High Juvenile Mortality Research Articles

Ontogenetic development in the morphology and behavior of loach (Misgurnus anguillicaudatus) during early life stages

Loach (Misgurnus anguillicaudatus) are a commercially important fish in China and an ideal aquaculture species. However, culturists experience high larval and juvenile mortality during mass production. To provide insight into ways to improve larviculture techniques, we describe the morphological characteristics and behavior of loach during the larval and early juvenile stages. Yolksac larvae ranged from 2.8 to 4.0 mm body length (BL) between days 0 to 4; preflexion larvae ranged from 3.6 to 5.5 mm BL between days 4 to 6; flexion larvae ranged from 4.8 to 8.1 mm BL between days 5 and 14; and postflexion larvae ranged from 7.1 to 15.7 mm BL between days 11 to 27; the minimum length and age of juveniles was 14.1 mm BL and 23 d, respectively. Loach are demersal from hatch through to the early juvenile stages. A suite of morphological characteristics (e.g., external gill filament and ventral mouth opening) and behavioral traits have developed to adapt to demersal living. We observed positive allometric growth in eye diameter, head length, head height, and pectoral fin length during the early larval stages, reflecting the priorities in the development of the organs essential for survival. Our results provide a basis for developing techniques to improve the survival of larval and juvenile loach during mass production.

INTERMITTENT BREEDING AND CONSTRAINTS ON LITTER SIZE: CONSEQUENCES FOR EFFECTIVE POPULATION SIZE PER GENERATION (Ne) AND PER REPRODUCTIVE CYCLE (Nb)

In iteroparous species, it is easier to estimate Nb (effective number of breeders in one reproductive cycle) than Ne (effective population size per generation). Nb can be used as a proxy for Ne and also can provide crucial insights into eco-evolutionary processes that occur during reproduction. We used analytical and numerical methods to evaluate effects of intermittent breeding and litter/clutch size on inbreeding Nb and Ne . Fixed or random litter sizes ≥ 3 have little effect on either effective-size parameter; however, in species (e.g., many large mammals) in which females can produce only one offspring per cycle, female Nb = ∞ and overall Nb = 4Nb (male) . Intermittent breeding reduces the pool of female breeders, which reduces both female and overall Nb ; reductions are larger in high-fecundity species with high juvenile mortality and increase when multiple reproductive cycles are skipped. Simulated data for six model species showed that both intermittent breeding and litter-size constraints increase Ne , but only slightly. We show how to quantitatively account for these effects, which are important to consider when (1) using Nb to estimate Ne , or (2) drawing inferences about male reproductive success based on estimates of female Nb .

INTENSE NATICID DRILLING PREDATION ON TURRITELLINE GASTROPODS FROM BELOW THE K-T BOUNDARY AT RAJAHMUNDRY, INDIA

Evidence of intense naticid drilling predation occurs on turritelline prey from a turritelline-dominated assemblage (TDA) which lies below the K-T boundary sections in Rajahmundry, India. Previously, it was believed that drilling frequency (DF) on turritelline taxa was low during the Cretaceous. Data from the study area indicates that the Cenozoic level of predation on turritelline taxa already occurred by the Late Cretaceous in the study area. The paleobiogeography of naticid predation is extended from the western world to India, which was located in the southern hemisphere during the Cretaceous. In addition to the high drilling frequency, the Indian fossil record shows that many aspects of naticid behavior; for example, size and site stereotypy, which are characteristic features of Cenozoic predators, were also established by the Late Cretaceous. These data support previous views that the Mesozoic Marine Revolution had minimal influence on morphological change in Late Cretaceous turritelline gastropods and that turritelline gastropods may have developed behavioral and/or physiological antipredatory adaptations. TDAs in general may indicate tremendous fecundity that may act as a buffer against high juvenile mortality due to predation.

