish behaviours and the bioenergetic consequences of a changing environment. Fish performance in the wild and within a complex environment can be investigated by analysing individual-level field metabolic r...

Field metabolic rate (FMR) is key to understanding individual and population-level responses to environmental changes, but is challenging to measure in field conditions, particularly in aquatic environments. Here we show that FMR can be estimated directly from the isotopic composition of carbon in fish otoliths (δ13Coto). We describe the relationsh...

Capelin (Mallotus villosus) is an important trophic node in many Arctic and sub-Arctic ecosystems. In Godthåbsfjord, West Greenland, the zooplankton community has been shown to change significantly from the inner part of the fjord, which is impacted by several glaciers to the shelf outside the fjord. To what extent this gradient in zooplankton comp...

Atlantic salmon, Salmo salar L., is found throughout the North Atlantic, with thousands of rivers having spawning populations. In Greenland, spawning is limited to one river in West Greenland, the Kapisillit River (64˚N), and the salmon are limited to the lower few kilometres of the system. Using mark–recapture, it was estimated the parr population...

Parallel evolution and the extent to which it involves gene reuse has attracted much interest. Whereas it has theoretically been predicted under which circumstances gene reuse is expected, empirical studies that directly compare systems showing high and low parallelism are rare. Three‐spine stickleback (Gasterosteus aculeatus), where freshwater pop...

Coexistence in the same habitat of closely related yet genetically different populations is a phenomenon that challenges our understanding of local population structure and adaptation. Identifying the underlying mechanisms for such coexistence can yield new insight into adaptive evolution, diversification, and the potential for organisms to adapt a...

Lumpfish (Cyclopterus lumpus) is a highly commercial semi-pelagic fish found throughout the North Atlantic. In West Greenland, lumpfish are distributed along a 1600 km continuous north–south gradient, and is an ideal candidate for studying the effects of latitude and environment on key life history traits (LHT). We describe the spatial variation in...

While marine reefs are degraded globally, the responses of fish to marine reef restoration remain uncertain, particularly in temperate waters. This study measured the effect of marine boulder reef restoration on the behaviour of Atlantic cod, Gadus morhua L., in a Natura 2000 area using acoustic telemetry. Cod were tagged and released in the study...

Accurate knowledge on fish trophic ecology and its modifications is crucial for understanding the impact of global change on ecosystems. In this context, we investigated the value of the δ¹³C and δ¹⁵N of otolith soluble organic matter (SOM) for identifying temporal diet shifts in American Silver Perch (Bairdiella chrysoura) over a 30-years period c...

Sandeel (Ammodytes spp.) are forage fishes and form a crucial link in the flow of energy from phytoplankton to marine top predators in the North Atlantic. The nutritional value of the sandeel is linked to the presence of lipid-rich zooplankton species, which makes their trophic role vulnerable to climate-induced changes in the zooplankton community...

The occurrence of natal homing in marine fish remains a fundamental question in fish ecology as its unequivocal demonstration requires tracking of individuals from fertilization to reproduction. Here, we provide evidence of long distance natal homing (> 1000 km) over more than sixty years in Atlantic cod (Gadus morhua), through genetic analysis of...

Otoliths are remarkable recorders that store visual and chemical information that can be interpreted with regard to individual fish phenotype trajectory, life history events and environment. However, the information stored in the otoliths must be interpreted with the knowledge that the otolith is an integral part of fish sensory systems. This means...

Fishing and climate change impact the demography of marine fishes, but it is generally ignored that many species are made up of genetically distinct locally adapted populations that may show idiosyncratic responses to environmental and anthropogenic pressures. Here, we track 80 years of Atlantic cod ( Gadus morhua ) population dynamics in West Gree...

Fishing and climate change impact the demography of marine fishes, but it is generally ignored that many species are made up of genetically distinct locally adapted populations that may show idiosyncratic responses to environmental and anthropogenic pressures. Here, we track 80 years of Atlantic cod (Gadus morhua) population dynamics in West Greenl...

