Variation in abundance of Norwegian spring-spawning herring (Clupea harengus, Clupeidae) throughout the 20th century and the influence of climatic fluctuations

A long-term (1907–98) virtual population analysis (VPA) was made for Norwegian spring-spawning herring (NSSH), which is a huge pelagic fish stock in the north-east Atlantic. It shows that this herring stock has had large fluctuations during the last century; these fluctuations have mainly been determined by variations in the temperature of the inflowing water masses to the region. The spawning stock biomass (SSB) increased from a rather low level in the early years of this century and reached a high level of around 14 million tons by 1930. The spawning stock biomass then decreased to a level of around 10 million tons by 1940, but increased again to a record high level of 16 million tons by 1945. The stock then started to decrease and during the next 20-year period fell to a level of less than 50 000 tons by the late 1960s. Through the 1970s and 1980s, the stock slowly recovered and after the recruitment of strong year classes in 1983 and 1990–1992 the stock recovered to a spawning stock biomass of about 10 million tons. The long-term fluctuation in spawning stock biomass is caused by variations in the survival of recruits. It is found that the long-term changes in spawning stock abundance are highly correlated with the long-term variations in the mean annual temperature of the inflowing Atlantic water masses (through the Kola section) into the north-east Atlantic region. The recruitment is positively correlated with the average temperature in the Kola section in the winter months, January–April, which indicates that environmental factors govern the large-scale fluctuations in production for this herring stock.     

A synthesis of the life history and ecology of juvenile Pacific herring in Prince William Sound,Alaska

Physical and biological variables affecting juvenile Pacific herring (Clupea pallasi) in Prince William Sound (PWS) from 1995 to 1998 were investigated as part of a multifaceted study of recruitment, the Sound Ecosystem Assessment (SEA) program. Though more herring larvae were retained in eastern PWS bays, ages‐0 and ‐1 herring used bays throughout PWS as nursery areas. Water transported into PWS from the Gulf of Alaska (GOA) contributed oceanic prey species to neritic habitats. Consequently, variations in local food availability resulted in different diets and growth rates of herring among bays. Summer food availability and possible interspecific competition for food in nursery areas affected the autumn nutritional status and juvenile whole body energy content (WBEC), which differed among bays. The WBEC of age‐0 herring in autumn was related to over‐winter survival. The limited amount of food consumption in winter was not sufficient to meet metabolic needs. The smallest age‐0 fish were most at risk of starvation in winter. Autumn WBEC of herring and winter water temperature were used to model over‐winter mortality of age‐0 herring. Differences in feeding and energetics among nursery areas indicated that habitat quality and age‐0 survival were varied among areas and years. These conditions were measured by temperature, zooplankton abundance, size of juvenile herring, diet energy, energy source (GOA vs. neritic zooplankton), WBEC, and within‐bay competition.     

The highs and lows of herring: A meta‐analysis of patterns and factors in herring collapse and recovery

Pacific and Atlantic herring populations (genus Clupea) commonly experience episodic collapse and recovery. Recovery time durations are of great importance for the sustainability of fisheries and ecosystems. We collated information from 64 herring populations to characterize herring fluctuations and determine the time scales at low biomass and at high and low recruitment, and use generalized linear models and Random Survival Forests to identify the most important bottom‐up, top‐down and intrinsic factors influencing recovery times. Compared to non‐forage fish taxa, herring decline to lower minima, recover to higher maxima and show larger changes in biomass, implying herring are more prone to booms and busts than non‐forage fish species. Large year classes are more common in herring, but occur infrequently and are uncorrelated among regionally grouped stocks, implying local drivers of high recruitment. Management differs between Pacific and Atlantic herring fisheries, where at similarly low biomass, Pacific fisheries tend to be closed while Atlantic fisheries remain open. This difference had no apparent effect on herring recovery times, which averaged 11 years, although most stocks with longer recovery periods had not yet recovered at the end of the observation period. Biomass recovery is best explained by median recruitment and variability in sea surface height anomalies and sea surface temperatures—higher variability leads to shorter recovery times. In addition, the duration of recruitment failure is closely linked with low biomass. While recovery times rely on the nature of the relationship between spawning biomass and recruitment, they are still largely governed by complex and uncertain processes.     

