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

The gharial Gavialis gangeticus Gmelin is' endemic to the Indian subcontine nt and was on the-verge of extinction in India by the mid-1970's. As a cons ervation measure, since 1979 captive reared gharials have been reintroduced in several protected areas. The reproductive success and hatchling surviva l in one of these managed populations was determined by monitoring 124 nest s between 1987 and 1989. Population rate of increase in a 425 km stretch of the Chambal River, National Chambal Sanctuary, was determined by surveys e very 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 +/- 1.160) and n o 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 wa s 91.8%. and it did not vary among years (ANOVA, F = 0.075, p = 0.927). A s ubstantial number of eggs (32.1%) were lost between egg laying and hatching , largely due to eggs being damaged during nest searches, predation, desicc ation and unknown reasons. Predation losses increased between 1987 and 1989 , and varied significantly between years (ANOVA, F = 3.970, p = 0.021). Dur ing the study period the overall hatching success was 67.9%. Mean recruitme nt of 1-year old to the population was 7.7, 8.8 in 1987-1988 and 6.6% in 19 89-1990. This indicates 92.3% hatchling mortality within the first year. Th e egg to post monsoon survivorship was 6.6% in 1987-1988 and 4.3% in 1989-1 990; with a mean of 5.5% during the study period. The density of gharial in creased 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 eq uivalent to 19.6% p.a between:1979 and 1992. The total number of nests incr eased 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 = 0.002) or equ ivalent to 16;1% p.a. Variations in egg and hatchling survivorship, inconsi stency in the number of gharial released, the location and the time of rele ase, and mortality in fishing nets are biases in the data. (C) 1998;Elsevie r Science Ltd. All rights reserved.