Recruitment variation related to fecundity in marine fishes

2000 ◽  
Vol 57 (1) ◽  
pp. 116-124 ◽  
Author(s):  
S J Rickman ◽  
N K Dulvy ◽  
S Jennings ◽  
J D Reynolds
Keyword(s):  
Interannual Variation ◽  
Empirical Studies ◽  
Marine Fishes ◽  
Comparative Approach ◽  
Fish Stock ◽  
Closely Related Species ◽  
Stock Size ◽  
Evolutionary Relatedness ◽  
Spawning Stock ◽  
The Mean

An understanding of the processes that control recruitment variation is central to explaining the population dynamics of fishes and predicting their responses to exploitation. Theory predicts that interannual variation in recruitment should be positively correlated with the fecundity of fish species, but empirical studies have not supported this hypothesis. Here, we adopt a phylogenetic comparative approach, which accounts for evolutionary relatedness among stocks and species, to investigate this relationship. We calculated the mean fecundity of fishes from 52 stocks at the mean length of maturity and related this to interannual recruitment variation. We found that in 13 of 14 comparisons between stocks or closely related species, the stocks with higher fecundity have higher recruitment variation. This was true whether or not we controlled for spawning stock size. However, when the analyses were repeated using a traditional cross-species approach, which did not account for the evolutionary relatedness of stocks, the relationships were not significant. This is the first empirical study to link fecundity with recruitment variation and suggests that fecundity is an important component of fish stock dynamics.

Bias in Estimation of Stock-Recruit Function Parameters Caused by Nonrandom Environmental Variability

1988 ◽  
Vol 45 (3) ◽  
pp. 554-557 ◽  
Author(s):  
Michael J. Armstrong ◽  
Peter A. Shelton
Keyword(s):  
Monte Carlo ◽  
Random Distribution ◽  
Environmental Variability ◽  
Random Component ◽  
Periodic Forcing ◽  
Stock Size ◽  
Spawning Stock ◽  
The Mean ◽  
Parameter Precision ◽  
Parameter Values

Parameter estimation for stock–recruit models normally assumes a random distribution of residuals around the underlying function. Monte Carlo simulations, in which departures from the mean stock-recruit function were determined by periodic forcing with a random component, showed that bias may occur in the estimation of average parameter values if randomness is assumed. The bias occurred when the spawning stock size varied in-phase or out-of-phase with the periodic forcing and was greatest when the period was approximately twice the mean age of the spawning stock. In addition to bias, patterning of spawner stock size and recruitment data caused by the periodic variability gave misleading impressions of parameter precision.

Development of microsatellite markers at the National Agrobiodiversity Center in Korea for the genetic assessment of underutilized crops

2014 ◽  
Vol 12 (S1) ◽  
pp. S125-S129
Author(s):  
Gi-An Lee ◽  
Sok-Young Lee ◽  
Ho-Sun Lee ◽  
Kyung-Ho Ma ◽  
Jae-Gyun Gwag ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Microsatellite Markers ◽  
Germplasm Management ◽  
Underutilized Crops ◽  
Crop Species ◽  
Closely Related Species ◽  
Polymorphic Loci ◽  
Allele Number ◽  
The Mean ◽  
Genetic Assessment

The RDA Genebank at the National Agrobiodiversity Center (NAAS, RDA, Republic of Korea) has conserved about 182,000 accessions in 1777 species and is working at preserving agricultural genetic resources for the conservation and sustainable utilization of genetic diversity. The detection of genetic variability in conserved resources is important for germplasm management, but the molecular evaluation tools providing genetic information are insufficient for underutilized crops, unlike those for major crops. In this regard, the Korean National Agrobiodiversity Center has been developing microsatellite markers for several underutilized crops. We designed 3640 primer pairs flanking simple sequence repeat (SSR) motifs for 6310 SSR clones in 21 crop species. Polymorphic loci were revealed in each species (7–36), and the mean ratio of polymorphic loci to all the loci tested was 12%. The average allele number was 5.1 (2.8–10.3) and the expected heterozygosity 0.51 (0.31–0.74). Some SSRs were transferable to closely related species, such as within the genera Fagopyrum and Allium. These SSR markers might be used for studying the genetic diversity of conserved underutilized crops.

