At high latitudes, early life stage survival of fish is often associated with how spawning time relates to the timing of the spring bloom. With ocean warming, basic physiological rates of ectotherms, like fish, will speed up-including gonadal development rates, which dictate spawning time. Since warmer water is thought to influence the spring bloom timing differently than that of fish spawning time, the two may fall out of synchrony in the future. The precise mechanisms between temperature and gonadal development and spawning time have, however, been difficult to disentangle. Here, we take advantage of a series of independent laboratory experiments measuring individual oocyte development up to or near spawning for 153 Atlantic cod (Gadus morhua) kept between 3 and 12 degrees C. From these data we derive a predictive, mechanistic equation for daily oocyte growth rate as a function of temperature and oocyte developmental status (diameter). The vitellogenic oocyte growth follows an accelerating pattern, and the model predicts that spawning can advance by up to 7 days per 1 degrees C increase. Within-treatment variation is, however, of comparable magnitude to between-treatment temperature effects. The model was also tested in the field by back-calculating oocyte development of 82 fish (2018-2021) sampled at two locations along the Norwegian coast, using daily ambient temperatures from telemetry tags during vitellogenesis as model input. We find that Atlantic cod are able to initiate vitellogenesis over a period of several months in late summer and autumn, as well as regulate the oocyte development rate across a wide range of temperatures-both leading to significant phenotypic plasticity in spawning phenology.

Environmental stress may modulate predator–prey interactions by altering predator performance and thereby the strength of top-down control. In intertidal systems, air exposure during low tide can alter predator activity and feeding patterns. We experimentally tested how air exposure and habitat complexity influence feeding by the dogwhelk Nucella lapillus on blue mussels (Mytilus spp.) under natural temperature and light conditions during a summer to autumn transition on the west coast of Norway. Across 96 mesocosms, we manipulated low tide duration (0, 3, or 9 h) and macroalgae cover while tracking individual dogwhelk activity and consumption for nearly three months. Handling time (includes drilling and feeding) increased with mussel size following a power-law relationship, from 0.5 days for 10 mm mussels to about 20 days for 100 mm mussels, and was further increased by shell thickness. Macroalgae cover shortened handling time of large (57–73 mm) mussels by 22% but had no effect on small (17–33 mm) mussels. Prolonged air exposure (9 h) reduced proportion of prey-handling dogwhelks and total consumption relative to shorter exposure (3 h), despite leaving handling time unchanged. While cooler temperatures slightly shortened handling time (~ 4% per °C), they extended the complete cycle duration, from initiating handling of one mussel to initiating handling of the next, by roughly 10% per °C and decreased the proportion of prey-handling dogwhelks. Dogwhelks showed remarkable resilience, maintaining predation across all levels of air exposure, algae cover, and thermal regimes. This suggests that dogwhelks may be able to maximise energetic gains by choosing their vertical position in the intertidal zone according to beneficial microclimatic conditions, thus regulating their performance. Their locally persistent predation pressure may shape blue mussel populations in Norwegian waters, a widely distributed yet declining foundation species of major ecological importance in the Northern Hemisphere.

The ocean is increasingly used for industry, energy and recreation or protected for conservation, resulting in increasing spatial restrictions for fisheries. Simultaneously, producing seafood with a low climate footprint is becoming increasingly important. Despite this, the effects of spatial restrictions on the emissions of fishing fleets are poorly known. In the Northeast Atlantic, the withdrawal of the United Kingdom from the EU (Brexit) meant that the UK regained autonomy in its Exclusive Economic Zone (EEZ). This suddenly imposed a spatial restriction for several foreign fishing fleets targeting Northeast Atlantic mackerel (Scomber scombrus). Here, we use this natural experiment and open fisheries data to investigate how Brexit affected the performance and emissions of the Norwegian mackerel fishery. As the fleet was excluded from fishing grounds in the UK, the catch per fishing trip almost halved, while the number of trips per vessel doubled. As a result, fuel use intensity (FUI) more than doubled from similar to 0.08 to similar to 0.18 L fuel per kg mackerel. We estimate that this shift required an additional 23 million liters of fuel per year, causing additional fuel costs of similar to18 million annually and emitting an additional similar to 72,000 tonnes CO2 per year(.) The policy change undid similar to 15 years of improved fuel efficiency in Norwegian pelagic fisheries. These findings provide rare empirical evidence on how spatial restrictions can undermine progress towards decreasing greenhouse gas emissions in fisheries, highlighting the need to monitor and account for emissions in fisheries management and consider these trade-offs in marine spatial management.

