Density, age and sex structure of goitred gazelle (Gazella subgutturosa) in Golestan National Park

Introduction:
The goitred gazelle, which is classified as Vulnerable by IUCN has a very wide distribution across the Middle East, Pakistan, Central Asia, China and Mongolia. A few ecological studies have been conducted on some aspects of goitred gazelle, such as population dynamics, habitat selection, daily activity, and social organization. However, little is known about the population dynamics of Goitred gazelle in Iran. Among the artiodactyls in Golestan National Park, the Goitred gazelles have shown the most vulnerability to the poaching and increasing frequency and intensity of habitat destruction. The objective of this study was to determine the population dynamics of Goitred gazelle in different areas of Golestan National Park. 
Materials and methods:
Fieldwork was carried out in Golestan National park, Iran. The transect line sampling method was used to survey the population dynamics of Goitred gazelle, during the survey at each of the 24 transects, in 3 visits were conducted between February 2016 and July 2016. Data (number of individuals, sex and age of gazelles) were collected at each of 24 transects. To calculate the density of gazelles we used the DISTANCE 6.0 program. Differences in the lambing rate were evaluated using non-parametrical Kruskal-Wallis and Mann-Whitney U-test. All the statistical tests were performed using Minitab 15 and Ecological Methodology softwares. 
Results and discussion:
The results of density analysis showed that the Goitred gazelles had the largest and the smallest population size in Kohne Mirzabaylu and Rabat, respectively. Sex ratio was varied from 1.33 to 1.86. Moreover, the results of sex ratio showed that Almeh and Soulgerd populations had the best sex ratio. The number of middle-aged and older males was low in all gazelle populations. It means that a high portion of females prone to fertility could not mate. Many management strategies offer increase of mature males in population that resulted in increases in reproduction rate of females (Bender, 2002). Due to a few numbers of qualified females (6 years old and older), a considerable number of females could not mate. It means the males spend more time to collect the females and ward off the rival males and consequently the reproduction rate of females decreases. Yearlings (consist of male and female) and very old gazelles (more than 11 years old) had the highest and the lowest percent of Gazelle population, respectively. The highest percentage of lambs was occurred in Soulgerd and Kohne Mirzabaylu populations. This pattern of age class in lambs was due to high security in vicinity of these two areas to wildlife guard stations. There was no significant difference among different areas in lambing rate. This pattern was consistent with Varasteh (2004). 
Conclusion:
According to this study conducted on sex and age structure, lambing rate, and density of Gazelles in comparison with the past, it is quite obvious that the current trend of population dynamics is in decline and this is an alarm that indicate the need for urgent action to reduce the speed of population decline and for careful and long-term planning to management of Gazelles population.