Survival and habitat use by fledgling northern flickers in a fragmented forest landscape

ABSTRACTThe post‐fledging dependency period of birds is often characterized by high juvenile mortality, but fledglings in specific habitats may have increased survivorship. We describe habitat use by fledgling northern flickers (Colaptes auratus) in relation to the availability of patchy forest and prairie habitat in central British Columbia, Canada. We used radiotelemetry to monitor survival of fledglings according to their use of habitats during the dependency period. The fledglings occupied habitats with a higher density of trees than either random locations or nest sites and they switched from forested areas to more open grasslands after 7–10 days post‐fledging. Some moved >1 km from the nest within 4 days post‐fledging. Fledglings from nests in small tree clusters with little forest cover within 250 m moved farther from their nest within the first 4 days post‐fledging than fledglings from nests in larger forest patches. Fledgling survival was positively correlated with the amount of canopy cover and negatively correlated with the amount of forest cover at the larger landscape scale. Young flickers moved among habitat types, which may occur as a result of trade‐offs between predation risk and food abundance between habitats. We conclude that fledgling flickers at younger ages used dense forested areas and grassland habitat and forest at older ages to maximize survival and to access food sources. Maintaining patches of dense cover and the amount of forest cover on less than 35% of the landscape may improve fledgling survival of flickers. © 2014 The Wildlife Society.

Do naive juvenile seabirds forage differently from adults?

Foraging skills of young individuals are assumed to be inferior to those of adults. The reduced efficiency of naive individuals may be the primary cause of the high juvenile mortality and explain the deferment of maturity in long-lived species. However, the study of juvenile and immature foraging behaviour has been limited so far. We used satellite telemetry to compare the foraging movements of juveniles, immatures and breeding adult wandering albatrosses Diomedea exulans, a species where foraging success is positively influenced by the distance covered daily. We showed that juveniles are able to use favourable winds as soon as the first month of independence, but cover shorter distances daily and spend more time sitting on water than adults during the first two months after fledging. These reduced movement capacities do not seem to be the cause of higher juvenile mortality. Moreover, juveniles almost never restrict their movement to specific areas, as adults and immatures frequently do over shelf edges or oceanic zones, which suggest that the location of appropriate areas is learned through experience. Immatures and adults have equivalent movement capacities, but when they are central place foragers, i.e. when adults breed or immatures come to the colony to display and pair, immatures make shorter trips than adults. The long duration of immaturity in this species seems to be related to a long period of learning to integrate the foraging constraints associated with reproduction and central place foraging. Our results indicate that foraging behaviour of young albatrosses is partly innate and partly learned progressively over immaturity. The first months of learning appear critical in terms of survival, whereas the long period of immaturity is necessary for young birds to attain the skills necessary for efficient breeding without fitness costs.

Primary productivity controls on opportunistic bivalves during Early Jurassic oceanic deoxygenation

Severe paleoclimatic change during the Toarcian (Early Jurassic) oceanic anoxic event (OAE) was characterized by a negative δ 13 C excursion, increased weathering, higher seawater temperatures, oceanic deoxygenation, and mass extinction. We present abundance and size data (n ≈ 36,000) for the two dominant epifaunal bivalve species from the Toarcian OAE, Yorkshire, UK. We statistically correlate the biotic data with geochemical proxies for environmental change and show that our results are comparable with changes in present-day ecosystems affected by hypoxia. Bositra radiata dominated during declining oxygen levels immediately before the Toarcian OAE sensu stricto, and shell size doubled when δ 13 C org was decreasing, indicating a connection with primary productivity. Small Pseudomytiloides dubius dominated during the Toarcian OAE and varied sharply in abundance, indicating that it was highly opportunistic. P. dubius shell size is strongly related to Mo concentration, [Mo]; this indicates a relationship between size and N 2 -fi xing primary productivity via [Mo] limitation. A secondary factor contributing to small shell size was lower oxygen levels. After the Toarcian OAE diversity increased, P. dubius was less abundant and shell size doubled, indicating that bivalve populations were less limited by resources and conditions were more favorable. Size frequency distributions show that both Toarcian species had short life spans, rapid generation times, high recruitment, and high juvenile mortality. The opportunist Mulinia lateralis is a present-day analog for P. dubius. This research provides a case study for the long-term impacts of deoxygenation upon marine ecosystems, including that being observed today.

