Age-independent Method Research Articles

Effects of age and size on spawning and egg production in gag and scamp grouper off the southeastern United States

Abstract Stock assessments historically have used age- and size-independent methods to estimate reproductive output in marine fishes. Recent assessments have used total egg production (TEP), often assuming an invariant spawning frequency (SF) for all females. However, spawning parameters vary with age and size, which invalidates this assumption. This study investigated the age- and size-dependence of female spawning fraction, duration, and frequency in two economically valuable species, gag (Mycteroperca microlepis) and scamp (Mycteroperca phenax), in Atlantic waters off the southeastern United States, with the ultimate objective of quantifying the effect of these dependencies on TEP estimates. Spawning parameters had moderate-to-strong dome-shaped relationships with age and size (r2 = 0.63–0.94), peaking at intermediate ages and sizes. As larger, older females approach sexual transition, they may increase their lifetime reproductive success by shifting energy resources away from female reproductive investment (i.e. eggs) towards investment that will promote future male reproductive success (i.e. gonad transformation). The estimate of TEP based on age-dependent SF was 38% lower for gag and 41% lower for scamp than the estimate based on age-independent (AI) SF; therefore, the AI method overestimates stock productivity. Incorporating age- and size-based reproductive data into assessments can lead to more reliable stock productivity estimates and potentially improved management.

Evaluation of age-independent methods of estimating site index and predicting height growth: a case study for maritime pine in Asturias (NW Spain)

Site index is the most common measure of forest site productivity used worldwide, serving as an important baseline for forest-level planning and helping to formulate silviculture strategies. Site index is usually obtained through measurement of dominant height and stand age. However, age is not available in many cases, such as in most national forest inventories or when it is not a main determinant of growth. Age-independent methods have been developed to overcome this problem, allowing modelling of the dominant height growth and estimation of site index in the absence of age data. The purpose of this study was to compare the most widely used age-dependent method and several age-independent alternatives, namely the growth intercept method, the age-independent difference equation method and an iterative method proposed in this study. We used stem analysis and permanent sample plot data from Pinus pinaster Ait. stands in Asturias, Spain, to test the alternative methods. It was found that for site index estimation, a 7-year growth intercept was the most accurate method. However, for prediction of dominant height growth, an age-independent equation that depends on climatic factors performed best, even better than the traditional age-dependent site quality curves. The iterative method proposed in this study proved to be the least accurate alternative, although it performed well in predicting height growth for long intervals starting from low heights. Finally, we provide recommendations regarding when the different methods should be used.

The Initial Mass Function of the Stellar Association NGC 602 in the Small Magellanic Cloud withHubble Space TelescopeACS Observations

We present our photometric study of the stellar association NGC 602 in the wing of the Small Magellanic Cloud (SMC). The data were taken in the filters F555W and F814W using the Advanced Camera for Surveys (ACS) on-board the Hubble Space Telescope (HST). Photometry was performed using the ACS module of the stellar photometry package DOLPHOT. We detected more than 5,500 stars with a magnitude range of 14 \lsim m_{555} \lsim 28 mag. Three prominent stellar concentrations are identified with star counts in the observed field, the association NGC 602 itself, and two clusters, one of them not being currently in any known catalog. The Color-Magnitude Diagrams (CMDs) of both clusters show features typical for young open clusters, while that of the association reveals bright main sequence (MS) and faint pre-main sequence (PMS) stars as the members of the system. We construct the initial mass spectrum (IMS) of the association by applying an age-independent method of counting the PMS stars within evolutionary tracks, while for the bright MS stars we transform their magnitudes to masses with the use of mass-luminosity relations. The IMS of NGC 602 is found to be well represented by a single-power law, corresponding to an Initial Mass Function (IMF) of slope \Gamma\approx -1.2 for 1 \lsim M/M{\solar} \lsim 45. This indicates that the shape of the IMF of a star forming system in the SMC for stars with masses higher than 1 M{\solar} seems to be quite similar to the field IMF in the solar neighborhood.

