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Ecological forecasts are potentially of great value for managing fisheries and for stakeholders dependent on their long-term sustainability. Yet, most forecasting approaches are data-intensive, requiring information not just on the focal species but also on ecological interactions and the physical environment. Empirical dynamic modeling (EDM) is an equation-free approach to forecasting species' abundance using only data on past abundance, but the time series required for this approach must be long enough to reconstruct the dynamics of the system. This requirement is rarely met, especially for long-lived species. Here we used simulations and empirical data to demonstrate that incorporating time series from multiple age classes can improve our ability to forecast abundance compared to a single age class or index of total abundance. Including data from multiple age classes produced the greatest gains in forecast accuracy when time series were the shortest. Overall, our results show that the incorporation of age structure could allow EDM to be applied to many species for which relatively short time series would have previously been a limiting factor. Key words: forecast, age structure, ecology, population dynamics, empirical dynamic modeling, Introduction Predicting population changes is a critical component of sustainable fisheries management and conservation biology (Clark et al. 2001; Hobday et al. 2016; Payne et al. 2017; Jacox et al. [...]

Predicting the dynamics of harvested species is essential for assessing stock status and establishing index-based management strategies. However, conventional approaches for short-lived species predict dynamics poorly, possibly because unobserved interactions with other species and abiotic factors are often treated as noise. Alternatively, the empirical dynamic modeling (EDM) approach, which uses the time delays of the observed states to compensate for unobserved interactions, may improve the predictions for short-lived species. We test this idea using time series data of two federally managed, short-lived penaeid shrimp species, whose abundances were surveyed over 30 years (1987-2018) across the US Gulf of Mexico. We show that (i) abundance dynamics of these annual shrimp stocks are well-predicted by EDM, (ii) the dynamics are spatially similar across most of the gulf, and (iii) the stock dynamics are characterized by nonlinear density-dependent interaction and vary with temperature. Our findings suggest that EDM may be more responsive than single-species, catch-at-age models in assessing the stock dynamics for short-lived penaeid shrimp species. Key words: penaeid shrimp fisheries, short-lived species, nonlinear time-series forecasting, dynamic correlation, spatial synchrony, Gulf of Mexico fisheries management, Introduction Dynamics of short-lived marine species are notoriously difficult to predict, often exhibiting large fluctuations in population size and increased sensitivity to environmental variability compared with longer-lived stocks (Hsieh et [...]

Small pelagic fish support some of the largest fisheries globally, yet there is an ongoing debate about the magnitude of the impacts of environmental processes and fishing activities on target species. We use a nonparametric, nonlinear approach to quantify these effects on the Pacific sardine (Sardinops sagax) in the Gulf of California. We show that the effect of fishing pressure and environmental variability are comparable. Furthermore, when predicting total catches, the best models account for both drivers. By using empirical dynamic programming with average environmental conditions, we calculated optimal policies to ensure long-term sustainable fisheries. The first policy, the equilibrium maximum sustainable yield, suggests that the fishery could sustain an annual catch of ~2.16 * [10.sup.5] tonnes. The second policy with dynamic optimal effort, reveals that the effort from 2 to 4 years ago impacts the current maximum sustainable effort. Consecutive years of high effort require a reduction to let the stock recover. Our work highlights a new framework that embraces the complex processes that drive fisheries population dynamics yet produces simple and robust advice to ensure long-term sustainable fisheries. Si les petits poissons pelagiques soutiennent certaines des plus importantes peches du monde, un debat se poursuit quant a la magnitude des impacts de processus environnementaux et des activites de peche sur des especes visees. Nous utilisons une approche non lineaire et non parametrique pour quantifier ces effets sur la sardine du Pacifique (Sardinops sagax) dans le golfe de Californie. Nous demontrons que la pression de peche et la variabilite environnementale ont des effets comparables. En outre, pour ce qui est de predire les prises totales, les meilleurs modeles tiennent compte de ces deux facteurs. En combinant la programmation dynamique empirique aux conditions environnementales moyennes, nous etablissons les politiques optimales pour assurer la durabilite a long terme de la peche. La premiere politique, concernant le rendement equilibre maximal, indique que la peche pourrait soutenir des prises annuelles de ~2,16 * [10.sup.5] tonnes. La deuxieme politique, qui integre l'effort optimal dynamique, revele que l'effort durant les deux a quatre annees precedentes a une incidence sur l'effort equilibre maximal actuel. Des annees consecutives d'effort eleve requierent une reduction pour permettre au stock de se retablir. Nos travaux mettent en lumiere un nouveau cadre qui tient compte des processus complexes qui modulent la dynamique des populations de ressources halieutiques, tout en produisant des avis simples et robustes pour assurer la perennite de ces ressources. [Traduit par la Redaction], Introduction Small pelagic fish, such as sardines and anchovies, support the largest fisheries in the world, contributing up to 37% of global landings by weight (Essington et al. 2015), and [...]