Differential Movement Patterns of Juvenile Tengmalms Owls (Aegolius funereus) during the Post-Fledging Dependence Period in Two Years with Contrasting Prey Abundance

Fledgling behaviour and movement patterns throughout the post-fledging dependence period (PFDP), especially in relation to changing environmental conditions, have been rarely studied, despite the fact that this period is recognized as of crucial significance in terms of high mortality of juveniles. The PFDP can extend over quite a protracted period, particularly in birds of prey, and a knowledge of the movement patterns of individuals is fundamental for understanding mechanisms underlying survival, habitat use and dispersion. We radiotracked 39 fledglings of the Tengmalm’s owl (Aegolius funereus) in two years with different availability of prey: 2010 (n = 29) and 2011 (n = 10) and obtained 1455 daily locations. Fledglings reached independence on average in 45 days after fledging in 2010 (n = 22) and 57 days in 2011 (n = 6). Within years, the most important measures influencing the distance moved from the nest box were age of fledglings and number of surviving siblings present. Individual home range size and duration of PFDP in particular were dependent on maximal number of siblings seen outside the nest box. In the season with low prey availability fledglings were observed at greater distances from the nest box than in the year with higher prey availability (mean distance: 350 m in 2010 and 650 m in 2011) and occupied larger home ranges (mean: 30.3 ha in 2010 and 57.7 ha in 2011). The main factor causing these differences between years was probably the different availability of prey in these two years, affecting breeding success and post-fledging survivorship of the Tengmalm’s owls.

Physiological disturbances and behavioural impairment associated with the incidental capture of freshwater turtles in a commercial fyke-net fishery

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 21:13-23 (2013) - DOI: https://doi.org/10.3354/esr00504 Physiological disturbances and behavioural impairment associated with the incidental capture of freshwater turtles in a commercial fyke-net fishery Lauren J. Stoot1,2,*, Nicholas A. Cairns1,2, Gabriel Blouin-Demers2, Steven J. Cooke1,3 1Fish Ecology and Conservation Physiology Laboratory, Department of Biology, and 3Institute of Environmental Science, Carleton University, Ottawa, Ontario K1S 5B6, Canada 2Herpetology Laboratory, Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada *Email: ljstoot@gmail.com ABSTRACT: Turtles are caught as bycatch in commercial fisheries in both inland and marine waters. Turtle mortality associated with bycatch is concerning, as life-history characteristics of turtles, including high juvenile mortality and delayed sexual maturity, make them particularly susceptible to population declines following small increases in adult mortality. In eastern Ontario, Canada, freshwater turtles are encountered as bycatch in an inland commercial fyke-net fishery. Although some temperate turtle species can tolerate prolonged submergence, their ability to withstand submergence decreases as water temperatures increase such that turtles may experience severe physiological disturbances and mortality following prolonged forced submergence. The purpose of our study was to evaluate the sublethal physiological consequences and related behavioural impairments associated with fyke-net capture for 3 species of freshwater turtles (eastern musk turtle Sternotherus odoratus, northern map turtle Graptemys geographica and painted turtle Chrysemys picta). Individuals that were entrapped for 3 h at elevated water temperatures (23 to 29°C) displayed considerably higher blood lactate and lower blood pH compared to free-living individuals. This trend was consistent across species and sexes. Despite having the largest increase in blood lactate, musk turtles did not exhibit behavioural impairment from entrapment, whereas both map and painted turtles displayed low responsiveness to behavioural assessments following entrapment. Our results suggest that sub-lethal responses can be used to identify potential harm or fitness impacts even in the absence of immediate mortality. Assessment of behavioural impairments, which could compromise activity and potentially result in post-release mortality, is important for protected and at-risk species that exhibit high juvenile mortality and delayed sexual maturity. KEY WORDS: Bycatch · Conservation physiology · Entrapment · Submergence · At-risk · Sub‑lethal · Lactate Full text in pdf format PreviousNextCite this article as: Stoot LJ, Cairns NA, Blouin-Demers G, Cooke SJ (2013) Physiological disturbances and behavioural impairment associated with the incidental capture of freshwater turtles in a commercial fyke-net fishery. Endang Species Res 21:13-23. https://doi.org/10.3354/esr00504 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 21, No. 1. Online publication date: June 20, 2013 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2013 Inter-Research.

Population dynamics and taphonomy of the Late Triassic (Carnian) freshwater bivalves from Krasiejów (Poland)