Fishing and climate change impact the demography of marine fishes, but it is generally ignored that many species are made up of genetically distinct locally adapted populations that may show idiosyncratic responses to environmental and anthropogenic pressures. Here, we track 80 years of Atlantic cod (Gadus morhua) population dynamics in West Greenl...

Opinion & comment: Wisz et al. reply — Ingvaldsen et al.1 comment on our study assessing global fish interchanges between the North Atlantic and Pacific oceans for more than 500 species during the entire twenty-first century2. They propose that discrepancies between our model projections and observed data for cod in the Barents Sea are the result o...

Human activity has impacted many coastal fjords causing degeneration of the structure and function of the fish habitats. In Nørrefjord, Denmark, local fishermen complained of declining fish catches which could be attributed to eutrophication and extraction of sediments over several decades. This study aimed to establish blue mussel beds (Mytilus ed...

Throughout much of the Quaternary Period, inhospitable environmental conditions above the Arctic Circle have been a formidable barrier separating most marine organisms in the North Atlantic from those in the North Pacific1,2. Rapid warming has begun to lift this barrier3, potentially facilitating the interchange of marine biota between the two seas...

To forecast effects of temperature changes on recruitment and population dynamics of the Arctic copepod Calanus hyperboreus, laboratory experiments investigating temperature and food effects on early development were performed in Disko Bay, western Greenland, in 2009, and ascent rates of C. hyperboreus eggs collected in east Greenland were measured...

Migration has evolved as a strategy to maximise individual fitness in response to seasonally changing ecological and environmental conditions. However, migration can also incur costs, and quantifying these costs can provide important clues to the ultimate ecological forces that underpin migratory behaviour. A key emerging model to explain migration...

Stable isotope studies of long-term ecosystem change are often hampered by lack of archived tissue samples. Here, we provide a reliable method for extracting the organic matrix from fish otoliths, demonstrate differences in isotope values between the soluble and insoluble organic fractions, and provide the trophic enrichment factors (ε). The analys...

Stable isotopes of carbon (delta C-13) and nitrogen (delta N-15) were used to examine trophic structures in an arctic marine food web at small and large spatial scales. Twelve species, from primary consumers to Greenland shark, were sampled at a large spatial scale near the west and east coasts of Greenland. There was a significant positive latitud...

Capelin (Mallotus villosus Muller) is a key pelagic mediator of energy from lower to higher trophic levels in arctic waters. This is also the case in Greenland waters, but little is known of its feeding behaviour in this region. By analysing stable nitrogen isotopes and stomach content of capelin collected along 1500 km of the Greenland west coast,...

A 150 d laboratory diet-shift study was conducted on juvenile Atlantic cod Gadus morhua L. to examine (1) stable nitrogen and carbon isotope turnover rates, (2) the tissue-specific relative contribution of metabolism and growth to isotopic change, and (3) diet-tissue enrichment of the isotopes in white muscle, heart, whole blood, and cranial bone c...

Over the past 3decades, North Sea Atlantic cod (Gadus morhua) have exhibited variable length-at-age along with declines in spawning stock biomass and timing of maturity. Multiple factors affecting growth and development in fish acted on this economically important stock over the same period including warming waters and an intensive fishery. Here, w...

The leptocephalus larva of eels distinguishes the elopomorph fishes from all other bony fishes. The leptocephalus is long lived and increases in size primarily through the synthesis and deposition of glycosaminoglycans. Energy stored during the larval stage, in the form of glycosaminoglycan and lipids, is required to fuel migration, metamorphosis a...

Besides variable egg survival, previous studies suggested that the larval stage may be the most critical phase in determining Baltic cod recruitment variability, and that larvae need to conduct an ontogenetic vertical migration from hatching depths (>50 m) to upper layers with increased food availability in order to initiate first feeding, improve...

A good correlation has previously been established between primary production and production in higher trophic levels in the marine ecosystem on the Faroe shelf, but identification of potential intermediate species has been missing. Sandeel Ammodytes spp. is known to be of great ecological importance in other areas; thus, we investigated the relati...

