Stage-specific Abundance Research Articles

Density-dependence and environmental variability have stage-specific influences on European grayling growth

Fish somatic growth is indeterminate and can be influenced by a range of abiotic and biotic variables. With climate change forecast to increase the frequency of warming and unusual discharge events, it is thus important to understand how these variables currently influence somatic growth and how that might differ for specific age-classes and/ or life stages. Here, we used a 17-year dataset from a chalk stream in southern England to identify the abiotic and biotic influences on the growth of juvenile, sub-adult and adult life stages of European grayling (Thymallus thymallus), a cold-water riverine salmonid. The results revealed that interannual variations in grayling growth were well described by annual- and site-specific abiotic and biotic explanatory variables. We found divergent responses between life stages to increased temperature and unusual discharge during the main growth period with, for example, elevated temperatures related to increased juvenile growth but reduced sub-adult growth, and high discharge events related to increased sub-adult growth yet reduced juvenile growth. Conversely, stage-specific grayling abundance negatively influenced growth at each life stage, though only juvenile growth was impacted by the abundance of a competitor species, brown trout (Salmo trutta). These results emphasise the merits of testing a wide range of environmental and biological explanatory variables on fish growth, and across life stages. They also reveal the importance of maintaining high habitat heterogeneity in rivers to ensure all life stages can reduce their competitive interactions and have access to adequate flow and thermal refugia during periods of elevated environmental stress.

In vitro-in vivo and cross-life stage extrapolation of uptake and biotransformation of benzo[a]pyrene in the fathead minnow (Pimephales promelas)

Understanding internal dose metrics is integral to adequately assess effects environmental contaminants might have on aquatic wildlife, including fish. In silico toxicokinetic (TK) models are a leading approach for quantifying internal exposure metrics for fishes; however, they often do not adequately consider chemicals that are actively biotransformed and have not been validated against early-life stages (ELS) that are often considered the most sensitive to the exposure to contaminants. To address these uncertainties, TK models were parameterized for the rapidly biotransformed chemical benzo[a]pyrene (B[a]P) in embryo-larval and adult life stages of fathead minnows. Biotransformation of B[a]P was determined through measurements of in vitro clearance. Using in vitro-in vivo extrapolation, in vitro clearance was integrated into a multi-compartment TK model for adult fish and a one-compartment model for ELS. Model predictions were validated using measurements of B[a]P metabolites from in vivo flow-through exposures to graded concentrations of water-borne B[a]P. Significantly greater amounts of B[a]P metabolites were observed with exposure to greater concentrations of parent compound in both life stages. However, when assessing biotransformation capacity, no differences in phase I or phase II biotransformation were observed with greater exposures to B[a]P. Results of modelling suggested that biotransformation of B[a]P can be successfully implemented into in silico models to accurately predict life stage-specific abundances of B[a]P metabolites in either whole-body larvae or the bile of adult fish. Models developed increase the scope of applications in which TK models can be used to support environmental risk assessments.

Differential and developmental stage specific abundance of Zmdreb2a mRNA transcripts under drought stress and root development in Zea mays (L.)

Environmental stress constraints like temperature, drought and salinity affect plant growth, development and productivity negatively. In maize (Zea mays L.) water-deficiency affects flowering, pollination and embryo development. Transgenic plants having drought tolerance is a priority target in maize breeding programs worldwide. Various transcription factors play a key role in plant development and stress management. DRE-Binding Protein 2A (DREB2A) has been shown to play a central role in drought tolerance in Arabidopsis thaliana. The homologue of dreb2a in Zea mays is Zmdreb2a, a well-known transcription factor regulating genes induced under stress conditions. Studies indicated that Zmdreb2a transgenic plants show not only stress tolerance but also growth retardation. It is a major targeted gene for transgenesis to produce drought-tolerant plants. However, to make construct for transgenic plants, there is need to consider functional transcripts and regulating mechanism of Zmdreb2a mRNAs under drought condition. We have analyzed publicly available RNASeq data of leaf meristem, ovary and developing root and used a host of FastQC, Tophat, Cufflinks, Cuffmerge, Cuffdiff and ‘R’ packages to functionally characterize the differentially expressed genes (DEGs). In addition, prediction of protein structure, nuclear localization signals and transactivation domain were performed using cNLS mapper and 9aaTAD prediction tools. Alternative splicing of Zmdreb2a pre-mRNA was shown to be strongly associated with developmental stage and isoforms show fluctuating expression under stress. This study provides putative functional transcripts of Zmdreb2a, and NMD as a regulating mechanism to control their abundance.