Plankton indices explain interannual variability in Prince William Sound herring first year growth

This study examines the relationships between first year growth of juvenile Prince William Sound herring, temperature and their food. We present time series of herring first year growth, determined from scale measurements as a proxy for herring length, water temperature and indices of multiple trophic levels of plankton obtained from Continuous Plankton Recorder (CPR) sampling on the adjacent Gulf of Alaska shelf. We show that there was a significant correlation between herring growth and water temperature, when the three warmest years were excluded (the mean July and August temperatures were greater than 12.5°C in 1989, 2004 and 2005). There were also strong, significant relationships between the abundance of appropriately sized (for first‐feeding herring) planktonic prey groups and herring growth. First year herring growth was greater in years with higher abundances of diatoms, microzooplankton and small mesozooplankton but not related to variability in abundance of larger mesozooplankton (such as euphausiids and large copepods). Furthermore, the strong interannual relationship between diatoms and herring growth held true even in the warmest years where the relationship between temperature and growth broke down. We also found seasonal timing and abundance changes in the plankton in warm years that would make the prey more abundant during the summer months immediately after metamorphosis of the herring larvae. We thus conclude that young‐of‐the‐year herring may grow better in warm years because the timing of key prey is a better match for their first feeding.     

Long‐term variation in the abundance of Pacific herring (Clupea pallasii) from the Yellow Sea in the western North Pacific and its relation to climate over the past 590 years

A qualitative understanding of the long‐term variation in the population dynamics of Yellow Sea (YS) herring is particularly important for clarifying the evolutionary processes and driving mechanisms of the YS large marine ecosystem. Unfortunately, because of a lack of long‐term, continuous, and simultaneous monitoring data, the specific driving processes and mechanisms of climate effects on the population dynamics of YS herring remain largely unknown. In response to this scientific issue, we preliminarily propose the idea of reconstructing long‐term changes in YS herring abundance over the past 590 years (AD 1417–2004) based on historical documents and attempt to explore the impacts of climate on the population. Our results show that YS herring abundance maintained at a relatively high level from AD 1417 to 1870 (during the Little Ice Age); in contrast, the population declined significantly from AD 1870 to 2004 at different rates. In addition, we also found that there were strong relationships between the population abundance of YS herring and the Pacific decadal oscillation (PDO) and drought/flood cycles. We suggest that the fluctuations in YS herring abundance may be influenced by ocean–climatic circulation shifts throughout the North Pacific, especially the PDO.     

Climate‐induced year‐class fluctuations of whitemouth croaker Micropogonias furnieri (Pisces,Sciaenidae) in the Río de la Plata estuary,Argentina–Uruguay

The whitemouth croaker, Micropogonias furnieri, is exploited by coastal fisheries in the Plata estuary. Its age structure shows the predominance of certain year classes, which are indicative of recruitment variability. The estuary is affected by river discharge variations associated with climatic signals (El Niño Southern Oscillation and others). We hypothesize that recruitment may correlate: (i) negatively with runoff (low runoff would promote the stronger retention of ichthyoplankton); (ii) positively with temperature (higher temperatures should enhance larvae survivorship and/or expand the spawning season); and (iii) positively with the wind zonal component (stronger onshore winds should facilitate the retention of ichthyoplankton). A time series of the relative cohort strengths was constructed for the 1938–2000 period from the age frequencies based on otolith readings. We performed a spectral analysis of the biological and physical series, and we searched for co‐movements between them, which suggested the presence of mechanistic links. The results showed co‐movements for recruitment, runoff and air temperature series at approximately 6.5, 3.4 and 2.4 yr; the temperature reinforced the runoff effects on recruitment at the 6.5‐yr peak, and it weakened them at the 3.4‐ and 2.4‐yr peaks. Wind variability was not relevant for the time scales studied. To explore the mechanisms of retention, we modeled the effects of the runoff fluctuations on the dispersal of the eggs. Both the statistical and modeling results supported the hypothesis that the effects of extreme river discharges on retention may regulate croaker recruitment by promoting high (low) recruitment during low (high) discharge periods.     

