Out of sight or in too deep: Effect of visual barriers and water depth on agonistic behaviour and growth in hatchling saltwater crocodiles (Crocodylus porosus)

Abstract

This study tests the role of visual barriers and water depth on levels of agonistic behaviour and growth in hatchling Crocodylus porosus within the first 3 weeks of life. Ninety-six individuals from four separate clutches hatched over 2 days were divided across three treatments containing two groups with 16 individuals each: shallow water with no visual barrier (SW), shallow water with visual barriers (VB), and deep water with no visual barrier (DW). Body mass (BM, g) was measured at introduction and after 21 days, and was used as an index of growth. Behaviour was described and quantified in the night (17:00-08:00. h), when there is an innate peak in behavioural interactions, for three consecutive nights on two occasions (days 9-11 and 18-20 post-hatch). Visual barriers in open shallow water (VB: mean 0.7 interactions/night) nearly eliminated agonistic behaviour relative to SW (mean 10.8 interactions/night; P <6. g change in BM) and fast growing hatchlings (6-15. g increase in BM). Although this made statistical comparisons difficult, there was no clear effect of any treatment (P