Milk-derived mammary epithelial cells as non-invasive source to define stage-specific abundance of milk protein and fat synthesis transcripts in native Sahiwal cows and Murrah buffaloes.

The molecular physiology of milk production of two important dairy species; Sahiwal cows (Bos indicus) and Murrah buffaloes (Bubalus bubalis) are not fully understood due to constraints in obtaining mammary tissue samples because of sacred and ethical reasons. The present study suggests the use of milk-derived mammary epithelial cells (MECs) as a non-invasive method to understand molecular aspects of lactation biology in dairy animals. A total of 76 MECs were collected from five different lactation periods viz. colostrum (0-2), early (5-20), peak (30-50), mid (90-140) and late lactation (> 215 days) stages from Sahiwal cows and Murrah buffaloes to study the transcription kinetics of milk protein, fat synthesis, and their regulatory genes. Significant changes were observed in milk composition of both dairy species with lactation stages. High mRNA abundance of all milk protein and fat synthesis genes was observed in MECs of Murrah buffaloes as compared to Sahiwal cows. The mRNA abundance of caseins (CSN1S1, CSN1S2, CSN2, and CSN3) and whey protein (LALBA, LF) were higher in early lactation stage. Similarly, the expression of milk fat synthesis genes (SCD, BTN1A1, ACACA, GPAM, FAPB3, FASN) was also high in early lactation stage. The relative abundance of 4 regulatory genes (JAK2, STAT5, SREBF1 and EIF4BP41) remained high during early lactation indicating their regulatory roles in lactogenesis process. Overall, results suggested a significant effect of lactation stages on milk composition and transcription abundance of milk protein and fat synthesis genes. The present study establishes the fact that milk-derived MECs could be utilized as a valuable source to understand mammary gland functioning of native cows and buffaloes.

Seasonal size composition and abundance distribution of Euphausia pacifica in relation to environmental factors in the southern Yellow Sea

The seasonal size structure and spatial abundance distributions of Euphausia pacifica populations were investigated in the central part of southern Yellow Sea from August 2009 to May 2010. The abundance and biomass of E. pacifica were higher in spring and summer, and lower in autumn and winter. The mean abundance and biomass (calculated by carbon) were 74.94 ind./m3 and 8.23 mg/m3, respectively. Females with total length (TL) ranging between 10 and 19 mm in summer had a substantial contribution to the population biomass, whereas larvae of TL of 3–7 mm in spring were the main contributor to the population abundance. The sex ratio (female:male) showed a female bias in four seasons. Its value peaked in summer, and then decreased in autumn, spring, and winter successively. Cohort analysis revealed that the length-frequency distribution of E. pacifica could be characterized as one group with large animals (mean TL>12 mm) accompanied by one or two subgroups of small individuals (mean TL 32), whereas its larvae showed more abundance in inshore water with rich chlorophyll a, low salinity ( 11°C), especially in summer and autumn. Associations changed seasonally between stage-specific abundance and environmental factors.

Interactions among density, climate, and food web effects determine long-term life cycle dynamics of a key copepod

Increasing pressure on animal populations through climate change and anthro- pogenic exploitation fuel the need to understand complex life cycle dynamics of key ecosystem species and their responses to external factors. Here, we provide a novel, integrative study on the long-term population dynamics of Pseudocalanus acuspes, a key species in the Baltic Sea, explic- itly considering its distinct life-history stages, and testing for linear, non-linear, and non-additive climate and food web effects. Based on a unique data set of stage-specific abundance covering almost 5 decades of sampling (1960 to 2008, with 1408 samples), we use generalized additive mod- eling (GAM) and its respective non-additive threshold (TGAM) formulation to test for (1) density effects on subsequent life-history stages within the internal life cycle, (2) the effect of exogenous bottom-up (i.e. hydro-climatic) and top-down (i.e. predation) pressures, and (3) changes between bottom-up and top-down regulation. We show that linear density effects are always present, explaining a high proportion of interannual variability, while effects of external pressures are non- linear or non-additive and strongly stage- and season-specific. In general, younger stages of P. acuspes are more affected by atmospheric winter conditions and water temperature, whereas older stages are influenced by conditions of deepwater salinity and predation pressure. These bot- tom-up processes, however, are not necessarily stable, and can depend on the level of top-down predation pressure. Our study demonstrates the complex and non-stationary interplay between internal and external factors regulating long-term animal population dynamics.