Many important ecological questions require accounting for spatial variation in demographic rates (e.g., survival) and population variables (e.g., abundance per unit area). However, ecologists have few spatial modelling approaches that (i) fit directly to spatially referenced data, (ii) represent population dynamics explicitly and mechanistically, and (iii) estimate parameters using rigorous statistical methods. We therefore demonstrate a new and computationally efficient approach to spatial modelling that uses random fields in place of the random variables typically used in spatially aggregated models. We adapt this approach to delay-difference dynamics to estimate the impact of fishing and natural mortality, recruitment, and individual growth on spatial population dynamics for a fish population. In particular, we develop this approach to estimate spatial variation in average production of juvenile fishes (termed recruitment), as well as annual variation in the spatial distribution of recruitment. We first use a simulation experiment to demonstrate that the spatial delay-difference model can, in some cases, explain over 50% of spatial variance in recruitment. We also apply the spatial delay-difference model to data for rex sole (Glyptocephalus zachirus) in the Gulf of Alaska and show that average recruitment (across all years) is greatest near Kodiak Island but that some years show greatest recruitment in Southeast Alaska or the western Gulf of Alaska. Using model developments and software advances presented here, we argue that future research can develop models to approximate adult movement, incorporate spatial covariates to explain annual variation in recruitment, and evaluate management procedures that use spatially explicit estimates of population abundance. De nombreuses questions ecologiques importantes necessitent la prise en consideration des variations spatiales de taux demographiques (p. ex. de survie) et de variables relatives a la population (p. ex. l'abondance par unite de surface). Les ecologistes disposent toutefois de peu d'approches de modelisation spatiale qui (i) peuvent etre calees directement sur des donnees referencees dans l'espace, (ii) representent de maniere explicite et mecaniste la dynamique des populations et (iii) emploient des methodes statistiques rigoureuses pour l'estimation de parametres. Nous presentons donc une nouvelle approche de modelisation spatiale efficace sur le plan computationnel qui fait appel a des champs aleatoires plutot qu'aux variables aleatoires normalement utilisees dans les modeles regroupes spatialement. Nous adaptons cette approche a la dynamique a differences retardees pour estimer l'incidence de la mortalite naturelle et par peche, du recrutement et de la croissance individuelle sur la dynamique spatiale d'une population de poissons. Nous developpons plus particulierement cette approche pour estimer les variations spatiales de la production moyenne de poissons juveniles (appelee le recrutement), ainsi que les variations annuelles de la repartition spatiale du recrutement. Nous utilisons d'abord une experience de simulation pour demontrer que le modele spatial a differences retardees peut, dans certains cas, expliquer plus de 50% de la variance spatiale du recrutement. Nous appliquons egalement le modele spatial a differences retardees a des donnees sur la plie royale (Glyptocephalus zachirus) dans le golfe d'Alaska et demontrons que le recrutement moyen (pour toutes les annees) est le plus grand pres de l'ile Kodiak, mais que, pour certaines annees, le recrutement maximum est observe dans le sud-est de l'Alaska ou dans l'ouest du golfe d'Alaska. A la lumiere des modeles et avancees logicielles presentes, nous arguons que des travaux futurs peuvent mener a des modeles permettant d'estimer approximativement les deplacements des adultes, d'integrer des covariables spatiales pour expliquer les variations annuelles du recrutement et d'evaluer les procedures de gestion qui font appel a des estimations spatialement explicites de l'abondance de la population. [Traduit par la Redaction], Introduction Ecologists are increasingly tasked with understanding how population and community dynamics vary spatially. Understanding spatial processes is necessary to predict many important phenomena, including the impact of global climate [...]