Modelling the dispersal of herring and hake larvae in the Strait of Georgia for the period 2007–2009

The Strait of Georgia (SoG), between Vancouver Island and mainland British Columbia, is a larval rearing ground for both hake and herring stocks, which are commercially important. Year‐to‐year variability in larval retention within the strait is examined by simulating drift tracks of larvae for these species using an ocean circulation model and a particle‐tracking model. Larvae with different vertical swimming behaviors were tracked in the springs of 2007, 2008, and 2009. Since herring larvae mostly stay near the surface, their distribution is heavily influenced by the wind. Strong winds to the north soon after the hatching period tend to wash herring larvae out of SoG and winds to the south help retain herring larvae inside the Strait. In 2007, the model indicates a massive wind‐driven export of herring larvae which may have led to the observed failure of herring production. In contrast, hake larvae reside deeper in the water column (50–200 m). Their distribution is less sensitive to surface forcing but is shaped by a deep gyre with cross‐strait currents. This study also suggests that the northern and southern SoG are weakly connected for herring larvae dispersal, which makes both regions potentially important to recruitment.     

The influence of life history dynamics and environment on the determination of year class strength in North Sea herring (Clupea harengus L.)

The inter-annual variability in year class strength (1976–2000) of North Sea herring (Clupea harengus) was investigated using Paulik diagrams based on survey data and Virtual Population Analysis. The herring life cycle was split into five stages: spawning stock biomass (SSB), egg production, larvae, fish with 0 winter rings on the otolith (0-wr), 1-wr and 2-wr. Surveys were used as indices and Paulik analysis revealed relationships between stages. In 80% of the years, year class strength reflected SSB. Poorer than expected year classes were determined during the larva to 0-wr phase, whilst stronger than expected year classes were apparently determined during the 0-wr to 1-wr stage. There was no clear relationship between survival of young stages of herring and the abundance of Calanus finmarchicus but the year class strength of 0-wr and 1-wr had a negative relationship to bottom water temperature. Lower sea water temperatures in the North Sea are associated with higher Calanus abundance. The analysis shows that the strength of aberrant year classes of North Sea herring is determined between the pelagic larval and the juvenile stages.     

Does larval mortality influence population dynamics? An analysis of North Sea herring (Clupea harengus) time series

The daily mortality rates of North Sea herring early‐stage larvae are found to vary over decades. Larval abundance data were used with a spatio‐temporal oceanographic model to reconstruct temperature histories of the observed larvae. The histories were used in conjunction with a temperature‐based growth model to estimate larval age. Mean daily mortality rates were then estimated for the four spawning components (Downs, Banks, Buchan and Orkney/Shetland) using the vertical life table approach, which considers instantaneous abundances across all ages rather than following distinct cohorts. All spawning components, but especially Downs (in the south), exhibited a steady rise in mortality associated with increasing population size. In addition, the three northern components shared a distinct trend in mortality that was significantly correlated with ambient water temperatures experienced by the larvae during the respective time periods after hatching. This trend was also significantly negatively correlated with the residuals of the whole stock‐recruitment relationship. These findings were generally robust to assumptions about growth and hatch length of larvae. The compensatory increase in productivity in the late 1980s and poor recruitment since 2000 coincide with changes in the mortality of larvae younger than 30 days post hatch and covary with larval density and temperature. Thus we suggest that the mortality of early‐stage larvae does impact on the population dynamics in North Sea herring in its current productivity regime, implying a critical period in the determination of year class strength.     

Relationship between recruitment of Japanese sardine (Sardinops melanostictus) and environment of larval habitat in the low‐stock period (1995–2010)

Stock level of Japanese sardine (Sardinops melanostictus) was high from 1980s to early 1990s and low from late 1990s to 2000s. The warm and cold water masses in the vicinity of the Kuroshio axis from winter to early spring used to be critical for the recruitment in the high‐stock period, because most of the larvae were distributed there. However, the environmental fluctuation might not affect the recruitment in the low‐stock period. Some studies reported that spawning location and spawning season, and hence the larval habitat, differ depending on the stock level. Three points were investigated in this study: (a) how spawning location and spawning season shifted from the late 1990s, (b) confirmation of the distribution area of larvae in the recent low‐stock period and (c) whether the water temperature in the vicinity of the Kuroshio axis was still related to the recruitment in the low‐stock period. The spawning location and spawning season clearly changed after 1995. Consequently, particle tracking experiments suggested that the larvae appeared in the vicinity of the Kuroshio axis from winter to early spring decreased. Nevertheless, only the ambient temperature of larvae that appeared in the vicinity of the Kuroshio axis from winter had a significant negative correlation with an index of the recruitment in the low‐stock period. It is suggested that the warm and cold masses in the vicinity of the Kuroshio axis are critical for the recruitment regardless of the stock level.     