Estimated development times for stage-structured marine organisms are biased if based only on survivors

Stage duration is a key parameter in modeling population dynamics of stage-struc-tured populations, however stage duration can be difficult to estimate accuratelybecause calculations are based on survivors and fail to account for mortality. Herewe show a method by which development time and stage duration can be adjustedafter accounting for within-stage mortality. As an example, we use a previouslypublished data set on stage-specific abundances of the euphausiid, Euphausia pacificafrom four laboratory-incubated cohorts, raised from egg to juvenile stage. We useda stage-structured population model along with an inverse algorithm to estimatestage durations, both with and without considering mortality rates. Results suggestthat the overall stage duration from egg to furcilia was 48 days when mortalitywas considered, and 60 days when mortality was not included. Stage-specificmortality rates were generally lower than 10% per day for those stages with rela-tively high mortality rates (egg and naupliar stages and furcilia VI–VII) and ,4%for other developmental stages. However, the difference between the estimateswith and without considering mortality rates did not show a clear relationshipwith stage-specific mortality rates. More robust models that can incorporate thevariability in developmental pathways and physiological changes that occur duringthe molting process may be necessary to further investigate how age distributionwithin stage and mortality influence the estimation of stage duration.KEYWORDS: Euphausia pacifica; stage duration; stage-specific mortalitystage-structured population model; inverse technique

Tight junction proteins in zebrafish ovarian follicles: Stage specific mRNA abundance and response to 17β-estradiol, human chorionic gonadotropin, and maturation inducing hormone

In vertebrate epithelia, the tight junction (TJ) complex plays an important role in the regulation of paracellular permeability and contributes to mechanical stability. Using zebrafish, this study examined the possibility that TJ protein ‘machinery’ may contribute to the complex process of ovarian follicle development in fishes and be responsive to key endocrine factors that assist in the regulation of this event. Transcript encoding for 18 zebrafish claudin ( cldn) and 2 occludin ( ocln) orthologs were widely distributed in zebrafish tissues. All orthologs were detected in the ovary, albeit at varying levels of abundance. Using occludin as a marker, TJs localized to the periphery of ovarian follicles, corresponding to the position of granulosa and theca cells. Of the 20 orthologs examined, mRNA encoding for cldn g, d, and ocln were most abundant in whole ovary. As follicles transitioned from pre-vitellogenic to mid-/late-stage vitellogenic status, mRNA encoding for cldn a, b, d, g, h and 19 significantly declined. Transcript encoding for other orthologs (i.e. cldn c, e, f, i, j, 2, 7, 8, 10, 11, 12, 15, ocln and ocln b) did not significantly alter during follicle development. Exogenous 17β-estradiol had little effect on TJ machinery in pre-vitellogenic follicles, but reduced the abundance of cldn h and 10 in mid- to late-stage vitellogenic follicles. In mid-vitellogenic follicles human chorionic gonadotropin increased cldn d and g mRNA abundance, whereas maturation inducing hormone reduced cldn h and 19 mRNA abundance. The data supports a role for the endocrine regulation of TJ proteins in ovarian follicle development.

Construction and characterization of subtractive stage-specific expressed sequence tag (EST) libraries of the pinewood nematode Bursaphelenchus xylophilus

To establish expressed sequence tag databases of the two life stages (the dispersal and propagative stages) of pinewood nematode Bursaphelenchus xylophilus, subtractive EST libraries that were specific to the dispersal 4th larval stage (D4S) and the pine-grown propagative mixed (PGPS) stage were constructed by suppressed subtractive hybridization, and annotated by BLASTx and Gene Ontology (GO). A total of 1112 (57.7%) contigs from the D4S-cDNA library and 1215 (46.7%) contigs from the PGPS-specific cDNA libraries had matched BLASTx hits ( E ≤ 10 − 2 ), among which 913 (47.4%) and 960 (36.9%) contigs, respectively, were classified into three GO categories. A total of 14 genes were selected on the basis of stage-specific abundances and GO subcategories, and their transcription levels were analyzed by quantitative real-time PCR. We discussed the potentials of some stage-specific genes, such as sorbitol dehydrogenase, cysteine protease, venom allergen-like protein, and FMRFamide-like peptide, as diagnosis markers and novel control targets.

