Growth of Caiman crocodilus yacare in the Brazilian Pantanal

Zilca Campos,Guilherme Mourão,Marcos Coutinho,William E. Magnusson,Sean Rogers

doi:10.1371/journal.pone.0089363

Abstract

We studied growth of the caiman, Caiman crocodilus yacare, in the Brazilian Pantanal for 27 years between 1987 and 2013.We recaptured 647 of 7769 C. c. yacare initially marked in an area of 50 km2, in two ranches. We were able to determine size at age accurately for 24 male and17 female caimans that had been marked at hatching or less than 1 year old, and recaptured over periods of 5 to 24 years. The other 606 caimans were used to evaluate short-term growth rates. Age-size relationships were estimated using growth models from the Richards family of curves (full model, von Bertalanffy and monomolecular). The form of the relationships differed between analyses based on caimans of known age and analyses based on integration of growth rate on size relationships for caimans whose ages were not known. Individuals showed large variation in short-term growth rates, but data on known-age animals indicated little between-individual variability in long-term growth rates. There was evidence of a small effect of rainfall, but not temperature, on short-term growth of small caimans, but most variation in growth rates was unexplained by variables other than age and sex. Data on known-age individuals indicated that female C. c. yacare generally reach sexual maturity between 10 and 15 years of age. Because of the asymptotic relationship between age and size, deviations of observations from the model for age are larger than for size, and estimates of age at a given size have greater errors than estimates of size at a given age. Integration of growth rate on size relationships may be adequate for estimating size from age in many cases, but accurate estimates of age from size require data on known-age individuals over the size range of the species.

Highlights

Information on growth is important for many demographic models used in conservation biology and wildlife management
Most individuals in that size range did not have their sex recorded, similar growth rates of males and females were found for immature Crocodylus johnstoni [8]
Asymptotic growth models fit the data well for C. c. yacare, as they do for most crocodilians [8], suggesting that growth is determinate or growth of large animals is extremely slow

Summary

Introduction

Information on growth is important for many demographic models used in conservation biology and wildlife management. In the absence of measurements of individuals with known ages, the relationship between size and age can be estimated from data on many individuals which were captured twice, giving two sizes and a known interval between measurements for each animal Most researchers use the latter strategy, and try to establish size-age relationships by integrating data on short-term growth rates of individuals of different sizes [5]. These methods are controversial [6,7,8,9,10]. While there are good theoretical or practical reasons to use different models, choosing from them is difficult because there are limited data on known-age animals for validation

Methods

Results

Conclusion