Sonographic diagnosis of intrauterine growth restriction (IUGR) by fetal transverse cerebellar diameter (TCD)/abdominal circumference (AC) ratio

Objective: To evaluate the validity of TCD/AC ratio in predicting IUGR. Study design: Prospective descriptive analysis. Setting: Maharaj Nakorn Chiang Mai Hospital, Chiang Mai University. Subjects: Women meeting the inclusion criteria consisting of: (1) singleton pregnancies after 28 weeks of gestation; (2) known accurate gestational age; and (3) clinically suspected IUGR. Methods: The patients were sonographically examined for TCD/AC ratio. The best cut-off value of TCD/AC ratio in predicting IUGR was determined by a receiver operating characteristic (ROC) curve. The fetus with a TCD/AC ratio greater than the cut-off value would be antenatally diagnosed as IUGR for every gestational week. Standard definition of IUGR was a low birthweight, less than the l0 th percentile. Results: One hundred and sixty-seven pregnancies with suspected IUGR were analyzed. The prevalence of IUGR among the study group was 51.5%. The best cut-off value of the TCD/AC ratio for predicting IUGR was 15.4%, giving the sensitivity, specificity, positive predictive value and negative predictive value of 73.26%, 80.25%, 79.75%, and 73.86%, respectively. Conclusion: The sonographic fetal TCD/AC ratio as a gestational age-independent method can be helpful in antenatal diagnosis of IUGR, especially in pregnancy with uncertain gestational age.

Fetal transverse cerebellar diameter/abdominal circumference ratio in assessing fetal size.

To test the usefulness of the fetal transverse cerebellar diameter/abdominal circumference (TCD/AC) ratio in predicting known small-for-gestational-age (SGA) infants. The relationship between fetal TCD and AC throughout the second half of pregnancy was investigated in 635 well-dated, normal pregnancies and examined with regard to gestational age and infant birth weight percentiles. One hundred eighteen (19%) fetuses were excluded due to inadequate visualization of the fetal cerebellum. A strong correlation was noted between gestational age determined by the last menstrual period and both fetal TCD (r2 = 0.91338) and AC (r2 = 0.89361) in fetuses with birth weights between the 10th and 90th percentiles (n = 407; mean 14.4, S.D. 1.2). Although the TCD/AC ratio showed a poor correlation with gestational age (r2 = 0.15788), a slight increase was noted during gestation. A TCD/AC ratio greater than 15.5 was present in 80% of SGA infants when measurements were performed within 1 week of delivery. Fetal TCD/AC ratio as a gestational age-independent method could improve diagnostic sensitivity and specificity in the early detection of fetal growth abnormalities.

Ultrasonographic detection of abnormal fetal growth with the gestational age-independent, transverse cerebellar diameter/abdominal circumference ratio

We prospectively evaluated the accuracy of a gestational age-independent method of detecting abnormal growth, the transverse cerebellar diameter/abdominal circumference ratio, and compared this with standard ultrasonographic methods of growth assessment. We prospectively studied 825 low-risk obstetric patients and 250 patients having risk factors for fetal macrosomia (n = 92) or growth retardation (n = 158). Measured fetal parameters included the biparietal diameter, head circumference, transverse cerebellar diameter, abdominal circumference, and femur length. The estimated fetal weight, head circumference/abdominal circumference, cerebellar diameter/abdominal circumference, and femur length/abdominal circumference ratios were calculated. Reference curves for these parameters were created from a cross-sectional analysis of the low-risk group. Univariate analysis was used to determine the sensitivity, specificity, predictive values, and odds ratios of each individual parameter in identifying a small- or large-for-gestational-age infant. A multivariate logistic regression model with a variable selection procedure was then used to determine whether significance remained when we controlled for other parameters. Within the low-risk group, the transverse cerebellar/abdominal circumference ratio was gestational age independent between 14 and 42 weeks with a mean of 13.68 +/- 0.96. A value exceeding 2 SD of the mean was significantly associated with birth or a small-for-gestational-age infant, being abnormal in 98% and 71% of asymmetrically and symmetrically growth-retarded infants, respectively. Significance was maintained in the multivariate regression model. The ratio was not helpful in detecting the large-for-gestational-age infant. The fetal transverse cerebellar diameter/abdominal circumference ratio is an accurate, gestational age-independent method of identifying the small-for-gestational-age but not the large-for-gestational-age infant.

Diet and attrition in the Natufians.

AbstractThere is a high correlation between the rate of dental attrition and the physical consistency of the diet. Hypotheses concerning types of diet and methods of food preparation in prehistoric populations may therefore be tested by comparing attrition rates in the specimens under investigation with standards derived from groups of known dietary status. For such comparisons the age factor is of paramount importance, but difficult to assess accurately in fragmentary skeletal material. The use of attrition gradients rather than mean attrition scores provides an age independent method for comparison of attrition rates. When Natufian specimens from three different sites (Kebara, El Wad and Eynan) were compared by this method, significant differences in the gradient of attrition were found at one site, Kebara. The incidences of caries and periodontal disease were also lower at this site, and taken in conjunction with the low level of attrition were considered to relate to differences in the vegetable content of the diet between the individuals recovered from Kebara and those recovered from El Wad and Eynan.