Reproductive success of the Argentine anchovy,Engraulis anchoita,in relation to environmental variability at a mid‐shelf front (Southwestern Atlantic Ocean)

The mid‐shelf front (MSF) of the Buenos Aires province continental shelf in the Southwestern Atlantic Ocean plays a central role in the pelagic ecosystem of the region acting as the main spring reproductive area for the northern population of the Argentine anchovy Engraulis anchoita and supporting high concentrations of chlorophyll as well as zooplankton, the main food of anchovy. To investigate the influence of environmental variability on the reproductive success of E. anchoita, we analyzed a 13‐yr time series (1997–2009) of environmental data at MSF including chlorophyll dynamics, as well as zooplankton composition and abundance, ichthyoplankton distributions, and recruitment of E. anchoita. Spring chlorophyll concentrations showed high interannual variability and were mainly influenced by changes in water temperature and vertical stratification, which in turn control nutrient supply to the surface. Chlorophyll dynamics (magnitude, timing, and duration of the spring bloom) explained most of the variability observed in E. anchoita recruitment, most likely via fluctuations in the availability of adequate food for the larvae. Our results suggest that satellite ocean color products can be valuable tools for understanding variability in ecosystem dynamics and its effects on the recruitment of fish.     

Transport and survival of Japanese sardine (Sardinops melanostictus) eggs and larvae via particle‐tracking experiments

Particle‐tracking experiments were performed to infer the distribution of larvae of the Japanese sardine (Sardinops melanostictus) and to detect effects of transport environment on sardine recruitment, using the output of a high‐resolution ocean general circulation model and observed data of sardine spawning grounds during 1978–2004. By the 60th day following spawning, approximately 50% of the larvae had been transported to the Kuroshio Extension (KE). Whereas the spawning period and grounds changed markedly in relation to the stock level, the proportion of larvae transported to the KE remained relatively constant and no significant correlations were found between sardine recruitment and the transport proportion. Instead, the recruitment was found to be correlated with physical parameters including the mixed layer depth and the sea surface temperature along several major transport trajectories of sardine larvae. The correlations were most significant for the trajectories in the region 0.5° south to 1° north of the Kuroshio axis (defined as the location of velocity maxima at each longitude) and for larvae spawned in February and March during the high stock period (1978–94), and for larvae spawned in March and April during the low stock period (1995–2004).     

An investigation of the biological basis of recruitment,growth and adult survival rate variability of Pacific herring (Clupea pallasi) from British Columbia: a synthesis

I explored the biological basis of variation in recruitment (age 3 abundance), growth and age‐specific adult survival rate for the major populations [West Coast Vancouver Island (WCVI), Strait of Georgia, Central Coast, North Coast and Haida Gwaii] of Pacific herring (Clupea pallasi) that inhabit British Columbian waters. The analyses were based on a synthesis of time series of empirical observations of herring population characteristics (egg deposition, age‐specific abundance and size) and prey, competitor and predator biomass/abundance. Recruitment was not correlated among populations. Recruitment variability was explained for WCVI herring only, as a consequence of prey (the euphausiid Thysanoessa spinifera) biomass during August in each of the first 3 years of life, and the biomass of piscivorous Pacific hake (Merluccius productus) during the first year of life. Recruit mass and adult mass‐at‐age were correlated among populations and over ages within populations. Recruit mass was affected by T. spinifera biomass in August of the first and third years of life. Adult mass‐at‐age variability was determined mainly by size at the beginning of the growth season, but also by T. spinifera biomass in August. Age‐specific adult survival rates were not correlated among the five populations. Survival rates decreased with age; there were additional population‐specific effects of somatic mass and T. spinifera biomass in August. The analyses were repeated using physical oceanographic explanatory variables. Only recruit mass variation was explained significantly by physical oceanographic variables, and the biological‐based explanation of recruit mass variability accounted for more of the variation.     