Questing height of nymphs of the bush tick, Haemaphysalis longicornis, and its closely related species, H. mageshimaensis: correlation with body size of the host

Parasitology ◽  
2004 ◽  
Vol 128 (5) ◽  
pp. 503-509 ◽  
Author(s):  
T. TSUNODA ◽  
S. TATSUZAWA
Keyword(s):  
Body Size ◽  
Sika Deer ◽  
Cervus Nippon ◽  
The Body ◽  
Haemaphysalis Longicornis ◽  
Primary Host ◽  
Closely Related Species ◽  
Glass Tubes ◽  
Vertical Glass ◽  
The Mean

The questing height (i.e. ambush height) of ticks on a plant plays an important role in host selection. To test the hypothesis that the questing height of ticks in a locality had adapted to the body size of the host in that locality, we examined the questing height of nymphs of the ticks, Haemaphysalis longicornis and H. mageshimaensis, at 7 locations in Japan. Sika deer, Cervus nippon, is the primary host of these ticks and there is considerable geographical variation in the body size of sika deer. Multiple regression analysis revealed that the questing height in the field was influenced by the height of the plants and by the body size of deer at a location. However, the questing height of ticks at some locations may have been constrained by the height of the plants and might not be the same as their intrinsic questing height. When ticks were placed in vertical glass tubes in the laboratory, the questing height of ticks from a locality was correlated with the mean body size of deer at that locality. Therefore, the prominent cue determining the questing height of H. longicornis and H. mageshimaensis seems to be the body size of the host deer.

scholarly journals What Have We Learned from Empirical Studies of Unemployment Insurance?

ILR Review ◽  
1979 ◽  
Vol 33 (1) ◽  
pp. 95-95
Keyword(s):  
Uniform Distribution ◽  
Unemployment Insurance ◽  
Total Population ◽  
Empirical Studies ◽  
Policy Research ◽  
Review Article ◽  
Coverage Rate ◽  
Unemployment Duration ◽  
Waiting Period ◽  
The Mean

TIMOTHY J. CARR of Mathematica Policy Research, Inc. has brought to our attention an error in an example provided by Finis Welch in his July 1977 Review article, “What Have We Learned from Empirical Studies of Unemployment Insurance?” On page 459 Welch stated that under his assumptions (of a uniform distribution of unemployment duration from zero to twenty weeks and a two-week waiting period), the mean duration among those not receiving benefits, given an 80 percent coverage rate, would be six weeks. Actually, with an 80 percent coverage rate, the mean duration would be 7.43 weeks. According to Welch, this can be verified by the following calculations: With fraction, C, of the population covered and with 10 percent of covered employees not receiving benefits, the fraction of the total population not receiving benefits is [Formula: see text] and expected or mean duration is [Formula: see text] So, with C = 0.8, expected duration is (10.0 − 7.92) / (1 − .72) = 2.08/.28 = 7.43. EDITOR

Meta-analysis of the effects of mastery learning on students’ academic achievements in Nigeria

2018 ◽  
Vol 10 (4) ◽  
pp. 547-555
Author(s):  
Maxwell Okwudili Ede ◽  
Uwakwe Okereke Igbokwe
Keyword(s):  
Effect Size ◽  
Learning Strategy ◽  
Mastery Learning ◽  
Empirical Studies ◽  
Sampling Technique ◽  
Content Type ◽  
Research Results ◽  
Academic Achievements ◽  
Ex Post ◽  
The Mean