The Krasiejów clay pit (SW Poland) has so far been known for yielding mass accumulations of Late Triassic (Carnian) vertebrate fossils. However, unionoid bivalves occur abundantly within the 1 metre-thick shell-rich lacustrine interval at Krasiejów. They are most commonly preserved as shell imprints in the claystone or mudstone. A layer-by-layer quantitative sampling for shell external moulds was conducted directly in the bedding planes at two sites. The most numerous findings come from red and variegated layers in the upper part of this interval, which correspond to a well-aerated sediment. Single valves dominate at both sites and in all layers; valves in butterfly position are rare. The abundance of single valves throughout the sedimentation of the whole interval, both juveniles and adults, indicates that this interval represents the graveyard of a stable, reproducing population. The only exception is a bedding plane in the upper part of the lacustrine interval with numerous concretionary infills of closed valve interiors. They were presumably killed by a sudden load of sediment and, after the early diagenetic cementation was completed, they were winnowed from the mud. The mortality pattern is characterised by a high juvenile mortality (peak at about 13mm), and a slight increase in subadult mortality (peak at about 30mm; adult specimens reach 55mm). Complete lack of early juvenile shells representing the stage with prominent ornamentation may have resulted from predation rather than from size-selective post-mortem preservation. The course of ontogeny shows virtually isometric growth. The range of variability of shell proportions within and between layers suggests the succession of monospecific populations. The Krasiejów lacustrine interval represents the oldest insight into the dynamics and taphonomy of unionoid palaeocommunity.

Seed dormancy and germination of an endangered coastal plantEryngium maritimum(Apiaceae)

INTRODUCTION Eryngium maritimum L. is a littoral species growing on sand dunes and shingle beaches. Although it is listed among the species widespread in western and southern Europe, overall its population is declining (Van der Maarel & Van der Maarel-Versluys, 1996). The species is included in the Red Data Book of Latvia (Fatare, 2003) and is protected in several other European countries. In northern Europe and in the Baltic Region it grows near the limits of its current area of distribution and therefore is at a greater risk of extinction because in small and isolated populations there is a risk of inbreeding depression. For example, in Eryngium alpinum partial self-incompatibility causes lower seed set in selfing plants and selfing negatively affects seed mass and germination (Gaudeul & Till-Bottraud, 2003). A survey of E. maritimum populations along the Skagerrak coast was conducted and the persistence prospects of this species were evaluated as low in these localities due to the small size and fragmentation of individual populations (Curle et al., 2007). Population surveys were also conducted in Poland and Lithuania (Olsauskas, 1996; Labuz, 2007). While in some cases the decline of E. maritimum is linked to habitat disturbance, a population can be threatened also due to limited generative reproduction, affected both by low seed production and low germination as well as high juvenile mortality (Curle et al., 2007; Aviziene et al., 2008). It was suggested also that a decrease of the physiological fitness of E. maritimum individuals in northern populations is associated with lower photosynthetic productivity due to high precipitation and low air temperature (Andersone et al., 2011). Seeds of the Apiaceae family are often morphologically or morphophysiologically dormant (Finch-Savage & Leubner-Metzger, 2006). Seeds with morphological dormancy have small, differentiated embryos that need time to develop before a seed can start to germinate (Baskin & Baskin, 2004). Morphophysiologically dormant seeds also have a physiological component of dormancy and therefore require a dormancy-breaking pretreatment. Depending on the type of the physiological component, different combinations and length of warm and cold stratification can be required (Baskin & Baskin, 2004). Preliminary research on E. martimum seeds (J. Necajeva, unpublished results) confirmed that seeds of this species have underdeveloped embryos at the time of maturation and seed dispersal and, in addition, seeds require dormancy-breaking treatment (cold stratification) to germinate. Other researchers also reported that cold stratification is necessary to break the dormancy of E. maritimum seeds (Walmsley & Davy, 1997; Curle et al., 2007). The results of previous studies probably give sufficient information to develop an effective method of germinating E. maritimum seeds. However, to our knowledge, there have not been any detailed studies of the physiology of the germination process in E. maritimum. The physiological component of seed dormancy is related to the effect of temperature on dormancy breaking and germination. From the point of view of seed physiology, this action of temperature is related to changes in the activity of gibberellins and abscisic acid in the seed. This is why exogenous gibberellins can in some cases substitute for the effect of dormancy-breaking temperatures (Nikolaeva et al., 1985; Finch-Savage & Leubner-Metzger, 2006). When seeds have complicated physiological mechanisms of dormancy release and germination, it is difficult to predict or model germination in natural conditions because the effects of temperature and soil moisture are not straightforward. The morphological component of dormancy can be studied using embryo size-class structure, and is a way to understanding the dynamics of germination within a batch of seeds. We can put forward the hypothesis that the germination rate depends on the degree of embryo development at the time of maturation. …

Terebella phosphatica Leriche (Polychaeta) associated with phosphatic crusts and particles (Lower Turonian, Bohemian Cretaceous Basin, Czech Republic)