Understanding the process of recruitment is fundamental to fisheries biology and management. However, recruitment in natural populations is highly variable and rarely well described by classical stock-recruitment relationships (SRRs). Recent analyses suggest that the age composition of the spawning biomass may play an important role in the mismatch between SRRs and data. Here we develop a generalization of the Ricker SRR that incorporates age structure by allowing mortality and fecundity rates to depend on maternal age. We provide a flexible SRR with biologically interpretable parameters that can be estimated from existing fisheries time series and use a Bayesian framework that enables parameters to be informed by experimental data. We apply our method to the Icelandic population of Atlantic cod (Gadus morhua) and show models that include age structure effects outperform the classical Ricker SRR that ignores age structure. Our results indicate a strong effect of spawning stock age structure on recruitment dynamics in this population. Our approach provides a biologically interpretable and immediately applicable method for investigating the consequences for spawning stock age structure on recruitment. La comprehension du processus de recrutement est un aspect essentiel de la biologie et de la gestion des peches. Le recrutement au sein de populations naturelles est toutefois tres variable et les relations stock-recrutement (SSRs) classiques en fournissent rarement une description adequate. Des analyses recentes suggerent que la composition par age de la biomasse de frai pourrait etre un important facteur explicatif de la non- concordance des SSR et des donnees. Nous presentons une generalisation de la SRR de Ricker qui integre la structure par age en permettant que les taux de mortalite et de fecondite dependent de l'age maternel. Nous fournissons ainsi une SRR souple contenant des parametres pouvant etre interpretes d'un point de vue biologique et qui peuvent etre estimes a partir de series chronologiques existantes sur les peches et nous utilisons un cadre bayesien qui permet la definition des parametres a partir de donnees experimentales. Nous appliquons cette methode a la population islandaise de morue franche (Gadus morhua) et demontrons que les modeles qui integrent les effets de la structure par age donnent de meilleurs resultats que la SSR de Ricker classique, qui n'en tient pas compte. Nos resultats indiquent un effet marque de la structure par age des stocks reproducteurs sur la dynamique du recrutement dans cette population. Notre approche offre une methode pouvant etre appliquee immediatement et permettant des interpretations biologiques pour etudier les repercussions de la structure par age des stocks reproducteurs sur le recrutement. [Traduit par la Redaction], Introduction The fundamental law of population biology is that species cannot increase without bound. When viewed in a single species context, this means that density dependence must act on survival, [...]

While much effort has been directed at determining the spatial scales of adaptation in thermal reaction norms for growth, it is widely assumed that these reaction norms have high temporal stability. Water temperatures in the Gulf of Alaska in 2007 were the coldest on record since the mid-1970s and we present evidence that the thermal reaction norm for growth of age-0 Pacific cod (Gadus macrocephalus) in this cohort differed significantly from two adjacent cohorts. In addition to exhibiting higher growth potential at low temperatures, the 2007 cohort had a higher mean vertebral count, consistent with the widespread thermal effect known as 'Jordan's Rule.' Variation among cohorts in these physiological and morphological traits suggests a persistent response to environmental history (epigenetic effect). Temperature-induced phenotypic plasticity in the reaction norm for growth has significant implications for using growth rates to evaluate habitat quality and illustrates the complex responses of fishes to climate variability., Introduction Temperature is a primary driver of all aspects of the physiology of ectotherms including growth potential. As such, the relationship between water temperature and potential growth rate ('temperature-dependence of [...]

