MOVEMENTS AND ACTIVITY LEVELS OF NILE CROCODILES IN THE LAKE ST LUCIA ESTUARINE SYSTEM
Xander Combrink, Jonathan Warner, Ricky Taylor and Colleen Downs
Ezemvelo KZN Wildlife, University of KwaZulu-Natal, School of Life Sciences

 

Abstract
The Lake St Lucia estuarine system is the largest estuary on the continent and one of the last remaining estuaries with a viable Nile crocodile (Crocodylus niloticus) population. It hosts the largest crocodile population in a single waterbody in South Africa and is the most southern viable C. niloticus breeding population in Africa. Twenty-one GPS-GSM transmitters were attached to male and female (nesting and non-nesting), adult and sub-adult crocodiles from 16 September 2009 to 1 May 2012. The mean active transmitter field days was 367.89 ± 56.80 S.E., range: 0 – 1081. The overall activity level, based on successful displacements between GPS fixes, was 41.3 %, and it differed significantly throughout the day (X2 = 1356.08, df = 5, p = 0.00). After a low activity period from 10:00-13:00 (30.0 %), activity levels increased to 36.1 % from 14:00-17:00, peaking at 46.7 % between 18:00-21:00. Between 22:00-01:00 activity decreased somewhat to 45.4 % and were sustained at a level of 44.8 % from 02:00-09:00. Late morning (10:00-13:00) saw a marked decrease in activity to 30.0 %. There was a significant seasonal effect on activity (X2 = 2191.98, df = 3, p = 0.00). Crocodiles were most active in autumn (49.9 %) and marginally less in summer (48.1 %). During spring activity decreased even further to 38.9 % and crocodiles were least active during the winter season (30.5 %). There was a significant difference in the mean daily movements of crocodiles (One-way ANOVA: F (17, 6767) = 92.90, p = 0.00) with an adult female (293 cm TL) making the longest daily movements (2853.96 ± 66.45 S.E., Median 2330.8 m) and a sub-adult (204 cm TL), the shortest (212.75 ± 93.89 S.E., Median 96.9 m) daily movements. We conclude that size, sex, reproductive status and habitat were all important predictors of Nile crocodile activity levels and movement. Insights from this study will improve effective management of the species in the Lake St Lucia estuarine system.

 

Presentation Topic

MOVEMENTS AND ACTIVITY LEVELS OF NILE CROCODILES IN THE LAKE ST LUCIA ESTUARINE SYSTEM
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Email Xander Combrink