Aim: Bergman patterns, the tendency of organisms to be larger at higher latitudes and lower temperatures, are a well-studied biogeographic pattern. Yet, there is no consensus on the driver or underlying mechanisms. We aim to scrutinize the influence of several key proposed drivers of Bergmann patterns (temperature, seasonal light availability, prey size and seasonal abundance) on optimal body size in planktivorous fishes across high latitudes in the Northeast Atlantic.Location: Northeast Atlantic between 55 and 75 degrees N, with implications for high-latitude oceans globally.Time period: Present day.Major taxa studied: Pelagic planktivorous fishes, with Atlantic herring (Clupea harengus) as model organism.Methods: We use a model that incorporates explicit mechanisms for vision-based feeding and temperature-dependent physiology of a planktivorous fish to explore how intrinsic and extrinsic constraints affect energy budgeting and thereby expected optimal body size based on bioenergetics. We run the model at latitudes with increasing seasonality and test the individual and joint effects of relevant drivers.Results: A Bergmann pattern emerges from the interaction between visual feeding opportunities and temperature-dependent physiology. Small individuals profit from faster energy processing at higher temperatures in the south, whereas large individuals benefit from a lower metabolic cost at colder temperatures and more daylight hours for feeding in the north. In isolation temperature, daylight hours, and prey size each produced Bergmann patterns, but the most pronounced pattern arose from all drivers combined.Main conclusions: Studying biogeographic body size patterns requires a holistic view, accounting for interactions between drivers and both intrinsic and extrinsic constraints on energy budgeting. Across latitudes, temperature effects on digestion and metabolism interact with effects of light availability, prey size and abundance on food accessibility, and thereby shape the optimal size. Our study highlights how details of ecological mechanisms and lifestyles are important for improving predictive ability.

The risk of predation is an important driver that tailors life histories in various ways. Using an evolutionary model based on hormonal control, we study how different predation regimes affect adaptive risk-taking and growth in fish populations. Growth, metabolism and foraging in the modelled fish are regulated by three simplified hormone functions: growth hormone, orexin, and thyroid hormone. A dynamic state-dependent optimization model finds optimal hormone profiles for adaptive growth strategies in juvenile fish. We consider a gradient from species where behaviour and metabolic activity have large consequences for risk (typically benthic and camouflaged species), to the opposite endpoint where behaviour may modify predation risk to a smaller degree (as in the pelagic). Along this gradient, the model predicts changes in the pace of life from slow to fast, enacted by up-regulation of the three hormone functions which in turn increase foraging and metabolism and change the priorities of energy reserves versus growth. Under all types of predation risk investigated, growth is faster when food availability is higher. Energy reserves are maintained primarily during periods of poor food availability and are used to accelerate growth during periods when food availability is high. The thyroid hormone function is up-regulated predominantly when food availability is high and has an important role in trade-offs balancing energetic gain and survival. At the individual time scale, the hormone system improves organismic flexibility and robustness. Over the phylogenetic time scale, hormone system adaptations have also restricted the phenotypic plasticity of individuals.

Changes in physiological processes can reveal how individuals respond to environmental stressors. It can be difficult to link physiological responses to changes in vital rates such as growth, reproduction and survival. Here, bioenergetics modelling can aid in understanding non-intuitive outcomes from stressor combinations. Building on an established bioenergetics model, we examine the potential effects of parasite infection on growth rate and body condition. Parasites represent an overlooked biotic factor, despite their known effects on the physiology of the host organism. As a case study, we use the host-parasite system of Eastern Baltic cod (Gadus morhua) infected with the parasitic nematode Contraceacum osculatum. Eastern Baltic cod have during the past decade experienced increasing infection loads with C. osculatum that have been shown to lead to physiological changes. We hypothesized that infection with parasites affects cod growth negatively as previous studies reveal that the infections lead to reduced energy turnover, severe liver disease and reduced nutritional condition. To test this, we implemented new variables into the bioenergetics model representing the physiological changes in infected fish and parameterized these based on previous experimental data. We found that growth rate and body condition decreased with increased infection load. Highly infected cod reach a point of no return where their energy intake cannot maintain a surplus energy balance, which may eventually lead to induced mortality. In conclusion, parasite infections cannot be ignored when assessing drivers of fish stock dynamics.

