size: 5036KB - Crocodile Specialist Group

Fitting Curves to crocodilian Aqe-size Data:
sone Hesitant Recommendal ions
by
C. L. Abercroirbie. III
wofford College
Spartanburg, SC 29303
USA
frrtroiluction
While we are gathered together every tvro years, somebody
usually gets up to tell us about crocodiltan growth rates, and
as he or she tafks, most of us stay around to listen. Beyond
nere politeness, there are at least three reasons for our
forbearance. First, we believe that the relationship betr{reen
crocodilian age and size is biologically interesling and
directly relevant to most nanagement strategies. Second, we
understand that after you've caught a croC which is to be
released, you must do sonethinq to justify the trouble,
expense, and fun of the hunt. Measuring an aninalrs size is
rrdoing something," and if one can also es€ablish an age for the
varhint, so nuch the better. Third, as scientists most of us
really like to measure things, to systernatize our neasurenencs,
and to te]1 other scientists about what we have neasured. In
our vork rre concentrated on the t'systenatiz ingtr part of the
process, and to do so r^re have (1) evaluated th; fit of three
nodels to sanples from a population of sinulated crocs whose
underlying growth pattern is known and (2) tried to deternine
horat wefl severaf hodels perforrn inductively vhen we use then to
generalize beyond sanples from an actual ciocodile population.
This paper is divided into six sections. In the first
ve explain how we createa our population of sirnulated crocodil_
aans and how we took satmples froh it. In the second section we
describe the rnodel s hrhich we fit to the samples. In the third
section ve evaluate the fit of the variouJ rnodels. Next, in
section four, we describe another set of models and explain how
we applied then to sanples frorn a population of c;ocodvtus
acutus. In the fj.fth section. we evaluate rnodel perfonnance.
And in our concfusion we offer tentative recommendaiions on hovr
one night sunlnarize crocodilian growth patterns.
Section I! Sinulateal populatiorls anal gaDples for AnaLygis
we constructed a simulated crocodile population whose
nembers grow according to a known function. we;Ilornred random
wariability around that qrowth function (rnean ahplitude of the
variability is proportional to a given aniha-l,s predicted
size). Frorn ttrat population we tooi trl'enty-five priUaUitity
sanples according to each of three different sahpli;g schenes.