The polychaete worm Terebella phosphatica Leriche occurs at the locality of Plaňany (Bohemian Cretaceous Basin) together with remains of the Atreta-Bdelloidina community, attached to the crystalline cobbles and boulders at the base of the Bílá Hora Formation, Whiteinella archaeocretacea Zone, the Lower Turonian. Terebella formed tubes with agglutinated phosphatic particles, mostly faecal pellets, firmly attached to the substrate. The surrounding phosphatic lag containing not only faecal pellets, but also coprolites, various indeterminate phosphatic particles and remains of phosphatized and unphosphatized macrofauna (ichthyolites, bivalves, sponges, crinoids) served as a source of phosphatic particles for the construction of the worm tubes. Formation of the phosphatic lag and the production and phosphatization of its components have been evaluated in relation to repeated phosphogenic episodes during which the phosphatic crusts covering the substrates encrusted by epifauna were formed. Three phosphogenic episodes alternated with episodes of substrate and crust colonization. The tube construction of Terebella shows size- and shape- selective use of particles both during growth and in relation to position in the tube wall. Orientation of faecal pellets normal to the tube axis was found at the bases of the tube walls. High juvenile mortality found in some areas of the substrate was probably due to stress caused by turbulent sedimentation nearby. All the phenomena described probably are part of the unique sequence of short-term events that characterizes the condensed sedimentation of the basal Lower Turonian in the Bohemian Cretaceous Basin. The tubes of the polychaete worm Terebella phosphatica described here are not only the first find of this species in the Bohemian Cretaceous Basin, but also the oldest so far known from any part of the world.

Predation on an Upper Trophic Marine Predator, the Steller Sea Lion: Evaluating High Juvenile Mortality in a Density Dependent Conceptual Framework

The endangered western stock of the Steller sea lion (Eumetopias jubatus) – the largest of the eared seals – has declined by 80% from population levels encountered four decades ago. Current overall trends from the Gulf of Alaska to the Aleutian Islands appear neutral with strong regional heterogeneities. A published inferential model has been used to hypothesize a continuous decline in natality and depressed juvenile survival during the height of the decline in the mid-late 1980's, followed by the recent recovery of juvenile survival to pre-decline rates. However, these hypotheses have not been tested by direct means, and causes underlying past and present population trajectories remain unresolved and controversial. We determined post-weaning juvenile survival and causes of mortality using data received post-mortem via satellite from telemetry transmitters implanted into 36 juvenile Steller sea lions from 2005 through 2011. Data show high post-weaning mortality by predation in the eastern Gulf of Alaska region. To evaluate the impact of such high levels of predation, we developed a conceptual framework to integrate density dependent with density independent effects on vital rates and population trajectories. Our data and model do not support the hypothesized recent recovery of juvenile survival rates and reduced natality. Instead, our data demonstrate continued low juvenile survival in the Prince William Sound and Kenai Fjords region of the Gulf of Alaska. Our results on contemporary predation rates combined with the density dependent conceptual framework suggest predation on juvenile sea lions as the largest impediment to recovery of the species in the eastern Gulf of Alaska region. The framework also highlights the necessity for demographic models based on age-structured census data to incorporate the differential impact of predation on multiple vital rates.

Barnacles (Cirripedia, Thoracica) and associated epibionts from sea turtles in the central Mediterranean

The association patterns and ecology of sea turtle epibionts, and especially obligate epibionts, are still poorly known. Epibiont communities were investigated in the central Mediterranean Sea in relation to the host habitat and seven species of barnacles, three amphipods, one crab, and one tanaid were found on 117 loggerhead sea turtles, Caretta caretta. Particular attention was given to barnacles, some of them being obligate turtle epibionts, with a total of 3330 individuals examined, among which high intraspecific aggregation was observed. Results indicate that (i) the species composition of barnacles varies among turtles frequenting not only different geographic areas but also different habitats in the same area, (ii) different species have marked preferences for hosts frequenting pelagic vs. benthic habitats, and also (iii) for body parts of the host representing microhabitats with different features and trophic opportunities, (iv) settlement is favoured by the presence of conspecific individuals and possibly also (v) by individuals of related species, notably Chelonibia testudinaria that may act as a pioneer species, and finally (vi) barnacles show rapid turnover on turtles, with relatively short lives, rapid growth, and high juvenile mortality.