PurposeThe purpose of this paper is fivefold: to identify the various results of previous empirical studies on the effect of mastery learning and students achievement in Nigeria schools; determine the effect size for each of the studies examined; determine the mean effect size of the overall studies examined; find out the mean effect size of studies that examined the effect of gender on academic achievement in mastery learning strategy; and determine the mean effect size of studies that examined the effect of school locations on academic achievements using mastery learning strategy.Design/methodology/approachThis study adopted survey research design using theex postfacto procedure. This study being meta-analytical used already existing data (research results). The sample of research reports included both published and unpublished research reports on the effects of mastery learning on students’ academic achievements in Nigeria between 1980 and 2016. The study adopted a purposive sampling technique in selecting the sample. This was to ensure that studies: were centered on mastery learning and students’ academic achievements; were carried out in Nigeria; appeared in published and unpublished literature between 1980 and 2016; have the statistical values of the research results of each independent variable to be considered (e.g.t-test values,χ2values and correlation values).FindingsThe study revealed that the mean effect size for all the studies was 0.536, indicating a positive mean effect size. The strategy, thus, has a significant effect on students’ achievements. School location, also, did not mediate in the use of the strategy.Practical implicationsBased on the findings of this study, the following recommendations were made: teachers should use this teaching strategy to enhance students’ achievements in difficult concepts in different subject areas. Since the result of this study has shown that the strategy has positive and large effect size, government and school proprietors should, with the collaboration of higher institutions concerned with teacher education, endeavor to organize seminars and workshops to serving teachers to enable them embrace effectively the principles and processes of implementing the strategy in the classroom. Since the result of this study has established the size of the effect of mastery learning strategy on the academic achievements, subsequent researchers should no longer direct their efforts in determining its effects on academic achievements but on the ways of improving the use of the strategy in teaching at all levels of education.Originality/valueAvailable literature has shown that though most previous research findings revealed that mastery learning approach has an effect on academic achievements of students, no efforts have been made toward resolving the inconsistencies of those results by integrating them and establishing the extent of the effect of the strategy on academic achievements. This study, therefore, was designed to fill these gaps created by the non-existence of integrated studies on effects of mastery learning and academic achievements of students in Nigerian schools.

Catch and Release in Marine Recreational Fisheries

2002 ◽  
Keyword(s):  
Striped Bass ◽  
Growth Parameters ◽  
Size Composition ◽  
Hudson River ◽  
Sensitivity Analyses ◽  
Selective Mortality ◽  
River Population ◽  
Spawning Stock ◽  
The Mean ◽  
Size Limits

<em> Abstract.</em>—One component of the management regimen employed to rebuild the Atlantic coastal migratory stock of striped bass <em> Morone saxatilis </em>was the imposition of large size limits to reduce fishing mortality to zero, on the 1982 and subsequent year-classes, until 95% of the females had an opportunity to reproduce at least once. Such size limits introduce size-selective mortality that favors the survival of slower-growing members of the population and may select for slower growth in succeeding generations. Size-at-age data from the Hudson River population were used to examine the effect of alternative size limits on the length distributions of survivors by age using simulation. The results indicate that minimum sizes currently in use can cause profound changes in the size composition of the spawning stock. The mean asymptotic length of unfertilized eggs under equilibrium conditions was estimated as an index of the extent to which these changes may influence future growth. With the current best estimates of growth parameters and fecundity at size, this index was reduced by only about 3%. However, because of the size-selective mortality in the existing fishery and uncertainty arising from sampling difficulties, growth is probably poorly characterized by the existing data. Sensitivity analyses revealed that some reasonable combinations of growth and minimum sizes can induce changes in the mean asymptotic length of unfertilized eggs by more than 10%, which would be about 30% in terms of asymptotic mean weight. The extent to which this selective force might be expressed in succeeding generations is uncertain. However, reliance on minimum sizes to constrain catch has the potential to cause profound changes in growth and probably should not be adopted for long-term management of striped bass until this problem is better understood.

scholarly journals On Efficient Estimation of Process Variability

Symmetry ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 554
Author(s):  
Tanveer Akhlaq ◽  
Muhammad Ismail ◽  
Muhammad Qaiser Shahbaz
Keyword(s):  
Numerical Study ◽  
Empirical Studies ◽  
Efficient Estimation ◽  
Process Variability ◽  
Good Insight ◽  
Exponential Method ◽  
Process Dispersion ◽  
The Mean ◽  
Insight Into ◽  
Better Than

Variability or dispersion plays an important role in any process and provides insight into the spread of data from some central point, usually the mean. A process with less spread is preferred over a process in which values differ greatly from the mean. Various methods are available to estimate the process dispersion by using information on the variable of interest. Certain additional variables provide good insight to estimate the process dispersion. In this paper, we propose an efficient method for the estimation of process variability by using the exponential method. The properties of the proposed method were studied. We conducted simulation and empirical studies to compare the proposed method with some existing methods of estimation of variability. The results of the numerical study show that our proposed method is better than the other methods used in the study.

scholarly journals An explicit solution for calculating optimum spawning stock size from Ricker’s stock recruitment model

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e1623 ◽  
Author(s):  
Mark D. Scheuerell
Keyword(s):  
Explicit Solution ◽  
Model Fitting ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Stock Size ◽  
Points Of Interest ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Explicit Formulae ◽  
Recruitment Model