Patterns of connectivity are important in understanding the geographic scale of local adaptation in marine populations. While natural selection can lead to local adaptation, high connectivity can diminish the potential for such adaptation to occur. Connectivity, defined as the exchange of individuals among subpopulations, is presumed to be significant in most marine species due to life histories that include widely dispersive stages. However, evidence of local adaptation in marine species, such the Atlantic silverside, Menidia menidia, raises questions concerning the degree of connectivity. We examined geochemical signatures in the otoliths, or ear bones, of adult Atlantic silversides collected in 11 locations along the northeastern coast of the United States from New Jersey to Maine in 2004 and eight locations in 2005 using laser ablation inductively coupled plasma mass spectrometry (ICP-MS) and isotope ratio monitoring mass spectrometry (irm-MS). These signatures were then compared to baseline signatures of juvenile fish of known origin to determine natal origin of these adult fish. We then estimated migration distances and the degree of mixing from these data. In both years, fish generally had the highest probability of originating from the same location in which they were captured (0.01 0.80), but evidence of mixing throughout the sample area was present. Furthermore, adult M. menidia exhibit highly dispersive behavior with some fish migrating over 700 km. The probability of adult fish returning to natal areas differed between years, with the probability being, on average, 0.2 higher in the second year. These findings demonstrate that marine species with largely open populations are capable of local adaptation despite apparently high gene flow. Key words: Atlantic silverside; connectivity; gene flow; local adaptation; Menidia menidia; northeastern U.S. Coast; otolith chemistry; population structure.

Maternal effects are increasingly recognized as important drivers of population dynamics and determinants of evolutionary trajectories. Recently, there has been a proliferation of studies finding or citing a positive relationship between maternal size/age and offspring size or offspring quality. The relationship between maternal phenotype and offspring size is intriguing in that it is unclear why young mothers should produce offspring of inferior quality or fitness. Here we evaluate the underlying evolutionary pressures that may lead to a maternal size/age--offspring size correlation and consider the likelihood that such a correlation results in a positive relationship between the age or size of mothers and the fitness of their offspring. We find that, while there are a number of reasons why selection may favor the production of larger offspring by larger mothers, this change in size is more likely due to associated changes in the maternal phenotype that affect the offspring size--performance relationship. We did not find evidence that the offspring of older females should have intrinsically higher fitness. When we explored this issue theoretically, the only instance in which smaller mothers produce suboptimal offspring sizes is when a (largely unsupported) constraint on maximum offspring size is introduced into the model. It is clear that larger offspring fare better than smaller offspring when reared in the same environment, but this misses a critical point: different environments elicit selection for different optimal sizes of young. We suggest that caution should be exercised when interpreting the outcome of offspring-size experiments when offspring from different mothers are reared in a common environment, because this approach may remove the source of selection (e.g., reproducing in different context) that induced a shift in offspring size in the first place. It has been suggested that fish stocks should be managed to preserve these older age classes because larger mothers produce offspring with a greater chance of survival and subsequent recruitment. Overall, we suggest that, while there are clear and compelling reasons for preserving older females in exploited populations, there is little theoretical justification or evidence that older mothers produce offspring with higher per capita fitness than do younger mothers. Key words: egg size; fisheries management; life-history theory; marine protected areas; maternal effects; optimal offspring size.