A NONINVASIVE DEMOGRAPHIC ASSESSMENT OF SEA LIONS BASED ON STAGE‐SPECIFIC ABUNDANCES

A pressing need exists to develop new approaches for obtaining information on demographic rates without causing further threats to imperiled animal populations. In this paper, we illustrate and apply a data-fitting technique based on quadratic programming that uses stage-specific abundance data to estimate demographic rates and asymptotic population growth rates (lambda). We used data from seven breeding colonies of California sea lions (Zalophus californianus) in the Gulf of California, Mexico. Estimates of lambda were similar to those from previous studies relying on a diffusion approximation using trends in total abundance. On average, predicted abundances were within 24% of the observed value for the inverse estimation method and within 29% of the observed value for the diffusion approximation. Our results suggest that three of the seven populations are declining (lambda < 1), but as many as six may be at risk. Elasticity and sensitivity analyses suggest that population management in most sites should focus on the protection of adults, whose survival generally contributes the most to lambda. The quadratic programming approach is a promising noninvasive technique for estimating demographic rates and assessing the viability of populations of imperiled species.

Seasonal and spatial variation in abundance and egg production of Paracalanus parvus (Copepoda: Calanoida) in/out Jiaozhou Bay, China

The spatial distribution of stage-specific abundance and reproduction of the copepod Paracalanus parvus were studied from October 2005 to September 2006 in the Jiaozhou Bay. This copepod occurred continuously in this bay throughout the year. The species reached the lowest abundance in April and peaked in June. From October to December, distribution center mainly occurred in offshore water and at the mouth of the bay. In winter, early copepodites and adults gradually decreased and till February, most of the population was only comprised of CIV–CV stages. Overwintering copepodites matured in March and males tended to mature before female. From May to September, each stage occurred in the population and gradually reached high abundance. Temperature and chlorophyll a (Chl- a) concentration in the three stations can't clearly explain the seasonal variation in stage-specific abundance, so we surmised the important effect of the Yellow Sea. Egg production rate (EPR) reached its lowest in winter and peaked in June at 60.8 eggs female −1 day −1 in nearshore water. In the warming period, EPR in nearshore water was statistically higher and EPR > 10 eggs female −1 day −1 lasted longer than that in offshore water, showing the importance of nearshore water for recruitment of P. parvus. Our study showed that EPR was positively related to temperature and total chlorophyll a in offshore water and mouth of the bay. In nearshore water, the relationships between EPR and temperature and Chl- a in three size fractions were not the same as those in offshore water, suggesting complicated ecosystem in such a eutrophic area in warming period.

Seasonal dynamics and mortality rates of Calanus helgolandicus over two years at a station in the English Channel

The stage-specific abundance and egg production rates of Calanus helgolandicus were determined on a near-weekly basis over 2 yr at a 50 m deep station in the SW English Channel (Stn L4). Mortality rates were derived using a vertical life-table approach across eggs, nauplii and also the CV-adult stage pair. The results demonstrate strong seasonal patterns in the mortality rates of egg and nauplii and the CV-adult stage pair, but with different relative rates and somewhat dif- ferent seasonalities. Mortality was highest in the egg and egg-NI stages, averaging 6.1 and ~1.5 d -1 , respectively, with the percentage surviving through the egg-NI stage pair often <<10%. Although the instantaneous removal rate of eggs was significantly related to adult abundance (p < 0.001, r 2 = 0.221), densities of adult C. helgolandicus seemed too low to account for these rates. Examination of the relationship between CV-adult female mortality and the abundance of the dominant invertebrate predators revealed statistically significant relationships (p < 0.001 r 2 = 0.276 for chaetognaths; p < 0.001 r 2 = 0.125 for siphonophores); however, the variability explained by temperature was much higher (p < 0.001 r 2 = 0.652). The egg-NI and NI-NII stage pairs also showed a highly statistically significant positive relationship between mortality and temperature. For the first time we compared mortality rates for egg-NI using 2 vertical methods — one using measurements of egg and NI abun- dance (Method A) the other using egg production rates and NI abundance (Method B) — and found the two to be similar, although Method B gave higher values. Finally, as many mortality equations do not consider the bias resulting from the presence of eggs incapable of hatching in the field, we derived and applied new equations for mortality of eggs and egg-NI (Method A) that incorporated egg hatching success. At low hatching success or low mortality rates, this correction can alter esti- mates of mortality rates significantly.