Variability of oceanographic and meteorological conditions in the northern Alboran Sea at seasonal,inter‐annual and long‐term time scales and their influence on sardine (Sardina pilchardus Walbaum 1792) landings

Time series of European sardine (Sardina pilchardus) landings from 1962 and environmental variables from 1978 in the northern Alboran Sea are analysed. European sardine spawns in the northern Alboran Sea from mid‐autumn to late winter at a temperature range slightly higher than the one observed in the nearby Eastern North Atlantic and the North Western Mediterranean. Individuals hatched during autumn and winter are incorporated to the fishery during the following summer and autumn producing the maximum annual landings. These landings show both a decreasing long‐term trend and a strong inter‐annual variability. Although further research is needed, the warming trend of sea surface temperature and the decrease in upwelling intensity inferred from empirical orthogonal function (EOF) analyses could have some influence on the negative trends of sardine landings. The inter‐annual variability of sardine abundance seems to be related to the wind intensity at a local scale, the second principal component of the chlorophyll concentration and the sardine abundance during the preceding year. If the inter‐annual variability is considered, a linear model including these three variables with a one‐year time lag allows to explain 79% of the sardine landings variance. If the negative linear trend is also considered, the model explains 86% of the variance. These results indicate that the body condition of spawners, linked to the food availability during the preceding year, is the main factor controlling the recruitment success. The possibility of predicting sardine landings 1 year in advance could have important implications for fishery management.     

The effects of survey design and circulation pattern on the perceived abundance of herring larvae: a case study for Norwegian spring spawning herring (Clupea harengus)

A larval survey is used in the annual assessment as an index of the spawning stock size of Norwegian spring spawning herring (Clupea harengus). To test how inter‐annual fluctuations in circulation pattern, survey design and execution of the survey affected the larval abundance estimate we conducted simulated surveys using a model framework with idealized assumptions to model larval drift and sampled larvae using several realistic survey scenarios. The results suggest that inter‐annual variations in circulation pattern alone can have a profound effect on the perception of larvae abundance and that the direction of the survey (north to south versus south to north) can have a significant effect on the estimated abundance, particularly if hatching occurs over a short period of time. Additionally, disruptions to a continuous survey schedule also have an effect and, as such, sampling strategies in case of disruption to the survey are proposed.     

Variation in reproductive potential and influence on Icelandic herring recruitment

Explaining recruitment variation in fish is essential for successful fishery management and is consequently under constant review, with an increasing focus on how maternal factors, relative to environmental influences, operate at the level of individual female spawners and extend from the spawning stock through to recruitment. We estimate total egg production (E) in Icelandic summer‐spawning herring (Clupea harengus) from 1963 through 1999 by using sequential population analyses (SPA) and their estimates of stock biomass and recruitment, various size and maturity metrics, and individual fecundity estimates that rely on total length and the condition of the spawners. Generalized linear models indicate that maternal effects are of significance in explaining SPA‐based recruitment‐at‐age‐3 (R). The best model explained 64% of the variation in R and incorporates E constrained to the repeat spawners (40%), the NAO winter index (18%) and ocean temperature (6%). The latter two represent the winter and spring periods subsequent to year‐class formation. Recruit spawner contributions to E were of no significance in explaining variation in R despite the fact that they could contribute as much as 55% of E when their contribution to E was consistently underestimated by a factor of ～ 2, based only on their contribution to spawning stock biomass. We conclude that the spawning potential of the repeat spawners should replace total spawning stock biomass for determining recruitment potential in stock assessment. In addition to the incorporation of oceanographic factors, this would provided a more cautious and risk‐adverse approach.     

Pacific herring, Clupea pallasi, recruitment in the Bering Sea and north-east Pacific Ocean, II: relationships to environmental variables and implications for forecasting

Previous studies have shown that Pacific herring populations in the Bering Sea and north-east Pacific Ocean can be grouped based on similar recruitment time series. The scale of these groups suggests large-scale influence on recruitment fluctuations from the environment. Recruitment time series from 14 populations were analysed to determine links to various environmental variables and to develop recruitment forecasting models using a Ricker-type environmentally dependent spawner–recruit model. The environmental variables used for this investigation included monthly time series of the following: southern oscillation index, North Pacific pressure index, sea surface temperatures, air temperatures, coastal upwelling indices, Bering Sea wind, Bering Sea ice cover, and Bering Sea bottom temperatures. Exploratory correlation analysis was used for focusing the time period examined for each environmental variable. Candidate models for forecasting herring recruitment were selected by the ordinary and recent cross-validation prediction errors. Results indicated that forecasting models using air and sea surface temperature data lagged to the year of spawning generally produced the best forecasting models. Multiple environmental variables showed marked improvements in prediction over single-environmental-variable models.     