Each member of a breeding pair benefits if the other does more of the parental investment, so there is scope for behaviours that can be interpreted as both cooperative and competitive games between males and females. Extra-pair mating, widespread among socially monogamous birds, adds extra conflict but also potential opportunity to these social interactions. We analyse an individual-based model of a social environment with simple behavioural strategies where game-like patterns and cooperative outcomes emerge. The model focuses on three evolving traits: female propensity for extra-pair copulations and male investment in territorial behaviour and care. Male traits are reaction norms that use experienced within and extra-pair copulations as information input. We found that female extra-pair mating provided incentives for males to reduce territorial aggression and increase care for offspring. However, when adult survival was higher, male investment in care and territoriality changed from being negatively to positively correlated. This happened because longer life expectancy gave more behavioural opportunities for males, where nest desertion maximises lifetime male fitness when female extra-pair copulation is high. This outcome evolved gradually, with stable periods of intermediate extra-pair mating and low territoriality. These were punctuated by cycles of high extra-pair mating, nest desertion, reduced extra-pair mating and relapse to aggressive territoriality before a new stable phase was established. Each successive trait cycle was faster and smaller, indicating that through evolution of reaction norms, the gene pool has a long history that canalizes the evolution of behaviours, which can be interpreted as emergence and refinement of frequency-dependent games. Significance statement Most birds that mate in monogamous pairs engage in extra-pair copulations. Males of some species invest (in varying proportions) in offspring that are genetically related only to their social female. The great variability of extra-pair mating levels among different species and populations, supported by numerous field studies, indicates that social and ecological factors play a crucial role in shaping the behaviour. We analyse a computer model in which extra-pair mating evolves concurrently with male reproductive investments in territory defence and offspring care and show how common ecological trade-offs may change the social dynamics within a breeding population and lead to the emergence of complex social interactions between males, females and their neighbours.

Blue mussels (Mytilus spp.) are declining around the world. In western Norway, they have widely disappeared from rocky shores but still thrive on floating structures. Other refugia are cracks in rocks, exposed sites, and low-salinity habitats. Climate change, pollution, disease, parasites, hybridization, and failed recruitment might not alone be able to create such distribution patterns. We hypothesized that crawling predators that are unable to reach floating structures may drive the present decline in western Norway. A known crawling predator without a pelagic stage and sensitive to low salinity and high wave action is the dogwhelk Nucella lapillus . Tributyltin (TBT) contained in anti-fouling paint rendered this snail sterile, but TBT is now banned, and populations are recovering rapidly. We first surveyed floating structures together with nearby rocky shores for blue mussels and dogwhelks. Blue mussels were present on all surveyed floating docks (65% area covered), but only on 18% of rocky shores (≤5% area covered). Similarly, blue mussels were found on 83% of tree branches suspended in water without bottom contact, but only on 1% when branches touched the seafloor. We then conducted a predator exclusion experiment with caged blue mussels (40-80 mm). In cages, mortality due to factors other than dogwhelks was extremely low (<1%) and confirmed that blue mussels continue to thrive when out of reach of predators. If dogwhelks or other crawling predators such as crabs or sea stars created the observed distribution pattern, then environmentally friendly mariculture with blue mussels growing on rafts and longlines might still have high potential in Norway.

Using a dynamic optimisation model for juvenile fish in stochastic food environments, we investigate optimal hormonal regulation, energy allocation and foraging behaviour of a growing host infected by a parasite that only incurs an energetic cost. We find it optimal for the infected host to have higher levels of orexin, growth and thyroid hormones, resulting in higher activity levels, increased foraging and faster growth. This growth strategy thus displays several of the fingerprints often associated with parasite manipulation: higher levels of metabolic hormones, faster growth, higher allocation to reserves (i.e. parasite-induced gigantism), higher risk-taking and eventually higher predation rate. However, there is no route for manipulation in our model, so these changes reflect adaptive host compensatory responses. Interestingly, several of these changes also increase the fitness of the parasite. Our results call for caution when interpreting observations of gigantism or risky host behaviours as parasite manipulation without further testing.