Many ectotherms exhibit striking latitudinal gradients in lifespan. However, it is unclear whether lifespan gradients in distantly related taxa share a common mechanistic explanation. We compiled data on geographic variation in lifespan in ectotherms from around the globe to determine how much of this intraspecific variation in lifespan may be explained by temperature using the simple predictions of the metabolic theory of ecology. We found that the metabolic theory accurately predicts how lifespan varies with temperature within species in a wide range of ectotherms in both controlled laboratory experiments and free-living populations. After removing the effect of temperature, only a small fraction of species showed significant trends with latitude. There was, however, considerable residual intraspecific variation indicating that other, more local factors are likely to be important in determining lifespan within species. These findings suggest that, given predicted increases in global temperature, lifespan of ectotherms may be substantially shortened in the future. ectotherms | intraspecific | longevity | MTE

An important task in evolutionary biodemography is to determine the schedule of survival and reproduction as the outcome of natural selection acting on life histories. We do this by using a model in which the state of the organism is characterized by mass and accumulated damage, both of which are affected by activity and which affect the rate of mortality. Focusing on growth during the juvenile period, we determine the level of activity that maximizes reproductive value. Given this, we are able to project forward and determine the trajectory of mortality for an individual following the optimal life history, given the physiological and reproductive parameters. We show that there are two main classes of juvenile mortality trajectories: U-shaped (such as recently reported for prereproductive humans) and steadily declining and we are able to connect the shape of the mortality trajectory with the physiological and reproductive parameters characterizing the life history. Our work shows the importance of state in models of evolutionary biodemography and the power of modern computational methods to illuminate biological process. free-radical theory | disposable soma | life history theory | dynamic programming

Analyses of changes in size distributions over time frequently suggest that mortality rates depend on body size. Such observations, however, are probably confounded with changes in size due to growth. We describe a parametric method by which the size dependence of both mortality and growth may simultaneously be inferred from pairs of size distributions collected at different times. The method is tested in a Monte Carlo study and found to have sampling properties similar to those of other methods that require more data. Survival of the first winter of life appears to be size dependent in a diverse array of taxa, although few prior studies have accounted for growth. Analysis of sizes of Menidia menidia (Atlantic silverside) from three different latitudes revealed that changes in size distributions through winter resulted from growth in southern populations and mortality in the north. Winter mortality was better described by a power function of size than an exponential. Allometric exponents increased with latitude and were greater than predicted from metabolic- or starvation-based models. The steepness of the estimated survivorship curves imply that winter mortality in M. menidia is more consistent with a threshold effect perhaps attributable to offshore migration. Key words: Atherinidae; Atlantic silverside; Bergmann size clines; body size; latitudinal gradient; maximum likelihood; Menidia menidia; Monte Carlo simulation; selection; size-dependent mortality; winter mortality.

Fishery management plans ignore the potential for evolutionary change in harvestable biomass. We subjected populations of an exploited fish (Menidia menidia) to large, small, or random size-selective harvest of adults over four generations. Harvested biomass evolved rapidly in directions counter to the size-dependent force of fishing mortality. Large-harvested populations initially produced the highest catch but quickly evolved a lower yield than controls. Small-harvested populations did the reverse. These shifts were caused by selection of genotypes with slower or faster rates of growth. Management tools that preserve natural genetic variation are necessary for tong-term sustainable yield., It is well established that wild pest and pathogen populations may evolve in response to anthropogenic forces of mortality (1), but is the same true of fisheries? Fishing mortality is [...]

The research data on the size-dependent survival in the early life history of fish was utilized to obtain estimates of standardized selection differentials from 40 studies. The results revealed that 77% of estimated selection differentials favored larger size and that the strength of selection was more than five times compared to those observed in terrestrial taxa.

Juvenile growth is submaximal in many species, suggesting that a trade-off with juvenile growth must exist. It is shown that swimming performance decreases with the square of growth rate, providing the first demonstration of a nonlinear cost of growth.

In order to address the issue, scientists used two populations of menidia menidia with disparate intrinsic growth rates. The results confirmed that growth was insensitive to predation risks: neither population appeared to modify growth rates in response to predation levels.