Baltic cod recruitment – the impact of climate variability on key processes

Abstract Large-scale climatic conditions prevailing over the central Baltic Sea resulted in declining salinity and oxygen concentrations in spawning areas of the eastern Baltic cod stock. These changes in hydrography reduced the reproductive success and, combined with high fishing pressure, caused a decline of the stock to the lowest level on record in the early 1990s. The present study aims at disentangling the interactions between reproductive effort and hydrographic forcing leading to variable recruitment. Based on identified key processes, stock dynamics is explained using updated environmental and life stage-specific abundance and production time-series. Declining salinities and oxygen concentrations caused high egg mortalities and indirectly increased egg predation by clupeid fish. Low recruitment, despite enhanced hydrographic conditions for egg survival in the mid-1990s, was due to food limitation for larvae, caused by the decline in the abundance of the copepod Pseudocalanus sp. The case of the eastern Baltic cod stock exemplifies the multitude effects climatic variability may have on a fish stock and underscores the importance of knowledge of these processes for understanding stock dynamics.

AN EXPERIMENTAL TEST OF FRAGMENTATION AND LOSS OF HABITAT WITH ORYZAEPHILUS SURINAMENSIS

This research used a model experimental system to explore the joint effects of resource fragmentation and resource deterioration on population dynamics. The system provides a rapid test of conservation theory and can aid in planning for large and expensive studies. The investigation subjected the sawtooth grain beetle, Oryzaephilus surinamensis (L.), to five experiments in which population abundance was monitored over time. Metapopulations were created by connecting adjacent vials of flour with rubber tubes. The metapopulations were arranged in rings, and food was replenished at two-week intervals. The experiments examined populations in (1) habitats becoming increasingly fragmented, (2) dynamically fragmenting structure with concurrent loss of resources over time, (3) static structure, dynamic resource loss and differing numbers of patches, (4) static structural arrangements with dynamic resource loss that mimic resource deterioration and destruction, and (5) static arrangements of connected fragments with an equal total amount of food in a few large patches or several small patches. Time series of stage-specific abundances were compared in repeated-measures ANOVA. The results show that populations respond in nonlinear ways to both the amount of food and area provided. Within a confined area, when food is plentiful, individual interaction limits population abundance. When the amount of food is reduced, population abundance becomes food dependent. Immediate increase in immature abundance was a characteristic of fragmentation while a delayed reduction of adults was characteristic of food reduction. The stage-specific interaction at intermediate food levels shows birth and death processes that control this system, and elucidates the relationship between area and food that is integral to the dynamics of patchy populations.

The Yellow Sea Cold Bottom Water--an oversummering site for Calanus sinicus (Copepoda, Crustacea)

The vertical distribution and stage-specific abundance of Calanus sinicus were investigated on three key transects in the southern Yellow Sea and the northern East China Sea in August 1999. The results showed that in summer C. sinicus shrank its distribution area to the central cold (less than or equal to10degreesC) bottom water in the Yellow Sea, i.e. the Yellow Sea Cold Bottom Water, remaining in high abundance (345.7 ind m(-3)). In the northern East China Sea on a transect from the mouth of the Yangtze River to the Okinawa trench, only a few individuals appeared in the inner side and none had been found either in the upper layer or in the deep layer of the outer shelf area. The population of C. sinicus in YSCBW consisted of mainly adults (46.83%) and C5 (37.41%). C1-C4 only accounted for 15.76%. The low proportion of the earlier copepodite stages and the high female:male ratio (11.39) indicated that the reproduction of C. sinicus in YSCBW was at a very low level due to the low temperature and low food concentration. It is concluded that the dramatic decrease of C. sinicus population in the shelf area of China seas in summer is caused by the shrinkage of its distribution area and the YSCBW served as an oversummering site.

Distribution and population dynamics ofParacalanus parvus, Paracalanus crassirostris, andAcartia bifilosa (copepoda, calanoida) in the Bohai Sea

Paracalanus parvus, Paracalanus crassirostris, andAcartia bifilosa are dominant and widely distributed in the Bohai Sea, and comprise and important part of zooplankton in terms of biomass as well as production rate. In order to understand their seasonal distribution and population dynamics, their stage-specific abundance in different months of the year were analyzed based on the never analyzed yet samples collected in 1959. The three species showed clear and remarkable seasonal variation in abundance, which maximized in spring and summer, when they formed high biomass patches or concentrations in the nearshore area. ForParacalanus parvus, two peaks were observed in the annual circle, one in June and the other in September. ForParacalanus crassirostris, one peak occurred in summer and a small one in December. The seasonal pattern ofAcartia bifilosa was different in different in different regions. In Bohai Bay it had a two-peak pattern, with the first large peak occurring in May and the second one in October. In Laizhou Bay, a winter peak in December and January could be observed besides the spring one. The number of generations during the reproductive season for the three species was estimated based on the annual cycle in abundance and ambient temperature.