Recruitment,distribution boundary and habitat temperature of an arcto‐boreal gadoid in a climatically changing environment: a case study on Northeast Arctic haddock (Melanogrammus aeglefinus)

Climate change is expected to have major effects on the distribution and abundance of fish. In spite of extensive research on the topic in high‐latitude marine ecosystems, the mechanistic understanding of how temperature impacts recruitment and distribution of arcto‐boreal fish stocks remains elusive. Exemplified by an arcto‐boreal gadoid in the Barents Sea, the Northeast Arctic (NEA) haddock (Melanogrammus aeglefinus), we investigate the effect of ecosystem temperature (here temperature from a fixed reference section) on abundance and distribution boundaries between 1981 and 2008. During this time interval there has been a trend of increasing temperature in the ecosystem. We compare the ecosystem temperature with the species habitat temperature of NEA haddock (i.e., ambient temperature of the population) – two temperature approaches representing the indirect and direct environmental impacts on fish, respectively. In addition to the temperature effects, density‐dependent effects on distribution boundaries are considered. The study is based on swept area density estimates and spatial temperature data collected annually in winter surveys. We found a positive relationship between ecosystem temperature and abundance, a connection related to both direct and indirect mechanisms with short‐term and long‐term pathways. Distribution boundaries are, on a year‐to‐year basis, more related to abundance than ecosystem temperature. The long‐term trends, however, indicate a north‐eastward shift in distribution boundaries, probably indirectly related to the coinciding ecosystem temperature increase. In spite of the gradual increase in ecosystem temperature, the abundance of 4‐ to 7‐ year old NEA haddock expanded into colder waters. Thus, our results show how different the two temperature approaches may be.     

Migrations and hydrography determine the abundance fluctuations of blue whiting (Micromesistius poutassou) in the Barents Sea

The Barents Sea is the north‐eastern fringe of the distribution of blue whiting (Micromesistius poutassou). Fluctuations in distribution and abundance of blue whiting in the area have been marked. Two hypotheses are put forward to explain these fluctuations. First, rich year classes in the main Atlantic stock of blue whiting may contribute to increased abundance in the Barents Sea. Second, variations in hydrography, such as influx of warm Atlantic water, may be particularly important in this fringe area. We investigated these hypotheses using data from bottom trawl surveys conducted during the period 1981–2006. Variations in abundance (measured either as incidence or density) and distribution were correlated with recruitment in the Atlantic stock of blue whiting as well as hydrographic conditions. Regression analyses indicated that the abundance fluctuations are primarily determined by variations in recruitment of Atlantic blue whiting, a strong year class leading to high abundance in the Barents Sea the year after spawning. However, salinity anomaly in the Fugløya–Bear Island transect during the previous year, an indicator of high inflow of Atlantic water, had also a significant, positive effect. Thus, the data suggested a climatic modulation of dynamics that were primarily determined by recruitment of blue whiting in the main Atlantic stock. Analyses of size structure as well as earlier studies on population genetics supported this conclusion.     

Forecasting fish stock dynamics under climate change: Baltic herring (Clupea harengus) as a case study

Climate change and anthropogenic disturbances may affect marine populations and ecosystems through multiple pathways. In this study we present a framework in which we integrate existing models and knowledge on basic regulatory processes to investigate the potential impact of future scenarios of fisheries exploitation and climate change on the temporal dynamics of the central Baltic herring stock. Alternative scenarios of increasing sea surface temperature and decreasing salinity of the Baltic Sea from a global climate model were combined with two alternative fishing scenarios, and their direct and ecosystem‐mediated effects (i.e., through predation by cod and competition with sprat) on the herring population were evaluated for the period 2010–2050. Gradual increase in temperature has a positive impact on the long‐term productivity of the herring stock, but it has the potential to enhance the recovery of the herring stock only in combination with sustainable fisheries management (i.e., F_msy). Conversely, projections of herring spawning stock biomass (SSB) were generally low under elevated fishing mortality levels (F_high), comparable with those experienced by the stock during the 1990s. Under the combined effects of long‐term warming and high fishing mortality uncertainty in herring SSB projections was higher and increasing for the duration of the forecasts, suggesting a synergistic effect of fishery exploitation and climate forcing on fish populations dynamics. Our study shows that simulations of long‐term fish dynamics can be an informative tool to derive expectations of the potential long‐term impact of alternative future scenarios of exploitation and climate change.