In socially monogamous bird species, males and females tailor their reproductive strategies to that of the other. Interactions are complex, and have elements of both conflict and cooperation. Breeding process is further complicated with the occurrence of matings outside the pair bond, which is a frequent phenomenon in these species. Extra-pair mating has clear benefits for males, but cuckolded males may withdraw care and resources at a cost to females, which produces an unbalanced costs-to-benefits ratios within the mating pair. We used an individual-based model with social networks approach, to study how female extra-pair mating strategies may affect male investment in offspring care and territorial defence. In our model, extra-pair copulation rate is a female-driven strategy; we use two adjustable male traits—care and territorial defence—that co-evolve with that strategy and control the number of extra-pair copulations initiated by a social female. The model utilises very simple rules of behaviours between individuals that lead to the emergence of evolved changes in mating strategies on a large scale. We show how extra-pair copulations initiated by females in their neighbourhood can reduce territorial defence and wasteful aggression between the males across the whole population. We propose that female mating behaviour and male responses are flexible traits that might serve as potential drivers of the evolution of cooperation.

In May 2021, the Norwegian parliament voted unanimously to again require the use of two evaluators to assess all student work given a grade on the A-F scale in higher education. This revision of the law regulating higher education marks a return to a rule that had been rescinded with the Quality Reform of 2001, and has the potential to lead to a cascade of negative consequences for the quality of practices in STEM higher education. We first provide an overview of the problem, and then offer practical, constructive, and evidence-based suggestions for how instructors can meet these requirements while still offering students opportunities to gain formative feedback, to engage in deep and meaningful learning, and be assessed in ways that are aligned with the intended learning outcomes of the course. These recommendations are certainly not exclusive to a STEM learning context, but two of us (CJ and SC) are STEM educators and bring that perspective to this work.

Aim Mesopelagic fishes have a near-global distribution in the upper 1,000 m from tropical to sub-Arctic oceans across temperature regimes. Yet, their abundance decreases poleward and viable populations seem excluded from high latitudes. Why? Location North Atlantic between 50-85 degrees N, with implications for high-latitude oceans globally. Time period Present-day. Major taxa studied Diel vertically migrating (DVM) mesopelagic fishes. Methods We use a mechanistic, state-dependent life-history model to characterize DVM mesopelagic fishes. This model links light-dependent encounters and temperature-dependent physiology, allowing optimal DVM strategies to emerge. We run the model along a latitudinal gradient with increasing seasonality in light and track individual fitness-related measures, that is, survival and surplus energy, through the annual cycle to make predictions about population consequences. Results Mesopelagic fishes thrive in the oceans' twilight zone, and many are dependent on periods of darkness for safe foraging near the surface, before migrating back to depth during daytime. When daylight lasts for 24 hr during the Arctic summer, these fish are trapped in deep waters void of prey because it is never safe to forage in the shallow waters where zooplankton prey are found. Hence, they are left with two poor options, starvation at depth or depredation while foraging. Our model predicts surplus energy, vital for reproduction and growth, to halve from 50-85 degrees N and annual survival to drop by two-thirds over a narrow range of 10 degrees of latitude around the Arctic Circle. Thus, low recruitment and high predation mortality during summer make polar waters population sinks for mesopelagic fishes because of the extreme seasonality in light. Main conclusions At high latitudes, foraging mesopelagic fishes are exposed to sunlight in upper waters also at night. This makes them easy prey for visual predators, which limits their poleward distribution. Our findings highlight the importance to think beyond temperature to explain high-latitude range limits.

In ecological sciences, animal diets are often simplified to ‘resources' or ‘caloric quantities'. However, in the present study, we investigated the optimal foraging strategy of Atlantic codGadus morhuawhen both macro‐ and micro‐nutritional requirements are accounted for. Proteins cannot be synthesized from fatty acids, so the proteins for gonad development must come from other dietary sources. In addition, micronutrients are required in smaller quantities. For example, for cod, arachidonic acid (ARA) acts as a micronutrient precursor for prostaglandins, which is important for reproduction. We formulated a dynamic state‐dependent model to make predictions about optimal diet choice and foraging behavior. We applied the model to a case study in the strait between Denmark and Sweden. The model predicted that energy acquired from dietary protein should be twice that acquired from lipids, with a small increase in the lipid requirements when gonads are growing. The model also predicted that the ‘energy sparing effect of lipids' made it beneficial to engage in risky foraging activity to supplement a lean diet with a little bit of fat. When we constructed the model to also optimize ARA uptake, the cod consumed relatively more ARA‐rich crabs in the months prior to spawning, despite the otherwise poor energetic value of this prey. In support of the model predictions, field observations indicated that lipid stores reached a peak shortly after the arrival of the lipid‐rich migrating herring and the fatty acid signal of these herring were evident in the liver of nearly all cod. Three month later, only half of the cod contained the herring‐derived fatty acid signal, supporting the predicted shift in prey type prior to spawning. From these model predictions and field observations, we conclude that, also in the wild, nutritional requirements can be at least as important as pure energy acquisition.

