Reproductive success, hatchling survival and rate of increase of gharial Gavialis gangeticus in National Chambal Sanctuary, India

Abstract

The gharial Gavialis gangeticus Gmelin is endemic to the Indian subcontinent and was on the verge of extinction in India by the mid-1970's. As a conservation measure, since 1979 captive reared gharials have been reintroduced in several protected areas. The reproductive success and hatchling survival in one of these managed populations was determined by monitoring 124 nests between 1987 and 1989. Population rate of increase in a 425 km stretch of the Chambal River, National Chambal Sanctuary, was determined by surveys every alternate year between 1988 and 1992. The mean clutch size (36.51±0.65 eggs) showed no significant variation between years (ANOVA, F=0.821, p=0.443). Number of infertile eggs per clutch was (2.99±0.160) and no significant difference in the mean number of infertile eggs per nest was found between years (ANOVA, F=0.534, p=0.588). The overall fertility was 91.8%. and it did not vary among years (ANOVA, F=0.075, p=0.927). A substantial number of eggs (32.1%) were lost between egg laying and hatching, largely due to eggs being damaged during nest searches, predation, desiccation and unknown reasons. Predation losses increased between 1987 and 1989, and varied significantly between years (ANOVA, F=3.970, p=0.021). During the study period the overall hatching success was 67.9%. Mean recruitment of 1-year old to the population was 7.7, 8.8 in 1987–1988 and 6.6% in 1989–1990. This indicates 92.3% hatchling mortality within the first year. The egg to post monsoon survivorship was 6.6% in 1987–1988 and 4.3% in 1989–1990, with a mean of 5.5% during the study period. The density of gharial increased from 1.93 gharial/river km in 1988 to 2.52 during 1992. The overall exponential rate of increase in the population was 0.179 ( p=0.012) or equivalent to 19.6% p.a between 1979 and 1992. The total number of nests increased from 45 in 1987 to 57 in 1989. The average annual exponential rate of increase in the nesting between 1979 and 1989 was 0.149 ( p=0.0002) or equivalent to 16.1% p.a. Variations in egg and hatchling survivorship, inconsistency in the number of gharial released, the location and the time of release, and mortality in fishing nets are biases in the data.