Population structure of the turtle podocnemis erythrocephala in the Rio Negro Basin, Brazil

Abstract

The Red-headed Amazon River Turtle (Podocnemis erythrocephala) is the smallest species of the family Podocnemididae yet is frequently captured for human consumption. Our objectives were to (1) determine the relative abundance of this population and those factors that influence numbers, and (2) characterize the population structure using carapace length, sex ratio, and proportion of adults to verify the influence of sample methods and environmental factors. We sampled turtles in 2003-2008 in the Ayuanã River, the middle Rio Negro, Amazonas State, Brazil. We captured turtles using trammel nets and freediving. Females were larger and weighed more than males. The capture method influenced the size, sex ratio, percentage of juveniles, and the capture index. This population of P. erythrocephala had a sex ratio of 0.41male:1female and 40 were juveniles. The frequency of recaptures was ≤ 22 of a sample (n 4432), indicating that only a part of the population was captured. The low density of humans (one person per 3.4 km2) living in the region, and having the nesting beaches distributed along the river, probably contributes to the large number of turtles captured. However, these natural populations of P. erythrocephala need to have long-term monitoring in this region in order to monitor the effect of human's consuming this species; this effect can only be quantified by long-term monitoring.