Environmental and biological factors associated with the stage-specific abundance of brown shrimp (Penaeus aztecus) in Louisiana: applying a new combination of statistical techniques to long-term monitoring data

Several short-term and small-scale correlative studies have associated brown shrimp (Penaeus aztecus) recruitment with high densities of sub-adults, high salinity, warm temperature, low river flow, and low precipitation. In this paper, we address criticisms of traditional correlative studies by using a spatially and temporally extensive dataset, by comparing stepwise multiple regression (SMR) to Bayesian model averaging (BMA), and by investigating nonlinear relationships with generalized additive models (GAMs). We use this combination of statistical methods to examine relationships between annual, stage-specific abundance estimates and environmental factors. BMA and SMR resulted in models with similar explanatory power, but BMA suggested fewer linear predictors. GAMs did not suggest nonlinear relationships among stage-specific abundance estimates. Postlarval abundance was not well described by any model. Juvenile abundance was partially described by environmental variables such as temperature, water clarity, and water level. Adult abundance was well described by early-juvenile abundance, salinity, and temperature. These results suggest that juvenile abundance may be the critical component in determining year-class strength of brown shrimp. Identifying mechanisms that regulate juvenile production within the estuary will be a critical step in effectively managing Louisiana's brown shrimp resource.

Environmental and biological factors associated with the stage-specific abundance of brown shrimp (&lt;i&gt;Penaeus&lt;/i&gt; &lt;i&gt;aztecus&lt;/i&gt;) in Louisiana: applying a new combination of statistical techniques to long-term monitoring data

Environmental and biological factors associated with the stage-specific abundance of brown shrimp (&lt;i&gt;Penaeus&lt;/i&gt; &lt;i&gt;aztecus&lt;/i&gt;) in Louisiana: applying a new combination of statistical techniques to long-term monitoring data

Physiology and population structure of Calanus finmarchicus (Copepoda: Calanoida) during a Lagrangian tracer release experiment in the North Atlantic

A population of Calanus finmarchicus was followed in the open sea for a period of 10 days at the end of June 1996 using a tracer release method. Gut fluorescence, egg production, carbon content and stage specific abundance, together with phytoplankton concentration and composition, were measured during this period. Chlorophyll levels were less than 1 µg l-1 and the phytoplankton population was dominated by coccolithophorids. Gut fluorescence decreased during a period with strong winds, whereas egg production remained constant. Estimated phytoplankton ingestion was too low to cover egg production requirements. However, the microzooplankton concentration seemed to be high enough to complement phytoplankton ingestion, enabling egg production carbon require- ments to be covered. C/N ratios of adult females and stage CV were low, indicating low levels of lipid storage. The population was dominated by stage CIV, but shifted to a dominance of younger stages during the study. Mortality calculated from population structure indicates that higher death rates occurred at stage CV.

Shifting control of recruitment of walleye pollock Theragra chalcogramma after a major climatic and ecosystem change

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 198:215-224 (2000) - doi:10.3354/meps198215 Shifting control of recruitment of walleye pollock Theragra chalcogramma after a major climatic and ecosystem change Kevin M. Bailey* Alaska Fisheries Science Center/NOAA, Seattle, Washington 98115, USA *E-mail: kevin.bailey@noaa.gov ABSTRACT: The critical stage in the life history of walleye pollock Theragra chalcogramma at which recruitment is largely determined has shifted in the Gulf of Alaska population. This change follows a major environmental regime-shift in the late 1970s and subsequent dominance of the ecosystem by long-lived predatory flatfishes and cod. An exploratory life table of data on stage-specific abundances was constructed to analyze decadal-scale changes in population demographics. Prior to the mid-1980s, recruitment was correlated with larval mortality, which was largely influenced by environmental conditions. After the mid-1980s, the larval mortality/recruitment relationship eroded, and there was a trend for greater juvenile mortality coinciding with an increase in the abundance of predatory flatfishes and cod. Control of recruitment appears to have shifted in recent years from environmental effects on larvae to biological control of juveniles. Ecosystem change and regime status need to be considered when evaluating mechanisms underlying fish-population dynamics. KEY WORDS: Climate change · Recruitment · Regime shift · Ecosystem · Gulf of Alaska · Population dynamics Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 198. Publication date: June 05, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.