Synchronous reproduction of birds has often been explained by benefits from nesting together, but this concept fails to explain observed intraspecific variation and climate-mediated changes of breeding synchrony. Here, we present a theoretical model of birds that store resources for reproduction (capital breeders) to show how breeding synchrony, clutch size, and offspring recruitment respond to changes in timing of first possible breeding date. Our approach is based on individual fitness maximization when both prebreeding foraging and offspring development are time constrained. The model predicts less synchronous breeding, smaller clutch size, and higher chances for offspring recruitment in capital breeding birds that advance their nesting. For contrast, we also show that birds that need to acquire resources during egg laying (income breeders) do not change nesting synchrony but increase clutch size along with earlier breeding. The prediction of stronger nesting synchronization of capital breeders in years with late nesting onset is confirmed by empirical data on breeding synchrony of a high-latitude capital breeding sea duck, the common eider (Somateria mollissima). We predict that in warming high-latitude ecosystems, bird species that depend on stored reserves for reproduction are expected to desynchronize their nesting.

Seasonality in light becomes increasingly extreme at high latitudes, both in terms of the diel light–dark cycle and the duration of light summers and dark winters. In contrast to temperature, this latitudinal gradient in light seasonality is not affected by climate change. A key question is therefore whether light may act as a fixed constraint on warming-driven redistributions of organisms at high latitudes. One answer is provided by studying mechanistic models of visual foraging and temperature-driven physiology along latitudinal gradients to project where populations survive and acquire resources to reproduce, and where they demise. Here we contrast such models for two widespread planktivorous fish types. We identify two processes through which seasonality in light can act as a barrier to poleward range expansions at high latitudes: (1) longer dark winters lead to greater depletion of overwinter energy stores and (2) a longer duration of midnight sun entails higher foraging-related predation mortality. Using mechanistic models that incorporate visual foraging and temperature-driven physiology for two fish types, the authors reveal how latitudinal light gradients, which are not affected by climate change, can constrain warming-related shifts to high latitudes.

Growth is an important theme in biology. Physiologists often relate growth rates to hormonal control of essential processes. Ecologists often study growth as function of gradients or combinations of environmental factors. Fewer studies have investigated the combined effects of environmental and hormonal control on growth. Here, we present an evolutionary optimization model of fish growth that combines internal regulation of growth by hormone levels with the external influence of food availability and predation risk. The model finds a dynamic hormone profile that optimizes fish growth and survival up to 30 cm, and we use the probability of reaching this milestone as proxy for fitness. The complex web of interrelated hormones and other signalling molecules are simplified to three functions represented by growth hormone, thyroid hormone, and orexin. By studying a range from poor to rich environments, we find that the level of food availability in the environment results in different evolutionarily optimal strategies of hormone levels. With more food available, higher levels of hormones are optimal, resulting in higher food intake, standard metabolism, and growth. By using this fitness-based approach we also find a consequence of evolutionary optimization of survival on optimal hormone use. Where foraging is risky, thyroid hormone can be used strategically to increase metabolic potential and the chance of escaping from predators. By comparing model results to empirical observations, many mechanisms can be recognized, for instance a change in pace-of-life due to resource availability, and reduced emphasis on reserves in more stable environments.

Although the phenomenon of skipped spawning has been described in numerous fishes, time-series are scarce. We used the presence of post-ovulatory follicles in histological gonad slides from females not developing oocytes for Northeast Arctic (NEA) haddock Melanogrammus aeglefinus from 2009 to 2012 to construct a length-based statistical model giving the probability that a non - developing female was skipping spawning, as opposed to not being sexually mature. This model was then applied on demographic winter survey data from the Barents Sea from 1989 to 2014. This indicated large annual variation in skipping numbers. Comparing these survey estimates to the total annual ICES stock numbers, we found that skipping peaked in the years 1994-1996 and 2009-2014, when the median yearly estimate of skipped spawners was 20-45 % of all females aged >= 3 years. In contrast, only similar to 3 % of females at age >= 3 years skipped spawning in 2007. The proportional representation of skipped spawners at the stock level appeared linked to stock energy reserves with more skipping occurring when energy levels were low. Skipping also became more frequent with increasing population age, i.e. when immatures were less abundant, although the very largest/oldest fish tended to spawn. Because the proportion of NEA haddock that skips spawning is variable and can be high, understanding variation in this phenomenon and its drivers may improve population dynamic models.