Shallow-water refuge paradigm: conflicting evidence from tethering experiments in a tropical estuary

The shallow-water refuge paradigm has been globally applied to help explain the high abundances of juvenile fishes that utilise shallow-water estuarine nursery habitats. Despite the wide application and acceptance of the paradigm, there is little direct evidence to indicate that small juvenile fishes benefit from reduced predation pressure in shallow water habitats relative to adjacent deeper waters. The present study employed chronographic tethering experiments to examine patterns in predation potential across a depth gradient (0.2 to 3 m) in the lower reaches of a tropical estuary in northeastern Queensland, Australia. Over 6 mo, 17 replicate experimental trials were conducted, deploying a total of 183 tethered fish prey. Despite the clear and consistent patterns found in the few previous studies elsewhere in the world, there was no significant effect of depth on predation pressure, and thus no evidence of lower predation pressure in the shallow relative to the adjacent deeper estuarine waters examined in the present study. The findings suggest that the shallow-water refuge paradigm may be too simplistic for diverse and complex tropical estuarine nursery grounds.