Stock-recruitment models have been used for decades in fisheries management as a means of formalizing the expected number of offspring that recruit to a fishery based on the number of parents. In particular, Ricker’s stock recruitment model is widely used due to its flexibility and ease with which the parameters can be estimated. After model fitting, the spawning stock size that produces the maximum sustainable yield (SMSY) to a fishery, and the harvest corresponding to it (UMSY), are two of the most common biological reference points of interest to fisheries managers. However, to date there has been no explicit solution for either reference point because of the transcendental nature of the equation needed to solve for them. Therefore, numerical or statistical approximations have been used for more than 30 years. Here I provide explicit formulae for calculating bothSMSYandUMSYin terms of the productivity and density-dependent parameters of Ricker’s model.

scholarly journals Connecting VIX and Stock Index ETF with VAR and Diagonal BEKK

2018 ◽  
Vol 11 (4) ◽  
pp. 58
Author(s):  
Chia-Lin Chang ◽  
Tai-Lin Hsieh ◽  
Michael McAleer
Keyword(s):  
Global Financial Crisis ◽  
Empirical Studies ◽  
Stock Index ◽  
Conditional Heteroskedasticity ◽  
Exchange Traded Funds ◽  
Sample Period ◽  
Full Data ◽  
Data Set ◽  
Lm Test ◽  
The Mean

As stock market indexes are not tradeable, the importance and trading volume of Exchange-Traded Funds (ETFs) cannot be understated. ETFs track and attempt to replicate the performance of a specific index. Numerous studies have demonstrated a strong relationship between the S&P500 Composite Index and the Volatility Index (VIX), but few empirical studies have focused on the relationship between VIX and ETF returns. The purpose of the paper is to investigate whether VIX returns affect ETF returns by using vector autoregressive (VAR) models to determine whether daily VIX returns with different moving average processes affect ETF returns. The ARCH-LM test shows conditional heteroskedasticity in the estimation of ETF returns, so that the Diagonal BEKK (named after Baba, Engle, Kraft and Kroner) model is used to accommodate multivariate conditional heteroskedasticity in the VAR estimates of ETF returns. Daily data on ETF returns that follow different stock indexes in the USA and Europe are used in the empirical analysis, which is presented for the full data set, as well as for the three sub-periods Before, During, and After the Global Financial Crisis. The estimates show that daily VIX returns have: (1) significant negative effects on European ETF returns in the short run; (2) stronger significant effects on single-market ETF returns than on European ETF returns; and (3) lower impacts on the European ETF returns than on S&P500 returns. For the European markets, the estimates of the mean equations tend to differ between the whole sample period and the sub-periods, but the estimates of the matrices A and B in the Diagonal BEKK model are quite similar for the whole sample period and at least two of the three sub-periods. For the US Markets, the estimates of the mean equations also tend to differ between the whole sample period and the sub-periods, but the estimates of the matrices A and B in the Diagonal BEKK model are very similar for the whole sample period and the three sub-periods.

scholarly journals Evaluation of the absolute levels of acoustic estimates of the 1983 year class of Norwegian spring-spawning herring

2003 ◽  
Vol 60 (3) ◽  
pp. 480-485 ◽  
Author(s):  
Ingolf Røttingen ◽  
Sigurd Tjelmeland
Keyword(s):  
Working Group ◽  
Assessment Model ◽  
Stock Size ◽  
Blue Whiting ◽  
Realistic Picture ◽  
Absolute Sense ◽  
Spawning Stock ◽  
The Absolute

Abstract The 1983 year class of Norwegian spring-spawning herring was large and, in retrospect, increased the spawning stock by more than two million tons when it recruited in 1987–1988. This paper summarizes and evaluates the acoustic estimates of the 1983 year class in the period 1983–2001. The key to the evaluation is a minimum stock based on the number of the 1983 year class caught in the international fishery and the year-class estimates made by the ICES Northern Pelagic and Blue Whiting Fisheries Working Group in 2002 using the SeaStar assessment model. The period of analysis covers a change in instrumentation, around 1990, from the SIMRAD EK400/Nord integrator to the EK500/BEI integrator system. The application of the acoustic estimates in the assessment and management of this herring stock is reviewed. It is concluded that the stock size was underestimated when the acoustic estimates were used in an absolute sense in the 1980s. In the 1990s the acoustic estimates were tuned to stock-size indices obtained from other methodologies and this approach seems to have given a realistic picture of the development of the 1983 year class.

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