Managing for extinction? Conflicting conservation objectives in a large marine reserve

Establishment of the Papah¯ anaumoku¯ akea Marine National Monument (PMNM) in 2006 was heralded as a major advance for marine conservation. The PMNM is one of the largest no-take marine reserves in the world (36,207,439 hectares) and includes all of the Northwestern Hawaiian Islands (NWHI). Despite the protection, within its boundaries one of Hawaii’s most charismatic marine species, the endemic Hawaiian monk seal (Monachus schauinslandi), is declining towards extinction. In contrast, monk seal abundance is increasing in the largely unprotected Main Hawaiian Islands. High juvenile mortality in the NWHI has been identified as the demographic factor responsible for the population decline. The ecological drivers of the dynamic are unknown. We evaluate an intervention proposed by the Pacific Islands Fisheries Science Center within the PMNM in a situation in which there is little or no precedent of theory to support management decisions, and then examine the conflicting conservation mandates that pose challenges for monk seal conservation. Benefits of intervention include the potential to maintain subpopulations in the NWHI, and therefore preserve the metapopulation structure, and it will provide additional time for management agencies to continue studies to understand factors limiting population growth. If conditions inside the PMNM do not improve, however, juvenile seals will continue to experience poor survival and subpopulations in the NWHI will continue to decline in spite of intervention. The long-term success of any intervention requires the underlying ecological reason for the NWHI population decline, which is currently unclear. The failure of the PMNM to conserve endangered Hawaiian monk seals highlights conflicting goals of different conservation agendas, the need to understand ecosystem function and large-scale ecosystem interactions, and the necessity of adaptive management.

Shifting threats faced by the San Clemente sage sparrow

AbstractThreats to a species' persistence are likely to change as conservation measures reduce some threats, while natural and anthropogenic changes increase others. Despite a variety of potential underlying mechanisms, extinction threats will be manifested through one of the 3 components of population dynamics: reducing population growth potential, increasing population variability, or lowering the population ceiling. Consequently, effective management can be guided by monitoring programs and population models that examine each of these components. We examined the potential for a coupled monitoring and modeling effort to guide management of species‐at‐risk while accounting for evolving risks using the case study of the threatened San Clemente sage sparrow (Amphispiza belli clementeae). Originally listed due to a low population ceiling imposed by severe habitat loss, we found that the major threat to San Clemente sage sparrow persistence has shifted to low population growth potential driven by high juvenile mortality. We further found that successful mitigation of high juvenile mortality will shift the primary threat to drought frequency, which is predicted to increase on San Clemente Island as a consequence of global climate change. The latter shift is a consequence of the boom‐bust ecology exhibited by San Clemente sage sparrows in response to rainfall—likely a common characteristic of short‐lived terrestrial vertebrates in arid environments. Our ability to successfully recover this species hinges on a comprehensive monitoring and modeling program incorporating all 3 components of population dynamics informing changes in management priorities to reflect shifting threats. Our study indicates that the next critical step to recovering sage sparrows is to understand and mitigate the causes of high juvenile mortality. In response to these predictions, the United States Navy has funded a radio‐telemetry study to determine the cause(s) of juvenile mortalities. © 2011 The Wildlife Society.

Life‐history tables of the Mediterranean fin whale from stranding data

AbstractThe conservation of long‐lived species requires extensive, in‐depth knowledge of their population structure and vital rates. In this paper we examine the structure of the Mediterranean fin whale (Balaenoptera physalus) population based on the available mortality figures from European stranding network databases compiled over the past 22 years. Such data has enabled us to lay out a first life‐history (mortality) table of the population using a simple age‐structured demographic model with three life‐tables: calf, immature and mature. Our results reveal a high mortality rate in the first stage of life (77% per year), which decreases during the immature stage and falls further during the mature adult stage. In addition, we have calculated the corresponding life expectancies at birth (e0), at entry in the immature stage (e1) and at maturity (e2) under different hypotheses on survival at the maximum age of 90 years (s90) ranging between 0.1 and 3% of newborns still alive. The life expectancy at birth (e0) at the lower bound of the chosen range (s90 = 0.001) is about 6 years, entry in the immature stage (e1) is 8.2 years, and entry in the mature stage (e2) is about 15.6 years. This large increase is the consequence of the higher mortality in the first two stages compared with the mature one. The life expectancies are 10.1, 14.3, and 37.8 years for s90 at the upper bound of the chosen range (s90 = 0.03). The resulting population intrinsic growth rates (r) ranged between −1.3. and +1.7 per year. High juvenile mortality patterns imply that the stationary reproductive value (the number of female offspring produced by each female after a given age x) at the start of maturity reaches a value about seven times higher than at birth. Only optimistically high survival patterns of older individuals would allow positive intrinsic growth rates, thereby enhancing the chances of the population survival.