Capelin is a planktivorous key fish species in many subarctic ecosystems representing the link between lower trophic levels and apex predators. Little is known, however, of capelin in Greenland waters, but it has been suggested that size and growth increases due to difference in food availability and temperature conditions along a 1,500km south–nor...

Elucidating the relative roles of dispersal and retention of juvenile stages is an important issue for understanding population structure and evolution in marine organisms. We investigated the genetic population structure of juvenile Atlantic cod (Gadus morhua) within the transition zone between the North Sea and the Baltic Sea, employing nine micr...

Hedeholm, R., Grønkjær, P., Rosing-Asvid, A., and Rysgaard, S. 2010. Variation in size and growth of West Greenland capelin (Mallotus villosus) along latitudinal gradients. – ICES Journal of Marine Science, 67: 1128–1137. Capelin (Mallotus villosus) is the dominant pelagic species in the West Greenland ecosystem. Historical data are re-examined and...

The relationship between temperature and growth of juvenile Greenland halibut (Reinhardtius hippoglossoides Walbaum) from 1993 to 2003 was studied in West Greenland offshore waters. In 1993–1996 the average temperature was 2.0°C but it increased to 3.4°C in 1997 and remained at this level for the rest of the study period. Concurrent with the temper...

1. Return of large‐bodied zooplankton populations is of key importance for creating a shift from a turbid to a clear‐water state in shallow lakes after a nutrient loading reduction. In temperate lakes, recovery is promoted by submerged macrophytes which function as a daytime refuge for large zooplankton. However, recovery of macrophytes is often de...

Abstract  Optimal behavioural strategies of aquatic organisms may change with environmental conditions such as turbidity. It was hypothesised that pike, Esox lucius L., adapts to low visibility and potential-reduced foraging opportunities by an increase in activity and pelagic residence in turbid conditions. Diel activity and habitat use of pike (5...

The otoliths of laboratory-reared larval and juvenile perch Perca fluviatilis of known age were analysed to determine the age of otolith formation and validate the formation of daily increments. There was a linear relationship between number of increments and age in days post-hatching, although by 82 days post-hatching daily increment counts undere...

We used the radiated shanny Ulvaria subbifurcata as a model species to explore the relative gut fullness from hatch to metamorphosis of wild larvae, and compared these values with those of laboratory-reared larvae fed at maximum rates. Ingestion rates of most wild larvae were above starvation levels but below the maximum feeding levels of laborator...

SummaryA study on cod egg mortality was carried out in the Bornholm Basin (southern central Baltic Sea) toward the end of July 1996. An initial egg aggregation marked by a satellite-tracked drifter buoy was sampled repeatedly over an 11-day period; profiles of temperature, salinity and dissolved oxygen were concurrently recorded. Three replicate es...

Bang, A., Grønkjær, P., and Lorenzen, B. 2008. The relation between concentrations of ovarian trace elements and the body size of Atlantic cod Gadus morhua. – ICES Journal of Marine Science, 65: 1191–1197. Trace metals in the ovaries of fish are transferred from the female via the yolk to the offspring, which makes the early life stages susceptible...

Population structure was previously believed to be very limited or absent in classical marine fishes, but recently, evidence of weakly differentiated local populations has been accumulating using noncoding microsatellite markers. However, the evolutionary significance of such minute genetic differences remains unknown. Therefore, in order to elucid...

The structural complexity of coral reefs is important for their function as shelter and feeding habitats for coral reef fishes, but physical disturbance by human activities often reduce complexity of the reefs by selectively destroying fragile and more complex coral species. The damselfish Springer's demoiselle Chrysiptera springeri primarily utili...

A number of evolutionary mechanisms have been suggested for generating low but significant genetic structuring among marine fish populations. We used nine microsatellite loci and recently developed methods in landscape genetics and coalescence-based estimation of historical gene flow and effective population sizes to assess temporal and spatial dyn...

In this study, short-term growth and feeding behaviour were compared among juvenile European flounder Platichthys flesus reared in enclosures in either their native habitat (bare sand or vegetation) or transferred to the opposite habitat. Growth was poorest in the vegetated habitat regardless of origin of the fish. The effect of the habitat shift d...