Sex ratio and sexual size dimorphism in Purple Sandpiper Calidris maritima chicks

Capsule The uneven sex ratio in favour of males found in flocks of Purple Sandpipers is not evident in chicks; female chicks are lighter than males. Aims To test if there is an uneven sex ratio at hatching and to investigate whether sex ratio changes during chick growth and after fledging. Methods Sex of chicks was determined (by DNA) and each chick given a unique combination of colour‐rings for later re‐sightings. Biometric measurements were made for comparisons between the sexes. Results The sex ratio of 97 chicks did not deviate significantly from parity, 52.6% males (95% CI: 42.2–62.8%), and there was no evidence that the sex ratio changed as chicks grew older. However, sightings of colour‐ringed birds in their first year indicated a change to 61% males. The same sex ratio (61% males) was observed among wintering birds in Iceland. Chicks already showed sexual size dimorphism in skeletal measurements as is also found in full‐grown birds. Female chicks were relatively lighter than males, suggesting poorer condition. Conclusions The uneven sex ratios seen in non‐breeding flocks of Purple Sandpipers are not determined at hatching but might arise owing to higher juvenile mortality among females soon after fledging. This may result from the relatively lighter mass of female chicks.

On the importance of life history and age structure in biological invasions

The age specific patterns of reproduction and mortality dictated by the life history of an organism apply to potential invaders as well as resident species of an area, but whether certain life history traits are more invasive than others is an unresolved issue. We analyze a two-population system of an invading and a resident species and test the effects of age on the probability to invade when the organisms are iteroparous or semelparous. The life history characteristics of the populations are projected in Leslie matrices, and the probability that the invader exceeds different population sizes is calculated by Monte Carlo analysis. The simulations show that (a) the invasion probability of an iteroparous organism increases with age until the individuals introduced are mature for first reproduction, and then becomes independent of age; (b) the invasion probability is more age sensitive for iteroparous organisms with high juvenile mortality (Type III organisms) than for those with a lower (Type I); (c) invading semelparous organisms are most affected by competition from resident organisms; (d) variations in vital rates of semelparous residents have greater influence on the invasion probability of an iteroparous organism than variations in traits of the invader.

Effect of supplementary stocking of juvenile brown trout,Salmo trutta, on yield in a Norwegian mountain reservoir

The effect of supplementary stocking of juvenile (age 0+), hatchery-reared, brown trout, Salmo trutta L., on annual yields was assessed in a Norwegian mountain reservoir between 1979 and 2007. Fishing was mainly carried out by local fishermen with benthic gillnets. During the study period, annual stocking ranged from 0 to 52 500 fish (19.8 ha−1). No stocking has been carried out since 1997. Annual yield varied from 1650 to 5653 kg, corresponding to 0.62–2.13 kg ha−1. Exploitation rate in terms of number of gillnets and mean weight of 6+ fish (age when catchable size was reached) explained 64% of the variability in catches. Stocked fish contributed very little to the yield or catch-per-unit-effort, exhibiting no positive correlation with stocking density. The lack of contribution from stocked fish was probably caused by a competitive bottleneck in the eroded epibenthic zone, causing high juvenile mortality. If stocking continues, it is recommended that fish with body lengths >15–20 cm are used.

Conservation Status of the First Known Population ofPolygala balansaein Europe

We studied the natural history as well as the conservation status of the first-known population of Polygala balansae in Europe (Granada, SE Spain). In the study area, we located only one population occupying a small patch of 1920 m2, between 120 and 160 m a.s.l., with 246 mature individuals. The species is classified as Critically Endangered (CR), under the following criteria: severely fragmented, inferred continuous decline, small population size, and continuing decline inferred from the number mature individuals. The main threats over the population are: spreading subtropical tree-crops and encroachment of human settlements for tourist purposes, plus natural causes (drought, wild or human-mediated fire, limited dispersal, poor recruitment/ reproduction/regeneration, high juvenile mortality, low densities and restricted range). Finally, passive and active conservation measures are proposed in order to guarantee the survival of the species.